Watershed Approach to Mitigating Hydrologic Impacts of Transportation Projects: Conduct of Research Report (2022)

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233 Appendix A. Annotated Bibliography An annotated bibliography of the resources reviewed for this research is provided in this appendix. The full citation is provided followed by relevant information from the reference. AECOM 2014. HSPF Hydrologic Modeling and SUSTAIN Stormwater modeling of the Gorst Creek Watershed, AECOM Seattle Washington, June. The report is a description of application of HSPF and SUSTAIN for a particular watershed in Washington and a case study that describes how the HSPF model for the watershed was constructed, how its output is fed to SUSTAIN, and how SUSTAIN is used to select appropriate BMPs for a Master Plan. The report is useable as a template for a guidance document of how to assemble a model of before/after conditions to evaluate the impact of a highway project on a watershed. It is not useable as-is but does provide a reasonable template to help build a guidance document. A SUSTAIN-like tool might be a productive product (or even adaptation of parts of existing SUSTAIN) for State DOTs. Armson, D., P. Stringer, and A. R. Ennos 2013. “The Effect of Street Trees and Amenity Grass on Urban Surface Water Runoff in Manchester, UK,” Urban Forestry and Urban Greening, 12 (2013) 282–286. This study measured the runoff from plots covered by grass, asphalt, and asphalt with a tree in the center. Trees and their associated tree pits reduced runoff from asphalt by as much as 62%. The reduction was more than interception alone could have produced, and relative to the canopy area was much more than estimated by many previous studies. This document is important for the current study in that a quantitative value is reported for the effect of intentional vegetation. The authors concluded that most of the effect is attributed to infiltration and storage (in excess of canopy interception). This document is important for the current study in that a quantitative value is reported for the effect of intentional vegetation and will be useful to establish performance ranges in the development of potential toolkit(s) for various BMP/GI practices either on-site or off-site. Baek, S-S., D-H. Choi, J-W Jung, H-J Lee, H. Lee, K-S Yoon, and K. H. Cho 2015. “Optimizing Low Impact Development (LID) for Stormwater Runoff Treatment in Urban Area, Korea: Experimental and Modeling approach,” Water Research. Authors apply SWMM and a MATLAB wrapper to select LID devices to control stormwater quality in an urban basin. The scale was small (less than 1 square mile). The paper is best described as a case study. The study is at too small scale to be directly useful, however the wrapper to generate SWMM input files to test different combinations of LID devices is a transferable idea to a guidance tool. The tool need not be SWMM, but the concept of multiple software tools interacting is meaningful. Bair, B. not dated. Stream Restoration Cost Estimates, retrieved from https://www.st.nmfs.noaa.gov/st5/Salmon_Workshop/11_Bair.pdf. This document is a regional study (Pacific Northwest) of stream restoration, including stream surveys, a subbasin assessment, and watershed analysis. It mentions benefits of increased water

234 quality and wildlife/habitat restoration and addresses the costs of stream bank stabilization ($46,000 to $222,000 per river mile on public lands), channel rehabilitation ($41,000 to $137,000 per river mile), and riparian reforestation ($4,000 to $8,000 per river mile; average of $110 per acre). Relevant to the current project it offers a line-item breakdown of typical restoration costs. Beck S.M., M. R. McHale, and G. R. Hess 2016. “Beyond Impervious: Urban Land-Cover Pattern Variation and Implications for Watershed Management,” Environmental Management, DOI 10.1007/s00267-016-0700-8. The authors explore a series of urban catchments within a range of impervious cover to evaluate how land cover varies among them. Using examples from the literature the potential effects of land-cover pattern variability for urban watershed management are examined. Land cover pattern and stormwater infrastructure metrics are created and applied to explain pattern variability. The analysis demonstrated that land cover patterns vary substantially among urban catchments, and that trees and grass (lawns) are divergent cover types in urban systems. Importantly the authors describe a metric that incorporates connectivity as part of the measure. Two important contributions from this paper are a pattern quantification technique that produces color raster of computed metrics -- like a QR code for a watershed; six metrics are employed that would be meaningful for the response component of hydrologic modeling in the toolkit for mitigating hydrologic impacts of highway projects. The six metrics are directly applicable, but the visual raster is promising as a way to encode behavior in a fashion amenable to machine learning to encode anticipated response. As watershed properties are changed, the raster would change, or even more importantly the raster could be used to determine watersheds where mitigation on/off site might not be workable. Bechtel B, Micheal F, Mills G, Ching J, See L, Alexander P, O’Connor M, Albuquerque T, Andrade MF, Brovelli M, Das D, Fonte CC, Petit G, Hanif U, Jimenez J, Lackner S, Liu W, Perera N, Rosni NA, Theeuwes N, Gal T 2015. “CENSUS of cities: LCZ classification of cities (Level 0),” ICUC9—9th International conference on urban climate jointly with 12th symposium on the urban environment. Authors examine the concept of Local Climate Zones to generate a derivative level 0 classification of land coverage (a metric) that is comparable between locations. The LCZ metric will be useful to quantify land availability from a hydrologic perspective to serve as mitigation. The natural extension to a response (hydrologic) model is implicit in the paper, but not explored -- however the concept of a metric is relevant. Bello A.-A.D., Hashim N.B., Haniffah R.M. 2017. “Impact of urbanization on the sediment yield in tropical watershed using temporal land use changes and a GIS-based model,” Journal of Water and Land Development, No. 34 p. 33–45. DOI: 10.1515/jwld-2017-0036. The authors apply HSPF and GIS tools to examine effects of land use changes on a watershed response. The paper also simulates growth (development) of the watershed to examine how response to sediment production changes over time. The paper is a case study of how to use HSPF. The authors are focused on outlet responses, and little is presented on how interior changes to the watershed (other than land use) impact the drainage system.

235 Bledsoe, B., Lammers, R., Jones, J, Clary, J., Earles, A., Strecker, E., Leisenring, M., Struck, S., and McGuire, A. 2016. Stream Restoration as a BMP: Crediting Guidance. Water Environment Research Foundation (WERF) Project WERF1T13. Available at: https://www.waterrf.org/research/projects/stream-restoration-bmp-crediting-guidance. The report provides a technical framework for quantifying the water quality benefits of a specific suite of stream restoration practices (stabilization, riparian buffers, in-stream enhancement, and floodplain reconnection). It explores a credit trading system focused on water quality. Brown, P. and Lant, C. 1999. “The Effect of Wetland Mitigation Banking on the Achievement of No-Net-Loss,” Environmental Management, 23: 333 https://doi.org/10.1007/s002679900190. This article assesses the effectiveness of wetland banking programs in the United States. It considers acreage impacted, method of compensation, compensation ratio, and percentage of wetland area lost. Geographic locations of municipalities with wetland banking programs are also accounted for, as well as spatial relationships between impact and mitigation sites. Key findings include: • As of January 1, 1996, 74% of wetland mitigation banks are achieving no-net-loss. • Overall, wetland mitigation banks will lose 52% of their acreage as credited wetlands are converted to other land uses. • The issue of wetland loss is best addressed on an individual bank basis. This study of the overall impact of wetland mitigation banks concludes that mitigation banking can work within a watershed if it is applied correctly, and the banking process properly verified. While not all mitigation banks achieve a no-net-loss result, any individual watershed can see the hydrologic benefits of wetland banking if they are effectively managed and credited. Bassi, A., Cuellar, A., Pallaske, G., and Wuennenberg, L. 2017. Stormwater Markets: Concepts and Applications, December.) This report provides case studies of technological approaches and financing of stormwater management at several locations throughout North America. It covers aspects of stormwater markets (fees, practices, etc.), including mitigation banking and offers cost estimates for various GI that impact water quality, quantity, or both. The report identifies recent attempts to develop stormwater markets in the United States (Washington D.C., Philadelphia PA, and Lancaster PA), including implementation options for creating a stormwater market (credit trading, mitigation bank, social impact bonds, in-lieu fees, permittee-responsible mitigation), challenges (impact of technology, incentive for economic buy- in, geographic size of market, distinguishing clear units of trade, and more). For each of the stormwater markets in the U.S., the report provides background information, the primary stormwater management decisions, the results, and the replicability of the program. Buttle, J. M. 2011. “Streamflow response to headwater reforestation in the Ganaraska River Basin, southern Ontario, Canada,” Hydrol. Process., 25: 3030-3041. doi:10.1002/hyp.8061 This study seeks to assess the effect of reforestation on larger drainage basins as opposed to smaller basin, which the author believes less is known about. The Ganaraska River Basin (GRB) is 267 km2 and saw an increase in forest cover from 13 km2 to 31 km2 from 1945 to 1990. The streamflow metrics between 1960 and 2007 were compared to a nearby control basin where

236 reforestation had not occurred. The metrics used for comparison were annual streamflow, low flows, and peak flows. Key findings include: • Little difference was found in annual runoff between the GRB and the control basin. This is possibly a result of the humidity and precipitation in the area, as differences due to forest cover are usually the most prominent in drier areas. • A decrease in peak flows was found in the GRB compared to the control basin. This is due to the added forest cover decreasing the potential for frozen soil to generate runoff during spring storms. • Low flows from the GRB increased in comparison to the control basin. This suggests that in addition to decreased runoff potential, reforestation has increased groundwater recharge by prolonging spring snowmelt and increasing infiltration potential. Unlike other studies reviewed, this article focuses on one reforested drainage basin. It also incorporates the effects of snowmelt on a watershed and how it affects hydrologic metrics. Because the study addresses a single basin, it is useful for drainage basins in similar climates, but less so for other climates, particularly warmer ones. The study shows, in contrast to other studies, that annual streamflow was not significantly altered in the GRB, as opposed to decreasing. This means that for similar climates and basins, reforestation might function to reduce peak flows while not affecting water supply, which is one of the main downsides to adding forest cover. However, the article hypothesizes that the reason annual streamflow did not decrease is because it is in a wet region, so water supply might not be an issue. It is worth exploring situations where reforestation has reduced peak flows while keeping annual flow about the same in drier regions. Cappiella, K., Stack, B., Battiata, J., Nees, D., and Fraley-McNeal, L. 2014. Potential Application of Stormwater Banking in the Chesapeake Bay Watershed Using Two Case Studies, October. This report describes a recent site-specific study of stormwater banking focused on water quality. It outlines a methodology for assessing potential locations for stormwater banking and provides an evaluation of different program types (mitigation banking, off-site mitigation, fee-in-lieu, nutrient trading, and stormwater fee credits). The report provides an estimation of site-specific costs for bioretention, impervious cover removal, ditch enhancement, rain garden, etc. at select locations. Center for Watershed Protection (CWP) 2012. Guidance for Developing an Off-Site Stormwater Compliance Program in West Virginia, Prepared for the West Virginia Department of Environmental Protection, December. The report summarizes three (some in development at that time) programs for runoff volume trading: Washington DC, Saint Paul, MN, and Fredericksburg, VA. The programs consider both off-site mitigation and payment in-lieu. The report highlights guidance for programs and a model ordinance for an MS4 that may include: • Establishing a trading ratio of 1.5:1 for the volume of runoff associated with the first 0.6 inches to be traded for an off-site practice, and 2:1 for the subsequent 0.4 inches.

237 • Guidance, through modeling or monitoring, for estimating runoff volume reduction of reforestation (Appendix F). (Provides some numerical estimates that appear to require further development.) • Guidance, “through equivalent BMP approach,” for estimating runoff volume reduction of stream restoration (Appendix G). (Provides some numerical estimates that appear to require further development.) Center for Watershed Protection 2017. Fact Sheet "Accounting for Trees in Stormwater Models and Calculators," Center for Watershed Protection, 8390 Main Street, 2nd Floor, Ellicott City, MD 21043 url: https://www.cwp.org/wp- content/uploads/2017/09/modelsandcalculatorsSeptversion.pdf (accessed 15 Jul 2019). Fact sheet contains a brief description of anticipated effects of runoff reduction from trees and vegetation intentionally incorporated into an area. The document summarizes methods and tools to account for the ability of GI to reduce runoff and remove pollutants. It is organized into two categories: • Methods for incorporating GI into runoff models • Models and calculators for estimating the functions, benefits, and economics of GI The document also contains a list and assessment of various model tools (specific software) available including web links to the various tools. The fact sheet appears to precede (or possibly be a product summary) of a research project conducted by the same entity: Center for Watershed Protection, Inc., $200,000 for “Using a Novel Research Framework to Assess Water Quality Impacts of Urban Trees” This research team will quantify the stormwater treatment value of trees across urban forest types. The project will identify urban forest characteristics that influence the water and ecosystems and determine whether more complex urban forest types result in greater runoff volume reduction. The status and results of this project (a final report) are unknown at the present. This report has utility for the current project in that it addresses an issue of how to modify environment to change runoff volumes (by using vegetation as a store and/or sink). Chagrin River Watershed Partners (CRWP) 2009. Floodplain Restoration and Storm Water Management: Guidance and Case Study, March. This document lists the benefits of floodplain restoration, including flood control, erosion control, natural capital value, water quality protection, groundwater recharge and protection, and ecosystem protection. It identifies Pennsylvania as only state with floodplain restoration in their BMP Manual (at the time of publication). The focus is two off-site, out-of-kind techniques—floodplain reforestation and floodplain reconnection/expansion. The document addresses appropriate landscape conditions and design considerations for the different techniques. It provides cost estimate ranges for various components of: 1) floodplain reforestation, including: soil amendments, rubble removal, invasive plant removal, container trees, and balled and burlapped trees; and 2) floodplain reconnection/expansion, including: lowering the floodplain, raising the stream and regenerative stormwater conveyance.

238 Clary, J., J. Jones, M. Leisenring, E. Strecker, B. Bledsoe, R. Lammers 2017. Stream Restoration BMP Database: Version 1.0 Summary Report, prepared for the Water Environment and Reuse Foundation. The Stream Restoration BMP Database is a relatively recent effort to catalog standardized information about the performance and costs of various stream restoration approaches. The focus is on stream restoration broadly described as “bed and bank stabilization, riparian buffer restoration, in-stream enhancement, and floodplain reconnection.” Each type is described, including variations within a category. Although hydrology data (e.g., event data) are included, the focus is on water quality, including sediment. The first version, Database 1.0, is limited in its usefulness and most of the initial studies currently do not include the recommended data. This report notes that “while most researchers indicate a net benefit to water quality, habitat, and biology, as well as other functional attributes, some researchers noted limited or even negative consequences to the restoration efforts.” The database relates to “stream restoration crediting guidance completed under WERF-1T13 "Stream Restoration as a BMP” Choi, Y., H. Yi, and H-D Park 2011. “A new algorithm for grid-based hydrologic analysis by incorporating stormwater infrastructure,” Computers & Geosciences, 37 (2011) 1035–1044. The authors present an Adaptive Stormwater Infrastructure algorithm, to incorporate ancillary datasets related to stormwater infrastructure into the grid-based hydrologic analysis. The concept represents a useful simplification of a drainage system (at large scale) that preserves response but reduces computational effort. The infrastructure simplification methods described in the paper will be useful in the current project. Costanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, S., O’Neill, R., Paruelo, J., Raskin, R., Sutton, P., and van den Belt, M. 1997. “The Value of the World’s Ecosystem Services and Natural Capital,” Nature: Vol. 387. The report provides broad evaluation of 17 ecosystem services from gas and climate regulation to pollination, soil formation, and food production and assesses the value of the entire biosphere at an average of $33 trillion per year. The value of biomes that comprise the biosphere is calculated at $4.7 trillion for forests, $4.8 trillion for wetlands, etc. While a seminal work on the value of natural capital and ecosystem services, the macro-level valuation does not reduce in a meaningful way to valuation of the ecological services potentially provided by landscape modification at a scale relevant to mitigation of site-specific highway projects. Costanza, R., Wilson, M., Troy, A., Voinov, A., and Liu, S. 2006. “The Value of New Jersey’s Ecosystem Services and Natural Capital,” New Jersey Department of Environmental Protection. Available at https://pdxscholar.library.pdx.edu/iss_pub/15/. This document provides evaluation of ecosystem services at the state level that is further differentiated at the county, watershed, and subwatershed levels. It provides a methodology (value transfer, hedonic analysis, and spatial modeling) for translating the valuation made in studies like Costanza (1997) and other regional/state studies to a narrower scope. However, the estimation and calculations involved in moving from the macro-scale to micro-scale may not satisfactorily address particularities that could emerge from a site-specific valuation.

239 DelDOT/DNREC 2019. Memorandum of Agreement between the Delaware Department of Transportation (DelDOT) and the Delaware Department of Natural Resources and Environmental Control (DNREC) for stormwater banking across DelDOT projects, draft. This draft MOA provides a mechanism for DelDOT to mitigate for the “Resource Protection Event” (defined as the storm having the annual probability of occurrence of 99 percent). The stormwater bank is only for use by DelDOT for projects where it is demonstrated that on-site mitigation is not feasible. The bank consists of credits and debits at DelDOT project sites and must be used within the same HUC 8/HUC 10 watershed. Credits and debits are measured in units of cubic feet of stormwater volume. Detwiler, S. 2015. Rivers and Roads: Opportunities to Better Integrate Green Infrastructure and Transportation Projects in Atlanta, GA, and Toledo, OH. This document provides a direct linkage between GI and transportation projects. It primarily addresses transportation infrastructure within U.S. cities, although highways are noted. It notes the potential motivations for, and limitations to, implementation of GI in highway construction, namely land use restrictions and funding. The document is less focused on cost data, which are typically sourced from other reports and studies, and more on the benefits (primarily water quality) of GI. Most importantly, the document provides recommendations on planning, project development, and funding for State DOTs (Toledo, OH and Atlanta, GA) in implementing GI. District of Columbia Department of Energy and Environment (DC-DOEE) 2019. Stormwater Retention Credit Trading Program. Available from https://doee.dc.gov/src (retrieved 7/31/19). This website offers numerous links to the SRC Trading Program in Washington, D.C., ranging from market data on SRCs to eligibility and evaluation programs in place. It is concerned specifically with the reduction of stormwater runoff volume and is focused primarily on GI and the removal of impervious surfaces. The metric – the SRC – is defined as one gallon of retention capacity for one year. The program is an example of a well-documented program for generating and selling credits through the installation of GI or the removal of impervious surfaces. The website contains information on potentially useful programs such as a price lock program, a startup grant program, and a site evaluation program. Elliott, A. H., S. A. Trowsdale, and S. Wadhwa 2009. “Effect of Aggregation of On-Site Storm- Water Control Devices in an Urban Catchment Model,” Journal of Hydrologic Engineering, Vol. 14, No. 9, September 1, 2009. ©ASCE, ISSN 1084-0699/2009/9-975–983/ Authors examine modeling approach to estimate effect of spatially distributed on-site devices such as detention tanks and bioretention. The author's goal was to reduce computational burden imposed by modeling the cumulative catchment-scale effects of such devices at the scale of a land parcel or finer, and then to model each device separately. The author's used the MUSIC model to perform the various scenario calculations. The document mentions SWMM, however it is not clear if it was employed in the study (unlikely). The influence of aggregation was assessed by comparing the predictions of the aggregated models against the predictions of the detailed model. Aggregation had little effect on the predictions of maximum concentration when the devices were sized in proportion to the impervious area and

240 when there was high soil permeability. Aggregation to a single device increased peak flow compared with the detailed model, by up to 38.1% for bioretention and less for other devices. The peak flow increase was a consequence of reducing the range of travel times in the aggregated drainage network. Aggregation to seven devices had considerably less effect on peak flow (8.7% increase). Addition of variability to the size of the devices introduced further aggregation effects. Methods to extend the aggregation approach to cater for variability in device sizing are proposed in the paper. The results of the study suggest that aggregation can be used to reduce computational and input data demands, with little penalty in terms of prediction accuracy. The implication for the research is that aggregation can be accomplished without loss of accuracy, but it cannot be done naively. While the study reviewed was specific to water quality devices, the concepts are directly applicable to volumetric control approaches, and the present study will need to provide guidance for how to aggregate processes (for off-site mitigation) to maintain a suitable accuracy (or estimate of accuracy). Elliott, A. H., and S. Trowsdale 2007. “A review of models for low impact urban stormwater drainage,” Environ. Modelling Software, 22(3), 394–405. Ten existing stormwater models are compared in relation to attributes relevant to modeling LID. The models are based on conventional methods for runoff generation and routing, but half of the models add a groundwater/baseflow component and several include infiltration from LID devices. The models also use conventional methods for contaminant generation and treatment such as buildup-washoff conceptual models and first order decay processes, although some models add treatment mechanisms specific to particular types of LID device. Several models are capable of modeling distributed on-site devices with a fine temporal resolution and continuous simulation, yet the need for such temporal and spatial detail needs to be established. There is a trend towards incorporation of more types of LID into stormwater models, and some recent models incorporate a wide range of LID devices or measures. SWMM is specifically reviewed and compared to MOUSE. Of the 10 models, these two are "distributed" hydrology, hydraulics, and device models. The remaining eight models are lumped in their hydrologic behavior. The lumped approach makes their use easier but begs the accuracy question. The author of the paper also authored another paper reviewed where he concluded that aggregation (lumping) is adequate, but that aggregation cannot be arbitrary. For the current project, again SWMM is identified as a useful tool, but is also mentioned as a tool for experts. The question of aggregation will (again) matter -- guidance on how to aggregate (or disaggregate) will be a necessary component of the work product. Farley, K. A., Jobbágy, E. G. and Jackson, R. B. 2005. Effects of afforestation on water yield: a global synthesis with implications for policy, Global Change Biology, 11: 1565-1576. doi:10.1111/j.1365-2486.2005.01011.x This article assesses empirical data on the effects of carbon sequestration programs, such as reforestation and afforestation, affect water yields in 26 different catchments. The two hydrologic characteristics that were observed were annual runoff volume and low flow. The effects of different vegetation types used for afforestation were also calculated. It was also found that afforestation has a greater effect in reducing low flow than annual runoff volumes. Key findings include:

241 • Afforestation of eucalyptus trees decreased annual runoff more than pine trees. • Afforestation of grasslands decreases annual runoff more than afforestation of scrublands. • Deforestation impacts are most pronounced during dry periods. • Forest management affects small/moderate peak flow rates more significantly than runoff volume. • Proportionally, low flow was reduced more than total annual flow. • In regions where natural runoff is less than 10% of mean annual precipitation, afforestation can cause a complete loss of runoff. • In regions where natural runoff is 30%, afforestation can cut runoff in half. • Streamflow response typically begins within 5 years of planting, with maximum runoff reductions occurring 15-20 years after planting. This study assesses the effectiveness of afforestation in reducing low flows and total annual flow. The conclusions drawn can be used to guide both the vegetation that should be planted and the location it should be planted in. For example, if the goal in a certain watershed is to reduce low flows and total annual flow by the greatest magnitude possible, this study shows that one would plant eucalyptus trees rather than pine trees and so in a grassland region rather than a scrubland. Additionally, if flows do not have to be greatly reduced and pine trees are cheaper/easier to plant, they may be used in afforestation. One warning made in this article was that of the downsides of afforestation. In regions with water shortages, a reduction in low flows and total annual runoff may worsen those shortages. This article also does not address the effects of afforestation on peak flows and volumes specifically, so further research is needed to see if it can be used to reduce flooding. Filoso S, Bezerra MO, Weiss KCB, Palmer MA 2017. “Impacts of forest restoration on water yield: A systematic review,” PLOS ONE 12(8): e0183210. https://doi.org/10.1371/journal.pone.0183210 This article assesses empirical data from various studies on the effects of forest restoration (reforestation) and other forms of forest cover expansion (afforestation) on water yield, which includes the direct metrics of low flow and annual flow. Data was taken from 167 articles to assess these water yield. In addition, 43 of these articles produced data on indirect metrics such as flood frequency, groundwater recharge, and infiltration. Key findings include: • 80% of all study cases reported that reforestation and afforestation decreased water yields, while 6% reported an increase in water yields. • The remaining studies reported no change, mixed results, or unclear data. • 82% of studies with data on peak flows and flooding frequency reported a decrease in those metrics. • 67% of studies with data on groundwater levels reported a decrease in water level with expanded forest cover. • 83% of studies reporting on infiltration capacity reported an increase in capacity.

242 This study assesses the effectiveness of reforestation and afforestation in reducing low flows and total annual flow by aggregating data corresponding to projects where those processes occur. However, it does not go into the specifics on how best to reduce water yields through those processes, simply that a reduction will most likely occur. Unlike other studies, it does give insight into the effects of reforestation and afforestation on peak runoff rates, flooding frequency, and groundwater recharge. Recommendations were made to monitor changes in water yield and other hydrologic data for future reforestation and afforestation projects, even if those projects are not hydrology driven. This can help us better understand and quantify the unintended consequences of forest cover increase, such as a decrease in water supply. Gao, Yongxuan, Richard M. Vogel, Charles N. Kroll, N. LeRoy Poff, and Julan D. Olden 2009. “Development of Representative Indicators of Hydrologic Alteration,” Journal of Hydrology. The objective of the study was to develop a small set of independent and representative hydrologic indicators that can best characterize hydrologic alteration. The paper mentions that over 170 hydrologic indicators have been developed to describe different components of flow regimes, including the IHA to evaluate hydrologic changes focused on reservoirs and other forms of river regulation. The results revealed that the recently introduced metrics “ecodeficit” and “ecosurplus” can provide a good overall representation of the degree of alteration of a streamflow time series. Ge, S. G. Zhou, Z. Zhang, X. Wei, S. G. McNulty, and J. Vose 2005. “Forest and Water Relationships: Hydrologic Implications of Forestation Campaigns in China,” U.S. Forest Service Miscellaneous Publications Series https://www.srs.fs.usda.gov/pubs/ja/ja_sun012.pdf. This study examines the effects of both reforestation and afforestation (both referred to as forestation) on the hydrology of the areas surrounding these processes. It does so by drawing on existing literature in this field as well as observing and predicting the future effects of forestation on watersheds in China, where urbanization and poor land management have caused forested areas to disappear and erosion to become more common. Key findings include: • Long-term empirical data shows a varied response to deforestation in the United States. • A paired watershed study conducted at Coweeta Hydrologic Laboratory showed that deforestation increased streamflow by 200-400 mm/year. • However, peak flow rates in a watershed near New Brunswick showed that peak flow rates were not significantly affected after 23.4% forest removal. • Deforestation impacts are most pronounced during dry periods. • Forest management affects small/moderate peak flow rates more significantly than runoff volume. • Predicted effects of forestation in China based off current literature: 1) forestation and converting croplands to tree farms will likely reduce annual streamflow, as trees use more water than crops, 2) generally, forestation will likely not reduce peak flows and volumes, meaning it will have a minimal impact on flooding, and 3) hydrologic benefits from forestation are low in the short term, as trees take a long time to grow and begin to uptake a significant amount of water. This investigation into the effects of forestation in China does yield some predictions that can be applied to the same practices in the United States. One major limitation of the study is that it does

243 not distinguish between the effects of reforestation and afforestation. While it can be assumed that reforestation has mainly occurred to replace China’s diminishing forests, it is important to separate the two. The conclusions drawn in this study show that reforestation and afforestation might not be effective in reducing peak flows and volumes from storms but can reduce annual streamflow. This means that they may not be efficient ways of reducing flooding or mitigating development. In addition, the length of time it takes forestation to work to reduce flows means that detention may be better for doing so if a timely solution is needed. Georgia Forest Commission (GFC) 2011. Does Reforestation Pay? This report provides a succinct summary of the long-term economic benefits of reforestation and works through brief examples of NPV and internal rate of return at different costs, scenarios, site indices, etc. It also provides assumptions and concrete data points involved in the economic cost/value of reforestation, though does not address costs or economic benefits specific to hydromodification. Gomez-Baggethun, E. and Barton, D.N. 2013. Classifying and valuing ecosystem services for urban planning. Ecological Economics 86(2013) 235-245. Available at: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.870.7709&rep=rep1&type=pdf This paper presents a synthesis of economic approaches to ecosystem services valuation and identifies many of the key connections between ecosystem attributes and specific services valued by people in urban settings. It discusses how each of a variety of economic valuation methods may be able to be applied at different geographic scales. It is potentially useful as a primer on some of the more common approaches to economic valuation of ecosystem services. Gorte, R. 2009. U.S. Tree Planting for Carbon Sequestration, May. The author estimates, noting wide variation, the range of carbon sequestration based on afforestation of crop or pastureland (2.2-9.5 metric tons/acre/year) and reforestation (1.1-7.7 metric tons/acre/year). (Afforestation is the act of growing trees in a previously barren area, as compared to reforestation, which addresses re-growing trees in forested areas that have been cleared or are experiencing tree loss.) The paper addresses the scope of land requirements for afforestation and potential costs (ranging from $250 to $2000 per acre) and covers implications/limitations of the program for its target audience (U.S. Congress). The relevant parts of the reference are that it gives data points on the cost of afforestation. However, it does not address changes in hydrology associated with afforestation. Guida, R. J., Swanson, T. L., Remo, J. W. F., and Kiss, T. 2015. “Strategic floodplain reconnection for the lower Tisza River, Hungary; Opportunities for flood-height reduction and floodplain-wetland reconnection,” Journal of Hydrology, 521, 274-285. doi:http://dx.doi.org.mines.idm.oclc.org/10.1016/j.jhydrol.2014.11.080 This article assesses techniques to reduce flooding in the Lower Tisza River in Hungary. Currently, levees play a large role in holding back flood waters, but they also have depleted historical wetlands and disconnected floodplains. Because flood levels have been rising steadily for the river, possible solutions are being considered including heightening levees and reconnecting floodplains by either removing or relocating levees. This article explores the impacts of these options through various modeling techniques by trying to balance four objectives: flood-

244 level reductions, minimized levee-rebuilding costs, wetland reconnection, and minimized human impact. Key findings include: • A scenario which involved removing all levees would have the greatest hydrological benefits but would impact too many people. • Existing levees prevent some areas from being flooded but causes flooding in other areas. • Removing levees in certain areas could cause flood areas to widen, but also flood heights to decrease. • The best option as indicated by the models was removing the levees along the west side of a reach of the river. • This option was considered a better overall option than heightening the existing levees, which shows that a situation could arise where levees should be removed. • The option of heightening the levees came at the least socioeconomic price but would do the least to rehabilitate the floodplain. While this study is a single case study and based off a model, it could be used to guide decision- making processes for similar projects and models. The metrics it uses to rank the different options could easily apply to different rivers in the United States. While model inputs and techniques would have to be changed, this article could provide a framework for investigation into levee removal and cost-benefit analysis. Guida, R. J., Jonathan W.F. Remo, and Secchi, S. 2016. “Tradeoffs of strategically reconnecting rivers to their floodplains: The case of the lower Illinois river (USA),” Science of the Total Environment, 572, 43-55. doi:http://dx.doi.org.mines.idm.oclc.org/10.1016/j.scitotenv.2016.07.190 This article explores the costs and benefits of alternative strategies to reconnect the La Grange segment of the Illinois River to its floodplain. Historic alterations to the river, such as levee construction and draining of wetlands have increased flood levels, which in turn leads to continuous heightening of levees. Different floodplain rehabilitation options include removing all levees, setting back existing levees 500 m, setting back existing levees 1000 m, removal of levees in the most critical areas, and leaving in place all levees with the intention of heightening them in the future. Both the monetary/societal costs and hydrological benefits of these options are considered. Key findings include: • Considering only economic costs, maintaining and heightening the existing levees is by far the most effective. However, this option would not have nearly the same floodplain rehabilitation effects and may only serve to kick the can down the road until the levees have to be heightened again. • If levees are going to be set back, it may involve property buyouts for those behind the current levees. • For the La Grange segment, the levees that would have to be removed to provide the highest economic benefit are also the most expensive to remove. • Levee removal not only improves floodplain connectivity but provides other ecosystem services as well.

245 This study provides not just a framework for floodplain connectivity options in the Illinois River, the methods used can be tweaked to apply to rivers around the country as they undergo similar problems. One lesson this case teaches is to anticipate an increase in peak flows and volumes when building levees and other flood control structures. The existing levees were probably built as close to the river as possible so as not to inhibit development, but as the watershed got developed over time, the flows increased to the point where they were in the wrong location and had to be heightened. Another takeaway is the danger of draining and developing in wetlands. Had the wetlands surrounding the river been left in place, they could have helped to absorb floodwaters and prevented the levees from needing to be raised. Haris, Harizah & Chow, Ming Fai & Usman, Fathoni & Mohd Sidek, Lariyah & A Roseli, Z & D Norlida, M. 2016. Urban Stormwater Management Model and Tools for Designing Stormwater Management of Green Infrastructure Practices. IOP Conference Series: Earth and Environmental Science. 32. 012022. 10.1088/1755-1315/32/1/012022. This document presents review of well-known modeling tools and an assessment of applicability for GI applications. SWMM (EPA; XP-; MIKE-), HSPF are specifically reviewed. A table of quantity components representable in the model list is provided (Table 3). A table of GI-specific models and case studies are provided (Table 4). Tables 3 and 4 in the document are useful to guide the current research project, not only as a starting point, but also as a prospective product. Table 3 in the document has assessment categories somewhat incorrectly assigned, however the concept is valuable and adaptable. Holland, Craig 2016. “Financing Solutions for Stormwater Runoff,” Environmental Finance, Naturevest, 15 June, https://www.environmental-finance.com/content/analysis/financing- solutions-for-storm-water-run-off.html. Washington, D.C. instituted a first-of-its-kind SRC trading program as part of an update to its building codes in 2013. The program created options to build stormwater management on site or combine on-site management with an off-site credit purchase. This private-to-private credit market primarily serves land development, but the concept is scalable and replicable. Costs could be substantial at larger watershed scale, but projects could have potential to be investment opportunities. Huang, M., Zhang, L., and Gallichand, J. 2003. “Runoff responses to afforestation in a watershed of the Loess Plateau, China,” Hydrological Processes, 17(13), 2599-2609. This study uses a paired watershed approach to explore the hydrologic impacts of afforestation in north-western China. Deciduous trees were planted on 80% of the area of a 1.15 km2 watershed and the hydrology of this watershed was compared to a similar watershed that had not undergone afforestation. The rest of the afforested watershed remained as natural grassland. Data was collected between 1956 and 1980. Key findings include: • Reforestation decreased the average magnitude of high flow by 8.78% and shortened high flow duration by 2.2 days compared to the reference time frame flows. • Estimated cumulative runoff yield in the treated watershed was decreased by 32%. • Annual runoff reduction increases with the age of the planted trees, with a maximum reduction of 50% 15 years after planting.

246 • Reduction in monthly runoff occurred mainly from June through September, with little runoff reduction occurring at other times in the year because the trees are deciduous. • The treated watershed saw a decrease in runoff volume and peak flows during storm events, with a more significant decrease in peak flows. This study shows the hydrologic benefits of afforestation. While this article does not compare different types of vegetation/forest cover added, it does stress the importance of increasing evapotranspiration rates of the vegetation within the watershed to achieve those benefits. It also shows that deciduous trees will mainly reduce runoff rate from spring to late summer. Afforestation of deciduous trees can also feasibly reduce flooding by decreasing peak flow rates and runoff volumes. It is also shown here to reduce water yield, which comes along with the possible negative effect of reducing water supply in already stressed areas. Low-flow effects were not mentioned in this article. Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). 2015. Preliminary guide regarding conceptualization of multiple values of nature and its benefits, including biodiversity and ecosystem functions and services (deliverable 3(d)). Available at: https://www.ipbes.net/policy-support/methodological-guidance. This is a preliminary guidance document produced in 2015 as part of an ongoing project by IPBES to establish systematic consideration of ecosystem services and biodiversity in the international policy arena. It provides good background material for the state-of-the-art approaches to ecosystem valuation and high-level considerations that may be relevant to this research— particularly the human element of ecosystem valuation. Jones, C., B. McGee, L. Epstein, E. Fisher, P. Sanner, E. Gray 2017. Nutrient Trading by Municipal Stormwater Programs in Maryland and Virginia: Three Case Studies, World Resources Institute, Washington, DC. The report evaluated existing nutrient trading programs and “concluded [that] three factors are critical to successfully introducing nutrient trading in the stormwater sector: the existence of a clear regulatory basis for trading, a stormwater discharge permitting strategy that allows and facilitates trading, and effective outreach to the agricultural community.” Jones, J., Swanson, F.J., Wemple, B. C., and Snyder, K.U. 2000. “Effects of roads on hydrology, geomorphology, and disturbance patches in stream networks,” Conservation Biology, Vol 14, No. 1, pp 76-85. Largely an ecology paper relating impacts of transportation infrastructure on biological hydrology. The authors examine the ecology of research watersheds in Oregon. There is no reported modeling, although the interpretation appears to be the result of correlation analysis. Joksimovic, D., Z. Alam 2014 “Cost Efficiency of Low Impact Development (LID) Stormwater Management Practices,” Procedia Engineering: Vol. 89. This paper describes a recent study of LID techniques in Canada. The authors argue that the most cost-effective solutions for runoff reduction are an infiltration trench in combination with green roofs. The paper includes cost comparisons among various combinations of LID techniques in an urban area and plots capital costs of LID techniques against the runoff reduction achieved with those techniques.

247 Kalantari, Z., Briel, A., Lyon, S.W., B. Olofsson, and L. Folkeson 2014. “On the utilization of hydrological modelling for road drainage design under climate and land use change,” Science of the Total Environment, 475 (2014) 97–103. Authors compare structure sizing for road drainage structures using methods that do/do not consider process-based representations of a landscape's hydrological response. The study quantifies potential increases of runoff in response to future extreme rain events in a 61 km2 catchment (40% forested) in southwest Sweden using a physically based hydrological modeling approach. The authors use MIKE-SHE and MIKE-11 as coupled hydrology and hydraulic models. The research findings highlight the utility of physically based hydrological models to identify the appropriateness of road drainage structure dimensioning. The focus is on sizing drainage structures at the transportation/stream interface to convey the remotely generated runoff, the ideas in the paper can be easily reversed to estimate the impact of transportation infrastructure on upstream and downstream response as well as incorporate engineered change (or at least influence) on systemic responses to mitigate effects of new or reworked infrastructure. Kalantari, K., Ferreira, C.S.S., Koutsouris, A.J., Ahlmer, A-K., Cerdà, A., Destouni, G. 2019. “Assessing flood probability for transportation infrastructure based on catchment characteristics, sediment connectivity and remotely sensed soil moisture,” Science of the Total Environment, 661 (2019) 393–406. The authors examine a statistical probability estimation model of flooding at major road-stream intersection sites, where water, sediment and debris can accumulate and cause failure of drainage facilities and associated road damages. Two areas in south-west Sweden, affected by severe floods in August 2014, are used in representative case studies for this development. A set of physical catchment descriptors (PCDs), characterizing key aspects of topography, morphology, soil type, land use, hydrology (precipitation and soil moisture) and sediment connectivity in the water- and sediment-contributing catchments, are used for the predictive flood modeling. The modeling is a flood-frequency-analysis type of modeling; watershed models are NOT used in the study. Integrate the spatiotemporal characteristics of remotely sensed soil moisture in indices of sediment connectivity is employed allowing for investigation of the role of soil moisture in the flood probability for different road-stream intersections. The results suggest five categories of PCDs as especially important for flood probability quantification and identification of particularly flood-prone intersections along roads (railways, etc.): channel slope at the road- stream intersection and average elevation, soil properties (mainly percentage of till), land use cover (mainly percentage of urban areas), and a sediment connectivity index that considers soil moisture in addition to morphology over the catchment. The authors two case studies, indicate the most important model variables for identifying particularly flood-prone intersection sites in these cases: a combination of topographical (Elevation and Channel slope), soil type (mainly till percentage) and land cover (specifically urban cover) characteristics, along with a modified sediment connectivity index accounting for soil moisture in addition to landscape morphology. The concept of PCDs (a metric) is relevant to the current project. The important metrics are not surprising however the concept of sediment connectivity index is somewhat novel in the context of drainage engineering. Like other papers that use/propose metrics the research role will be to define these into useable terms and provide ways to calculate the metrics.

248 Karamouz, M., Ana Hosseinpour, A., and Nazif, S. 2011. “Improvement of Urban Drainage System Performance under Climate Change Impact: Case Study,” Journal of Hydrologic Engineering, Vol. 16, No. 5, May 1, 2011. ©ASCE, ISSN 1084-0699/2011/5-0–0. StormNET (appears to use EPA SWMM hydraulics engine) is used to drive an algorithm to find the effective BMPs for improving the performance of an urban drainage system in dealing with floods. In this algorithm, the effects of climate change and anthropogenic changes on the urban flood regime and characteristics are evaluated. For this purpose, long-lead rainfall series under climate change effects are developed using downscaling methods. The Tehran metropolitan area is considered as the case study. The BMPs are evaluated based on their effectiveness in reducing the flood volume and peak with the least cost. The concepts in this paper are applicable to the mitigation research with extensions to larger physical scale unit processes. The author's algorithm does admit diversions and storage elements (detention ponds) as BMPs so the scaling might be quite straightforward. The model appears to be specific and research to generalize (as a semi-automated) seems necessary. Kim, J. and J. H. Ryu 2019. “Modeling Hydrological and Environmental Consequences of Climate Change and Urbanization in the Boise River Watershed, Idaho,” Journal of the American Water Resources Association, 55 (1): 133-153. The authors employed HSPF and land use/land cover changes (influenced by climate models) to estimate changes in stream flows in Idaho. Several land use scenarios were used to reflect increasing urbanization and loss of pre-urban conditions. The changes on a percent basis were small (5 percent). The total land area is unchanged and the changes are represented as a re- apportionment of existing quantities (like portfolio re-balancing). The authors report that springtime and winter impacts are substantial in their study. These impacts were observed even in the baseline land use scenarios, so the climatic change imparts a substantial signal in their estimates -- nevertheless the land use changes are not trivial. This document is relevant as an idea to use scenario approaches to estimate responses to different conditions. Furthermore, choosing to believe their modeling is adequate, it does not take large changes (as a percentage) in land use/land cover conditions to impact a watershed response -- hence volume management by leveraging land uses is feasible. King County Water and Land Resources Division (December 2017). How In-Lieu Fee Mitigation Works. (https://www.kingcounty.gov/services/environment/water-and- land/wetlands/mitigation-credit-program/HowILFWorks.aspx) This document provides an example of an off-site, out-of-kind tool—specifically in-lieu fee. In- lieu fees are paid to a local government or nonprofit natural resources management entity that is responsible for the mitigation (description from the U.S. Army Corps of Engineers and USEPA). The document provides a brief overview of in-lieu fees and outlines a process for mitigating construction impacts. In-lieu fees are not considered as part of the current project because the approach may or may not result in mitigation occurring within the watershed of the project impact.

249 King, D. and Hagan, P. 2011. Costs of Stormwater Management Practices in Maryland Counties, October. This reference addresses the costs of GI based on an extensive literature review. It outlines cost estimates (per impervious acre treated) for several GI solutions; including up-front costs, annual maintenance costs, etc. It includes several helpful tables in the appendix, including adjustments to cost estimates based on site/region. Landers, D. and Nahlik, A. 2013. Final Ecosystem Goods and Services Classification System (FEGS-CS). U.S. Environmental Protection Agency, Washington, D.C. EPA/600/R-13/ORD- 004914. Available at: https://cfpub.epa.gov/si/si_public_record_Report.cfm?Lab=NHEERL&dirEntryId=257922. This reference describes an approach for the systematic quantification of ecosystem services by classifying categories of services on which to focus. Due to criticisms associated with the outlining of broad categories of ecosystem services, such as in the 2005 Millennium Ecosystem Assessment, this document explores principles for defining a specific set of ecosystem services on which to focus. The report is aimed at technical practitioners with the goal of establishing norms for defining, describing, and quantifying ecosystem services. It therefore has potential direct relevance to the current NCHRP effort. Lantin, A. et al. 2019. Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff, NCHRP Report 918 (Project 25-53). Although focused on TMDLs and not stormwater quantity, the report includes relevant background information for the current project. An important question is how transferrable the concepts transfer from TMDLs to stormwater quantity. Key elements include” • A chapter (Chapter 8) addressing “Effectiveness of Innovative Solutions,” which include trading programs and on-site/off-site approaches. Mentions also “stormwater banking, pollutant trading, off-site mitigation off-site control, and other holistic compliance strategies.” • Notes that TMDL strategies involve “solutions within the DOT right-of-way and watershed-based stormwater management efforts.” • At a high level describes an off-site versus on-site planning track. • States that there are “two major categories of watershed-based approaches: pollutant equivalency methods and restoration of ecosystem services. Pollutant equivalency methods include stormwater banking, pollutant trading, payment in-lieu, and off-site mitigation. In these approaches, pollutants are removed from other sources in the watershed to offset the excess pollutant load from the MS4. Restoration of ecosystem services generally refers to habitat restoration projects. This strategy offsets excess pollutant loads by improving the hydrology, geomorphology, and/or ecological processes within a degraded portion of a watershed. These projects often have multiple benefits for the entire watershed that go beyond off-setting loads.” • Identification that “The ability to institute watershed-based approaches depends on the flexibility of existing legal frameworks. Permittees are often subject to multiple levels of regulation, including at the local, state, and national levels.”

250 • Notes that “Watershed-based approaches are more applicable to certain pollutants than others.” • Identifies the following key considerations for trading programs: • “For a trading program to be successful, there must be enough permittees within a watershed who are able to exceed contaminant removal requirements (credit generators), and who cannot adequately meet contaminant removal requirements (credit buyers).” • “The list of potential partners for restoration efforts is likely larger than for trading programs, as nonprofits, nongovernmental organizations, and research and education- oriented groups are often willing to assist in these efforts.” • “A crediting program must define baseline conditions, baseline requirements, trading ratios, methods for the calculation of credits, and methods for credit accounting and tracking (Sammans et al. 2015).” • “Five categories of trading ratios are commonly used: delivery, location, equivalency, retirement, and uncertainty (EPA, 2007).” • “Where restoration projects are involved, tools such as a Watershed Health Index can be useful (EPA, 2018). Watershed Health Indices consider six ecological attributes (landscape condition, habitat, hydrology, geomorphology, water quality, and biological condition), and calculate index values that can be used to compare health within a group of watersheds.” • Discusses nutrient offset/crediting programs in North Carolina, Virginia, and California. • Mentions conversion of agricultural property to natural land as a measure. • Mentions that the “The Environmental Trading Network provides a comprehensive collection of existing and planned water quality trading and other environmental market- based programs (Keiser & Associates, LLC, 2018).” Laurent M. Ahiablame, L. M., Engel, B.A., and I. Chaubey 2012. “Effectiveness of Low Impact Development Practices: Literature Review and Suggestions for Future Research,” Water Air Soil Pollution, 223:4253–4273. A literature review of LID practices by process (type of LID; permeable pavement, green roof, bioretention basins), focused mostly on water quality performance. The review includes a section on modeling LID for estimating water quality enhancement. There is little explicit emphasis on volumetric control. Authors review in some detail use of SWMM, SUSTAIN, and L-THIA-LID as such tools. The authors conclude with a remark that research is needed for scale-up to represent LID performance at large physical scales within a region. Quoting from the paper: "Scaling of results from lot scales to larger scales (e.g., watershed, region) will be a key advancement to evaluate LID practices so that specific processes such as the transport and transformation of pollutants, interflow, first flush, and erosion can be incorporated in watershed models to accurately represent LID practices." This scaling issue likely still exists -- since the writing of this paper there has been substantial effort employed in SWMM to address specific LID/GI processes within the tool. This document

251 contains an extensive literature list (a bit dated) that can be examined to obtain performance estimates for any guidance tools created. Lemly, J., J. B. Johnson, L. Gilligan, and Erick Carlson 2013. Setting Mitigation in the Watershed Context: Demonstration and Description of Colorado’s Watershed Approach to Wetland Compensatory Mitigation, Colorado State University. The report describes a general watershed approach specifically for wetland mitigation involving three components: “1) building program partnerships, 2) setting watershed goals, and 3) using monitoring and assessment information to inform decision-making based on the established goals.” The method is referred to as the Colorado Watershed Approach. Although it applies to wetlands mitigation, some of the concepts may be broader and more applicable to the current project. Martin, D. M., J. W. Labadie, and N. L. Poff 2015. “Incorporating Social Preferences into the Ecological Limits of Hydrologic Alteration (ELOHA): A Case Study in the Yampa-White River Basin, Colorado,” Freshwater Biology. Using the ecological limits of hydrologic alteration (ELOHA) framework, which takes a regional approach towards assessing relationships between human‐caused river flow alterations and social–ecological benefits, this study incorporates social preferences into environmental flow management problems using a case study. This study presents development of a decision support tool to prioritize river basin criteria and to rank river segments in order of combined hydro‐ ecological and social environmental flow needs. Massoudieh, A., Aflaki S., Panguluri, S. 2016. User’s Manual for Green Infrastructure Flexible Model (GIFMod) Contains link to: Massoudieh, A., M. Maghrebi, B. Kamrani, C. Nietch, M. Tryby, S. Aflaki, S. Panguluri (2017), A flexible modeling framework for hydraulic and water quality performance assessment of stormwater green infrastructure, Environmental Modeling and Software, 92, pp 57–73. GIFMod is a computer program used to construct models for evaluation of the performance of stormwater green infrastructure (GIs) and other types of urban and agricultural BMPs. The program is designed to provide a good level of flexibility to the users to set up the model configuration and to select the processes governing the hydraulics and water quality. Therefore, GIFMod can be applied to evaluate a wide variety of GI-related water quality problems. A model build using GIFMod should be conceptualized as an interconnected set of different types of media ranging from surface water to vadose zone and groundwater. Modeling of GI performance in GIFMod can be done in three levels including hydraulics, particle transport and constituent fate and transport. A GI model can be constructed by a combination of blocks representing surface water ponds, streams, overland flow, unsaturated soil, saturated media and storage that are connected either through natural interfaces, pipes, or other user-defined connectors. The model appeared to be useful -- however upon deeper examination the model is intended for a scale far too small for the NCHRP application. The model is intended to be at the device scale (to model how a device itself performs). Quoting from the paper: "GIFMod can be used in conjunction with existing watershed models such as SWAT (Arnold et al., 1998) and SWMM (Rossman 2004, 2015). For instance, the output hydrographs and/or pollutographs from these models could be used as input to GIFMod to

252 consider the processes effecting performance in more detail. Similarly, GIFMod could be used to estimate effective parameters used by the watershed models such as water capture rate or pollutant removal rates based on the more detailed hydraulic and fate/transport relationships available to the modeler in GIFMod. These values would be used to parameterize the more simplified representation of GI in the watershed models." It may have utility later in the research as a tool to generate performance parameters for devices to be aggregated into larger scale responses. McCleary, R. B. 1999. A Stormwater Banking Alternative for Highway Projects. The document outlines an agreement between state agencies for addressing the mitigation of stormwater quality off-site. It notes the parameters and logistics regarding stormwater management controls—system of credits/debits, funding stormwater banking projects, etc. The document is focused on water quality, not quantity, but could serve as a blueprint for agreements within state agencies in other contexts. Naturally Resilient Communities (NRC) 2017. “Naturally Resilient Communities - Case Studies,” NRCSolutions.org, http://nrcsolutions.org/wp- content/uploads/2017/05/NRC_CaseStudies_Tucson_AZ.pdf, Accessed July 20, 2019. Naturally Resilient Communities (NRCSolutions.org) is a partnership of the American Planning Association, American Society of Civil Engineers, Association of Floodplain Managers, National Association of Counties, and the Nature Conservancy with support from the Kresge Foundation. The Green Streets Active Practice Guide in Tucson, Arizona integrated GI directly into all publicly funded roadway development projects. They define GI as areas that treat the first 0.5” of rainfall that falls within public right-of-way (ROW), and complete infiltration is required within 24 hours. The program receives public funding. Reported costs are $23.00 per square foot with net benefit annualized over 10 years of $82,270.00/yr. Results of the program include reduction in flooding and pollution (mainly fecal coliform and copper) which are a benefit to public health. National Ecosystem Services Partnership. 2016. Federal Resource Management and Ecosystem Services Guidebook. 2nd ed. Durham: National Ecosystem Services Partnership, Duke University. Available at: https://nespguidebook.com. This guidebook, in three parts, was developed as the capstone to the FRMES project undertaken by the NESP, which brought together representatives from a variety of U.S. federal agencies, academia, nongovernmental organizations, and think tanks to develop consistent approaches to incorporating consideration of ecosystem services into federal resource management decision- making processes. Section 3 of the three-part guidebook is titled “Ecosystem Service Assessment Methods” and includes a framework for considering the benefits of ecosystem services that highlights the needs for benefit-relevant indicators (i.e., to account for potential variability in value depending on a variety of site-specific factors) and provides tools for identifying relevant ecosystem services (e.g., causal chains). This reference appears to be highly applicable to the current effort because it highlights processes that may be relevant to decision-making regarding the geographic placement of alternative off-site, out-of-kind techniques; and properly accounting for potential co-benefits. Further, because it comprises guidance for federal agencies, any leverage of the guidance provided within the document(s) should be consistent with federal rules and norms, which would be beneficial for any guidance provided to State DOTs across the country.

253 Naturally Resilient Communities (NRC) 2019. “Maywood Avenue Stormwater Volume Reduction Project, Toledo, Ohio.” NRCSolutions.org, http://nrcsolutions.org/maywood-avenue- stormwater-volume-reduction-project-toledo-oh/, Accessed July 20, 2019. The Maywood Ave. Stormwater Volume Reduction Project in Toledo, OH included community maintained bioswales, rain gardens, and pervious sidewalks. The project received American Recovery and Reinvestment Act stimulus funding and partnered with the U.S. Department of Agriculture (USDA) and Consumer Services, Green jobs Youth Program, Natural Resource Conservation Service, and had a Green Reserve 20% set aside. The project improved water quality, reduced flooding, and planted bioswales in beautified neighborhoods. Odefey, J., Detwiler, S., Rousseau, K., Trice, A., Blackwell, R., O’Hara, K., Buckley, M., Souhlas, T., Brown, S., and Raviprakash, P. 2012. Banking On Green: A Look at How Green Infrastructure Can Save Municipalities Money and Provide Economic Benefits Community- wide, April. This document reports on the benefits of GI. It is designed for use by municipal and utility officials, elected representatives, and the public. It includes sections on benefits such a cost- effective runoff management, increased energy efficiency and reduced energy costs, reduced economic impacts from flood events, and protection of public health and a reduction of illness- related costs. Ogden, F. L., Pradhan, N.R., Downer, C.W., and Zahner, J.A. 2011. “Relative importance of impervious area, drainage density, width function, and subsurface storm drainage on flood runoff from an urbanized catchment,” Water Resources Research, Vol. 47, w12503, doi:10.1029/2011wr010550, 2011. Authors use the GSSHA model to study response on a 5 square mile watershed and examine the importance of land use and related metrics on runoff generation. Findings were that increases in drainage density (development) and imperviousness had substantial impact on the response. The study used a concept of "width function" to express the comparative width of drainage network with respect to the total watershed width (available portion of watershed to actually carry discharge), which was demonstrated to be important with respect to runoff production. The width function might be a useful metric to develop to perform simplified estimation for highway impact on watershed (or watershed impact on highway). ODOT ongoing. “Assessment of Existing and Potential Volume Reduction for Post Construction Stormwater Management,” ODOT research. This multi-year research project scheduled for completion in 2021 is to develop additional options for post-construction BMPs suitable for use by ODOT in meeting stormwater quantity and quality mitigation requirements. The identified need is to be able to address the current limitations of space in the ROW and the frequent occurrence of soils with poor infiltration characteristics. Opperman, J. 2014. A Flood of Benefits: Using Green Infrastructure to Reduce Flood Risks. The document explores the benefits in floodplain ecosystem services ranging from nutrient sequestration to open space and recreation, with a specific focus on protecting the productivity of freshwater fisheries. It heavily emphasizes the role of GI. The document also addresses the benefits of floodplain ecosystem services and notes specific constraints in the implementation of GI (such as lack of familiarity among engineers and decision-

254 makers, amount of land required, economic impacts of reduced agricultural production, and more) in flood management and identifies possible solutions (multiple sources of funding, flood compatible agriculture, etc.). Parrish, J. 2018. Off-Site Stormwater Crediting: Lessons from Wetland Mitigation. U.S. Environmental Protection Agency, Region 9. April. Available at: https://www.epa.gov/sites/production/files/2018-10/documents/off- site_stormwater_crediting_lessons_from_wetland_mitigation-2018-04.pdf This reference identifies a host of lessons learned from wetland mitigation banking that are applicable to stormwater banking; as well as recommendations for effectively creating stormwater banking programs. It also identifies important permitting and program design elements, particularly for MS4s. Patora, K. 2009. Final Cost-Benefit and Least Burdensome Alternative Analysis, August. Retrieved from https://fortress.wa.gov/ecy/publications/documents/0906026.pdf. The reference provides a comparison of wetland mitigation banking with the preexisting method of concurrent mitigation in Washington. Regarding the decision to switch from concurrent mitigation to wetland mitigation banking, the study places the benefit of wetland mitigation banking at up to $2.3 million per year. The reference contains sections on the quantified costs and benefits of concurrent mitigation vs. wetland mitigation banking. The sections are somewhat confusing and poorly organized. Concurrent mitigation generated a median loss of $3.7 million annually. Wetland mitigation banking generated a median loss of $1.3 million annually. The reference includes an extensive resource reference list on the value of wetland services and costs of wetland construction. Penniman, D. C., M. Hostetler, T. Borisova, and G. Acomb 2013. "Capital Cost Comparisons between Low Impact Development (LID) and Conventional Stormwater Management Systems in Florida," Suburban Sustainability: Vol. 1: Issue 2, Article 1. DOI: http://dx.doi.org/10.5038/2164-0866.1.2.1 Available at: http://scholarcommons.usf.edu/subsust/vol1/iss2/1. The article describes the implementation of LID in four projects in Florida, which are a mix of residential, commercial, and roadway, including the amount, type, and/or location of the space involved in the project as well as differences between conventional and LID options. It covers projects using structural (permeable surfaces, soil amendments, underdrains, etc.) and non-structural (low-impact landscaping, minimized soil stripping and/or compaction, etc.) LID practices and contains cost comparison between conventional and LID for a small (1.25 miles) roadway project. Though LID was more expensive than conventional in embankment and sidewalk surfacing costs, overall LID showed a 12 percent cost savings over conventional techniques.

255 Poff, N. L., B. D. Richter, A. H. Arthington, S. E. Bunn, R. J. Naiman, E. Kendy, M. Acreman, C. Apse, B. P. Bledsoe, M. C. Freeman, J. Henriksen, R. B. Jacobson, J. G. Kennen, D. M. Merritt, J. H. O’Keeffe, J. D. Olden, K. Rogers, R. E. Tharme, and A. Warner 2010. “The Ecological Limits of Hydrologic Alteration (ELOHA): A New Framework for Developing Regional Environmental Flow Standards,” Freshwater Biology. The paper introduces a method for establishing relationships between flow alteration and ecological responses. Poresky A., M. Gray, E. Strecker, K. Havens, Y. Li, K. Koryto, S. Taylor, L. Larsen, T. Dietrich, M. McCabe, and R. Pitt 2019. Limitations of the Infiltration Approach to Stormwater Management in the Highway Environment, NCHRP (Project 25-51), contractor draft final report (1/31/19). After heavy emphasis in prior stormwater quality efforts to emphasize infiltration, this report discusses the limitations inherent in the approach. Because the current study is not emphasizing in-kind techniques, the findings are not directly applicable to this study. Prudencio, L. and S. Null 2018. “Stormwater management and ecosystem services: a review,” Environmental Research Letters 13 (2018) 033002. Available at: https://doi.org/10.1088/1748- 9326/aaa81a. Reference documents the range and extent to which ecosystem services are accounted for in literature on stormwater management, particularly use of GI. It provides a good overview of the extent of types of ecosystem services documented in GI stormwater literature. Radavich, K. A. 2015. Assessing the effect of best management practices on water quality and flow regime in an urban watershed under climate change disturbance. Master's Thesis. Colorado School of Mines. This thesis illustrates how the characteristics of distinctive BMP types influence compliance and flow regimes. The focus was on water quality aspects. The thesis used SUSTAIN for the quality components and SWMM-CAT to provide the volumetric (quantity) inputs. Infiltration-dominated BMPs reduced the total pollutant load at the outlet, but residual pollutants were more concentrated, whereas treat and release-dominated BMPs resulted in lower pollutant concentrations and better compliance at the outlet, but higher pollutant loads were observed with minimal peak flow reduction. The thesis author concluded that stormwater modeling at the watershed scale can ultimately inform strategic BMP selection based on current and future hydrologic characteristics and desired outcomes; essentially validating the conjecture of the research project. The thesis is largely a single case study, and not transportation infrastructure specific. Richter, B. D., J. V. Baumgartner, J. Powell, and D. P. Braun 1996. “A Method for Assessing Hydrologic Alteration within Ecosystems,” Conservation Biology, Vol 10, No. 4 (August). This paper proposes a method to evaluate ecological responses to modifications to river flows: IHA. It includes 32 indicators resulting in 64 tests of central tendency and dispersion of the 32 indicators based on “biologically relevant hydrologic parameters.” The method attempts to: 1) “statistically characterize the temporal variability in hydrologic regimes using biologically relevant statistical attributes, and 2) to quantify hydrologic alterations associated with presumed

256 perturbations…by comparing the hydrologic regimes from pre-impact and post-impact time frames.” The IHA is based on daily means flows. Considering the fundamental hydrologic regimes: magnitude, timing, frequency, duration, and rate of change. The method presumes a defined impact, e.g., a dam or diversion, but the source of changes could be multiple, e.g., a dam, watershed development, and climate change.) The paper also discusses changes in flora and fauna including bottomland forests. Sammans, E., F. Snead, E. Strecker, M. Leisenring, S. Sahu, K. Havens, M. Venner 2015. Feasibility Study for the Development of a Framework for an Effective Stormwater Quality Credit/Banking/Trading System, Federal Highway Administration, Final Report. As stated in the report “the goals and objectives …are 1) to provide a synthesis of water quality crediting program components and 2) to assess the state of the practice for stormwater quality banking and credit systems currently being used at national, state, and local levels, and 3) provide practical recommendations for DOTs on the use of water quality crediting to meet regulatory requirements for stormwater quality.” The report applies predominantly to water quality but does include some mention of stormwater volume reduction credits. The report discusses program challenges and considerations with crediting programs including regulatory acceptance, demonstration of on-site infeasibility, overlapping requirements for water quantity, appropriate standards, calculating and tracking credits, funding, skills for administering the program, administrative time and costs, legal issues, stakeholder involvement, public outreach, and public transparency. Sanderson, J. S., N. Rowan, T. Wilding, B. P. Bledsoe, W. J. Miller, and N. L. Poff 2011. “Getting to Scale with Environmental Flow Assessment: The Watershed Flow Evaluation Tool,” River Research and Applications. The study focused on “environmental flows,” which are defined as “the quantity, timing and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihood and well-being that depend on these ecosystems.” It also discusses ecological limits of hydrologic alteration (ELOHA) methodology. Sahin, V. and M. J. Hall 1996. “The effects of afforestation and deforestation on water yields,” Journal of Hydrology, Volume 178, Issues 1–4, 1996, Pages 293-309, ISSN 0022-1694. https://doi.org/10.1016/0022-1694(95)02825-0. (http://www.sciencedirect.com/science/article/pii/0022169495028250) This article assesses how removal of vegetative cover in a catchment changes the water yield (the quantity of water available for water supply purposes) of that catchment by using a linear regression analysis from 145 different experiments. It examines the effects of the removal different forest types, such as conifer-type forests and eucalyptus-type forests. The effects of afforestation through the addition of scrub-type vegetation to previously unvegetated areas are also explored. Key findings include: • For a 10% decrease in cover, yield from a conifer-type forest increased by 20-25 mm. • For a 10% decrease in cover, yield from a eucalyptus-type forest increased by 6 mm. • For a 10% decrease in cover of deciduous hardwood, yield increased by 17-19 mm.

257 • For a 10% increase in cover through afforestation of scrub, yield decreased by 5 mm. This study mainly assesses the effectiveness of deforestation on water yield. While not directly applicable to the effects of reforestation and afforestation, some conclusions can be drawn about the effects of different forest types on water yield, whether that forest type is increasing or decreasing. For example, because the yield increase in conifer-type forest cover removal is higher than the yield increase eucalyptus-type forest removal, it can be inferred that adding conifer-type forest cover through either reforestation or afforestation would decrease water yield more than adding eucalyptus-type forest cover. The main issue with this study is that it assesses the effects of deforestation, not reforestation or afforestation. While some conclusions about the vegetation used to add forest cover can be drawn, they are not directly applicable to this research. However, when development in forest areas is occurring, this data study can be used to guide where that development should occur to least increase water yield, mitigating the need for future restoration of forest cover. Shaw, A. I. 2019. “Hydrological Modeling of the Paligad Watershed (India) Using HSPF Model,” International Journal of Environment and Climate Change, 9(4): 217-228, 2019; Article no.IJECC.2019.017 ISSN: 2581-8627. A case study using HSPF with projections made by changing climate forcing terms. The author provides a good description of the calibration process used. The relevance to the current study is a case study of how to implement HSPF at the 20 square mile size, but the paper uses relatively coarse distributed information (on a watershed with low urban land use component). Stelk, M. and J. Christie. 2014. Ecosystem Service Valuation for Wetland Restoration, March. Retrieved from https://www.aswm.org/state_meeting/2014/ecosystem_service_valuation_for_wetland_restorati on.pdf. The reference provides a general description of ecosystem service valuation and offers several case studies that examine various ecosystem services. It lists benefits of wetlands (not necessarily specific to or resulting from landscape modification): fisheries production, wildlife habitat, water quality buffering and pollution control, wave attenuation and erosion control, production of forestry products and natural crops, flood conveyance and flood storage, carbon storage and sequestering, and groundwater recharge. In addition, it provides a quantification of ecosystem services in specific locations (at level of city and watershed). As an example, for the City of Portland’s Water Management Program, the study showed that, over a 100-year period, the following values stemmed from the named ecosystem services: flood abatement ($14.6 million), biodiversity maintenance ($5.7 million), air quality improvement ($2.5 million), water quality improvement ($2.3 million), and cultural services ($5.9 million). The Comparative Valuation of Ecosystem Services tool produced the above figures. An interdisciplinary team created the tool, which implemented three economic valuation methods (hedonic value, contingent value, and avoided cost/replacement value). Within the tool, calculations were made regarding ROI, discounts on future values, and more.

258 Strecker, E., A. Poresky, R. Roseen, R. Johnson, J. Soule, V. Gummadi, R. Dwivedi, A. Questad, N. Weinstein, E. Ayers, and M. Venner 2015. Volume Reduction of Highway Runoff in Urban Areas: Guidance Manual, National Academies of Sciences, Engineering, and Medicine, Washington, DC: The National Academies Press, NCHRP Report 802, (Project 25-41). This report provides design and implementation guidance for on-site, in-kind volume reduction BMPs. Key elements include: • Description of a few (related) metrics for evaluating Volume Reduction Approaches (VRA): volume reduction, retention design storm size, frequency of discharge, and flow duration. • Identification of different urban highway types and how they may affect BMP implementation. • Listing of a menu of BMPs (VRAs) included in the evaluation. • Listing (Table 38) of a high-level “summary of potential forms of watershed-scale approaches.” Where relevant, these have been incorporated in the current project. Taylor, S., M. Barrett, M. Leisenring, S. Sahu, D. Pankani, A. Poresky, A. Questad, E. Strecker, N. Weinstein, and M. Venner 2014. Long-Term Performance and Life-Cycle Costs of Stormwater Best Management Practices, NCHRP Report 792 (Project 25-40). This report focused on the evaluation of the long-term pollutant removal and life-cycle costs of in-kind, on-site BMPs. Key features include: • Use of 343 NCDC (COOP) hourly precipitation gauges within an evaluation tool. Some gauges had 5-minute resolution.) The report discussed NCDC climate divisions. • Use of numerous SWMM runs to quantify volume reduction and pollutant removal performance. • A spreadsheet tool for estimating costs of BMPs including retrofits for seven types of BMPs. Provides specific costs. • An important warning that the tool “should not be viewed as applicable to any specific BMP installation for a particular storm event.” Toriman, M. E., Karim, O.A., Mokhtar, M., Gazim, M. B., Abdullah, M. P. 2010. “Use of InfoWork RS in modeling the impact of urbanisation on sediment yield in Cameron Highlands, Malaysia,” Nature and Science, 2010;8(2):67-73. (ISSN: 1545-0740). Authors use InfoWorks RS as a tool to examine effect of changing land use conditions. Initially this appeared to be another potential tool, however InfoWorks RS is a riverine simulator, so the inputs are derived from another tool for this study. The sources of the hydrological inputs are not well described.

259 United Kingdom Environment Agency. 2017. Working with natural processes to reduce flood risk. Project Description and Documents. October 31. Available at: https://www.gov.uk/government/publications/working-with-natural-processes-to-reduce-flood- risk. This is a compendium of documents created through the implementation of a research and analysis project by the Environment Agency of the United Kingdom to compile and synthesize findings from research into the use of natural processes—including restoration of rivers and floodplains, woodlands, and other natural landscapes—to help mitigate flooding risks into a central location. There are clear parallels between this effort and the current effort for NCHRP. Compiled documents include an Evidence Directory (highlighting the effectiveness of “WWNP” approaches), results of a literature review, and results of detailed evaluations of 65 case studies, as well as other documents. In particular, as part of the evaluation of case studies, an attempt was made to quantify the ecosystem service benefits, as well as the hydrological benefits of considered techniques (e.g., floodplain woodland restoration, use of leaky barriers, soil and land management, etc.) and individual cases. It was beyond the scope of this literature review, at this time, to fully evaluate the quantification approaches employed for each case study; however, this compendium of documents has the potential to yield significant insights into approaches to assess the effectiveness and costs and benefits of landscape modification projects specifically designed to address stormwater. U.S. Army Corps of Engineers (USACE) 2008. Alternate Green Stream Bank Stabilization Methods, June. Retrieved from http://www.boritcag.org/pdf/US%20Army%20Corps%20of%20Engineers%20Stream%20Bank %20stabilization%20methods%20June%202008.pdf. This reference is an update to a prior stream bank stabilization study with specific focus on green solutions. It provides a limited breakdown of cost estimates for construction options at two work sites. It includes a comparison of gray/GI, including cost difference, for projects on two creeks located near Philadelphia, PA. U.S. Army Corps of Engineers (USACE) 2014. Cost-Estimation Tool for Low-Impact Development Stormwater Best Management Practices [PDF file]. Retrieved from https://www.wbdg.org/FFC/ARMYCOE/PWTB/pwtb_200_1_135.pdf. This document addresses environmental benefits (air quality, urban heat island, energy consumption, and climate change mitigation) of LID. It covers the costs of LID techniques (capital costs and maintenance) and shows how LID techniques (green roofs, rain gardens, curb- contained bioretention, in-curb planter vaults, cisterns) are represented (and the extent to which they are customizable) within the model. The document notes the impact of site/region on overall design considerations and project costs. The document demonstrates steps in a cost-estimation tool, specifically unit costs and/or costs per square feet for the LID techniques listed above.

260 U.S. Department of Transportation (USDOT) 2014. Advancing a Sustainable Highway System: Highlights of FHWA Sustainability Activities, Federal Highway Administration, June. Retrieved from https://www.sustainablehighways.dot.gov/documents/FHWA_Sustainability_Activities_June20 14.pdf. This document provides a broad overview of the “triple bottom line of sustainability” (environmental, economic, and social values). It addresses a wide range of sustainability practices, including a description of stormwater quality banking. However, it is focused on water quality, not quantity. U.S. Environmental Protection Agency (USEPA) 2007. Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices, December. Retrieved from https://www.epa.gov/sites/production/files/2015- 10/documents/2008_01_02_nps_lid_costs07uments_reducingstormwatercosts-2.pdf. This document briefly addresses numerous case studies throughout the United States that utilized a variety of LID practices. It describes benefits of LID in three categories: • Environmental: Pollution abatement, protection of downstream water resources, groundwater recharge, water quality improvements/reduced treatment costs, reduced incidence of CSOs, and habitat improvement. • Land Value and Quality of Life: Reduced flooding and property damage, real estate value/property tax value, lot yield, aesthetic value, and public spaces/quality of life/public participation. • Compliance Incentives: Regulatory compliance credits. The document provides cost breakdowns of conventional and LID approaches for the different case studies. Generally, but not always, LID costs less. Techniques covered included: bioretention, cluster building, reduced impervious area, swales, permeable pavement, vegetated landscaping, wetlands, and green roofs. U.S. Environmental Protection Agency (USEPA) 2017. Water Resources Registry (https://watershedresourcesregistry.org/), USEPA Region 3 Water Protection Division, Office of State and Watershed Partnerships. The objective of the WRR is “to map natural resource areas that are a priority for preservation or restoration.” Current state registries include Delaware, Maryland, Pennsylvania, Virginia, and West Virginia; other state registries are in development. The registries include many types of data layers that vary from state to state. Each state also includes pre-determined analyses of the layers that are available to identify priority areas. Walsh, C., Booth, D., Burns, M., Fletcher, T., Hale, R., Hoang, L., Livingston, G., Rippy, M., Roy, A., Scoggins, M., and Wallace, A. 2016. “Principles for Urban Stormwater Management to Protect Stream Ecosystems,” Freshwater Science, 35, 398-411. The reference offers a description of stormwater management at the watershed level that explores how flood mitigation impacts and alters hydrology. It offers five “critical principles” of stormwater control measures (SCMs) that protect stream ecosystems:

261 • Identify stream ecosystems to protect or restore and establish a target for their ecological state. • Post-development water balance should mimic predevelopment water balance. • SCMs should deliver flows in a quality and flow regime that mimic, as much as possible, dominant predevelopment hydrologic processes. • Design SCMs to prevent untreated flows to streams in all but rare, large storms. • Apply SCMs to all impervious surfaces in the catchment of the target stream. The authors identify challenges and co-benefits that arise from the implementation of their principles for SCMs. The challenges are: 1) losing excess volume of water generated by reduced evapotranspiration; 2) delivering appropriate flow regime from infiltration and filtration technologies; and 3) social and institutional constraints. The co-benefits are: 1) increased water supply; 2) flood mitigation; 3) terrestrial biodiversity; 4) urban cooling/agriculture; 5) climate change resiliency; and 6) human well-being. Overall, the reference provides principles that ensure and protect desired hydrological conditions while pursuing solutions at the catchment level. Weinstein, N. et al. 2017. “A Watershed Approach to Mitigating Stormwater Impacts” NCHRP Report 840 (Project 25-37). The report describes a comprehensive approach for evaluating in-kind/out-of-kind and on- site/off-site techniques within a watershed for stormwater quality. Key features of the report are: • Listing of the regulatory/environmental regulations that may apply to transportation projects that affect implementation of the watershed approach. • Use of nationally available datasets for evaluating mitigation techniques including the USEPA’s EnviroAtlas, augmented by information from NOAA’s NCEI (precipitation and other climate information) and the USDA NRCS Web Soil Survey.” Criteria for dataset evaluation in watershed assessments included: 1) availability, 2) applicability, 3) acceptability, and 4) manageability. • The watershed unit of analysis was the HUC-12 level. (Average size is 37 mi2.) • Description of ecosystem services which are divided into three groups: 1) provisioning services, 2) regulating services, and 3) other services. (See Table 11). Discusses ecosystem services assessment tools such as EcoMetrix and ESII. • Describes several types of out-of-kind mitigation that affects hydrology: • Stream improvement techniques such as physical enhancements that restore natural stream morphology and function, including grading engineered meanders, installing grade control features, planting riparian vegetation, placing large woody debris, and using similar forms of bank and stream channel protection controls. • Wetland restoration or creation. • Uplands restoration. • Floodplain reconnection.

262 • Reductions in impervious surface connectivity. • Infrastructure improvements and maintenance (e.g., removing accumulated legacy pollutants on sediments retained in conveyance systems). • Land preservation. VHB Inc. 2016. “Celery Fields Regional Stormwater Facility Integrated Management Plan”. http://www.sarasota.wateratlas.usf.edu/upload/documents/Celery-Fields-Regional-Stormwater- Facility-Integrated-Management-Plan-VHB-9-16-16-FINAL.pdf, Sarasota County Government, Public Utilities Stormwater. Accessed July 26, 2019. Required functions of this regional facility include flood control (the primary function) and stormwater attenuation along with wetland compensatory mitigation. While the facility and project are not specifically related to transportation projects, its concepts are applicable. Pesticide impacted soil restrictions are in place over a portion of the project area. Vidon, P., and A. P. Smith 2008. “Assessing the influence of drainage pipe removal on wetland hydrology restoration: A case study,” Ecological Restoration, 26(1), 33-43. Retrieved from http://mines.idm.oclc.org/login?url=https://search- proquestcom.mines.idm.oclc.org/docview/20765303?accountid=25386 This article is a case study investigating the restoration progress a riparian wetland after the removal of drainage pipes. The pipes were removed to re-establish wetlands that had been damaged after their installation. The standard for restoration of the wetlands involved the area having an average water table depth of less than 10 cm below ground surface for 6 months out of the year and a water table depth of less than 30 cm for at least 14 days after growing season. The main concern with this experiment was that the pipes’ former locations would still act as conduits and drain the wetlands. Key findings include: • Wetland delineations and water table depths showed that wetland hydrology had been established upon the removal of the pipes in naturally poorly drained soils. • The removal of the pipes by cutting them into sections, removing them by hand, then compacting the disturbed soil was sufficient to re-establish the wetland hydrology that was present before the pipe. Removal of drainage pipes in the manner described in this case study could be a simple way to re-establish wetland hydrology in an area where wetlands have been drained. It is worth studying areas to determine if this practice can be applied. One note of caution is to remember the original reason the drainage pipe was there in the first place. If the site will flood without it, it should not be removed. There are cases where the pipe is taking drainage both from a past wetland and from another site. In this case, it is possible that the pipe can still be removed to re-establish the wetland if the off-site drainage is directed elsewhere. Virginia Department of Transportation (VDOT) 2019. Application of the VSMP Regulations as it relates to utilization of Nutrient Credits as an off-site compliance option, June [PDF file]. Retrieved from http://www.extranet.vdot.state.va.us/locdes/electronic_pubs/iim/IIM251.pdf. The document notes the role of water quantity controls in reducing downstream pollutant loads. The VDOT program is focused primarily on nutrient credits and notes that those credits cannot be used for addressing water quantity.

263 Wang, X., Shuster, W., Pal, C., Buchberger, S., Bonta, J. and Avadhanula, K. 2010. “Low Impact Development Design—Integrating Suitability Analysis and Site Planning for Reduction of Post-Development Stormwater Quantity,” Sustainability, 2467-2482; doi:10.3390/su2082467. Authors applied NRCS runoff generation model on research watersheds using hypothetical LID strategies. Essentially the placement of the development was used to change CN values apportioned to the watershed. The authors report that anticipated increases in runoff depth are half as large using LID strategies as opposed to conventional strategies. The modeling is too simplistic for the current project. If there is desire for an overly simplistic tool, then this document would be a place to start. Wanielista, M.P., "Stormwater Management and Conservation," Seminole County Planning Conference, January 7, 1991. This presentation includes a comparison of annual Econlockhatchee River flow records in relation to surrounding roadway and development projects. The author includes a discussion of reuse methods designed to decrease flooding and pollution. Water Environment Research Foundation (WERF) 2018. “Framework and Tools for Quantifying Green Infrastructure Co-Benefits and Linking with Triple Bottom Line Analysis.” WERF Project: SIWM4T17; Project Manager: Dr. Harry Zhang. Available at: https://www.werf.org/a/ka/Search/ResearchProfile.aspx?ReportId=SIWM4T17. (Presentation available at: www.waterrf.org/resources/expertsymposiums/Lists/PublicExpertSymposiums/Attachments/74/ SWMC18-Zhang.pdf). This WERF project is ongoing and the presentation is dated 2018. The project is coordinated with the ERF CLASIC project (WERF 2019). Sixteen utilities participating nationwide. It is investigating the Triple Bottom Line Analysis as a comprehensive benefit-cost analysis of the financial, social, and environmental costs and benefits of a project or program over time, and to whom they accrue. The project is developing an economic framework and accompanying tool to quantify GI benefits at the community level. Runoff reduction is the GI benefit that utilities are most interested in quantifying and monetizing. Co-benefits of GI include water quantity, water quality, biodiversity/habitat and wildlife, energy saving and heat mitigation, climate resilience, flood management, air quality, green parks, increased property values, green jobs, reduction of noise impact of traffic, use of green streets. Water Environment Research Foundation (WERF) 2019. “Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs (CLASIC).” WERF Grant: CR-83617301-0; Project Manager: Dr. Harry Zhang. Information available at: https://www.werf.org/c/Lifecycle_Costs/Community- enabled_Lifecycle_Analysis_of_Stormwater_Infrastructure_Costs.aspx. The goal of this ongoing project is to produce a tool that evaluates costs and benefits of stormwater infrastructure. It provides user with life-cycle costs, value of environmental, social, and financial benefits, and hydrologic performance (reduction of peak runoff, volume, and pollutant load) of stormwater infrastructure options (gray, green-gray, and green).

264 Water Environment and Reuse Foundation (WERF) 2017. Agricultural BMP Database, (http://www.bmpdatabase.org/agBMP.html), Version 2.0 Data Summary. The Agricultural BMP Database is water quality focused and currently oriented toward researchers (no user interface provided). It includes three overall practice types (groups) including: 1) In-field management practices (crop-related practices such as nutrient management, tillage, etc.); 2) Edge-of-field treatment practices (treatment practices such as buffer strips, constructed wetlands); and 3) In-field constructed practices (land-shaping practices such as terraces, grassed waterways, and other relatively permanent features that help to minimize erosion). It includes tile drains and other types of field drainage. Water Research Foundation (WRF) 2019. International Stormwater BMP Database, (http://www.bmpdatabase.org/index.htm), accessed July 31, 2019. The International Stormwater BMP Database is supported by a coalition of partners led by the WRF, and includes the USEPA, the FHWA, American Public Works Association, and the Environmental and Water Resources Institute of ASCE. It is an MS Access database that includes information on a variety of BMPs including cost and performance. It is coordinated with the National Stormwater Quality Database, which includes event precipitation and runoff depths. The website includes various reports including one that provides a critique of volume reduction estimates in the database. Wetland Solutions Inc. 2010. “Deep Creek West Regional Storm Water Treatment Wetland Facility – Tracer Study.” http://www.wetlandsolutionsinc.com/download/TreatmentWetlands/Deep%20Creek%20Tracer %20Report.pdf St. Johns River Water Management District, Accessed July 26, 2019. This project utilizes a wetland cell to treat agricultural stormwater on regional scale. Tracer dye testing was used to assess nutrient removal efficiency. Significant hydraulic short circuits were present in the original configuration which reduced performance. Evaluation of additional project options found significant costs associated with earthwork to deepen treatment areas required to increase residence time. Willamette Partnership 2013. Willamette Partnership Ecosystem Credit Accounting System. General Crediting Protocol Version 2.0, Portland, OR (Updated 2017). As described in the document: “This document is a guide for those interested in quantifying the benefits or impacts of their actions on aquatic habitat, upland habitat, and water quality. The Ecosystem Credit Accounting System described in this General Crediting Protocol (Protocol), includes the protocols, standards, and quantification methods through which actions that affect the environment are translated into quantified, verified, and tradable units.” The protocol currently supports nine currencies (or credit types) in three categories: 1) aquatic habitat (floodplain habitat, salmon habitat, wetland habitat), 2) upland habitat (oak woodland habitat, sagebrush/sage-grouse habitat, upland prairie/Fender’s blue butterfly habitat), and 3) water quality (nitrogen, phosphorus, thermal). The protocol lists quantification methods (Figure 2.2.1). Although hydrology is not included in the protocol the information is relevant for the current study effort.

265 World Water Assessment Programme (WWAP) 2018. The United Nations World Water Development Report 2018: Nature Based Solutions for Water, Paris, UNESCO, unesdoc.unesco.org/images/0026/002614/261424e.pdf. NBS are defined as “inspired and supported by nature and use, or mimic, natural processes to contribute to the improved management of water. The defining feature of an NBS is, therefore, not whether an ecosystem used is ‘natural’ but whether natural processes are being proactively managed to achieve a water-related objective. An NBS uses ecosystem services to contribute to a water management outcome. An NBS can involve conserving or rehabilitating natural ecosystems and/or the enhancement or creation of natural processes in modified or artificial ecosystems. They can be applied at micro-(e.g., a dry toilet) or macro- (e.g., landscape) scales.” Wright, T., J. Tomlinson, T. Schueler, K. Cappiella, A. Kitchell, and D. Hirschman 2006. Direct and Indirect Impacts of Urbanization on Wetland Quality, Center for Watershed Protection, December. This summary includes an evaluation of more than 100 studies conducted on the direct and indirect impacts of urbanization on wetlands. Half of the studies reviewed impacts associated with changes in wetland contributing areas. The studies included a comparison of peak flows in natural wetlands versus altered and filled wetlands, showing higher peak stages in altered areas. Wu, J. Y., Thompson1,J. R., Kolka, R. K., Franz, K. J. , and T. W. Stewart 2013. “Using the Storm Water Management Model to predict urban headwater stream hydrological response to climate and land cover change,” Hydrol. Earth Syst. Sci., 17, 4743–4758, www.hydrol-earth- syst-sci.net/17/4743/2013/doi:10.5194/hess-17-4743-2013. Scenario modeling was used to estimate the sensitivity of an urban watersheds response to change(s) in both climatic inputs and land use inputs. The approach was applied to measured stream flows that sampled several different land coverage inputs (hence that variability is a measured value) and different climatic inputs (estimated). Hydrological responses were quantified using three indices: unit area peak discharge, flashiness (R−B Index; Richards–Baker Index), and runoff ratio. Stream hydrology was strongly affected by watershed percent impervious surface. The sample watersheds studied were up to 500 acres. The hydrologic indices: unit area peak discharge, flashiness (R−B Index; Richards–Baker Index), and runoff ratio are useful for the current project as computable values by State DOTs in their work. The ability of these indices to quantify change could be a tool to estimate the value of off- site mitigation strategies. These indices scale like the basin-development-factor (another relatively computable value to quantify basin hydrologic response). The response in the study was more affected by land use change than by the climatic input change -- but the changes were substantial (on a percent basis), a finding that supports the concept of selected off-site redirection of runoff to various land uses to mitigate the effect on/of transportation infrastructure. Xu, Z.; Liu, W.; Wei, X.; Fan, H.; Ge, Y.; Chen, G.; Xu, J. 2019. “Contrasting Differences in Responses of Streamflow Regimes between Reforestation and Fruit Tree Planting in a Subtropical Watershed of China,” Forests, 10, 212. This article explores the hydrologic effects of fruit tree planting, a common practice used to combat poverty and restore environments in developing countries. It does so by evaluating both peak flows and low flows from the 261.4 km2 Jiujushui watershed, which is in a subtropical region of China. This assessment was done by analyzing streamflow data during three stages: reference

266 (control) from 1961 to 1985, reforestation from 1986 to 2000, and fruit tree planting from 2001 to 2016. Key findings include: • Reforestation decreased the average magnitude of high flow by 8.78% and shortened high flow duration by 2.2 days compared to the reference time frame flows. • Decreases in high flows usually point to a decrease in flooding. • Fruit tree planting increased the average magnitude of high flows by 27.43% compared to the reference time frame flows. • Possibly due to the disturbance of existing earth and weed/small vegetation removal associate with tree planting, which increases runoff rates. • Reforestation increased the average magnitude of low flows by 46.38% and shortened high flow duration by 8.8 days compared to the reference time frame flows. • Fruit tree planting had little to no impact on low flows in the watershed. This study bolsters the idea shown in many other articles that reforestation will help to lower peak flows, which would presumably reduce flooding in the area downstream. It goes further exploring the effects of adding different types of vegetation cover, this time focusing on fruit trees, which it finds to increase peak flows while not changing low-flow regimes. While planting fruit trees might accomplish the primary goals of combatting poverty and environmental restoration, it may have negative hydrologic effects that could hamper those goals. Zhang, X. and Y. Song 2014. “Optimization of wetland restoration siting and zoning in flood retention areas of river basins in China: A case study in Mengwa, Huaihe River Basin,” Journal of Hydrology, Volume 519, Part A, 2014, Pages 80-93. ISSN 0022-1694. This study develops a methodology to identify the best sites for wetland restoration in flood retention areas in China to increase the capacity and functionality of those retention areas. A GIS tool was developed and applied to a flood retention area in the Huaihe River Basin, where models showed improved flood retention, ecological benefits, and economic benefits after testing floods from previous years. Key findings include: • Strategically location wetland restorations can optimize the flood retention, ecological, and economic benefits of that restoration. • The GIS tool used to locate ideal locations for wetland restoration can be applied to watersheds in other countries. • Ecologic benefits included water purification and a cleaner water supply. • Economic benefits were 3-5 times the local GDP. This article shows the functions of a GIS tool that would be extremely useful in optimizing wetland restoration in watersheds around the world. A tool such as this would be especially useful in developing areas where there is little space to expand existing detention areas, so existing ones must be restored. If one were to apply this tool to a watershed in the United States, they must ensure that the input parameters have been adequately changed to reflect the watershed it is being used for, as the watershed characteristics in China may be vastly different. In addition, one must determine that wetland restoration or construction is the right method to rehabilitate a particular watershed in the first place.

267 Zölcha, T., Henzeb, L., Keilholzc, P., and S. Pauleitb 2017. “Regulating urban surface runoff through nature-based solutions – An assessment at the micro-scale,” Environmental Research 157 (2017) 135–144. The study assessed the performance of two GI types - trees and green roofs - on relevant hydrological processes, especially surface runoff. The two measures were applied in scenarios of different greening quantity and for heavy rain events of different intensities as projected for the future. This scenario approach revealed that both trees and green roofs contribute positively by interception, evapotranspiration, and infiltration. The authors use MIKE-SHE as the tool for their examination; it is similar to HSPF. In the study the authors applied the tool at 1-meter grid scale, which is an absurd resolution for the current project, however it can help define a minimum sensitivity for a postulated off-site component to have measurable impact. Importantly the authors interpret the GI benefit as having a large storage component which will be manifest in the current project as an important physical component of any strategy to mitigate hydrologic impacts of highway projects.