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Pages 6-14

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From page 6...
... 6Background A first step in comparing on-site BMP effectiveness with other potential stormwater mitigation measures is to identify the data necessary to conduct a baseline watershed assessment using data analysis and GIS technology. Baseline assessments provide an accounting of existing watershed conditions and allow state DOTs a way to identify and prioritize areas for environmental improvement.
From page 7...
... Watershed-Based Mitigation Datasets 7 Physical Geographic Features Political Geographic Features Topography and soils Protected/endangered species habitat Hydrology (surface water flow data; gauging data) and pollution characteristics Watershed boundaries (most commonly being the Hydrologic Unit Code [HUC]
From page 8...
... 8 A Watershed Approach to Mitigating Stormwater Impacts focuses on nationally available datasets, though the same selection criteria can be used to evaluate other available datasets: • Criteria 1: Availability. Data are easily accessible and available for use on a nationwide basis or, at a minimum, within the 48 contiguous states to serve the purpose of tool creation for a national audience.
From page 9...
... Watershed-Based Mitigation Datasets 9 • Watershed characterization – The data can be used to evaluate watershed conditions (e.g., habitat, water quality, or ecosystem functions) that may be addressed or that may benefit from the DOT's action to mitigate in alternative ways to traditional stormwater BMPs, for stormwater impacts.
From page 10...
... 10 A Watershed Approach to Mitigating Stormwater Impacts rely on datasets maintained by resource agencies. In some cases, programmatic agreements or memorandums of understanding record required data maintenance efforts, reducing both the maintenance burden on the DOTs and the agreed quality and applicability of the data among the partner agencies.
From page 11...
... Watershed-Based Mitigation Datasets 11 The majority of the watershed assessment datasets reviewed placed greater emphasis on the ecology of the system in order to identify high priority habitat or wetland restoration opportunities. Including ecosystem services analyses in watershed assessments can help track the economic and social consequences of changes to ecological conditions and provide a unique approach to determining equivalency of impacts that are often not considered in stormwater mitigation efforts.
From page 12...
... 12 A Watershed Approach to Mitigating Stormwater Impacts Table 3 provides a description of the qualitative scoring criteria used to evaluate datasets available through EnviroAtlas based on availability, applicability, acceptability, and manageability needs. The evaluation of datasets was limited primarily to those of potential use for comparing stormwater mitigation options, with some additional datasets evaluated that have value for comparing ecosystem services.
From page 13...
... Watershed-Based Mitigation Datasets 13 Criteria Criteria 1: Availability Criteria 2: Applicability D es cr ib es w at er qu an tit y D es cr ib es w at er qu al ity W at er sh ed ch ar ac te riz at io n Ev al ua te s ec o sy st em se rv ic es H el ps id en tif y an d ev al ua te w at er sh ed pr io rit ie s Sp at ia lly li nk s pr oje ct to m iti ga tio n ne ed / o pp or tu ni ty ENVIROATLAS DATA LAYER Acres of crops that have no nearby pollinator habitat SW N N Y Y Y N Atmospheric nitrogen deposition data by 12-digit HUC (2006 and 2002) SW N Y Y Y Y Y Average annual precipitation 1981-2010 by HUC-12 SW Y N Y N Y N Biodiversity conservation metrics SW N N N Y Y Y Biological nitrogen fixation in natural/semi-natural ecosystems by SW N Y Y Y Y Y Ecosystem rarity metrics by 12-digit HUC 12-digit HUC HUC-12 SW N N Y Y Y Y HUC-12 polygons SW N N Y N Y Y Land cover NW N N Y Y Y Y Land cover on wet areas SW N N Y Y Y Y Morphological Spatial Pattern Analysis connectivity SW N N Y Y Y Y NatureServe analysis of imperiled or Federally listed species by R/NW N N Y Y Y Y Percent impervious NW N N Y Y Y Y Percent urban land cover by 12-digit HUC SW N N Y Y Y Y Percent stream buffer zone as natural land cover SW N N Y Y Y Y Potentially restorable wetlands S N N Y Y Y Y Protected lands SW N N Y Y Y Y Rare ecosystems R/NW N N Y Y Y Y Synthetic N fertilizer application to agricultural lands by 12-digit HUC SW N Y Y Y Y Y 303(d)
From page 14...
... 14 A Watershed Approach to Mitigating Stormwater Impacts value and amount of transportation activities occurring in the watershed. Depending on the confidence in the dataset, users may decide to apply a factor of safety to account for uncertainty or lack of information.

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