Watershed Approach to Mitigating Hydrologic Impacts of Transportation Projects: Conduct of Research Report (2022) / Chapter Skim
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66 Chapter 5. Identification and Evaluation of Co-Benefits This chapter provides a framework for considering co-benefits, as well as costs, of the out-of-kind mitigation techniques introduced in Chapter 2.
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67 additionally discusses well-accepted methods for conducting a more detailed economic analysis when a more precise accounting of co-benefits is needed (e.g., when project partners require it, or monetization of co-benefits is required for a given mitigation alternative to move forward)
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68 models to more explicitly evaluate the magnitude of given co-benefits (Section 5.3 describes existing methods and models available to DOTs for this purpose)
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69 Table 5.1. Descriptions of categories of environmental changes resulting from mitigation techniques.
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70 Table 5.2. Description of categories of co-benefits resulting from environmental changes.
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71 5.2. Screening Assessment of Co-benefits and Costs of Mitigation Techniques The ecosystem service co-benefits screening analysis is step 8B of the overarching decision framework described in Figure 3.1.
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72 8B3. Assess the relative magnitude of the co-benefits.
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73 require engaging economics experts. If no, the analyst may decide only to work through steps 8B1-8B3.
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74 extent to which the co-benefits of any given technique need to be evaluated are likely to be variable, dependent on the context established in step 8B1, including who potential collaborating external partners/stakeholders are, whether they may be providing matching funding for the mitigation, and what their priorities may be. However, the second step in the screening stage of co-benefits evaluation involves carefully considering the causal chains for the range of mitigation techniques being considered.7 This principally involves considering the specifics of the site and project.
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75 Figure 5.3. Generic causal chain for wetland restoration and creation mitigation.
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76 Table 5.3. Site-specific factors for wetland restoration and creation mitigation.
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77 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Water supply maintenance • Soil type and wetland design, which can affect the wetland's ability to absorb precipitation and flows, maintain baseflows in adjacent streams, or promote infiltration and replenish alluvial aquifers • Designated use of hydrologically connected water bodies (e.g., connection to existing or potential drinking water or irrigation water sources) • Availability of substitute water sources (value is increased where substitutes are scarce)
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78 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Non-use and cultural values • Ability of wetland to improve fish and wildlife habitat or biodiversity for species that are protected (e.g., ESA-listed species) or enjoy historical or cultural significance (i.e., via provision of vegetation as a food source and more clean water)
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79 and welfare. Furthermore, vegetated wetlands can improve air quality – also contributing to improved human health.
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80 through non-use or cultural values. State DOTs should consider the proximity of populations that enjoy these non-use or cultural values.
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81 climate resilience, and property values.11,12 Table 5.4 identifies the ecological and socioeconomic factors that determine whether these co-benefits are relevant to a given project. Because of the time it takes for some forests to mature, some of the co-benefits of forest restoration and creation projects may not be relevant in the short term.
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82 Figure 5.4. Generic causal chain for forest restoration and creation mitigation.
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83 Table 5.4. Site-specific factors for forest restoration and creation mitigation.
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84 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Improved human health and welfare • See "improved drinking water quality" co-benefit for factors associated with drinking water • Potential of chosen tree species to absorb air pollutants (sulphur dioxide, ozone, nitrogen oxides, particulates) • Potential for tree canopy to decrease local air temperatures • See "improved drinking water quality" co-benefit for factors associated with drinking water • Proximity of project site to areas where people live, work, and gather • Size of population in airshed Timber and forest product harvest benefits (resource harvesting)
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85 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Non-use and cultural values • Ability of forest to improve wildlife habitat or biodiversity for species that are protected or enjoy historical or cultural significance (i.e., via provision of vegetation as a food source, more clean water, habitat space) • Location of project relative to manmade hazards (e.g., traffic and the potential for vehicle collisions)
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86 sedimentation and pollutant transport into the waterway. The extent to which these ecological features translate into benefits for the public depends on whether the water source is connected to drinking water destinations, the water rights context, the number of people served by the water source, and other socioeconomic characteristics.
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87 framework for evaluating the site-specific attributes of State DOT projects that may result in climate stabilization benefits.13 A variety of forest attributes may also translate into higher property values for nearby residents (Kim and Johnson 2002)
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88 Figure 5.5. Generic causal chain for stream restoration and improvement mitigation.
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89 Streams may also provide climate stabilization benefits where vegetative buffers provide carbon sequestration services and/or carbon cycling that occurs within the stream bed itself (Larson and Harvey 2017)
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90 Table 5.5. Site-specific factors for stream stabilization, restoration, and improvement mitigation.
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91 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Non-use and cultural values • Ability of project to improve habitat for and therefore populations of protected or culturally important fish species • Presence of other larger species with protections or cultural significance that prey on the directly benefiting fish species • Changes in the quality or status of a stream where local populations hold cultural values • Location of project relative to man-made hazards (e.g., traffic and the potential for vehicle collisions) , projects located farther from hazards reduce wildlife fatalities • Proximity of populations that have cultural values for species benefiting Climate stabilization • Carbon sequestration potential of stream and timeframe anticipated (available biomass, carbon in stream bed, turbulence, and flow)
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92 Figure 5.6. Generic causal chain for uplands restoration mitigation.
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93 Table 5.6. Site-specific factors for uplands restoration mitigation.
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94 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Non-use and cultural values • Ability of project to improve habitat for and therefore populations of protected or culturally important wildlife species • Changes in the quality or status of a landscape that has cultural value for local populations • Location of project relative to manmade hazards (e.g., traffic and the potential for vehicle collisions) , projects located farther from hazards reduce wildlife fatalities • Proximity of populations that have cultural values for species benefiting Increased property values • See "improved landscape aesthetics" co-benefit for factors associated with viewshed • Number of residential properties with a view of new, natural landscapes Climate stabilization • Carbon sequestration potential of vegetation planted, baseline soil carbon level, and adjacent available biomass (climate stabilization may be a long-term benefit as vegetative biomass mature but may be less substantive in the short term)
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95 Where an uplands restoration project is likely to result in water supply maintenance, it also has the potential to improve the health and welfare of the public through the provision of cleaner water. Like forest restoration projects, the analyst should consider whether the vegetation used in uplands restoration has the potential to reduce contaminant sources and to clean the water destined for drinking water sources.
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96 An analyst should consider the baseline land use relative to the newly restored landscape when determining whether carbon sequestration may be a benefit of a given project site.
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97 socioeconomic factors that could be affected by a State DOT project. For instance, modifying some agricultural practices may result in better maintenance of the local water supply, both from the perspective of maintaining water within the agricultural system (i.e., for irrigation purposes)
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98 overall well-being of water consumers. A reduction in application of harmful chemicals can also benefit the farm workers who apply them, due to less skin contact and inhalation and the potential to avoid the adverse effects of close contact with regulated chemicals.
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99 Table 5.7. Site-specific factors for agricultural practice modification mitigation.
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100 Co-Benefit Site-specific ecological factors that contribute to the provision of ecosystem services Site-specific socioeconomic factors that contribute to the value of ecosystem services Increased agricultural yields (resource harvesting) • Potential for improved agricultural practices to result in increased crop or livestock yields (note that in some cases, changes in agricultural management practices may reduce crop yields, for example no-till and cover crops)
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101 5.2.2.6. Tracking Ecosystem Services Co-Benefits To facilitate tracking the specific set of ecosystem services provided by each of the mitigation techniques, Table 5.8 presents a template table assembled from each of the technique-specific causal chains.
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102 Table 5.8. Identifying relevant co-benefits by mitigation technique.
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103 Co-benefits Mitigation techniques Wetland restoration, creation Forest restoration, creation Stream stabilization, restoration, and improvement Uplands restoration Agricultural practices modification and land conversion Y/ N Descripto r Y/ N Descripto r Y/ N Descripto r Y/ N Descripto r Y/ N Descripto r Commercial fishing benefits (resource harvest) Timber and forest products harvest benefits (resource harvest)
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104 5.2.3. Assess the Relative Magnitude of Co-Benefits (Step 8B3)
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105 new users) , in which case an analyst should first determine if such analysis is feasible and, if so, what assumptions are most tenable.
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106 Table 5.9. Summary of potential benefit-relevant indicators by co-benefit and mitigation technique.
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107 Co-benefit Potential benefit-relevant indicators Mitigation techniques Wetland Forest Stream Uplands Ag* Increased or improved recreational opportunities Number of new (increased)
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108 Co-benefit Potential benefit-relevant indicators Mitigation techniques Wetland Forest Stream Uplands Ag* Non-use and cultural values Number and type of fish and wildlife benefiting for which the public may hold non-use values (e.g., threatened or endangered species or species of local, cultural import)
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109 5.2.4. Screening Evaluation of Costs (Step 8B4)
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110 In most cases, existing approaches for cost estimation used for traditional stormwater mitigation costing may be applied for purposes of estimating mitigation technique costs; however, cost data from mitigation techniques that have already been implemented in similar settings may also be used to inform cost estimates. In such cases, when existing project examples are used to inform or derive costs, attention should be given to the following aspects of existing project costs: • Major site-specific factors associated with costs.
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111 In addition to comparing costs against mitigation alternatives, the DOT should evaluate the mitigation technique costs in the context of the overall transportation project costs. Mitigation may be a significant component of a total transportation project cost.
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112 Table 5.10. Process, data sources, and length of time by co-benefits screening analysis step.
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113 Step Process Data sources Length of time involved Step 8B2: Identify cobenefits through established causal chains Use the generalized causal chain diagrams provided in Chapter 5 to determine if a mitigation technique may lead to specific ecosystem service co-benefits. Organize findings around site-specific ecological and socioeconomic factors.
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114 Step Process Data sources Length of time involved Step 8B3: Assess relative magnitude of co-benefits Use Table 5.8 from Chapter 5 to summarize findings from step 8B2 by alternative. Include any BRIs or other quantified characteristics identified in step 8B2, include others as the data allows.
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115 Step Process Data sources Length of time involved Step 8B5: Compare costs and benefits across alternatives to rank mitigation options based on project objectives Rank techniques based on number and magnitude of co-benefits taking into consideration DOT and collaborator priorities. Not applicable.
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116 5.3. Detailed Analysis of Co-Benefits and Costs of Mitigation Techniques As described in Section 5.2, the screening analysis approach can range from a relatively simple assessment (identifying which categories of co-benefits are likely relevant to a given mitigation application)
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117 evaluation of co-benefits would justify a specific alternative technique. The mitigation technique alternatives should be sufficiently defined to allow for a more detailed determination of the specific costs (within the same cost categories discussed above)
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118 HEC-WAT focuses on watershed-based water quality modeling and the U.S. Forest Service provides forest ecosystem carbon yield tables for use in calculating forest carbon storage and sequestration benefits.19 Given the breadth and scope of these models, and that only in rare cases will the DOT engage them to evaluate individual project mitigation alternatives, this guidance does not describe all of the available models for every mitigation technique and ecosystem service combination.
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119 additionally includes recommendations for data sources to meet the relatively high ecological data requirements for modeling for some services (e.g., water quality)
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120 Tool and Developer Description Ecosystem Services Included Availability *
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121 In the case of many environmental improvements, markets do not exist to provide direct measures of WTP. In these cases, economists utilize two groups of methods to estimate WTP – "revealed preference" methods and "stated preference" methods.
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122 Table 5.12. Ecosystem service co-benefit valuation methods and data requirements.
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123 Benefit transfer is a method of analysis that relates results from existing, relevant studies to a new policy question when conducting primary research is not feasible or practical. Benefit transfer is an accepted and widely applied technique in resource economics.
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