California Rapid Assessment Method for Wetlands - State Water ...

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California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 3 Delineating a vernal pool system requires careful examination of aerial imaging and field reconnaissance to identify the pathways of surface flow that links pools together. Once the flow path of a system has been traced, then the large pools and small pools are separately coded on the site imagery (Figure 3.6). There are no fixed numerical criteria for distinguishing large pools from small pools; large pools are simply much larger than small pools. Table 3.9: Steps to delineate a vernal pool system and its component large and small pools. Step Vernal Pool System Delineation Task On the site imagery, trace the interconnected pathways of surface flow for 1 one pool system up to 10 ha in size (see Table 3.7). 2 Delineate and number all large pools within the pool system from Step 1. 3 Delineate and number all small pools within each pool system from Step 1. 4 The pools delineated in Steps 2 and 3 comprise the AA. 5 Randomly select three small pools and three large pools from the AA. These pools will be assessed individually and their scores will be averaged. • • • • • • • Riverine Figure 3.6: • • • • • • • • • Small Pool Large Pool Flow Path Example map of one vernal pool system and its component elements. 34
California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 3 3.5.7 Special Considerations for Post-assessment Analysis For CRAM scores to be comparable they must be standardized in terms of time (i.e., scores should represent comparable amounts of assessment effort during comparable years and times of year), and in terms of space (i.e., for any given wetland type, the scores should represent comparable amounts of wetlands, and these should have hydrological and ecological integrity; see Section 3.5.2 above). For a variety of reasons, scores that do not meet these standards cannot be compared and cannot be combined into datasets. For example, assessments that take longer or that involve larger areas are likely to encounter more structural complexity and therefore yield higher scores. The use of Assessment Windows (see Section 3.4 above), fixed assessment times (i.e., no assessment should take longer than one half day in the field), recommended AA sizes, and guidelines for assembling data of varying vintage will achieve more consistent assessment results. To achieve the spatial standards, each AA for each wetland type should fall within a standard size range that is large enough to incorporate the natural processes of homeostasis that characterize the wetland (see discussion of AA integrity in Section 3.5.2), but small enough to meet the time constraints (see Table 3.7). An additional spatial consideration for ambient surveys is that the probability of any wetland within a given area being selected for assessment increases with its size, and weighting CRAM scores for the inclusion probabilities of their associated AAs depends on having a standard AA size range for each wetland type. For more information about ambient sampling design go to http://epa.gov/nheerl/arm/designing/design_intro.htm. Standardizing the shape of AAs (e.g., having all AAs be circles or squares of fixed size) may increase the ease with which they are delineated, but may also lead to a disregard of features such as water control structures that affect AA integrity. Standardizing the shapes of AAs is less important than standardizing their sizes. 3.5.8 Special Considerations for Assessing Projects For the purposes of CRAM, a “project” is an area of wetland that is subject to physical change as authorized under Section 404 of the US Clean Water Act, under the State’s 401 Certification Program, or under Section 1600 of the State’s Fish and Game Code. Such projects are often at least partly delimited by property lines or other administrative or legal boundaries. Wetland restoration projects, mitigation projects, mitigation banks, and wetlands that are targeted for development (i.e., impacted wetlands) are often delimited by property lines. Property lines, jurisdictional limits, and other administrative or legal boundaries should not automatically be used to delineate AAs, except for the assessment of a project, in which case the wetland and its AA(s) are confined to the project boundaries. A formal wetland Jurisdictional Delineations (JD) in good standing for a project can be used in the absence of any other wetland map to define the wetland and to help delimit the AA(s). If the project is much larger than one AA, then the process outlined in Appendix I should be used to assess multiple AAs. 35
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