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

California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 3
is assumed to be the scale at which the internal workings of the wetland yield the least variability
in form and structure. For example, the s-shaped curve created by two consecutive river bends
tends to have a wave length equal to 10x the average width of the river through the bends
(Leopold 1994). Also, large estuarine wetlands tend to consist of a number of drainage networks
of very similar length and drainage area for any given drainage order (Collins et al. 1987, Collins
and Grossinger 2004). Shorelines can be characterized by alternating reaches of erosion and
deposition that repeat themselves at certain spatial scales relating to wave fetch and shoreline
geology (e.g., Philips 1986). Observing the patterns of self-similarity for a given wetland type can
help identify the dimensions of the appropriate AA.
3.5.2 AA Size
For any given wetland type, larger AAs might tend to yield higher CRAM scores. This is because
CRAM is especially sensitive to wetland structural complexity, and larger AAs can afford more
opportunity to encounter variability in structure. For any given wetland type, having AAs of very
different sizes can introduce variability into CRAM scores.
As stated above, one of the primary considerations for delineating an AA is its hydrogeomorphic
integrity. The boundaries of the AA should be established based on clear breaks in
surface hydrology, sediment supply, or geomorphology (see Tables 3.5 and 3.6 below).
Experience has shown, however, that most of the AAs of each wetland type that are delineated
according to indicators of hydro-geomorphic integrity fall within a narrow range of size,
although their shapes are more variable. This suggests that size guidelines can be applied to the
process of establishing an AA without necessarily violating the criterion for the hydrogeomorphic
integrity of the AA.
Furthermore, in some cases the self-similar, self-organizing, integral area of a wetland is not
clearly evident. For example, some wet meadows, brackish estuarine wetlands, large riverine
systems, and fringing wetlands of playas and lacustrine systems lack obvious hydrological breaks
or other features that clearly demarcate changes in water supplies or sediment supplies. In these
cases, overall size may be the dominant criterion for delineating the AA.
The preferred AA size is generally greater for types of wetlands that tend to have broad, level
planes than for wetlands fringing steep terrain. The size-frequency distribution of wetlands for
each wetland type (a Level 1 analysis) was also considered when the recommendations for AA
sizes were being developed.
Examples of features that should be used to delineate an AA, and other features that should not
be used, are listed in Tables 3.5 and 3.6 below. The preferred and minimum AA sizes for each
wetland type are presented below in Table 3.7.
To the degree possible, the delineation of an AA should first be based on the hydro-geomorphic
considerations presented in Tables 3.5 and 3.6. But, if these considerations are not applicable, or
if the resulting AA is more than about 25% larger than the preferred size presented in Table 3.7,
then the AA delineation should rely only on the size guidelines. The number of AAs per wetland
will depend on the purpose of the assessment, as outlined in Table 3.8.
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