modified for use at the watershed scale. To delineate at this scale, riparian corridors were
mapped for hydrogeomorphic surfaces representing a combined bankfull and active
floodplain and a separate abandoned floodplain terrace (Fig. 3), which were later
interpreted for return-interval requirements under Section 404. Individual vegetation units
at the speciesassociation level were sampled at 169 sites to develop a characterization of
the indicators for both wetlands and other WoUS. By combining field sampling results
for wetland occurrences within various mapped vegetation types with the flood frequency
information obtained from the geomorphic surface map, probability ratings intended for
regulatory purposes were developed to accommodate all variations. Six categories of
wetland or WoUS ratings were assigned to each of the riparian vegetation units, with
ratings ranging from always regulated to upland or not regulated (Table 1).
Table 1. Wetland / WoUS ratings assigned to riparian vegetation types
Rating
Description
1
Types meet the criteria for a wetland or WoUS 100% of the time
2
Types meet the criteria for a wetland or WoUS 6798% of the time
3
Types meet the criteria for a wetland or WoUS 3366% of the time
4
Types meet the criteria for a wetland or WoUS 232% of the time (primarily uplands)
5
Types meet the criteria for a wetland or WoUS <2% of the time (primarily uplands)
6
Unregulated upland
The probability ratings used in the report can be interpreted in two ways:
A rating describes the probability of whether a map unit may be regulated, based
on the presence of wetland or Ordinary High Water indicators that meet the
criteria for these regulated types of aquatic resources, and
A rating describes the reliability of predicting whether a unit is regulated across
the watershed, as represented by the frequency statements associated with each
rating.
For example, cattail swamps always have the field indicators present to meet the criteria
necessary to be considered a wetland, and they are consistent for those features at all sites
across the watershed. A map unit with a high probability of having positive wetland
indicators present and high level of predictability at all sites receives a rating of 1.
However, for mulefat (Baccharis salicifolia), a species with facultative wetland status
that occurs in various landscape positions with and without wetland indicators, the
reliability factor is less. In abandoned floodplain terraces of the San Margarita and San
Jacinto watersheds, we found mulefat in both wetland and upland sites. Our ability to
predict its probability of being regulated is almost 50:50. Therefore, we assigned it a
rating of 3, which predicts that it would be considered regulated 3366% of the time.
That rating implies that the map units require further site-specific investigations to
determine if a particular site would be considered regulated. If a visit is done at a
particular mulefat site and it is decided that the specific location isn't regulated, it can be
deleted from the files; if the specific site is determined to be regulated, then the time
needed to correct any boundaries of the wetland should be highly reduced. So precision
ERDC/CRREL TN-04-4
5
Previous Page
