4
ERDC TR-04-1
1.3
GENERAL APPROACH TO THE IDENTIFICATION OF
OHWM INDICATORS
Methods for identifying and classifying wetlands for various purposes have
generally taken a multi-factor approach based on two or more environmental
features or kinds of evidence. Thus, wetland identification and classification rely
heavily on hydrology, soil, and vegetative characteristics (Environmental Labo-
ratory 1987, Cowardin et al. 1979, Mitsch and Gosselink 1993, Soil Conservation
Service 1994, Tiner 1999, Wakeley 2002). In addition, recent efforts to develop
functional assessment approaches have used hydrogeomorphic classifications to
identify groups of wetlands that function similarly (Brinson 1993).
Likewise, in the arid Southwest, with its distinct climate and physiography,
various landscape features lend themselves to identification of jurisdictional
limits in arid fluvial systems. Unlike most wetlands, the soils in arid stream
channels are typically Entisols (i.e., young soils with little horizon development)
(Fanning and Fanning 1989), reflecting the dynamics of recent flood events and
transport of sediments within the channel. Thus, the use of hydric soils (Natural
Resources Conservation Service 2002) or their features for delineating arid
streams is limited since these systems rarely develop redoximorphic features. The
river flow regime, characterized by patterns of variation in surface flow magni-
tude, duration, frequency, and timing, has been termed the "master variable"
shaping the associated aquatic and riparian environments (Poff et al. 1997). The
size and shape of a river channel is controlled in large part by the dominant
discharge in a particular region (Chapter 3). Riparian plant communities in the
arid Southwest occur along streams as linear corridors and typically contrast
sharply with upland deserts or grasslands (Chapter 4). These communities
typically have a distinctive composition and structure that is influenced by the
hydrodynamics of the channel. To meet the needs of the COE, field indicators of
the OHWM must be specific responses to the hydrodynamics of the stream, and
they must be readily observable to a field investigator throughout the year. Given
these requirements, this review focuses on fluvial geomorphology and vegetation
as the two major landscape features best representing antecedent hydrologic con-
ditions in arid stream channels.
Previous Page
