Chapter 1. Introduction and Summary of
Ordinary High Water Mark Indicators
ROBERT W. LICHVAR AND JAMES S. WAKELEY
1.1
PROJECT BACKGROUND
Arid-land fluvial systems are critically important environments that provide
valuable ecological benefits to the Nation. Small streams and rivers convey
floodwaters and help ameliorate flood damage; maintain water quality and quan-
tity; provide habitat for plants, aquatic organisms, and wildlife; and determine the
physical characteristics and biological productivity of downstream environments
(Brinson et al. 1981, Davis et al. 1996, Meyer et al. 2003). Ephemeral and inter-
mittent streams dominant the stream types of the arid southwestern United States.
For example, in Arizona most of the stream networks--96% by length--are clas-
sified as ephemeral or intermittent (Beven and Kirby 1993). Arid stream systems
are located within montane, piedmont, or basin landscapes and have rough bed
surfaces that are related to the stream gradient and watershed lithology, slowing
the movement of water and allowing for water infiltration and recharge of
groundwater (Knighton 1998). Fluvial morphology within these channels is fre-
quently associated with extreme discharge events; streams and floodplains trap
sediments and nutrients in addition to attenuating flood waters (Graf 1988, Leo-
pold 1994). The accumulation of sediments and nutrients and the availability of
water are also instrumental in maintaining the high levels of biological diversity
associated with arid streams (Naiman et al. 1993). Some of the same fluvial fea-
tures that maintain physical, chemical, and biological functions also may be
useful for identifying Federal jurisdictional limits. This review is intended to help
identify useful field indicators resulting from fluvial processes that can be used to
locate the extent of Ordinary High Water (OHW) in arid-land streams.
Delineating the extent of Federal jurisdiction in wetlands and other "Waters
of the United States" (WoUS) is fundamental to Corps of Engineers (COE) and
Environmental Protection Agency (EPA) responsibilities under Section 404 of
the Clean Water Act (33 U.S.C. 1344). As part of these responsibilities, COE
Districts in the southwestern U.S. and elsewhere must be able to delineate the
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