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ERDC TR-04-1
extent of WoUS in arid areas. In 2001 the COE South Pacific Division published
guidelines for use in determining jurisdictional limits for WoUS in the arid
Southwest. These guidelines discussed pertinent literature regarding arid-land
fluvial systems, types of flow regimes, general indicators of high water stages,
and a matrix approach for establishing the presence of jurisdictional waters. The
intent of the document was to describe physical features useful for identifying
Ordinary High Water Marks (OHWM) and provide a method that would improve
the accuracy and consistency of jurisdictional determinations. No effort was
made to investigate all potential indicators, their relationship to storm or flood
return intervals, or their reliability. In January 2003, representatives from the
COE and EPA met in San Francisco and initiated a plan to refine OHWM indi-
cators and methods for intermittent and ephemeral streams in the arid Southwest.
A number of objectives were identified at the San Francisco meeting to
increase the accuracy and reliability of field indicators of OHWM. These were:
1. Undertake a literature review to assess existing information on fluvial
hydrology, geomorphology, and vegetation;
2. From the literature, develop a list of potential indicators for testing and
subsequent field use;
3. Survey the COE districts in the arid Southwest for further comment and
input;
4. Develop a testing protocol to determine what flood return intervals were
associated with the development of certain physical features of stream
channels;
5. Test the field indicators across the arid Southwest to determine their
reliability and subregionalize the indicators if necessary; and
6. Develop the protocols necessary for applying OHWM field indicators for
jurisdictional purposes.
This report addresses items 1 and 2 above. One goal of this review was to
discuss the climatic and hydrologic influences on potential OHWM indicators.
The temporally and spatially variable streams of arid regions typically flow only
during storm events and remain dry the remainder of the year. Therefore, indica-
tors for field identification of OHWM may differ greatly from those used in
wetland delineations. In Chapter 1 we provide the background and highlight key
concepts influencing the development of OHWM indicators, propose a working
definition of OHW, and summarize potential OHWM indicators identified from
the literature. Chapters 2, 3, and 4 review and synthesize available literature on
fluvial hydrology, geomorphology, and vegetation in the arid Southwest and
provide support for our selection of potential OHWM indicators.
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