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The Coachella Valley fringe-toed lizard (Uma inornata) is a federally listed threatened species that inhabits active sand dunes in the vicinity of Palm Springs, California. The Whitewater Floodplain and Willow Hole Reserves provide some of the primary remaining habitat for this species. The sediment-delivery system that creates these active sand dunes consists of fluvial depositional areas fed episodically by ephemeral streams. Finer fluvial sediments (typically sand size and finer) are mobilized in a largely unidirectional wind field associated with strong westerly winds through San Gorgonio Pass. The fluvial depositional areas are primarily associated with floodplains of the Whitewater—San Gorgonio Rivers and Mission Creek—Morongo Wash; other small drainages also contribute fluvial sediment to the eolian system. The eolian dunes are transitory as a result of unidirectional sand movement from the depositional areas, which are recharged with fine-grained sediment only during episodic floods that typically occur during El Niño years. Eolian sand moves primarily from west to east through the study area; the period of maximum eolian activity is April through June. Wind speed varies diurnally, with maximum velocities typically occurring during the afternoon.
Development of alluvial fans, alteration of stream channels by channelization,
in-stream gravel mining, and construction of infiltration galleries were thought
to reduce the amount of fluvial sediment reaching the depositional areas upwind
of Uma habitat. Also, the presence of roadways,
railroads, and housing developments was thought to disrupt or redirect eolian
sand movement. Most of the sediment yield to the fluvial system is generated
in higher elevation areas with little or no development, and sediment yield
is affected primarily by climatic fluctuations and rural land use, particularly
livestock grazing and wildfire. Channelization benefits sediment delivery to
the depositional plains upwind of the reserves by minimizing in-channel sediment
storage on the alluvial fans.
The post-development annual sediment yield to the Whitewater and Mission Creek—Morongo
Wash depositional areas are 3.5 and 1.5 million ft3/yr, respectively,
covering each depositional area to a depth of 0.2 to 0.4 in. Given existing
sand-transport rates, this material could be depleted by eolian processes in
8 to 16 months, a rate consistent with the presence of persistent sand dunes.
However, these depletion times are likely minimum estimates, as some eolian
sand is seen to persist in the immediate vicinity of depositional areas for
longer time periods. Transport rates may be reduced by the presence of vegetation
and other windbreaks.
Because they are perpendicular to prevailing winds, the infiltration galleries
on Whitewater River trap fluvial and eolian sediment, reducing sediment availability.
Also, the presence of the railroad and Interstate 10 redirect eolian sand movement
to the southeast along their corridors,potentially eliminating the Whitewater
depositional area as a sand source for the Willow Hole Reserve. Using directional
wind data, we discuss the potential for eolian sand transport from the Mission
Creek—Morongo Wash depositional area to Willow Hole.
Abstract
Introduction
Purpose and Scope
Acknowledgments
Background
Habitat Requirements of Uma inornata
The Fluvial System in the Coachella Valley
The Eolian System in the Coachella Valley
Methods
Quaternary Geologic Mapping
Climatic and Hydrologic Data
Delineation of Drainage and Depositional Areas
Fluvial Sediment Yield
The Power-Function Approach
The Flood-Frequency, Rating-Curve Technique
Non-Contributing Drainage Areas
Particle-Size Distributions
Historical Wind Energy and Direction
Sand-Transport Potential
The Dune Mobility Index
Historical Changes in Eolian Deposits
A Conceptual Model of the Sand-delivery System in the Northern Coachella Valley
Fluvial Sediment Transport
Quaternary Geologic Units
Fluvial Sediment Yield and Delivery
Eolian Transport
Historical Wind Speed and Direction
Sand-Transport Potential
Spatial Variations in Sand-transport Potential
Dune Mobility
Actual Sand Transport
Historical Changes in Area of Sand Dunes
Linkages Between the Fluvial and Eolian Transport Systems
Rates of Eolian Transport
Mission Creek – Morongo Wash Depositional Area
Conclusions
Abbreviated Answers to Questions Posed by the U.S. Fish and Wildlife Service
References Cited
Appendix 1. Descriptions of Quaternary Geologic Map Units
Alluvial Units
Colluvial and Eolian Deposits
Appendix 2. Available Daily Stream-flow Data for the Northern Coachella Valley Through 2001
For additional information write:
Regional Research Hydrologist
U.S. Geological Survey
345 Middlefield Road
Menlo Park, CA 94025
Copies of this report can be purchased from:
U.S. Geological Survey
Information Services
Building 810
Box 25286, Federal Center
Denver, CO 80225-0286
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