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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 WhitewaterSan Gorgonio Rivers and Mission CreekMorongo 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 CreekMorongo 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 CreekMorongo Wash depositional area to Willow Hole.
Purpose and Scope
Habitat Requirements of Uma inornata
The Fluvial System in the Coachella Valley
The Eolian System in the Coachella Valley
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
Historical Wind Energy and Direction
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
Historical Wind Speed and Direction
Spatial Variations in Sand-transport Potential
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
Abbreviated Answers to Questions Posed by the U.S. Fish and Wildlife Service
Appendix 1. Descriptions of Quaternary Geologic Map 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
Box 25286, Federal Center
Denver, CO 80225-0286
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