Piedmont-Fan Flood Hazard Analysis From Geomorphology and Surface Water Hydrology, Hudspeth County, Texasby Jeffrey R. Keaton, Sergent, Hauskins & Beckwith, Salt Lake City, United States,
Roy J. Shlemon, Sergent, Hauskins & Beckwith, Salt Lake City, United States,
Richard H. French, Sergent, Hauskins & Beckwith, Salt Lake City, United States,
David R. Dawdy, Sergent, Hauskins & Beckwith, Salt Lake City, United States,
Abstract: A 2-mi2 (5.2 km2) site selected by the Texas Low-Level Radioactive Waste Disposal Authority was technically evaluated for local west Texas governmental agencies by a team including the authors. This site is located on a piedmont-fan surface within the Hueco Bolson on tributaries of the Rio Grande. The 12-mi2 (31 km2) drainage basin includes the southern edge of the Diablo Plateau where flat-lying Cretaceous limestone is exposed in a 600-ft (183-m) high escarpment. The 100-yr flood plain is a regulatory exclusion for siting low-level radioactive waste facilities. The FEMA Flood Insurance Rate Map (FIRM) shows a narrow strip of Zone A cross the site; however, the geomorphic appearance of the piedmont-fan surface indicates that the floodplain is much more extensive. The piedmont-fan surface is characterized by creosote and scattered mesquite, low relief, and a gentle southwestern slope. A near-surface calcrete, possibly 400,000-yr old, is regionally extensive. However, trenches to about 20 ft (6 m) deep reveal that (1) the calcrete is laterally discontinuous and has been cut locally by latest Pleistocene and Holocene gravel-filled channels; (2) fluvial fine sand and silt and discontinuous intercalated buried paleosols overlie the channels and calcrete; (3) probable middle to late Holocene bars and channels locally interfinger the post-calcrete deposits; and (4) the modern surface is geomorphically active and bears only a weak cumulic (pedogenic) soil profile.
Subject Headings: Floods | Surface water | Geomorphology | Geohazards | Hydrology | Soil analysis | Risk management | Drainage basins | Radioactive wastes | Site investigation | Waste sites | Waste disposal | North America | Texas | United States | Rio Grande
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