UIS Commission on Karst Hydrogeology and Speleogenesis
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Johnson, K.S.; Wilkerson, J.M.
Land, L.; Doctor, D.H.; Stephenson, J.B.
Gypsum karst causes relocation of proposed cedar ridge dam, throckmorton county, texas
Sinkholes and the Engineering and Environmental Impacts of Karst: Proceedings of the Thirteenth Multidisciplinary Conference, May 6-10, Carlsbad, New Mexico: NCKRI Symposium 2. Carlsbad
Carlsbad
2013
133
140

Cedar Ridge Dam and Reservoir will be built to supply water for the city of Abilene, Texas. The original damsite (CR) was to be located on Clear Fork of Brazos River in Throckmorton County, but initial coring of the damsite encountered unsuspected gypsum beds in the Permian-age Jagger Bend/Valera Formation. Gypsum is a highly soluble rock that typically contains karst features, and its presence in a dam foundation or impoundment area could allow water to escape from the reservoir. A decision was made to look at potential sites farther upstream (to the southwest), where west-dipping gypsum beds would be deeper underground and karst problems would be minimized or eliminated.The first phase of the relocation was a comprehensive field study of Clear Fork Valley, upstream of the original damsite, to identify gypsum outcrops; gypsum was exposed at only one location, just above damsite CR. The second phase of the study was examination of nearly 100 petroleum-test geophysical logs to identify, correlate, and map the subsurface gypsum and associated rock layers upstream of the original damsite. The gypsiferous sequence is 30–45 m thick, and consists of 8 gypsum beds, mostly 1–3 m thick, interbedded with red-brown and gray shale units 1–10 m thick. Gypsum beds comprise 25–30% of the gypsiferous sequence. Gypsum beds dip uniformly to the west at about 7 m/km (about 0.4 degrees), and thus the uppermost gypsum is at least 23 m beneath the newly proposed damsite (A), about 8 km to the southwest.Subsequent coring and other studies of the new damsite A confirm that gypsum beds are 23 m beneath the newly proposed dam. There is no evidence of solution channels or other karst features beneath this site, and thus there is little likelihood of water loss from the reservoir at the new site due to gypsum karst.

SINKHOLE; GYPSUM KARST; THROCKMORTON COUNTY; TEXAS; Cedar Ridge Dam; Reservoir; Abilene
978-0-9795422-7-5
Johnson, K.S.; Wilkerson, J.M., 2013, Gypsum karst causes relocation of proposed cedar ridge dam, throckmorton county, texas , 133 - 140 http://www.karstportal.org/sites/karstportal.org/files/KIP-0011735-25.pdf