Overview

The Webster Dam and Reservoir is located within the High Plains Province of Kansas. The geologic conditions involved are relatively simple, as all subsurface beds are nearly horizontal. No major faults or faulting is known in the area. Some movement has occurred within the Niobrara and Carlisle formations, with joints and small faults being the existing evidence. Moisture moving along the faults created planes of weakness where sliding could occur. All deposits are of a sedimentary, no igneous or metamorphic rocks are exposed or close to the surface in the Webster area. Unconsolidated Pleistocene deposits mantle the older consolidated sediments except for a few erosional hills and bluffs formed by the more resistant Fort Hays limestone. The deposits involved in the construction of Webster Dam ranged in age from Cretaceous (Carlisle shale) to Recent (river Alluvium). Tertiary deposits are not found at the damsite but do occur adjacent to the upper reaches of the reservoir. The Carlisle shale is the bedrock underlying the river alluvium; the Fort Hays or Smoky Hill members of the Niobrara formation underlie the uplands. The Carlisle shale is a marine of upper Cretaceous age and Gulfian Series and has an average thickness of 300 feet. The Niobrara formation, Upper Cretaceous age, conformable overlays the Carlisle shale. It is composed of two easily distinguished members. The Fort Hays, the lower member, is composed of several massive chalky limestone beds separated by thin shale or bentonite layers.

General

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Hydraulics & Hydrology