Construction of supplemental principal spillway at Clear Fork of the Trinity, Site 23

Clear Fork, Site 23 is a 49-foot-high homogeneous earthfill dam located on Squaw Creek in the Willow Park community of Parker County, Texas, about 20 miles west of Fort Worth, Texas. The dam was constructed in 1957 under Public Law 534, administered by the USDA, Natural Resources Conservation Service. The dam is operated and maintained by Parker County Soil and Water Conservation District to provide sediment storage, flood control, and supple- mental irrigation water for a nearby golf course. The dam was constructed as a Low Hazard dam. Subsequent development of the area downstream of the dam resulted in upgrading the hazard classification to High Hazard. The dam was rehabilitated in 2000-2001 to reduce the duration of flood storage and meet high hazard hydrologic criteria. One of the modifications to address the deficiencies was constructing a 30-inch inside diameter auxiliary principal spillway (outlet works)conduit through the embankment. This dis- charge feature was constructed by boring and jacking a steel carrier pipe through the embankment and subsequently lining the pipe with an internal lining pipe. The embankment/carrier pipe contact and the carrier/liner pipe annulus were both grouted. Additional components of the auxiliary principal spillway include a filter diaphragm around the conduit, a concrete hooded inlet structure with trashrack, and a lined plunge basin. Constructing additional discharge capacity using this method was cost effective, reduced the exposure to inflow during construction, and did not require a large excavation and reconstruction of the embankment. 10 pp.