A watershed is the geographical boundary within which water flows after a storm event. A typical watershed is depicted in Diagram 1below.
The McLennan and Hill Counties Tehuacana Creek Water Improvement District #1 (District) is an agency initiated by the federal government in the late 1960’s to reduce flooding and erosion in the Tehuacana Creek Watershed. The Tehuacana Creek originates in Hill County and proceeds through McLennan County to the Brazos River.
Project Area
The Tehuacana Creek watershed covers 310 square miles and includes portions of Hill, McLennan, and Limestone counties (Tehuacana Creek Water Control and Improvement District 2005). The stream originates in Hill County and flows 31 miles from Hill to McLennan County and joins the Brazos River south of SH 6, about five miles east of Waco (Figure 1). Several tributaries that drain eastern portions of McLennan County feed into Tehuacana Creek. Little Tehuacana Creek is the largest tributary and starts in West, Texas, joining Tehuacana Creek approximately a mile north of US 84. Tradinghouse Creek Reservoir, located on Tradinghouse Creek in the southeastern portion of the Tehuacana Creek watershed, is the largest reservoir in the watershed. The reservoir provides cooling water to the Luminant Tradinghouse Power Plant.
Located in the Texas Blackland Prairie, Ecoregion 32 (Griffith 2004), the naturally fertile soils consist of rich minerals weathered from limestone, shale, and marl (USDA 1992). These fertile soils provide rangeland for beef and dairy cattle. Corn, wheat, hay, grain sorghums, soybeans, and nursery crops are the main crops grown in McLennan County (Ramos 1999). The flat-to-rolling terrain also supports mesquite, cacti, water-tolerant hardwoods, conifers, and grasses (Handbook of Texas 2006b).
During the 1950’s the Tehuacana Creek watershed experienced floods that eroded and damaged farmland, crops, roads, and bridges. As a result of the extensive damage throughout the watershed, Public Law 566 was passed by the 83rd Congress and is known as The Watershed Protection and Flood Prevention Act (USDA 1977). Under Public Law 566, the United States Department of Agriculture (USDA) assisted in building 27 flood control dams along the stream and its tributaries to help eliminate damage during future flood events (NRCS 1998). The USDA also installed 32 grade stabilization structures and did channel work on 10.1 miles of the stream (USDA 1977). The channel work included the enlargement and straightening of Tehuacana Creek from the mouth of Tradinghouse Creek to the mouth of Cottonwood Creek, which enters Tehuacana Creek from the east, upstream from US 84 (USDA 1958). In order to fund the flood control structures, the Tehuacana Creek Water Control and Improvement District 1 was created by Public Law 566.
The final Environmental Impact Statement for the Tehuacana Creek watershed flood control project estimated that the flood control structures would reduce the sediment load for the watershed from 242,000 tons to 112,000 tons annually (USDA 1977).
In 1958, it was noted that the northern part of the watershed had high erosion rates due to steep slopes, a predominance of row-crop farming, and inadequate soil conservation treatment (Figure 2). The southern part of the watershed has lower erosion rates due to more pasture land and bank slopes less than two percent (USDA 1958). The flood control structures and the land treatment plan took into account the differences within the watershed and installed treatments accordingly.
There are three governing entities to the District; McLennan County, the Natural Resource Conservation Service, a component of the U.S. Department of Agriculture, and a local elected board, the McLennan and Hill Counties Tehucana Creek Water Improvement District. Every land owner in the district is levied a tax used to maintain the 32 flood control stuctures in the watershed. These structures were built in the 1960’s with federal bonds which were were re-paid by tax revenue.
The District is the local body comprised of Board members elected from landowners in the watershed. Their responsibility is to respond to issues related to the flood control structures, manage vegetation on the dam sites, manage regular maintenance issues associated with the dam or drawdown structure, determine needs for the district to operate by state standards and levy taxes accordingly. The taxes are collected by the McLennan County Tax office.
A drawdown structure is a mechanism that allows a lake to be kept at a constant level. It is engineered to allow floodwaters to drain at a relatively slow rate from the lake to reduce the potential for downstream flooding in the watershed.
Draw down mechanism