Wildlife Habitat Appraisal for the Proposed Allens Creek Reservoir Site


This project was conducted by the University of Houston Clear Lake during the period of May 15, 1995 through August 31, 1995 under contract with Texas Parks and Wildlife Department (TPWD), Resource Protection Division. The purpose was to perform a wildlife habitat appraisal of the proposed Allens Creek Reservoir (approximately 8,400 acres) located in Austin County near Sealy, Texas. The Allens Creek Reservoir has been proposed as part of the Trans-Texas Water Program (Texas Water Development Board 1994). Specifically, this project was to classify, delineate and map the major vegetation cover types, develop mitigation requirements, and estimate the extent of jurisdictional wetlands. Floristic descriptions for each major vegetation cover type, and a table with the acreage of each cover type were to be developed, along with mylar overlays of the vegetation cover maps at a scale of 1:24,000, a vegetation cover acreage table, and this report of project results, including mitigation and compensation estimates, and a preliminary wetlands delineation.

Project Area

The proposed Allens Creek Reservoir is located in southern Austin County, Texas. Allens Creek, with its head waters near the town of Sealy, lies within the Brazos River flood plain and flows into the Brazos River approximately one-half mile below the proposed Allens Creek Reservoir dam. The proposed reservoir is roughly bounded by SH 36 on the west, FM 1458 on the east, Mixville Road on the north, and FM 1093 on the south. The reservoir is to fill the area of a Brazos River meander bounded on all sides by a bluff except the east edge. The pond level is to be 118 feet above mean sea level. The proposed reservoir is in the Gulf Prairies and Marshes ecological area 4 of Texas (McMahan et al. 1984). The climate is classified as subtropical, receiving an average of 4 to 4.5 inches of rainfall monthly. Average annual low temperature is 56 to 57°F, and average annual high temperature is 79 to 80°F (Larkin 1983). Figure 1media download(PDF 20.9 KB) shows the location of Austin County and the proposed reservoir.

The proposed reservoir has been used extensively for agricultural purposes since being settled by Europeans. Recently, crops grown include cotton, sorghum, corn and soybeans. Cattle grazing has also occurred. This area is subject to periodic flooding by the near-by Brazos River.


The TPWD's Wildlife Habitat Appraisal Procedure (WHAP) (Frye 1995) was used in this project. The procedure was designed to "allow a qualitative, holistic evaluation of wildlife habitat for particular tracts of land statewide without imposing significant time requirements in regard to field work and compilation of data." (Frye 1995) At the direction of TPWD, Sections IA (Biological Habitat Components) and IB (Impact Assessment and Calculation of Mitigation Requirements) were used extensively, while Section II(Significance of Protected Fauna and Flora) was used only minimally and Section III (Management Components Evaluation) was not used at all. The WHAP is based on the following assumptions:

The WHAP is not designed to evaluate habitat quality in relation to specific wildlife species.

To become familiar with the proposed Allens Creek Reservoir, information was obtained employing several different techniques. The area was hiked extensively in May, June and July by 2 two-person teams. In July aerial photographs were taken during fly-overs by team members in a light aircraft. Professional high-altitude aerial color infrared photographs and black-and-white aerial photographs of the area were purchased and studied. A U.S. Geological Survey 7.5 minute quad 1:24,000 topographic map, and environmental studies by Houston Lighting and Power were also used. All of these information sources were used to ensure that all areas within the proposed reservoir were classified into an appropriate vegetation cover type. The above information sources along with a geographical positioning system (GPS) (Garmin Company, Inc.) device was used to determine boundaries of each cover types. A geographical information system (GIS) (ArcInfo 3.40+, ArcView 2.0, ESRI Co. Redlands, CA) was used to digitize the areas for each cover type, compute acreage and produce mylar and paper maps of the proposed reservoir.

WHAP scores are based on a minimum of seven representative sites for the vegetation cover type of crops, bottomland forest, and grass. Only two parks, both relatively small in size, exist in the proposed reservoir, so only two WHAP sites were assessed. The bluff forest vegetation cover type, although different enough to warrant its own type, had a very consistent vegetation species distribution, so only four WHAP sites were used. For the above vegetation cover types, many more locations were inspected to ensure the use of representative sites in WHAP score calculations. WHAP scores were also computed for the area 0.5 mile on either side along Allens Creek, downstream from FM 1458 to the confluence with the Brazos River. Although not to be flooded by the reservoir, this area is assumed to suffer major changes in habitat quality due to proposed rerouting of Allens Creek downstream from FM 1458. All mitigation / compensation estimates were calculated using an Excel spreadsheet patterned after the tables in Wildlife Habitat Appraisal Procedure (Frye 1995) and Texas Water and Wildlife (Frye and Curtis 1990).

Vegetation physiognomic classes (e.g., Bluff Forest) were further defined according to plant association (e.g., Pecan/Elm/Hackberry Bluff Forest) by referring to The Vegetation Types of Texas Including Cropland (McMahan et al. 1984) and Plant Communities of Texas (Texas Natural Heritage Program 1990). A wetlands consultant, Dr. John Jacob, was subcontracted by the University of Houston Clear Lake to develop an estimate of the wetlands on the proposed reservoir property. In conjunction with this effort, the Soil Survey of Austin and Waller Counties Texas (Greenwade 1984) aided in determining soil types. Hydric soils were located using the Hydric Soils of the United States (Soil Conservation Service 1985).

A conservative estimate of potential jurisdictional wetlands was made during a two day period in June. Further study is required to refine wetland boundaries, and should result in an overall reduction of areas identified as wetlands compared to this preliminary estimate.