History of Small Watershed Projects in Texas
The U.S. Soil Conservation Service is actively engaged in the installation of flood and soil erosion reducing measures in Texas under the authority of the "Flood Control Act of 1936 and 1944" and "Watershed Protection and Flood Prevention Act" (Public Law 566), as amended. The Soil Conservation Service has found a total of approximately 3,500 floodwater-retarding structures to be physically and economically feasible in Texas. As of September 30, 1970, 1,439 of these structures had been built.
This watershed-development program will have varying but important effects on the surface and ground-water resources of river basins, especially where a large number of the floodwater-retarding structures are built. Basic hydrologic data under natural and developed conditions are needed to appraise the effects of the structures on the yield and mode of occurrence of runoff.
Hydrologic investigations of these small watersheds were begun by the Geological Survey in 1951 and are now being made in 12 study areas (fig. 1). These investigations are being made in cooperation with the Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant County Water Control and Improvement District No. 1. The 12 study areas were chosen to sample watershed having different rainfall, topography, geology, and soils. In five of the study areas, (North, Little Elm, Mukewater, little Pond-North Elm, and Pin Oak Creeks), streamflow and rainfall records were collected prior to construction of the floodwater-retarding structures, thus affording the opportunity for analyses of the conditions "before and after" development. A summary of the development of the floodwater-retarding structures in each study areas of September 30, 1970, is shown in table 1.
Objectives of the Texas Small Watersheds Project
The purpose of these investigations is to collect sufficient data to meeting the following objectives:
1. To determine the net effect of floodwater-retarding structures on the regimen of streamflow at downstream points.
2. To determine the effectiveness of the structures as ground-water recharge facilities.
3. To determine the effect of the structures on the sediment yield at downstream points.
4. To develop relationships between maximum rates and/or volumes of runoff with rainfall in small natural watersheds.
5. To develop a stream-system model for basins with floodwater-retarding structures.
6. To determine the minimum instrumentation necessary for estimating the flood hydrographs below a system of structures, as needed for downstream water-management operation.
Purpose and Scope of this Basic-Data Report
This report, which is the eleventh in a series of basic-data reports published annually for the Calaveras Creek study area, contains the rainfall, runoff, and storage data collected during the 1970 water year for the 77.2-square-mile area above the stream-gaging station Calaveras Creek near Elmendorf, Texas. The location of floodwater-retarding structures and hydrologic-instrument installations in the area are shown on figure 2.
This investigation was scheduled to continue through periods of both above- and below-normal precipitation, but on September 1, 1967, the San Antonio City Public Service Board began construction of Calaveras Creek Dam. This reservoir will serve as a cooling basin for power plants to be built in the future, with most of the water to be pumped from the San Antonio River. In the interim, it is being used as a recreation facility. The dam was completed in December 1968, and pumpage into Calaveras Lake from the San Antonio River started in January 1969. Much of the study area is inundated by the reservoir, which covers about 4,300 acres (fig. 2). The reservoir controls 65 square miles of the area about the stream-gaging station Calaveras Creek near Elemendorf.
The recording gage at Calaveras Creek floodwater-retarding structure No. 6 is continued in operation to monitor time-associated hydrologic changes on a drainage area of this size.
The staff gages at floodwater-retarding structure No. 10 were continued in operation to provide an index to flow below Calaveras Lake. The two recording rain gages (2R, 11R) and two of the standard rain gages (5S, 8S) were continued in operation.
In subsequent years, data for Calaveras Creek and Escondido Creek subwatersheds, which are both in the San Antonio River Basin, will be published under one cover because the work in both subbasins has been decreased.
To facilitate the publication and distribution of this report at the earliest feasible time, certain material contained herein does not conform to the formal publication standards of the U.S. Geological Survey.