PROJECT LOCATION

WALKER Dickinson Bayou is located in southeast in the COUNTY San Jacinto-Brazos Coastal Basin. The bayou originates north of the City of Alvin in Brazoria MONTGOMERY COUNTY County and flows east approximately 24 miles WALLER LIBERTY COUNTY COUNTY through Galveston County where is drains to AUSTIN COUNTY HARRIS COUNTY , a secondary bay of . CHAMBERS Dickinson Bayou COUNTY Major named tributaries that flow to Dickinson COLORADO Watershed COUNTY FORT B END Bayou include Gum Bayou, Benson Bayou, Magno- COUNTY lia (Geisler) Bayou, Bordens Gully, Cedar Creek, WHARTON COUNTY BRAZORIA GALVESTON COUNTY COUNTY and LaFlore’s Bayou.

MATAGORDA COUNTY PROJECT DESCRIPTION The study was designed to evaluate water quality over a period of time at several locations along Dickinson Bayou. The project focused on the tidal BACKGROUND portion of the bayou, a very sluggish water body Dickinson Bayou is on the state’s list of water bodies dominated by a deep, v-shaped channel with an not meeting water quality standards for dissolved average depth of 10-15 feet. oxygen (DO) and bacteria levels. As a result, the bayou does not meet its aquatic life use nor its contact Data collection devices were deployed at each of recreation use, creating a possible environmental and/ nine sites for five consecutive days each month from or public health concern. To address these problems, a July 2000 to August of 2001. In addition, water partnership was formed between the Galveston County quality samples were taken for laboratory analysis. Health District (GCHD), the -Galveston Area The U.S. Geological Survey collected supplemental Council (H-GAC), the U.S. Geological Survey biological data. Data analysis was performed on the (USGS), and the Texas Commission on Environmental resulting data values to form generalized Quality (TCEQ) to conduct a special study. conclusions about the bayou. Dickinson Bayou currently does not meet state requirements for aquatic life or contact recreation

MAJOR FINDINGS of the study confirmed that Runoff from significant rainfall events contributes salinity, ambient temperature, and rainfall runoff, as to the high bacteria concentrations. Also, higher well as algal blooms and organic loading influence bacteria levels were found at sampling sites in Dickinson Bayou’s low DO levels. more rural settings, probably due to greater use of

septic systems and rangeland runoff. Study Dickinson Bayou Special Special Bayou Dickinson A saltwater wedge (“halocline”) was found extending from The Dickinson Bayou watershed is Dickinson bay upstream to experiencing land use changes as a Cemetery Road. result of urban, commercial, and rural Saltwater tends to encroach more development. These changes will during warmer, drier summer continue to cause biological, chemical, months. Little or no encroach- and physical pressures on the bayou and ment occurs during the rainy, its ability to absorb and process the cooler, winter months. This halocline creates a increased loading from point and nonpoint source horizontal barrier between fresh and saltwater layers, pollution. preventing movement of DO between the two. Zero DO was frequently measured in the saltwater wedge, The TCEQ will use the gathered data and analysis while higher DO levels were generally found above to conduct modeling on the bayou to determine that wedge, in the fresher water. The halocline how to proceed with completing a watershed action disappeared only during high flow periods following plan for addressing the low DO occurrence and significant rainfall events. reducing the bacterial contamination.

Contact Info: Jean Wright, Special Projects Coordinator Todd Running, Clean Rivers Program Manager Galveston County Health District Pollution Control Division Houston-Galveston Area Council (713) 993-4549 (phone) 1205 Oak Street 3555 Timmons Lane, Suite 120 (713) 993-4503 (fax) P.O. Box 939 (409) 938-2301 (phone) Houston, TX 77027-6478 La Marque, TX 77568 (409) 938-2271 (fax)