Sabine River Authority of Texas
To: Interested Parties
From: Environmental Services
RE: September 1998 Water Quality Monitoring Report
This is the Sabine River Authority Water Quality Report for September 1998. This report was delayed due to equipment problems caused by lightning. Water quality sampling was performed September 15 through September 17. Weather during September can be characterized as warm and wet throughout the Basin, as Tropical Storm Francis brought windy weather and heavy rains to the Sabine Basin just prior to and during the September Water Quality Monitoring (WQM).
Upper Sabine Basin Above Toledo Bend Including Lake Fork and Lake Tawakoni
Most parameter values observed in the Upper Basin sites are consistent with water of high quality. However, heavy rainfall influenced water quality at many sites this month. These sites were characterized by high flow, low secchi depth, high turbidity, low conductivity, and high fecal coliform counts. The reservoir sites were nearly (LF2, LF3, LT23C, LT23D) or completely (LF2, LT23A) thermally stratified. A few sites were still stratified with respect to dissolved oxygen but LF2 and LT23A were completely mixed. LT23A had only about 2mg/l oxygen from surface to bottom. Additional data was taken at four lower-reservoir sites on Lake Tawakoni on 9/25/98 to research and document the low D.O. conditions and some taste and odor complaints from the City of Emory water system. These additional data were taken at LT23A; 500m out from the Dallas raw water intake; mid lake between the Dallas and Emory intakes; and a point 500m out from the Emory intake. At LT23A, dissolved oxygen was 0.60mg/l near the bottom (11.1m) and gradually increased to 2.71mg/l at the surface. Both sites near the intakes were well oxygenated (above 5mg/l) from bottom to surface in 4-6m of water. The mid-lake site, which was 11.3m deep, ranged from 0.20mg/l at the bottom, to 8.44mg/l at the surface. The two shallow water sites were pea-green in color from algal bloom conditions. Historically (since 1993) at LT23A, low oxygen levels from surface to bottom were seen on 9/6/95 and 9/4/96. This well-mixed, low D.O. condition may indicate the reservoir mixed (turned over) near the date of the sample. As seen in the present sample data, shallower sites, near the upper ends of the reservoirs, do not exhibit as severe an effect at mixing since they have a much smaller volume of water to circulate to the surface for atmospheric oxygenation. In addition, the ratio of anoxic, deep water to well oxygenated surface water is less at shallower sites.
Several other sites on Tawakoni and Fork indicated mixing was imminent at the time of sampling this month. These sites had only about one degree of difference in water temperature surface to bottom but significant difference in dissolved oxygen. Surface oxygen was also slightly less than 5mg/l at LF3 and the river site, SR11. Two reservoir sites, LT23A and LF3, exceeded screening criteria for ammonia and two other reservoir sites had elevated values. Again, lake turnover is a likely cause. Fecal coliform counts were high at most of the river sites. This is not uncommon after a significant rainfall and the resulting suspension of sediment. Turbidity was also high at these sites and conductivity was low from the rainwater runoff.
Lower Sabine Basin Including Toledo Bend to Morgan Bluff
Water Quality in the Lower Basin was affected by the extreme weather. Toledo Bend, while still well below normal pool elevation, rose 1.5 feet in approximately 5 days. River sites in the Lower Basin had high flow and at many sites water was over river banks. This influx of water into the Sabine River and reservoirs had a profound effect on water quality as non-point source contamination is washed into the system. Fecal Coliform values were elevated at most stations. Station TB6H had the highest value (87600 col/100ml) and only two locations (TB6A and SR5) had values within the numerical criteria for stream standards. Dissolved Oxygen values were below the numerical criteria for stream standards (5.0 mg/L) at Stations TB8, TB6I, TB6M, TB6L and TB6CN. Nutrient and turbidity values were high at several locations. Values for pH were below stream standards at five locations. Most Toledo Bend sites were stratified with respect to dissolved oxygen and temperature. This stratification was not as well defined or as shallow as the previous month.
Tidal Section of the Sabine Basin below Morgan Bluff
Values for stations in the tidal portion of the Sabine Basin were also affected by the extreme weather during and leading to the sampling event. Heavy rains and strong winds prevailed during the WQM which raised water levels, and lowered salinity, dissolved oxygen, and pH. Dissolved Oxygen values were low at Stations ICW1, BB1 and SRT1. Stations BB1 and ICW1 were the only sites where salinity was detected. Station BB1 had the highest value for Nitrate and Nitrite, the lowest dissolved oxygen value and the highest salinity. One site, Station SR1, had an elevated fecal coliform value (396 col/100ml).
This Report and additional data for these monitoring stations are available on our World Wide Web site (www.sra.dst.tx.us). If you have any questions or comments concerning this report, please contact: