Intensive Study of Dickinson Bayou Tidal. Segment 1103. November 27-29, 1984.




Kirkpatrick, J.S.

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An intensive survey of Dickinson Bayou tidal (Segment 1103) was conducted November 27-29, 1984. This segment extends from 4.0 Km (2.5 mi) below FM 517 to Dickinson Bay, a distance of 24.3 Km (15.1 mi). Most of the population is centered around the community of Dickinson, located in the middle portion of the bayou. Contact recreation and high quality aquatic life habitat are the designated water uses. Historical water quality data show occasional low dissolved oxygen levels and pH, frequently elevated fecal coliform counts, and persistently elevated phosphorus levels. Eleven mainstream stations, four tributaries, three wastewater discharges and one station in Dickinson Bay were sampled during this survey. Rainfal runoff prior to the survey resulted in dilution of the bayou and non-steady-state conditions. Field data did not indicate any particular problem areas. Concentrations of all parameters were within the established ranges or exceeded the minimum criteria established for the segment. Conductivity levels and vertical profile data were typical of tidal streams. Dissolved oxygen levels were lowest in the upper part of the bayou where density stratification was evident (Station D, E, and F). Laboratory analyses of water samples showed slightly higher levels of carbonaceous biochemical oxygen demand, Kjeldahl, ammonia, nitrite and nitrate nitrogen, orthophosphorus and total phosphorus at Station A (Dickinson Bayou above tidal, Segment 1104) than any station on the tidal portion of the bayou. Wastewater discharges into Segment 1104 probably were the main contributors of these elevated concentrations. Stations G, H and I had the next highest levels of nitrogen and phosphorus, which is probably a result of the four wastewater discharges in the vicinity. Chemical results from the three wastewater discharges indicated relatively typical secondary treatment levels. Flow measurements indicated about 0.342 m3/s (12.1 ft3/s) of tributary freshwater inflow to the segment, with most of it (69%) coming from Gum Bayou. Average width of the segment increased from about 125 m (49 ft) in the upper portion to about 840 m (2765 ft) at the lower end. Average depth was about 1.8 m (6.0 ft) in the upper end, 3.0 m (9.8 ft) in the middle, and 1.4 m ( 4.5 ft) in the lower part. Fecal coliform concentrations were high. The highest concentration was 46,500/100 mL at Station P on Gum Bayou. Dickinson Bayou at Gum Bayou confluence had the highest fecal coliform count of any mainstream station (13,350/100 mL). Specific sources of fecal coliforms were not investigated during this survey, but rainfall runoff contributed in transporting the bacteria from the sources to the bayou.


26 p.


hydrology; field measurements; water chemistry; fecal coliforms