Appendix 6.4 CHENIER PLAIN HYDROLOGICAL DATA AND HABITAT DATA. 



Appendix 6.4(1). Method for calculating phosphorus loading rates 



of Chenier Plain Basins. 



The general procedure was to divide the Chenier Plain into its natural 

 drainage basins: Vermilion Basin, Mermentau/Chenier Basin, Calcasieu Basin, 

 Sabine Basin, and the East Bay Basin. Each basin was then subdivided 

 into two functional components: (1) open water receiving bodies such as 

 Sabine Lake, Vermilion Bay, etc.; and (2) the drainage area, surrounding 

 each water body from which the runoff water is derived. The following 

 calculations were made: (1) total discharge into the water body; (2) 

 the phosphorus concentration for each discharge area; and (3) development 

 of the phosphorus input loading rate which determines the probability of 

 a receiving water body to become eutrophic. Finally, the volume of the 

 receiving water body, its flushing rate, and the salinity distribution 

 was used to determine the sensitivity of the water body to eutrophication. 

 Sensitivity was expressed by the following eutrophic states: permissible, 

 borderline, or dangerous. 



The system was found to be primarily controlled by agricultural run- 

 off, which is the land use category which will require the attention of 

 planners. Analysis of the phosphorus input loading rate shows the eutrophic 

 state and the significance of each nutrient source. The calculations were 

 subject to error because of the scarcity of data. Actual discharge data 

 were available from upstream portions of the major rivers in the study area, 

 but were generally not available where the streams discharged into the 

 Chenier Plain. Therefore, measurement data were extrapolated to calculate 

 annual discharge (m /yr) . The phosphorus data were also spotty and were 

 concentrated at point source discharges with little long-term data; read- 

 ings at useful downstream locations were available for only a few dates 

 per year. It was therefore necessary to classify the drainage area accord- 

 ing to land use, and calculate the phosphorus input (g/yr) by using load- 

 ing coefficients derived from the literature and modified by empirical in- 

 vestigations in other parts of coastal Louisiana (Craig and Day 1977) . 



The total phosphorus input was divided by the total discharge to ob- 

 tain an annual average P concentration loading rate (g/m-Vyr) which was 

 compared to a eutrophication state scale (Shannon and Brezonik 1971). The 

 comparison allowed an evaluation of the water body on a scale of permissible, 

 borderline, or dangerous. 



Water Discharge Calculations 



A complete survey of all discharge data source material was made for 

 each basin. The locations and values were tabulated and the available data 

 were evaluated. Generally, some data from measurement stations upstream 

 from the basin were available, but few empirical measurements of drainage 

 area- related discharge were available. Therefore, discharge was calculated 



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