from run-off values, in acre-ft/mi , multiplied by the total drainage area 

 for that particular bayou, river, or stream to obtain a total discharge 

 (m^/yr) . Areas were obtained from Sloss's inventory of drainage areas 

 (Sloss 1971). The data for each basin are listed in tables 6.4(la) to 

 6. 4 (Id). They show the discharge area, the calculated run-off value, and 

 the discharge in ft^/sec and m-Vyr. For East Bay, because of lack of data, 

 published run-off values were used with drainage areas to obtain a total 

 discharge. 



Phosphorus Discharge Calculations 



Phosphorus (P) data were so scarce that P input according to land use was 

 calculated. Sample calculations for point source input were made and in 

 all five cases the P input calculated from land use was at least double that 

 measured from known point source inputs. It was therefore accepted that 

 the land use method represented worst case conditions. 



Land use by basin was determined in acres from data published by the 

 Louisiana State Planning Office (Louisiana State Planning Office 1975). The 

 dated acreage of each land use category was multiplied by the appropriate 

 phosphorus loading coefficient to obtain the phosphorus inputs. These 

 were summed to produce a total basin annual P input in g/yr. This divided 

 by the water discharge gave a total concentration in g/m^/yr (Tables 6.4(2a) 

 to 6.4(2e). This concentration was compared with a three level index of 

 eutrophic state (Shannon and Brezonik 1971): permissible (P 0.12 g/m ) 

 meaning the amount of total P is permissible with no tendency towards eu- 

 trophication; borderline (0.12 g/m^ < P < 0.22); and dangerous (P < 0.22 

 g/m-*) meaning the amount of total P is at a level that this receiving body 

 is eutrophic. 



357 



