IV-402 



Figure IV. 1.18 shows the seasonal variation in precipitation for 

 selected coastal stations. This figure shows a rather varied dis- 

 tribution of precipitation throughout the national coastal areas 

 and Indicates the seasons when runoff could present problems. 



In addition to the pollutants carried in the runoff, the fresh 

 water Itself may stress the ecosystem through dilution of the 

 salinity to concentrations lower than those necessary to support 

 some life forms. A case in point is the annual killing of aquatic 

 vegetation 1n Tampa Bay with the onset of summer rains (Figure IV. 

 5.19). 



Last 1n runoff consideration is the degree of flow regulation or 

 water resource development upstream from the tidal environment. 

 These upstream impoundments, with the attendant flow regulation, 

 may have both beneficial and detrimental effects. The reservoirs 

 can serve as equalizing basins, providing a rather constant quality 

 of estuarlne fresh water inflow. The difference between regulated 

 flows and natural flows however, may cause ecological stress 

 through alteration of the salinity regime or the circulation pat- 

 terns. Table IV. 2. 11 is a compilation of flow regulation structures 

 on major estuarine streams. 



