Effects of Engineering Projects on Estuaries 



Richard A. Diener 



The value of estuaries as nursery and feeding grounds for many 

 commercially important species of fish and crustaceans is reflected in Texas 

 landings, of which approximately 98 percent by weight are of species in some 

 way dependent on estuaries. The cumulative effects of water development 

 practices upon these estuaries and upon the allied commercial fish production 

 will likely be extensive. Our present knowledge does not permit us, however, 

 to make accurate predictions of these effects upon marine fishery resources. 



Although the effects of development projects cannot yet be evalu- 

 ated accurately, several types of changes may be foreseen. The most ob- 

 vious alteration of existing conditions would be reduction of fresh-water dis- 

 charge through greater consumptive water use and increased total evaporation 



due to more exposed surface area in res- 

 ervoirs. A reduced discharge of fresh 

 water may alter the suitability of estuarine 

 areas by raising their salinity; by varying 

 salinity, circulation, and water inter- 

 change patterns; by draining surrounding 

 marsh areas through the lowering of river 

 levels; by reducing silt load and thus al- 

 tering deposition rates; and by reducing 

 inflow of terrigenous nutrient materials 

 required for primary productivity. 



As human population increases 

 with accompanying expansion of agricul- 

 tural and industrial interests, it is logical 

 to expect an increase of pesticides and 

 other pollutants entering the estuaries 

 with the waste waters and runoffs. In- 

 fluence of inshore waters upon the hydrol- 

 ogy and food cycles of offshore waters has 

 not been clearly defined, but is another 

 factor which must be considered when assessing the effects of drastic modifi- 

 cations of river systems and their associated estuaries. 



The Nueces River of Texas affords an excellent example of the many 

 extensive water development programs proposed for the various watersheds 

 draining into the Gulf of Mexico, either directly or indirectly through the es- 

 tuaries. From its headwaters in Edwards County in south central Texas, the 

 Nueces flows southeasterly for some 315 miles terminating in Nueces Bay, a 

 segment of the Corpus Christi Bay system. As the Nueces River is the larg- 

 est tributary of the Corpus Christi estuarine systenn, it is one of the chief 

 factors determining hydrological conditions therein. 



Typical spoil retention dike 

 used to keep spoil from fill- 

 ing in and thus destroying 

 valuable marsh habitat. 



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