IV-372 



conditions in an estuarlne system and result in gradual undesirable 

 changes 1n the ecosystem. 



Table IV. 2. 10 shows the amount of estuarine habitat lost by filling; 

 Table IV. 2. 11 lists the major river flow regulation structures 

 affecting rivers in the estuarine zone; Table IV. 5. 4 gives a general 

 idea of the numbers of miscellaneous structures in the estuarine zone. 

 These three tables indicate only of the extent of modification, not of 

 its effects. While destruction of habitat by filling is measurable, 

 the environmental changes wrought in an estuarine system by external 

 flow regulation or by internal structures are so closely associated 

 with its morphology that generalization is impossible. Table IV. 5. 4 

 shows that there are in the estuarine zone 752 jetties, dikes, and 

 breakwaters averaging nearly 1000 feet in length. These are all 

 solid structures specifically designed and placed to modify flow 

 patterns. While habitat damage may have been considered in the design 

 of many of these, it is unlikely that effects on the estuarine 

 environment were considered seriously in the placement of many of the 

 989 causeways and pier bridges within the estuarine system. 



Physical modification of estuarine systems may enhance the usefulness 

 of the biophysical environment. In fact, many modifications are made 

 deliberately to improve or protect an estuary for a specific use, but 

 often without consideration of the rffects on other uses. The side 

 effects of such modifications may be good or bad, depending on local 

 conditions. For example, the piers and abutments that support 



