233 



The effect of structures on increasing local subsidence rates should 

 be quantified, so that designs can include all components of apparent sea 

 level rise. 



Research is needed on methods to limit saltwater exchange through 

 locks, so as to improve their effectiveness. 



Much more research is needed to quantify the climatic consequences of 

 the greenhouse effect. This includes changes in rainfall and runoff plus 

 the frequency and strength of tropical and extratropical storms, since 

 these can affect structure design and planning as much as sea level rise 

 does . 



SECT. 8. SALTWATER INTRUSION 

 Text Discussion 



Climate changes may have an even more profound effect on saltwater 

 lintrusion than sea level rise has. Drier weather in agricultural areas 

 will lead to increased groundwater pumping, and wetter weather will have 

 the reverse effect. Recharge rates will be affected, but with a time lag 

 that may be considerable. 



Cost of water can completely change water use patterns; therefore, 

 many projections that seem reasonable now may be inoperative in 25 years, 

 as water becomes more scarce and as saltwater intrusion threatens supplies. 



If riverine intrusion (also subject to climate changes) changes water 

 supply or impoundment practices, groundwater use will be affected. If 

 river supplies are abandoned because of saltwater intrusion, there is 

 likely to be increased demand for groundwater sources, exacerbating the 

 groundwater problem. 



Tertiary effects may occur, such as occurred in St. Louis. In that 

 case a large decrease in groundwater pumping (caused by movement of 

 industry) let the groundwater level rebound to previous high levels, 

 flooding an area that had become highly developed during the period of low 

 water table. If saltwater contamination leads to abandonment of 

 groundwater pumping over a large area, similar responses could occur in 

 coastal areas. 



