21 



Flood and Storm Damage Protection 



In their natural condition, most wetlands serve to tem- 

 porarily store flood waters, thereby protecting down- 

 stream property owners from flood damage. After all, 

 such flooding has been the driving force in creating these 

 wetlands. This flood storage function also helps to slow 

 the velocity of water and lower wave heights, which 

 reduces the water's erosive potential. Rather than having 

 all flood waters flowing rapidly downstream and destroy- 

 ing private property and crops, wetlands slow the flow of 

 water, store it for some time and slowly release stored 

 waters downstream (Figure 20). In this way, flood peaks 

 of tributary streams are desynchronized and flood waters 

 do not all reach the mainstem river at the same time. This 

 function becomes increasingly important in urban areas, 

 where development has increased the rate and volume of 

 surface water runoff and the potential for flood damage. 



In 1975, 107 people were killed by flood waters and 

 potential property damage for the year was estimated to 

 be $3.4 billion (U.S. Water Resources Council 1978). 

 Almost half of all flood damage is suffered by agriculture 

 as crops and livestock are destroyed and productive land 

 is covered by water or lost to erosion. Approximately 1 34 

 million acres of the conterminous United States have 

 severe flooding problems. Of this, 2.8 million acres are 



urban land and 92.8 million acres are agricultural land 

 (U.S. Water Resources Council 1977). Many of these 

 flooded farmlands are wetlands or previously drained 

 wetlands. 



Although regulations required by the Federal Insurance 

 Administration may help reduce flood losses from urban 

 land, agricultural losses are expected to remain at present 

 levels or increase as more wetlands are put into crop 

 production. Protection of wetlands is, therefore, an im- 

 portant means of minimizing flood damages in the future. 



The U.S. Army Corps of Engineers has recognized the 

 value of wetlands for flood storage in Massachusetts. In 

 the early 1970's, the New England Division considered 

 various alternatives to providing flood protection in the 

 lower Charles River watershed near Boston, including: 

 (1) 55,000 acre-foot reservoir, (2) extensive walls and 

 dikes, and (3) perpetual protection of 8,500 acres of wet- 

 lands (U.S. Army Corps of Engineers 1976). If 40% of 

 the Charles River wetlands were destroyed, flood dam- 

 ages would increase by at least $3 million annually. Loss 

 of all basin wetlands would cause an average annual flood 

 damage cost of $17 million (Thibodeau and Ostro 1981 ). 

 The Corps concluded that wetlands protection — "Natu- 

 ral Valley Storage" — was the least-cost solution to 

 flooding problems. In 1983, they completed wetland ac- 

 quisition in the Charles River basin. 



i 



Ul 



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O 



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 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 



I 1 II II l' 

 i,l,l,l| I I f^ 



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ill' 



I I I I 



•^ Higher flood and higher flows 



Lower flood crest and 

 lower flows 



WETLANDS 



NO WETLANDS 



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 m 



X 



Q 

 O 

 O 



TIME 



Fig. 20. Wetland value in reducing flood crests and flow rates after rainstorms (adapted from Kusler 1983). 



