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directly support a large and diverse community of invertebrates and verte- 

 brates, including beaver and other fur-bearers, and, indirectly, animals that 

 inhabit adjacent upland areas but use the wetlands as a source of food and 

 water. The condition of wetland habitat is important for these animal popu- 

 lations. 



Hydrologlc and Hydraulic 



Hydrologic and hydraulic functions of wetlands include damping floods, 

 stabilizing shorelines or absorbing the destructive energy of storm waves, 

 and recharging groundwater sources. Different types of wetlands vary widely 

 in their ability to carry out these functions. 



Controlling floods may be the most important wetland function on a nat- 

 ional basis. Wetlands can serve as basins that both detain and retain flood 

 waters. Their effectiveness depends on their size and location in the drainage 

 basin, as well as on the hydrologic characteristics of the entire basin. Wet- 

 lands are most effective during floods of high intensity and short duration. 

 Statistical studies have shown that if a watershed has 15 percent of its area 

 in wetlands or lakes, peak flow will be 60 to 65 percent lower than if no wet- 

 lands or lakes are present. 24 / Case studies have been conducted at several 

 sites. Perhaps the best-known is in the Charles River basin in Massachusetts, 

 where the Corps of Engineers decided to acquire and protect more than 8,000 

 acres of wetlands because it was more cost-effective for flood control than 

 channelizing 10 miles of the river at an estimated cost of $30 million. 25 / 



24/ Clark and Clark, Scientists' Report, p. 54. 

 25/ Larson, Wetland Value Assessment, p. 5. 



