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Q lowering flood crests, minimizing erosion, and serving to reduce the 



< destructiveness of severe floods. In densely populated areas this is 



especially important, since urbanization intensifies the rate of runoff. 

 Buildings, concrete, and asphalt waterproof the land surface and tend 



q to concentrate large volumes of precipitation. Cities lack adequate 



soak-in areas and the runoff is usually rapid and in excessive amounts. 

 Wetlands, and especially flood plains, act as catchment basins and tend 

 to slow the speed of flood waters, thus minimizing flood damage. In 

 1955, when severe floods hit eastern Pennsylvania, many bridges were 

 washed out along the stream courses. However, two bridges of the type 

 destroyed elsewhere were still intact below the Cranberry Bog, a Natu- 

 ral Area preserved by The Nature Conservancy and recommended for 

 landmark status. That swamps provide natural storage for flood waters 

 has been demonstrated on the Alcovy River in Georgia (Wharton 

 1970), also recommended for landmark status. 



It has been estimated that a 6-inch rise in water over a 10-acre wet- 

 land places more than 1 .5 million gallons of water in storage with no 

 harm to the surrounding biota (Niering 1966). By slowing the velocity 

 of flow, wetlands minimize erosive processes and simultaneously act as 

 siltation basins. Wetland filling is often a combination of organic, 

 plant-derived, and inorganic, stream-carried sediments. 



Wetlands have been shown to play a significant role in ground-water 

 recharge. In the Ipswich River basin of Massachusetts the USDI 

 (1962) found that marshes and swamps functioned not only as water 

 storage and discharge areas but also occasionally as ground-water 

 recharge areas. In North Carolina along the Yellow River, Kilpatrick 

 (1964) found an alluvial aquifer below the flood plain that was 

 hydraulically contiguous with the surface waters of the stream. 



Productivity 



Fresh-water marshes and swamps are among the most productive 

 biological systems. Eugene Odum (1959) estimates the gross produc- 

 tivity of southern river swamps such as the Alcovy and Altamaha bot- 

 tomlands at 20,000 kcal/m 2 per year, which compares favorably with a 

 field of sugarcane (27,010). * the most productive, intensively managed 

 agro-ecosystem. Furthermore, wetland productivity is estimated to be 

 double the 20,000 figure on the most favorable sites. Hardwood 

 production reaches about 12 metric tons/ha (2.4 acres) per year. The 

 estimated timber productivity on the 2300-acre Alcovy River system is 

 estimated to be $1,578,720 per year ($686 per acre per year) based 

 on a 100-year period and at present market value. Fish productivity 

 averages 75 pounds per acre but may reach 1300 pounds per acre in 

 the backwaters and sloughs, according to the Georgia Game and Fish 

 Commission. Wharton ( 1970) estimates the total productivity value of 

 the Alcovy at $546,940 per year or $3,648,720 based on a 100-year 



'Day net production plus night respiration. 



