46 • Wetlands: Their Use and Regulation 



croaching on the basin's flood plains and wetlands 

 (1). The study predicted that the basinwide flood 

 level for the 100-year flood would increase 0.5 feet 

 if 10 percent of the flood plain/wetland storage 

 capacity were lost, and 3 feet if 50 percent of the 

 flood plain/wetland storage capacity were lost. Fill- 

 ing a wetland will reduce its storage capacity; if the 

 fill material rises above the level of the flood plain, 

 flood conveyance value also may be reduced. 



The effects of drainage on floodflows are slightly 

 more complicated. One point of view is that drain- 

 age increases floodpeaks by synchronizing and 

 speeding the runoff of water and by eliminating the 

 potential storage of runoff in wetlands. A contrast- 

 ing viewpoint is that drainage channels may reduce 

 floodpeaks by draining away heavy rains that other- 

 wise would have left the soil saturated through the 

 winter, reducing the storage available during critical 

 spring rain and snowmelt. Research to date has not 

 yet resolved this controversy.^ 



Shoreline Erosion Control 



Shoreline erosion is a natural process caused by 

 river currents during flooding, tidal currents in the 

 coastal areas, and wind-generated waves along the 

 shores of large lakes, broad estuaries, and ocean- 

 facing barrier islands. Boat wakes also can cause 

 considerable shoreline damage. 



Four characteristics of vegetated wetlands are 

 responsible for reducing erosion: 1) the low-gradient 

 shore that absorbs and dissipates wave energy (70); 

 2) the dampening and absorption of wave energy 

 by the plants themselves (44,95); 3) the root struc- 

 ture and peat development in wetlands that bind 

 and sfabilize the shore (71,76); and 4) the deposi- 

 tion of suspended sediment that is encouraged by 

 dense growth of wetland plants.'' 



'See the following references for reviews of information pertaining 

 to the impacts of wetlands draining on flooding: 1) L. J. Brunn, 

 J. L. Richardson, J. W. Enz, and J. K. Larsen, "Slreamflow Changes 

 in the Southern Red River Valley of North Dakota," North Dakota 

 Farm Research Bimonthly Bulletin, vol. 38, No. 5, 1981, pp. 11-14; 



2) John M. Malcolm, "The Relationship of Wedand Drainage to 

 Flooding and Water Quality Problems and Its Impact on the J. Clark 

 Salyer National Wildlife Refuge," FWS, Upham, N. Dak., 1979; and 



3) J. E. Miller and D. L. Frink, "Changes in Flood Response of the 

 Red River of the North Basin, North Dakota-Minnesota," U.S. Geo- 

 logical Survey, Open File Report 82-774, 1982. 



'Recent reviews of the scientific literature have been completed by 

 P. R. Adamus and L. T. Stockwell, "A Method for Wetland Func- 



Vegetated freshwater or saltwater wetlands lo- 

 cated adjacent to open but usually sheltered bodies 

 of water significantly reduce shoreline erosion 

 caused by large waves generated by occasional 

 storms and boat traffic' Wetlands adjacent to rivers 

 also may reduce riverbank erosion from strong cur- 

 rents during major flooding. Although it general- 

 ly is agreed that wetland vegetation does not nat- 

 urally establish itself in high-energy environments 

 where the potential for erosion is greatest, wetland 

 plants, once established, do help to control erosion, 

 stabilize the soil, encourage deposition of sediments, 

 and dampen wave energy. Isolated wetlands not 

 associated with larger bodies of water will not have 

 significant value for erosion control. 



Potential Economic Importance 



Shoreline erosion is a major problem in many 

 coastal areas. In Virginia, for instance, it has been 

 estimated that 1,476 hectares of tidal shoreline 

 eroded away between 1850 and 1950. This amount 

 represents approximately 20 percent of the 5 million 

 metric tons of sUt and clay that wash into Virginia's 

 estuaries annually (39). The impacts of shoreline 

 erosion include: loss of public and private proper- 

 ty and the subsequent loss of taxable income for 

 localities, filling of navigable waters with eroded 

 sediment, increased turbidity of waters, siltation 

 offish and wildlife habitat, and loss of recreationally 

 valuable sand beaches. Millions of dollars are spent 

 each year to reduce shoreline erosion and main- 

 tain the navigability of channels. 



Ability of Wetlands to Control Shoreline Erosion 



Wetlands not only resist erosion themselves, but 

 also protect the more easily eroded upland areas 

 shoreward of the wetland. Three studies have com- 



tional Assessment," U.S. Department of Transportation, Federal 

 Highway Administration, Office of Research, Environmental Divi- 

 sion, Washington, DC, 1983, p. 176. 



^Most of the existing literature on this function has been reviewed 

 in the following: 1) H. H. Allen, "Role of Wetland Plants in Erosion 

 Control of Riparian Shorelines," Wetlands Functions and Values: 

 The State of Our Understanding, P. E. Greeson, J. R. Clark, and 

 J. E. Clark (eds.) (Minneapolis. Minn.: American Water Resources 

 Association, 1979), pp. 403-414; 2) Carter, et al. (15); 3) R. G. Dean, 

 "Effects of Vegetation on Shoreline Erosional Processes," Wetland 

 Functions and Values: The State of Our Understanding, P. E. 

 Greeson, J. R. Clark, and J. E. Clark (eds.) (Minneapolis, Minn.: 

 American Water Resources Association, 1979), pp. 415-426; and 4) 

 Institute for Water Resources (88). 



