R.O. Woodward K.F. Higgins 1986 We determined drainage rates for wetlands in North and South Dakota with U.S. Fish and Wildlife Service 20-year easements, during (1961-1980) and after (1981-1984) contract protection. Average annual drainage rates were 10 times higher during the four postcontract years than during the 20 contract years on the same tracts of land. Twenty-year easements only delayed wetland drainage, and are of limited value for securing a long-term habitat base. application/pdf en Comparison of wetland drainage during and after protection by 20-year easements article