Effects of P.L. 566 Stream Channelization on Wetlands in the Prairie Pothole Region

The Wild Rice Creek Watershed project, in North and South Dakota was constructed under authority of the Small Watershed Protection and Flood Prevention Act (P.L. 83-566 as amended). Structural measures included 24.7 miles of channelization and four floodwater retarding dams. To measure the degree that channelization influenced drainage of prairie wetlands, drainage rates in a channelized tributary were compared to rates in an unchannelized tributary of Wild Rice Creek. Channelization had a direct impact on wetlands by channel drainage reduction of overbank flows, and by providing drainage outlets. Indirect (secondary) wetland losses are believed to have occurred outside of the channelized areas. Almost three times more wetland basins and seven times more acres of wetlands were drained in the channelized area than in the unchannelized area before construction (1952-60). Most of that drainage occurred after approval of the Watershed Work Plan. During the years of channel construction and the years following construction (1961-72) more than seven times as many wetlands were drained in the channelized area than the unchannelized area and more than ten times as many acres. Drainage was 3.5 and 6.5 times higher for the wetland basins and acres, respectively, in the channelized area versus the unchannelized during the 1952-72 period. When drainage of wetlands on two soil types was compared, rates were significantly higher (p\u3c.05) on the soil types in the channelized area than in the unchannelized area. Drainage rate of number of wetlands in the 1/4 sections adjacent to the channel was the same as in the 1/4 sections one mile from the channel. Evidently, depth of channel in relation to wetland basin elevation was the major influence on drainage of surface water. General conclusions concerning drainage in the Wild Rice Creek Watershed were: (1) drainage feasibility increased; (2) not only did the constructed channel stimulate drainage, but anticipation of the channel also had an effect; and (3) presence of the adequate drainage outlet was the major factor influencing decision by the landowner to drain