Spatial Extent, Timing, and Causes of Channel Incision, Black Vermillion Watershed, Northeastern Kansas

The Black Vermillion River (watershed area = 1310 square kilometers) contributes runoff and sediment into Tuttle Creek Lake, a large federal reservoir (volume = 327 million cubic meters) northeast of Manhattan, Kansas. Tuttle Creek Lake, completed in 1962, is filling with sediment faster than other federal reservoirs in the region. The lake’s conservation pool is about 40 percent full of sediment and is predicted to fill by 2023. Debate rages over the relative contribution of sediment from upland sources (largely croplands and pasture) versus channel incision. Our study determined the sediment production in the Black Vermillion River from channel incision. The spatial extent, timing, and causes of channel incision had not been investigated previously. We conducted a watershed-wide survey of channel cross-sections repeated at sites that were surveyed 45 years ago by the Soil Conservation Service. Channel depth 1963-2008 increased by a mean of 1.6 meters (maximum = 5.2 meters). Most channels are actively incising, or incising and widening. Channelization has reduced channel length by a significant portion and is the leading cause of incision. Rates of incision were also related to land cover, riparian vegetation, channel bed material, and geology. Bedrock is overlain in most of the watershed by Kansan age glacial till and loess, where incision prevails and is related to upland land cover, riparian vegetation, and drainage area. Our study is part of a larger effort that will compare sediment contributions from upland and channel sources in the watershed. Fig. 1 Typical channel incision, 1963-2008, Black Vermillion River, NE Kansas.