INVESTIGATING CAUSES AND EFFECTS OF FLOODING ON THE ROCK RIVER, LEBANON TOWNSHIP, DODGE COUNTY, WISCONSIN

The Rock River, a 300-mile tributary of the Mississippi River, winds its way through the varied glacial terrain of southern Wisconsin after sourcing north of the Horicon National Wildlife Refuge, a vast marshland, important for its migratory bird habitat. Below the refuge, the Rock River is managed by several dams on its way south and west to the Illinois border. Between the dam at Horicon and the upper dam in Watertown, WI, lie the townships of Lebanon, Ashippun, and Ixonia. These mostly rural towns boast productive agricultural lands of predominantly corn, soybeans, and alfalfa. They reside in the floodplain of the river, underlain by vast expanses of outwash sands and gravels, glaciolacustrine deposits, and tills. The only significant topographic variations are the vast number of drumlins that dot the landscape. Throughout the region, spring floods are common from snowmelt and spring rain. Surface flow over frozen ground through much of the spring exacerbates annual flooding, making it a part of life for residents in the area. However, over the last 15-20 years, this segment of the Rock River has seen an increase in flooding both in periodicity and retention of flood waters. Due to the delicate habitat of the wildlife refuge and the commissioned hydroelectric installation at the upper dam in Watertown, the residents and local governments of the Lebanon/Ashippun/Ixonia segment of the river have mostly been left to their own devices to monitor and manage flood events. Lebanon Township has been recording water levels for several years, but have yet to establish a definitive explanation for the increased retention of flood waters. Data show that high water events and flood retention do not correlate well with precipitation data for the region, especially through the late spring and summer months. A stream survey was conducted from Beaver Dam to Concord to rule out obvious impediments to flow such as beaver dams, woody-debris jams, or unregulated impoundments. The survey found no significant obstructions, but evidence suggests that tributaries may be contributing sediment to the Rock River and creating deltas within the main channel. Increased development and poor soil management could exacerbate this sediment loading and increase upstream water retention.