SEDIMENTATION OF THE LOUSY CREEK DELTA

Deltas form where the mouth of a river empties into a body of water and deposits the material the river transported from its watershed. Most deltas form over many years and develop facies in a coarsening-upward sequence. Lousy Creek is a small stream near Spring Valley, WI, that drains a watershed consisting of mostly silt loam soils and is used primarily for agriculture. Lousy Creek empties into a recently created reservoir. Weekly stream gauging and water sampling of Lousy Creek under normal flow conditions show the stream has an average sedimentation rate of 220 cubic feet (cf) per year. Under these conditions the delta would have taken about 1160 years to form. However, the earthen dam that formed the reservoir into which Lousy Creek presently empties was built in 1968, so the delta formation took place in about 30 years. It is estimated that Lousy Creek experiences about 24 hours of high flow events per year. With both high flow and normal flow, the sedimentation rate becomes about 1.7 x 10⁵ cf per year, and the time for delta formation becomes 46 years. This suggests that high flow events causing runoff and erosion of fields play a large part in the Lousy Creek delta formation. The sediment in the delta is composed mostly of silt and sand. The top 30-50 cm of sediment is high in silt, with the bottom 50-70 cm high in sand. It appears that there is no definite "classic" delta facies present in the Lousy Creek delta because it is young and hasn’t had the time to progress into the reservoir to create the coarsening-upward facies, however, the delta may in the first stages of developing the "classic" coarsening-upward facies.