Estimating Velocity of Floodwaters Using Multiple Field Techniques: An Investigation of the August 2007 Flooding In Farmers Park, Stockton, MN

On August 18^th and 19^th, 2007, southeastern Minnesota experienced one of the most devastating flood events in its history. A week-long series of smaller storms preceded a storm that dropped approximately 15 inches of rain in 24 hours. This rainfall, unabsorbed by the already saturated soil, led to the flash flooding of several area streams and caused millions of dollars in damage. The Fall 2007 Advanced Geomorphology class at Winona State University studied the aftermath of this flood event in Farmers Park, near Stockton, Minnesota. The flooding changed the landscape of the entire park (causing massive damage and redefining the flow pattern of the stream) and provided an excellent opportunity for studying fluvial geomorphology. The class reconstructed the velocity, and subsequently the discharge, of floodwaters traveling through Farmers Park based on channel deposits and high-water indicators. Field measurements of parameters of the Manning Equation (including slope and hydraulic radius) were used to calculate the velocity of the floodwaters. Pebble counts were used to conduct a shear stress analysis and to determine the stream competence. The data indicated that the floodwater velocity was 1.28 m/s and average discharge was 250.2 m³/s.