Making More Informed Decisions Helping small communities assess risk By Craig A. Ries and David A. Kubiske, P.E., P.S. (Contributing Editor), David Arthur Consultants, Inc. A small Michigan community was able to model potential flood levels and identify areas at risk by combining existing data with newly collected and highly accurate horizontal and vertical data around the floodplain. For a community located near a sizable river, accurately predicting flooding and managing the associated risks can be a difficult and relatively expensive task. This is true for the Village of Dundee. Located in southeastern Lower Michigan, the village is bisected by a river. Like many communities in the 1970s, the village adopted a combined sewer outfall (CSO) system as a result of water quality federal regulations and statements from the Department of Environmental Quality (DEQ). CSO systems combine sewer and storm water systems to dilute outflowing sanitary effluent returning to a river. Following changes in water pollution regulations and a better understanding of its causes, CSO systems were no longer endorsed. Under new regulations, CSO systems failed to meet the requirements of new laws. This was particularly true for the village due to overtaxing of the downriver treatment plant. Many communities replaced or modiThe digtal elevation model (here in gray scale) showing elevations in the Village's vicinity along with GPS data and GPS points marking some initial work on the CSO system shown as green dots www.esri.com fied sewer systems to meet the new regulations, and the village was no exception. It separated the storm and sewer lines it was aware of and Continued on page 28 ArcUser Winter 2010 27