Mapping Spatial Variation in Rainfall Intensity-Duration-Frequency Estimates Using a Geographical Information System

For hydraulic design purposes, the Michigan Department of Transportation (MDOT) currently uses rainfall intensity-duration-frequency (IDF) estimates for four rainfall zones in Michigan. The delineation of these zones is based on frequency estimates at gage sites and isopluvial maps developed by interpolation procedures and subjective judgment. The objectives of this study are to apply more objective interpolation procedures to regional frequency estimates and to develop an interactive geographic information system (GIS) interface capable of querying and displaying location-specific IDF curves. For each of seven durations (1, 2, 3, 6, 12, 18, and 24 hours), and for each of six event frequencies (0.5, 0.2, O.1, 0.04, 0.02, 0.01 per year), a rainfall intensity grid will be developed using a spatial interpolation procedure available in a commercial geostatistical software package or GIS. An interactive model capable of querying and displaying location-specific rainfall IDF estimates will then be developed to manage the rainfall intensity grid. Through the GIS interface, users will be able to select a specific geographic location within the state of Michigan and display IDF curves and other related information for the selected location. This product will provide water resource professionals with a faster, easier-to-use tool for determining appropriate rainfall intensity values for use in hydrologic engineering design.