Geospatial datasets and hydraulic models for the Grand River, Red Cedar River and Sycamore Creek near Lansing, Michigan (ver. 1.1, February 2023)

Hydrologic and hydraulic analyses were done for selected reaches of the Grand River, Red Cedar River and Sycamore Creek near Lansing, Michigan. To update and expand a portion of the Federal Emergency Management Agency detailed Flood Insurance Study, the U.S. Geological Survey (USGS) and the City of Lansing initiated a cooperative study. The study comprised a 3.2-mile reach of the Grand River, a 30.2-mile reach of the Red Cedar River, and a 12.0-mile reach of Sycamore Creek. Historical streamflow data from multiple streamgages, Grand River at Lansing, MI. (USGS station number 04113000), Red Cedar River at East Lansing, MI. (USGS station number 04112500), Red Cedar River near Williamston, MI. (USGS station number 04111379), and Sycamore Creek at Holt Road near Holt, MI. (USGS station number 04112850) along with regional regression equations were used to estimate instantaneous peak streamflows for floods with 10-, 4-, 2-, 1-, 0.2-percent, and 1-percent plus annual exceedance probabilities. The 1-percent plus flood elevation is defined by the Federal Emergency Management Agency as a flood elevation derived by using streamflows that include the average predictive error for the regression equation streamflow calculation for the Flood Risk project. This error is then added to the 1-percent annual exceedance probability flood streamflow to calculate the 1-percent plus streamflow. The annual exceedance probability streamflows were then used in a Hydrologic Engineering Center-River Analysis System step-backwater model to determine water-surface elevation profiles and flood-inundation boundaries for the 10-, 4-, 2-, 1-, 0.2-percent, and 1-percent plus annual exceedance probability floods, and a regulatory floodway, along a selected reach of each stream. Each hydraulic model was calibrated to the current stage-streamflow relations at each streamgage. Flood-inundation boundaries for the 1- and 0.2-percent annual exceedance probability floods and a regulatory floodway were mapped for each stream.