Channel modifications along the lower Blue River, Kansas City, Missouri. USGS.
The problem
Kansas City, Missouri, has flooded badly many times — most notably in 1951, 1961, 1977, 1984, 1990, 1998 and 2010. In the past 30 years, floods caused tens of millions of dollars in damage in the city and more than 25 casualties.
The USGS and the city run streamgages along the Blue River and its tributaries. But a water level at a gage is hard to translate into how deep and how far flooding will spread elsewhere. The answer is a library of flood-inundation maps, each tied to a stage at a streamgage. With the right map, emergency responders can see how severe a flood will be, which roads are or may be under water, and whom to warn or evacuate up- and downstream.
How the maps were made
The Blue River basin: flood-inundation map reaches and streamgages. USGS.
- Streamgages. The network has 15 streamgages that record stage every 15 minutes and send it by satellite each hour to the USGS National Water Information System. Ratings from nine gages and high-water marks from the June 14, 2010, flood were used to calibrate the models.
- Water-surface profiles. For 15 reaches, profiles over a range of flows were simulated with one-dimensional (HEC-RAS 4.1) or two-dimensional (FST2DH) steady-state hydraulic models. They update and sharpen earlier maps (2006 and 2008) and account for the widened, deepened and straightened lower Blue River channel the U.S. Army Corps of Engineers finished in 2010.
- Calibration. Maps were made for every 1-foot step in stage, from about bankfull to the 0.2% annual-chance flood (the "500-year" flood). Roughness values (Manning's n) were adjusted until modeled levels matched observed levels at the gages.
- Mapping. In a GIS, each water-surface profile was combined with a lidar-based terrain model, refined with channel and bridge surveys; HEC-GeoRAS drew the flood boundaries.
The USGS streamgage at the Blue Ridge Boulevard Extension, Kansas City. USGS.
Getting the maps to people
The USGS Flood Inundation Mapping Program website and its mapper show the map libraries, flood extents and depths for the modeled sites, and can produce custom maps for all 15 reaches. Links lead to:
- current stage and streamflow at the USGS gages the maps are tied to;
- the National Weather Service's Advanced Hydrologic Prediction Service, with forecast peak stages at forecast points.
The maps are detailed enough for managers to respond efficiently and make emergency decisions.
Sources
Based on David C. Heimann, Trina E. Weilert, Brian P. Kelly and Seth E. Studley, "Flood-inundation mapping for the Blue River and selected tributaries in Kansas City, Missouri, and vicinity, 2012," U.S. Geological Survey Fact Sheet 2015–3008 (2015), with the City of Kansas City; a work of the United States government in the public domain. The map and photographs are taken from the fact sheet's PDF; its flood maps drawn on aerial imagery, website screenshots and a banner photo from a local blog are not reproduced.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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