Fort Morgan Flood Inundation Mapping Study

Science Center Objects

In 2017, the U.S. Geological Survey (USGS), in cooperation with the Colorado Water Conservation Board (CWCB), studied floods in the historic record to produce a library of flood-inundation maps for the South Platte River at Fort Morgan, Colorado.
 

Digital flood-inundation maps for a 4.5-mile (7.2-kilometers) reach of the South Platte River at Fort Morgan from Morgan County Road 16 to Morgan County Road 20.5, were created.

The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the U.S. Geological Survey streamgage on the South Platte River at Fort Morgan (streamgage number 06759500).

Water-surface profiles were computed for the stream reach by means of a one-dimensional, step-backwater model. The September 15, 2013, and May 20, 2017, floods were used to calibrate the model, and the June 15, 2015, and May 29, 2017, floods were used to independently validate the model. Nine pressure transducers were deployed to record the stage at nine different locations along the reach and to document the floods of May 20 and 29, 2017, at the South Platte River at Fort Morgan streamgage.

Water-surface profiles were computed for the stream reach by means of a one-dimensional, step-backwater model. The September 15, 2013, and May 20, 2017, floods were used to calibrate the model, and the June 15, 2015, and May 29, 2017, floods were used to independently validate the model. Nine pressure transducers were deployed to record the stage at nine different locations along the reach and to document the floods of May 20 and 29, 2017, at the South Platte River at Fort Morgan streamgage.

The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging data having a 0.37-ft [0.11-m] vertical accuracy and 3.28-ft [1.00-m] horizontal resolution) to delineate the area flooded for stages ranging from 12 to 27 ft (3.66 to 8.23 m).

These flood-inundation maps, in conjunction with the real-time stage data from the USGS streamgage on the South Platte River at Fort Morgan, are intended to help guide the general public in taking individual safety precautions and provide emergency management personnel with a tool to efficiently manage emergency flood operations and post flood recovery efforts.

OBJECTIVES:

Map showing location of the study area for the U.S. Geological Survey streamgage on the South Platte River at Fort Morgan, CO

Map showing location of the study area for the U.S. Geological Survey streamgage on the South Platte River at Fort Morgan, Colorado

  1. Compile historic flood data from the Fort Morgan streamgage
  2. Collect additional stage data by deploying pressure transducers throughout the study area
  3. Collect and compile topographic and bathymetric data for selected cross sections and geometric data for structures and bridges along the study area
  4. Estimate energy-loss factors (roughness coefficients) in the stream channel and flood plain and determination of steady-flow data
  5. Compute water-surface profiles using the U.S. Army Corps of Engineers Hydrologic Engineering Center River Analysis System computer program
  6. Produce estimated flood-inundation maps at various stages using the U.S. Army Corps of Engineers Hydrologic Engineering Center GeoRiver Analysis System computer program
  7. Prepare flood-inundation maps, both as shapefile polygons that depict the areal extent of flood inundation and as depth grids that provide the depth of floodwaters, for display on a USGS flood-inundation mapping application.
Map showing the study area on the South Platte River at Fort Morgan, CO incl. pressure transducers and cross sections

Map showing the study area for the U.S. Geological Survey (USGS) streamgage on the South Platte River at Fort Morgan, Colorado (streamgage number 06759500), including pressure transducers and cross sections used to simulate flood stage.