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Flood-inundation maps for the South Platte River at Fort Morgan, Colorado, 2018

Scientific Investigations Report 2018-5114
Prepared in cooperation with the Colorado Water Conservation Board
By:  and 
https://doi.org/10.3133/sir20185114

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Abstract

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.

The hydraulic model was then used to compute 16 water-surface profiles for flood stages at 1-foot (ft; 0.3-meter [m]) intervals referenced to the streamgage datum and ranging from 12 ft (3.66 m) or below bankfull to 27 ft (8.23 m), which is 1 ft (0.3 m) greater than the highest recorded water level (25.73 ft [7.84 m] on September 15, 2013) at the South Platte River at Fort Morgan streamgage during its period of record; the 2013 flood exceeds the major flood stage of 21.5 ft (6.55 m) by more than 4 ft (1.2 m), as defined by the National Weather Service.

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.

Suggested Citation

Kohn, M.S., and Patton, T.T., 2018, Flood-inundation maps for the South Platte River at Fort Morgan, Colorado, 2018: U.S. Geological Survey Scientific Investigations Report 2018–5114, 14 p., https://doi.org/10.3133/sir20185114.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Creation of Flood-Inundation-Map Library
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Flood-inundation maps for the South Platte River at Fort Morgan, Colorado, 2018
Series title Scientific Investigations Report
Series number 2018-5114
DOI 10.3133/sir20185114
Year Published 2018
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Colorado Water Science Center
Description Report: vi, 14 p.; Data Release
Country United States
State Colorado
City Fort Morgan
Other Geospatial South Platte River
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
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