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Scientific Investigations Report 2014–5021

Prepared in cooperation with the Alabama Department of Economic and Community Affairs—Office of Water Resources

Simulation of Natural Flows in Major River Basins in Alabama

By Alexandria M. Hunt and Ana María García

Thumbnail of and link to report PDF (7.91 MB)Abstract

The Office of Water Resources (OWR) in the Alabama Department of Economic and Community Affairs (ADECA) is charged with the assessment of the State’s water resources. This study developed a watershed model for the major river basins that are within Alabama or that cross Alabama’s borders, which serves as a planning tool for water-resource decisionmakers. The watershed model chosen to assess the natural amount of available water was the Precipitation-Runoff Modeling System (PRMS). Models were configured and calibrated for the following four river basins: Mobile, Gulf of Mexico, Middle Tennessee, and Chattahoochee. These models required calibrating unregulated U.S. Geological Survey (USGS) streamflow gaging stations to estimate natural flows, with emphases on low-flow calibration. The target calibration criteria required the errors be within the range of: (1) ±10 percent for total-streamflow volume, (2) ±10 percent for low-flow volume, (3) ±15 percent for high-flow volume, (4) ±30 percent for summer volume, and (5) above 0.5 for the correlation coefficient (R2). Seventy-one of the 90 calibration stations in the watershed models for the four major river basins within Alabama met the target calibration criteria. Variability in the model performance can be attributed to limitations in correctly representing certain hydrologic conditions that are characterized by some of the ecoregions in Alabama. Ecoregions consisting of predominantly clayey soils and (or) low topographic relief yield less successful calibration results, whereas ecoregions consisting of loamy and sandy soils and (or) high topographic relief yield more successful calibration results. Results indicate that the model does well in hilly regions with sandy soils because of rapid surface runoff and more direct interaction with subsurface flow.

First posted May 27, 2014

For additional information, contact:
Director, Alabama Water Science Center
U.S. Geological Survey
AUM TechnaCenter
75 TechnaCenter Drive
Montgomery, AL 36117

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Suggested citation:

Hunt, A.M., and García, A.M., 2014, Simulation of natural flows in major river basins in Alabama: U.S. Geological Survey Scientific Investigations Report 2014–5021, 32 p.,

ISSN 2328–0328 (online)






Watershed Models for Major River Basins in Alabama

Model Configuration

Model Calibration

Calibration Results

Model Application


References Cited

Appendix 1. Series of Graphs Presenting Model Results

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