StreamStats for Alabama can be used to estimate flood magnitudes for exceedance probabilities of 50, 20, 10, 4, 2, 1, 0.5, and 0.2 percent for rural and urban streams. These exceedance probabilities correspond to recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. Equations also are available for estimating minimum 7-day average discharges with recurrence intervals of 2 and 10 years. The reports below document the methods used to develop the regression equations and to compute the basin characteristics used in the equations, and the errors associated with the estimates obtained from the equations. Users should familiarize themselves with these report before using StreamStats to obtain estimates of streamflow statistics for ungaged sites.
- Hedgecock, T.S., and Lee, K.G., 2010, Magnitude and frequency of floods for urban streams in Alabama, 2007: U.S. Geological Survey Scientific Investigations Report 2010–5012, 17 p.
- Hedgecock, T.S., and Feaster, T.D., 2007, Magnitude and frequency of floods in Alabama, 2003: U.S. Geological Survey Scientific Investigations Report 2007–5204, 28 p., + app.
- Hedgecock, T.S., 2004, Magnitude and frequency of floods on small rural streams in Alabama: U.S. Geological Survey Scientific Investigations Report 2004–5135, 10 p.
- Atkins, J. B.; Pearman, J. L., 1994, Low-flow and flow-duration characteristics of Alabama streams: U.S. Geological Survey Water-Resources Investigations Report 93-4186, 264 p.
Important Note to Users:
The Estimate Flows Using Regression Equations outputs from StreamStats provide estimates determined using peak-flow regression equations from each of the three peak-flow reports above. The regression equations from reports SIR 2004-5135 and 2007–5204 have ranges of applicability that overlap. It is recommended that users should give precedence to the estimates labeled “Small Basin Peak-Streamflow Statistics” (from SIR 2004-5135) when the drainage area for a selected rural site is less than 5 square miles. When the drainage area for a selected rural site is greater than 15 square miles, then use the estimates labeled “Peak-Streamflow Statistics” “Urban Peak-Streamflow Statistics” (from SIR 2010–5012) should be used only when (1) streams have drainage areas between 1 and 43 square miles, (2) urban land is at least 20 percent of the drainage area, and (3) the selected site is not in peak-flow hydrologic area 3.
The percent urban values provided by StreamStats were computed from the National Land Cover Dataset (NLCD) of 2006, whereas values used to develop the urban peak-flow regression equations were determined manually from 2006 aerial photography. As a result, the values from StreamStats do not exactly duplicate the values used to develop equations, and they may not reflect current land-use conditions. Users may wish to override the percentage of development values from StreamStats with newer land-use information that is more indicative of current conditions by use of the Edit Parameters and Recompute Flows tool. The error statistics presented in the Estimate Flows Using Regression Equations outputs are the published errors from the above reports. Errors from StreamStats for urban peak-flow estimates are likely somewhat larger than those presented in SIR 2010-5012 because of the added uncertainty of using the NLCD to determine land use.
StreamStats for Alabama was developed in cooperation the Alabama Department of Transportation, Alabama Office of Water Resources, Alabama Wildlife and Freshwater Fisheries, Alabama Office of State Climatologist, and Alabama Power.
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