## StreamStats in Missouri

Missouri StreamStats incorporates statewide regression equations for estimating rural peak flows with annual exceedance probabilities of 50, 20, 10, 4, 2, 1, 0.5 and 0.2 percent. These peak flows have recurrence intervals of 2, 5, 10, 25, 50, 100, 200 and 500 years, respectively. Missouri StreamStats also incorporates regional regression equations for estimating low-flow frequency statistics, including the 1 day-10 year; 2 day-10 year; 3 day-10 year; 7 day-10 year; 10 day-10 year; and 60 day-10 year recurrence intervals. In addition, equations are available for estimating urban peak flows (for areas which the percent impervious area is greater than 2.3%) with annual exceedance probabilities of 50, 20, 10, 4, 2, 1 and 0.2 percent. These peak flows have recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years, respectively. The reports below document the available regression equations in Missouri, the methods used to develop the equations and to measure the basin characteristics used in the equations, and the errors associated with the estimates obtained from the equations. Users should familiarize themselves with these reports before using StreamStats to obtain estimates of flows for ungaged sites in drainage basins.

- Southard, R.E., 2013, computed statistics at streamgages, and methods for estimating low-flow frequency statistics and development of regional regression equations for estimating low-flow frequency statistics at ungaged locations in Missouri: U.S. Geological Survey Scientific Investigations Report 2013–5090, 28 p., (Also available at http://pubs.usgs.gov/sir/2013/5090/.)
- Southard, R.E., and Veilleux, A.G., 2014, Methods for estimating annual exceedance-probability discharges and largest recorded floods for unregulated streams in rural Missouri: U.S. Geological Survey Scientific Investigations Report 2014–5165, 39 p.,(Also available at https://pubs.usgs.gov/sir/2014/5165/.)
- Southard, R.E., 2010, Estimating the magnitude and frequency of floods in urban basins in Missouri: U.S. Geological Survey Scientific Investigations Report 2010-5073, 27 p., (Also available at https://pubs.usgs.gov/sir/2010/5073/.)

Click on this link to obtain general information on the Missouri application, as well as specific sources and computation methods for basin characteristics.

**Notes on computing basin characteristics:**

When using the *Basin Characteristics* tool, if a value for basin shape (BSHAPE) is desired, then a two-step process is required. First, use the tool to compute either the adjusted or the unadjusted 10-85 stream slope (CSL10_85), and then use it again to compute BSHAPE.

**Notes on rural peak flow estimates in Regions 1 & 2:**

Rural peak flow estimates in regions 1 and 2, as identified in SIR 2014-5165, are estimated in part using a process which determines the longest flow path in a basin to a point on a stream. The published longest flow path values were calculated using a different method than StreamStats, so the estimates of error associated with peak flow values in these regions are larger than those published in the report. Estimated peak flow statistics calculated by StreamStats averaged 1.17% difference than published values, with some locations as high as 11.17% difference.

**Notes on low**** flow ****frequency estimates in Region** **1: **

Low flow frequency estimates for region 1 as identified in SIR 2013-5090, are estimated in part using a process which determines the longest flow path in a basin to a point on a stream. The published longest flow path values were calculated using a different method than StreamStats, so the estimates of error associated with the low flow frequency statistics in this region are larger than those published in the report. Estimated low flow frequency statistics averaged -1.66% difference from the published values, with some locations as high as -31.9% difference.

Missouri StreamStats was developed in cooperation with the Missouri Department of Natural Resources.

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