StreamStats for Indiana incorporates regression equations for estimating peak-flow frequency statistics at the 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals (equivalent to the 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, respectively) for unregulated streams throughout Indiana, and equations for estimating bankfull-channel dimensions of width, mean depth, and cross-sectional area for non-urban wadeable streams in the three largest physiographic regions of Indiana. These equations are implemented by use of two separate interactive map applications; one which provides the peak-flow estimates, and the other which provides the bankfull-channel-dimension estimates. The separate applications were necessary because flood-frequency estimates for many stream reaches in Indiana have been coordinated by the Indiana Department of Natural Resources, the Natural Resources Conservation Service, the U.S. Army Corps of Engineers, and the USGS. That is, these agencies have agreed on flood-frequency values for selected stream reaches for use in water-resources investigations and planning activities. Custom programming that was required to deliver the coordinated flood-frequency values precludes delivery of bankfull-channel-dimension estimates in the same output. Links to the separate applications are provided below. Users of the interactive map for estimating peak-flow statistics who select points along the coordinated stream reaches will be provided with the coordinated discharges instead of flow estimates obtained from regression equations. More information about coordinated discharges can be found here.
Note that regression equations are developed using streamflow statistics and basin characteristics for USGS-operated streamgages. The equations are applicable with known accuracy when they are applied at locations with basin characteristics that are within the ranges of the basin characteristics for the streamgages used to develop the equations. Estimates for user-selected sites with basin characteristics that are outside of those for the streamgages used to develop the equations are extrapolated. These extrapolated estimates should be used with caution, as their associated errors are unknown and may be large. StreamStats outputs provide the ranges of applicability for each basin characteristic that is used as an explanatory variable in the regression equations, and warnings when those ranges are exceeded.
General information on the Interactive Map application, as well as specific sources and computation methods for basin characteristics are available here.
The report below documents the peak-flow regression equations, the methods used to develop the equations and to measure the basin characteristics used in the equations, references to GIS data layers used in the analysis, 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 streamflow statistics for ungaged sites.
- Rao, A.R., 2005, Flood-Frequency Relationships for Indiana: Joint Transportation Research Program, Purdue University, FHWA/IN/JTRP-2005/18, 14 p.
Stream slope is used as an explanatory variable in the peak-flow regression equations for all hydrologic regions of Indiana except for region 8. The method used by StreamStats to compute stream slope is somewhat different than the method used to develop the dataset used by Rao (2005) for his regression analyses. The average difference between the StreamStats values of stream slope and the values used by Rao is about 4 percent, but differences for some individual stations exceeded 100 percent. As a result, users should consider that the errors associated with the flow estimates provided by StreamStats are probably somewhat greater than the published standard errors of prediction.
The StreamStats application for estimating peak-flow statistics for Indiana was developed in cooperation with the Indiana Department of Natural Resources.
The report below documents the development of the bankfull-channel-dimension equations, including (1) the methods employed for data collection, (2) the characteristics of the sites where data were collected, (3) the data-analysis methods used to develop the regression equations, (4) a comparison of results with eastern United States channel-dimension regression equations, and (5) limitations that should be considered by anyone who would apply the results:
- Robinson, B.A., 2013, Regional bankfull-channel dimensions of non-urban wadeable streams in Indiana: U.S. Geological Survey, Scientific Investigations Report 2013–5078, 33 p.
The bankfull-channel-dimension equations were developed for non-urban streams. Impervious surfaces and storm sewers can significantly alter runoff characteristics and the dimensions of channels that drain urbanized watersheds.
The StreamStats application for estimating bankfull-channel dimensions for Indiana streams was developed in cooperation with the Indiana Office of Community and Rural Affairs.
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