SELDM: Stochastic Empirical Loading and Dilution Model - Software page

Release Date:

Note: to access the main SELDM page click here.



Granato, G.E., 2013, Stochastic empirical loading and dilution model (SELDM) version 1.0.0: U.S. Geological Survey Techniques and Methods, book 4, chap. C3, 112 p., on CD-ROM.       Full CD-ROM and Report On-Line                       Compiled Software On-Line

See the SELDM project web page here


The Stochastic Empirical Loading and Dilution Model (SELDM) is designed to transform complex scientific data into meaningful information about the risk of adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. The U.S. Geological Survey developed SELDM in cooperation with the Federal Highway Administration to help develop planning-level estimates of event mean concentrations, flows, and loads in stormwater from a site of interest and from an upstream basin. Planning-level estimates are defined as the results of analyses used to evaluate alternative management measures; planning-level estimates are recognized to include substantial uncertainties (commonly orders of magnitude). SELDM uses information about a highway site, the associated receiving-water basin, precipitation events, stormflow, water quality, and the performance of mitigation measures to produce a stochastic population of runoff-quality variables. SELDM provides input statistics for precipitation, prestorm flow, runoff coefficients, and concentrations of selected water-quality constituents from National datasets. Input statistics may be selected on the basis of the latitude, longitude, and physical characteristics of the site of interest and the upstream basin. The user also may derive and input statistics for each variable that are specific to a given site of interest or a given area.

SELDM is a stochastic model because it uses Monte Carlo methods to produce the random combinations of input variable values needed to generate the stochastic population of values for each component variable. SELDM calculates the dilution of runoff in the receiving waters and the resulting downstream event mean concentrations and annual average lake concentrations. Results are ranked, and plotting positions are calculated, to indicate the level of risk of adverse effects caused by runoff concentrations, flows, and loads on receiving waters by storm and by year. Unlike deterministic hydrologic models, SELDM is not calibrated by changing values of input variables to match a historical record of values. Instead, input values for SELDM are based on site characteristics and representative statistics for each hydrologic variable. Thus, SELDM is an empirical model based on data and statistics rather than theoretical physiochemical equations.

SELDM is a lumped parameter model because the highway site, the upstream basin, and the lake basin each are represented as a single homogeneous unit. Each of these source areas is represented by average basin properties, and results from SELDM are calculated as point estimates for the site of interest. Use of the lumped parameter approach facilitates rapid specification of model parameters to develop planning-level estimates with available data. The approach allows for parsimony in the required inputs to and outputs from the model and flexibility in the use of the model. For example, SELDM can be used to model runoff from various land covers or land uses by using the highway-site definition as long as representative water quality and impervious-fraction data are available.


SELDM version - Update to change the database and code to modify a few items: (1.) Precipitation stations with latitudes on gridlines were not showing up in ecoregion statistics because of query. Tested ecoregions indicate that averages differ by less than 1% and medians differ by about 2.7% on average, but results are not significantly different at the 95% confidence interval. (2.) Ecoregion 13 and 80 both Northern Basin & Range. #13 should be Central Basin and Range #14 Should be Mojave/Southern Basin & Range. (3.) In Out.txt file, BMP output, change Irreducible Minimum Concentration to Minimum Irreducible Concentration. (4.) Added command DoEvents to run routine to reduce or eliminate "Not responding" messages while the model is running. (5.) Added full SELDM filename & Path to the out.txt file. (6.) Corrected problem in which copied analyses were created in default project directory. (7.) Fixed problems in load calculations for ng/L, pg/L, fg/L and other units. (8.) Added CalTrans TMDL constituents. July 24, 2018

SELDM version - Update to change the code so that copies of an analysis would use the Cunnane plotting position formula instead of the Blom plotting position formula. Each original analysis would use the Cunnane formula. Both plotting position formulas are correct, so analyses done with version 1.0.1 are not incorrect because of this difference. However, the two formulas produce slightly different exceedance percentiles and the manual provides information and equations for using the Cunnane plotting position formula. The change is in the Analysis form copy command code. June 1, 2016

SELDM version - Update to correct calculation of upstream and lake-basin transport curves. July 16, 2013

SELDM version - Initial release. March 27, 2013

System Requirements

SELDM is written in Visual Basic for Applications and therefore use is limited to Microsoft Windows operating systems. The graphical display forms require a screen resolution exceeding 1024 x 768 pixels.

Data Requirements

SELDM requires the latitude and longitude of the study site, the area, the imperviousness, the main channel length, main channel slope, and basin development factor for the highway site and the site of interest. SELDM also requires representative water-quality statistics for the site of interest and the upstream basin. Selected constituents have been pre-entered.

Output: Example Output Files

The example output text files are provided for inspection without installing or running the model. Input values used in the example are for demonstration only and should not be considered as recommended input values. The file ExampleAnalysisI81Out.txt includes an explanation for each output file type.
  ExampleAnalysisI81Out.txt -- Output Documentation File
  ExampleAnalysisI81-PS.txt -- Prestorm Streamflow
  ExampleAnalysisI81-PE.txt -- Precipitation Events
  ExampleAnalysisI81-SF.txt -- Stormflows
  ExampleAnalysisI81-DF.txt -- Dilution Factors
  ExampleAnalysisI81-HQ.txt -- Highway Runoff Quality
  ExampleAnalysisI81-Annual.txt -- Annual Highway Runoff Loads
  ExampleAnalysisI81-UQ.txt -- Upstream Water Quality
  ExampleAnalysisI81-DQ.txt -- Downstream Water Quality
  ExampleAnalysisI81-Lake.txt -- Lake Analysis

Installation package

For best results use the model installation file, it ensures that you have the proper drivers and settings. If you do not own a copy of Access the installation file will provide a runtime version for use with SELDM. The compiled version is available for advances Access users. The uncompiled Microsoft Access files listed under source code are provided for future use by model developers.
  SELDMv0103.exe -- Model installation file
  install.html -- SELDM installation instructions

Source Code (Version

SELDM is a Microsoft Access database application, but the model code can be incorporated into stand-alone software.
  Access 2000 format -- Uncompiled version (forward compatible)
  Access 2003 format -- Uncompiled version (forward compatible)
  Access 2010 format -- Uncompiled version (forward compatible)
  Access 2010 format -- Compiled (.accde) version (forward compatible)
  modMainSELDM.bas -- The main model code
  modPublicInterface.bas -- Subroutines are used throughout the application to standardize actions
  modPublicVariables.bas -- Public variables used in different forms and modules
  modStatistics.bas -- Code for statistical functions


Support for this software will include upcoming on-line training sessions and classroom training at selected locations, limited software support, and compilation of suggested improvements. Only limited assistance can be provided for applying SELDM to specific problems, but the forthcoming training modules should be sufficient for most users.


Limited support is provided for correcting bugs and clarification of how the code is intended to work. For a current list of known bugs and suggestions for improvement click here. For support or to provide feedback or suggestions for improvement, contact Greg Granato.


User Rights

This software and related material (data and documentation) are made available by the USGS to be used in the public interest and the advancement of science. You may, without any fee or cost, use, copy, modify, or distribute this software, and any derivative works thereof, and its supporting documentation, subject to the USGS Software User Rights Notice

Product Disclaimer

Any use of trade, product, or firm names is for decriptive purposes only and does not imply endorsement by the U.S. Government