InterpretSELDM version 1.0 The Stochastic Empirical Loading and Dilution Model (SELDM) output interpreter

The InterpretSELDM program is a graphical post processor designed to facilitate analysis and presentation of stormwater modeling results from the Stochastic Empirical Loading and Dilution Model (SELDM), which is a stormwater model developed by the U.S. Geological Survey in cooperation with the Federal Highway Administration. SELDM simulates flows, concentrations, and loads in stormflows from upstream basins, the highway, best management practice outfalls, and in the receiving water downstream of a highway. SELDM is designed to transform complex scientific data into meaningful information about (1) the risk of adverse effects from stormwater runoff on receiving waters, (2) the potential need for mitigation measures, and (3) the potential effectiveness of management measures for reducing those risks. SELDM produces results in (relatively) easy-to-use tab delimited output files that are designed for use with spreadsheets and graphing packages. However, time is needed to learn, understand, and use the SELDM output formats. Also, the SELDM output requires post-processing to extract the specific information that commonly is of interest to the user (for example, the percentage of storms above a user-specified value). Because SELDM output files are comprehensive, the locations of specific output values may not be obvious to the novice user or the occasional model user who does not consult the detailed model documentation. The InterpretSELDM program was developed as a postprocessor to facilitate analysis and presentation of SELDM results. The program provides graphical results and tab-delimited text summaries from simulation results. InterpretSELDM provides data summaries in seconds. In comparison, manually extracting the same information from SELDM outputs could take minutes to hours. It has an easy-to-use graphical user interface designed to quickly extract dilution factors, constituent concentrations, annual loads, and annual yields from all analyses within a SELDM project. The program provides the methods necessary to create scatterplots and boxplots for the extracted results. Graphs are more effective than tabular data for evaluating and communicating risk-based information to technical and nontechnical audiences. Commonly used spreadsheets provide methods for generating graphs, but do not provide probability-plots or boxplots, which are useful for examining extreme stormflow, concentration, and load values. Probability plot axes are necessary for evaluating stormflow information because the extreme values commonly are the values of concern. Boxplots provide a simple visual summary of results that can be used to compare different simulation results. The graphs created by using the InterpretSELDM program can be copied and pasted into word processors, spreadsheets, drawing software, and other programs. The graphs also can be saved in commonly used image-file formats.