Training: Flow Calibration Tutorial Introduction
This document is a hypertext/graphical tutorial on how to calibrate the NPSM/HSPF watershed model. From a user-selected BASINS data set, the tutorial starts by providing tips on watershed delineation, initializing the Nonpoint Source Model (NPSM), and determining appropriate initial settings and values for all interface inputs. The user is then guided in performing an initial model run, obtaining daily flow gage data, and postprocessor tips for comparing the output against observed data. The user is given some tips to help identify other potential big-picture issues in relation to how the model represents the watershed.
After providing a number of helpful tips regarding editing input parameters in the Data Editor, the tutorial lists 22 possible modeled/observed data discrepancies or calibration scenarios. For each of the 22 possible scenarios, the tutorial provides instructions on how to modify the relevant parameters in order to correct that discrepancy. Linked graphics include an overview of where each parameter influences storages and fluxes in the hydrologic cycle, as well as a single figure for each parameter demonstrating hydrograph sensitivity to that parameter. Each parameter is also hyperlinked to the location in BASINS Technical Note 6: Estimating Hydrology and Hydraulic Parameters for HSPF (EPA 2000) (PDF) (34 pp, 199K, About PDF) containing the parameter's definition, units, and recommended estimation method. BASINS Technical Note 6 also includes internal links between parameter summaries and a table that provides typical and possible minimum/maximum ranges for each parameter.
The calibration scenarios in this tutorial are derived directly from the HSPF Expert System for Calibration (HSPEXP) Users Manual (Lumb, et al., 1994) Appendix A which lists all the algorithms used in the program. While this guide assists in the calibration of HSPF based on visual comparisons of modeled and observed hydrographs, HSPEXP instead uses statistical comparisons. HSPEXP automatically generates statistical comparisons of model output against monitoring data, evaluating both specific storms as well as the overall model simulation. HSPEXP then instructs the user with canned advice based on a comparison of the statistical results against the algorithms upon which this tutorial is based. BASINS Technical Note 5 discusses using HSPEXP in conjunction with BASINS/NPSM (EPA 1999a) (PDF) (15 pp, 35K, About PDF). This tutorial complements the HSPF Expert System by providing the NPSM/HSPF user with graphics to better understand the impact of individual parameter changes on the model hydrograph, as well as by re-writing the HSPEXP User Manual Appendix A, and by providing additional setup and calibration guidance to users of the BASINS NPSM.