HSPEXP: E-xpert System for Calibration of the Hydrological Simulation Program Fortran
VERSION/DATE: Ver. 2.4 06/26/06
OPERATING SYSTEM: DOS
DOCUMENTATION (117 Pages):
Users Manual for an E-xpert System (HSPEXP) for Calibration of the Hydrological Simulation Program Fortran By Alan M. Lumbl, Richard B. McCammon and John L. Kiftle, Jr.
Also see HSPF
DOS-based computers having a math coprocessor and 4 mb of memory (supported: IBM-compatible computers with a 386 or greater processor).
Expert system software was developed to assist less experienced modelers with calibration of a watershed model and to facilitate the interaction between the modeler and the modeling process not provided by mathematical optimization. A prototype was developed with artificial intelligence software tools, a knowledge engineer, and two domain experts. The manual procedures used by the domain experts were identified and the prototype was then coded by the knowledge engineer. The expert system consists of a set of hierarchical rules designed to guide the calibration of the model through a systematic evaluation of model parameters.
When the prototype was completed and tested, it was rewritten for portability and operational use and was named HSPEXP. The watershed model Hydrological Simulation Program-Fortran (HSPF) is used in the expert system. This report is the users manual for HSPEXP and contains a discussion of the concepts and detailed steps and examples for using the software. The system has been tested on watersheds in the States of Washington and Maryland, and the system correctly identified the model parameters to be adjusted and the adjustments led to improved calibration.
OVERVIEW AND CONCEPTS
Watershed models have been used for more than two decades for the continuous simulation of river basin response to meteorologic variables of precipitation and potential evapotranspiration for flood forecasting, stormwater management, environmental impact assessments, and the design and operation of water-control facilities. Various parameters in the watershed models are modified to adapt the models to specific river basins. Some of the parameters can be estimated from measured properties of the river basins but others must be estimated by mathematical optimization or manual calibration. Optimization techniques used over the past two decades have not been totally satisfactory. Such techniques reduce the interaction between the model user and the modeling process and thus do not improve user understanding of the processes as simulated by the model and the actual processes in the watershed. Even though objective functions can be minimized by optimization, the physical meaning of such optimized model parameters is left, for the most part, unexplained. Manual calibration also has not been totally satisfactory because it requires experienced watershed modelers and there are more potential users of watershed models than there are experienced modelers. With that in mind, the expertise of the experienced watershed modeler was placed within the context of an expert system so that the less-experienced modelers can "manually" calibrate the model and improve their understanding of the link between the simulated processes and the actual processes. Ms report describes the expert system.
The watershed model Hydrological Simulation Program-Fortran (HSPF) (Bicknell and others, 1993) was selected as the basis for testing the feasibility of developing an expert system for parameter calibration. In earlier attempts, an expert system was developed to estimate initial parameters for HSPF (Gaschnig and others, 1981). That system weighted measured data on watershed characteristics with judgments on the importance of the characteristic in demng the value of the parameter. Unfortunately, the software for that system is not available.
PROCEDURES FOR MANUAL CALIBRATION OF HSPF
In the present effort, two experienced watershed modelers, Alan M. Lumb and Norman H. Crawford (Hydrocomp, Inc.), documented procedures used to manually calibrate the rainfall-runoff module of HSPF. Richard B. McCammon was the knowledge engineer on the project. These calibration procedures are divided into four major phases: (1) water balance, (2) low flow, (3) stormflow, and (4) seasonal adjustments. A fifth phase, to identify any bias within the model, was also documented. During each of the four major phases, a different set of calibration parameters was evaluated by comparing simulated streamflow with observed streamflow. In more than two decades of experience with HSPF and similar models over a wide range of climates and topographies, experienced modelers have learned which parameters can be meaningfully adjusted to reduce the error of estimation. Although the adjustments in parameter values during manual calibration produce an error of estimation not significantly different from mathematical optimization routines, the parameters developed from manual calibration can be more meaningful and useful for regional applications of the model to ungaged watersheds. Mathematical optimization tends to treat the model as a "black box" and usually considers minimization of only one criterion, which is typically the sum of the square of the difference between simulated and observed flows.
For the initial prototype of the expert system, a set of conditions was developed for each of the major calibration phases in which the user supplies or is prompted for the general observations of the differences between simulated and measured flows. For example, the user would be asked if simulated stormflows are too high in the summer, if total volumes of simulated flow are too low, and so forth. Given the user's responses, the initial prototype expert system identified the name of the parameter to be changed, direction of the change, and the reason for the change.