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HYDROLOGICAL SIMULATION PROGRAM - FORTRAN (HSPF) |
INTRODUCTION
The Hydrological Simulation Program-FORTRAN, known as HSPF, is a mathematical model developed under EPA sponsorship for use on digital computers to simulate hydrologic and water quality processes in natural and man-made water systems. It is an analytical tool which has application in the planning, design, and operation of water resources systems. The model enables the use of probabilistic analysis in the fields of hydrology and water quality management. HSPF uses such information as the time history of rainfall, temperature, evaporation, and parameters related to land use patterns, soil characteristics, and agricultural practices to simulate the processes that occur in a watershed. The initial result of an HSPF simulation is a time history of the quantity and quality of water transported over the land surface and through various soil zones down to the groundwater aquifers. Runoff flow rate, sediment loads, nutrients, pesticides, toxic chemicals, and other quality constituent concentrations can be predicted. The model uses these results and stream channel information to simulate instream processes. From this HSPF produces a time history of water quantity and quality at any point in the watershed.
BACKGROUND
HSPF is an extension and improvement of three previously developed models: 1) The EPA Agricultural Runoff Management Model (ARM), 2) The EPA Nonpoint Source Runoff Model (NPS), and 3) The Hydrologic Simulation Program (HSP, including HSP Quality), a privately-developed proprietary program. EPA recognized that the continuous simulation approach contained in these models would be valuable in solving many complex water resource problems. Thus, a fairly large investment was devoted to developing a highly flexible non-proprietary FORTRAN program which contains the capabilities of these three models, plus many extensions.
BENEFITS
HSPF is a valuable tool to water resource planners. Because it is more comprehensive than most systems, it permits effective planning. Benefits to the user include:
Flexibility in solving a wide range of water quantity and quality problems using a single model
APPLICATION AND USE
HSPF is currently the most comprehensive and flexible model of watershed hydrology and water quality available. It is the only available model that can simulate the continuous, dynamic event, or steady-state behavior of both hydrologic/hydraulic and water quality processes in a watershed. The model is also unusual in its ability to represent the hydrologic regimes of a wide variety of streams and rivers with reasonable accuracy. Thus, the potential applications and uses of the model are comparatively large including:
HSPF is designed so that it can be applied to most watersheds using existing meteorologic and hydrologic data; soils and topographic information; and land use, drainage, and system (physical and man-made) characteristics. The inputs required by HSPF are not different than those needed by most other simpler models. The primary difference in data needs is that long, rather than short time-series records are preferred. Typical long time-series records include precipitation, waste discharges, and calibration data such as streamflow and constituent concentrations.
MODEL CAPABILITIES
HSPF contains three application modules and five utility modules. The three application modules simulate the hydrologic/hydraulic and water quality components of the watershed. The utility modules are used to manipulate and analyze time-series data. A brief description of each of the modules follows.
Application Modules
The three application modules are:
As PERLND simulates the water quality and quantity processes that occur on pervious land areas, it is the most frequently used part of HSPF. To simulate these processes, PERLND models the movement of water along three paths: overland flow, interflow, and groundwater flow. Each of these three paths experiences differences in time delay and differences in interactions between water and its various dissolved constituents. A variety of storage zones are used to represent the processes that occur on the land surface and in the soil horizons. Snow accumulation and melt are also included in the PERLND module so that the complete range of physical processes affecting the generation of water and associated water quality constituents can be represented. Some of the many capabilities available in the PERLND module include the simulation of:
IMPLND is used in urban areas where little or no infiltration occurs. However, some land processes do occur, and water, solids, and various pollutants are removed from the land surface by moving laterally downslope to a pervious area, stream channel, or reservoir. IMPLND includes all of the pollutant washoff capabilities of the commonly used urban runoff models, such as the STORM, SWMM, and NPS models.
RCHRES is used to route runoff and water quality constituents simulated by PERLND and IMPLND through stream channel networks and reservoirs. A number of processes can be modeled, including:
Utility Modules
The five utility modules are used to access, manipulate, and analyze time series information stored by the user in HSPF's TSS (Time Series Store) and WDM (Watershed Data Management) files. These time series, such as hourly precipitation, daily evaporation, daily streamflow, are used by the application modules and are often a valuable resource in the analysis of a watershed's characteristics. The five utility modules are:
PROGRAM STRUCTURE AND DESIGN
HSPF consists of a set of modules arranged in an organized structure, which permit the continuous simulation of a comprehensive range of hydrologic and water quality processes. Experience with sophisticated models indicates that much of the human effort in model application is associated with data management. This fact, often overlooked by model builders, means that a successful comprehensive model must include a sound data management system. Otherwise, the user may spend so much time on data manipulation that actual progress on the simulation work itself is drastically retarded. For this reason, the HSPF program is planned around a time-series management system operating on direct access principles. The simulation modules read input data from the TSS and WDM files, and are capable of writing output to them. Because these transfers require very few instructions from the user, problems with data handling are minimized.
HSPF's design incorporates a hierarchy of program subroutines, each of which performs a major task during the program's execution. The subroutines are grouped into different levels of operations in a hierarchical structure.
Typical of these levels of operations is the Run Interpreter, which is a group of subprograms that reads and interprets the User Control Input. It provides instructions to HSPF's modules specifying the sequence of operations to be performed. It stores the initial conditions and the parameters for each operation in the appropriate file on disk, and creates an instruction file that will ensure that time-series data are correctly passed between operations, where necessary.
Other operations include TSS management modules used to create, modify, or remove data sets from the Time Series Store; operations supervision modules which use information supplied by the Run Interpreter and turn on appropriate application and/or utility modules as needed; and the actual application and utility modules which perform the hydrologic and water quality related simulation calculations.
The importance of this program structure lies in its modular design. This allows for the addition and/or replacement of individual modules and allows HSPF to be easily adapted for special applications designed by the user.
Obtain a copy of HSPF from the
Water Resources Division of the
