WWHM4

WWHM4 Overview

WWHM4 is a comprehensive continuous simulation hydrology and hydraulics modeling software package for use anywhere in the contiguous United States.

The purpose of WWHM is to provide a visually-oriented interactive tool that easily and accurately models the hydrology and hydraulics of both urban and rural drainages of all sizes. WWHM4 includes specialized tools to quantify stormwater and water quality impacts of land use changes on local streams and rivers to meet NPDES MS4 hydromodification requirements. It can also be used to review of development plans for compliance with local stormwater regulations, promote sustainable development practices, and educate the engineering community and public on the impacts of land use changes.

WWHM4 uses HSPF (Hydrological Simulation Program Fortran) as its computational engine. HSPF is the U.S. Geological Survey and U.S. Environmental Protection Agency continuous simulation hydrology software package. HSPF, since its introduction in 1980, has become the industry standard for hydrologic modeling.

The HSPF continuous simulation model is preferred over single-event hydrology models because of its ability to compute and keep track of all of the individual components of the hydrologic cycle including surface runoff, interflow, groundwater, soil moisture, and evapotranspiration. Surface runoff (also known as overland flow) is the first runoff component to reach the stream and is usually the major source of urban flood, as it is generated primarily by impervious surfaces. Interflow travels laterally through the upper soil layers until it reaches a conveyance system. Interflow moves more slowly than surface runoff, but can still cause flooding problems. Stormwater is the sum of surface runoff and interflow. Groundwater replenishes the aquifer and/or provides base flow to the stream. Evapotranspiration is the sum of evaporation from land surfaces and transpiration from plants. Urbanization decreases groundwater and evapotranspiration and increases stormwater runoff.

WWHM4 gives the user the option of using SWMM (Storm Water Management Model) to more accurately model complex hydraulic conditions that are not included in HSPF. SWMM is the U.S. Environmental Protection Agency hydraulic software package. WWHM4 integrates both HSPF and SWMM into a single package with automatic file conversion and data transfer between HSPF and SWMM computational engines