THE WATER, ENERGY, AND BIOGEOCHEMICAL MODEL (WEBMOD): SEMI-DISTRIBUTED HYDROLOGY AND WATER QUALITY DEVELOPED IN THE MODULAR MODELING SYSTEM

WEBMOD simulates hydrologic fluxes and solute concentrations using process modules coupled within the United States Geological Survey (USGS) Modular Modeling System (MMS). Hydrologic fluxes are simulated using routines developed for the USGS Precipitation Runoff Modeling System, the National Weather Service Hydro-17 snow model, and TOPMODEL, a topography-based hydrological model. PHREEQC, a low-temperature aqueous geochemical model, was tightly coupled to the hydrologic model to simulate reactions and isotopic fractionation as waters evaporate, mix, and react with the soils. Mass balance of water and solutes are tracked from the time that precipitation or irrigation reaches the surface to the time that the water leaves the watershed through evapotranspiration, river discharge, or regional groundwater flow.