Salinas Valley Watershed Model: Application of Hydrologic Simulation Program-FORTRAN (HSPF)

This model archive contains the datasets, procedures, and necessary program code used to describe the Salinas Valley Watershed Model (SVWM). The SVWM simulates the daily historical water balance and hydrologic conditions for the Salinas Valley study area including the many un-gaged tributary subdrainages in the rugged and mountainous upland areas surrounding flat-lying valley lowlands coinciding with developed areas including croplands irrigated with groundwater. The SVWM simulates the natural hydrologic system for the entire Salinas Valley watershed and adjacent coastal basins, excluding anthropogenic components such as pumping, diversions, irrigation, and reservoir operations, for the 70 years beginning October 1, 1948, and ending September 30, 2022. The SVWM uses two modeling applications; the Hydrologic Simulation Program – Fortran (HSPF, version 12.4; EPA, 2000) to simulate the natural hydrologic system (Bicknell and others., 2005) and the Basin Characterization Model (BCM; Flint and others, 2021) to develop spatially distributed, historical climate inputs for HSPF. The HSPF application simulates the daily surface water and shallow subsurface water storage and flow processes, including interception storage and evaporation on vegetation, surface retention storage and evaporation, pervious land soil water storage and evapotranspiration, runoff from impervious and pervious land areas, streamflow, recharge from pervious land areas, and recharge from streamflow seepage. Climate inputs developed using the BCM are daily precipitation, daily maximum and minimum air temperature, and daily potential evapotranspiration (PET) (Hevesi and others, 2022). SVWM parameters were estimated using geospatial data and then adjusted by trial-and-error fitting of simulated daily streamflow to long-term records of observed streamflow at 29 USGS stream gages (USGS, 2016) and to estimated daily surface water inflows to Nacimiento and San Antonio Reservoirs (Henson and others, 2022a). The trial-and-error calibration provided a good match between simulated and observed daily, monthly, mean-monthly, and annual streamflow. The simulated output components from the SVWM include evapotranspiration, land area runoff (overland flow, interflow, baseflow), recharge, and groundwater recharge for the 690 HRUs, as well as streamflow and stream seepage losses for the 690 stream reaches connecting the HRUs.