Featured Projects — Modeling Ecosystem and Temperature Modeling in the Russian River Watershed with HEC-ResSim Water Quality
The Sonoma County Water Agency (SCWA) provides all water supply and treatment to agricultural, industrial, and residential users in Sonoma County, in partnership with federal agencies. Through management that includes the major reservoirs of Lake Mendocino and Lake Sonoma, SCWA must balance the water needs of customers as well as flood control, recreational uses, and habitat requirements for threatened species including salmon.
A map view of the ResSim watershed components, including observed data stations (blue diamonds) and meteorological data stations (purple diamonds).
RMA Inc. partnered with SCWA to develop and calibrate a full ecosystem model using the U.S. Army Corp of Engineers Hydrological Engineering Center (USACE HEC) modeling platform HEC-ResSim, which was already employed by SCWA for performing reservoir analysis and forecasting. RMA constructed a new water quality watershed, including geometries, calibrated parameters for reservoirs and different river reaches, boundary conditions and dispersion characteristics. The project also included working closely with SCWA to collect and evaluate hundreds of different sources for flow data, atmospheric and meteorological data, and in-situ temperature, oxygen, nutrient, and other ecosystem data to use for as boundary conditions and calibration /validation.
Through the calibration process RMA researchers discovered that in summer, the low-flow Russian River acted more like a small, and often riparian-shaded, stream with very different heat transfer characteristics than a large bodies of water that ResSim was suited to simulating. RMA worked with the USACE HEC to develop and add published heat transfer parameterizations to ResSim for short and longwave radiation that allow for calibration of low-flow, riparian-shaded tributaries. These updates allowed RMA to calibrate temperature of the system to ~ ± 1C, including diurnal temperature variability and reservoir thermal profiles, using > 10 years of historical flow and temperature records (e.g. Figure 2).
Example ResSim reservoir water quality plot of temperature, showing vertical profiles (and comparison to observed data; lower left), time series at a particular selected depth (upper right), and a color contour across depth and time (lower right).
Also critical for aquatic habitat management is consideration of dissolved oxygen levels and mitigation of hypoxia. The ecosystem model in ResSim, based on NSM, was tuned using nutrient measurements, and phytoplankton and benthic algal parameterizations to simulate seasonal and diurnal dissolved oxygen variability in both the Russian River and Lakes Mendocino and Sonoma.
The public calibration report can he downloaded here.
Results and Benefits
The fully coupled ResSim hydrodynamic and ecosystem model will be used by SWCA for simulations that include both climate and operation forecasting of water resources, and simulations under Forecast Informed Reservoir Operations (FIRO) guidelines. Simulations of the Russian River watershed using ResSim Water Quality can now be evaluated for both hydrological variability and reservoir operations, and thermal and ecosystem management considerations.