Lower Mississippi River Forecast Center – Upper Tennessee River Basin Calibration

The National Weather Service (NWS) Lower Mississippi River Forecast Center (LMRFC), located in Slidell, Louisiana, required calibrations performed for 20 headwater (HW) basins, ten local areas, and five reservoirs for incorporation into the forecast system for the LMRFC area. Riverside Technology, inc. (RTi) performed calibration of the Sacramento Soil Moisture Accounting (SAC-SMA) model for eight HW basins and LAG/K routing model calibration for one river reach in the Upper Tennessee River Basin. RTi performed SAC-SMA calibrations for 11 HW basins and ten local areas, Joint Reservoir Regulation Operation (RES-J) modeling for four reservoirs, and LAG/K calibration for 16 reaches in the Yazoo River Basin in Mississippi. Additionally, RTi performed SAC-SMA calibration and RES-J modeling for the Elk River Basin in southern

Upper Tennessee River Basin Mean Areal Precipitation

Tennessee.

RTi reviewed the historical instantaneous and mean daily streamflow data provided by the LMRFC. These data were used to estimate average annual basin runoff for each sub-basin in the calibration period. Annual average estimates of Mean Areal Precipitation (MAP) were computed for each sub-basin from the MAP time-series, and average annual estimates of Potential Evapotranspiration (PET) were computed for each sub-basin from the Mean Areal Potential Evapotranspiration (MAPE) time-series. In order to validate the areal precipitation, PET, and discharge estimates, RTi conducted a water balance analysis. The water balance components were analyzed for consistency from sub-basin to sub-basin, and any anomalies observed were investigated and resolved. The water balance analysis was also used to provide insight into which sub-basins were thought to be hydrologically similar and how parameters varied among the sub-basins.

The Oconaluftee River in the Great Smoky Mountains

The SAC-SMA model was calibrated as the rainfall-runoff model for each sub-basin. Initial parameter estimates were derived from a combination of hydrograph analysis as well as an assessment of parameters from similar basins, topography, soils, land use, and other available geographic data. In addition, RTi provided calibrated variable LAG/K model parameters for several reaches. Parameters were estimated by trial and error routing of upstream-observed instantaneous discharge and comparing results to the instantaneous discharge at the downstream (receiving) basin site. RES-J models were derived from data provided in reservoir operations manuals and from time series data of reservoir releases and pool elevation.

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