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DMSTA simulations of typical CERP reservoir designs are demonstrated below. The hydrologic time series are simulations from the South Florida Water Management Model (SFWMM) or other reservoir water-balance models generating a daily water budget for a given inflow series and a fixed set of operating rules. They are presented here for demonstration purposes and do not represent current designs. A constant inflow concentration typical of regional runoff is assumed for each reservoir. Actual designs would utilize time-varying inflow concentrations reflecting contributions from individual basins and Lake Okeechobee releases, as well as seasonal and flow-related variations. The attached figures compare depth, hydraulic load, and concentration regimes of these design cases with the calibration datasets. The time series plots show "observed" vs. predicted depths and outflow volumes. The "observed" values are from SFWMM simulations. DMSTA constrains daily water depths to equal SFWMM results and predicts outflows from the water budget. Observed vs. predicted outflow volume series thus compare the water budgets developed by the two models. Differences may be partially attributed to seepage, which is ignored in these DMSTA demonstrations. The design version of DMSTA allows consideration of seepage. Reservoirs are simulated with using the biomachine calibration. Sensitivities to other models and K values are demonstrated. As expected, reservoirs with lower hydraulic loading rates tend to have higher P removals. While the calibrated K values for reservoirs are substantially lower than those for STA's, significant phosphorus removals are predicted because the reservoir hydraulic loading rates are also relatively low and performance is driven primarily by the ratio of K to hydraulic load (inflow rate / surface area). Predicted ranges of P removal for a 2-fold variation in K are on the the order of ~15% . This may over-estimate uncertainty associated with model predictions for datasets in the design HLR range, estimated at 9% for the biomachine model The uncertainty band may also be influenced by that fact that the reservoirs in general have greater variations in depth, as compared with the calibration datasets. With the exception of Compartment C, hydraulic loads and concentrations are within the ranges of the calibration datasets. The Compartment C hydraulic load (1.2 m/yr) is slightly below the lower bound of the dataset (1.3 m/yr), but the difference is not significant. Calibration results indicate that it is difficult to distinguish between the performance of the biomachine and first-order models, since they have similar standard errors when applied to datasets in the reservoir design range (9% and 11%, respectively). The 'Sensitivity to Model' column shows predicted P reductions using each model. The prediction range varies from 0 to 8%. The range is zero for the deep reservoir simulation ("AA"), which is closest to the current design concept for the EAA storage reservoir. Greater ranges in the other designs reflect greater variance in depth and concentration, Therefore, uncertainty regarding the choice of model formulation apparently has little impact on design simulations. Predicted outflow concentrations vary from 38 to 171 ppb for inflow concentration ranging from 100 to 200 ppb. This is within the 40-1000 ppb range of the model calibration datasets. Application of the model to reservoirs in urban basins will require extrapolation into lower concentrations ranges. For example, inflow P concentrations to the C11-West Impoundment have been estimated at ~25 ppb (Mactec, 2004). A conservative value for K should be used in those basins until the model is calibrated and tested in lower concentration ranges. While the project workplan called for demonstration in the Taylor Creek / Nubbin Slough basin, SFWMM reservoir simulations were not available for that basin. The updated design model (DMSTA2) will be distributed with input datasets that illustrate simulations of reservoirs and reservoir/STA combinations.
DMSTA Reservoirs Home DMSTA Home http://www.wwwalker.net/dmsta/reservoirs/simulations.htm 05/31/2005
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