OCR Text |
Show balance through time ( i. e. mass - not concentration ~ of salt in the various lake bodies vs. time) to support this claim. This information is available from the modeling work currently being conducted by DNR- USGS and should be included. c.) The hysteretic behavior of salt mass - lake volume changes has not been adequately discussed and evaluated with respect to salt balance implications of GSL. d.) Published literature reports a possibly significant difference in the chemistries of pre- 1991 deep brine layer in Gilbert Bay and Gunnison Bay brines. This should be examined so that questions of the source of the brine layer in Gilbert Bay and its disappearance can be addressed. e.) Insufficient effort has been invested in analyzing and documenting what can be learned about lake salinity from the available data on individual ions, especially K or Mg. 3. The causeway a.) The causeway created two water bodies where there was one. The causeway has resulted in an increase in salinity in Gunnison Bay with respect to Gilbert Bay. b.) The assumption that the permeability of the older causeway fill materials has dramatically decreased has not been verified. 4. The USGS model a.) The model calibration work currently underway has basically used only one parameter ~ causeway permeability ~ to calibrate the model. Is it possible that other potential calibration variables ( such as assumed causeway flows, evaporation rates and/ or estimates of net lake inflows, etc.) could produce as good or better calibration results? b.) Good modeling procedures include sensitivity analyses on all variables in which there is substantial uncertainty. Current plans for model sensitivity analyses do not include an examination of the sensitivity of model behavior due to uncertainty in input variable values and boundary conditions. Such analyses could shed further light on the quality of the calibration process and provide insight to critical system components. c.) Available publications show that previous calibrations of the USGS model consistently under- predict the elevation differential between Gunnison and Gilbert Bays prior to the causeway breach, and generally over- predict the elevation differential after the breach. This is perhaps a symptom of a systematic problem with the calibration, and if so might reflect directly on the principal calibration parameter considered, mean causeway permeability. d.) The USGS modeling effort used all available total salt and hydrologic data for the calibration, leaving no data for model validation. Had some data been reserved against 226 |