SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Attachment A - 3- Comments 3- Comments on Evaluation of San Joaquin River Flows at Stockton April 2001 5. As mentioned in item 1, the Report uses Equation [1], above, to estimate the StocktonNemalis ratio during the winter months. The equation contains the constant, C, which was derived using data from 1996 through 2000, which were above average wet years. Slight changes in the constant create substantial changes in the estimated Stockton flow. The only information in the Report to support the estimation of C, is a statement on page 18, `The accuracy of the predicted Stockton flows using the value C = 0.05 is not known for certain. However, this scenario predicts Stockton flows that correspond with the historical fractions of RWCF effluent concentrations in the San Joaquin River during January 1988." One month of data was used to substantiate the coefficient. It is not clear how much receiving water data was available or where in the river the samples were taken. 6. As mentioned above, the Report uses receiving water ammonia concentrations to substantiate the selection of the constant, C. Based on the receiving water ammonia concentration, effluent flow, and effluent ammonia concentration, an expected monthly Stockton SJR flow is calculated. The Report discounts higher C values (lower Stockton SJR flows) because the values predict extended periods of zero flow. For some reason, the bottom limit of flow is set to zero (see figures 14, 15, 16, and 17). The Report does not consider the possibility of daily net flow reversals (negative flow),which may be caused by low SJR flow and high export pumping and which have been presumed to occur in other flow models. In addition, it is not clear where or how often the ammonia samples were collected. 7. In the estimates of 1991 and 1992 Stockton flow (page 27), the Report states there were a few instances where ammonia concentrations in the San Joaquin River reached 60%to 100% (meaning very little to no dilution). The Report discounts this by stating, "...these instances were rare." It is not clear when, where, or how often the samples were collected, or how often the high concentrations occurred. This time period is important, because critical flow was measured at Vernalis during this time. The Report suggests the possibility that there are periods of limited or no dilution every year. 8. The Report does not provide information that would change the Regional Board's estimation of critical flows for the RWCF discharge. The Report asks to make considerations for future flows by stating that new tidal gates will be installed for each of the four barrier locations as part of the South Delta Improvement Program. The Report claims the tidal gates will be operational within the next 7 years, but does not provide any information about the implementing agency or the funding source. The flows in the SJR will be continually changing; and some may or may not ever come about. Use of real flow data with conservative assumptions for critical receiving water conditions remains the most accurate and reasonable approach to evaluate dilution.