Agenda - Council - 07/28/2015 - Laserfiche WebLink

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1.Conceptual framework uncertainty 2. Model parameter uncertainty 3.Calibration uncertainty 4. Predictive uncertainty Metro Model 3 predicts future aquifer conditions under a projected range of water demand. Because it is a steady-state model, it does not represent water levels for a specific day and time. Instead, it is intended to illustrate where aquifer water levels will come to equilibrium under a given water budget (recharge, pumping, baseflow). In other words, it illustrates where things will ultimately end up. This ability to compare regional groundwater impacts under different demand and source assumptions is what Metro Model 3 was designed, conceptualized, and calibrated for. It is used as a planning tool to inform regional planning, support this Master Water Supply Plan, and assess potential impacts associated with changes in regional pumping and/or land use change. The single biggest contributor to predictive uncertainty is uncertainty in future water demand. There is some uncertainty about how many people will live in the metro, where they will live, how much water they will use, or if sources of water will remain the same. This is where input from city administrators and engineers is critical; no one knows the city and its water supply better than the city or utility staff. Therefore, Metropolitan Council has worked closely with city staff to learn more about population, population served, per capita water use, water sources, and well locations. Appendix 2 describes the method used to evaluate future water demand. The process included an exploration of predictive uncertainty resulting from the variability of the historical data the projection was based on and the use of different projection methods. Based on this work, water demand projections are represented as a range of future conditions. The Metropolitan Council recognizes the error in the model compared to the real world. This error can be minimized when comparing model output to model output. Drawdown shows you the change between two conditions, the starting and ending place doesn't matter as much as the difference between the two conditions. Even with model error, the model is a valuable tool for informing water supply planning in the region. Table 2 - Uses for "out of the box" Metro Model 3 Acceptable Marginally Acceptable* Not Acceptable Compare regional scenarios General well field placement Localized well field optimization Compare sub -regional scenarios Estimate groundwater/ surface water connections Site specific evaluations Identify areas where more information is needed Wellhead protection plans Predicting time dependant water table elevations Identify possible problem areas *The model can be used as a "back of the envelop calculation" giving the user an idea of a starting place for further analysis. Metro Model 3 supports a flexible process for water suppliers and planners to explore a wide variety of different water supply approaches under a range of potential future conditions. This type of WATER SUPPLY MASTER PLAN- Draft June 2015 57