7.3.2 Tacoma Supply System

The scenario evaluation, with respect to Tacoma, has been separated into two sections, Tacoma M&I and Instream conditions.

Tacoma M&I

The following discussion describes the conditions of the Tacoma M&I supply with respect to reliability and a description of the shortfall events which occurred during the model runs.

Figures 7.12 and 7.13 portray the reliability of the Tacoma M&I water supply for the status quo and imminent supply scenarios. As expected, the reliability of Tacoma's supply system decreases as demands increase. Tacoma's annual reliability decreases dramatically in the year 2035, with the status quo scenario, while Tacoma's weekly reliability decreases to 92%. This indicates that many shortfalls occur during the simulation, some of which were relatively small in volume. The reliability provided by the imminent scenario stays above 98% both on an annual and weekly basis.

Figures 7.14 and 7.15 characterize the shortfall events which occurred during model simulations. As expected, the total shortfall for each year of investigation increases as demand increases.

Green River Instream Conditions

Figures 7.16 and 7.17 portray Green River instream conditions at both the Palmer and Auburn Gauges in both scenarios. The graphs illustrate instream flows including average flows at the gauges and the amount of water instream above minimum flow requirements. For both of the scenarios, the instream flows remains constant regardless of future demands upon the water system. This situation is due to Tacoma's increasing reliance upon groundwater as demands grow. As depicted, less water will actually be present instream after implementation of the Green River Habitat Conservation Plan.