8.0  Model Description    8.3.1  Tacoma Supply System    8.3.2  Reservoir Operations    8.3.3  Groundwater Sources    

Demands used in the Tacoma model were stipulated in Tacoma's most recent water supply plan (1998) and are based on Puget Sound Regional Council estimates. Historical demands through 1998 and projected demands are shown in Figure 8.25. Projected water demands are estimated through the year 2040.

Demands are not disaggregated between residential, commercial, or industrial demands. The model can be run using the low demand forecast (which includes Tacoma Water and City of Tacoma's Urban Growth Area) or the high forecast (which incorporates the same service areas with a higher projected demand). In CRYSTAL, Tacoma's base demand projections do not include demands associated with the South King County Regional Water Association (SKCRWA), which have been previously estimated at 15 mgd per year through 2050. These demands are incorporated as part of the Second Supply Project. If this project is activated, then SKCRWA demands are incorporated into CRYSTAL independently from Tacoma's demands.

Demand is calculated in CRYSTAL by multiplying an annual average base demand by seasonal scaling factors (Figure 8.26), which are based on supply data provided by Tacoma for period 1985-1998.