OBJETIVOS 23

1

Purpose

Utilize MOCASIM to perform water availability analysis and then quantify the potential benefits and impacts to the study partners and other water users in the Mokelumne basin resulting from proposed water supply projects identified in the MokeWISE Program.

2

Model Background

MOCASIM is a reservoir operations model designed to simulate water storage and diversion operations on the Mokelumne River. MOCASIM is capable of analyzing various operating strategies of Pardee and Camanche reservoirs on the Mokelumne River, assessing water

availability to serve EBMUD; Amador, Calaveras and San Joaquin counties; and then simulating newly proposed storage and diversion alternatives for beneficial use. MOCASIM also

incorporates imports from water supply developments in the American and Calaveras River Watersheds.

MOCASIM is a mass-balance simulation model. It uses either monthly or daily time-step (depending on the geographical area, as explained below) for the hydrologic period beginning in 1953 through 2010. Senior appropriations, fishery flows, and hydropower releases are based on historical and/or future levels of development in the basin, water rights and agreements, and reservoir operating rules.

The model was developed by AD Consultants in 2007 for the Mokelumne River Water and Power Authority (MRW&PA) and has been maintained and upgraded by AD Consultants ever since. The original version of the model concentrated on the Lower Mokelumne River system starting at the Mokelumne Hill gage upstream of Pardee Reservoir and culminating at the confluence with the Cosumnes River. The model was designed at the time to examine potential yield from the MORE Water Project, an off-stream storage reservoir that would capture non-appropriated high flows from the Mokelumne River and regulate this supply to an integrated system of conjunctive use projects to provide additional water supply and reliability for the region.

In 2012, MOCASIM was expanded to include representation of the Upper Mokelumne River Basin upstream of the Mokelumne Hill gage. The model was also enhanced to allow evaluating the water supply and hydroelectric benefits from future developments in the basin, including: Enlarged Lower Bear Reservoir, Raised Pardee Dam and MORE Water Project.

For the water supply benefits, the expanded MOCASIM could be used to evaluate the overall system non-appropriated water that could be managed in the additional storage created by the Enlarged Lower Bear Reservoir, Raised Pardee Dam and/or the off-stream storage reservoir at Duck Creek (MORE Water Project). These storage facilities could be operated in any sequence of development. Therefore, the expanded MOCASIM allows for the examination of the

October 2014 5

diverted at various points throughout the system for beneficial use, including groundwater recharge.

For the hydropower benefits, the expanded MOCASIM could be used to evaluate the additional generation of Project 137, resulting from the Enlarged Lower Bear Reservoirs, as well as the additional changes in generation from the Pardee and Camanche power plants.

Finally, MOCASIM is also equipped with the ability to assess the magnitude and duration of water availability for Groundwater Banking via existing or newly proposed diversion facilities in the system, by devising new agreements and water management policies amongst stakeholders.

3

Geographical Areas

MOCASIM in its present configuration encompasses two interrelated geographical areas: The Upper Mokelumne system and the Lower Mokelumne system. The model can simulate the operation of each geographical area independently or in sequence (from top to bottom).

The time-step for simulating the Upper Mokelumne is daily while the time-step for simulation the Lower Mokelumne is monthly. The primary reason is that the Upper Mokelumne is “peakier” hydrology wise, than the Lower Mokelumne. The combined reservoirs’ storage in the Lower Mokelumne is an order of magnitude greater than the Upper Mokelumne, thus providing higher degree of attenuation of flood events (which coincides with the actual practice of regulating flow below Camanche for safety and environmental considerations). Furthermore, most the water rights and agreements associated with existing water users on the Lower Mokelumne were defined on a monthly basis. Internally in the model, the difference in time-step resolution is handled by converting the daily outflow from the Upper Mokelumne to monthly inflow to the Lower Mokelumne. The transition point is the Mokelumne Hill gage at Hwy 49 Bridge gage (USGS #11319500), immediately upstream of Pardee Reservoir.

The following describe the characteristics and operating rules associated with each geographical area as simulated in MOCASIM.

3.1

Upper Mokelumne System

The flow regime in the Upper Mokelumne system is primarily dominated by the operation of PG&E Project 137 on the North Fork Mokelumne. Project 137 consists of two reservoirs: Salt Springs and Lower Bear reservoirs and five hydroelectric power plants: and Salt Springs #1 & #2, Tiger Creek, West Point and Electra powerhouses. PG&E operates these facilities with

consideration to power generation objectives, instream flow requirements mandated by the

Federal Energy Regulatory Commission, and in accordance with the Lodi Decreei_.

i

The Lodi Decree is a series of court decisions from the 1940’s and 50’s that mandate average monthly outflow from Salt Springs and Lower Bear reservoirs as function of reservoirs’ storage.

MOCASIM is coded to include the physical characteristics of the upper basin including PG&E reservoirs, waterways and power plants as well as all applicable operational rules for these facilities. Figure 1 shows an overview of the Upper Mokelumne system as coded into MOCASIM.

In addition to the existing system, a new feature was added recently to the model where by it is possible now to analyze the potential additional yield from the proposed Enlarged Lower Bear Project. This feature is explained in more detailed in Section 5 of the TM.