Southern California Edison (SCE) serves more than 13 million people in a 50,000-square-mile area of central, coastal and Southern California. Its main hydro asset, known as Big Creek, was America's first large-scale integrated hydroelectric project, begun in 1911. It is an integrated hydroelectric project consisting of 23 generating units in nine powerhouses with a generating capacity of approximately 1,000 MW, and six major reservoirs with a storage capacity of more than 560,000 acre-feet.
Market changes, as well as the introduction of the Vista DSS™ decision support system for detailed scheduling and optimization, have increased the need for and scope of inflow forecasting. Also, improved water management forecasting tools are needed in light of growing evidence of global climate change, since various studies show that the average April snow pack in western North America has been gradually declining in recent decades. In particular, the California Department of Water Resources has documented a compelling and statistically significant shift in recent decades from less snow pack to more rainfall, and earlier snowmelt.
In January 2007, SCE retained Hatch to implement Inflow Vista, the inflow forecasting component of the Vista DSS™ decision support system, for the Big Creek hydroelectric projects.
The drainage area was subdivided into a number of sub-watersheds to capture the differences in hydrologic characteristics, caused by the elevation range and weather patterns.
The Inflow Vista basin process model consists of a suite of models, including:
- Mean Areal Input Estimator
- Snowmelt Model
- Abstraction Model
- Watershed Routing
- Forecast Updating Function
The models translate current actual and forecast hourly values of precipitation (either as rain or snow) and temperature to runoff entering the river at specified locations. The model continuously simulates watershed storage variables snow pack, soil moisture and groundwater conditions.
Inflow Vista provides SCE with the capability of generating short-term inflow forecasts for both scheduling and flood management. This includes the ability to do sensitivity analysis based on a range of short-term weather forecasts. The longterm forecasting facilities in Inflow Vista allow SCE to generate a number of possible future inflow sequences for up to a year into the future, based on up-to-date watershed conditions, and a user-selected set of possible future weather patterns. These long-term forecasts provide inputs to LT Vista, for optimizing the management of seasonal reservoirs and determining the value of water in storage.
