The forecast system described has been developed to produce stream flow
forecasts at four locations in Central Puget Sound. Monthly experimental
forecasts are currently being produced for:
1) The Sultan River, total combined inflows to Spada Reservoir,
2) The South Fork Tolt River, at USGS gauge #12147600, above South Fork
Tolt Reservoir,
3) The Cedar River, at USGS gauge #12115000, above Chester Morse
Reservoir, and
4) The Green River, total combined inflow into Howard Hansen Reservoir.
Note: The forecasts provided here are
experimental and are provided to familiarize researchers and
potential users with the methods and performance of the
techniques used. The forecasts are offered with no guarantee of
appropriateness for any particular purpose. Use of these
forecasts for any purpose other than academic research is
therefore entirely at the discretion of the user, and the
authors , the CIG, PRISM, and the University of Washington accept no responsibility for the consequences
of such use.
Introduction
Forecasts and predictions
are an integral part of professional life. Everyday, forecasts are made
by individuals and institutions to aid in decision making. The importance
and accuracy of these forecasts vary greatly. A forecast can play an
essential role in a decision, or simply provide evidence contributing to a
decision. Some decisions require very accurate forecasts, while the
quality of other decisions can be greatly improved with forecasts that
simply indicate the general state of a variable of interest. Streamflow
forecasts often are important in developing reservoir operation and
management policies. Such forecasts can indicate whether conditions are
likely to be wetter or dryer than normal, and this information can aid in
both long-term and short-term operations.
For continental scale water
systems that are influenced significantly by snowpack, such as the
Columbia River Basin or the Colorado River Basin, forecasts made in
mid-April can be very accurate in predicting total streamflows for the
following six months. For smaller scale basins where rainfall plays an
important role, mid-April forecasts may provide significant insights, but
may not be as useful.
Extended seasonal forecasts
such as six-month forecasts can be beneficial in the Pacific Northwest by
indicating the likelihood of abnormal supplies. An extended forecast can
allow water manager to implement operations to minimize the damages of an
unusual event. In the case of an unusually large snow pack, water
managers can vacate more reservoir volume for increased flood control
protection and provide additional water for instream needs. In the case
of abnormally low snow pack, water managers can initiate water
conservation and encourage prepare for water curtailment measures, if they
prove necessary.
Streamflow forecasts are
most useful when integrated into management plans. This is especially
true for regional water supplies, where water shortages in one portion of
the system can be augmented by excesses in another. Regional streamflow
forecasts can encourage cooperation between water suppliers and resource
management agencies and provide valuable information in quantifying the
range of events that are likely to occur in the future.
Objectives
The goal of this project is
to develop a stream flow forecasting system for the major surface water
supply systems of the Central Puget Sound region. The purpose for
creating this streamflow forecast is to provide water managers at the
local utilities with a tool they can use to better inform decisions they
make regarding the operations of their water supply and power generation
systems. Pursuant to this purpose, there are several features of the
forecast system that need to be examined in order to increase the utility
and functionality of the forecast for its intended users. A secondary
goal of this project is to compliment existing forecasts made by
individual utilities while providing a transparent forecast for the region
as a whole.
Puget Sound water managers
operate with their systems with specific goals. Many of the goals can be
met if water storage levels are maintained within a range of values for
the given time of year. The operational range of these systems are
defined by a variety of factors, including annual patterns of municipal
water demand, the need to maintain empty storage for flood control, the
need to provide adequate instream flows for aquatic wildlife, and seasonal
variations in the wholesale power market. Due to the many and varied
system constraints, the amount of operational flexibility available in
most systems is limited to the use of hedging strategies, or small
deviations from standard operations, performed with the intent of gaining
some operational, environmental, or social benefit. In this context,
hedging can imply both reductions in releases from reservoirs during dry
periods, or increase in releases when water is plentiful. Within this
management environment, the benefit to be gained from using a
climate-based streamflow forecast, is the ability to devise better and
more effective hedging strategies than those which could be formed by an
examination of historic streamflows alone. Local utility managers have
indicated that the ability of a forecast to provide a projection of
either, average, below average or above average flows for the upcoming
open to six months would be adequate to inform their decision to apply a
hedging strategy in a particular season.
More on Forecast Components and Methods
More of Forecast Skill
More on Forecast Interpretation
References
Updated
02/08/2006
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