PR 48 05 BONNEVILLE POWER ADMINISTRATION FOR IMMEDIATE RELEASE: FRIDAY, May 6, 2005 Contact: Mike Hansen | , BPA (503)-230-5131     MEDIA ADVISORY Fast facts about weather and hydropower PORTLAND, Ore. - April showers and snow helped raise river flow levels and snowpack, but not nearly enough to compensate for the dry winter when it comes to the hydropower system. As of early May, flows for the water year were forecast to be just 74 percent of average. With a warmer season ahead, chances of gaining ground grow slimmer. Here are some "factoids" to keep in mind when reporting weather-related stories concerning the hydropower system. The water year for the Federal Columbia River Power System is a hydrological cycle that runs Oct. 1 through Sept. 30. The January-July period is often referred to because it is a key period covering flood control operations (January-April) and the majority of the runoff period (April-July) for the Columbia Basin. The volume of water is measured in - million acre-feet (Maf). One Maf is the amount of water it takes to cover one million acres, one foot deep. The Dalles Dam is often referenced when talking about water supply forecasts or streamflows because it is a major downstream point on the Columbia River. It summarizes the flow from all the upstream tributaries that make up the Columbia River Basin drainage area. Although Bonneville Dam is the last project on the Columbia River before reaching the Pacific Ocean, The Dalles Dam and its location have a longer stretch of recordkeeping than other areas. The Northwest River Forecast Center's (NWRFC) May early bird forecast of runoff is for 74.2 Maf, or 69 percent of normal, for the January-July period at The Dalles. For the water year, it is 101.8 Maf or 74 percent of normal. Percentages for the NWRFC's forecast are based on the 30-year period 1971-2000. Runoff includes rainfall, snowmelt and groundwater contributions to the rivers and streams. The NWRFC water supply forecast is a projection of the runoff volume that is expected to enter the hydropower system over a period of time. Since streamflows during the snowmelt season account for about 80 percent of the January through July period, the water supply forecasts depend heavily on the amount of snow accumulated across the Basin. The amount of snowpack - now only about 67 percent of normal - isn't the only thing that will affect the streamflows and the hydro system. The shape (timing and rate of snowmelt) is also a factor. Energy planners hope for a relatively normal shape that allows for refilling reservoirs and helps carry a little more runoff into the summer. Warmer than average spring temperatures mean snow melts early, causing streamflow levels to drop more quickly and be lower than otherwise anticipated later in the summer. River conditions across the Columbia Basin are highly dependent on snowmelt. The amount of snow accumulation and runoff each year affects electricity supply and prices in the Northwest more than in any other part of the country because the Northwest relies on hydropower significantly more than any other place in the United States. About half of all electricity in the region comes from hydropower. Submitted for distribution on 05-06-2005 at 8:57 AM

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