City increases well water use
Warm and dry weather prompts move
Because of an unusually long spell of warmer-than-usual weather with little rain, the Portland Water Bureau is increasing the amount of water it pumps from the city's underground wells for at least two weeks.
The city's primary source of water comes from two dams in the Bull Run Watershed. The bureau has been adding water from the Columbia South Shore Well Field since Aug. 15.
Although bureau officials had expected substantial rains to begin replenishing the watershed this week, the wet weather has not materialized - prompting the officials to increase the amount of well water from 10 million to 55 million gallons a day for the foreseeable future.
"Rain is the primary supply source for Portland's Bull Run Watershed supply, said Water Bureau administrator David G. Shaff. "Rains have not been as substantial as earlier predictions said they might be.'
The city's current demand for water is running between 95 to 105 million gallons a day. Demand earlier this week went as high at 115 million gallons on Oct. 3. High temperatures are now predicted to climb into the 70s by next week, with no rain in sight.
'New long-range forecasts suggest the fall rains that refill the Bull Run reservoirs are a couple of weeks away,' Shaff said. 'It's prudent to extend the Bull Run supply now. These higher groundwater flows ensure reliable supply until fall rains do start again. Portland is fortunate to have a second water supply. Few cities do."
This summer and early fall has been drier than usual, meaning the well water pumps already have been used longer than normal. The well water pumps are used after the amount of water leaving the Bull Run watershed exceeds the amount flowing into it - a period the bureau calls 'drawdown.'
Since 1963, according to bureau statistics the median day the drawdown period has begun is July 9. This year it began on June 22, nearly three weeks earlier. The median day for ending the drawdown is Oct. 3. As of Thursday, the drawdown period had already lasted two days longer than that.
The primary reason the drawdown period is longer this year is the less than usual rainfall. According to the bureau, the median rainfall in the watershed since 1963 from July to September has been 5.42 inches. This year only 3.76 inches of water fell in the watershed during that time.
Temperatures have also been higher than normal for much of the past month, a trend now expected to continue into through next Tuesday.