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Dry days testing water supply
With Bull Run still in drawdown mode, city taps underground field
Because of an unusually long spell of unseasonably warm and dry weather, the Portland Water Bureau is increasing the amount of water it pumps from the city's underground wells for at least the next week - and possibly much longer.
'We'll continue using the pumps until we've had a couple inches of rain, and the long-range weather forecast predicts more rain next week and the week after that - until we can say, 'We're in the Oregon rains again,' ' said Portland Water Bureau administrator David Shaff.
The city's primary source of water comes from rainfall stored behind two dams in the Bull Run Watershed. The bureau has been adding water from the underground Columbia South Shore well field since Aug. 15.
Although bureau officials had expected substantial rains to begin replenishing the watershed lastweek, the wet weather did not materialize - prompting the officials to increase the amount of well water from 55 million to 70 million gallons per day on Thursday.
'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,' Shaff said.
The city's current demand for water is running between 100 million and 110 million gallons per day. High temperatures are predicted to continue in the 70s into next week, with little rain in sight, according to the long-range weather forecast received by the bureau Wednesday.
This summer and early fall have 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.'
Shaff said the bureau can continue pumping water out of the ground wells for months, if necessary.
'We're just barely tapping them now. We can pump 100 million gallons a day out of them for 90 days if we need to,' he said.
According to bureau statistics, since 1963 the median day the drawdown period has begun is July 9. This year it began June 26, more than two weeks earlier. Since 1963, Oct. 3 has been the median day the drawdown period has ended.
As of today, the drawdown period already has lasted 10 days longer than that.
The primary reason the drawdown period is longer this year is less than usual rainfall to date.
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 also have been higher than normal for much of the past month, a trend expected to continue through Tuesday.