The greater metropolitan area of Portland has a population of say about one mill
ID: 285027 • Letter: T
Question
The greater metropolitan area of Portland has a population of say about one million people. The average consumption of water by the residents of Portland is 40 gallons per person per day. The source of Portland’s domestic water supply is streamflow from forested watershed of the Bull Run watershed in the Cascade Range that forms the scenic backdrop to Portland. The average annual water yield of the Bull Run watershed is about 45 inches (area inches). If you assume that all the streamflow is be used for domestic water supply, how large a watershed is needed to supply Portland’s domestic water needs?
Explanation / Answer
The greater metropolitan area of Portland has a population of say about one million people.The river water drains into two reservoirs, in which more than 17 billion gallons are stored. The average consumption of water by the residents of Portland is 40 gallons per person per day. The source of Portland’s domestic water supply is stream flow from forested watershed of the Bull Run watershed in the Cascade Range that forms the scenic backdrop to Portland. The average annual water yield of the Bull Run watershed is about 45 inches (area inches). The Bull Run Watershed should be 102 square miles and should be protected. It can collect water from rain and melted snow which then can be flown to the Bull Run River and its tributaries to meet the supply of the people of Portland.
To protect the water supply from contamination afforestation is done. Bull Run Lake is the natural highest lake in the watershed. When it is full, its surface is at 3,174 to 3,178 feet above sea level. Water from the lake seeps through the ground into the river at a rate of 20 to 25 million gallons a day and flows into artificial reservoirs at two points further downstream. The Portland Water Bureau built Dam 1 is a concrete arch-gravity dam. And 2 dam is an earth fill dam with a maximum storage capacity of 6.8 billion gallons. About 23% of the watershed's annual runoff is diverted to the city's water supply.
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