Portland, OR

Did you know that Portland’s drinking water is supplied by rain rather than snow melt?

You’d think living so closely to Mount Hood would mean that Portland’s water supply would come from the melting snows and glaciers of Mount Hood, but no, Portland’s water comes from our annual rains. And as there is a ridge between Mount Hood and the Bull Run Watershed, snows directly from Mt Hood cannot enter the system. Actually, a little bit of groundwater enters the system, but not much, maybe 5% of the total water.

Portland’s source for water is called the Bull Run Watershed. Portland first tapped this valuable source for clean water in 1895, and it has been providing the city with some high quality drinking water ever since that time. So high quality, in fact, that the city does not filter the water. The water may, however, take on a tint by late summer, as the reservoirs are at their lowest and running into the sediments of smaller creeks, according to the Portland Water Bureau.

The pale tint this year results from the first flush of organic material from vegetation that has been washed from the forest floor and stream channels into the reservoirs in the Bull Run watershed. Each summer the reservoirs levels diminish as the metropolitan area uses drinking water from this stored supply in the Mt. Hood National Forest. In the fall, rains return and refill the reservoirs. The Water Bureau anticipates that these rains will in turn flush the colored water from the reservoirs.

Typically, when the fall refill occurs, the reservoir levels are at their lowest. Streams flowing into the reservoirs travel farther along the creek beds to reach the reservoirs, running through sediments that are not exposed in other seasons. This can also add color to water.

And that is from a press release from 2005, so it is not clear whether this tinting happens every year. I’d suspect so. Especially now that water levels are down in general, you know, global warming and all. Then again, warmer air means more precipitation, so it could mean more water in the reservoirs at the beginning of the summer.

Now, what makes this particular watershed so clear as to not need filtration? A couple of things. First, the geology of the area is volcanic basalt that is 10 to 20 million years old and that basalt is not prone to erosion like other rock. The Bull Run River flows over this basalt from Bull Run Lake, a natural reservoir, to the City’s reservoirs. Basalt’s stability means less sediment in the water. Additionally, the area has not been over-logged. Old growth forest accounts for more than half the total area. Old growth and forestation in general hold down the soil on the hillsides, which means… less sediment in the water.

We are very lucky in Portland to have such quality in our drinking water. I can tell you, living in Chicago, after the clean waters of Michigan, Portland’s water is mighty nice. However, there are impending issues for Portland’s drinking water supply. The biggest issue for Portland, and most of the world, is of course growth.

Portland, Oregon, water supply, public, city, watershed, Bull Run, Mount Hood, Mt Hood, volcanic, basalt, growth, drinking water, reservoirs