The Bull Run watershed has provided drinking water to the Portland, Ore., metropolitan area since 1895. It also plays an important role in supporting the ecosystem of the Sandy and Lower Columbia rivers, where steelhead, chinook, coho, and chum salmon populations are declining significantly.
Released in 2008, the Bull Run Water Supply Habitat Conservation Plan (HCP) outlines how the Portland Water Bureau will reverse that trend over 50 years. The HCP’s water temperature management plan is critical to reviving fish stocks.
Building up breeding grounds
The bureau diverts and stores water in two reservoirs that together hold almost 17 billion gallons. The Sandy River is supplied by the Bull Run reservoir. During summer, with water being pulled from the top warmer layer of the reservoir, the river would get too warm for fish to spawn.
Bureau managers consulted with engineering firm Brown and Caldwell on a plan to regulate the river’s temperature: Pull water from the much-cooler reservoir bottom and, based on readings at several points along the river, control the amount of cold water feeding the river.
To make that happen they needed technology that could set a desired flow rate of cold water. The reservoir fill height has an inlet pressure of 45 psi and water goes into the river at atmospheric pressure. Thus, in addition to being able to measure flows exceeding 83,000 gpm, the system had to be robust enough to withstand pressure drops of 45 psi to 0 psi.
Next page: Extreme pressure, flow changes