Detroit Lake project could foul Salem drinking water, lead to water shortages, city says

A major construction project at Detroit Lake could foul the source of Salem’s drinking water and lead to citywide water shortages, city officials said in comments submitted to the U.S. Army Corps of Engineers.

The Corps is planning to build a 300-foot tower and floating screen at Detroit Dam to improve water temperature and fish passage for salmon and steelhead in the North Santiam River.

But the $100-million to $250-million project could require draining the reservoir for one or two years, leading to a dramatic impact on Salem’s water supply, which comes from the North Santiam.

“It’s clear that we have some significant concerns about this project,” Salem City spokesman Kenny Larson said.

Full report: Major dam project could empty Detroit Lake for years, in fish recovery plan

Corps officials stressed they’re in the early planning phases and will study the project’s impact on Salem’s water supply, among other factors, in the coming year.

A draft decision on the project and plans are expected around fall 2018 or winter 2019, while construction would begin around 2021.

“The Corps values input from the community and is looking forward to reviewing the comments, including from the city of Salem,” Corps spokesman Tom Conning said. “All comments will be used to shape the scope of our analysis.”

The primary concern expressed by Salem officials centers on the project’s impact to water quality and quantity.

Here’s a breakdown of their concerns.

Foul drinking water

Salem officials worry that warmer-than-normal water temperatures, and contaminants from the bottom of Detroit Lake, could impact Salem’s water quality during construction.

They pointed to “DDT bound sediment” being released into the McKenzie River during construction of a similar project, at Cougar Reservoir, 10 years ago.

“The city is concerned about the possible release of contaminants in the silt at the bottom of the reservoir,” city officials wrote.

In addition, city officials said, low water in Detroit Lake and Big Cliff Reservoir may lead to high water temperatures in the North Santiam. That, in turn, could lead to water impacted by toxic algae blooms in city drinking water supply.

“Algal blooms can negatively impact water treatment by clogging filters, production of algal toxins and taste and odor issues …” officials wrote.

Muddy water

City officials are worried construction also will lead to muddy or “turbid” water in the North Santiam, impacting the city’s water filtration process.

They pointed out that construction of a similar project, at Cougar Reservoir, created high turbidity on the McKenzie River for four months.

“The turbid water will dramatically affect the city’s ability to utilize slow sand filtration operations … and will create significant operations challenges,” the city’s comments said.

Water shortages

In order to supply Salem with enough water to meet normal demands, the North Santiam River needs to be running at around 700 to 800 cubic feet per second.

But with Detroit Lake close to empty during construction, city officials are worried there won’t be enough water in the river, especially in late summer, leading to potential shortages.

“If this occurs, the city will be unable to produce enough drinking water to meet the needs of its community,” officials wrote. “Salem water customers may face some level of water curtailment for potentially long periods of time.”

Algae and ‘offensive odors’ in Salem

Water from the North Santiam is diverted into both Mill and Pringle creeks, which run through Salem.

City officials said lower and more turbid flows from the North Santiam, passed into the two creeks, could impact Salem’s parks and homes along Mill and Pringle creeks.

“Many homes and businesses are located streamside,” the city wrote. “Lower flows with increased turbidity in Mill and Pringle creeks will likely have a negative effect on water quality by causing increased steam temperatures, algal blooms and offensive odors. The city also is concerned about harmful algal blooms extending into the various waterbodies within the city parks, which are fed by North Santiam River source water.”

Shorter construction timeline

Salem officials said they would like the Corps to consider “alternative construction practices” that minimize effects on the North Santiam River.

The federal agency said the cheapest and safest plan is keeping Detroit Lake almost empty for two full years, followed by alternative plans that keep the lake dry for closer to one year.

But Salem officials suggested a type of construction that “could reduce the time period of impact and minimize the reservoir drawdown level.”

Zach Urness has been an outdoors writer, photographer and videographer in Oregon for 10 years. He is the author of the book “Hiking Southern Oregon” and can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on Twitter at @ZachsORoutdoors.

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