Good snowpack doesn’t ensure good water levels

Tom Conning

Public Affairs Office

This past winter, Oregon received plenty of precipitation and snowpack was more than 170 percent of its average in some areas, according to the National Resources Conservation Service. Many people may believe this is cause for celebration in a state that has seen drought conditions during much of the past few years. And although it is good news, snowpack doesn’t mean Portland District’s reservoirs will be full throughout the summer.

Portland District doesn’t depend on snowpack to fill its reservoirs according to Salina Hart, Reservoir Regulation and Water Quality Section chief.

Water from spring runoff fills Green Peter Reservoir near Sweet Home, Oregon, Apr. 12. Portland District reservoirs don’t depend on snowpack to fill. Instead, the reservoirs depend on spring and early summer rain. (Corps of Engineers photo)

“Snowpack equates to less than 10 percent of the Willamette system storage,” said Hart. “In order to fill the reservoirs, we need a healthy supply of spring and early summer rain.”

Portland District refilled its 11 Willamette Valley and two Rogue River Basin reservoirs in preparation for the spring and summer conservation season. That stored water supports a variety of purposes, most notably fish and wildlife, hydropower and recreation.

Balancing the competing needs of the various purposes is a continuous task the Corps does in collaboration with its water management partners. Refill season is one of those processes where the Corps balances capturing water from weather events and filling reservoirs based off of federal law.

However, high reservoir water levels are very important to recreation enthusiasts.

“Visitors enjoy boating, fishing, swimming and camping at our reservoirs,” said Christie Johnson, Willamette Valley Project park ranger. “When water levels are low, some visitors get upset because they do not understand how water is managed to meet the different purposes of the dams and reservoirs throughout the year.” Lower water levels make some boat ramps unusable and some people may not be able to walk longer distances to the shoreline to fish or swim, Johnson continued.

Green Peter Reservoir, near Sweet Home, Oregon, and 10 other reservoirs in the Willamette Valley are full. That stored water supports a variety of purposes, most notably flood risk management, fish and wildlife, hydropower and recreation. (Corps of Engineers photo)

Reservoir levels can decrease by varying degrees during the summer due to lack of additional precipitation, early spring snowmelt as opposed to summer snowmelt and federal rules specifying the minimum amount of water released from each dam to maintain downstream river flows for fish and wildlife environments, irrigation and municipal water supply.

Portland District uses forecasts from the National Weather Service to guide our decision-making for the reservoir conservation plans said Hart. “Generally, Detroit (Reservoir) looks great for being on track to refill.” “It’s hard to say for how long we will be full.”

Another factor that contributes to varying water levels are other Corps efforts to make dam repairs or conduct surveys at the dams and reservoirs. For instance, the Corps will draw down three Willamette Valley reservoirs early this recreation season for spillway gate repairs

Refill season generally begins in February and ends in May.