A primer on flood risk management

Water pours through all the spillway gates at Lookout Point Dam located near Lowell, Oregon. These spillway gates are only used when large amounts of water need to be moved out of the reservoir after a big storm.  Before 2006, the last time all five gates were open was 1996.  Anyone remember the flood of 1996?  That flooding occurred even with all 13 dams holding back water because of very unusual weather conditions. (Corps of Engineers photo)

Water pours through all the spillway gates at Lookout Point Dam located near Lowell, Oregon. These spillway gates are only used when large amounts of water need to be moved out of the reservoir after a big storm. Before 2006, the last time all five gates were open was 1996. Anyone remember the flood of 1996? That flooding occurred even with all 13 dams holding back water because of very unusual weather conditions. (Corps of Engineers photo)

 

Oregon and southwest Washington has experienced pretty significant rainfall in the past week or two. This raises the question in some people’s minds about the risk for flood in these areas and how Portland District manages its reservoirs to keep people and property safe during the region’s major rainy season from November to February. Here’s a quick primer about our flood risk management operations –

In late January and early February 1996, the Corps manipulated the storage dams in the Willamette Basin to hold backwater and lessen flooding, reducing river levels two feet in Portland and at other Willamette Valley locations. It is estimated that the Corps' flood control projects in the basin prevented flood damages at Portland of $1.1 billion. (Corps of Engineers photos)

In late January and early February 1996, the Corps manipulated the water flow in the Willamette Basin to hold backwater and lessen flooding, reducing river levels two feet in Portland and at other Willamette Valley locations. It is estimated that the Corps’ flood control projects in the basin prevented flood damages at Portland of $1.1 billion. (Corps of Engineers photos)

  • We store incoming water behind our dams in the Willamette Valley and Rogue River Basin during flood season, which is between November and May, when significant rain events are more likely. We release it between May and November to support water recreation, regain storage space for the next event and to aid downstream migration of juvenile fish. Our regulators monitor reservoir levels, downstream flows, weather forecasts and snow melt predictions to make real-time decisions about how much water to release from each reservoir. Willow Creek Dam in eastern Oregon also stores water in its reservoir.
  • Our 13 Willamette Valley Project dams operate together as a system for a variety of purposes, the foremost of which is saving lives and reducing property damage from floods. Our dams regulate about 88 percent of the total basin runoff that reaches the Jasper gauge above Eugene, 42 percent that reaches Salem, and 27 percent that reaches Portland. Our dams in the Rogue River Basin operate in a similar manner.
  • Dams on the Columbia River are considered run-of-river dams, meaning water passes through them with no reservoir storage. But this doesn’t mean we don’t operate them for floods – during the region’s Flood of 1996, the Corps regionally operated dams in Washington, Oregon and Montana – in coordination with Bureau of Reclamation and flood managers in southern Canada – to hold back water and keep from flooding downtown Portland and other areas at risk.
  • In late January and early February 1996, the Corps manipulated the storage dams in the Willamette Basin to hold backwater and lessen flooding, reducing river levels two feet in Portland and at other Willamette Valley locations. It is estimated that the Corps' flood control projects in the basin prevented flood damages at Portland of $1.1 billion. (Corps of Engineers photos)A great deal of the water in any given river is not regulated by our dams, and our reservoirs do not have unlimited capacity. But we can significantly reduce the level of floods and the damage they cause. Since the Willamette Valley Project was completed, the dams have prevented $23.4 billion in flood damages (as of June 2015). This number is calculated by looking at the potential cost of damages if the dams were not there. For example, during a January 2006 storm, the dams held back huge amounts of water that would have caused wide-spread flooding in the valley.
  • As an example of our flood risk management operations, spillway gates at Lookout Point dam near Lowell, Oregon are only used when large amounts of water need to be moved out of the reservoir after a big storm. Before 2006, the last time all five gates were open was 1996; due to very unusual weather conditions, flooding occurred even though all 13 dams in the Willamette Valley held back water.

In order to manage flood risk, the Corps of Engineers employs a Reservoir Regulation Team, and their main job is to determine how much water to release from the Corps’ 13 Willamette Valley and two Rogue River Basin project dams, as well as John Day Project’s Willow Creek Dam. They’re on call 24 hours a day, 365 days a year. They keep reservoir pool elevations within designated limits, which is important to communities located downriver, even if they don’t know the role plays in managing flood risk.


For more information and articles about Portland District’s flood risk management practices, visit:

Regulators behind the scenes keep reservoirs, rivers on target

New technology means better water management when flood season arrives 

Flood Preparedness and Recovery (Portland District Website)


 

Torrential warm rain followed heavy snowfall, ravaged much of the Pacific Northwest between Dec.18, 1964 and Jan. 7, 1965. The flood struck hardest in the Willamette, lower Columbia, Rogue, Umpqua and Coquille river basins, inflicting great damage. Photos and news articles of the time showed homes, farms, railways and roads washed away or destroyed. (Corps of Engineers photos) Torrential warm rain followed heavy snowfall, ravaged much of the Pacific Northwest between Dec.18, 1964 and Jan. 7, 1965. The flood struck hardest in the Willamette, lower Columbia, Rogue, Umpqua and Coquille river basins, inflicting great damage. Photos and news articles of the time showed homes, farms, railways and roads washed away or destroyed. (Corps of Engineers photos)

Torrential warm rain followed heavy snowfall, ravaged much of the Pacific Northwest between Dec.18, 1964 and Jan. 7, 1965. The flood struck hardest in the Willamette, lower Columbia, Rogue, Umpqua and Coquille river basins, inflicting great damage. Photos and news articles of the time showed homes, farms, railways and roads washed away or destroyed. (Corps of Engineers photos)

Torrential warm rain followed heavy snowfall, ravaged much of the Pacific Northwest between Dec.18, 1964 and Jan. 7, 1965. The flood struck hardest in the Willamette, lower Columbia, Rogue, Umpqua and Coquille river basins, inflicting great damage. Photos and news articles of the time showed homes, farms, railways and roads washed away or destroyed. (Corps of Engineers photos)

 

Tags: