Snake River Basin snowpack, inflows, post-wildfire conditions create potential flood risks

An April 1 near-average snowpack and current seasonal runoff forecasts throughout the Snake River Basin prompted regional water managers to U.S. Army Corps of Engineers-Walla Walla District rate the 2016 spring flood potential at normal to slightly above normal.

“Although most areas typically at-risk of seasonal flooding haven’t experienced any major issues yet this year, the amount of snowpack remaining in the mountains still poses the chance that even regulated flows may approach flood stage, especially if significant precipitation or unexpectedly warm temperatures occur,” said Steve Hall, Walla Walla District’s water-management program manager.

The Walla Walla District’s area of operations includes about 107,000 square miles, primarily encompassing the Snake River Basin, in parts of six states: Washington, Oregon, Idaho, Wyoming, Utah and Nevada. 

Cumulative precipitation amounts within the Walla Walla District varied from 117-174 percent of average for the lower-Snake River area, and from 98-139 percent of average for the middle- and upper-Snake River areas, from October 2016 to March 2016. The Clearwater River Basin is at 144 percent of normal.

Basin precipitation data was obtained from the National Weather Service (NWS) River Forecast Center in Portland, OR.

Unregulated streamflows for major basins in the Walla Walla District were 92 percent of average for the Snake River near Heise; 108 percent of average for the Boise River at Lucky Peak Dam, near Boise; 118 percent of average for the North Fork Clearwater River at Dworshak Dam, near Orofino; and 92 percent for Lower Granite Lake inflows on the lower-Snake River near Pomeroy, Washington.

Snowpack measurements reported by the Natural Resource Conservation Service (NRCS) on April 1, 2016, varied between 102-114 percent of average in the lower-Snake River area, 67-115 percent of average in the middle-Snake River area, and 96-110 percent of average in the upper-Snake River area. Individual sub-basin snowpack reports are available on the NRCS website http://www.wcc.nrcs.usda.gov/basin.html. 

The April 1 forecasts of spring runoff varied between 39-129 percent of average throughout the District. In general, the forecasts for most sub-basins within the Snake River Basin are just below average to just over average.

The April through July runoff volume forecast for the Snake River at Lower Granite Dam is 19.5 million acre-feet (AF) or 98 percent of average.

As of April 1 storage for major reservoirs within the Walla Walla District is normal and varies between 28-99 percent full. Most major reservoirs with flood-risk-management responsibility have adequate space available based on the current volume forecasts and ten-day weather forecasts. 

Dworshak Reservoir is currently transitioning to refill operations while releasing spring augmentation flows per NOAA’s Federal Columbia River System biological opinion to benefit juvenile salmon and steelhead outmigration. Spring snowmelt in the Clearwater sub-basin appears to be occurring earlier than normal. 

Additional reservoir storage summaries are available on the NRCS website http://www.wcc.nrcs.usda.gov/basin.html. 

“By the first of April, most of what we’re going to see in snowpack accumulation has peaked, making it somewhat easier to predict what affect precipitation and temperatures will have on reservoir inflows. Flood potential within the district is reevaluated daily throughout the month of April and May,” Hall explained. “Those living in areas where wildfires occurred last year should be especially alert to potential flooding conditions.”

Wildfires in Washington, Idaho and Oregon during 2015 resulted in large, exposed, burned areas, highly prone to flash flooding and erosion. Walla Walla District provided technical assistance to assess post-wildfire conditions and associated flood risks in Clearwater and Idaho counties, Idaho because of the elevated threat to the local communities.

For this spring, the greatest threat of flooding in these areas would be caused by rain-on-snow events in April and May. The district is monitoring conditions and coordinating with state and local jurisdictions in the event additional requests for assistance or flood support are needed.

Corps emergency management staff communicate with local officials to obtain on-site observations from communities in which flooding frequently occurs. 

The Corps works with states, counties and other public entities to provide necessary resources and information. The Corps does not have authority to provide disaster assistance directly to individuals. 

The first responsibility for protecting life, homes and property from flood damage rests with the individual. Local governments and agencies, such as flood control districts, may share in this responsibility, and together form a community's first line of defense in preventing flood damages.

Occasionally, however, local resources are not able to minimize the effects of flooding. The Corps’ flood assistance program is intended to supplement state and local governments and special-purpose districts when more help is needed.

Walla Walla District is prepared to assist states and municipalities with flood-management support. That assistance could include technical expertise, supplies and materials, equipment or contracts for emergency flood-fighting work. District flood support teams and technical experts are ready to deploy should local emergency managers request Corps assistance. 

State and local agencies needing disaster assistance from the Corps should contact the Walla Walla District Emergency Management Office at 509-527-7146, or 509-380-4538.

Individuals and business owners are encouraged to contact local emergency management agencies to ensure they understand how to prepare, respond and recover from a flood.

In harm’s way after the fire

By Elizabeth Morgan

Clearwater County’s Emergency Management team, under the direction of Don Gardner, advised those residing along Orofino Creek, near the area burned in the Orofino-area Municipal Fire this past year, of some potential risks in the fire’s aftermath.

Of the 22 people who attended the public meeting Feb. 22, more than half were officials from the city and county, the National Weather Service out of Missoula, MT, and a field officer from the Bureau of Homeland Security. 

Issues of concern

Hydrologist Ray Nickless of Missoula’s National Weather Service described the patterns he’s noted in regions affected by wildfires. He shared a couple of fairly recent videos illustrating the intensity of debris flows and flash floods near Salmon and Helena, MT, where wildfires had burned two to three years ago.

As jaws dropped and eyebrows were raised, Nickless assured his audience that the acreage we lost in last summer’s fire was much smaller than those in the videos. 

Geological and terrain studies performed by both the Corps of Engineers and the Forest Service illustrated areas where the fire had burned the hottest, and its impact on the ground.

Aerial maps indicated the draws and drainages along the steep hillside which flow toward Orofino Creek which were of particular concern.

“Presently,” said Nickless, “even though there are many dead trees along the hillside, their roots are still holding the soil. We will be more watchful once those roots begin to decompose in the next couple of years when the potential for harm is greater.

Still, this winter’s precipitation and recent wet weather isn’t as threatening as it might seem, and still not bad as spring rains continue in April and May. Nickless predicts the greatest potential danger in the months of July and August, when our area experiences torrential downpours from thunderstorms which seem to come from out of the blue.

A heavy amount of precipitation within a short period of time is something we need to watch, such as those thunderstorms producing one-half inch or more of rain within 30 minutes to an hour’s time. 

Landslide vs. mudslide, debris flows, flash floods

Landslides are slow to evolve. Signs of trees bending, telephone poles, retaining walls or fences leaning are another indicator. Watch for new cracks or unusual bulges in the ground.

Mudslides, debris flows, and flash floods can transpire much faster. These are harder to predict and often occur with little warning.

By planning ahead, and knowing ahead of time how and where to access the heavy machinery, we can clear debris from the creek if needed. It would be much easier to clear than if there were to be a mudslide. If debris were to lodge against the bridge or take it out, the situation becomes much worse.

What the city and county are doing

“As a county and city we felt it important to let you know what we know,” said Gardner. 

Having done his homework, Gardner will apply for the F MAG (Flood Mitigation Assistance Grant) from FEMA (Federal Emergency Management Agency) for $400,000. The application’s closing deadline is March 10.

“It will take a couple of months to be approved and a few months beyond that to receive the money,” Gardner explained. “We’re looking toward the fall, before we have the funds. Then we’ll restore, reforest, and replant, then worry about weeds, as they love that open ground.”

Traditionally, government assistance is designated for roads, bridges, courthouses, etc. “This is one of those rare grants which is actually permitted to be spent on private lands,” assured Gardner.

“From my perspective, I see no issues this winter,” said Gardner. “The roots are still intact, and soon new grasses and growth will help stabilize the hillside. Later, this summer, there will be some concern, but next year, next summer, we’re going to have to be vigilant. The good thing is we have time to think about how to deal with it.”

For now, NOAA Weather Radios were distributed to those at the greatest risk for weather coverage and severe storm alerts available 24/7.

The radio helps to keep people informed of severe storms in neighboring counties and can sometimes send a warning three-five hours ahead of the storm. Still for some systems it may only be 45 minutes. But 45 minutes still allows for time to evacuate. 

If you were unable to attend but live in an area at risk, please contact Don Gardner at the Clearwater County Office of Emergency Management at 2200 Michigan Ave. or call (208) 476-4064. 

What individuals can do…before

Be aware of your surroundings.

Have a plan before it is needed.

Inform neighbors of any potential hazards.

Notify the sheriff’s office where and with whom (contact number) you are staying, should it be necessary to self-evacuate.

Help a neighbor who may need special assistance.

Stay alert and awake. Many fatalities occur at night, when people are sleeping.

And after…

Plant trees, grasses and shrubs to help stabilize the soil.

Trees which have been burned and are not being harvested may be used by placing them horizontally on the hillside to catch or impede the speed of debris and rocks being washed down.

A word of caution to homeowners: “Flood insurance does not cover mud slides.”

Having a plan doesn’t always guarantee that things will go the way we would like them to, but it does make us think beforehand and allow extra time to prepare. Make and review your plan with your family and loved ones at least once a year.

Last summer, we watched half of our town go up in smoke, with nary a warning. Let’s use this information and this time to prepare whatever and wherever we can. Being ready and alert will make all the difference.