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Flood
Flood Summary
According to the National Oceanographic and Atmospheric Agency (NOAA), flash floods in the United States are responsible for more deaths than any other storm event phenomenon. Flash flooding usually is the byproduct of very heavy rains in a short period of time over a small geographic area, all of which combine to cause small streams to turn violent. Flooding as a natural hazard is a long-recognized and historically significant event in parts of Morrow County. Flash flooding, which is the prevalent flooding event in Morrow County, can be poorly predicted by weather reports because most often the floods are a result of a microburst, which simply overwhelms both natural and constructed drainage systems. These failures can cause damage to downtown and farms in the floodplain areas. Emergency services, transportation, power, water and wastewater services, business and hazardous materials storage may be substantially disrupted and can affect the population located in or near the flooded area.
Flood History, Locations, and Impacts in Morrow County:
In addition to many localized floods in the Willow Creek drainage through the years, including the 1903 flood in which many lives were lost, Morrow County participated in emergency declarations for flooding in February 1996 and January 1997. The County suffered damages to roadways and private property on Rock Creek, Willow Creek, Hinton Creek, and Upper Butter Creek roads in 1997, and the cost was estimated to be at least $250,000.
South Morrow County
Willow Creek in the southern portion of the County is famous in Oregon for the 1903 flash flood that caused the death of more than 200 people. It was a summer thunderstorm flood and was caused by a large amount of concentrated rainfall and a lack of vegetation in the watershed to slow it down. The City of Heppner, where the flood occurred, lies in a valley surrounded by steep slopes and sits at the confluence of four streams: Willow Creek, Hinton Creek, Balm Fork, and Shobe Creek. The steep slopes of the hills surrounding these creeks, along with the prevalence of severe thunderstorms in the area, contribute to the likelihood of flash flooding. According to the Heppner City Plan (1999), there was one flood per 4.6 years on average between 1883 and 1971. Due to this high incidence of flash flooding on the Willow Creek and other streams, the City of Heppner and the U.S. Army Corps of Engineers built the Willow Creek Dam across Willow Creek. This dam was completed in 1982 and the area subject to flooding was significantly reduced. However, since the Willow Creek Dam was constructed to intercept the waters from Willow Creek and Balm Fork only, the major flood hazard reduction occurred between the face of the dam and the confluence with Shobe Creek. Below Shobe Creek, an extensive area of the valley floor is still considered by FEMA as a designated flood hazard area. The flooding that occurred in 1971 was documented to have originated in the Shobe Creek watershed. As a result of the 1971 Shobe Creek flood, extensive work was done to construct a series of diversions in the Shobe Creek drainage, along with the conversion of cropland to the Conservation Reserve Program (CRP) under a program sponsored by the Soil Conservation Service. Since the construction of the Willow Creek Dam and the work done on the Shobe Creek drainage, no significant flooding has been documented within the City of Heppner.
Lexington and Ione are also located on Willow Creek and experience localized flash flooding events. The U.S. Army Corps of Engineers has indicated that several of the tributaries of Willow Creek below the Willow Creek dam have the potential for flash floods and warrant consideration toward providing a degree of flood protection. The drainage is Blackhorse Creek at Lexington, Reitmann and Lorraine Canyons at Ione, and Rhea Creek at Ruggs. The Corps recommended that protection be investigated and provided if found to be feasible.
The Flood Insurance Study for FEMA completed in 2004 on the Willow Creek and tributaries detailed new determinations of the 10, 50, and 100 year discharges to be used in the Morrow County Flood Insurance maps. The new study proposed smaller flood discharges due to the construction of the Willow Creek Dam and drainage work on Shobe Creek. But, the study revealed an increase in discharges coming from the drainage near Ione.
North Morrow County
The Columbia River is not one of concern as far as extreme flood conditions because it is so regulated by upstream dams that it does not present a problem in Morrow County. There are, however, other flash flooding incidents in the northern portion of the County that do cause damage and disruption for the citizens and businesses of the County. The May 19, 2006 storm event is a good example of how a summer thunderstorm event can cause damage. The storm precipitated record-breaking hail and rain enough to wash out areas of local roads such as Bombing Range Road and portions of Highway 730.
