Holbrook - At a work session held Monday, April 21, it was suggested the Winslow Levee be raised to prevent future flooding.
This suggestion was presented by County Hydrologist Tom Hieb. He made this suggestion based on the nearing completion of two studies ordered by the Navajo County Flood District.
The studies determined the flood capacity of the Winslow Levee, delineated flood hazards along the Little Colorado River near Winslow, and investigated sediment and channel stability issues along the river from Holbrook to Winslow.
Hieb presented the findings of the studies to the Board of Supervisors, acting as the board of directors for the flood control district, April 21. He noted that while no action was required, the board needed the information prior to budget hearings.
He explained that a study commissioned in September 2000 indicated that the sediment building up in the river was threatening the bridges and levees in Winslow, Joseph City and Holbrook. What the study showed, Hieb said, is that the Little Colorado River went through a sediment build up episode between 1940 and 1980 that resulted in a buildup of three to four feet of sediment.
Since 1980, Hieb said, the sediment has eroded somewhere between two and five feet. He said it is not likely that there will be any further erosion. He noted that the most likely cause of the buildup is a change in the climate. “At the present time, it does not appear that sediment is building up on the Little Colorado River between Holbrook and Winslow,” Hieb said. He noted that no action needed to be taken to reduce the sediment between Holbrook and Winslow.
The Winslow Levee, Hieb said, is stable at this time. Delph Engineering completed a flood hazard study on the 7.2 miles of the Winslow Levee. The levee, he said, is an engineered structure. The county’s first involvement with the levee was during the 1960s. Then, from 1971 to 1979, the county spent $600,000 building and repairing the levee. During that same period of time, the U.S. Army Corps of Engineers spent an additional $400,000 on the levee.
While the levee met Federal Emergency Management Agency standards when it was built, Hieb said it does not meet the freeboard requirements now. Additionally, he said, the study showed that the levee does not have a 100-year flood capacity. Its capacity, he said, is for an approximately 50-year flood.
Delph Engineering made some improvement options regarding the Winslow Levee. They include removing the tamarisks along the river bank, realigning the levee, excavating the river channel, raising the levee and purchasing flood-prone property. The costs of these options range from approximately $1.2 million to $17 million.
Hieb noted that of all the options, raising the levee was the most feasible. He said, “It has the lowest difficulty and highest probability of success.”
The steps necessary to raise the Winslow Levee, Hieb said, include hiring a consultant, hiring a contractor and planning for 12 to 24 months of construction.