Even with repairs, Army Corps commander says he cannot risk filling dam reservoir to capacity
StoryEven after interim repairs are completed to the federally owned and operated Howard Hanson Dam, there is still a “1 in 4 chance” that water may have to released that could cause the Green River to overtop its banks and flood the valley, according to a briefing today before a Metropolitan King County Council committee from the local commander of the U.S. Army Corps of Engineers.
Col. Anthony Wright told the Council’s Committee of the Whole that he expects to complete interim repairs to the seeping right abutment of the dam and test them by November 1. Combined with work underway to raise the heights of the levees along the Green River, he estimated the risk of catastrophic flooding is reduced from one-in-three to one-in-four.
“Col. Wright made it clear that we need to be prepared for an increased risk of flooding for the next five years,” said Councilmember Bob Ferguson, chair of the Committee of the Whole. “The Council is united in its willingness to work with the federal government and other jurisdictions to make sure everything is being done to be prepared.”
“I appreciate all that the Army Corps is doing to create a safety net for the Green River Valley this flood season,” said Councilmember Reagan Dunn. “We all know that with a potential catastrophe of this size interagency coordination and communication is absolutely vital and so far I believe our communities are doing a great job of working with each other and the Corps to keep everyone informed. At the end of the day, it’s not just the dam but the levees as well that must hold strong to protect our communities and businesses.”
“I want to thank Col. Wright and the Army Corps of Engineers for their incredible work,” said Councilmember Julia Patterson. “When the Council first learned about the problem, we wanted to make sure the federal government, including the Army Corps, was doing everything it could to fix the problem. We are now assured beyond a doubt that this is happening.”
After the Army Corps discovered excessive amounts of water seeping through an earthen landslide area abutting the dam after last January’s record rainfall, Col. Wright said he began work to inject grout into the earthen material in an effort to prevent a washout that could threaten the integrity of the dam. He said the primary holes have been drilled and the drilling of secondary holes is almost complete. When the so-called “grout curtain” is finished, he said engineers will run tests to check the effectiveness of the repairs. He stressed that even with positive test results, he cannot risk filling the reservoir behind the dam to capacity this winter because the grout curtain will reduce but not completely stop the seepage.
The Corps is working with the King County Flood Control District to ensure that levees along the Green River are upgraded to federal standards, mostly by removing vegetation from around the tops of the levees so that federal inspectors can check for damage. Those upgrades will make the levees eligible for federal rehabilitation and restoration funding if they are damaged by a flood event.
“If the levee is damaged while it is in an ineligible status, I cannot support the repair with federal funds,” said Col. Wright. “For post-flood repairs, it has to be in the program in order for me to federally cost-share it. Our inspectors are ready to go out when the upgrades are complete.”
“I am reassured that the County and the Corps are doing all they possibly can to limit the risk of flooding in the Green River Valley this winter,” said Councilmember Kathy Lambert. “I am also encouraged that the Corps is working on 17 additional flood-prevention projects in the state, including work in the flood-prone Snoqualmie Valley.”
“Col. Wright has informed us about the work being done on the federal level to reduce the potential of a catastrophic flood,” said Councilmember Pete von Reichbauer. “But even with these preparations, it’s vital that preparation on a state, local and neighborhood level continue. That cooperation will ensure the safety of the people who live and work in the Green River Valley.”
“Col. Wright brought some good news—that the U.S. Army Corps of Engineers will soon complete the first phase of strengthening the Howard Hanson Dam—but he made it clear that there is still a significant threat of flooding,” said Council Chair Dow Constantine. “It is imperative that residents of Green River Valley communities join our preparation efforts by creating personal flood plans to better protect their homes and families in the event of a flood.”
Col. Wright praised the cooperation of King County, the Flood District and the local cities for their preparations with the public, calling it a “textbook example of all echelons of government working very closely together.” He said 750,000 sandbags were being delivered for distribution today, with 750 of those sandbags being “supersacks:” doorway-sized plastic and fiber bags filled with rock and gravel.
While Col. Wright said the sandbags will help prevent the overtopping of levees, he cautioned communities against getting into what he called “levee wars,” the building of levee protections higher than those erected in other areas. “This creates the risk of damaging the levees under their own weight” and causing them to collapse, said Wright. “Building the system up to capacity is an appropriate balance to prevent overtopping while still not placing too high of an over-burden.”
“It is imperative that all levels of government work together to protect the residents of the Green River Valley from the devastating impacts of flooding,” said Councilmember Larry Gossett. “Col. Wright said that he was impressed with King County’s preparations for potential flooding. The partnerships on the federal, state and local level are the first defense in preparing for what we hope will not occur within the Valley.”
“The message from the federal government today is that the work underway to shore up the dam is no substitute for a sound, permanent fix,” said Councilmember Larry Phillips. “The federal government needs to do all in its power to speed up and effectively complete permanent repairs that will ensure the safety and economic stability of those who live and work in the Green River Valley.”
Col. Wright acknowledged that the grout curtain is a temporary repair, and that the best-case scenario for completing a permanent repair — such as a concrete cut-off wall which could be placed along the earthen abutment — could be three years. He said that length of time includes designing the repair, acquiring the federal funding, and actual construction time.
Col. Wright is the federal official responsible for making the ultimate decision on whether to release water from the dam, or risk the catastrophic failure of the dam due to excessive pressure on the weakened structure. While his goal is to minimize the risk, he stressed that those in the potential flood zone need to make the necessary preparations. “Water will go were it wants to,” he said. “We can do some things to adjust that, but people looking at maps thinking they are dry should not use that as a reason not to get flood insurance or take appropriate precautions.”
Further briefings on the federal Howard Hanson Dam flood threat will be heard in Committee of the Whole. The County is also hosting a series of public meetings on the Howard Hanson flood threat.
View the materials presented by Col. Wright: