Lowell Creek disaster threat assessed
Imagine a wall of water rushing down Jefferson Street after topping the Lowell Canyon Dam and emergency spillway, carrying with it rocks, boulders, uprooted trees and other debris. Its power is great enough to pick up cars and large objects and carry them along, and to structurally damage buildings in its wake. The first buildings to feel the brunt of the deluge would likely be the Providence Seward Medical Center and Glacier View apartments on Jefferson Street, which lie directly below the dam.
As the surging water descends down Jefferson Street, it fans out through First and Second avenues, perhaps even Third Avenue, flowing down the very heart of downtown Seward, and its main business district until it reaches Resurrection Bay or whatever stands in the way — Alaska SeaLife Center, Alutiiq Pride Shellfish Hatchery, UAF Marine building.
This scenario was painted by the U.S. Army Corps of Engineers Alaska Division representatives who held a public meeting April 25 at the Seward Marine Center’s K.M. Rae Building. The meeting was to review the Lowell Creek Project’s history, discuss the types of expected flooding emergencies, and how the risk can be minimized. With the assistance of new flood-inundation maps, the Corps presented four different scenarios that could happen given the right set of circumstances. The hypothetical surges were superimposed over aerial photos of Lowell Creek and downtown Seward, based on two dimensional hydraulic modeling, and using alluvial fan flooding equations.
The floods could occur with enough rainfall over a short-period of time to overwhelm the existing system and overtop the dam, such as 17 inches in 24 hours. Flood surges could also occur if the tunnel was partially or fully blocked by trees and boulders, or if there is a landslide in the canyon above. An alluvial landslide could cause the creek’s flow to change direction, then the water would flow wherever it wants to go, according to the Corps’ engineers. They do not believe there is an active landslide zone above the dam currently, but alluvial glacial fan areas frequently change.
None of the 33 people who attended appeared surprised by the inundation maps showing where the water might run, its velocity and depth, or by the Corps’ description of the effects it might cause. Many were longtime residents who have seen the kind of flooding that happens here before, and are resigned to the inevitability of another flood occurring. Concern they may feel is tempered by the financially daunting task of attempting to minimize the risk by creating a more effective dam project.
The window for the city to take action, with federal assistance and a federal construction cost-split share of 50/50, is only seven years, as the congressional authorization for the Corps’ involvement in the tunnel, (plus its inflow and outflow) ends in November 2022. At that time the diversion tunnel becomes the city’s sole responsibility. The Corps’ involvement in inspecting and maintaining the dam itself was inadvertently left out of the current congressional authorization, but Corps engineers said the dam appears to be still in good shape.
Prior to the diversion tunnel and dam project, downtown Seward regularly flooded from Lowell Creek. For example, the 1917 flood that washed away the schoolhouse, and destroyed or damaged a number of homes, and the one that destroyed the local hospital the very next year. In 1926-27 a timber flume construction was built that routed the flow through the city down Jefferson Street. That construction failed in 1935, however, due to another flood that brought down an estimated 10,000 cubic yards of debris, and caused major damage to the power plant and railroad facilities.
The Lowell Creek concrete-lined tunnel and dam project, then built to take care of the problem, simply was not created to handle the type of 100-year storms that can happen here, said David Frenier, PE, the chief of the engineering division with the Corps’ Alaska District. Like similar projects, it was created to lower the risk from major natural events, not prevent it entirely. Even the $10-15 billions that the federal government spent on new flood structures in Louisiana following the devastation of Hurricane Katrina will only enable those areas to withstand flooding from a Category 3 hurricane, not a Category 4 or 5 hurricane, he said.
The project did help lower the risk for many years, but more recently a screening level risk assessment by the Corps has showed the Lowell Creek risk clear as “Conditionally Unsafe.” The assessment that has proved to be true. Most residents remember July 29, 2009, when storm-driven tides and heavy rain washed out the trails along the waterfront, and Lowell Point Road was closed when gravel overwhelmed the Lowell Creek Bridge and water ran across its approaches. (Flooding also affected Old Mill Subdivision, Box Canyon Creek, Old Exit Glacier Road, Nash Road and Clear Creek during the storm.)
They also remember October 2006, when high tides, warm temperatures and the remnants of Typhoon Xansand dumped 9 to 15 inches of rain in a 48-hour period. Lowell Point Road was closed by a landslide and destruction of the bridge as the creek piled 15 feet of gravel and debris onto it, flooding the Shellfish Hatchery and Seward pump station and destroying ASLC’s new fresh water pump-house. Flood water also ran across the airport runways and closed Seward Highway at mile 3.5.
“The emergency spillway dumps the water right into the middle of Seward right now. If they’d had a crystal ball, Jefferson Street would have been a greenbelt area,” Frenier said. “It all comes down to how much money the community is willing to spend to reduce the risk, to prevent that maximum surge release.”
The next step that Seward could undertake would be a joint feasibility study to determine which of the 18 alternatives listed in a reconnaissance study in 1992 would be best for the city to pursue. That study might cost the city and federal agency approximately $2-3 million, and take up to three years to complete, according to the Corps’ engineers. The alternatives ranged from widening the existing tunnel, building another parallel tunnel, building a “y” structure with two entrances, making Jefferson Street into a green-area/spillway, to removing upstream vegetation. Once a choice is made, both entities could take the next step toward implementing the plan.
In the interim, the Corps recommended that the city conduct an upstream survey, remove trees and possibly landslide material upstream, and replace the fence at the top of the dam with one that can open and allow heavy equipment through during an emergency. The city also should develop an Emergency Action Plan and increase monitoring and surveillance of the site, they said.
Unfortunately for the public, in two of the four emergency scenarios presented, there would only be seconds of warning time before a flood surge hit. In the other two, the warning time is seconds to possibly an hour or more, they said. Relocating the hospital was not even up for discussion, and prior to the hospital’s construction, a consultant who strongly recommended that it be built on stilts was “run out of town,” said Councilman Bob Valdatta.
It is interesting to note that the seven-member Seward Bear Creek Flood Service Area Board, the entity that advises the city and borough on flood matters, has had two of its four “Seward City” seats remain vacant for quite some time, and has had difficulty finding anyone to fill them. The board also has had to cancel meetings several times due to the lack of a quorum.