Strong Reasons For a Mendenhall Lake Levee

Should the City consider a levee around Mendenhall Lake?

October 7, 2024

By David Ignell

During last Thursday’s special session conducted via Zoom, Juneau City Manager Katie Koester presented the Assembly with a short list of flood-fighting options for future jokulhlaups. All of these options involved placing either small sandbags or large sand structures alongside homes in the Valley.

None of the options considered building a permanent levee along the shoreline of the Mendenhall Lake that many Juneau residents began asking for over a month ago.

After Koester’s presentation, the Assembly approved her recommended ordinance and took the first official step toward placing large sand structures in people’s backyards along four miles of the riverbank. Mayor Beth Weldon commented at the end of the meeting, “We know this is a short-term solution, but it may end up being the long-term solution, too, so people should be aware of that.”

The large sand structures are containers called “Hesco barriers.” Each container is 3 feet wide, 3 feet wide and 4 feet high. The plan calls for City employees to position the containers on top of the riverbank and then fill them with sand by a loader on site.

In places where a barrier higher than 4 feet is desired, the City intends to build a pyramid-like structure with two bags on the bottom and one bag on top. The resulting barrier would be 6 feet wide and 8 feet high.

The Hesco barriers will be stacked against each other in a single file line for long distances. On the east side of the river, the plan calls for placing them from just south of the back loop bridge all the way to the Airport Dike Trail, south of the runway. Along the west bank of the river, the barriers will be placed only in areas where homes or commercial buildings stand.

While watching the Assembly meeting, the questions foremost on my mind were these: How will the Hesco barriers prevent the river from continuing to erode and undermine the riverbanks? What’s to keep these giant sandbags from falling into the river and perhaps creating additional downstream hazards?

My thoughts centered on the raw power of the turbulent water in 2023, which cut away 150’ of forested land before undermining the concrete foundations of two homes and a condominium building. That destructive force was captured in a video taken by a local resident and posted on YouTube.

If the embedded roots of those tall trees and the concrete footings couldn’t protect those homes, how do the Hesco barriers stand even a remote chance? It seems probable that millions of taxpayer dollars will be washed away and once there’s a gap in the Hesco barriers, the rest of the Valley will be vulnerable to widespread flooding.

It isn’t clear why the Assembly didn’t consider the Mendenhall Lake levee a flood-fighting solution on Thursday. In an email exchange I had with Koester on September 24, she wrote the Lake levee was “included as possible options we talked through when we held a meeting with agency representatives and technocrats. At that meeting, it became clear that we needed to pivot to flood fighting in the short term and that any longer-term approach would likely require a combination of efforts.”

I arranged a conference call with Bruce Sexauer, the Chief of the Army Corps of Engineers for the Alaska District located in Anchorage. Joining me on the call were some of the local advocates for building the Mendenhall Lake levee: Frank Bergstrom, a fluvial geomorphologist; Ed Neal, a scientist who worked for the US Geological Survey for 20 years; and Wayne Coogan, a public works contractor whose company built Thunder Mountain High School adjacent to the river. The Corps cited Neal’s work in their 2015 Mendenhall River Flood Inundation Study.

After hearing from us, Sexauer called the Lake levee a “very viable solution.”

My previous article outlined the basic Lake levee idea. To recap, a 10-15’ high levee would be constructed along the existing shoreline of Mendenhall Lake from the visitor center parking lot to just past Skater’s Cabin. The vertical height of the levee could be combined with a 5-10’ lowering of the elevation of the river bottom near the campground where the lake drains into the river.

About 80% of the levee material could be dredged from the lake bottom, further increasing its capacity. The other 20% of the material would be rock trucked in from the Stabler Point Quarry, less than 10 miles away. Besides the raw materials, Juneau presently possesses the equipment and the workforce to complete construction of this levee by next summer if work begins immediately. But that window of time is closing.

As noted in my previous article, the science behind the Lake levee idea is sound. Mendenhall Lake already acts as a valuable reservoir, helping to contain the dangerous flood waters from the downstream population. The lake’s surface area is roughly 1100 acres. Creating an additional 15,000 to 25,000 acres of storage area could account for nearly half of the water in Suicide Basin.

The levee would be designed to incorporate a gate structure where the lake meets the river. The gate could then be used to manage the level of the lake and the amount of water entering the Mendenhall River.
Sexauer is a civil engineer with substantial experience in flood risk management and is well versed in the Corps Emergency Management programs through planning and implementing multiple levee rehabilitation projects.

From an engineering standpoint, Sexauer would want to make sure that the glacial moraine forming the shoreline of Mendenhall Lake is structurally sound to support such a levee and the water behind it. If the data doesn’t already exist, core samples could be drilled to verify the anticipated structural integrity of the glacial moraine before construction begins.

However, Sexauer said the Corps’ hands are somewhat tied politically from proceeding to construct the Lake levee. He said the Corps will be responsive to what the City wants to do. If the City is in favor of building the Lake levee, then the Mayor needs to request it and the Corps will begin pursuing it.

Under a comparative analysis, lining miles of the Mendenhall River with the Hesco barriers has significant complications that the Lake levee doesn’t. First, the City will need to seek the approval of anywhere from 150-200 property owners to place the barriers in their backyards. Some of those homeowners may not want them, leading to forced entries under the City’s emergency powers, lawsuits and acrimony.

This problem isn’t an issue under the Lake levee plan. The federal government is the only landowner along the Mendenhall Lake shoreline. In fact, the May 2023 Final Environmental Impact Statement for the Glacier Visitor Facility calls for a raised trail along the shoreline, connecting the visitor center with the campground on the other side of the river which a bridge spanning the two sides. The Lake levee is simply an enhancement of this plan.

Second, the Hesco barriers will be a very intrusive process for many homeowners. The loaders filling the containers will rip up yards and landscaping. The City will need to demolish decks, fences, greenhouses and sheds in the way. Some homes won’t have enough space in the backyard to place the barriers, perhaps forcing the City to condemn those properties and purchase them. In many places the ground won’t be level and trees will be in the way, creating additional engineering challenges.

The homeowners affected by the Hesco barriers may have substantial claims against the City for property damages caused by the installation of the barriers. During Thursday’s meeting, some of the Assembly members warned that putting in the Hesco barriers may result in increased property taxes for all residents and/or City services being substantially cut.

Third, the City anticipates that the Hesco barriers will need to remain in place on these private properties anywhere from 5-10 years if they last that long and don’t fall into the river. The containers will need to be maintained and possibly replaced after 5 years. The City will assert the right to enter onto properties to tend to maintenance. It may be next to impossible for any of these homeowners to sell their property for an extended period of time.

Fourth, even if the levees help to protect upstream properties, the increased concentrated flow of the river may overwhelm downstream defenses causing more damages to those properties. This could expose the City to extensive liability. Our courts could become flooded with flood claim litigation.

Fifth, the City warns that some soils along the edge of the riverbank may already be insufficient to support the Hesco barriers. This could cause either premature failure in the system which could comprise the effectiveness of downstream barriers.

There are likely numerous locations along the river where flood waters could get behind the Hesco barriers. If that happens, the containers could act as an impediment to water returning to the river in downstream locations after the peak flood passes. The barriers would act to prolong the high water in neighborhoods, hampering any necessary rescue efforts and increasing damage.

Sixth, in addition to the soil erosion risk, the river could overflow the banks where no barriers are placed and carve a completely new path. Sexauer anticipates that future floods will break the new records established in the last two years. A 20’ flood is foreseeable.

Could the Loop Road east of the bridge act as a conduit for water to cut a new course towards Duck Creek, leading to the substantial loss of life predicted 40 years ago? In checking out elevations of that area on Google Earth, it seems possible a 20’ flood could do that.

None of these aforementioned problems are an issue under the Lake levee plan. The federal government is the only landowner. There will be no structures to remove, the ground will be level, and no trees will be in the way. Maintenance can be performed regularly on government property without invasion of privacy. Protection of upstream homes won’t come at the expense of downstream homes. Protection of homes prone to flooding off the riverbanks won’t come at the expense of their neighbors on the river’s edge.

The Lake Levee makes a lot of sense. Before giving its full approval to the Hesco barrier plan, the Assembly wants to hear from the public at its regular meeting on October 21.

About the writer

David Ignell was born and raised in Juneau, where he currently resides. He holds a law degree from University of San Diego and formerly practiced as a licensed attorney in California. He has experience as a volunteer analyst for the California Innocence Project, and is currently a forensic journalist and author of a recent book on the Alaska Grand Jury.