SUMMARY OF THE JUNEAU FLOOD CRISIS AND A PERMANENT SOLUTION

Victims. Hundreds of Juneau residents are victims of direct damage; many are victims of multiple events year after year.  Furthermore, the collective monetary damage on paper (devaluation) of undamaged surrounding homes being labeled as in a flood zone is even greater. Public infrastructure has been damaged extensively.  The entire community suffers under the stigma of impending repeat disasters. Every citizen in Juneau is damaged to varying degrees.  

Temporary Solutions. Government agencies are currently responding with temporary downstream remedies to be paid by tax assessments on directly affected properties in addition to federal and local government funds. These remedies include manufactured “Hesco” barriers filled with sand installed behind homes along the riverbank. These barriers will not stop the river from surging.  Rather, they are only intended to prevent the surging river from flooding neighborhoods.  News reports indicate the estimated cost of these temporary solutions is approaching $30-million.

Permanent Levee Solution. Concerned citizens are advancing a permanent solution:  a traditional earthen levee at Mendenhall Lake. The Mendenhall Levee would include a passive outflow control structure to detain the outburst water thereby preventing the river from surging above its capacity. The passive outflow control structure will allow the river to flow freely while only blocking excess flow that might cause danger downstream. The blocked flood water gets detained behind the outlet structure and levee.  The river continues to flow at its maximum safe volume until the lake storage goes back down to normal. The outlet structure will have an overflow feature to accommodate the unlikely event the detained water exceeds reservoir capacity. The estimated quantities of these variables are shown on the attached data sheets with topical illustrations. The cost of this permanent solution is estimated at about $31-million.

When additional sources of flooding emanate from the glacier as predicted, the levee will continue providing perpetual value as a permanent safety feature. Over time, it will blend seamlessly into the natural landscape, evolving into a functional and aesthetically pleasing feature. It will serve as an elevated recreational trail similar to the one known as the Juneau Airport Dike Trail. This proposed levee project has the highest probability of success when compared to all other proposed solutions. Moreover, it is a permanent solution.

Equity. The proposed levee will not impose a disproportionate burden on any single homeowner or individual. Rather, it will benefit all members of the community fairly and equitably, especially lower-income and disadvantaged groups who may be particularly vulnerable to the impacts of flooding. Construction and maintenance will be a collective community effort to further ensure no inequities are created.  In summary, the levee represents a practical and enduring solution resulting in fairness, inclusivity, and shared prosperity for all residents.

 Below is a list of pertinent facts related to the levee initiative.

Problem Facts: 

1. Nature of Flood: Glacial Outburst Flood from Suicide Basin and eight other tributaries.
2. Outbursts will continue and are likely to grow.
3. There are additional upstream basins that may release in the future.
4. Efforts to contain uncontrolled flow in the existing channel could have unwanted impacts. such as, erosion of bridge structures.
5. Volume of Flood: 43,388 AcFt. (August 2024).
6. Peak Mendenhall River Flow: 32,000 cfs (August 2024).
7. Rate of Release (“watershed” time of concentration) ~24 hr.
8. Bridges at Risk: 1) Back Loop bridge, 2) Thunder Mt School Pedestrian bridge, 3) Montana Creek pedestrian bridge, 4) Brotherhood bridge.
9. Collectively, in the Mendenhall Valley there is over $3Billion of public and private assets at risk of either direct or indirect damage from an unpredictable glacial release event.
10. There have been significant outburst floods since 2011, high property losses 2023, 2024.
11. The situation could easily become life threatening.

Solution Facts:

12. Proposed permanent solution is a flood control detention basin at Mendenhall Lake including a passive control structure at outlet (levee). The existing lake already acts as a detention basin to which adding the levee will make it fully functional.
13. There are additional upstream basins that may release in the future.
14. Efforts to contain uncontrolled flow in the existing channel could have unwanted impacts such as erosion of bridge structures.
15. By controlling river flowrate, erosion and flooding can be limited.
16. The most 1) readily constructed, 2) easily maintained, 3) reliable long-term solution with the fewest unknowns is to increase the capacity of Mendenhall Lake.
17. An earthen levee could easily be constructed with material available on site.
18. Approximately 18’ height and 14’ top width.
19. Impermeable fabric lining.
20. Slopes stabilized with shot rock obtained from the CBJ quarry at Stablers Point.
21. A flow control structure (bridge/dam) at the outlet of the lake of pile supported reinforced concrete, allowing rafting during normal water levels and foot traffic.
22. No impact on fish passage.
23. There will be no impact to Visitor Center, bus and overflow parking, Skater’s Cabin or Dredge Lake.
24. The Mendenhall Campground will be protected from flooding.
25. The Levee will be easily incorporated into the USFS plans to upgrade the lake area.

Cost:

26. If the project is designed and permitted in an expedited manner, and constructed under several separate contracts simultaneously, it could be completed within a few months at ~$31Million.

Note: See media file “Mendenhall Flood Solution Levee” attached hereto.