Homer Landslide Assessment & Planning for Hoonah Landslide Assessment
Attendees: Ian Johnson, Jeromy Grant, Jackson Combs, Julian + Ramon, Ryan, Elizabeth Figus, Dennis Gray, Faith Grant, Jackie Dick, Neal Schenfelder, Nicole Williams, Rebekah Sawers, Ernestine, Bob Wagner, Andy S, Bill Miller, Amelia Wilson, Marlene, Stan Savland, Alexandria Contreras, Bambi, Mary, (On Zoom: Jessie Dybdahl, Lyna Martin, Sean Egan)
AGENDA
- Josh Roering guest speaker on Zoom, presenting Homer plan page by page (framework to use in Hoonah), key points:
- Reminder that Homer has different geology from Hoonah
- Debris flow video(s)
- Break down the jargon
- Announce plans for June and July (gift card drawing winner announced at the July meetings)
- Hoonah Landslide Survey Kick-Off
- Lunch provided and door prize drawing at the end
Meeting Goal : look at examples of landslide assessment in Hoonah and understand landslide concepts. Think about how to adapt other plans to our needs. We reviewed the plan from Homer landslide risk assessment and talked about how we plan to create similar maps for Hoonah.
]Key points and discussion topics from the presentation
- What evidence do we have in Hoonah for different types of landslides? Debris flow landslides are the most typical type in SEAK
- Change is documented historically through photos, but now through LIDAR
- How do debris flow landslides act like avalanches? Slope angle is important (30-35 degrees, up to 40 degrees are the sweet spot); but debris flow landslides can keep growing as they go, in a chain reaction-type situation, often staying narrow up high and spreading and growing at the bottom (super dangerous for communities at the bottom of slopes); avalanches are often the same width at top and bottom
- Other issues = how much rain, how much root structure, soil depth, and how much material a debris flow can pick up along the way
- Debris flows, move fast
- Hoonah can create a susceptibility map that combines steepness, water, and soil thickness to get more precise than the Homer runout maps (just steepness)
- Question: what time of year are these most likely in Hoonah? Josh mentioned AR season August-Dec (Ian notes say Sep, Figus heard Dec); the audience was initially thinking spring thaw, but Josh said fall actually
- Question: where will these models be focused for Hoonah? Just in town or also berry areas and other harvest areas. It would be nice to understand risks when out harvesting too
- Request to have Hoonah maps be overlayed on clear town maps with street names
- Question about insurance pool options for landslides
- Sitka did a study/assessment on insurance pools for this, found not viable, Jacque Foss
- Useful to know how much rain is too much rain in a given area, something to look into for Hoonah (what amounts of rain in the past have triggered landslides, including rain on snow events, now thought to be part of the deadly Wrangell slide) because different across communities
- NRCS putting up 10 more Snotel sites around SEAK to better track snow and rain on snow events
- Before meeting start, Jackie shared sketches of areas she had noticed a lot of water draining down the hills in developed neighborhoods, as well as properties she has concerns about because they were fully cleared of trees
- Day before meeting Bob Wagner asked what can be done for areas already developed if/when it is determined that they are at high risk? He also said his personal biggest concern are the Lituya Bay-type tsunami slides, triggered by earthquakes
Dennsi Gray requested any modeling pay special attention to critical infrastructure areas like the water source for Hoonah
What’s Next?
In June we’ll be meeting with Khuti partners to look over new maps for Hoonah with debris flow modeling and other landslide related mapping.
Be the first to comment