Hwy 410 Chinook Pass Landslide Situational Update and Report
Meeting Summary
1. Potential Flood Issues;
Terry Keenhan with the Yakima Public Services Flood Control Zone District (FCZD) reported the new channel was designed to handle a 100 year flood and he anticipates it will. They expect to see some changes in the channel as the river flow works on new channel. The group discussed how the river would be monitored. Terry advised anyone wishing to monitor the river should check the Cliffdel Gage on the National Weather Service
website http://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?CLFW1UH
The FCZD will be monitoring the gage as will others throughout the winter. The FCZD will also be monitoring the new channel watching for changes or potential problems.
The flood Stage for the Naches River, at Cliffdel, after being adjusted down for the reduced channel capacity during the event and construction has been returned to pre landslide levels.
A question was asked if there were going to be any impacts on the upstream or downstream river channel. Upstream there are no changes expected but it will be monitored. Downstream however significant river structures were installed to protect the area of the Woodshed Restaurant, the Nile Loop Road Bridge, and residents down river. Some changes will take place but nothing significant is expected. Don Whitehouse advised after spending a significant amount of time in the area he was impressed with the Counties channel design and how it moved the river away from the highway and other structures. Don also reported some significant boulders were removed from under the Nile Loop Rd Bridge that should improve high water flows moving through the area.
As far as the monitoring of the river on a regular basis the group had consensus that we would return to normal operations. In other words there would be no specific monitoring of river flow in the new channel other than those planned by the FCZD. We would monitor gages and receive reports as we would for any other portion of the river systems in the valley. There was a comment that normally if we get into a flood fight the Corps of Engineers would be available to assist and that would be the case here as well.
There was one caveat; no one can fully predict what Mother Nature will do! Being prepared is still prudent in this event.
2. Landslide Safety
Isabella Sarikhan a Geologist with the Department of Natural Resources provided a brief overview of the slide and their studies so far. There are still a lot of unknowns. She reported they were not sure if all of the energy in the slide had been expended or if it had stopped moving. She indicated the slide could be unstable for quite some time meaning potentially years. Isabella advised one of the WSDOT drill holes indicated movement so they were not sure yet.
Don Whitehouse briefed the group on the drilling operation. There are 24 drill holes planned with 16 – 17 complete. The movement Isabella talked about was in drill hole #15 that is about 200 feet deep. The movement observed was about an inch. The radar monitoring the slide did not detect any movement so no one is sure what is happening yet. This was a very deep slide being deeper than originally thought. The drill holes on the upper portions of the slide are about 500 feet deep and on the lower end 300 feet. The drilling is anticipated to be complete in the 2nd week of January. Once complete the holes will be checked weekly for movement. If none is detected the monitoring will be bi-weekly then monthly and so on. If there is movement detected the monitoring will again be more often.
The ground radar installed shortly after the slide occurred has not detected any movement other than some minor rock falls at the upper scarp. The WSDOT intends to keep the radar in place until their work is completed on the slide for safety of their crews. Once the work is complete they intend to remove the radar. Last month the bill for the radar was $83,000 so this is not a cheap piece of equipment.
Because of the depth of this slide there does not appear to be a mechanical fix to stabilize it. A is or is not decision is needed before a decision on a permanent fix can be made.
A question was asked about blasting the remaining portions of the slide to stabilize the area. This was reported as a rumor that has been circulating in the valley. The answer given was there will be no blasting for many reasons.
3. Sightseers
It was discussed that it would be difficult to keep everyone out of the area because of its size and terrain features. There was very little concern of the slide moving and causing issues with people. There was concern for safety of those going to the area because the terrain is rugged and now there is snow. Private property was discussed and Frank Freshwater said he would contact the owner and help with their issues. The public message we should be putting out is don’t go there. Especially near the scarp at the top where there is continual rock fall and many unknowns.
There are safety messages and signs in access areas. The signs provide a clear message don’t go there. There is private property in the area and if there are people intending to go they should have permission.
The conversation went into possibilities of another event. Isabella, DNR Geologist, advised there was little probability of another major slide in the near future. However, energy will more than likely build up and there will be another slide as there has been in the past. This may take several decades though.
4. Temporary Hwy 410 Detour Route
Don Whitehouse advised their work on the Temporary Detour is complete for this winter. In the spring there will be some need for additional signage, stripping, and barricades to accommodate the summer traffic with Chinook Pass open.
A question was asked about additional white markers on the Nile Loop Road. Don advised the road is built to state standards and did not think there was going to be any more. If this was a county road there would be no markers at all was reported.
5. Permanent Hwy 410 Update
WSDOT anticipates a geotechnical report sometime in early summer. This will determine the options available to install a permanent fix. The options as they are known now are 1. Build up the area around the toe to facilitate the new road. 2. Go over the top of the slide building up the approaches and not excavating the slide itself. 3. Cross the river with a new bridge follow the far valley floor and build another new bridge to get back across the river. The most desirable is #1 because it would be the easiest and would cost less. The least desirable is #3 because it is complicated and expensive. Whatever the decision will be it will be a long process because of the required environmental review and request for funding. If all goes well, and if all goes well, a year from now contracts will be issued for the road around the slide with anticipated construction year of 2011.
6. Other issues
Because of the desire to keep the affected residents informed and answer their questions a public meeting at the Nile Valley Church was set for the 2nd Thursday January 14th at 1800 hrs.
The group discussed how fortunate we all were in this event. Things turned out very well. Change the scenario and have, what history tells us was coming, a high water event or flood and what happened in the Nile Valley would change significantly.
