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<\/a><\/p>\nYou know, there is a place just above Marblemount — that I didn’t talk a lot about this the other night — but there was a huge landslide there that actually blocked the Skagit River. I’m talking about these landslides right here, because the bedrock geology of the valley is different above Marblemount and it changes again right at Damnation Creek. We\u2019ve mapped six big landslides just in that little area. There are others up the valley above us, and the other area of concern is the Cascade, where the geology is similar as in the area I just mentioned.<\/p>\n
I’ve done some risk assessments. And, they define risk being about hazard, value and vulnerability. Certainly, when you’re sleeping in your home, you\u2019re vulnerable. And your value is really high. So it comes down to how to characterize the hazard.<\/p>\n
Many of these landslides are very old, like the ones up there above Marblemount. The one that I’ve studied is 8000 years old. Then you know from my report, the one right above Rockport is only five or six hundred years old. So it’s a difficult hazard to quantify in terms of when and where. I think it’s real and I think it certainly bears consideration when we come up with new alternatives.<\/p>\n
DH: I focused on the channel that they were envisioning, feeling that the creation of that channel presenting the river with the opportunity to change direction to a greater extent than planned \u2013 they were talking about a thirty percent volume of the river flowing through that channel and then back out.<\/p>\n
Lisa Fenley (LF): I think the other thing is that they can’t guarantee 30%!<\/p>\n
DH: Exactly.<\/p>\n
JR: Right.<\/p>\n
LF: Once you open that they can’t say.<\/p>\n
DH: It was a design intention.<\/p>\n
LF: It was a design intention but not true reality.<\/p>\n
DH: Jon, if you owned a home right here, how would you feel about something as aggressive as the channel?<\/p>\n
JR: To me, the iffy part of the old preferred design was putting those structures in the river to put 30% through Barnaby. But if you combine that with a landslide or a big flood, and the wood racks up on that — now all of a sudden it\u2019s 60% going in.<\/p>\n
Rivers are very sensitive. Once it reaches a tipping point, there\u2019s positive feedback, and erosion brings in more water, I would be concerned that eventually it would redirect the river.<\/p>\n
That’s one of the reasons we\u2019ve been studying the soils out there. What\u2019s in-between you and Barnaby slough is important. Is it all silt and sand?<\/p>\n
LF: They know what the elevation is. If you stand in our driveway, it\u2019s the same as Barnaby.<\/p>\n
JR: I can see how that would concern you, but it would concern me more if there were thirty feet of difference between you and Barnaby, because that gives the water a lot of energy to drop that far.<\/p>\n
JR: I think really the concern is from erosion on this terrace edge.<\/p>\n
If we have a hundred year flood, there is going to be water everywhere. And what happens out there\u2026. it may make it better for some people slightly. I think that early models showed it would take pressure off of that one corner of Martin Road. It will be interesting to me how to demonstrate with any certainty how a given design would perform in 20 or 30 years, or after some large event.<\/p>\n
LF: And, I think the other thing is just the natural sediment of the river. You know how after a flood it piles up , just moving the gravel and the sand can redirect the river. What has happened up there recently is all part of this huge plan. It\u2019s hard not to think that when they say they may not have to do more because the dolosse (reinforced concrete blocks used to build revetments to protect against erosion) are working.<\/p>\n
DH: So, if there was a channel, it seems intuitively obvious to me that if you create an opportunity for something wild like the Skagit River to move and then an unexpected event intensifies the movement of the water through the channel, we\u2019ve got a big problem. My background is in health insurance and for years I\u2019ve thought about risk. So, I talked with an expert on risk assessment and told him about the channel idea, asking him how he would look at it. He said, \u201cWell, it serves to increase the extent of things that could occur as well as the severity of the consequences.\u201d If you envision a bell curve and look at the tail of it representing less frequent events, we\u2019re talking about lengthening the tail and thickening it. The channel would increase the probability of greater harm.<\/p>\n
They don\u2019t seem to respond with much empathy or concern or even curiosity about this point of view, but it is valid.<\/p>\n
JR: Several of us on the technical committee are curious about why the river has gotten so straight through there. I suspect that it’s more than just the highway and the riprap, that it was Seattle City Light cutting off 70% of the sediment supply to the river there at Barnaby. It\u2019s a big effect on a river to cut off 70% of the sand and gravel, and very well could have changed it from a meandering to a straight channel.<\/p>\n
And, redirecting that through that floodplain I think is risky. One thing changes on the river than the model is not accurate anymore.<\/p>\n
LF: And you have to maintain it to the model, That is not going to happen.<\/p>\n
JR: It\u2019s a dynamic process, but the water can be modeled, and I don\u2019t doubt the accuracy of the flood water model, but what is difficult to model is the wood and sediment. It takes more information and different information and experience to predict. I\u2019ve been in this business for thirty some years and it\u2019s tough to predict. I shy away from saying I know what the river is going to do because too often I\u2019ve been wrong.<\/p>\n
LF: It\u2019s Mother Nature and you can\u2019t predict Mother Nature.<\/p>\n
JR: There are very few things in Mother Nature as unpredictable as a river.<\/p>\n
It\u2019s really important to separate risk from flooding and risk from erosion. A 100-year flood is going to put water everywhere and it really isn\u2019t going to matter so much what the preferred alternative is in terms of flood water. I think actually opening up some of the Barnaby sloughs and taking out the dike and levee to let the water spread out and let it slow down could be a benefit to landowners. Redirecting the river into the floodplain by partially blocking the modern river channel\u2013 now, that’s a different ballgame.<\/p>\n
LF: Alternative number four (the design idea of constructing a wide and deep channel to direct part of the Skagit River southwestward into the Barnaby Slough) is what we all get a little heated about.<\/p>\n
DH: This LiDAR image is very interesting because it shows how historically the Skagit meandered and how the valley really looks like an essentially flat sloping plane with little relative variation in depth as it descends.<\/p>\n
The historical meandering pattern of the Skagit River is less visible in a regular aerial photo like this one:<\/p>\n<\/a><\/p>\n