3 ms·

> try to correlate it with slide events Interesting idea, have you though about how you plan on making the correlation? Two thoughts I just wanted to throw ou

by ggcdn 9y ago

> try to correlate it with slide events Interesting idea, have you though about how you plan on making the correlation? Two thoughts I just wanted to throw out there: -As slopes fail, I think they tend to stabilize themselves, so it might be that only increasingly intense periods of rainfall would cause further slides. -Slope stability depends on pore water pressure, which is more akin to ground water saturation, rather than rainfall. The two can probably be related, but its going to depend on the rainfall intensity minus the losses from permeability of the soil (together, they introduce time into the equation)

japhyr 9y ago
I alluded to this in another comment, but I'll be a little more specific. When it's raining hard and I want to assess slide risk for my own sake, I look at several factors: - what's the total rainfall over the last ~6 hours; - what are the average wind speeds, and gusts? - how quickly are the rivers rising, and how much have they risen overall? I think there's a signature in here, where if all these factors are above critical values then a slide is much more likely to occur. I need to test this by identifying how often this set of critical values have been reached over the last xx years, and then see if that correlates to known slide activity. I think the river gauge is an indirect measure of ground water saturation. If the river gauge is rising at maximum steepness, that's an indication that the ground is fully saturated. If it's raining hard and the river gauge is not rising at maximum steepness, then the ground isn't fully saturated. That's why the river gauge is a key part of this slide risk signature. Fortunately we've had a river gauge in place since before the recent spate of slides. These discussions are motivating me to take the next steps on this analysis. I think I'll do some analysis tonight, and see how far I can get. > As slopes fail, I think they tend to stabilize themselves, so it might be that only increasingly intense periods of rainfall would cause further slides. That's an interesting thought. There's lots of steep land, so there's plenty of land that hasn't slid for a long time but could slide under the right conditions. Repeated slides probably won't release as much material, but then again slides remove what vegetation was holding a slope together. So if a slide doesn't fully unload a slope, I wonder how stable the remaining debris might be.

by ggcdn 9y ago

japhyr 9y ago

I alluded to this in another comment, but I'll be a little more specific. When it's raining hard and I want to assess slide risk for my own sake, I look at several factors: - what's the total rainfall over the last ~6 hours; - what are the average wind speeds, and gusts? - how quickly are the rivers rising, and how much have they risen overall? I think there's a signature in here, where if all these factors are above critical values then a slide is much more likely to occur. I need to test this by identifying how often this set of critical values have been reached over the last xx years, and then see if that correlates to known slide activity. I think the river gauge is an indirect measure of ground water saturation. If the river gauge is rising at maximum steepness, that's an indication that the ground is fully saturated. If it's raining hard and the river gauge is not rising at maximum steepness, then the ground isn't fully saturated. That's why the river gauge is a key part of this slide risk signature. Fortunately we've had a river gauge in place since before the recent spate of slides. These discussions are motivating me to take the next steps on this analysis. I think I'll do some analysis tonight, and see how far I can get. > As slopes fail, I think they tend to stabilize themselves, so it might be that only increasingly intense periods of rainfall would cause further slides. That's an interesting thought. There's lots of steep land, so there's plenty of land that hasn't slid for a long time but could slide under the right conditions. Repeated slides probably won't release as much material, but then again slides remove what vegetation was holding a slope together. So if a slide doesn't fully unload a slope, I wonder how stable the remaining debris might be.