9 September 2011
Updated: Rainfall impacts from Irene and Lee
Posted by Dave Petley
As my fellow AGU blogger Dan Satterfield has pointed out in a post today, heavy rainfall from the former tropical storm Lee across eastern USA is falling on ground that has already been saturated by the passage of tropical storm Irene. The latest storm appears to be generating substantial rainfall totals. This NASA image derived from TRMM data shows rainfall totals for the period 31st August to 8th September:
The upshot is serious flooding and landslide problems. Two substantial ones are being reported at the moment. First, this news report describes what appears to be a rather interesting failure on the banks of Chickamauga Lake in Tennessee:
Half a million dollars worth of property slides straight into Chickamauga Lake, and now the homeowner is describing how it all happened. Ed Cagle lives on Harrison Bay and woke up early Tuesday morning to hear his dock, pool, and backyard slam into the water below. Cagle tells us he had a 65 foot retaining wall installed about 10 years ago. He says it had all the proper draining tubes and reinforcements, but it simply couldn’t withstand the ten inch downpour.
The homeowner does appear to be right that this is a failure of a sheet pile wall. It is slightly surprising to see it deformed in this way. I wonder how deeply it was founded into the ground:
Meanwhile, across in New Jersey there are reports of a landslide at Liberty Township in Warren County, near to Mountain Lake. According to the news reports, this has occurred on Lewis Lane, which Google Maps indicates is at the following location:
So far one home has been lost, and 50 families habve been evacuated:
I wonder what this rainfall will be doing to the Keene Valley landslide in New York as well (see here for details from earlier in the year).
Update: The Philadelphia Inquirer has a really interesting cumulative rainfall graphic for the year to show just how substantial this recent precipitation sequence has been:
Meanwhile, landslides are wreaking havoc elsewhere:
- Seven people were killed today in Xinjiang in China in a landslide. Interestingly, the report suggests that this might be another mine waste accident.
- Six people were killed, and another is missing, in Uttaradit in northern Thailand.
- Heavy rainfall is expected in the typhoon Talas affected areas of Japan today. This news report warns of the potential for collapse of landslide dams created by the previous event: “The land ministry’s regional branch warned Thursday that dams created by landslides in Gojo, Nara Prefecture, and Tanabe, Wakayama Prefecture — which are believed to have filled up with muddy rainwater — could be breached as early as Thursday night, possibly causing serious flooding downstream. Concerned about the possible breach of such a dam upstream, the village of Totsukawa in Nara Prefecture instructed around 300 villagers in about 160 households to evacuate. In Gojo, around 70 people in 40 households were ordered to evacuate, while in Tanabe 30 people in 19 households were ordered to do so.”
[…] Dave Petley over at the Landslide blog has a great post on the consequences of all this […]
How do you generate these maps. Is there a handy online tool somewhere, like this?
I have seen sheet pile walls fail like this before, there are generally two reasons: insufficient embedment or pile section is too light. The pile toe will rotate in the ground for the first case and the pile will bend at or just below ground level for the second. Generally, canterlevered sheet pile walls are limited to a maximum height of 4m to 5m before supplementary support is required.