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Flooding around the world (early June edition)

Cross-posted at Highly Allochthonous

Got flood fatigue yet? Too bad, because the wet weather and the high water keeps coming. Here is a quick round up of the notable flood-related news of the week.

High water on the Mississippi River, La Crosse, Wisconsin, 21 April 2011

Front row seats for water levels above flood stage on the Mississippi River, La Crosse, Wisconsin, 21 April 2011

Mississippi River

Floodwall (with emergency height added) in Omaha, Nebraska during the record 1952 floods.

Floodwall (with emergency height added) in Omaha, Nebraska during the record 1952 floods. Will that record be broken this year? (Image from Nebraska DNR.)

Missouri River

Heavy snowpacks in the Missouri River watershed (an areally large, but volumetrically smaller contributor to the Mississippi) have led to near-record flooding that is on-going along its whole length from Montana to Missouri. It’s not getting as much media attention as the Mississippi River, but water levels may stay above flood stage for months. Right now there are heavy rains occurring in parts of the basin, with more rain in the forecast, which will only add to flood problems.

Like the Mississippi, the Missouri is heavily managed by the Corps of Engineers, which is taking some criticism for residents in affected cities. There have also been evacuations because of seepage under levees and concerns about the possibility of failure. Like all big river/developed world flood stories, this one is a complicated mix of huge volumes of water, complicated multi-purpose river management plans, and unwise historical floodplain development.

  • In Historic Flooding On Mississippi River, A Missed Opportunity To Rebuild Louisiana:
    http://www.huffingtonpost.com/2011/06/09/in-historic-flooding-on-m_n_873623.html
  • Flooding from heavy rain in Guizhou province, southwestern China on 6 June 2011 (photo: Xinhua)

    Flooding from heavy rain in Guizhou province, southwestern China on 6 June 2011 (photo: Xinhua)

    China

    For months, China has been stricken by its most intense drought in 60 years, but right now it’s too much, not too little, water that is the problem. Flooding since the 1st of the month has affected East China’s Jiangxi Province and 12 provinces in central and southern China, and more rain is in the forecast for many areas. Intense rains over the last few days have caused the evacuation of more than 100,000 people and killed at least 54.

    Elsewhere

    The Flood Observatory is also reporting on-going flooding in Colombia, the Philippines, Algeria, Haiti and the Dominican Republic, Canada, India, and Upstate New York/Vermont’s Lake Champlain area. In every one of these places, people are losing their homes and lives. While volcanoes and earthquakes shake things up spectacularly now and again, every single day, somewhere in the world, there’s a devastating flood going on.

    Flood risks in the aftermath of the Sichuan earthquake

    As the casualty count continues to climb in China’s Sichuan province following the May 12th M 7.9 earthquake, authorities are struggling to provide shelter and prevent disease amongst the 5 million people displaced by the quake. Seismologists are warning that there is still the potential for large aftershocks, and many people are still jittery. But there’s also another potential danger lurking in the mountain valleys of Sichuan province – that of floods of water released by the failure of dams.

    Some of these dams are man-made and suffered structural damage in the earthquake, like the 150 m Zipingpu dam near Dujiangyan. NPR reported:

    One of its abutments sank 10 centimeters (4 inches). The force of the earthquake opened cracks in the dam wall. But, officials say,
    Zipingpu remains structurally stable and safe.

    Still, here’s an ominous thought: The reservoir at Zipingpu can hold up to 1.1 billion cubic meters of water. The Water Resources
    Ministry says the city of Dujiangyan, with a population of more than 600,000 people, “would be swamped” if the dam failed.

    An even more ominous threat is from landslide dams. During the earthquake, large landslides were knocked loose from the steep mountain slopes and came to rest in the narrow valleys below. The landslide deposits can block river flow and create a reservoir upstream. Eventually the water level will overtop the dam, and the reservoir will stabilize. Unless, of course, the erosive power of the overtopping is enough to cause dam failure, the pressure of the water is stronger than the unstable dam can support, or an aftershock destabilizes the deposits.

    In the week following the quake, 24 lakes had formed in the area affected by the earthquake. NASA has incredible images of one of those lakes, filling the valley and flooding two villages. The image is shown below.

    NASA Image

    The largest dam appears to be 3.5 km upstream from Beichuan, a town of 30,000 that has been the hardest hit by the earthquake and resulting landslides This dam is apparently still inaccessible because of blocked roads in mountain passes, but it is reported to be 2 km long and blocking the Qingjiang River. Another dam is 70 m high and 300 m wide, and it blocked the Chaping River and destroyed a hydropower station. =A smaller dam is 7 m high, 33 m wide, and 100 m long, and it holds back 606,000 cubic meters of water. At least one evacuation has already taken place when a landslide dam threatened to burst. Researchers are trying to develop plans to safely drain the lakes before catastrophe occurs.

    This isn’t the first time Sichuan province has faced this threat. In 1786, a M 7.75 earthquake triggered a landslide that blocked the Dadu River. F.C. Dai and colleagues (2005) did meticulous historical and geomorphic research to reconstruct the events that followed. The landslide dam was 70 m high and held back 50 million cubic meters of water in a reservoir area of 1.7 square kilometers. A large aftershock hit the area 10 days after the main quake, and it caused the dam to fail. The resulting flood had a peak discharge of ~37,000 cubic meters per second, but the real tragedy is that the flood killed 100,000 people living downstream. The landslide dam on the Dadu was not spectacularly large (the largest existing landslide dam is in Tajikstan and is 550 m high), but the deaths from downstream flooding make it the most catastrophic dam failure on record.

    Journal articles cited:

    Dai et al. 2005. “The 1786 earthquake-triggered landslide dam and subsequent dam-break flood on the Dadu River, southwestern China” Geomorphology 65: 205-221. doi:10.1016/j.geomorph.2004.08.011

    Stone, R. 2008. Landslides, flooding pose threats as experts survey quake’s impact. Science. 320:996-997. http://www.sciencemag.org/cgi/content/full/320/5879/996

    Other news sources are linked above.