11 March 2011

Earthquakes, Tsunami, and Freshwater Supplies

Not a tsunami, but you get the idea... (credit Wikimedia Commons)
While our hearts and thoughts are with the Japanese people and everyone who has suffered from the massive earthquake that capped several days of seismic activity off the Pacific coast of Japan last night, we can make contributions to many organizations that will be assisting the Japanese in their relief and recovery efforts.  One is UNICEF, to which Japan itself has contributed significantly in recovery from past natural disasters.  Though Japan has not yet requested disaster assistance from the UN, workers and volunteers remain ready to help everyone around the Pacific that has been affected by the earthquakes and tsunami.  The Red Cross is always a worthwhile contribution as well.

I wanted to provide a quick look at some of the effects of earthquakes and tsunami on freshwater resources in affected regions.  Usually these things are not considered until the relief and recovery effort is underway, but they are considerations right from the start of the natural disaster to keep in mind.  Specifically, there are four impacts to be aware of:

credit Fukushima Minpo/AFP/Getty Images/Boston Globe
[1] Broken infrastructure: consider the picture of the house at right, included in The Boston Globe's collection of aftermath images.  Every water supply and sewer pipe under that road is likely severed.  The house and road will need to be demolished before rebuilding, and while that guarantees that new water and sewer infrastructure will come to the neighborhood, it will be a long time before the work is done and the areas is habitable again.  There are millions of Japanese in this situation, though many are not even as lucky as the owners of this home; those who live here may be allowed back into the home to retrieve many of their belongings after it is stabilized.  With thousands of coastal homes swept away completely by the post-quake tsunami especially in the Sendai area closest to the off-shore epicenter, so many Japanese have no homes to which they can return.  Their landscape is forever altered by the tsunami wave.  Roads, rails (for which Japan is famous the world over), and municipal services such as water, electricity, and sanitary and storm sewers are all affected by the earthquake and subsequent tsunami.  Without freshwater supplies and adequate sanitation facilities, the population becomes vulnerable to illnesses and disease, creating a larger and lingering crisis in public health.

credit Kyodo News/Associated Press/Boston Globe
[2] Tsunami contamination of surface waters is a common but only recently-recognized effect.  The tsunami itself may finally be more predictable, but its impacts on the stricken coastlines and people are not.  Depending on the height of the tsunami wave(s), which were recorded at 4m or more in the area of Sendai following the M8.9 off-shore quake, rivers and reservoirs and canals in the coastal region can be affected profoundly by the inundation of sea water among freshwater supplies.  What was once relatively pure freshwater, even drinkable supplies with minimal treatment needs, are rendered useless without full filtration and chemical treatment.  For an area that does not already have these services in place, getting freshwater to the citizens while also establishing new treatment facilities for long-term recovery of sustainable freshwater sources will be a considerable logistical and engineering challenge.  Even further, as the seawater infiltrates the coastal aquifer, those who depended previously on fresh groundwater will find only brackish supplies that, again, require filtration and treatment at the point of use.

credit Saitama Shimbun/Associated Press/Kyodo News/Boston Globe
[3] Soil liquefaction is an effect that was widespread during the earthquakes in Christchurch, New Zealand, in both September 2010 and February 2011.  It does not seem to be such a problem in the volcanic soils of Japan, especially with such advanced practices in foundation engineering for earthquake conditions, although those areas in cities with heavily altered soil foundations (e.g. roads and railways) can be affected significantly.  Essentially, structures built on a slope such as an alluvial fan, where a river empties out across a valley and continually supplies water to the soils both near to the river and at considerable distances, are vulnerable when the shaking effect of the earthquake jostles that soil, turning it into a slurry-like mud.  The result, when there are differential forces at the soil surface and this slurry has an outlet through which it can escape, is the collapse of foundations and whole buildings.  This is not a landslide or debris flow effect, as we might see at coastal cliffs in California or elsewhere in coastal valleys around the Pacific.  Picture a volume of soil and rock about the size of your home, and which you thought was stable and solid such that your home is built right on top of it.  Now picture that soil turned to a coarse but very thin mud, oozing away faster than you can retain it.  Where does your home go, with nothing underneath it?

[4] Dam failures: according to HydroWorld, "a dam the northeast Fukushima prefecture of Japan broke and homes were washed away, Kyodo News reported" [links added] following the largest of the off-shore earthquakes last night.  For masonry dams, such as the iconic concrete arch-gravity dams like Hoover and Glen Canyon in the American Southwest, the likelihood of catastrophic failure in an severe earthquake event is high.  For such dam types, shaking can cause massive cracks in both the dam face and its abutments, allowing the reservoir water to pour through in massive quantities over a short time and removing the standing remainder of the dam entirely.  For rock-fill and earth-fill embankment dams, which are far more common throughout the world, the process of earthquake liquefaction is again a possibility for those soils that are always in contact with the reservoir waters.  Not only can the failure of the dam lead to downstream flooding and fatalities, but the reservoir itself is lost in the process, making life far more difficult on the survivors as well.  The population's dependable source of freshwater, for domestic and agricultural and industrial uses, disappears entirely, and any flood protection provided by the reservoir and dam are foregone for the time that is taken to engineer and build a replacement structure.

Author's note: I owe many thanks to @oocscience for our pre-quake discussion that helped me line out a few of these issues, though at that time I was thinking of another post entirely...we were indeed messing with fate.

1 comment:

M. Garcia said...

Author's note #2: I'm pleased to announce that this post was reprinted on the Project WET blog on 14 March 2011. My first reprint! Hoo-ray!