Debris removal is very important after tsunami attack.
Receding currents were noticeably strong and carried a large amount of debris into the sea.
(Courtesy of S. Takahashi, PARI)

Regards,

Parminder

----- Original Message ----- 
From: "Kelly" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, April 02, 2011 4:38 PM
Subject: Re: Tsunami Run-up, River Channels, etc.


> Related to the final point about clogged rivers, there are three impacts
> which may occur: 1) the flow of debris into the rivers and streams has
> likely resulted in clogging (this happened in Sri Lanka, but on a relatively
> small scale, but still enough to lead to local flooding when the rains
> came), 2) damage to embankments and flow management structures may result in
> out-of-bank flows during the rainy season, but also tidal surges up-stream
> and tidal damming of rivers during flood periods and 3) the transport of
> sediment up-stream by the waves, which has narrowed and reduced channel
> depth and thus reduced drainage capacity. 
> 
> Immediately, clearing debris is a necessary part of the first phase of the
> recovery process, and drainage systems (in towns as well as larger
> river-based systems) should be part of these efforts. 
> 
> Assessing the need for repairs to flood protection and river channeling
> systems would also be priority in the overall damage assessment process.
> Rebuilding flood (and sea wave) protection structures will likely take time.
> This process would profit from a stronger eco-system based approach, with
> somewhat less reliance on built structures and more on using eco-systems
> such as wet lands to reduce the risk from flooding where feasible.  
> 
> Regards, 
> Kelly
> 
> -----Original Message-----
> From: Natural hazards and disasters
> [mailto:[log in to unmask]] On Behalf Of COPE, David
> Sent: Sunday, March 27, 2011 12:24 AM
> To: [log in to unmask]
> Subject: Tsunami Run-up, River Channels, etc.
> 
> Dear list members
> 
> I'm not an expert on natural disasters, but obviously they impinge on our
> work - and I am expecting increased parliamentary interest over the next
> months.
> 
> What's more, having been in Tokyo at the time of the earthquake (attending a
> meeting to discuss their creating an office similar to ours to serve their
> parliament), I have something of a personal interest.
> 
> So, I wanted to share some ideas with you experts - and seek your views.
> 
> First, I am hoping that there has been some really good aerial/satellite
> photography of the extent of the March 11th tsunami run-up for the affected
> areas on the north east coast of Japan.  Presumably, the debris and
> destruction will pinpoint the extent of the run-up from the coastline very
> clearly.
> 
> Those of you who have visited Japan will know of the incredible amount of
> coastal engineering intended to resist tsunamis (although I don't think any
> was designed for a 10-15m impact, as tragically indicated at the Fukushima
> power plants).
> 
> The extent of run-up at particular points could perhaps be correlated with
> the level of anti-tsunami protection installed prior to the event?  It
> strikes me that information on this could be really useful for informing
> anti-tsunami defences around the world.
> 
> It appears that some anti-tsunami defences (sea gates) were not activated in
> time, or failed to activate - perhaps some of you saw the harrowing video of
> the fire department team who were manually attempting to shut such a gate
> when the tsunami struck, leading to the deaths of most of the team.
> 
> Second, I wanted to raise a concern regarding 'knock-on' effects.  Again,
> the videos from Japan showed clearly how the tsunami has dumped presumably
> millions of tonnes of debris in river channels, as the water retreated.
> 
> Obviously, and rightly, attention is focussed on humanitarian relief,
> temporary shelters, etc.  But, I am worried about those clogged river
> channels.
> 
> Again, any of you who has been to Japan will have seen how the rivers are
> channeled, embanked, etc. - and all with good reason, because their
> gradients are usually very steep, certainly compared with UK rivers.
> 
> In a few months (starting June), the rainy season will occur in Japan
> (precipitation charts for Sendai are readily available on the web).
> 
> And it sure does rain!
> 
> I am just wondering about the implications of that regarding rising river
> levels confronting debris-clogged channels downstream - and causing a second
> natural disaster, maybe even impacting temporary rehousing, (which
> presumably will be put on higher ground above the devastated areas).
> 
> I'll pass on any good advice to my contacts in Japan.
> 
> All the best.
> 
> 
> 
> Professor David Cope
> Director
> Parliamentary Office of Science and Technology
> Houses of Parliament
> Westminster, London SW1P 3JA
> UK
> 
> tel:  +44 (0)20 7219 2840 (PA)
> fax: +44 (0)20 7219 2849
> email: [log in to unmask]
> 
> POST's Web Site:  www.parliament.uk/post
> ________________________________________
> 
> 
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