Blogs from the Coastal Structures Team - Tohoku, Japan Earthquake and Tsunami of 2011 - page 82

“beehives.” Several of the tetrapod units had been separated from the main structure,
while all the beehive units were still in place. Inspection of some of the aerial
photographs taken prior to March 11 may help determine the general condition of
each section of armor units before the tsunami.

Koizimi Beach provided a view of how quickly tsunamis can change a beach. Before
the 19-meter inundation by the tsunami, there was about a 20-meter wide beach with
a wide 30 to 50-meter wide green belt behind a vertical seawall. The recreational
beach and green belt were gone. The wall was almost completely destroyed, with
only one small section in the center and an end section that was embedded into
bedrock remaining. Behind the end wall section, there was almost two meters of
vertical scour. Offshore we observed a sand shoal that most likely had been deposited
by the river. We saw little sand in the back shore area which caused us to wonder
where all the sand went and how many years it will take for the river to rebuild the
shoreline back to what had been there before.

We also observed several bridge structures -
the massive Utatsu Bridge on Route 45 that
had five high spans each about 75 meters
wide, and some nearby low-profile bridges.
The Utatsu Bridge suffered inundation of
almost 16 meters high, and it seemed to have
failed catastrophically, with the spans lifted
off their supports. In contrast, the low-profile
bridges showed little signs of damage. We
observed a similar contrast between high and
low profile structures at Shizugawa.

The New Kitakama Bridge was 2.5 to 3
kilometers upriver from the coast and had
been considered to be safe from tsunami
inundation. However, the bridge of about 20
meters in height and 300 meters wide, with
50- to 75-meter-wide spans, was also
destroyed.

Figure A.11 Utatsu Bridge in
Minamisanriku. The bridge spans
had been lifted off the connectors
by the tsunami. (Source: Brian N.
Jones)

We had about a 20-minute detour on sharply
curving roads to get to the next upstream river
crossing. Clearly loss of this bridge and many
others like it will disrupt traffic for a long to
come.

Also near the new Kitakama Bridge is the Okawa Elementary School. During the
tsunami, water rushed over the river training wall and levee and onto the playing field
where the students had assembled for evacuation. Tragically, many did not get to