Serious Erosion of the Southern Sendai Coast Due to the 2011 Tohoku Earthquake Tsunami and Its Recovery Process - Post-Tsunami Hazard: Reconstruction and Restoration - page 223

Fig. 15.5 Aerial video images taken by Tohoku Regional Bureau's helicopter “Michinoku” at
( a ) Fukanuma Beach (16:02 JST, March 11; 10 km northeast of the Sendai Airport), ( b ) Abukumagawa
River mouth (16:33 JST, March 11; see also Fig. 15.5b ), ( c ) Yokosuka Beach and northern
Yamamoto Coast (16:37 JST, March 11; see also Fig. 15.5c ), and ( d ) southern Yamamoto Coast
(16:39 JST, March 11; see also Fig. 15.5d ) (Source: Udo et al. 2013 (modifi ed); Japan Society of
Civil Engineering)

15.4.2 Characteristics of Coastal Morphology Change

Due to Wind Waves After Tsunami

Regarding shore morphology changes (Figs. 15.2 and 15.3 ), the old river channel in
Area A recovered promptly (Hirao et al. 2012 ). In Area B, the sandbank of the river
mouth was newly formed in a slightly upper-stream area compared to that before the
tsunami by around March 2012. In Area C and D, the eroded coastline changed to
form pocket beaches within a year after the tsunami.
On nearshore morphology changes (Fig. 15.4 ), in Area A, the movement of an
offshore sandbar (shown by deposition and erosion areas in the longshore direction
in Fig. 15.4a ) was noticed at a depth less than 5 m similarly to that before the tsu-
nami. In Area B, deposition was signifi cant from April 2011 to February 2012;
thereafter, deposition at the river mouth and its seaward erosion occurred similarly
to those before the tsunami. In Area C, erosion at a depth between 5 and 10 m and
deposition at a depth less than 5 m were noticed from April 2011 to February 2012;
thereafter, deposition and erosion appeared alternately in the longshore direction
similarly to those before the tsunami. In Area D, erosion was noticed at a depth less