| Bed Shear Stress and Bottom Change due to Tsunami
in a Strait |
 |
| - The Development of the Bed Shear Stress
Evaluation Method in a Strait - |
| Hideo OHTANI *1, Takao
TOUE *2, Makoto TAKAO *3, Naoki
FUJII *4 and Masanori OHMORI *4 |
| Tsunami causes erosion and accretion in a harbor
or a bay, which may result in the collapse of structures and the damage of
harbors. It is important to calculate the accurate sea bottom changes by Tsunami.
The large pressure gradient transforms the velocity vertical distribution in
a strait or a bay mouth where the flow is locally accelerated and decelerated
sharply. It is necessary to study the propriety of the method by which the
bottom shear stress is estimated by the mean flow formula. Characteristics
of the velocity distribution and the bottom friction velocity of tsunami are
carefully investigated by experiments in a narrow strait where the Shields
number is more than 10. When the velocity distribution becomes uniform in the
acceleration phase the bottom friction velocity increases by the large velocity
gradient near the bottom. Based on these results, the bottom changes are calculated.
The results show good agreements to the observation. |
| keywords: |
Tsunami, bed shear stress, tractive
force, bottom change, simulation |