Irrigation Reservoirs destructed by the Tokachi-Oki Earthquake and Consequent Inundations

Abstract

More than 100 irrigation reservoirs were damaged by the Tokachi-Oki Earthquake in the eastern part of Aomori Prefecture and the embankments of about 10 reservoirs were severely destroyed causing floods in the lower areas.
1) Damages of embankments are mostly the cracks parallel to the direction of embankments, but especially in Kamikita, where many embankments were almost wholly destroyed, the cracks are at right angle to the embankments.
2) The destruction process of reservoirs in Shimokita was in the same way by and large.
3) Increased water by preceding 3 days' heavy rainfall enlarged the submerged areas, and augmented flood water-levels and damages of floods.
4) The flood-currents were swift and strong for several hundred meters from the point of destruction.
5) In the lower areas, the influence of landforms changes the nature of flood currents. When the floods weakened, the influence of micro-landforms, drainage channels, or stagnant water due to the preceding heavy rainfall came into play.