洪水時の高茎草本の挙動と粗度係数

抄録

Tall, hard-stemmed, herbaceous plants (altherbosa) such as Miscanthus sacchariflorus and Phragmites communis are typical plants found growing along the rivers in Japan, and these plants are closely related to waterfront landscapes and living organisms things in and around rivers. In times of flood, areas densely covered with these herbaceous plants become “dead water” or “near dead water” areas, so if these plants occupy a sizable portion of the channel cross section and aren’t not pushed down by floods water, the discharge capacity of the channel is badly affected. It is therefore important to set the roughness coefficient at a proper level according to whether or not the plants are actually pushed down or not.

In this study, the results of observation of herbaceous plants pushed down by water in a river and in a laboratory flume are reviewed. The criteria for judging of altherbosa behavior and the methods of estimating roughness coefficient are also studied by adding newly collected test data and field survey data to existing data used for the conventional method of determining roughness coefficient. The study proposes methods for judging of altherbosa behavior and for estimating the roughness coefficient in a river section where the plants are grow higher than the flood water level.