| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 97 === The typhoons induce disasters of landslides and debris flow, bringing amount of large woody debris (LWD) which blocked the river and affected the flood expellant, and water supply in Taiwan. According to above results, the government has focused on the problem of LWD seriously. There are three main functions for LWD in a river: (1) To intercept the sediment on the river bed. (2) To block and separate the water flow. (3) To stabilize the river bank and lessen the scour.
Above all, this experiment conducts the scour depth and sediment export of channel river bed with or without LWD in the channel. We explore the river patterns of the inter-relationship with the LWD, and analyse the LWD’s deposition pattern and speed in different channels.
Results indicate that LWD within the channel not only block and separate the flow effectively, but also change the river morphology. Because LWD which reduse the water flow could lessen the scour on river bed, and induse the bars formed of LWDs downstream side. LWD jam was accumulated by LWDs. Pools and Bars are formed in the LWD jam’s upstream and downstream. It could provide habitats for aquatic organisms, and increase the overall biodiversity of the river. In the deposition patterns, LWD parallel to the water has the highest percentage, followed by oblique, and finally for the perpendicular. When the ratio of channel width and LWD length is less than 0.5, the longer the higher proportion of the deposition of the LWD is parallel to water. When the ratio is greater than 0.5, the LWD is easier to deposit perpendicular to the flow. The size of the LWD diameter to the deposition pattern has no significant relationship. Moving speed is inversely proportional with the LWD lenth; the size of the LWD diameter to the moving speed has no significant relationship. LWD jam will be more effective in blocking the LWD from the upstream, and reduce the moving speed of LWD. And LWD could stably deposit in oblique or perpendicular to flow when LWD were accumulated.
|
|---|
