Study of Bend Scour and Spur Protection for Fengshan River of Taiwan

The rivers of Taiwan are rushing because of the steep terrain. Loose soils are also tended to cause severe scours during typhoon period. The toe scour problem, especially in river bends and hydraulic structures, are common in Taiwan. In most cases of the broken bank, the concave side of bank is suffered by the severe oblique impact of the flood. To study the problem, the study conducted a down scaled experiment, which in the similarity to the cross section 27–34 of Fengshan River of Hsinchu County, to measure the maximum scour depth and patterns for studying the mechanism of erosion. The results of general bend scour experiment (without spur) showed that the riverbed resulted in a small amount of accumulation on the concave side of bank before the bend. The scouring was mainly occurred on the convex side of band. The flow rate showed the cross sections on the downstream of the concave side of bank has a faster velocity as the compared to the other side. The flow velocity in the downstream section of the concave side of bank was slowed down after the spurs were set. The results also showed that the reduction rates of scour volume were 7.97% and 4.65% on the 10-yr and 20-yr return period of discharge respectively. The maximum scouring depth was occurred at the front of spur after it was built. In addition to the maximum scour depth front of the spurs, the scouring along the downstream was founded getting away from the bank. The study indicated that building spurs can effectively ease the front erosion of spur and downstream scouring.