Shelter effect evaluation of the willow works bank protection method: a case study for Beinan River Reach 2009 Typhoon Morakot event

Abstract

Beinan River is one of the rivers with perfect ecology and full of culture values in Taiwan. It is also the habitat of many freshwater fish species. Besides, the local agricultural crops are famous for exports due to its natural environment, too. Therefore, for these reasons, the hydraulic associations set a series of ecological constructions for waterfowl and fish species around the agricultural water intake areas. For instance, the river bank protection designs the willow works and the fascine mattress by the 8th River Management Bureau for ecological function and hydraulic protection in flood season. In this study, the concept and the methodology of the fish protection habitat predicted model is revealed. Beside the simulated hydraulic models, the indoor experiments of the willow works were conducted to gain the roughness. The hydraulic methods by one- and two-dimensional are used for simulation in flood season (2009 Typhoon Morakot event) to bring up the habitat protection locations. The experimental results showed that for the Manning’s n of the willow works is between 0.1322 and 0.1333 which corresponding height to the real field is about 144–176 cm. Therefore, it provided the revetment roughness data during the shelter effect evaluation. From the velocity distribution, it proves that the vegetated revetment can reduce the flow velocity. Fulfilling previous two main steps in experiment and model calibration, the shelter effect is made good going on discussion. Most of references indicated that the vegetated revetment provided suitable and excellent habitat condition, but rare of them provided the proof in data. This study presents that the WUA is 34,939.94 m2 and PUA is 1.53% at the highest discharge of Typhoon Morakot. The whole protection concepts, simulation methods, and results can be utilized for future plan and design of river engineering.