Technical Studies


Study on overall planning of eco-hydraulics and benefit assessment of diversion dike in Touchien River’s estuary (1/2)

Influenced by the flow and sediment transport among wave, tide and river’s discharge, the morphology of Touchien River’s estuary has migrated dramatically in the past years. Several plannings of Touchien River’s estuary had been done by the Water Resources Planning Institute (WRPI), and the Second River Management Office since 2005, which included the review on improvement planning, physics experiments, mathematical tests, and engineering projects. The engineering projects of the estuary had been completed for about two years; it presented that river bed started deposition, so the benefit of setting Jiugang Island diversion dikes, setting Kulingjiao concave bank dikes, and dredging the estuary should be assessed and investigated persistently. In addition, aiming at raising the concept of restoring and conserving ecological environment of rivers, both ecological environment and hydraulic engineering should be integrated into the overall planning of eco-hydraulics engineering of Touchien River’s estuary, which combines hydrology, geography, humanity, biology, and land utilization.

This study is carried out in two years. In this (first) year, according to the sediment transport model, ecology investigation, humanity investigation, and assessing the benefits of Jiugang Island diversion dike and other associated engineering works, it would provide a reference of overall planning of eco-hydraulic engineering of estuary. This planning included several parts: measuring supplementary cross sections, taking twice ecological census of indicator species, calibrating and verifying sediment transport model, investigating hydraulic and erosion mechanisms of Jiugang Island diversion dike, assessing the effectiveness of associated engineering measurements, doing surveying, and holding seminars of residents.

According to the treatment benefit assessment of Touchien River’s estuary; after Kulingjiao Dikes completed and experienced Soulik, and Trami Typhoons, it shaped bank revetments between each dike. Bank revetments could prevent the footing erosion and enhance safety of river control works. In addition, to create a habitat, bank revetments have great benefit to ecological restoration. The results of numerical model also indicated that, Jiugang Island diversion dike raises 3% discharge in the right channel; this could balance both the water level and velocity between left and right channels of Jiugang Island; furthermore, the upstream inflow attacking the head of Jiugang Island could be reduced, which could improve the efficiency of flood prevention.

Simulation analysis of Jiugang Island stated that, under the situation with bank protection around the island, no flooding occurred under Q10. Besides, bank protection around Jiugang Island has recreational fuction. Estuary dredging could reduce flood level and ensure the banks of not being flooded under Q10; also, the gravel produced by dredging could be used for filling channel; economic or river preventative benefits would be obtained through dredging.