Technical Studies

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 plans of Touchien River’s estuary had been proposed and executed by the Water Resources Planning Institute (WRPI), and the Second River Management Office since 2005, including the Review Improvement Planning, model experiments, mathematical tests, and engineering projects. The engineering projects of the estuary have been completed about two years ago. However, the estuary bed started to deposit. Hence, the benefit of building Jiugang Island diversion dikes, Kulingjiao concave bank dikes, and dredging the estuary should be assessed. In addition, aiming at restoring and conserving estuary’s ecological environment, both ecological environment and hydraulic engineering should be integrated in the overall planning of eco-hydraulic engineering of Touchien Estuary, which combines hydrology, geography, humanity, biology, and space utilization.

This study is carried out in two years. In this (second) year, work items include taking three ecological census of indicator species, simulating the long-term morphologic change of Touchien Estuary, assessing the effectiveness of the proposed countermeasure, proposing an overall planning of eco-hydraulics engineering, and recommending land-use management. According to the sediment transport simulation result of several improvement engineering layouts of Jiugang Island diversion dike and other associated engineering works, an overall improvement engineering layout was recommended and assessed. On the overall improvement engineering layout with building a 32m in length, 2m in width, EL. 6m protection structure between Jiugang Island and diversion dike, shortening the length of no.1 Kulingjiao spur dike to 80m and dredging, it would decrease the water stage of the design discharge Q₁₀₀ (8,530cms) on average about 0.5m in the Touchien Estuary, and enhance flood protection capability of Jiugang Island under Q₂₀. By integrating the analysis of 5S model, comments of citizen participation, and the benefit assessment of the overall improvement engineering layout, an overall planning of eco-hydraulics was recommended. Through dredging, bed material size of the estuary will change and this will be helpful for ecological restoration of indicator species. Furthermore, the advantages of the existence of indicator species include guiding water course, protecting bank, purifying water, and increasing bio-diversity.