Assessment of Ecosystem Impacts by Engineering Measures Using the Concept of Building with Nature

Abstract

A field investigation monitored a river restoration indicator, Kandelia, following the idea of Building with Nature (BwN). The main objective of the present study is to understand the relationship between Kandelia growth areas and river patterns; such an understanding can support river watershed management after engineering measures have altered rivers. The fitness-existence of Kandelia was evaluated through measurements and numerical simulations of river discharge, flow velocity, and depth of the river flow. The ecological survey results showed that although the quantity of Kandelia exhibited periods of growth and decline, the overall quantity did not change substantially. Even though the growing area shrank, the number of Kandelia plants did not decline and the biomass density increased. The flow rate was less than 0.4 m/s, equivalent to static. The numerical simulations indicated that the downstream sandbar area favored the growth of Kandelia, even under floodwater after typhoons had brought rain. When typhoons bring rain, the upstream has a high flow rate, which is not conducive to plant growth. A 5S model and a SWOT analysis were used for a comprehensive analysis. The indicator Kandelia is a local ecosystem index of environmental impacts after engineering measures have been conducted. The results may be used as a reference for river watershed engineering planning and to enhance the concept of BwN.