Coupling Temperature Measurement and Stream Heat Budget Model to Evaluate Impact of River Restoration on the First-order Alpine Stream in Taiwan

Distributed temperature sensing (DTS) is improving rapidly and provide opportunity for high spatial and temporal resolution. It has emerged as a unique and powerful tool for ecological application. The first-order stream of Chichiawan Creek in Taiwan is the crucial habitat for the endangered species of Formosan land-locked salmon, but the stream fragmentation, no surface streamflow, seriously reduced the salmon population, hampering the rehabilitation work. The utility of combining DTS, long-term water level data, temperature profiles, and electrical resistivity tomography (ERT) were demonstrated to comprehensive understand the exchange process beneath the first-order stream. Stream heat budget modeling with HFLUX has been developed through the field measurements along with local meteorological data and unmanned aerial vehicle (UAV) image to simulate the stream temperature and evaluate the exchange rate of energy gain and loss. The results show that the spatial and temporal variations of cold water inflows has been observed and the groundwater and hyporheic inflow have been differentiated using the statistical method. The significance of groundwater and hyporheic inflow can contribute certain amount of water as the ecological base flow at the downstream and reduce the water temperature during the summer time. If the river restoration is conducted to prevent the stream fragmentation, the model results indicate that the amplitude of daily stream temperatures can be reduced. Less stream surface and steeper stream slope are also projected to decrease stream temperatures. The quantitative evaluation method demonstrated here, based on extensive measurements and numerical models, is able to predict the precise level of impact of river restoration on the key environmental objective before actually conducting the efforts.