以 HFLUX 模式模擬亞熱帶山區間歇性河段熱收支情形

Abstract

河道中河川水、伏流水與地下水的交互作用對河流的生物地球化學循環及間歇性流動特徵有著關鍵的影響卻鮮少被量化，而溫度作為一種良好的天然示蹤劑，可用以量化各水文通量於時空上所造成的熱收支變化。七家灣溪上游的有勝溪是櫻花鉤吻鮭域外放流的重要棲地之一，近年卻經常發生斷流現象，導致鮭魚棲地擴張受限而影響復育成效。本研究以緊鄰羅葉尾溪下游、長約1924公尺的有勝溪間歇性河段為研究對象，結合分散式溫度感測器 (fiber-optic distributed temperature sensor, FO-DTS)、河流熱收支模型 (HFLUX)、空拍機影像、氣象資料及現地調查數據，識別並量化河段中地表水與地下水 （含伏流水）之間的交互作用。分析2019年06月23日至06月25日的溫度測量結果顯示有11個活躍的伏流水區域及3個地下水流入的位置；HFLUX模式並成功模擬觀測水溫，其正規化均方根誤差 (nRMSE) 僅3.12 %，模擬結果顯示中游河段有較高的入滲潛勢，而下游則是地下水主要進入的河段。綜合分析結果認為地表水與地下水的交互作用是影響間歇性流動河段其河川水溫變化的主因，並影響其斷流潛勢。本研究結果增進了對於源頭溪流的水文過程及能量收支的知識。

Surface water and groundwater interactions between the stream and the hyporheic zone profoundly affect river intermittency and biogeochemical processes, yet they are rarely quantified. As an excellent natural tracer, temperature was used to quantify unknown patterns of hydrologic fluxes and to understand their impact on heat budget over time and space. The Yousheng Creek (a first-order upstream of Chichiawan Creek in Taiwan) is one of the crucial habitats for the endangered species of Formosan land-locked salmon. In recent years, stream fragmentation seriously limited the expansion of the salmon habitat, hampering the rehabilitation work. This study takes heat as a tracer to examine exchange processes in the intermittent reach of Yousheng Creek, with the application of fiber-optic distributed temperature sensor (FO-DTS). The combined use of FO-DTS, deterministic stream heat budget model (the HFLUX computer program), drone imagery, meteorological measurements, and field surveys allowed for identifying, quantifying, and mapping groundwater inputs beneath the 1924 meters reach. Analysis of the temperature traces measured from June 23rd to June 25th, 2019, have identified 11 active hyporheic zones and three groundwater inflows, providing significant cooling in the study section. HFLUX successfully modeled the river temperature through time and space with a normalized root mean square error of 3.12%. Inference from the model indicates a series of high infiltration zones at midstream whereas primary groundwater input from the downstream. The results suggest that different groundwater contributions along the Yousheng Creek significantly impact river temperatures and may lead to streamflow disconnection. These insights of groundwater-surface water interactions can be applied to improve the knowledge of hydrology processes and energy budgets in headwaters.