Model Development for Shi-Chung River Hot Springs and Analysis of Groundwater Level and Temperature Change

四重溪是通往牡丹鄉的必經之地，因有天然溫泉自地下湧出，故古稱「出湯」，又因此處環山盆地，河川貫穿其間，早期居民出入均由河川涉水，步行四層彎島河川，故又俗稱「四重溪」，日治時代與北投、陽明山、關仔嶺並稱台灣四大溫泉，溫泉是屬於碳酸氫鈉鹼性泉，水溫約在50至60度之間，ph值約7.9~8之間，其水質屬於鹼性之碳酸泉。 近年來四重溪溫泉區的水位有逐年下降的趨勢，且水位的變化幅度很大，顯示該區溫泉資源有超抽之虞。為了避免溫泉資源的枯竭，對於水位與水溫的變化需有更精確之掌握，因此本研究探討四重溪區域的降雨入滲及抽水對於水位水溫的影響，及推測合理用水量，並且以不同的抽水比例，來看對於水位與水溫的影響。研究中先以SWAT模式來模擬有效入滲量，此部分需要事先蒐集土地利用、土壤地質、地表高程、河川水系與氣象資料，接著將模擬出之有效入滲量當作SHEMAT的輸入值，並配合設定水文地質與熱傳參數、可能破裂帶位置、邊界與初始條件後，SHEMAT可模擬溫泉水位及水溫之變化。 最後，模式之校正以屏東縣政府所核準之各家溫泉業者抽水水權量為初始值來調校，得到的抽水量高峰為12月1047噸/日，而抽水量最少的月份則是7月719噸/日，同時得知對於越靠近溫泉區中心的觀測井，其模擬效果越好，整體校正與驗證之水位與水溫趨勢符合觀測值變化。此外，校正與驗證的結果可進行合理用水量之推估，並依合理抽水量做比例上的調整來看水位與水溫的變化，可得知儘管以合理抽水量來抽水水位於一年內並無法回升至初始值，且水溫會因為抽水的增加而有降低的趨勢。最後，本研究分析有無入滲對於水位與水溫的變化，可以看出有入滲可以有效的提高四重溪溫泉區各井3.8-6.9公尺的水位，但對於水溫可以看出水溫的變化會使水溫降低0.1℃。Shi-Chung River is the passage through which people go to Mu-Dan village, and there are nature hot springs welling from the underground which we call Chu-Tang in the ancient times. There is basin surrounded by mountains, and rivers flow across. Ancient people always come in and go out along four bending and hard walking river by ford, so we call Shi-Chung River. Shi-Chung River Hot Springs is one of the four great hot springs which are Bei-Tou, Yang-Ming Mountains, and Guan-Zi-Ling Hot Springs in Taiwan during the Japanese occupation. The temperature ranges from 50 to 60℃; ph between 7.9 and 8. The Shi-Chung River Hot Springs belongs to the carbonate spring. Recently, the continuous and acute decline of groundwater level in Shi-Chung River Hot Spring zone indicates possible overdraft of the hot spring resources. In order to avoid exhausting the hot spring resources, a better understanding of the groundwater level and temperature change in this area is necessary. In this study, the impact of precipitation and pumping on water level and temperature is investigated. This study also use different pumping quantity to observe the change of level and temperature. SWAT is applied to simulate the effective infiltration. This step requires gathering information such as land-use, soil-geology, surface elevation, river systems and weather. The effective infiltration then serves as input in SHEMAT. Along with setting hydrogeology and thermal parameters, the position of fractures, and the boundary and initial conditions, SHEMAT can simulate the change of water level and temperature. The pumping is calibrated starting with the permitted water rights for pumping by Pingtung government for all local hot spring hotels. As a result, the peak pumping is calibrated as 1,047 ton/day in December and foot pumping as 719 ton/day in July. Moreover, the model is better calibrated at the center of the hot spring zone, and the overall simulated pattern of water level and temperature match the observation. In addition, the simulate values can be used to conjecture the reasonable pumping quantity. We adjust the reasonable pumping quantity’s scale to study the influence of groundwater level and temperature, and know groundwater level can’t rise to initial value even if we use the reasonable pumping quantity to pump. The temperature will decrease, because the pumping quantity will be increasing. Finally, the influence of effective infiltration on groundwater level and temperature change is analyzed. The groundwater level increases by 3.8m-6.9m level and temperature decreases by 0.1℃ with the existence of infiltration among all observation wells