供水系統承載力評估方法與水資源應變機制之研究

Abstract

永續發展之精神在於不造成環境退化的前提下，善用環境資源以支持經濟社會之持續發展。為符合永續之精神，在掌握現有與規劃中之水利設施下，同時考慮供水系統容忍之缺水風險水準，分析能提供之供水能力，並考量未來供水承載力限制下，規劃區域發展之水資源需求。蘭陽溪流域因過去缺水不嚴重，所以尚未興建水庫，又因其地區發展已久，已建置完善之供水系統，此相較台灣其他地區獨特的水資源供水發展，當未來若面臨可能之缺水危機時，正好可以改善台灣過去之水資源系統發展較不考慮環境資源限制與退化等問題，以更符合永續性的概念規劃未來因應缺水之應變機制。本研究分析蘭陽溪水資源系統之供水承載力，並模擬未來需水量可能改變情形。根據未來供水承載力進行敏感度分析，可得到滿足缺水風險下之敏感因子包絡線。此外，以永續利用為願景，在降低缺水與善用環境資源並不造成退化的前提下，探討水資源遇缺水情形之各種應變方法，提出不同缺水情形之供水策略，包括地下水作為備援用水、地下水作為常態用水、與增加蓄水設施進行地表地下水聯合營運。 另外，本研究透過設計案例，根據不同缺水情形之應變機制想法中，提出當缺水程度達到需要增加蓄水設施來增加蓄水，則可結合地下水抽水，將地表水水庫與地下水皆視為常態供水系統進行聯合營運。藉由水庫操作規線之概念，依據地下水累積洩降率加以分區，並透過禁忌演算法優選出同時考慮缺水最少且地下水累積洩降率最小之最佳供水比例，分配地表水與地下水之供水量，建立地表水與地下水之供水規則與聯合營運操作規線。根據研究結果可知，增加地下水累積洩降率分界個數可使目標函數值越來越小，且使用聯合營運優選會得到較只以地表水作為唯一供水來源及使用地表水且將地下水當作備援用水更佳之結果。

The spirit of sustainable development is not only using the environmental resources efficiently for economic and social development but also protecting the environment from degrading. To implement the spirit, analyzing the carrying capacity of water supply due to present and planning facilities and tolerance of water shortage is important. Also, considering the limits of future carrying capacity can scheme the development of future regional water resources. The Lanyang creek watershed is a unique area of water supply development in Taiwan. It rarely has severe water shortage. Therefore, no reservoir is built in the area. However, to support the long-time developments, it has well-built water supply systems. According to the Lanyang creek Watershed’s special development, a different development of water resource system with more environmental considerations can be put into practice when it confronts with possible water shortage risks. This study analyzes the carrying capacity of water supply systems of Lanyang creek watershed and future water demands. According to the results of sensitivity analysis on future carrying capacity, the envelopes of key factors can be determined to make sure not exceeding acceptable risks of water shortage. Moreover, with the vision of sustainable development, this study discusses the measures dealing with water shortage and brings up the water supply strategies for different shortage situations. The measures include using groundwater as backup supply, using groundwater as normal supply, and constructing water-storing facilities to conduct conjunctive operation of surface water and groundwater. Base on the design case study on the measures of conjunctive use of surface water and groundwater, this study proposes constructing water-storing facilities to increase retaining water and pumping groundwater for normal water supply. This study develops conjunctive operation rule curves, which extends the concept of reservoir operation rule curves to the conjunctive use of surface water and groundwater and allows pumping groundwater during the non-drought periods. The rule curve’s goal is to minimize the total water shortage and groundwater drawdown and the Tabu search and the stepwise method are applied to fine the optimal operational rule curves. According to the results of design case study, the optimized conjunctive operation rule curves can reduced more water shortagethan using surface water only or using groundwater as backup.