The Optimal Strategy of Sustainable Reservoir Management from a Long-term Perspective

因降雨時空分布不均和可用水資源有限等問題，水庫建用以調蓄水資源，滿足農業灌溉、工業用水、民生需求等目的，水庫壩體阻斷自然輸砂機制致使大量泥砂沉積，淤砂不僅減少水庫蓄水空間，也縮短水庫營運壽命且危害壩體安全，成為一大隱憂。面對此等難題，泥砂清淤為工程上經常使用的手段，然而計畫性的清淤成效不如預期，淤砂速度始終快於清砂效能，嚴重的淤砂會迫使許多水庫面臨退役的問題，影響水庫永續利用的規劃。在某個特定時間，應當重新評斷壩體的續存問題，其中拆壩也是需考慮的選項之一，以往研究多半關心拆壩後對環境所造成的影響，然而拆除壩體的同時，河川可以在短期內得迅速移除庫內淤積泥砂，恢復自然條件。在未來，若是水庫廢棄無法再生利用，旱季時造成供水不足，成為社會的重要問題。若視水庫相當於一種社會資源，在技術可行下，資源再生也將成為一種解決方式，本研究基於原壩址可以拆除後再重新興建的假設上，嘗試將清淤規劃結合壩體的再生進行探討，透過最佳化工具和經濟分析，在長期水庫效益最大化的前提下，基於資源理論的觀點，建構模式以模擬不同條件下短期或長期的水庫操作，分析清淤時間點和清淤量之決策等，最終，評估是否將水庫視為可更新資源或不可更新資源利用，相較於不可更新資源，研究須探討庫容的再生對模式的影響。本研究期望努力的最後，能夠提供水庫操作者具備永續性且有效的水庫淤砂處理的政策原則及方案擬定概念。Reservoir management faces a crucial challenge from watershed sedimentation, which can significantly influence the sustainability of reservoirs. To maximize value of reservoirs and extend its lifespan, strategies of more effective and sustainable reservoir operation are always desired. For this purpose, sediment removal schemes such as dredging and flushing are usually considered; otherwise, dam decommissioning is also widely discussed. The issues raised after dam decommissioning are should we rebuild it, remove it, or just deposit the dam as it is. In the previous studies, retrofitting dam and sediment removal issues are discussed separately in the aspect of reservoir benefit estimation. However, it is very likely that sediment management might be related to dam removal problem. Using an economic analysis and an optimization, this study established a model to explore the log-term reservoir management regarding sediment removal and dam removal, thereby identifying whether operate reservoirs as renewable resources or non-renewable resources at the end of reservoir’s life. As a renewable resource, lifespan of reservoir could be extended indefinitely in contrast to as a non-renewable resource. As a consequence, we expect a better strategy can be proposed for sustainable management of reservoirs