以灌溉放淤作為烏山頭水庫永續防淤策略之探討研究

烏山頭水庫完工迄今，水庫總容量減少約48%，累積淤積量約7,432萬立方公尺。此水庫係於日治時代所興建，當初並未規劃設置相關水庫排淤設施，同時因為水庫下游官田溪河道狹小，難以實施水庫下游河道放淤。基於水庫永續的需求，本研究針對水庫淤積浚渫、水庫減淤、排砂可行性作調查分析，經由庫容逕流比、庫容來砂比、水源利用率等指標，確定出烏山頭水庫防淤策略宜由「集水區保育」及「機械清淤」著手。並且利用烏山頭水庫每年供給灌溉用水達7億立方公尺之優勢，規劃出從主庫區越壩抽泥放淤至下游灌溉系統，以抽泥船設置專管越壩排放至現有烏山頭電廠尾水道下游嘉南大圳圳路，再藉由南、北幹線放淤至下游河道或灌區農田。灌溉放淤須配合全年的灌溉計畫及灌溉用水執行放淤的時機，並須預先探討灌溉圳路沿程落淤潛勢，以及抽泥放淤對水庫及圳路既有設施可能的影響共三個層面。2014至2015年度以實際辦理測試放淤驗證了所研議的操作構想。統計資料顯示，自本研究研議以灌溉放淤後，烏山頭水庫年清淤量提升至新的級距，尤其以2018年的低水位操作放淤效果最佳，年放淤量達19.6萬立方公尺。透過引水減淤及灌溉放淤，年放淤目標設為17萬立方公尺，除使烏山頭水庫年淤積量達到平衡外，另可讓下游灌區的農田獲得水庫淤泥以滋養地力。

關鍵字

烏山頭水庫；水庫減淤；灌溉；放淤；永續利用

並列摘要

Wushantou reservoir has been completed for almost one hundred years. Its capacity has been reduced by 74 million cubic meters due to siltation, which is approximately 48% of its initial capacity. The reservoir lacks desilting facilities, and the downstream Guantian Creek is too small to implement silt-releasing during flood periods. Under the goal of sustainable management of the reservoir, this research studied different possible desilting methods. We recommended to take the advantage of this reservoir's annual irrigation water supply of 900 million cubic meters, dilute the reservoir silt into released irrigation water, and bring those fine particles into the downstream farmland through irrigation operations. Through this operation, the reservoir can reach the goal of reducing silt by 170,000 cubic meters per year, which not only balances the reservoir capacity, but also nourishes the downstream farmland.

並列關鍵字

Wushantou reservoir ； Reservoir desilting ； Irrigation ； Silt-releasing ； Sustainable management

參考文獻

Annandale, G.W., Morris, G.L., and Karki, P., Extending the life of reservoirs: sustainable sediment management for dams and run-of-river hydropower, World Bank Publications, Washington, D.C., 2016.