嘉南大圳為臺灣嘉南地區農田水利灌溉系統之重要命脈，其中南幹線為涵蓋面積廣闊之主幹輸水渠道，為確保灌溉效率與水資源調控安全，分水門與制水門的聯合操作策略扮演關鍵角色，其中，分水門需配合幹線的水位操作其開度，確保分水門以後之各支線汲取足夠水量以供應下游灌區，制水門則配合各分水門取水順序來調節幹線水位。
本研究聚焦於南幹線分水門與制水門的調控策略，結合現地資料與 HEC-RAS 模式之變量流模擬功能，針對開度設定與水量調節機制進行模擬。於簡化後的南幹線模型，分析在下游分水門穩定取水的情況下，分水門及制水門開啟時機與開度調整的機制。
研究透過南幹線斷面幾何資料建立水理模型，模擬不同開度條件下之水位與流量變化，並透過流量–開度曲線及實際操作案例，提出一套安全性高且具應變彈性之閘門操作建議模式，相關成果可作為灌溉管理單位於南幹線制水門常態操作或緊急應變之參考依據。

The Chianan Irrigation System is one of the most important agricultural irrigation infrastructures in Taiwan, supporting extensive farmlands in the Chianan Plain. Among its components, the South Main Canal serves as a major conveyance channel responsible for distributing irrigation water to multiple downstream sub-canals through a series of check gates and division gates. Stable and accurate flow regulation in this canal is critical for ensuring irrigation efficiency, equitable water allocation, and operational safety. However, in practice, gate operations are often conducted based on empirical experience, which may induce undesirable unsteady flow effects such as excessive water level fluctuations, prolonged stabilization time, and operational inefficiency.
This study aims to investigate and evaluate gate control strategies for flow regulation in the South Main Canal by applying a one-dimensional unsteady flow numerical model. The objectives are to analyze the hydraulic responses of the canal system under different gate operation scenarios, to identify key factors affecting water level stability, and to propose rational gate adjustment strategies that can reduce transient disturbances during irrigation operations. The numerical simulations consider various gate opening sequences, opening rates, and coordinated operations between check gates and division gates.
The simulation results demonstrate that gradual and coordinated gate operations significantly reduce peak water level fluctuations and shorten stabilization time compared to abrupt or uncoordinated adjustments. The findings highlight the importance of operation sequence and adjustment rate in mitigating unsteady flow propagation within irrigation canals. The proposed control strategies provide practical guidance for improving operational performance and enhancing the reliability of irrigation water delivery in large-scale canal systems.

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