輪灌區灌溉配水之研究

Studies on irrigation water distribution under water scarcity conditions: The Technique of Distribution Factor for water allocation in rotational irrigation systems

童伯倫(Belembaye Tongongar)

指導教授 ： 甘俊二 ； 陳鈞華

國立屏東科技大學/農學院/熱帶農業暨國際合作系所/博士(2008年)

摘要

由於氣候變遷、人類不當使用及用水部門競相爭水，致使水資源變為更加地有限。再有限水資源之情況下，不僅再乾旱地區也在多雨地區更為明顯。當然氣候因子和人類活動，亦為造成地表水源（如以水庫湖泊為主要灌溉水源）缺水主因。
灌溉配水在缺水期間對於灌溉管理者與農民間更具挑戰，此期間多數灌溉系統常無法有效執行灌溉。甚多研究者提出各種方法與策略，但仍無一通用方法值得推薦使用。
為深入探討灌溉配水運作，選定嘉南水利會之烏山頭灌區獨立灌溉系統之2005及2006年2年4季水稻生長期中，評估配水效率之4個執行因子（足夠性、效率、均等性、相依性）。此4因子之分析結果顯示，足夠性因子在2005及2006年間其值分別為0.83及 0.77，此值顯示公平且低相依性，相對地對灌溉配水系統而言可考慮為有效率及均等性。相依性因子在2間其值分別為0.22及 0.24，此值表示較低執行性 。 此配水操作之較低考靠度，
他們理解到不確保作物生育期間有足夠灌溉用水供給，可使農夫積極調整作物栽培以適應。
本文提出分配因子（DF）之技術應用於配水模式中，分配因子技術於缺水期間，以有限灌溉水量在灌區內指定灌溉區組輪流依序灌溉。分配因子（DF）之配水技術具有動態供水特性，在缺水情況且渠道容量有限情況下，DF被允許組織在灌區內作物生育用水量去作有效配置， DF為指標角色，能設定合理分配之決策。DF應用在嘉南水利會之烏山頭灌區之24個輪區，2年共8個水稻生育期間（GS1-GS8），DF之平均值為0.78且變異係數為0.35。
在GS1和GS2期間發現 DF>1，顯示在此記錄期間配水並無缺乏。在生長期GS3、 GS4、GS5、GS6和GS8顯示為中度缺水之一群，而GS7所對應為嚴重缺水對5個生長期 (GS3-GS6和GS8) DF之配水技術，強調一次灌溉時需分成3組但只灌溉2組而生長期 GS7 DF之配水技術，一次灌溉時需分成2組但只依序灌溉 以GS8為例全部所需灌溉用水量為 2094m3/s，且 DF=0.602。
此值指出在輪區之灌溉區分為3組（Ⅰ、Ⅱ和Ⅲ組），一次僅能灌溉2組。如前次分配灌溉組別為（Ⅱ＋Ⅲ組），則灌溉損失水量為228m3/s，且DF=0.84。如分配灌溉組別為（Ⅰ＋Ⅲ組），則灌溉損失水量為191m3/s，且DF=0.83。而末次分配灌溉組別為（Ⅰ＋Ⅱ組），則灌溉損失水量為59m3/s，且 DF=1.33。
2組灌溉中田間所需總用水量為1087.25m3/s，但考慮損失且DF配水應用所需灌溉水量為1441.42m3/s，因此前次之2組灌溉中可多提供水量354m3/s(或32.5%)供作下順序之次2組灌溉。綜合上述結果即在嚴重缺水情況下，DF技術可在有限水資源在輪灌區中分組依序灌溉，而達到合理分配及使用水源。

關鍵字

水缺乏 ； 灌溉評估 ； 損失 ； 分配因子 ； 輸水 ； 農田需水量

並列摘要

Water resources become limited due to climate imbalance, competition among the water user sectors and human abnormal practices. It was observed that water becomes scarce not only in arid and drought prone areas but also in regions where rainfall is abundant. Also, the climate factors and human activities are so far the main cause of shrinking of many surface waters such as lakes and rivers which are the major irrigation water suppliers. Irrigation water distribution becomes then more challenging both for irrigation managers and farmers. As a consequence, most irrigation systems are working below their potential performance because of water shortages. Many methods and strategies were developed and implemented by researchers to address this situation; however none deserves to be universally applicable.
In light of deep changes occurred during the last decade in the management of Chianan Irrigation Association (CIA), performance assessment of water delivery system was carried in Wushantou independent system during four growing seasons of rice cultivation in 2005 and 2006. Adequacy, efficiency, equity and dependability were four performance indicators which were analyzed. Results showed that the overall values for adequacy indicators were 0.83 and 0.77 implying fair and poor performance for yesar 2005 and 2006 respectively. Conversely, water delivery system was considered efficient and equitable. Dependability indicator values of 0.22 and 0.24 indicated poor performance for both years. This low reliability in the delivery operations is far to helping farmers to adjust the crops to grow because they are not assured of an adequate supply at the time of need.
A model of water distribution called “the technique of Distribution Factor” was developed in this study to consider how the deficit can be assigned to blocks within the system in case of water shortage.
The Distribution Factor (DF) is a technique of water distribution based on the dynamic character of the supply over the growth stages (GS). It allows organize allocation of the available water in the farm within the limit of channel capacity, plays the role of an indicator of water shortages level and helps make decisions for setting up a rational distribution.
The technique was applied to a set of 24 farms supplied by a lateral of Wushantou canal system in Chianan Irrigation Association.
For the eight growth stages (GS1-GS8) of rice crop, DF mean value was 0.78 with a coefficient of variation of 0.35. It was found that in GS1 and GS2, DF>1 indicated that no water scarcity has been recorded. The growth stages GS3, GS4, GS5, GS6 and GS8 fell in the category of moderate water shortage while GS7 corresponded to the severe water shortage. For five growth stages (GS3-GS6 and GS8), DF technique imposes three rotational groups of which only two must be irrigated at once. In GS7, the farm will be split into two rotational groups which will be irrigated alternatively.
In GS8 for example, the total water discharge required was 2094 m3/s and DF= 0.602 indicating that two out of the three rotational groups (I, II and III) should be irrigated at once. If the division was such as the last two groups (II+III) might be irrigated all together water loss and DF values should be 228 and 0.84 respectively. If the first and the third groups (I and III) must be irrigated at the same time, water loss and DF value are 191 and 0.83 respectively. The last division option that consisted of irrigating I and II alternatively with III showed DF= 1.33 and water loss = 59. The total water need for two groups were 1087.25m3/s but DF yields only 1441.42 m3/s of water. So a provision of 354 m3/s or 32.5% of water required for the two groups could be used in the next irrigation turn for the last group. The overall results showed that even in case of severe water shortage, DF technique helped distribute rationally the existing resource among the rotational irrigation groups.

並列關鍵字

water scarcity ； irrigation assessment ； losses ； distribution factor ； water delivery ； farm water demand

參考文獻

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