本研究以水田水收支平衡為基礎理論,利用坡度可調式之砂箱模型進行試驗,實驗桃園大圳灌區在不同坡度條件下(坡度為1/100、1/150、1/200)之四種土壤(粘土、粘質壤土、砂質壤土、砂土)的迴歸水計算方程式,再以該諸方程式為基本計算式,依土壤別、坡度及水路分佈系統為輸入條件,建立一系統之地區迴歸水量估算模式。 以桃園大圳灌區為區域迴歸水推估模式之應用區域,該模式估算結果以田間小給水路之輸水損失為20%,其引水量為灌溉計畫水深之1.25倍的正常灌溉下,桃園大圳各支線迴歸水佔引水量之比例約為29.41%~50.01%;而桃園大圳12條支線之灌區總引水量為902,785 m3/day,所產生總迴歸水量為348,027 m3/day,其總迴歸水量佔總引水量之比例為38.55%,而該迴歸水已反覆利用在灌溉者約有267,489 m3/day,灌區之最末端因迄今尚沒有抽水設備而流入大海者約有80,538 m3/day。
Water budget balance theorem is used as the basic theory in this research. By using the slop-adjustable sandbox experiment (S=1/100, 1/150, 1/200), the basic equations of return flow in Taoyuan Main Canal irrigation area for the different soils ( clay, clay loam, sandy clay loam and sandy loam ) can be obtained. Furthermore, a systematical estimated model of the regional return flow will be established due to these equations. According to the results of the estimation model, the return flow is 29.41%~50.01% in proportion to irrigation water in every secondary canal of Taoyuan Main Canal based on 20% water conveyance loss in the farm ditch, and 1.25 times for plan water requirement. The gross water requirement is 902,785m3/day, and total amount of the return flow is 348,027m3/day in the irrigation area of Taoyuan main canal. The total amount of the return flow is 38.55% in proportion to total irrigation water. The amount of the return flow which the repeated irrigation is about 267,489m3/day, and flowing to the sea is about 80,538 m3/day in the end of the irrigation area.