Surge Flow Border Irrigation Using an Automatic Drop Gate Samir Mohamed Ismail, Gerald L. Westesen, William E. Larsen MEMBER ASAE SENIOR MEMBER ASAE ABSTRACT L OW flows can be utilized effectively for surge flow border irrigation by accumulating the flow then releasing the water and letting it flow across the field. An automatic drop gate was developed to perform this task. It was then tested in the laboratory to check performance and to determine the discharge equation. Field experiments were conducted to compare surge flow border irrigation using the automatic drop gate, with conventional continuous flow. INTRODUCTION Many farmers receive irrigation water in stream sizes too small for efficient border irrigation. Uneven water application and drainage problems then occur. An alternative to these continuous flows and uneven water applications is available. Small continuous flows can be accumulated, then released as a large flow for a short time interval. The resulting intermittent application of water, commonly called surge flow, under some conditions can provide a more uniform intake opportunity time and thus increase water distribution uniformity. Stringham and Keller (1979) first suggested surge flow as a method of automating cutback furrow irrigation. Surge flow with furrows is accomplished by cycling inflow to the field to produce a series of water pulses flowing over the field surface. These intermittent water applications lead to a discontinuity in the infiltration process, often resulting in a reduction in surface layer permeability (Walker et al., 1982). Surge flow with border irrigation, as presented in this paper, varies from that done with furrows because the outflow rate varies. One device used to control water in this fashion is an automatic drop gate. AUTOMATIC DROP GATE Small continuous flows can be accumulated, then released using an automatic drop gate (Ismail and Westesen, 1983; Ismail, 1984). The gate opens automatically when the water level on its upstream side rises to a predetermined elevation and remains open until the water surface drops to a lower predetermined level. The gate then returns automatically to its normally closed position by action of a counter balance weight. This gate has the following advantages: 1. The gate opens and closes automatically. Article was submitted for publication in April, 1984; reviewed and approved for publication by the Soil and Water Div. of ASAE in September, 1984. Presented as ASAE Paper No. 84-2092. The authors are: SAMIR MOHAMED ISMAIL, Assistant Professor, Agricultural Engineering Dept., Alexandria University, Alexandria, Egypt; GERALD L. WESTESEN, Professor, and WILLIAM E. LARSEN, Professor and Department Head, Agricultural Engineering Dept., Montana State University, Bozeman. 2. The gate can be designed to utilize any available head between the reservoir water surface and the land irrigated. 3. The head ditch can be utilized as a reservoir. 4. No electronic system or timer is needed to control the cycle. 5. Minimal management is required. 6. The gate is easily designed and economically fabricated. Theory of Operation The automatic drop gate mechanism is shown in Figs. 1 and 2. Equilibrium conditions for the gate occur at the closing position and at the opening position when the moments due to the counter weight equal the moments resulting from water acting on the gate. The gate opens automatically when the water level on the upstream side of the gate rises to a height such that the moments due to the resultant force from the water exceed the moments due to the counter weight. The gate remains open as long as the moments due to the water acting on the gate exceed the moments due to the counter balance. The gate then automatically returns to its normally closed position when the water level drops below the lower design level. Lever Arm Frame Floating Link Plastic Sheet Aluminum Gate Plastic Hinge Weight Fig. 1—Schematic drawing of dropgate. 532 © 1985 American Society of Agricultural Engineers 0001 -2351 /85/2802-0532$02.00 TRANSACTIONS of the ASAE—1985