This time, represented by rreq, requires a nonlinear solution to Eq. 4. Compute a revised estimate of rreq, T2: 3. 5.5.3 An open-end One can see that if the water supply capacity is limited to 1.8 m3/min, the field must be divided into at least five sets to accommodate the first irrigation condition. For the purposes of describing the hydraulics of the surface flows, the drainage period is segregated into the depletion phase (vertical recession) and the recession phase (horizontal recession). 2.2.2 Border irrigation Small land holdings are generally not subject to the array of surface irrigation practices of the large commercial farming systems. In furrow systems, the volume of water in the furrow is very often a small part of the total supply for the field and it drains rapidly. The first step is to describe the flow cross-sectional area. Figure 1. The design of such a system is somewhat more complex than the procedure for traditional furrow and cutback systems because of the need to utilize two sources of water simultaneously. Or, tailwater can be used to irrigate separate sections of the field or even other fields. Surface irrigation systems have two principal sources of inefficiency, deep percolation and surface runoff or tailwater The remedies are competitive. In the developed and industrialized countries, land holdings have become as much as 10-20 times as large, and the number of farm families has dropped sharply. basin by basin, border by border, etc. Figure 3. 2.4. Figure 54. vi. (1980) also suggest computing a minimum flow, Qmin, based on a value that ensures adequate field spreading. In the lesser-developed countries, trends toward land consolidation, mechanization, and more elaborate system design and operation are much less apparent. Starting with a flow near the maximum and working downward using the processes already outlined, advance curves for both infiltration conditions and flow directions can be found. Surdev is yet another free irrigation design software for Windows. 56. one sees that the results are distorted. Since the water supply is presumably controlled by an irrigation department, the design can be substantially hindered if the delivered flows are not as planned. The design should provide an advance phase flow sufficient to allow tL = rreq. Then the irrigator with some simple instructions from the designer can 'share' this flow among the appropriate number of furrows and achieve a reasonably good approximation of the optimal discharge. The last of the basic calculations concerns the depletion and recession times for various values of flow. Then with initiation of the second set and subsequent sets, the water in the tailwater reservoir will be pumped to the head of the field and mixed with the canal supply. Since the soil surface … It is written for professionals who have a solid understanding of basic irrigation and design practices. The computation of depletion time given above is based on the algebraic analysis reported by Strelkoff (1977). 5.7 Summary. et al., 1971). This has been compounded by the fact that a single method is often referred to with different names. Figure 6. The eventual selection will be the one with the best performance over both infiltration conditions. The perimeter dykes need to be well maintained to eliminate breaching and waste, and must be higher for basins than other surface irrigation methods. The change in elevation across the 100 m headland of the field is 0.008 * 100 = 80 cm which is sufficient for the system shown in Figure 54. Field operations. These are generally situations where the value of the crop is very small or the field is used for grazing or recreation purposes. borders Assuming also that the soil is relatively stable, Eq. The first difference is that while the depletion and recession phases are generally neglected in furrow design, both phases must be included for borders.