DEVELOPMENT OF MUSKINGUM-CUNGE ROUTING MODEL FOR DESIGN AND EVALUATION OF FURROW IRRIGATION

Abstract

Surface irrigation projects which account for almost all of the irrigated land areas of the world has been studied extensively by many investigators and their performance was found to be lower than expected. Many of these projects are constructed and operated without adequate technical input, with consequent low uniformity and efficiency of water application. However, irrigators are still faced with significant challenges in making both design and operation of surface irrigation systems more .efficient Data used in this study was collected from irrigations conducted at Kenana Sugar State site as reported in (Abd el Wahab, 2000) during the .1997-98 and 1998-99 irrigation seasons In this study a mathematical design approach for furrow irrigation was developed as spreadsheet model to simulate all hydraulic phases of water movement as an aid to design and to evaluate the performance of furrow irrigation. The irrigation model simulates the hydraulics of furrow irrigation at the field scale. The principal role of the model is the evaluation of alternative field layouts (field length and slope) and management .(practices (water application rates and cut-off times Input data requirements for the simulation component include field length, slope, infiltration characteristics (or advance data), target application depth, water application rate, Manning’s resistance and furrow geometry. A series of simple relations were presented for estimating the advance and recession phase, and performance of surface irrigation systems. The approach uses continuity equation to compute the advance time to field end and to half the distance to field end. The irrigation methods differ slightly in how the surface storage volume is computed. Initially a surface shape factor 7 is used to compute storage volume during advance phase; however, estimation of this storage volume was corrected during storage, depletion and recession phases by utilizing Muskingum-Cunge routing method. The subsurface volume calculations use a modified Kostiakov equation that includes both an initial sink term and a constant final infiltration rate. Recession calculations differ for each method. With sloping methods, adjustments to a straight line recession curve make recession estimates more reasonable. It is shown that the procedure can generate reasonable predictions of design performance over a range of conditions. Model verification was made by its comparison with FAO-surface-model, and zero-inertia model. Model application was is provided to put the method and its application into context by evaluating application efficiency for the .cases of short, medium and long furrows of Kenana Sugar Scheme Output includes a detailed advance-recession trajectory, distribution of infiltrated water, volume balance, run-off hydrograph, depth of water flow at the end of the field. In addition, a set of irrigation performance indicators (distribution uniformity, application efficiency, tail water ratio, and deep percolation ratio and deficit coefficient) is calculated, assuming that the infiltrated water follows a normal frequency distribution. In Kenana Scheme State the storage efficiency was found to be unsatisfactory, hence, .it suggested through model simulation to adjust the cut off time The approach is also conducive to sensitivity analysis for determining the impact of variations in input parameters on performance. Hence, model sensitivity to explore optimum operating polices for Kenana Sugar Scheme was made by running different scenarios of expected water application depths, inflow rates and furrow lengths. Study conclusions and recommendations for policy making and future research are summarized in .an ending chapter of the study