Determination of Manning Roughness Coefficient for Border Irrigation System

Abstract

Manning roughness coefficient "n" is one of the most important factors affecting the border irrigation design. The purpose of this study is to determine the Manning roughness coefficient values "n" for border irrigation in a clay loam soil with compacted and uncompacted soil under continuous and surge flow. The determination was based on the volume balance equation in the form of a differential equation that was solved with the forward finite difference. The results indicated that, soil surface compaction had its effect on n values of the first irrigation and had not any effect for the next irrigations. For continuous flow, at first irrigation, the values of n were 0.1915 and 0.164 for un-compacted and compacted soils respectively. At the second irrigation, the n values decreased by about 44.51% and 49.82% compared to the first irrigation for compacted and un-compacted soil respectively. However, after the second irrigation, the seedling of wheat resulted on increases the n values. The minimum value, 0.083, of n was achieved at the second irrigation for surge flow. While, the maximum value, 0.25, of n was found at the seventh irrigation for continuous flow. Also, by using surge flow, the n values were decreased compared with those for continuous flow without vegetation crop or with wheat crop.