Advances in mathematical modelling and the availability of high speed computers with considerable memory size is making it possible to study the hydraulics of border irrigation in a greater depth than every before. A zero inertia mathematical model was found to be reliable and inexpensive among the models available in border irrigation hydraulics and was used for this study to simulate free outflow flowing border irrigation. Special emphasis was given to the runoff produced from such a system. This study dealt particularly with, the identification of pertinent open channel variables affecting runoff in border irrigation, presentation of predictive graphical and mathematical solution to quantify runoff, and with utilization of these solutions in developing reuse system design criteria. Inflow rate, surface resistance, border slope, soil infiltration characteristics, application time (time of cutoff and length of run of the border) were among other variables studied. As one might expect, runoff was found to increase with slope, flow rate, application time and decrease with increase in infiltration rate, length of run and bed and vegetation drag. Considering the number of variables affecting runoff characteristics from a given irrigation, it was obvious to see a thorough examination of each variable in dimensional terms was practically impossible. Also, presentation of the results would have required too many graphs. Dimensional anslysis was used to solve this problem and in developing dimensionless runoff curves. The ability to quantify runoff made it possible to develop reuse system design formula for proper sizing of reuse systems under several operational requirements. Shape function for the ultimate infiltrated depth profile was used to get times of runoff and also calculate various efficiencies which are useful for evaluating the system. The study shows, through the use of reuse system, the potential application efficiency can be changed from present values of 60 percent to 90 percent in Arizona. It also can be used to demonstrate the saving in energy that can be realized through such system. Step by step procedures for the design of reuse system using graphical and mathematical solutions are presented with a sample problem worked out. It is expected that the result of this study can be used by designers as well as operators of border irrigation systems without any difficulty with the aid of a simple pocket calculator. Other uses of the study include getting optimal design for the system itself by evaluating various possible designs and classroom instruction on the application of dimensional analysis to open channel hydraulics problems and design of reuse systems.

Exploitation of groundwater and excess nutrient runoff are major issues plaguing agriculture and streams in the Lower Mississippi River Basin, and increased irrigation intensity has yielded a proportionate increase in water use. Quantifying the use and effects of conservation practices like on-farm water storage (OFWS) systems will justify continued adoption of these practices to mitigate groundwater decline and nutrient runoff. Since 2010, over 795 hectares of surface water storage has been added in the Big Sunflower River Watershed, and analysis of aquifer saturation shows a recent rise in the water table and a decrease in seasonal water table drawdowns. Modeling pre- and post- construction conditions of a small agricultural subwatershed shows little difference in runoff at the watershed outlet after the construction of an OFWS system, but field monitoring and modeling show more water retained within the system and the importance of management to maximize the benefits of conservation practices.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agronomy))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

Graduation date: 1990