Surface runoff is one of the most important problems which occur with moving sprinkler irrigation systems: it is particularly severe in centre pivot systems operated at low pressure. The consequences of surface runoff are waste of water, lower irrigation efficiency, soil erosion and removal of fertilizers from the field. An obvious indicator of the potential for runoff to occur during sprinkler irrigation is the appearance of surface ponding. Indeed, results from a stationary "time to ponding" test (using a minimum set of three constant water application rates) carried out on the farm, is commonly used to determine the irrigation rate in moving systems. This practice sometimes leads to the occurrence of runoff under moving systems, particularly centre pivot systems. / The primary aim of the investigation was to explore the phenomenon of soil surface ponding in stationary "time to ponding" tests (using constant water application rate) and in moving sprinkler irrigation systems (using variable water application rate), and to discover the relationship between these two sets of conditions, in order to improve the design and managements of these systems and avoid runoff. / A vital component of the investigation was the development of a laboratory rig which incorporated certain characteristics and properties, including: A special soil test bed containing 355mm depth of a loamy sand soil, together with a system continuously measuring and monitoring soil moisture content. The rig also included heating and suction systems to reduce and establish target soil moisture conditions before each test, and an efficient drainage system. Ponding was identified in 15 circular depressions on the soil surface. A water application simulator capable of being operated in both stationary and moving modes at different speeds, applying different constant and variable irrigation rates to the soil test bed with very small droplets. The nature of the supply closely approximated that of field installations. A continuous water application measurement device capable of measuring instantaneous water application rate and pattern as well as irrigation depth applied to the soil test bed. / Certain parameters, of necessity, were fixed for the investigation: these included the soil, the type of variable application pattern (parabolic), the range of speeds of the moving simulator (10% to 100% of maximum speed which was 345mm/minute) and the range of initial soil moistures (3% up to field capacity). Initial tests were carried out to determine a suitable water application rate: this was set as 103mm/h (average). The main set of tests was carried out using this average application rate under constant ("time to ponding") and variable ("onset of ponding") irrigation conditions at different soil moisture contents. / The main outcome of the research was that the maximum irrigation depth that can be applied by a moving system (variable pattern) without the appearance of ponding for any set value of initial soil moisture, is significantly less than the maximum irrigation depth which must be applied to produce ponding in a stationary system (constant pattern), operated with the same initial soil moisture and same average application rate. Therefore, the results obtained from a “time to ponding” test, if applied directly, overestimate the optimum water application rate and also the maximum irrigation depth which can be applied in moving irrigation systems, if they are to operate efficiently. / A relationship was established between the two sets of outcomes for corresponding soil and water application rate and pattern conditions. The apparatus and the method can be used for further research to discover similar relationships for different soil types and different water application rates and patterns in order to provide a general model. This model can be used to modify the optimum water application rate (obtained directly from stationary "time to ponding" tests) and, also, the maximum irrigation depth (through choice of speed appropriate to the initial soil moisture) in moving sprinkler irrigation systems, particularly in centre pivot systems. / Thesis (PhDCivilEngineering)--University of South Australia, 2005.
| Identifer | oai:union.ndltd.org:ADTP/267531 |
| Creators | Fathollahzadeh, Fardad. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
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