Infrastructure Engineering - Theses
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ItemMeasurement and modelling of irrigation channel seepage in northern Victoria( 1993)The earthen irrigation channel network in northern Victoria is operated and maintained by the Rural Water Corporation of Victoria. Water tables are now within 2 m of the surface throughout a large part of the irrigated area in northern Victoria. Groundwater accessions from seepage losses from earthen irrigation channels contribute to these high water tables and the associated problems of salinisation and water logging. Seepage tests using a pondage method were performed on two irrigation channels near Tatura (36° 26’ S, 145° 16’E) in north-central Victoria. Testing took place over two irrigation seasons (1989-90 and 1990-91) at both channel sites (Tatura East and Dhurringile). Testing also took place during a third irrigation season (1991-92) at the Tatura East site. This study is the most extensive of its kind ever completed within an Australian irrigation system. Seepage rates were calculated for all seepage tests performed (11 at the Tatura East site; 8 at the Dhurringile site). Seepage losses in the upstream pond of the Tatura East channel varied between 20 and 34 mm d-1. In the downstream pond this variation was 14 to 19 mm d-1 under normal pondage conditions. The difference between channel water level and aquifer head was the most significant factor in determining the seepage loss rate from the channel. The related problem of leakage (loss from the channel through holes in the channel bank) was highlighted in this study. Measurements of leakage losses were made in 5 of the 8 tests at the Dhurringile site and estimates of the relative magnitude of seepage and leakage losses were made. The average seepage loss (not including leakage ) during these five tests varied between 5 and 9 mm d-1. The data collected from the Tatura East site included channel water elevation and groundwater elevation in three piezometer transects perpendicular to the channel. Using these data, an existing computer model employing the boundary integral equation numerical method was modified to simulate the seepage processes occurring at this channel site. Physically based algorithms of deep seepage and net evaporation from the water table were added to the model during this study. Through calibration and validation of the model results to the field observations, the aquifer parameters were determined and the processes involved in the transmission of seepage away from the channel were identified.
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ItemThe evaluation of surge flow in border irrigation (with special reference to cracking soils)( 1993)Surge flow was identified as a potential method of improving farm water management to both reduce water use and minimise accessions to water table, and therefore to help address the salinity and water-logging problems facing the irrigated areas of the Murray-Darling Basin. Surge flow has been intensively researched in furrow irrigation in the USA, but border strips (which are the dominant application method in south-eastern Australia) and cracking soils have received minimal attention. This study investigated surge response in border irrigation with particular reference to cracking clay soils. Two years' field work resulted in a substantial data set covering four soil types and a range of management options. Surge flow reduces water use on cracking clays by 15-40% compared with continuous irrigation under similar conditions and given the same level of management. A negative response was observed on homogenous fine sandy loams, with up to 30% more water applied in surge flow. The positive response was obtained over a range of cycle ratios from 0.2-0.5 and with off-times from 30-300 minutes. Measured soil moisture distributions in the second season showed that application uniformity was better using long offtimes of around 300 minutes. Calculations of the water balance indicate that a greater proportion of applied water is retained in the root zone in surge flow and accessions are a small proportion of those in conventional irrigation. The strong field response was not supported by infiltration test data which recorded greater water intake in surge flow than in continuous tests. The recirculating infiltrometer over-estimated cumulative infiltration for both surge and continuous application, in both seasons. It was later observed that water advances in subsurface cracks in the off-time, up to 70 m ahead of the surface stream. Additional analysis indicates that the surge response is largely due to a mechanism connected with this phenomenon, which helps reconcile the disagreement between field and infiltration test data. Surges overlapped in every test and this phenomenon cannot be simulated by existing hydraulic models of surge flow and substantial revisions are needed before meaningful calibration can be undertaken. The field work provided a clear statement of the difficulty of obtaining infiltration data on cracking soils, and highlights the need for effective real-time estimation of infiltration parameters to overcome severe temporal and spatial variability in infiltration conditions. An inverse solution of the Zero Inertia model was developed, using a constrained Simplex optimisation algorithm to determine infiltration and roughness parameters from advance and depth profile data plus a compound objective function of the two. Global parameters, with reasonably effective predictive performance, were obtained using a compound objective function with continuous flow data sets and, more tentatively, for surge flow. This work provides practical possibilities for automation of border irrigation, using as little as two sensors to determine one roughness and one infiltration parameter from advance data, providing the Kostiakov exponent can be reliably classified. A minimum offour sensors are needed to identify two Simple Kostiakov infiltration parameters and one roughness value. Longer term, farm-scale trials are now required.