Infrastructure Engineering - Theses
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ItemA methodology for estimating yield from small ungauged rural catchments( 1991)An estimate of streamflow yield from ungauged catchments is often required by water management Authorities. A survey of Authorities indicated that the techniques used in computing streamflow yield from small ungauged rural catchments were limited to a range of empirical methods with questionable accuracy. There is clearly a need to develop a more reliable simplified methodology. The proposed methodology is based on the calibration of a rainfall-runoff model using a number of gauged catchments and the development of regression relationships between catchment physiographical characteristics and model parameters. The parameters are then used in conjunction with the rainfall-runoff model and meteorological observations to estimate streamflow yield from ungauged catchments. The 2-parameter rainfall-runoff model (MOSAZ) was developed only after a detailed study of actual evapotranspiration and parameter optimisation. Morton's model, based on Bouchet's complementary theory, proved to be an adequate method to calculate actual evapotranspiration from catchments. The model was tested with data from forested, native pasture and irrigated wheat catchments. The model is considered to be superior to methods based on pan evaporation as the actual evapotranspiration predicted using Morton's model is independent of the catchment cover and the prevailing soil moisture conditions in the catchment. A number of optimisation techniques based on direct search and gradient methods were tested for accuracy. From the methods tested, the pattern search and the Gauss-Marquardt algorithms proved to be superior. The interaction between satisfactory compliance with simple least squares error assumptions and the goodness-of-fit between observed and predicted streamflow was also studied. An important feature of the proposed methodology is the use of a multi-dimensional plotting routine termed Andrews' curves to separate the 184 catchments in the study region into a number of hydrologically homogeneous groups based on catchment physiographical characteristics which are related to MOSAZ model parameters. Regression relationships between MOSAZ model parameters and catchment physiographical characteristics were developed for one homogeneous group of catchments based on information from 17 catchments. The developed regression relationships were used to calculate streamflow from four test catchments to demonstrate the applicability of the developed methodology. As the results appeared promising, it is possible to extend the developed methodology to other homogeneous catchment groups.
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ItemSoil moisture and hydrology of the basalt plains of Western Victoria: a field and computer study of surface hydrology( 1979)This is a field and digital model study of surface hydrology. An attempt is made to relate field measurements to the assumptions of a physically-based deterministic rainfall-runoff model that has been proposed for widespread use in Australia. A major part of the field study was the measurement and interpretation of soil moisture contents obtained with a neutron moisture meter, and two methods were developed and used to provide calibrations appropriate to both locally variable soils and the large (55 km2) study area. Independent estimates of each of the major components of the water balance were made, utilizing data collected on the study by other authorities. Further measurements of field parameters were made to provide independent estimates of the appropriate parameter values for the digital model. A single year of data was used for development of the model and final selection of the parameter values. The prediction of the observed streamflow was used as the basis for this testing, and the hydrological validity of the assumptions upon which the model is based was then tested by a comparison of the internal prediction and the independent measurements of soil moisture contents. The model was found to behave reasonably well, but deficiencies in some of the algorithms were identified. A sensitivity analysis showed that the concept of an infiltration capacity is not important for runoff generation on this catchment, and that the spatial variability of the moisture holding capacity of the soil makes it virtually impossible to estimate this model parameter from field measurements alone. It was found that a simple approximation to this spatial variability provided a more realistic annual hydrograph, and reduced the accuracy required to determine the mean value of this moisture storage capacity from field measurements. The main conclusions are that deterministic models offer a useful approach to the understanding of surface hydrology, although further development is required before the parameter values for such a model can be determined solely from field measurements. The use of the field measurements and the model showed that the hydrology of this catchment is dominated by a nearly impermeable B horizon, that the concept of an infiltration capacity is irrelevant to the generation of storm runoff, and that the spatial variation of the moisture holding capacity of the soil is important. Particular topics for further study include the acceptance of spatial variability in the other algorithms of the model, and the hydrological validation of this and other models on other catchments.
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ItemTerrain-based hydrologic modelling for erosion studies( 1990)A hydrologic model is developed that enables the simulation of surface runoff by both infiltration excess and saturated source area mechanisms. The model, known as THALES, is designed to take advantage of the TAPES-C analysis of topography (Moore and Grayson, 1990). The TAPES-C analysis represents complex three dimensional terrain in a manner that allows the one dimensional form of the equations for water flow to be applied in THALES. The basic equations used to represent subsurface and saturation overland flow processes are tested on data collected from a laboratory sandbed. THALES is then applied to a 7 ha field site at Wagga Wagga in New South Wales, Australia, using published parameters and field measurements collected as part of an extensive field programme. The fit of the outflow hydrograph for a series of storms is fair for the runoff peaks but poor during periods without rain. The simulated position and growth of saturated areas coincide with the limited available information, indicating that at least the gross effects of subsurface water movement are being represented. While the predictive capacity of the model was relatively poor for the Wagga Wagga site, its use enhanced the analysis of the data by providing a quantitative framework for our conceptual understanding of catchment behaviour. THALES is also applied to an arid catchment in Arizona, U.S.A. where the hydrologic response is dominated by infiltration excess overland flow. The hydrographs at the catchment outlet and at two points within the catchment are simulated for a storm series. The results are highly dependent on the parameter values, which are poorly defined. This application of the model highlights the lack of measured field data and lack of methodology for the collection of data at a scale appropriate for modelling. THALES is used to examine the effect of different surface representations on estimates of distributed flow characteristics. The results show a wide variation in simulated response depending on whether surface flow is represented as sheet, rill or ephemeral gully flow. This highlights the uncertainty associated with the application of physically-based, hydrologic models in a predictive sense. The distributed flow estimates are a function of both the model structure as well as the parameter values. The interaction between model parameter values and model structure is illustrated by several examples. While a new model is presented, this thesis is primarily concerned with the wider issues relating to model use and with identifying, through example, some barriers to the improvement in modelling of small catchment hydrology with distributed parameter, process-based models. The problems identified relate to both the perception of model capabilities and the fundamental assumptions and algorithms used in model development. It is argued that many of the current hydrologic models cannot be used for predictive purposes in a physically realistic sense, because of uncertainty in the parameter values and errors in their basic process descriptions. The strength of these models is as analytical tools to be used in association with field data and to assist in the development of a quantitative understanding of catchment behaviour. The major limits to the development of physically-based models are listed as (i) our inability to represent the basic processes at a scale appropriate to the level of information required from the model, and (ii) the lack of field data and methodology for the collection of both input data and data suitable for validation, at the scale appropriate for the models. These conclusions indicate that a much closer relationship between model development and studies into the underlying processes defining catchment response is necessary.