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The format and content of this dissertation has been structured to meet the written and implicit ... more The format and content of this dissertation has been structured to meet the written and implicit requirements of the University of Southern Queensland's Engineering Doctorate and to demonstrate the levels of innovation and intellectual excellence expected of any doctorate. The research reported in this dissertation was initiated by hydrological design and analysis challenges encountered professionally, predominantly in developing data scarce regions of the world. The research spans four themes; catchment yield, catchment (spatial) rainfall synthesis, flood and contaminant routing, and the variance damping characteristics of linear storage. The overarching notion across all these themes is that with limited calibration data simple parsimonious models provide the highest predictive reliability. My first boss Doug Foster, Director of the UNSW Water Research Laboratory. An Engineer who understood learn by doing. My principal supervisor Dr Ian Brodie for his critical analysis, careful review, helpful suggestions and purposeful encouragement. My co-supervisor Dr Nigel Hancock for his objective review. My colleague Don Carroll for his professional review of a number of the Research Reports and willingness to be a sounding board for ideas and concepts. To all the Engineering and Scientific Hydrologists who freely provided their hard won data. Deborah Davis for words, equations, tables, figures, drawings and infinite good humour.
Water Resources Research, 1976
Many methods of estimating design floods from rainfall data involve a trial and error procedure t... more Many methods of estimating design floods from rainfall data involve a trial and error procedure to determine the duration of the design rainfall. An analytical expression for estimating the appropriate duration for use with a particular unit hydrograph is derived. This analytical expression permits the effects of other parameters significant to the estimation of the design flood, such as different storm characteristics, to be evaluated with ease. The analytical approach has considerable flexibility in that the mathematical expression linking unit hydrograph and rainfall characteristics permits the independent adjustment of one of the sets of characteristics. This is particularly advantageous where some form of dimensionless unit hydrograph is available for flood estimation. It means that storm characteristics may be varied from watershed to watershed without any changes being required in the expression for the unit hydrograph. A 'flexible' dimensionless unit hydrograph is also developed. INTRODUCTION Deterministic methods of design flood estimation such as the methods of Chow [1962] and the U.S. Department of Agriculture Soil Conservation Service [1964] aim to represent the interaction of rainfall and watershed characteristics. Both sets of characteristics are, in general, nonlinear, and consequently, an exact solution is difficult to obtain, even if the inputs are accurately known. To date no analytical solution has been developed which allows for the nonlinear characteristics of the design rainfall. The engineering approach has been to combine nonlinear rainfall characteristics with assumed linear watershed characteristics. In practice this involves the use of one of the many design procedures based on the unit hydrograph concept, e.g., the U.S. Department of Agriculture Soil Conservation Service [1964], Chow [1962], Pullen [1969], and Cordery and Webb [1974] methods. Each of these methods involves, by some trial and error procedure, the determination of the design storm duration which will maximize the peak discharge. The importance of this maximization procedure is well illustrated in Figure 1. An analytical expression for the critical storm duration will be developed for the case of nonlinear rainfall characteristics COmbined with linear watershed characteristics. The expression will then be used to consider the importance of several rainfall and hYdrograph characteristics in design flood estimation under thes e unit hydrograph type conditions. The special condition under which this expression for critical storm duration may be extended to nonlinear watersheds is also defined. THEORY Under linea r conditions the peak discharge of the D-hour unit hydrograph for a given watershed decreases as the'rainfall duration D increases. Conversely, for design rainfall of a specified return period th e depth of gross rainfall increases as the rainfall duration increases. The design peak discharge resulting from a storm of a particular duration D can be determined by simply multiplying the D-hour unit hydrograph peak discharge by the design depth of excess rainfall of duration D. For example, suppose that the peak discharge of the 2-hour Copyright ¸ 1976 by the American' Geophysical Union. unit hydrograph (unit depth equal to 1 mm) was 10 ma/s and the design storm excess for a duration of 2 hours was 70 mm, then the design peak discharge resulting from this 2-hour duration storm would be 70 X 10 = 700 ma/s. The storm duration which maximizes the peak discharge determined in this manner is the critical storm duration for a temporally uniform storm. 2, 23-46, 1971. U.S. Department of Agriculture Soil Conservation Service, Hydrology-watershed planning, in National Engineering Handbook, sect. 4,
The format and content of this dissertation has been structured to meet the written and implicit ... more The format and content of this dissertation has been structured to meet the written and implicit requirements of the University of Southern Queensland's Engineering Doctorate and to demonstrate the levels of innovation and intellectual excellence expected of any doctorate. The research reported in this dissertation was initiated by hydrological design and analysis challenges encountered professionally, predominantly in developing data scarce regions of the world. The research spans four themes; catchment yield, catchment (spatial) rainfall synthesis, flood and contaminant routing, and the variance damping characteristics of linear storage. The overarching notion across all these themes is that with limited calibration data simple parsimonious models provide the highest predictive reliability. My first boss Doug Foster, Director of the UNSW Water Research Laboratory. An Engineer who understood learn by doing. My principal supervisor Dr Ian Brodie for his critical analysis, careful review, helpful suggestions and purposeful encouragement. My co-supervisor Dr Nigel Hancock for his objective review. My colleague Don Carroll for his professional review of a number of the Research Reports and willingness to be a sounding board for ideas and concepts. To all the Engineering and Scientific Hydrologists who freely provided their hard won data. Deborah Davis for words, equations, tables, figures, drawings and infinite good humour.
Water Resources Research, 1976
Many methods of estimating design floods from rainfall data involve a trial and error procedure t... more Many methods of estimating design floods from rainfall data involve a trial and error procedure to determine the duration of the design rainfall. An analytical expression for estimating the appropriate duration for use with a particular unit hydrograph is derived. This analytical expression permits the effects of other parameters significant to the estimation of the design flood, such as different storm characteristics, to be evaluated with ease. The analytical approach has considerable flexibility in that the mathematical expression linking unit hydrograph and rainfall characteristics permits the independent adjustment of one of the sets of characteristics. This is particularly advantageous where some form of dimensionless unit hydrograph is available for flood estimation. It means that storm characteristics may be varied from watershed to watershed without any changes being required in the expression for the unit hydrograph. A 'flexible' dimensionless unit hydrograph is also developed. INTRODUCTION Deterministic methods of design flood estimation such as the methods of Chow [1962] and the U.S. Department of Agriculture Soil Conservation Service [1964] aim to represent the interaction of rainfall and watershed characteristics. Both sets of characteristics are, in general, nonlinear, and consequently, an exact solution is difficult to obtain, even if the inputs are accurately known. To date no analytical solution has been developed which allows for the nonlinear characteristics of the design rainfall. The engineering approach has been to combine nonlinear rainfall characteristics with assumed linear watershed characteristics. In practice this involves the use of one of the many design procedures based on the unit hydrograph concept, e.g., the U.S. Department of Agriculture Soil Conservation Service [1964], Chow [1962], Pullen [1969], and Cordery and Webb [1974] methods. Each of these methods involves, by some trial and error procedure, the determination of the design storm duration which will maximize the peak discharge. The importance of this maximization procedure is well illustrated in Figure 1. An analytical expression for the critical storm duration will be developed for the case of nonlinear rainfall characteristics COmbined with linear watershed characteristics. The expression will then be used to consider the importance of several rainfall and hYdrograph characteristics in design flood estimation under thes e unit hydrograph type conditions. The special condition under which this expression for critical storm duration may be extended to nonlinear watersheds is also defined. THEORY Under linea r conditions the peak discharge of the D-hour unit hydrograph for a given watershed decreases as the'rainfall duration D increases. Conversely, for design rainfall of a specified return period th e depth of gross rainfall increases as the rainfall duration increases. The design peak discharge resulting from a storm of a particular duration D can be determined by simply multiplying the D-hour unit hydrograph peak discharge by the design depth of excess rainfall of duration D. For example, suppose that the peak discharge of the 2-hour Copyright ¸ 1976 by the American' Geophysical Union. unit hydrograph (unit depth equal to 1 mm) was 10 ma/s and the design storm excess for a duration of 2 hours was 70 mm, then the design peak discharge resulting from this 2-hour duration storm would be 70 X 10 = 700 ma/s. The storm duration which maximizes the peak discharge determined in this manner is the critical storm duration for a temporally uniform storm. 2, 23-46, 1971. U.S. Department of Agriculture Soil Conservation Service, Hydrology-watershed planning, in National Engineering Handbook, sect. 4,