Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2007. / Includes bibliographical references (p. 43-46).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 149-153). Also available in electronic version.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains viii, 95, 55 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: David R. Maidment. Vita. Includes bibliographical references.

Thesis (M.S.)--University of Montana, 2007. / Title from title screen. Description based on contents viewed July 31, 2007. Includes bibliographical references (p. 86-94).

The problem of selecting appropriate mathematical models for use in studying hydrological phenomena has created a situation in which the choice of suitable models by hydrologic practitioners has become exceedingly complex. The extensive comments in the literature indicate that neither the traditional system of technical journals nor the more modern computer -based retrieval schemes have really solved the problem. Further examination shows that similar problems have arisen in many fields, hence a well organized attack on the specific problem of hydrologic model choice can have a more general application. The present problem is identified as a requirement to codify and make accessible to users information in a more directly user oriented format. The problem of model choice arises at several levels, ranging from decision on what fundamental structure to use, to choice of parameters, and on to model calibration and validation. This paper is focused on a scheme to aid in model structure choice. The essential ingredients of model structure choice, and indeed of many choice processes, are extracted and embedded in a generalized set theoretic mathematical notational framework in order to give some insight into the nature of the problem. Within this framework the specialized features of the model choice problem are analyzed, and a specialized model is developed for assisting in model choice and all problems similarly situated. These considerations lead to the development of a finite vector of objective statements with codified responses prepared by a panel of qualified researchers who are willing and able to construct the essential information in a user oriented format. It is required that the panel not only couch their information in objective oriented terms but that they also generate value judgments for the individual components. In this way, those using the system can take advantage of the expert opinions embedded in the model while, at the same time, tailoring the choice to meet their own specific needs and aspirations. This results in what is defined as a mathematical CHOICEMODEL. The implementation of a system for interactive computation of the CHOICEMODEL is described in detail, and the associated computer programs are presented in appendices. A detailed instruction manual is given, and the implementation of the method is illustrated by an easily understood model of the ingredients of the problem of selecting an 8 -track stereo tape deck for home use. The plan is outlined whereby hydrologic choice models can be developed within the CHOICEMODEL system by a selected panel of expert EVALUATORs.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 142-155).

Submitted in fulfillment of the requirements of the Degree of Master of Technology: Civil Engineering, Durban University of Technology, 2014. / Streamflow modelling remains crucial to decision-making especially when it concerns planning and management of water resources systems in water-stressed regions. This study proposes a suitable method for streamflow modelling irrespective of the limited availability of historical datasets. Two data-driven modelling techniques were applied comparatively so as to achieve this aim. Genetic programming (GP), an evolutionary algorithm approach and a differential evolution (DE)-trained artificial neural network (ANN) were used for streamflow prediction in the upper Mkomazi River, South Africa. Historical records of streamflow and meteorological variables for a 19-year period (1994- 2012) were used for model development and also in the selection of predictor variables into the input vector space of the models. In both approaches, individual monthly predictive models were developed for each month of the year using a 1-year lead time. Two case studies were considered in development of the ANN models. Case study 1 involved the use of correlation analysis in selecting input variables as employed during GP model development, while the DE algorithm was used for training and optimizing the model parameters. However in case study 2, genetic programming was incorporated as a screening tool for determining the dimensionality of the ANN models, while the learning process was further fine-tuned by subjecting the DE algorithm to sensitivity analysis. Altogether, the performance of the three sets of predictive models were evaluated comparatively using three statistical measures namely, Mean Absolute Percent Error (MAPE), Root Mean-Squared Error (RMSE) and coefficient of determination (R2). Results showed better predictive performance by the GP models both during the training and validation phases when compared with the ANNs. Although the ANN models developed in case study 1 gave satisfactory results during the training phase, they were unable to extensively replicate those results during the validation phase. It was found that results from case study 1 were considerably influenced by the problems of overfitting and memorization, which are typical of ANNs when subjected to small amount of datasets. However, results from case study 2 showed great improvement across the three evaluation criteria, as the overfitting and memorization problems were significantly minimized, thus leading to improved accuracy in the predictions of the ANN models. It was concluded that the conjunctive use of the two evolutionary computation methods (GP and DE) can be used to improve the performance of artificial neural networks models, especially when availability of datasets is limited. In addition, the GP models can be deployed as predictive tools for the purpose of planning and management of water resources within the Mkomazi region and KwaZulu-Natal province as a whole.

The problem of selecting appropriate mathematical models for use in studying hydrological phenomena has created a situation in which the choice of suitable models by hydrologic practitioners has become exceedingly complex. The extensive comments in the literature indicate that neither the traditional system of technical journals nor the more modern computer-based retrieval schemes have really solved the problem. Further examination shows that similar problems have arisen in many fields, hence a well organized attack on the specific problem of hydrologic model choice can have a more general application. The present problem is identified as a requirement to codify and make accessible to users information in a more directly user oriented format. The problem of model choice arises at several levels, ranging from decision on what fundamental structure to use, to choice of parameters, and on to model calibration and validation. This paper is focused on a scheme to aid in model structure choice. The essential ingredients of model structure choice, and indeed of many choice processes, are extracted and embedded in a generalized set theoretic mathematical notational framework in order to give some insight into the nature of the problem. Within this framework the specialized features of the model choice problem are analyzed, and a specialized model is developed for assisting in model choice and all problems similarly situated. These considerations lead to the development of a finite vector of objective statements with codified responses prepared by a panel of qualified researchers who are willing and able to construct the essential information in a user oriented format. It is required that the panel not only couch their information in objective oriented terms but that they also generate value judgments for the individual components. In this way, those using the system can take advantage of the expert opinions embedded in the model while, at the same time, tailoring the choice to meet their own specific needs and aspirations. This results in what is defined as a mathematical CHOICEMODEL. The implementation of a system for interactive computation of the CHOICEMODEL is described in detail, and the associated computer programs are presented in appendices. A detailed instruction manual is given, and the implementation of the method is illustrated by an easily understood model of the ingredients of the problem of selecting an 8-track stereo tape deck for home use. The plan is outlined whereby hydrologic choice models can be developed within the CHOICEMODEL system by a selected panel of expert EVALUATORS.

The use of trichlorofluoromethane (C1₃CF) as a refrigerant, aerosol-can propellant, and foam-blowing agent leads to the subsequent release of C1₃CF into the atmosphere. During the mid-1970's, the build-up of C1₃CF in the stratosphere resulted in much atmospheric research investigating the destruction of the earth's ozone layer by C1₃CF. C1₃CF enters the hydrologic cycle during precipitation. Hydrologic investigations led to the detection of C1₃CF in ground water and postulation of C1₃CF as a tracer and age dating technique. The Edwards Aquifer in the vicinity of San Antonio, Texas, was chosen as a test case for demonstration of C1₃CF as an environmental tracer. The aquifer has been modeled for mass transport using extensive tritium measurements to calibrate and verify a discrete-state model (DSM). The DSM was the first successful attempt at modeling both flow and mass transport in that aquifer. Without changing the calibration, the DSM was used to model the input-output and predict the concentration of C1₃CF in the aquifer. Field sampling of surface water, well discharge, springs, and the atmosphere was done in 1977 in order to compare actual with predicted results. C1₃CF was measured using a custom field operable gas chromatograph (FOGC). The FOGC has a solute-stripping bottle, a backflushing column, a pulsed electron capture detector, and an automatic peak-window integrator. The theoretical detection limit is 10⁻⁴ grams per second. The FOGC was calibrated for a dynamic range of 0.25 to 300 picograms, using a permeation tube and dynamic gas sampler. The FOGC can measure C1₃CF in ground waterat concentrations of 0.01 picograms per milliliter (pg/ml) within 2 percent. Analysis and interpretation of the ground-water data indicated two distinct associations -- regional data points and plume data points. The regional data points fell into two separate groups, those above and those below the lower calibration limit. The data points were high in the recharge areas, intermediate in the center of the aquifer, lower at the discharge points (springs), and below the calibration limit in areas of low circulation in the aquifer. Comparison of the regional data with other investigations indicates that the C1₃CF technique works. The data points in the plume area indicate artificial introduction of C1₃CF into the aquifer near San Antonio. The distribution of the concentrations follows the flow paths toward the springs and confirms the movement of ground water as determined from previous investigations utilizing other techniques. The artificial introduction of C1₃CF may have been accidental or intentional. It appears that about 15 liters C1₃CF would be required to produce the concentrations detected. Air sample concentrations of C1₃CF (0.42 pg/ml) were about half those reported for recent global measurements. Surface water concentrations of C1₃CF (0.12 pg/ml) were very close to recent global measurements (0.13 pg/ml), but below the input to the model (0.34 pg/ml). The data indicate that the C1₃CF technique is workable in the Edwards Aquifer and should be in other systems containing water recharged during the last 30 years. The consistency of the data indicates that the technique probably is more usable than tritium because of the much simpler input function. The FOGC is appealing because of its portability, low cost, and ease of operation.