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.

<p> Regional climate models project that precipitation in the Great Plains of North America will become characterized by more intense rainfall events separated by longer dry periods. Changing seasonal precipitation patterns may differentially favor grassland productivity in ecosystems dominated by either cool or warm season grass species, and thus influence carbon uptake and loss in these systems. Furthermore, model estimates of ecosystem respiration based primarily on soil temperature could overestimate respiration by failing to account for the effects from saturated conditions during heavy precipitation events. This research contrasted water and carbon fluxes during two years with different intra-annual precipitation within a cool season mixed grassland and compared to a neighboring warm season grassland in Rocky Flats National Wildlife Refuge, Colorado, USA. Results from this study showed a significant positive relationship between the accumulated April/May precipitation and growing season carbon uptake in the cool season, smooth brome-dominated grassland. In addition, significant rainfall in the autumn of 2013 played a role in the early spring growth and carbon uptake in 2014. Comparisons between eddy covariance and soil flux-gradient observations and model estimates of soil respiration showed that during the extreme precipitation event in September 2013, processed-based models better characterized fluxes as compared to empirical models based on soil temperature. The study also found that the cool season grassland was a net sink of carbon during the spring and autumn whereas the neighboring warm season tallgrass prairie was a net sink during the summer. In addition, the study found that the grasslands had considerably different sensitivities to water limitations, with grasses in the tallgrass prairie having a higher water use efficiency (WUE). The comparison of the adjacent semiarid grasslands at Rocky Flats NWR improves our understanding of the response to changing precipitation between cool season and warm season dominated grasslands. This research underscores the importance of expanding grassland research to understand how the composition of grasses will influence carbon cycling, especially as precipitation patterns shift with changing climate. Moreover, this research will add to observations during extreme precipitation events, which can improve both empirical and process-based models of soil respiration.</p>

Work has been successfully performed by the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) to synthesize the nation’s hydrologic data. Through the building of a national Hydrologic Information System, the organization has demonstrated a successful structure which promotes data sharing. While data access has been improved by the work completed thus far, the resources available for discovering relevant datasets are still lacking. In order to improve data discovery among existing data services, a model for the storage and organization of metadata has been created. This includes the creation of an aggregated table of relevant metadata from any number of sources, called a Master SeriesCatalog. Using this table, data layers are easily organized based on themes, therefore simplifying data discovery based on concepts. / text

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.

No description available.

<p> Flow regime, the magnitude, duration and timing of streamflow, controls the development of floodplain landforms on which riparian vegetation communities assemble. Streamflow scours and deposits sediment, structures floodplain soil moisture dynamics, and transports propagules. Flow regime interacts with environmental gradients like climate, land-use, and biomass-removing disturbance to shape riparian plant distributions across landscapes. These gradients select for groups of riparian plant species with traits that allow them to establish, grow, and reproduce on floodplains &ndash; <i>riparian vegetation guilds.</i> Here I ask, <i>what governs the distributions of groups of similar riparian plant species across landscapes?</i> To answer this question, I identify relationships between riparian vegetation guilds and communities and environmental gradients across the American West. In Chapter One, I discuss guild-based classification in the context of community ecology and streams. In Chapter Two, I identified five woody riparian vegetation guilds across the interior Columbia and upper Missouri River Basins, USA, based on species&rsquo; traits and morphological attributes. I modeled guild occurrence across environmental gradients, including climate, disturbance, channel form attributes that reflect hydrology, and relationships between guilds. I found guilds&rsquo; distributions were related to hydrology, disturbance, and competitive or complementary interactions (niche partitioning) between co-occurring guilds. In Chapter Three, I examine floodplain riparian vegetation across the American West, identifying how hydrology, climate, and floodplain alteration shape riparian vegetation communities and their guilds. I identified eight distinct plant communities ranging from high elevation mixed conifer forests to gallery cottonwood forests to <i>Tamarisk</i>-dominated novel shrublands. I aggregated woody species into four guilds based on their traits and morphological attributes: an evergreen tree guild, a mesoriparian shrub guild, a mesoriparian tree guild, and a drought and hydrologic disturbance tolerant shrub guild. Communities and guilds&rsquo; distributions were governed by climate directly, and indirectly as mediated through streamflow. In Chapter Four, I discuss the utility of guild-based assessments of riparian vegetation, current limitations to these approaches, and potential future applications of the riparian vegetation guild concept to floodplain conservation and management. The classification of vegetation into functional trait-based guilds provides a flexible, framework from which to understand riparian biogeography, complementing other models frameworks for riparian vegetation.</p>

<p> This study investigated the effects of riparian vegetation on sediment transport rates and flow dynamics in the South Platte River just downstream of Fort Lupton, Colorado. FaSTMECH, a two-dimensional coupled fluvial and hydraulic model, was used to compute flow characteristics (velocity and depth) in addition to sediment mobility characteristics (shear stress and sediment flux) for four discharge levels ranging from 5% of bankfull flow to bankfull flow (Qbf). Estimates of a dimensionless drag coefficient (Cd) representative of the middle-aged bushy willows found on the river banks at the study site were used to create a spatially variable roughness in the model throughout the river reach. Model results show that during average annual flood events, vegetation on the river banks causes increased drag forces on the flow, leading to an increased proportion of flow being diverted into the main channel and resulting in higher velocities. The spatial distribution of shear stresses collapse under these conditions with an order of magnitude decreases over river banks and significant increases throughout the main channel. Sediment fluxes in the reach increase by nearly an order of magnitude with the presence of bank vegetation, however, the greatest differences occur during Qbf when the highest fraction of the sediment is mobile. Further analysis of vegetation effects was conducted by performing a sensitivity analysis by altering the representative non-dimensional vegetation drag coefficient by as much as +/- 400%. These alterations represent differences in vegetation density, height, orientation, leafy/leafless structure, age, rigidity, and vegetation type. Although there is a relationship between sediment fluxes and changes in Cd, there only exists a 14% increase in transport at Qbf between the two exterior limits of Cd.</p>

<p> The traditional paradigm of baseflow generation assumes a uniform water table contributes baseflow evenly across a watershed. This thesis considers an alternate paradigm in which baseflow originates from a mix of localized sources that drain at different rates. Four forested headwater catchments across the United States were examined for spatial variability in baseflow sources by analyzing fractional baseflow contribution from each subcatchment relative to the catchment outlet. This revealed that subcatchment flow contributions changed dynamically through time, supporting the idea of different drainage rates in different places. A parallel linear reservoir model, which is predicated on heterogeneity in flow sources and not groundwater hydraulics, was used to simulate results consistent with observations in some of the study catchments. These results support the idea that in some locations baseflow recession may be better explained by landscape spatial heterogeneity than by aquifer hydraulics. </p>

<p> This dissertation combines field and laboratory work to examine how delta hydrology and sedimentology affects trace element cycling in marsh porewaters. This work was prompted by our lack of understanding of the hydrogeochemistry in the lower Mississippi Delta and how biogeochemical reactions affect fluxes of groundwater constituents to the ocean. In particular, I measured the concentrations of a suite of redox-sensitive trace elements (Fe, Mn, V, As) to determine the dominant geochemical reactions operating in marsh aquifers. </p><p> Because much more is known about As, I first conducted a study comparing V geochemistry along flow paths in a reducing sand aquifer in Texas and an oxidizing bedrock aquifer in Nevada. In agreement with other studies, V concentrations are much higher under oxidizing alkaline conditions. Under the reducing, circumneutral conditions of the Carrizo Sand aquifer, V concentrations are low but relatively constant, owing to complexation with dissolved organic matter. Similar observations regarding V geochemistry are observed in marsh groundwaters. Specifically, in pore waters of organic-rich sediment experiencing sulfate-reducing conditions, V concentrations are high owing to V complexation with organic matter, whereas in coarser-grained sediments, V may be removed from solution by adsorption. Arsenic geochemistry in pore waters varies as a function of depth. In the shallow subsurface, As concentrations are high and stabilized in solution by formation of thioarsenates. At depth, As appears to be sequestered through coprecipitation with pyrite.</p>