Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008. / Full text also available online. Scroll down for electronic link.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. David E. Loper, Florida State University, College of Arts and Sciences, Geophysical Fluid Dynamics Institute. Title and description from dissertation home page (viewed Jan 14, 2005). Includes bibliographical references.

Magister Scientiae - MSc / The Western Klein Karoo-Montagu area is located in the mid-eastern of the Western Cape Province , South Africa. In most of the study areas within semi-arid climatic zone , groundwater plays an important role in meeting both agricultural and urban water requirements. Developments of agriculture depend on more and more groundwater supply from Table Mountain Group (TMG) sandstone aquifer system in the study area. Groundwater recharge is considered as one of the most important factors governing the sustainable yield of groundw ater exploitation. There have been few studies on the recharge estimation of the TMG aquifer system in the Montagu area. Thus accurate and reliable recharge estimation of the TMG aquifer system in the Montagu area is important. The TMG aquifer in the Montagu area comprises approximate 4,000m thick sequence of sandstone with an outcrop area of 3,124 km2, which is recharge area. The outcrops are characterized by mountainous topography with sparse to dense vegetation, shallow and intermittent diverse soils and mean annual rainfall of 350-450 mm/yr. Based on detail analysis and interpretation of factors influencing recharge, water balance method is used to estimate recharge rates by using readily available data (rainfall, runoff, temperatures). Other estimate methods are difficult to be applied due to the limited information available in the study area. In this study, the water balance approach based on empirical evapotranspiration and runoff model is employed to determine and analyse long-term average water recharge. The long-term average recharge is modelled as a function of the regional interaction of the site conditions: climate, soil, geology and topography. Modelling is performed according to the outlined procedure using long-term climatic and physical data from the different rainfall period of different gauge stations. As results, actual evapotranspiration, direct runoff and recharge have been quantified. The recharge ranges vary from 0.1 mm/yr to 38.0 mm/yr in the study area, and the values less than 20.0 mm/yr are predominant. Relatively low recharge rates coincide with low precipitation in most regions. Recharge is less than 5.0 mm/yr if mean annual precipitation (MAP) is less than 400 mm/yr. The ranges of 10.0-20.0 mm/yr of recharge occur in precipitation ranging from 600 mm/yr to 1,200 mm/yr. The recharge rates exceeding 20.0 mm/yr are more related to the precipitation with 800 mm/yr or more. The low recharge rates less than 2.0 mm/yr are related to single high rainfall event in the study area. The total recharge volume of the outcrop of the TMG in the study area is approximately 54.2× 106m3/yr . Approximately 29.3% of the stream flow may be contributed by recharge in terms of baseflow. The recharge in the study area increases with increasing precipitation, but recharge percentage is non-linear relationship with the precipitation. Separate high rainfall events mainly contribute recharge if annual precipitation is extremely low in the study area. Spatial distribution of recharge is associated with the variations in precipitation, geological and geomorphologic settings in the study area. The method used yields a point estimate and then ext rapolate s to the whole study area. The ranges of recharge may be exaggerated or underestimated due to the finite number of the rainfall stations in the outcrop of the TMG of the study area. After comparison to other recharge estimates from early studies in the area, the estimates are considered as reasonable and reliable. The feasibility of the water balance approach in semi-arid area is confirmed as well. The estimates based on the water balance model should be crosschecked before they are applied for management of groundwater resources. / South Africa

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Natural groundwater storage can be improved by constructing a subsurface barrier that is a subsurface dam, in order to capture the subsurface flows and raise the groundwater levels (GWLs) in the sediment layers. Subsurface dams are preferable to surface dams because of lower evaporation, higher functionality, lower cost of construction, lessened risk for contamination and the possibility of utilizing land over the dam. Therefore subsurface dams constitute an affordable and effective method for the sustainable development and management of groundwater resources. The aim of this research project was to develop and test methods for the assessment and location of subsurface dams in water resources management. From previous experiences it has been established that locating suitable sites for construction of subsurface dams plays an important role in the overall success of these dams. Therefore, in order to locate suitable sites, two approaches were followed. The first was the Boolean approach using topographical, geological and landcover data in a geographic information system (GIS) environment for a previously glaciated terrain near Stockholm. The results of the Boolean approach were complemented by a groundwater balance model and a topographic wetness index (TWI). The second approach involved spatial multi-criteria analysis (SMCA) applied to a region with different geological and hydrological conditions. SMCA was applied in Northern Pakistan using factors such as topography, geology, landcover, soil thickness and TWI. Two weighting techniques, the analytic hierarchy process (AHP) and the factor interaction method (FIM), were employed and compared. The Factor removal technique was employed to assess the sensitivity of the model for each factor. Aquifer thickness is an important factor while planning subsurface dams and data regarding the soil thickness is often not available at larger scale. Therefore a simplified regolith model (SRM) was developed for estimating the regolith thickness in previously glaciated terrain with a high frequency of rock outcrops, based on a digital elevation model (DEM) and an optimized outcrop search algorithm. In order to analyse the dynamics of the groundwater flow, a transient 3D groundwater flow model was developed for a subsurface dam. Methods applied to locate suitable sites for the construction of subsurface dams showed some promising results and need to be applied and tested in areas with different hydrological and geological conditions. The Boolean approach is a simple method that could be used during early planning stages for locating suitable sites for the construction of subsurface dams. The SMCA framework enabled the integration of knowledge for decision making, where the weights had a more significant influence on the results than the choice of the weighting method. AHP was considered to be the more robust model for assigning weights in this study. The factor removal technique showed that the modeling results were least sensitive to soil depth and most sensitive to land cover for the construction of subsurface dams. SRM showed reasonable results and could be used in engineering projects prior to detailed field investigations in formally glaciated terrain when borehole data is not available. The groundwater flow modelling results helped to develop some sustainable pumping scenarios to demonstrate the benefits of the subsurface dam. Groundwater flow model results also facilitated the selection of a suitable site for placing a subsurface dam in order to maximize the groundwater storage upstream. It was concluded in this project that the subsurface dams could sustainably be used to mitigate the water supply issues in formerly glaciated humid terrain such as in Sweden and dry climatic areas such as in Pakistan. Moreover, subsurface dams can play an important role in water resources management in coastal areas of formerly glaciated terrain, where saltwater intrusion is a rising environmental issue. Also in dry climatic areas like in Pakistan, methods such as SMCA could make the planning step more robust before the actual construction of dams. Themethods and findings presented in this thesis can be considered to be one tentative step of scientific contribution for better analysis, assessment and the location of subsurface dams. / <p>QC 20160210</p>

Project Completion Report OWRT Project A- 076 -ARIZ The work upon which this publication is based was supported in part by the United States Department of the Interior as authorized under the Water Research Act of 1964, as amended. / Constant head borehole infiltration tests are widely used for the in situ evaluation of saturated hydraulic conductivities of unsaturated soils above the water table. The formulae employed in analyzing the results of such tests disregard the fact that some of the infiltrating water may flow under unsaturated conditions. Instead, these formulae are based on various approximations of the classical free surface theory which treats the flow region as if it were fully saturated and enclosed within a distinct envelope, the so- called "free surface." A finite element model capable of solving free surface problems is used to examine the mathematical accuracy of the borehole infiltration formulae. The results show that in the hypothetical case where unsaturated flow does not exist, the approximate formulae are reasonably accurate within a practical range of borehole conditions. To see what happens under conditions closer to those actually encountered in the field, the effect of unsaturated flow on borehole infiltration is investigated by means of two different numerical models: A mixed explicit - implicit finite element model, and a mixed explicit -implicit integrated finite difference model. Both of these models give nearly identical results; however, the integrated finite difference model is considerably faster than the finite element model. The relatively low computational efficiency of the finite element scheme is attributed to the large humber of operations required in order to reevaluate the conductivity (stiffness) matrix at each iteration in this highly nonlinear saturated -unsaturated flow problem. The saturated -unsaturated analysis demonstrates that the classical free surface approach provides a distorted picture of the flow pattern in the soil. Contrary to what one would expect on the basis of this theory, only a finite region of the soil in the immediate vicinity of the borehole is saturated, whereas a significant percentage of the flow takes place under unsaturated conditions. As a consequence of disregarding unsaturated flow, the available formulae may underestimate the saturated hydraulic conductivity of fine grained soils by a factor of two, three, or more. Our saturated -unsaturated analysis leads to an improved design of borehole infiltration tests and a more accurate method for interpreting the results of such tests. The analysis also shows how one can predict the steady state rate of infiltration as well as the saturated hydraulic conductivity from data collected during the early transient period of the test.

The problem of evaluating the parameters of the mathematical model of an unconfined aquifer is examined with a view toward development of automated or computer -aided methods. A formulation is presented in which subjective confidence ranges for each of the model parameters are quantified and entered into an objective function as linear penalty functions. Parameters are then adjusted by a procedure which seeks to reduce the model error to acceptable limits. A digital computer model of the Tucson basin aquifer is adapted and used to illustrate the concepts and demonstrate the method.

Chapter I presents an investigation of a TCE-contaminated aquifer beneath Tucson International Airport, Arizona. Shallow soil gas (< 2m deep) was collected and analyzed for halocarbon contaminants to determine the relationship with vadose zone and groundwater contamination directly below. The TCE plume in shallow soil gas was mapped with 46 probes and spanned 3 orders of magnitude in concentration (< 0.001 to 2.0 μg/L). TCE concentrations in water from 5 monitoring wells around the Airport property ranged from 4 to 2800 ppb and had a correlation coefficient (r) of 0.90 with TCE concentrations in shallow soil gas. Vertical borings were completed to the water table at four locations in order to obtain profiles of soil gas contamination, air porosity, and water saturation. Vertical concentration gradients and effective diffusion coefficients were used to calculate flux rates for volatile organic contaminants (VOC's). Flux values ranged from 0.094 to 680 pg/day per m² for the four borings, and an annual mass transfer of TCE from groundwater to the atmosphere was estimated at 4 kg over the 0.5 km² site. Contaminant concentrations in shallow soil gas provided an accurate indication (r = 0.94) of vadose zone flux on a site-specific basis. The success in delineating the areal extent of subsurface contamination via soil gas sampling is not diminished by geologic or hydrologic anomalies if they are not laterally extensive compared to the plume. Chapter II introduces an environmental rates model which provides an estimate of the subsurface fate of volatile organic chemicals. Six hydrochemical indices are estimated (dissolved flow retardation, immiscible flow retardation, air-water partitioning, soil gas diffusion, hydrolysis, biodegradation) from compound-specific properties and site-specific characteristics. In addition, the carcinogenic potential and metabolic intermediates (two biochemical indices) of 75 volatile organic chemicals are estimated from the compounds' chemical structure. The model output is designed to assist water resource and environmental decision-makers in assessing the severity of existing problems and in avoiding potential problems.

This research investigated the ecological significance of GW-SW interactions in the hyporheic zone of two Scottish mountain rivers (the Girnock Burn and the River Feshie).  The research comprised three components: (i) an assessment of the influence of GW-SW interactions on the spatio-temporal variability of hyporheic hydrochemistry and macroinvertebrate community structure, (ii) an evaluation of the influence of GW-SW dynamics on small-scale spatio-temporal variability in hyporheic thermal regimes, and (iii) an investigation of the spatial relationship between Atlantic salmon <i>Salmo salar </i>(L.) spawning distributions and patterns of GW-SW exchange in a braided river reach. In the Girnock, marked inter- and intra-reach differences in hyporheic water quality were found and linked to spatio-temporal variability in GW-SW exchange.  Up to 25% of the spatial variability in invertebrate community structure could be accounted for by differences in hyporheic water quality.  Community composition varied markedly between winter, spring and summer seasons, with the relative importance of individual water quality variables differing between seasons. There was much heterogeneity in streambed temperature regimes across the study reaches, with data suggesting that long-residence groundwater contributed significantly to hyporheic exchange.  However, at small (cm to m) scales thermal variability was most likely explained by the interaction of reach-scale GW-SW exchanges with smaller-scale, current-bed form induced hyporheic exchange. In a braided section of the River Feshie, spatially complex and temporally dynamic GW-SW exchange patterns occurred.  Salmon spawning was concentrated in locations characterised by upwelling groundwater at depth, with up to 66% of spawning sites recorded in groundwater dominated channels.