Batch and column experiments were performed to investigate the adsorption of bacteriophage MS-2 to silica at pH 5. Linear isotherm analysis of batch experiment data gave partition coefficient (KP) estimates of 270 cm³/g and 580 cm³/g for 4°C and 24°C, respectively. Breakthrough-type column experiments indicated that sorption and desorption were slow, as evidenced by a slow approach to breakthrough and tailing of the desorption limb. A non-equilibrium advection-dispersion model with all adsorption sites on the silica assumed to be kinetically controlled was used to model the column data. The model-generated parameters yielded Kp estimates 1000-fold smaller than those given by isotherm analysis and indicated that the time scale for desorption is on the order of 1-6 hours.

Iodine, a minor constituent in ground water, is valuable as an indicator of subsurface sources of salinity. A review of iodine geochemistry reveals that exceptions to conservative behavior include sorption onto iron and aluminum oxides and incorporation into marine organic matter with additional enrichment due to sorption. Data from the Milk River aquifer in Alberta, Canada indicate that iodide in the ground water is derived from residual waters in the fine grained, marine sediments within the sandstone formation. This localized enrichment of iodide is superimposed on a more general enrichment of halides downgradient from the recharge area, probably due to ion filtration.

This thesis l concerned with the mathematical modelling of open channel flows governed by the Saint-Venant equations, which are used as a prediction or identification tools. A survey of the literature in these fields identified the problems in need of Immediate research. Numerical test runs were then devised which led to projecting a clear picture as follows. The performance of twn widely used Implicit finite difference schemes, the 4-point box and 6-point staggered schemes were compared In a wide range of circumstances. it is concluded that both schemes produce 'very close results, but the staggered scheme is prone to convergence problems In some extreme cases. It was also noted that a sharp change in geometric configuration of compound channels produced discontinuous features on the aim ulated depth and discharge hydrographs. The inability of the staggered scheme In handling a head-discharge relationship as a downstream boundary condition was tackled by proposing and implementing a scheme of second order accuracy. As model data are generally corrupted withh errors and noise, their effects together with that of other factors on the Identified friction parameters we Investigated. The results demonstte the paramount Importance of the effect of a choice of objective function on the Identified parameters. While the individual values of the identified M2nning n may vary from one flood event to another, their mean is shown both numerically and rigorously to be dependent upon the choice of objective function. It is shown that an objective function formulated by using absolute errors performs ideally and produces reliable results even in the presence of autocorrelated Gaucian noise samples. The mean of the Identified parameters is also found to be adversely affected if the observation station is affected by localized disturbances. Sensitivity of objective functions to the variation In the value of the friction parameter Is also found to be an Important factor, as Insensitivity leads to ill-conditioning.

Thesis (MScAgric (Agricultural Economics)--University of Stellenbosch, 2009. / This thesis constitutes a socio-economic study that centres on determining the economic value of groundwater in rural and agricultural uses. Limpopo Water Management Area (WMA1) and Luvuvhu/Letaba Water Management Area (WMA2) were studied in this thesis. In WMA1 table potato irrigation in the Polokwane agricultural area was studied, while Gaphago, Leokaneng, Kanana and Mohlajeng villages were studied for rural household groundwater use. In WMA2 tomato irrigation in the Mooketsi agricultural area was studied, while Lemondokop, Sereni and Hamashamba villages were studied for rural household groundwater use. Scoping field trips to the study area as well as secondary data revealed that groundwater was the dominant water source in all these selected study epicentres. In the Polokwane agricultural area, the farms typically relied on numerous boreholes. In the Mooketsi commercial farming area, groundwater was the dominant water source for most years, except when flush floods replenished farm dams. When flush floods occurred, farmers partially substituted surface water for groundwater because of economic reasons. This study determined the economic value of groundwater in two use sectors. First, determining the utility value of groundwater in selected rural households using the contingent valuation method. Utility value was defined by Dupuit (1844) and Marshall (1879) as the maximum sacrifice expressed in money terms which each consumer would be willing to make in order to acquire an object. Open-ended questions were used to determine willingness to pay during contingent household groundwater valuation. The overall mean willingness to pay for satisfactory household groundwater for the study area was R2.28 per kilolitre of groundwater.

A multitude of transitional water supply and distribution interventions are continually piloted in Kenya’s fast-growing urban settlements to meet national and global MDG targets, yet visible problems persist regardless of the investments made. This research evaluates the performance of four interventions led by public utilities and non- governmental organisations in the low-income settlements of Nairobi, Kisumu and Nakuru counties. To understand the service improvement received by the residents, this study used qualitative data from interviews and focus group discussions and quantitative data from 1,168 household surveys. Service level analysis results showed making water more affordable using pre-paid technology reduced the effective price by 75% and increased consumption per household by 20 litres per day, resulting in the highest service progress. Improving water accessibility for the very poor via hosepipe door-step delivery reduced the burden on women carrying water by 43% although efforts failed to reduce the pricing structure, limiting the progress. Subsidised ‘first-time’ metered plot connections to increase the utility customer base experienced shortages in water supply and reluctance from landlords, restricting development. Despite showing no positive change, 81% of residents continued to rely on expensive self-supplied boreholes which were all contaminated. Although the utilities have made positive strides in service improvement, in the context of universal service this study has shown that the very poor remain the most difficult to access, forming the target of discrete interventions that experience difficulties in influencing a reliable supply, sustained price reduction and/or good water quality – essentially what is needed most. In investigating the longer term supply and demand shortfall, this study concludes that the equitable supply and innovative distribution of point source groundwater, with a bias for the poorest, could be the most resilient transitional solution for the utility to promote in the foreseeable future, out of necessity rather than desire.

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In fractured rocks of low permeability, the hydraulic properties of the rock mass are strongly influenced by the connectivity and fracture geometry of the fracture system, the stiffness and deformational properties of fracture surfaces and the geostatic stresses. This dissertation demonstrates through theoretical analysis the sensitivity of fracture connectivity and flow rate to fracture radius, fracture density and measurement scale. Percolation factor and percolation frequency are suggested as indices of connectivity and flow rate. Models of hydromechanical coupling, normal closure and simple geometrical joint systems are proposed to study fracture porosity and fracture permeability and are compared with measured values from published papers. Fracture surface characteristics are expressed as indices of JRC and JCS. The relation between fracture aperture and geostatic stress is also examined. Based on the percolation process, a three dimensional discrete fracture model with statistical parameters of fracture geometry is developed to investigate the relations between the connectivity and flow rate and the percolation factor and percolation frequency. This model has the capability to generate a fracture network and to solve for steady state flow. The flow through each fracture is discretized by the boundary element method. By performing numerical simulation, the percolation threshold was found to be in the range of 0.9 to 2.4 for orthogonal joint sets. There is a rapid increase in flow rate with increasing fracture density or fracture length as the percolation factor reaches the percolation threshold. The percolation factor and percolation frequency are scale-dependent. A fracture network with large fractures and a high fracture density has a high percolation frequency and a high percolation factor. A network with high percolation frequency and percolation factor has a high flow rate. A constitutive model linking the initial conducting aperture, mechanical conducting aperture, JRC, JCS, geostatic stress and fracture geometries can be used to predict fracture porosity and fracture permeability in terms of depth. Preliminary comparison with field data shows that models comprising three orthogonal sets and disc-type fracture models can be used to simulate observed behavior. Fracture porosity and fracture permeability based on a model of three orthogonal sets can be used to predict flow through volcanic rocks. For sedimentary rocks a model incorporating a model of three orthogonal sets and one parallel set can be used with varying levels of confidence.

Study of the main channels of an ephemeral discontinuous stream shows the presence of pool-riffle morphology scoured into underlying Holocene muds. Pools are defined as starting at the point of maximum bed slope and reaching half the distance downstream to the next point of maximum bed slope. Pool-riffle morphology correlates well with high-stage hydraulics. Channel fill along pools is subject to hydraulicjump scour during intermediate-stage flows. Pools are preferentially scoured during high-stage discharges with flow completely in the tranquil flow regime. During large-stage flows, channel fill is almost completely washed away and the variable slope of the exposed mud subfloor is found to show negative exponential correlation to energy gradients, sediment transport, and shear. Reaches of steep bed slope and low shear become the locus of kinematic particle interference and gravel deposition during recession from high stages. During low-stage flow, relationships between bed slope and energy expenditure are the reverse of those during high-stage flow. Evidence indicates that certain discontinuous streams and their fans evolve to braid chute units along gullies comprising steep slope, braided channels upstream of a single-channeled chute of low slope. During large discharges, shear and sediment transport are higher along chutes, causing net scour of channel fill. This fill is stored along the braided channels of the next braid-chute downstream. During low-stage flows, the reverse occurs. Thus, the braid-chute functions as a morphologic unit to maintain evenness of sediment transport in an environment of variable flow sizes. Long-term sediment-budget deficit is indicated by gradual scour of channel subfloors. In all braid-chutes, the bed slope of the braid is greater than the slope of the flood surface, and both are greater than the bed slope of the chute. Along chutes, average low-stage energy slopes approximately equal bed slopes. As stages rise, energy slopes increase with increasing discharge so that at bankfull stages, they approximate the flood-surface slopes. This relationship allows the inference of a feedback link between channel slopes and flood-surface slopes along a chute. Along braided channels, energy slopes decrease with increasing stage. Hypothetically, the contrasting energy-gradient changes with discharge could produce a system in which bankfull stages are reached simultaneously along the entire braid-chute. Data for discontinuous streams indicate that they may be analogous to noncontinuous braided perennial streams. Braided reaches in such perennial streams may be correlated to the alluvial fans below discontinuous channels. Straight and sinuous perennial channels between braided reaches may be analogous to the discontinuous channel. Bed slopes of the discontinuous channel and its analogues are flatter than those of adjoining flood surfaces. This contrast in gradients brings flow close to the level of the flood plain at some point downstream where the flow can begin to spread laterally onto this surface. In the ephemeral environment, this downstream branching usually takes place over a riffle. The fan, which lies below the studied discontinuous stream, contains braided-channel flow, mixed channel flow and sheetflow, and sheetflow, respectively, in a down-fan direction. It is postulated that a low water to sediment discharge ratio over a long time span would produce net deposition in the fan as well as in the discontinuous channel upstream. This, in turn, would force the fanhead to migrate upstream over the filling channel. Valley alluviation, thus caused by a discontinuous stream, would construct an elongate, tabular body of sediments composed of coarse channel deposits at the base overlain by laterally extensive channel sands and sheetflood sands. Above these, there would be finer grained sheetflood silts.