Several hydrological studies claim that available water resources in a catchment are affected by large scale afforestation, especially where the regional rainfall is considered marginal for the support of silviculture. Nevertheless, the mechanisms and magnitude of the perturbations to the receiving water resources due to afforestation are still not clearly understood. To improve this understanding an intensive hydrological experiment has been initiated in the small grassed Weatherly catchment of the Mondi, North East Cape Forests. Details of the soil water dynamics on the Molteno formations in the catchment have been be studied. This research presents a description and first results of the establishment of an experiment which comprises monitoring the water budget of the grassed catchment prior to the afforestation of the catchment to plantations of exotic trees. The studies currently include, monitoring the infiltration and redistribution of soil water on a hillslope as well as monitoring of interflow mechanisms and localised mechanisms of soil water accumulation influenced by the topography and geology of the catchment. In addition to the intensive soil water monitoring, specific experimentation has been conducted at various locations on the hillslope. These comprise macropore flow process studies and 2-dimensional tracer experiments. Details of these experiments as well as the automated soil water and groundwater monitoring instrumentation are presented. An intensive soil survey on a 30 m x 30 m grid as well as a comprehensive measurement strategy of soil physical and hydraulic properties are highlighted. A review of 2-dimensional numerical hillslope soil water process models is also presented. Results from this research show that on hillslopes underlain by Molteno sandstones localised perched water tables form. These water bodies, upon reaching a critical height above the bedrock cascade downslope as interflow recharging the water bodies downslope. The response to infiltration increases downslope and in the toe region interflow occurs readily in response to rainfall compared to the midslope where substantial rain needs to infiltrate. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

Sugarcane hauliers in South Africa have high variations in vehicle payloads, which influence both transport economics and the legitimacy of their operations. Increasing economic pressure due to declining sugar prices and ever increasing fuel prices has invoked interest to improve vehicle utilisation and reduce costs, while complying with the local traffic legislation. On-board weighing technologies, such as on-board load cells, could assist operators to control their payloads more accurately and hence reduce the frequency of both over and under loaded consignments. In this study, an investigation is conducted to evaluate the feasibility of on-board weighing systems in the South African sugarcane transport industry. An overview of on-board weighing systems is presented. The overview gives insight into the technical composition of an on-board weighing system as well as presenting various benefits and drawbacks that are associated with an on-board weighing system. Earlier studies conducted on the use of on-board weighing systems are scrutinised and evaluated and it is concluded from these that vehicle utilisation could be improved, while concurrently reducing the overloading of vehicles. Field research was conducted to evaluate the accuracy and consistency of on-board weighing systems currently being utilised in the sugarcane transport industry as well as to determine the critical factors that influence the effectiveness of the system while assessing if overloading of vehicles was reduced when on-board weighing systems were employed. It was concluded that the systems evaluated were reasonably accurate with mean error being 0.4 tons. The consistency of the systems was good with 75% of all measurement being within 0.5 tons of each other. The critical factors determining the effectiveness of the on-board weighing systems were established as being management of the system as well as cane variety and quality. Overloading was reduced by 9% in one field evaluation and 5% in another. Further reduction can be realised through tighter management of the on-board weighing systems. An economic evaluation of an on-board weighing system was performed using the capital budget method. This method was used to determine the pay off period required to realise the investment into an on-board weighing system for scenarios where the payload is increased by 2, 3 and 4 tons and transport lead distance is 20, 40, 60, 80, and 100 km. The shortest pay off period occurred when the lead distance was 60 km and the time was 1, 2 and 3 years for payload increases of 2, 3 and 4 tons respectively. For lead distances of 40, 60 and 80 km the investment is worthwhile and considerable returns in investment can be realised, however, for the other lead distances the pay off period could be deemed to be too long. From the observation made during the field evaluation together with the literature studied, guidelines for the use of on-board weighing systems under various transport scenarios were formulated and are presented in chapter six. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2009.

The purpose of this study was to develop a framework to assess irrigation design and operating strategies. This objective was achieved successfully and the framework was applied to formulate guidelines to increase farm profitability whilst using scarce resources, such as water and electricity, effectively. The study was targeted at sugarcane irrigated with semi-permanent irrigation systems. “ZIMsched 2.0”, a water balance and crop yield prediction model and the “Irriecon V2” economic assessment model were available at the start of the study. The missing link, however, was a relatively cost effective and efficient method to design and cost irrigation hardware alternatives. Irrigation hardware impacts on both the agronomic and economic performance of systems, for example, through different peak design capacities and associated operating limitations. Thus, a novel, spreadsheet-based irrigation design tool, with an automated costing component, was developed to complete the framework. The framework was used to investigate the costs and benefits of potential design and operating solutions to a selection of irrigation issues, including: over-irrigation on shallow soils, the opportunity to shift electricity use out of expensive peak periods and, the opportunity to demonstrate the benefits of deficit irrigation strategies. For shallow soils, the increase in system hardware costs, needed to better match water application to soils, increased margins due to more effective water use. Innovative deficit designs and operating strategies allowed for reductions in water and electricity costs. The reduced costs, however, did not always offset yield penalties and revenue loss resulting from water stress. The financial benefits of deficit irrigation strategies were shown when water savings were used to convert dry land cane into irrigated cane. This highlighted the differences between the direct and opportunity costs of water. Finally, a field work component, relating to the precise monitoring of irrigation strategies and corresponding crop responses was included in this study. Systems which enabled soil water potential and stalk extension to be monitored remotely via the internet were considered useful for the successful implementation of an optimum irrigation strategy. The easily accessible data allows for effective decision making and more importantly, reassures famers of the current state of their crop. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2009.

Anthropogenically-induced climate change has the potential to have serious implications on aquatic ecosystems and may ultimately affect the supply and quality of freshwater lakes and rivers throughout the world. As a class of ecosystems, inland waters are vulnerable to climatic change and other pressures, due to their small size and their position in the landscape. There is therefore a need to assess the impact of projected climatic change on aquatic ecosystems. Owing to this need, ecological indicators have been developed as a method of quantifying, identifying, monitoring and managing the ecological integrity of aquatic environments. The aim of this research was to develop techniques in order to conceptualise the higher order impacts of projected climate change on environmentally related streamflows and water temperature in South Africa, and to simulate these using an appropriate hydrological model. For this dissertation the downscaled daily climate output from the ECHAM5/MPI-OM General Circulation Model (GCM) was used as an input into the daily time step conceptualphysical ACRU Agrohydrological Modelling System in order to simulate the impacts of projected climate change on selected eco-hydrological indicators at the Quinary Catchment spatial scale. In this research these indicators were grouped into two broad categories: 1. Ecological Flow Indicators and 2. Water Temperature Indicators. The results of this research took the form of maps and time series graphs. The ecological flow indicator results investigate the magnitude and duration of flow events and were analysed spatially for the 5 838 hydrologically interlinked and cascading Quinary Catchments constituting the southern Africa study region. The ECHAM5/MPI-OM GCM projects the magnitude and duration of both annual subcatchment runoff and accumulated streamflows to increase in the eastern parts of southern Africa for the intermediate future climate scenario (2046 - 2065), with this trend strengthening in the distant future climate scenario (2081 - 2100). The computationally intensive water temperature indicator results were analysed spatially at the scale of the Thukela Catchment. The Thukela catchment was selected as a case study area because of its diversity - in altitude, rainfall, soils and ecological regions, as well as in its population geography and levels of education and employment. This diversity presents a challenge to studies of impacts of projected climate change, including its potential impacts on water temperatures. The spatial analyses indicate that subcatchment runoff, accumulated streamflows and mixed maximum water temperature are all likely to increase under projected future climate conditions. A temporal investigation, in the form of time series analyses, focused on four water temperature indicators and was performed for 15 selected Quinary Catchments, located within the Thukela Catchment. These temporal analyses indicate that the absolute variability (i.e. standard deviation) of both individual subcatchment runoff and accumulated catchment streamflows, are projected to increase in the future, while the relative variability (i.e. coefficient of variation) is likely to remain much the same or even decrease slightly over time period. These temporal analyses also indicate that there is a noticeable difference in the mixed maximum water temperature within a single Quaternary Catchment due to hydrological flow routing, with an increase in water temperatures as the water cascades downstream from the upper Quinaries to the Quinaries at lower altitudes. The techniques developed and used in this research could aid decision makers involved in ecological and water management planning. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Soil material exported from river catchments by soil erosion is a key issue in environmental sustainability. Although soil erosion processes have been thoroughly investigated, their dynamics, specifically the continuity of erosion processes and sediment source locality, are less studied. The aim of this investigation was to evaluate the changes in the fluxes and characteristics of sediments during their downslope and downstream transport. The study was conducted in a 1000 ha catchment of the Drakensberg foothills, South Africa. Sediment fluxes were monitored at nested scales during the 2009-2011 rainy seasons using 1×1m and 2×5 m erosion plots and H-flumes coupled to automatic samplers from 23 ha, 100 ha catchments. In addition, soil texture, colour and total organic carbon and nitrogen contents in sediments exported from the nested scales and a 1000 ha catchment were compared to in-situ surface and sub-surface soil horizons in a 23 ha catchment river bank and hillslope soils and fluvial sediments. There was a sharp increase of sediment fluxes with increasing slope length (846±201 gm-1y-1 for 1 m2 vs 6820±1714 gm-1y-1 for 10 m2), revealing a limited contribution of splash erosion compared to rain-impacted flow erosion. Sediment fluxes decreased to 500±100 gm-1y-1 and 100±10 gm-1y-1 at the 23 ha and 100 ha catchments respectively, indicating the occurrence of sedimentation during sediment downslope and downstream transport. A principal component analysis (PCA) suggested that rain impacted flow erosion efficiency at the 10 m2 scale was significantly correlated with soil bulk density, clay content and antecedent rainfall (P<0.05). Moreover, strong correlations existed between runoff, sediment concentration and soil loss and selected soil surface and environmental variables at the plot scales. Correlations became weaker at the catchment scales due to increasing landscape heterogeneity and the complexity of soil erosion dynamics. An additional PCA suggested that stream bank erosion contributed to 63% of the soil loss from the 23 ha catchment. During their downstream transport, sediments were discriminated by the second PCA axis, which correlated with the clay and fine silt content, 100 ha sediments showed negative coordinates to this axis while 1000 ha catchment sediment had positive coordinates. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

South Africa, in common with all countries with arid or semi-arid climatic conditions, is facing the consequences of irrigation development without effective subsurface drainage. The quality of irrigation water is also decreasing and hence more water is required for leaching. This is resulting in low irrigation water productivity, as a consequence of shallow water tables, thus limiting crop growth. This study investigated the nature and causes of shallow water table problems in the sugarcane fields of Pongola, South Africa. The DRAINMOD model was also assessed for its reliability to be used as drainage design tool in the area. A water table map of a 32 ha sugarcane field was generated using groundwater table data monitored in 36 piezometers from September 2011 to February 2012. Nearly 12 % of the 32 ha sugarcane field was found to be affected by shallow water tables of less than the 1.0 m Design Water Table Depth (WTD). The inability of the adopted Drainage Design Criteria (DDC) to cope with drainage needs was found to be the cause of the poor drainage problem. On the other hand, analysis of WTDs in a field with a poorly-maintained subsurface drainage system confirmed that the drainage problem is exacerbated by poor drainage maintenance. It was recommended that the subsurface DDC in the area be revisited and that timely maintenance also be provided The DRAINMOD model was calibrated and verified using actual WTD and Drainage Discharge (DD) data. The model evaluation results revealed that the DRAINMOD model can reliably predict WTDs, with a Goodness of fit (R2), Mean Absolute Error (MAE) and Coefficient of Residual Mass (CRM) of 0.826, 5.341 cm and -0.015, respectively. Similarly, the model evaluation results in predicting DDs were also good, with R2, MAE and CRM of 0.801, 0.181 mm.day-1 and 0.0004, respectively. A further application of the validated model depicted that drain pipes installed at depths ranging from 1.4 m to 1.8 m and a spacing ranging from 55 to 70 m, with a design discharge of 2.5 to 4.2 mm.day-1, were adequate in ensuring safe WTDs between 1.0 and 1.5 m in clay-loam soil. On the other hand, drain depths ranging from 1.4 to 1.8 m and spacing between 25 and 40 m, were found to be appropriate in maintaining WTDs between 1.0 and 1.5 m in clay soil, with drainage design discharge ranging from 2.5 to 5.1 mm.day-1. These findings suggest that the current drain spacing needs to be reduced, in order to maintain the 1 m design water table depth. Finally, for the adoptability of the DRAINMOD model in the area, the Rosetta program, a component of the HYDRUS-2D, was tested for its reliability in estimating saturated hydraulic conductivities required by the DRAINMOD model. Results of the investigation revealed that the program can reliably be used to estimate saturated hydraulic conductivities from easily accessed soil data (% sand, silt, clay and soil bulk density), with R2, MAE and CRM of 0.95, 0.035 m.day-1 and -0.031, respectively. Nonetheless, calibration of the DRAINMOD model based on saturated hydraulic conductivity estimated by the Rosetta program was recommended. The findings of this research will form the basis for implementing an agricultural drainage policy that will ensure sustainable rain-fed and irrigation crop production systems in South Africa. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

The objective of the study was to update and improve the reliability and accuracy of short duration (s 24 h) design rainfall values for South Africa. These were to be based on digitised rainfall data whereas previous studies conducted on a national scale in South Africa were based on data that were manually extracted from autographic charts. With the longer rainfall records currently available compared to the studies conducted in the early 1980s, it was expected that by utilising the longer, digitised rainfall data in conjunction with regional approaches, which have not previously been applied in South Africa, that more reliable short duration design rainfall values could Ix: estimated. A short duration rainfall database was established for South Africa with the majority of the data contributed by the South African Weather Bureau (SAWB). Numerous errors such as negative and zero time steps were identified in the SAWB digitised rainfall data. Automated procedures were developed to identify the probable cause of the errors and appropriate adjustments to the data were made. In cases where the cause of the error could be established, the data were adjusted to introduce randomly either the minimum, average or maximum intensity into the data as a result of the adjustment. The effect of the adjustments was found to have no significant effect on the extracted Annual Maximum Series (AMS). However, the effect of excluding erroneous points or events with erroneous points resulted in significantly different AMS. The low reliability of much of the digitised SAW B rainfall data was evident by numerous and large differences between daily rainfall totals recorded by standard, non-recording raingauges, measured at 08:00 every day, and the total rainfall depth for the equivalent period extracted from the digitised data. Hence alternative techniques of estimating short duration rainfall values were developed, with the focus on regional approaches and techniques that could be derived from daily rainfall totals measured by standard raingauges. Three approaches to estimating design storms from the unreliable short duration rainfall database were developed and evaluated. The first approach used a regional frequency analysis, the second investigated scaling relationships of the moments of the extreme events and the third approach used a stochastic intra-daily model to generate synthetic rainfall series. In the regional frequency analyses, 15 relatively homogeneous rainfall clusters were identified in South Africa and a regional index storm based approach using L-moments was applied. Homogeneous clusters were identified using site characteristics and tested using at-site data. The mean of the AMS was used as the index value and in 13 of the 15 relatively homogeneous clusters the index value for 24 h durations were well estimated as a function of site characteristics only, thus enabling the estimation of 24 h duration design rainfall values at any location in South Africa. In 13 of the 15 clusters the scaling properties of the moments of the AMS were used to successfully estimate design rainfall values for duration < 24h, using the moments of the AMS extracted from the data recorded by standard raingauges and regional relationships based on site characteristics. It was found that L-moments scaled better and over a wider range of durations than ordinary product moments. A methodology was developed for the derivation of the parameters for two Bartlett-Lewis rectangular pulse models using only standard raingauge data, thus enabling the estimation of design values for durations as short as 1 h at sites where only daily rainfall data are available. In view of the low reliability of the majority of short duration rainfall data in South Africa, it is recommended that the regional index value approach be adopted for South Africa, but scaled using values derived from the daily rainfall data. The use of the intra-daily stochastic rainfall models to estimate design rainfall values is recommended as further independent confirmation of the reliability of the design values. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

Policy makers, water managers, farmers and many other sectors of the society in southern Africa are confronting increasingly complex decisions as a result of the marked day-to-day, intra-seasonal and inter-annual variability of climate. Hence, forecasts of hydro-climatic variables with lead times of days to seasons ahead are becoming increasingly important to them in making more informed risk-based management decisions. With improved representations of atmospheric processes and advances in computer technology, a major improvement has been made by institutions such as the South African Weather Service, the University of Pretoria and the University of Cape Town in forecasting southern Africa’s weather at short lead times and its various climatic statistics for longer time ranges. In spite of these improvements, the operational utility of weather and climate forecasts, especially in agricultural and water management decision making, is still limited. This is so mainly because of a lack of reliability in their accuracy and the fact that they are not suited directly to the requirements of agrohydrological models with respect to their spatial and temporal scales and formats. As a result, the need has arisen to develop a GIS based framework in which the “translation” of weather and climate forecasts into more tangible agrohydrological forecasts such as streamflows, reservoir levels or crop yields is facilitated for enhanced economic, environmental and societal decision making over southern Africa in general, and in selected catchments in particular. This study focuses on the development of such a framework. As a precursor to describing and evaluating this framework, however, one important objective was to review the potential impacts of climate variability on water resources and agriculture, as well as assessing current approaches to managing climate variability and minimising risks from a hydrological perspective. With the aim of understanding the broad range of forecasting systems, the review was extended to the current state of hydro-climatic forecasting techniques and their potential applications in order to reduce vulnerability in the management of water resources and agricultural systems. This was followed by a brief review of some challenges and approaches to maximising benefits from these hydro-climatic forecasts. A GIS based framework has been developed to serve as an aid to process all the computations required to translate near real time rainfall fields estimated by remotely sensed tools, as well as daily rainfall forecasts with a range of lead times provided by Numerical Weather Prediction (NWP) models into daily quantitative values which are suitable for application with hydrological or crop models. Another major component of the framework was the development of two methodologies, viz. the Historical Sequence Method and the Ensemble Re-ordering Based Method for the translation of a triplet of categorical monthly and seasonal rainfall forecasts (i.e. Above, Near and Below Normal) into daily quantitative values, as such a triplet of probabilities cannot be applied in its original published form into hydrological/crop models which operate on a daily time step. The outputs of various near real time observations, of weather and climate models, as well as of downscaling methodologies were evaluated against observations in the Mgeni catchment in KwaZulu-Natal, South Africa, both in terms of rainfall characteristics as well as of streamflows simulated with the daily time step ACRU model. A comparative study of rainfall derived from daily reporting raingauges, ground based radars, satellites and merged fields indicated that the raingauge and merged rainfall fields displayed relatively realistic results and they may be used to simulate the “now state” of a catchment at the beginning of a forecast period. The performance of three NWP models, viz. the C-CAM, UM and NCEP-MRF, were found to vary from one event to another. However, the C-CAM model showed a general tendency of under-estimation whereas the UM and NCEP-MRF models suffered from significant over-estimation of the summer rainfall over the Mgeni catchment. Ensembles of simulated streamflows with the ACRU model using ensembles of rainfalls derived from both the Historical Sequence Method and the Ensemble Re-ordering Based Method showed reasonably good results for most of the selected months and seasons for which they were tested, which indicates that the two methods of transforming categorical seasonal forecasts into ensembles of daily quantitative rainfall values are useful for various agrohydrological applications in South Africa and possibly elsewhere. The use of the Ensemble Re-ordering Based Method was also found to be quite effective in generating the transitional probabilities of rain days and dry days as well as the persistence of dry and wet spells within forecast cycles, all of which are important in the evaluation and forecasting of streamflows and crop yields, as well as droughts and floods. Finally, future areas of research which could facilitate the practical implementation of the framework were identified. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

In this study, geophysical measurements (Electrical Resistivity Tomography-ERT) and remote sensing techniques were applied in the Thukela river basin at various scales to complement the classical hydrometeorological networks. Detailed process hydrological studies were carried out at the Potshini catchment in the Thukela river basin to provide an in-depth understanding of the influence of different land use management practices, notably the impact of conservation tiJlage practices, on runoff generation and soil moisture retention characteristics at field scale. The general trend that was observed in the field studies is that conservation tillage systems influenced the partitioning of rainfall, by significantly reducing surface runoff over agricultural lands under conservation tillage practices, with a reduction ranging from 46 to 67%. The field soil-water balance studies also indicated that more soil moisture was retained in plots under conservation tillage practices compared to plots under conventional tillage and hence the wider adoption of such a practice could influence the partitioning of rainfall across scales. The field based study was integrated into catchment process studies where a classical hydrometrical network was complemented with geophysical measurements (ERT) along catchment transects to determine the interaction of the surface and sub-surface water and the relative contribution of the subsurface water to catchment response. The study revealed that the shallow ground water contributes significantly, close to 75%, of the stream flows in the Potshini catchment, especially during the dry seasons, with the response of the shallow ground water being a function of both the rainfall intensity and daily total amount. The potential of integrating the catchment process studies with the larger river basin scale was explored through the evaporative term of the water balance by applying the Surface Energy Balance Algorithm for Land (SEBAL), a remote sensing methodology, to estimate total evaporation (ET) from the Moderate Imaging Spectroradiometer (MODIS) satellite images. This was validated with ground measurements from a Large Aperture Scintilometer (LAS) installed in the Potshini catchment. Good comparison was established between the remotely sensed estimates and LAS measurements with a deviation range of between -14 to 26% on discrete days, where the deviation was defined as the departure of the remotely sensed estimates of ET from the respective LAS measurements. The results from this study compare well with results from similar studies in other countries with different climatic conditions. Subsequently, the evaporative water use of various land uses in the upper Thukela river basin was assessed using MODIS images. Commercial forestry was identified to be the land use with a consistent and relatively high evaporative water use In the study area. High evaporation rates over water bodies were observed during the wet summer season when both the natural and man made water bodies were at full capacity. Nevertheless, it is recognized that the inherent low resolution ofthe MODIS images could have impacted on the SEBAL results. Finally, a conceptual framework, drawing the strengths of classical hydrometeorological networks, geophysical measurements, isotope tracers and remote sensing is suggested with the potential of enhancing our understanding and conceptualization of hydrological determinants across scales. The relevance of the framework to water resources management is highlighted through its application to the Potshini catchment and the Thukela river basin using results and findings from this study. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2008.

Understanding of the hydrological cycle and processes such as interception span as far back as the times of the Renaissance, when Leonardo da Vinci (1452-1519) first described it. However, there remains a gap in the knowledge of both canopy and litter interception in South African forest hydrology. Interception is typically considered to constitute only a small portion of total evaporation and in some models is disregarded or merely lumped with total evaporation, and not considered as a separate process. Interception is a threshold process, as a certain amount of water is required before successive processes such as infiltration and runoff can take place. Therefore an error introduced in modelling interception, especially disregarding it, will automatically introduce errors in the calibration of subsequent models/processes. In this study, field experiments to assess these two poorly understood hydrological processes, viz. canopy and litter interception were established for the three main commercial forestry genera in South Africa, namely, Pinus, Acacia and Eucalyptus as well as an indigenous Podocarpus henkelii stand, thus, accounting for interception of “broad leaf”, “compound leaf” and “needle leaf” trees in order to provide further insight into these processes. The study took place at two locations in the KwaZulu-Natal Midlands over a period of three years. The first site is the Two Streams catchment, located in the Seven Oaks area, about 70km north-east of Pietermaritzburg where the study on the commercial plantation species took place. The second site was the Podocarpus henkelii stand in Karkloof near Howick, 40km north of Pietermaritzburg. From the field data collected (cf. Chapter 2) it was observed that canopy storage capacity, an important parameter governing interception, was not constant and changed with rainfall intensity, with lower intensity events resulting in a higher storage capacity. Building on these findings, a physically based canopy interception model that is based on the well known Gash model was developed, and is referred to herein as the “variable storage Gash model”. While canopy interception is dependent on many factors including the storage capacity, potential evaporation, rainfall intensity and rainfall duration, the litter interception is largely dependent on the storage capacity due to the evaporative drivers under the canopy such as radiation, temperature and wind speed being moderated by the above canopy. From these finding, a litter interception model based on idealised drying curves from litter samples collected at the study sites was also developed (cf. Chapter 3). From the field data, it was found that the canopy interception for Eucalyptus grandis, Acacia mearnsii and Pinus patula was 14.9, 27.7 and 21.4% of mean annual precipitation (MAP) respectively. The simulated canopy interception using the “variable storage Gash model” was 16.9%, 26.6% and 23.3% for E. grandis, A. mearnsii and P. patula respectively. The litter interception measured for E. grandis, A. mearnsii and P. patula was found to be 8.5, 6.6 and 12.1% of MAP respectively, while the simulated litter interception using the idealised drying curve model corresponded well with the measured results and were 10.1%, 5.4% and 13.4% for E. grandis, A. mearnsii and P. patula respectively. The idealised drying curve model is site and species specific and is therefore not transferable to other locations. Conversely, the “variable storage Gash model” is transferable as it is not site and species specific, and relies on readily measureable and available information. Building on field studies, this was then used to simulate the canopy interception for Eucalyptus, Acacia mearnsii and Pinus in South Africa (including Lesotho and Swaziland) for all quinary catchments in which commercial forestry could be grown, i.e. a mean annual precipitation of greater than 600 mm.year-1 (cf. Chapter 4). It was found that, depending on the location and genus, canopy interception loss can be as high as 100 to 300 mm per year or approximately 10% to 40% of MAP. This relates to a mean interception loss of between 1.0 and 3.0 mm per rainday, highlighting the spatial variability of canopy interception. To further investigate the spatial variability of canopy interception, at various spatial scales, remote sensing technology was applied to estimate leaf area index (LAI) for use in modelling/estimating canopy storage capacity and canopy interception (cf. Chapter 6). The NDVI, SAVI and Vogelmann 1 vegetation indices were used in the estimation of the LAI. It was found the Vogelmann 1 index produced the best results. As models to estimate canopy interception typically require LAI and storage capacity, it was calculated that the ability to estimate these parameters over large areas is valuable for water resources managers and planners. An often neglected consideration of canopy and litter interception is its role in determining the water use efficiency (WUE) of a forest stand (cf. Chapter 5). This component of the study was undertaken in an indigenous Podocarpus henkelii stand as well as a commercial Pinus patula stand in Karkloof in the KwaZulu-Natal Midlands. The sap flow (transpiration) was measured in both the P. henkelii and P. patula stands using the using the Heat Pulse Velocity (HPV) technique in order to determine the productive green water use. The canopy and litter interception was measured in the P. henkelii site, but was modelled in the P. patula site using the “variable storage Gash” and idealised drying curve models, in order to estimate the non-productive green water use. It was found that the canopy and litter interception for P. henkelii was 29.8% and 6.2% respectively, while the modelled canopy and litter interception for P. patula was 22.1% and 10.7% respectively. If only the productive green water use (transpiration) is considered, then the water use efficiency of P. henkelii and P. patula was found to be 7.14 g.mm-1 and 25.21 g.mm-1 respectively. However, from a water management perspective it is important to consider the total green water use efficiency (transpiration + interception), which reveals a significantly lower water use efficiency of 3.8 g.mm-1 and 18.8 g.mm-1 for P. henkelii and P. patula respectively. To extend the study to a globally relavent issue, the possible impact of climate change on canopy interception was investigated, as forests growth is critically linked to climate (cf. Chapter 7). To achieve this, the CABALA model was used to model LAI and transpiration of Eucalyptus grandis and Pinus patula under 9 different climate change scenarios, including changes in temperature, rainfall and atmospheric CO2. The simulated LAI values from the CABALA model for all 9 climate scenarios were then used to simulate canopy interception using the “variable storage Gash model”. Results show that LAI may increase by as much as 24% and transpiration may decrease by as much as 13%, depending on the scenario, location and tree species. However, it was found that canopy interception does not change greatly, leading to the conclusion that under climate change conditions, canopy interception may not become a more dominant component of the hydrological cycle than it currently is as the changes under climate change are likely to be less than the natural variability from year to year. However, canopy interception remains an important consideration for water resources management and planning both currently and in the future. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.