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Techniques for assessing the impacts of wetlands on hydrological responses under varying climatic conditions.Gray, Ryan Paul. January 2011 (has links)
Wetlands are considered sensitive eco-tones that provide numerous goods and services, not only
to the communities which are immediately dependent upon them, but also to the many
downstream stakeholders who benefit from the hydrological influences that wetlands have on a
catchment.
The three main objectives of this study, the foci of which included an assessment of impacts of
wetlands on catchment hydrological responses (viz. flood attenuation and streamflow regulation)
in the Thukela catchment under varying geographical and climatic conditions, are:
· A modification and validation of the ACRU Model’s Wetland Routine;
· Assessing impacts of wetlands on hydrological responses from catchments in varying
climatic regions under historical climatic conditions; and
· Assessing impacts of wetlands on catchment hydrological responses for climate change
scenarios by using outputs from a Regional Climate Model (RCM).
The ACRU Model was selected to undertake the daily hydrological simulations, while historical
climate data and climate information derived from the C-CAM Regional Climate Model were
used as inputs into the model. These varying climatic inputs, as well as the changes in water
fluxes between simulations with and without the wetlands routine switched on, enabled the
author to assess the impacts of wetlands on catchment hydrological responses under varying
climatic conditions. The ACRU wetland routine initially did not produce output in line with
conceptualisation of wetlands processes. As a result of this, certain modifications had to be made
to the model to ensure that the results obtained mimicked wetlands hydrological processes
realistically.
A validation was performed on the re-configured ACRU wetlands routine to show that the
simulated results of impacts of wetlands on catchment hydrological responses were realistic when
compared to findings from the literature review (e.g. in regard to streamflow regulation and flood
attenuation). These validation results also show that the impacts of wetlands on catchment
hydrological responses are dependent on the level of soil water saturation of the wetland at the
start of a streamflow event and the volume of the streamflow event in relation to the relative size
of the wetland.
The results further illustrate that wetlands have a relatively small flood attenuation and
streamflow regulation impact on mean annual catchment hydrology at the outlet of the 29 136
km2 Thukela catchment. However, mean monthly results show pronounced effects (20 – 30%) of
flood attenuation in the summer months and streamflow regulation throughout the year,
especially in the drier winter months. The climate change scenario results illustrate that the
impact of wetlands on hydrological responses are virtually entirely masked by the impact of
climate change, with only minor changes shown on outflows of the Thukela between climate
change scenarios without and with wetlands. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Ground and satellite-based assessment of hydrological responses to land cover change in the Kilombero River Basin, Tanzania.Munishi-Kongo, Subira. 21 July 2014 (has links)
Changes in land use and land cover are a global issue of concern, especially with regard to
possible impacts on biophysical processes which affect the hydrological functioning of a
system. Tanzania is no exception to this concern. This study, therefore, addresses the
implications of land use alterations on the hydrodynamics of the Kilombero River Basin,
specifically with regard to the Kilombero Valley’s wetlands and water resources, which have
been altered and exploited to a great extent.
As its starting point, the study embarked on mapping the current land cover in the Kilombero
Basin and the quantification of the historical changes. The study revealed significant changes
and, in recent years, increased rates of clearing natural vegetation cover and conversion to
agricultural land. The most affected area of the Basin was the Kilombero Valley, a Ramsar
Site and formerly extensively inhabited by wildlife, but which now has 62% of its area
converted into agricultural and/or human settlements. In line with this observation, the study
used two approaches for the impact analysis, a regional scale and a local scale approach.
Plant physiology, soil moisture and micro-meteorological measurements were undertaken to
quantify the impact of land cover change at local scale. Sensing techniques were then applied
to assess the spatial extent of the changes and the basin scale (regional) impact thereof.
Investigation of hydrological processes at a local scale placed emphasis on the implications
of forest conversion from indigenous Miombo woodland to exotic Teak (Tectona grandis)
forests. Field measurements showed the distinctive nature of Teak trees consumptive water
use, both in quantity as well as in regard to the seasonal variation as compared to the native
Miombo woodland forests. Teak was found to have higher transpiration rates, both during the
rainy season (where the rates were approximately 10-fold higher than that of Miombo) and
the period immediately after the cessation of rainfall, with consumptive water use rates being
four-fold higher than that of Miombo. This contrast in water use was further observed in the
measured soil water fluxes which evidenced a large difference in the components of the soil
water balance. Less recharge was observed in the Teak forests suggesting significant impacts
on the replenishment of groundwater resources in the study area.
Assessment of the basin scale impacts of the land cover changes on the evapotranspiration
(ET) regime was undertaken using the Surface Energy Balance System (SEBS) remote
sensing model. Validation was provided by the Teak field sites and through the monitoring of
ET from sugar cane using a Large Aperture Scintillometer (LAS). Results suggest a decrease in ET during the dry season. There is a clear transition of ET that follows the land cover
transition from the natural and more adaptable vegetation, to rain-fed dependent crops and
bare lands, where minimal ET is observed during the dry season. Similar seasonal leafing,
and therefore a similar ET pattern, is observed with the conversion of natural forests to
deciduous plantation forests. Irrigated crops, on the other hand, were found to have
persistently higher ET throughout the year regardless of rainfall variability. This implies that
land cover change in the Kilombera Valley is resulting in higher water use and less recharge
in the wet season and a correspondingly lower ET (and possibly lower river flow) in the dry
season than would occur under natural conditions.
This research provides valuable information relevant to all stakeholders in the Kilombero
River Basin (i.e. both smallholders and commercial sugarcane farmers, the forestry industry,
Basin Water Authorities etc.). This information will help to inform decision-making around
the sustainable management of the water resources in the Kilombero Valley for food security
as well as for sustaining livelihoods and ecosystems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Simulation modelling of sugarcane harvest-to-crush delays.January 1998 (has links)
Long delays between harvesting and crushing of sugarcane lead to excessive deterioration in the
quality of sugarcane. The aim of this project was to develop a computer based model of sugarcane
harvesting and delivery systems that could be used to investigate methods of reducing harvest-to crush
delays. A literature review was conducted and simulation modelling was chosen as the most
appropriate modelling technique for the situation of sugarcane harvesting and delivery and the
purposes of this project. The Arena modelling system was chosen as the simulation software with
which to construct the model.
A model was developed on the scale of a particular sugar mill and the area of farms supplying it
with cane. The Sezela mill on the south coast of KwaZulu-Natal, South Africa was chosen as a
case study on which to develop and test the model. The model integrated a harvesting and
transport section which represented all the individual farms or combinations of farms in the area
with a millyard section.
After the model had been verified and validated, it was used to investigate the effect of a number
of different scenarios of harvesting and delivery systems and schedules on harvest-to-crush delays
in the Sezela mill area. The results of the experimental runs performed with the model indicated
that the most significant decreases in harvest-to-crush delays could be brought about by matching
harvesting, delivery and milling cycles as closely as possible. It was also evident that burn-to-cut
delays where daily burning is not practised constitute a large proportion of overall harvest-to crush
delays. The model proved to be useful in making comparisons between systems and in
providing a holistic view of the problem of harvest-to-crush delays. Recommendations for future
developments of the model include adding a mechanical harvesting component and making the
model more easily applicable to other mill areas. / Thesis (M.Sc.Eng.)-University of Natal, 1998.
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Spatial and temporal variations of water and nutrient fluxes within a steep-sloped agricultural catchment.Orchard, C. M. January 2012 (has links)
A proper understanding of the spatial and temporal variations of runoff and nutrient fluxes are
critical in understanding catchment hydrology. Runoff and nutrient fluxes may exhibit large
variations both spatially and temporally, but this issue has largely been overlooked in the
existing literature. The present study intends to respond to two main research objectives: (a)
improve the understanding of the spatial and temporal variations (i.e. the dynamics) of
overland flow (OF) and its factors of control and (b) quantify the evolution of runoff, nutrient
and sediment fluxes from hillslope crest to catchment outlet.
The research study was undertaken in a 1000 ha agricultural catchment of the Drakensberg
foothills in the Bergville District, KwaZulu-Natal, South Africa under rangeland, small scale
agriculture and commercial agriculture. The first objective was to evaluate the dynamics of
OF during four rainfall seasons (2007 to 2011) by using 1×1m² microplots (n=15) located at
five landscape positions within the rangeland upper part of the catchment. Automatic tipping
buckets linked to a datalogger were used to estimate the delay between the start of the rain
and the start of OF, which corresponded to the time of runoff initiation (TRI). Multivariate
analysis was applied to the OF data and the information on selected environmental factors
(rainfall characteristics, selected soil physical properties, soil water content and soil surface
conditions). Nested scales of 1 and 10 m2 plots, and 23, 100 and 1000 ha catchments equipped
with buckets for plots and conventional H-flumes for catchments, were used to quantify the
downstream evolution of water and nutrient (C, NO3
- and P) fluxes. The fluxes were
compared with data from the shallow and deep groundwater (GW) collected from piezometers
and boreholes, respectively. This allowed for the determination of the mixing sources at the
three catchment outlets, using stable isotopes of water (to differentiate between old and new
water) and silica concentrations to identify soil water (SW) contributions.
The average OF rate varied 2.3-fold across the Potshini Catchment (from 15% footslope to
35% backslope), while the average TRI varied by a 10.6-fold factor (between 0.6 minutes in
the bottomland and 6.4 minutes at the footslope position). TRI temporal variations correlated
the most with the duration of rainfall (Pearson r coefficient of 0.8) and the cumulative amount
of rainfall after the onset of the rainy season (r=-0.47), while TRI spatial variations were
significantly controlled by soil crusting (-0.97<r<-0.77). Water fluxes were found to increase
iii
from the microplot scale (208 l/m2) to the runoff plot scale (350 l/m2, delivery ratio of 1.68).
The scale ratios calculated for the period of 2010-2011 show that there was a steady decrease
in the delivery of water from the hillslope scale to the catchment scale. Cumulative water
fluxes were found to be 316 l/m2 at the 23 ha catchment and 284 l/m2 at the 100 ha catchment
(delivery ratios of 0.90 and 0.89 respectively). Water fluxes decreased sharply to 198 l/m2 at
the 1000 ha catchment outlets (delivery ratio of 0.70). Runoff at the 23 ha catchment outlet
was sourced from the mixing of GW (average of 63%), OF (22%) and SW (15%.) At the 100
ha outlet, GW contributions decreased to 50%, while OF contributions remained constant at
22% and SW contributions increased to 28%. The main contributor at the 1000 ha catchment
was GW (55%) followed by SW (37%) and OF (8%). During the strongest rainfall event of
the study period, OF contributed 97% to total runoff at the 23 ha catchment outlet, whilst at
the 100 ha catchment, OF and SW both contributed 50% each. Groundwater in all cases was
the major contributor to runoff at the 1000 ha catchment outlet. Both dissolved organic
Carbon (DOC) and particulate organic Carbon (POC) increased from the microplot (8.44 and
25.51 g/m2 for DOC and POC) to the plot scale (14.92 and 26.91 g/m2). Lower yields
occurred at the 23 ha catchment than on the hillslope (5.03 g/m2 and 8.18 g/m2). From the 23
and 100 ha catchment outlets, POC sharply decreased to 0.06 g/m2, while DOC increased
considerably to 9.58 g/m2. This pointed to the decomposition of POC, which not only releases
CO2 to the atmosphere but also adds DOC to runoff. At the 1000 ha catchment, POC yields
were minimal due to a lack of eroded sediments whilst DOC decreased slightly (6.42 g/m2).
These results yield a better understanding of the processes of water, nutrient and Carbon
movements within landscapes.
A further understanding of the processes leading to changes of nutrient and carbon fluxes
needs to be performed in order to link this study with the overall ecosystem functioning of a
landscape. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Characterisation of the hydrological processes and responses to rehabilitation of a headwater wetland of the Sand River, South Africa.Riddell, Edward Sebastian. January 2011 (has links)
The erosion of headwater wetlands in the Sand River catchment, in the lowveld of north-eastern South Africa has led to a focus on their rehabilitation, both for livelihood security for those that use them for subsistence agriculture, as well as for provision of streamflow regulation services for the Sand River itself. One such wetland, the Craigieburn-Manalana itself undergoing severe erosion was subject to technical rehabilitation using concrete weirs and gabion dams to stabilize the erosion gullies during 2007. Through a series of papers the research discussed in this thesis examined the response of the wetland?s hydrodynamics to the implementation of these measures. Through the installation of a network of hydrometric apparatus the research has shown that the wetlands hydrology is largely controlled by the presence of both horizontal and vertical clay aquicludes within a hydraulically conductive sandy matrix. The sequence of these aquicludes had allowed for artesian phreatic surface phenomena identified in a relatively hydrologically intact region of the wetland. The gully erosion had initiated hydraulic drawdown of the wetland?s water table leading to the desiccation of the system. The construction of a buttress weir within the erosion gully had restored the wetlands hydrodynamics to that typical of conditions upstream of a clay-plug. The research also explored the role that clay plays in terms of controlling the wetland?s hydro-geomorphic setting through geophysical analysis. A conceptual model was then derived that states that these wetlands are held in place by clay-plugs that form through clay illuviation from the hillslopes at regions of valley confinement. This has important implications for the connectivity of wetland process domains. The research also determined the inputs of surface and subsurface flows to the wetland and it was found through detailed examination of soil moisture responses and variably saturated soil physics modelling using the HYDRUS model, that the wetland is hydrologically connected to its contributing hillslope by threshold induced preferential flow pathways, via macropores, that only respond after specific antecedent soil moisture conditions are met. In addition, the thesis describes novel approaches to use information provided by soil scientists for the development of catchment hydrological models. It was shown that the use of this hydropedology information improved the low flow response function of the catchment model, ACRU. This development has important implications for up-scaling of catchment process domains, or hydrological response units by being able to generalize on hillslope hydrological responses based on configuration of their soil type elements. The research also undertook to examine the role that the wetlands play in catchment processes. It was found through water budgeting, supported by hydrological time-series, stable isotope analysis and the quantification of vegetation water use within the wetland and contributing catchment, that these wetlands do not augment baseflows during the dry season. Furthermore, it is only early on during the wet season that these systems may attenuate peak flows, thereafter they act as conduits for high storm flows. Similarities emanated from this research with previous hydrological studies of headwater wetland systems in southern Africa and these are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Assessment of agro-ecosystem sustainability across varying scales in South Africa.Walker, Nicholas James. January 2005 (has links)
Maize production plays an important socio-economic role in rural communities of the Highveld
region of South Africa, yet it is becoming increasingly difficult to produce maize economically
with current agricultural policy conditions and existing management systems. This has direct
socio-economic impacts for both commercial farmer and small-scale farmer. Sustainable
commercial maize production is not only a question of yields, but also of protection of the
environmental resource base, social welfare, and the livelihoods of farmers per se as well as
the surrounding rural and urban communities. Sustainability for the small-scale farmer, on the
other hand raises questions of equity, economic viability and household food security.
Therefore, information is required to ascertain whether an existing agro-ecosystem can be
identified as sustainable, and what facets of that system make it sustainable or
unsustainable. To begin to answer these key questions it is important to state, and to some
extent attempt to standardise, the definitions of agricultural sustainability.
Agro-ecosystem sustainability with regard to maize production was assessed at the regional
scale of the Highveld of South Africa as well as at, the Quaternary Catchment scale and the
smallholder farm scale. Von Wiren-Lehr's (2001) goal orientated system was considered an
appropriate and practical system by which agro-ecosystem sustainability across a range of
scales could be investigated.
At the regional scale, optimum management strategies for each of the 497 Quaternary
Catchments in the Highveld region were devised, based on present climatic conditions and
using an index which was based on mean yields and yield variability. Economic returns and
their impact on sustainability were then also assessed under plausible future climate
scenarios.
At the Quaternary Catchment scales optimum management strategies were ascertained by
using a sustainability index. These strategies were then modelled under present and
plausible future climate scenarios. The results from the sustainability modelling showed that a
maize crop will benefit, especially with respect to mean grain yields, from an effective
doubling of atmospheric CO2 concentrations. However, this benefit can be counteracted when
there is a concurrent increase in temperature, particularly of 2°C or more.
At the smallholder scale, a range of management options was assessed. These options
included several types of tillage practices in combination with applications of either inorganic
fertiliser or manure. The management strategies were modelled under present climate
conditions and under plausible climate change scenarios for southern Africa. The
conventional tillage type (disc) was ranked highest under most of the climatic conditions
modelled, including present climate conditions. This was in contrast to actual yields from
smallholder farmers (-1 ha field size) in the Potshini area, near Bergville in the KwaZuluNatal
province of South Africa, who have experienced an increase in yield when conservation
tillage practices have been used on their land (Smith et al., 2004).
The sustainability of agro-ecosystems depends on the maintenance of the economic,
biophysical and social components that make up the system (Belcher et al., 2004). The
modelling performed for the Highveld region built on previous work and for the first time
incorporated daily temperatures and ISCW soil information into CERES-Maize. The intention
was to incorporate other agro-ecosystem functions, as well as yield, into the sustainability
assessment. Only limited research has previously been carried out in South Africa with
respect to modelling smallholder agro-ecosystems and sustainability. This research sought to
model the smallholder system along with the impacts that climate change would have on
sustainability and associated food security. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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Rainwater harvesting systems and their influences on field scale soil hydraulic properties, water fluxes and crop production.Kosgei, Job Rotich. January 2009 (has links)
South Africa, in common with many parts of Sub-Saharan Africa, is facing increasing water
shortages. Limited available water arising from a low and poorly distributed rainfall, must
supply domestic, agricultural, industrial and ecosystem needs. Agricultural activities of
smallholder farmers, who largely occupy arid to semi-arid areas, are rainfall-driven as they do
not have the capacity to develop conventional water sources, such as boreholes and large dams.
This situation has led to persistent food shortages, low income and a lack of investments,
resulting in high dependency levels of which examples include over reliance on social grants,
household crop production that largely relies on external inputs and availability of cheap
unskilled labour. A growing global perception that water for agriculture has low value relative
to other value uses could further jeopardize the already over exploited agricultural water.
Developing economies such as South Africa are likely to favour, in terms of water allocation,
e.g. electricity generation through steam turbines relative to irrigation needs because industry
plays a more significant role in the economy.
While substantial scientific research has resulted in enhanced yields through in-situ water
harvesting and soil and water conservation, as well as crop and soil fertility management and
plant breeding, less work has been done to assess the impact of intermittent dry spells on crop
yield, particularly with regard to smallholders. Indeed, the interventions that have been
promoted to smallholders may provide little buffer against such events. In addition, the increase
in yield from many such efforts has been marginal and inconsistent, leading some to conclude
that semi-arid environments are hydrologically marginal, have no significant agricultural
potential and any attempts to intensify agricultural activities would lead to severe environmental
degradation.
This study investigated the rainwater harvesting and storage potential among rainfed farmers in
a summer-rainfall region of South Africa. The influences of this practice on soil hydraulic
properties, water fluxes and crop production is detailed in subsequent chapters.
Using historical meteorological data, this study commenced with an investigation of the factors
that influence the length of maize (Zea Mays L.) growing seasons notably the prevalence of
early season dry spells and late season low temperature which could be responsible for
persistent low maize yields amongst smallholder rainfed farmers (Chapter 2). An increasing
trend of dry spells was observed which was found to influence sowing dates and the length of
the growing season. The influence of no-tillage (NT) as an intervention to secure more root-zone soil moisture was
investigated in comparison to conventional tillage (CT) practices. Field experiments, with the
aim of quantifying the extent to which water productivity and yields can be improved among
smallholder rainfed farmers in the Potshini catchment, Thukela basin; South Africa (Chapter 8),
were conducted during both the dry and growing seasons from 2005/06 – 2007/08 seasons at
four sites with similar soil textural properties and slopes. Each site was developed as a runoff
plot and was fitted with moisture and runoff measuring devices. Meteorological parameters
were measured from a weather station installed nearby. A snapshot electrical resistivity survey
was used to compliment soil moisture profiling. The analyses of the different measurements
provided information on various water flow paths and potential downstream hydrological
effects (Chapter 3). The average cumulative runoff was 7% and 9% of seasonal rainfall in NT
and CT treatments over the three seasons.
Changes over time in soil hydraulic properties due to tillage were examined at two depths
through infiltration tests and determination of their bulk densities. These included changes in
steady state infiltration rate and hydraulic conductivity (Chapter 4), interaction between soil
infiltration and soil characteristics (Chapter 5) and water conducting porosity and water
retention (Chapter 6). In 50% of the sites, NT treatments showed significantly higher hydraulic
conductivity compared to CT treatments.
In response to an unexploited opportunity identified to produce vegetables in winter, an
assessment of the potential for runoff water harvesting systems using polyethylene lining as an
alternative cost-effective construction method for underground rainwater storage systems,
particularly in areas where groundwater levels fluctuate rapidly was undertaken (Chapter 7).
The process from conceptualization through design, construction and utilization of the stored
water is described and recommendations for the design and construction of such systems made.
Finally, various case studies which highlight the potential impact of improved soil profile
moisture storage, the additional benefits of water stored in tanks and recommendations for
tailored policies to support household food and income generation are made (Chapter 8). / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.
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Development and evaluation of model-based operational yield forecasts in the South African sugar industry.Bezuidenhout, Carel Nicolaas. January 2005 (has links)
South Africa is the largest producer of sugar in Africa and one of the ten largest
sugarcane producers in the world. Sugarcane in South Africa is grown under a wide
range of agro-climatic conditions. Climate has been identified as the single most
important factor influencing sugarcane production in South Africa. Traditionally,
sugarcane mill committees have issued forecasts of anticipated production for a
region. However, owing to several limitations of such committee forecasts, more
advanced technologies have had to be considered. The aim of this study has been to
develop, evaluate and implement a pertinent and technologically advanced operational
sugarcane yield forecasting system for South Africa. Specific objectives have
included literature and technology reviews, surveys of stakeholder requirements, the
development and evaluation of a forecasting system and the assessment of
information transfer and user adoption. A crop yield model-based system has been
developed to simulate representative crops for derived Homogeneous Climate Zones
(HCZ). The system has integrated climate data and crop management, soil, irrigation
and seasonal rainfall outlook information. Simulations of yields were aggregated from
HCZs to mill supply area and industry scales and were compared with actual
production. The value of climate information (including climate station networks) and
seasonal rainfall outlook information were quantified independently. It was concluded
that the system was capable of forecasting yields with acceptable accuracy over a
wide range of agro-climatic conditions in South Africa. At an industry scale, the
system captured up to 58% of the climatically driven variability in mean annual
sugarcane yields. Forecast accuracies differed widely between different mill supply
areas, and several factors were identified that may explain some inconsistencies.
Seasonal rainfall outlook information generally enhanced forecasts of sugarcane
production. Rainfall outlooks issued during the summer months seemed more
valuable than those issued in early spring. Operationally, model-based forecasts can
be expected to be valuable prior to the commencement of the milling season in April.
Current limitations of forecasts include system calibration, the expression of
production relative to that of the previous season and the omission of incorporating
near real-time production and climate information. Several refinements to the forecast
system are proposed and a strong collaborative approach between modellers,
climatologists, mill committees and other decision makers is encouraged. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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A study on reducing primary transport costs in the South African timber industry.Lusso, Cary D. January 2005 (has links)
Harvesting and transport accounts for up to 70% of the total production cost of roundwood in South Africa. This invokes an interest to improve harvesting systems through the introduction of improved equipment, road networks and more refined operating techniques. A literature review was conducted which investigated the various harvesting systems and equipment with a focus on ground based extraction, as it accounts for 96% of the timber being extracted annually in South Africa. A review of forest roads in South Africa was also conducted and it was concluded that at present there has been little focus on the upgrading and maintenance of forest road networks. It was concluded that the most significant reduction in transport costs would be achieved by reducing the distances travelled by expensive extended pnmary transport (R5.83 t-1.km-1) and by allowing less expensive secondary terminal transport (R0.4 t-1.km-1) to move further into the plantations. This could only be achieved by investing large amounts of capital into the upgrading of forest roads to a standard suitable to service secondary transport vehicles. A model was developed which was able to determine the tonnage of timber needed to flow over a particular road that will warrant the upgrading cost. The model was applied to two study areas, the first study yielded no results due to the already dense network of B- class roads, possibly excessive. The second study area identified three possible road upgrades to improve the existing transport system. A full costing of the existing and modified transport system was completed and a significant cost saving was shown, not accounting for the road upgrading cost. Capital budgets were used to account for more complex parameters, such as tax and discount rates, previously excluded from the simple model. These were used to determine the economic viability of the upgrades and to evaluate the suitability of the model. The model proved to be successful and confirmed that forest roads can be optimised accompanied by significant cost savings. The model is generic and simple allowing for easy application to a variety of situations and is also flexible to modifications. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.
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The development and assessment of techniques for daily rainfall disaggregation in South Africa.Knoesen, Darryn Marc. January 2005 (has links)
The temporal distribution of rainfall , viz. the distribution of rainfall intensity during a storm, is an important factor affecting the timing and magnitude of peak flow from a catchment and hence the flood-generating potential of rainfall events. It is also one of the primary inputs into hydrological models used for hydraulic design purposes. The use of short duration rainfall data inherently accounts for the temporal distribution of rainfall, however, there is a relative paucity of short duration data when compared to the more abundantly available daily data. One method of overcoming this is to disaggregate courser-scale data to a finer resolution, e.g. daily to hourly. A daily to hourly rainfall disaggregation model developed by Boughton (2000b) in Australia has been modified and applied in South Africa. The primary part of the model is the . distribution of R, which is the fraction of the daily total that occurs in the hour of maximum rainfall. A random number is used to sample from the distribution of R at the site of interest. The sample value of R determines the other 23 values, which then undergo a clustering procedure. This clustered sequence is then arranged into 1 of 24 possible temporal arrangements, depending when the hour the maximum rainfall occurs. The structure of the model allows for the production of 480 different temporal distributions with variation between uniform and non-uniform rainfall. The model was then regionalised to allow for application at sites where daily rainfall data, but no short duration data, were available. The model was evaluated at 15 different locations in differing climatic regions in South Africa. At each location, observed hourly rainfall data were aggregated to yield 24-hour values and these were then disaggregated using the methodology. Results show that the model is able to retain the daily total and most of the characteristics of the hourly rainfall at the site, for when both at-site and regional information are used. The model, however, is less capable of simulating statistics related to the sequencing of hourly rainfalls, e.g. autocorrelations. The model also tends to over-estimate design rainfalls, particularly for the shorter durations . / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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