Browsing by Author "Clulow, Alistair David."

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An analysis of transfer pricing theory and an investigation into the domestic transfer pricing practices of large listed South African industrial companies.
(1997) Vally, Imtiaz A. S.; Chukwuogor-Ndu, Chiaku.; Clulow, Alistair David.
An analysis of transfer pricing theory reveals that there are three main objectives of a transfer pricing system: the attainment of goal congruence, the facilitation of fair divisional performance evaluation and the promotion of divisional autonomy. A critical evaluation of suggested theoretically correct transfer pricing methods suggests that the simultaneous attainment of all three objectives is a difficult goal to be realised by a single transfer pricing method. The most appropriate method to suit a particular set of circumstances is contingent upon those circumstances. The transfer pricing objective considered most important in practice by large listed South African industrial companies is the facilitation of fair divisional performance evaluation. Objectives relating to simplicity and ease of application are also rated more highly than goal congruence. Both these findings are somewhat surprising based on the review of current literature. The domestic transfer pricing methods used by large listed South African industrial companies are fairly evenly split between cost and non-cost-oriented methods. The most frequently used primary transfer pricing method is market price. The use of mathematical programming and economic marginal cost prices is practically non-existent. These findings are consistent with the findings of some recent overseas studies. Policies relating to the selection of the transfer pricing method, the purchase of intermediate goods and services and the settlement of transfer pricing disputes reflects some head office management involvement in the transfer price decision process in most cases. Three organisational variables appear to have a significant association with a firm's choice of transfer pricing method. Firstly, companies with a low level of interdivisional trading use non-cost oriented transfer pricing methods whereas companies with a high level of interdivisional trading use cost-oriented methods. Secondly, transfer pricing methods selected as a result of some head office management involvement tend to be cost-oriented whereas methods selected by the divisions themselves tend to be non-cost-oriented. Thirdly, cost-oriented methods tend to be used in companies in which transfer pricing disputes are normally settled by some form of head office intervention and non-cost oriented methods are used in those companies in which disputes are normally settled by the divisions themselves.
Assessment of maize crop health and water stress based on multispectral and thermal infrared unmanned aerial vehicle phenotyping in smallholder farms.
(2021) Brewer, Kiara Raynise.; Clulow, Alistair David.; Sibanda, Mbulisi.; Mabhaudhi, Tafadzwanashe.
Abstract available in PDF.
The contribution of fog to the water balance along the eastern escarpment of South Africa.
(2017) Aldworth, Tiffany Anthea.; Toucher, Michele Lynn.; Clulow, Alistair David.
Fog is a frequent phenomenon in South Africa, occurring mostly on the west coast and along the mountains forming the southern and eastern escarpments. Fog measurements are, however, neglected in water balance studies, resulting in an underestimate of the precipitation input to catchments that experience frequent fog occurrences. World-wide, tropical montane cloud forest (TMCF) studies have proven that fog deposition, facilitated via the interception of fog droplets by vegetation, can represent a significant fraction of the total hydrological input. In South Africa, limited literature exists on the contribution of fog to the country’s water yielding catchments. In particular, information on fog patterns and its contribution to the water balance is extremely scarce in the mountains forming South Africa’s eastern escarpment, where only one study has been previously conducted. Additionally, no forestry studies in the country have attempted to quantify fog. Thus, the aim of this study was to determine the contribution of fog to the water balance of two research catchments of different land use types and altitudes, situated along South Africa’s eastern escarpment. These sites included the Cathedral Peak research catchments and Two Streams; Cathedral Peak is a high altitude montane grassland catchment, whereas Two Streams is at a lower altitude and afforested by exotic plantations. At Two Streams, fog and the climatic conditions were monitored over a 16-month period (July 2015 to October 2016) and additional measurements of throughfall, stemflow and soil water content were carried out in an Acacia mearnsii plantation, to further determine the fog contribution in a forest plantation. At the Cathedral Peak research catchments, fog and the climatic conditions were monitored at three sites, including Mike’s Pass Meteorological Station, Catchment VI and a High Altitude site. Monitoring was conducted over a 14-month period (September 2015 to October 2016) at Mike’s Pass and over a two-month period (August 2015 to September 2015) at Catchment VI and the High Altitude site. Fog was found to be prevalent, occurring frequently and for long durations, potentially contributing fairly substantial amounts of water to the water balance. It occurred all year round, but was predominantly a summer phenomenon, however, it comprised a greater proportion of the total precipitation during the dry winter season. At Mike’s Pass, fog represented a contribution of almost 30 % during several drier months. At Two Streams, during the driest month of August 2015, fog represented a contribution of approximately 38 % of the total precipitation. Fog increased with altitude as a whole, but changes in other topographic features (i.e. hillslope orientation and slope) over short distances, meant that the delivery of fog was not uniform from one point to another at the same altitude. Fog occurrence and water yield increased with wind speed, although this was not found to be a very significant relationship. A stronger relationship between wind direction and fog was observed, particularly at Mike’s Pass, the higher altitude site, which was better exposed to fog-bearing winds. At Two Streams, fog did not facilitate throughfall of rainfall or contribute to soil water. The indirect effects of limiting wet canopy evaporation and transpiration rates were suggested to be a more relevant effect of fog on the water balance. These findings further the understanding of the contribution of fog to the water balance along the eastern escarpment of South Africa and will assist in future long-term climatological studies of fog and low cloud occurrence in the region.
Detection and early warning of lightning and extreme storm events in KwaZulu-Natal, South Africa.
(2020) Mahomed, Maqsooda.; Clulow, Alistair David.; Mabhaudhi, Tafadzwanashe.; Savage, Michael John.; Chetty, Kershani Tinisha.; Strydom, Sheldon.
Abstract available in pdf.
Effect of elevated CO2 concentration on growth, development and postharvest characteristics of sweetcorn (Zea mays L. var. saccharata)
(2022) Dlulisa, Balungile Precious.; Bertling, Isa.; Clulow, Alistair David.
Abstract available in PDF.
Influence of land cover degradation on the water balance of the Northern Drakensberg high altitude mesic grasslands, South Africa.
(2022) Gray, Byron Andrew.; Toucher, Michele Lynn.; Clulow, Alistair David.; Savage, Michael John.
Mountainous regions provide vital ecosystem services, such as water provisions to low land areas. However, these regions are also considered sensitive to the effects of environmental change, due to their high levels of endemism and biodiversity. Thus, environmental change within these regions could have significant consequences beyond the extent of the region itself. An important implication of environmental change is the impact a change in land cover could have on the water balance of a catchment, especially within the headwater catchments. The Drakensberg mountains in South Africa, is such a mountain region, which is vital for its provision of ecosystem services and generation of water resources. This mountainous region is under threat from anthropogenic environmental change. The Drakensberg mountain range has been identified within South Africa as a strategic water source area (SWSA) and within the Northern-Drakensberg SWSA exists the Maloti-Drakensberg Park, which is a protected area managed by Ezemvelo KZN Wildlife and a World Heritage site. The Northern-Drakensberg mountain range natural grasslands are under threat from two forms of land cover change degradation, that of woody encroachment and following disturbance, invasion of bracken fern. Woody encroachment occurs within the natural grasslands following the removal of fire, which is of concern within the protected areas, where fire is a current management tool to maintain the natural grassland cover. Outside the protected area, disturbances due to human activities such as overgrazing and poor land management have led to a substantial level of degradation occurring, providing ideal conditions for the invasion of bracken fern. To safeguard and maintain the assurance of supply from an important SWSA of South Africa, there is the need for improved understanding on the impacts of land cover change and degradation within the Northern-Drakensberg mountain range on the water balance of the region. Thus, the overall aim of this thesis is to understand the influence of land cover change related degradation on the water balance of the Northern-Drakensberg high-altitude mesic grasslands and what this in turn means for the water supply generated from this SWSA of South Africa. To achieve the main aim, the research was scaled from a point measurement to a basin scale where management decisions are made. To improve our understanding of the impact of degradation related land cover change on the water balance an observational approach is required. Located within the Maloti-Drakensberg Park is the long-term Cathedral Peak research catchments which provided the platform for the observation component of this research. Of interest in the Cathedral Peak research catchments were three hydrologically individual catchments. Catchment III which consists of a degraded bracken fern land cover following the historical research experiments within the catchment on the impacts of commercial Pinus patula plantation on streamflow. Despite rehabilitation efforts following the removal of the plantation, the catchment transitioned to a degraded state and is currently near-completely invaded with bracken fern. Catchment VI which is under natural grassland condition, is managed with a bi-annual spring burn as proven best practice within the Drakensberg region. This catchment formed the baseline catchment for this research. Catchment IX is a woody encroached land cover following the protection of fire since the 1950s as part of research into the implications of removing fire from the natural grasslands. These three catchments provided the ideal platform from which the change in water balance components under each land cover could be monitored and investigated. The process of evapotranspiration (ET), which forms the connection between the energy and water balances, is well understood to be one of the most affected components of the water balance following a change of land cover. Therefore, ET was the focus of the initial point observation research. Due to the cost and stringency of the prominent method for ET measurement of eddy covariance (EC), an alternative more financially feasible method of surface renewal (SR) was tested over both Leucosidea sericea (woody) and Pteridium aquilinum (bracken) vegetation in comparison to EC. It was determined that the SR method, and in particular the SR dissipation theory (SRDT) method, which is independent of EC, was the best alternative and cheapest method to EC. The SR method is now used within the Cathedral Peak research catchments for long-term estimations of ET over both vegetation canopies. During this research, calibration factors (α) for the surface renewal 1 (SR1) method were determined for both the Leucosidea sericea (woody) and Pteridium aquilinum (bracken) vegetation types for winter and summer. Having confirmed the SRDT ability as an alternative to EC, the seasonal ET of Leucosidea sericea (woody) and Pteridium aquilinum (bracken) was determined. Providing first insight into the seasonality of ET over these vegetation types. Both vegetations followed a similar seasonal ET cycle to the natural grasslands, with the largest difference occurring in winter when the grasslands become dormant. It was also found that the energy balance was altered under the degraded land covers, with both forms increasing available energy and latent heat flux. Following the understanding of the seasonal change in ET through point measurements, the research focus was scaled up to the research catchment. A comparison of catchment VI and IX was conducted to identify changes in the headwater catchment water balance between the natural grassland and woody encroachment land covers. Long-term data sets of precipitation and streamflow from the Cathedral Peak research catchments, in combination with the seasonal ET observations showed that over time, as woody encroachment increased, the catchment rainfall:runoff response ratio decreased, as did streamflow under woody encroachment compared to natural grassland. Having gained an understanding of the impacts on a water balance of a headwater catchment, hydrological modelling in combination with scenario analysis was used to understand the impacts on water supply from the upper-uThukela catchment were both land cover degradation threats left unmanaged. Land cover parameters were unavailable for Leucosidea sericea (woody) and Pteridium aquilinum (bracken), and therefore were derived from understanding gained during observation. The ACRU agrohydrological model was utilised and confirmed to simulate current land cover conditions within the upper-uThukela satisfactorily at both the headwater and catchment levels. It was identified that both forms of land cover change resulted in a reduction in streamflow. This was largest for woody encroachment. The most affected flows were the low flows and winter dry period flows. Headwater catchments were also identified as the most impacted by land cover change. The key conclusions of the research were: • that the surface renewal methodology is a viable alternative for obtaining estimates of evapotranspiration over indigenous vegetation types; • that the energy balance and ET of woody vegetation in comparison to the natural grassland was significantly altered; • the importance of fire, as not only a management tool for the maintenance of the natural grasslands, but also to ensure the sustainability of the vital water resources and ensuring water security; • that there is an evident lag between the onset of degradation in the form of woody encroachment and the resultant impacts on streamflow; • the disproportionally large impact degradation related land cover change within these headwater catchments has on the downstream water balance relative to low land catchments. Following the analysis and with the understanding gained, it is recommended that the natural grasslands continue to be managed using fire, and continued protection of the natural grasslands needs to be maintained. Observation within these headwaters is key to improving the understanding of change and to drive decision making, allowing for the optimal management of the important SWSA.
The long-term measurement of total evaporation over Acacia mearnsii using large aperture scintillometry
(2007) Clulow, Alistair David.; Savage, Michael John.
A large aperture scintillometer (LAS) was operated continuously over a distance of 575 m from 19 August 2006 to 29 September 2007 in the South African KwaZulu-Natal midlands mistbelt area over Wattle (Acacia mearnsii). The LAS measurements of the structure parameter of the refractive index of air ( 2 n C ), were used to calculate the sensible heat flux. The shortened energy balance equation was used to estimate the latent energy flux as a residual from which the total evaporation (ET) was calculated. The LAS estimates of sensible heat flux during the short transition period (1 hour) between stable and unstable conditions were on occasion erroneous and required verification. Advection was also found to affect sensible heat flux estimates. Long-term operation of the LAS was however found to be possible even at remote sites, producing reliable and continuous results. The LAS estimates of sensible heat are sensitive to zero-plane displacement height and wind speed data impact and these should be derived as accurately as possible. Tree heights were measured at monthly intervals and a zero-plane displacement and effective height were calculated every two weeks. The sensible heat flux was thus processed in two week blocks of data corresponding to progressive effective heights. The tree growth rate was consistent over time and was not affected by seasonality, indicating that reduced air temperatures, rainfall and solar irradiance in winter are not limiting growth. The average growth rate was 0.37 m per month or 4.5 m per year. The LAS ET was compared to the American Society of Civil Engineers - Environmental and Water Resources Institute (ASCE-EWRI) short grass reference evaporation (ETsz) for a seven-month period and was found to compare favourably (R2 = 0.78) with outliers caused by advection and rainfall events. Calculations of grass reference evaporation at hourly and daily intervals provide different results. The daily estimates are lower than the hourly estimates by 17 % on average. Where hourly data is summed to calculate a daily ETsz, night-time values should be included. The LAS ET measurements were validated against the Priestley and Taylor (1972) method of estimating ET and found to be in good agreement (R2=0.94). The Priestley and Taylor daily total latent energy flux, from 22 August 2006 to 29 September 2007, was 9 % higher than the LAS results on average. The Bowen ratio for the entire period is less than 1, indicating that the latent energy flux dominates at the site. The ET over the period of measurement (13 months) is 1250 mm and the rainfall is 750 mm. This confirms previous results at the site using the Bowen ratio energy balance method showing that the ET exceeds the rainfall by 45 % and justifies further research into soil water, ground water and root interactions in the deep soil profile.
Potential of pre-and postharvest illumination of cherry tomato, a climacteric fruit, to reduce the ripening period and enhance yield and quality while maintaining shelf life.
(2017) Ngcobo, Bonga Lewis.; Bertling, Isa.; Clulow, Alistair David.
Tomato (Solanum lycopersicum) is the most-consumed horticultural commodity worldwide because it is diverse in use, attractive and contributes significantly to the health and nutrition of humans. There are many different types of tomato cultivars, such as the classic round, plum and baby plum, cherry, beefsteak, vine or truss and cocktail tomatoes. Baby tomatoes, also termed ‘cherry tomatoes’, have become particularly popular as fruit vegetables, due to their taste, particularly sweetness, high nutritional value and health benefits, as well as their attractive colour, particularly in the presentation of food.Many horticultural commodities are nowadays cultivated under supplemental lighting, such as ultraviolet C (UV-C), light emitting diodes (LEDs), and high-pressure sodium (HPS) so as to improve yield and reduce ripening period since the demand of tomato, particularly cherry tomato is increasing significantly which forces tomato growers to make use of controlled environment to meet the increasing demand. The use of LEDs in protected cultivation is gaining popularity as it can improve yields and enhance certain phytochemicals. Light-emitting diodes (LEDs) represent a relatively new technology for the greenhouse industry, as they emit light of narrow bandwidths. These lights are affordable and they do not contain unnecessary, low quality wavelengths. Therefore, LEDs can be employed to promote growth of fruit and vegetables in agriculture, particularly in horticulture, as they aid in plant development. Further, LEDs are easily controllable light sources and their use can improve the nutritional content of certain commodities, while improving or maintaining yield and giving high quality produce. Light affect the presence of phytonutrients in tomato fruit, such as carotenoids, vitamin C and phenolics. The general aim of this study was to determine if certain treatments are able to fast-forward colour change, while maintaining the fruit quality of cherry tomato. Two experiments were conducted, one in the glasshouse and another one in the post-harvest laboratory at the University of KwaZulu-Natal in 2017. The first experiment was designed to evaluate the effect of pre-harvest red and blue light treatment on colour, ripening, chlorophyll and carotenoid concentration as well as overall quality of the cherry tomato cultivars (‘Cherry Little Wonders’ and ‘Goldilocks’).When fruit were mature green, the a* values of the twelve trusses of the same age, six from each cultivar, were selected to receive light treatment. Six trusses, three of each cultivar, were illuminated with FLC-10W-R Red LED light (RL) and another six trusses, three of each cultivar, were illuminated with FLC-10W-BL blue LED light (BL). It was ensured that the distance from each light source to the truss was the same and it was also ensured that the light was equally distributed to every truss. Certain fruit were marked in each truss for analysis of quality parameters or measurements such as colour, size, firmness, TSS, chlorophyll and carotenoids. In this study pre-harvest red and blue light significantly affected the measured quality attributes of two cultivars (‘Cherry Little Wonders’ and ‘Goldilocks’), a red and yellow cherry tomatoes respectively. Light treatments did not have a significant effect on fruit size (P > 0.05) The size of all light-treated fruit was bigger than that of untreated fruit from day 15 to day 25, however there was no statistical significant difference between treated and non-treated fruits (P > 0.05). Yellow cultivar had a lower a* value and higher value of b*(green to yellow) from day 10 to day 25. A steady decrease in colour b* was observed in red cv while a sharp increase was observed in yellow cv, but fruits that were illuminated with red light had a higher b* value on both cultivars. Following treatment, L* (lightness) steadily decreased in treated and untreated tomato fruit for the first 10 days. Thereafter, a rapid decrease in L* was observed. A sharp decrease in chlorophyll concentration and a corresponding increase in carotenoid synthesis during the fruit ripening process was observed Chlorophyll a, b and carotenoid concentrations in tomato differed significantly (P < 0.01) between treatments, with the control maintaining the highest Chl a and Chl b values until day 25. There was a statistical significant difference between untreated and treated fruit in terms of changes in Chl a and b (P < 0.05). The red cv treated with BL and the yellow cv treated with RL showed a rapid decrease in Chl a. The accumulation of lycopene commenced in treated tomatoes 10 days after treatment, but for the first 10 days there was no statistical difference between the treated and non-treated fruit (P < 0.05). The lycopene concentration of yellow tomatoes was lower that of red tomatoes. The firmness of treated and non-treated fruit was similar the same in all fruit for the first five days postharvest, except in the yellow cv treated with BL. This treatment lost firmness most rapidly. Light also prevented the occurrence of diseases and disorder. The second study was conducted to investigate the effects of post-harvest red and blue LED light treatments on two cultivars of cherry tomatoes, red (‘Cherry Little Wonders’) and yellow (‘Goldilocks’) which received light at different stages of development, while on the plant as well as postharvest. The response of tomato cultivars that received post-harvest light treatment did not differ significantly with the cultivar that was treated and allowed to ripen on the tree. Light treatments were able to enhance colour development more on cherry tomato fruits treated at mature green compared to those treated at turning stage. The effect of light on chlorophyll a and b on fruits varied according to the cultivars. Fruit that were treated at turning stage had lower chlorophylls initially and then a steady rate of change was observed while a sharp/rapid degradation of chlorophylls was observed in fruits treated at mature green. Light effects on degradation of chlorophylls had no significant difference within the stage at which plants received the treatment. Lycopene was the major pigment in red cv of cherry tomatoes. It was influenced equally by red and blue lights, with fruit treated at mature green had more lycopene that those treated at turning stage. There was a significant difference between treatments and the control in terms of lycopene and β-carotene content which were higher in fruits treated at mature green. There was no significant difference (P < 0.05) in change in mass of fruit that received red and blue lights and non-treated fruits meaning that light did not have a negative effect on tomato fruits treated at mature green stage and at turning stage. Light treatments were able to prevent the occurrence of diseases on all the treatments.
Productivity and water use of commercial forestry species and their potential impact on surface water resources in two forestry areas of KwaZulu-Natal, South Africa.
(2023) Kaptein, Nkosinathi David.; Clulow, Alistair David.; Toucher, Michelle Lynn.; Everson, Colin Stuart.; Germishuizen, Ilaria.
Abstract available in PDF.
Quantification of the water-use dynamics of the dominant plant communities of the Eastern Shores in the iSimangaliso Wetland Park for improved water resource management.
(2015) Clulow, Alistair David.; Everson, Colin Stuart.; Price, Jonathan.; Jewitt, Graham Paul Wyndham.
No abstract available.
Temperature dynamics within a low-cost aquaponic system and the possibe effects of climate change.
(2019) Mkhize, Minenhle Godslove.; Clulow, Alistair David.; Taylor, Simon Michael.; Lagerwall, Gareth.
The agricultural sector is facing impeding challenges due to climate change. There is enough evidence showing that climate change has a significant impact on agricultural production. Marginalized communities that lack financial resources and depend on agricultural crop production, are the most vulnerable to climate change effects, which further exacerbates 5 their food insecurity. Existing literature hypothesizes that aquaponics, using Tilapia, has potential in addressing climate change effects in agriculture. However, the low average winter temperature hinders successful adoption of low-cost aquaponic systems using Tilapia fish. The implication of cool conditions (South African temperatures) are more extreme for a low-cost, poorly resourced aquaponic users because they lack temperature regulation 10 systems to maintain optimal temperatures and are simply subject to the surrounding environmental conditions. Therefore, the purpose of this study was to understand the temperature dynamics of a low-cost aquaponic system and the possible effects of future climate change. A study was conducted at KwaDeda, a poor rural community in the Ndwedwe area of 15 KwaZulu-Natal. The two objectives were to (1) understand how the surrounding environmental air temperature affects the water temperature of a low-cost aquaponic system and, to (2) assess the implications of future climate change on a low-cost aquaponic system. Two weather stations (22 km apart) were installed, one to measure hourly environmental air temperature conditions and the other to measure the conditions within the plastic tunnel of 20 a low cost aquaponic system (from June – November 2019). The environmental air temperature had no immediate relationship with water temperature. However, there was an observed lag of 4 hours from the environmental air temperature peak to water temperature peak, which varied slightly with seasonality. The conditions within the tunnel were generally hotter than the outside environmental conditions during the day, 25 however, at night, the tunnel air temperature dropped to be the same and sometimes even lower the outside environmental temperature. The air temperatures in winter and resulting water temperatures of the low-cost aquaponic system was well below the optimum range for Tilapia (22-32 °C). Low-cost systems provide limited means to control water temperature. Therefore, further investigation into low-cost methods to reduce the cooling of the tunnels 30 at night, which later results in cooling of the water, is required. The projected future climate was shown to be both advantageous and disadvantageous for the low-cost aquaponic system. The projected increase in average air temperature due to climate change will be positive for South African conditions, which are generally quite cool for Tilapia. However, extreme weather conditions such as intense storms, high wind speed and hail, that are predicted with climate change, may be a threat to low-cost aquaponic infrastructure. Research into improving the design of low-cost tunnels that can withstand adverse weather conditions is recommended.
The implementation of UAV multispectral imagery for gully mapping, Okhombe Valley, KwaZulu-Natal Drakensberg, South Africa.
(2023) Riddle, Lyndon Paul.; Hill, Trevor Raymond.; Clulow, Alistair David.
The availability, cost, and applicability of Unmanned Aerial Vehicles (UAVs) are rapidly altering the way we perceive the landscape, can access sites, and model the landscape as it unfolds through remote sensing technologies. It falls to present and future researchers to take advantage of this and use the technology to improve our understanding of our surroundings. One way that geomorphologists would be able to take advantage of the improvements in technology is to use the UAV to map soil processes, in particular erosion. The current methods and technology for mapping gully erosion do not look at the smaller features but rather the landscape as a whole. The purpose of this research was to assess the prospects of UAV technology mapping gully erosion. Specifically, the study investigates the application of the UAV imagery to other technologies or methods in mapping gully erosion activities. This was achieved by testing the multiple available modelling software, by mapping objects of known shapes and volumes to determine which software produced results comparable to that of the known shapes. Tests were conducted to determine if this software and UAV combination would have the ability to map and 3D render soil erosion, thus allowing researchers to verify if this technique could be implemented into mapping gully systems. From these tests, it was found the UAV was able to improve the resolution to that of the available methods. Obtaining a resolution of 0.03m would allow geomorphologists to map and situate the soil erosional landscapes and map the test objects. The software package AgiSoft MetaShape had the highest accuracy and reliability in mapping various objects making it ideal in the mapping of smaller erosional features. Multiple erosional landscapes were mapped using a UAV and the attached RGB sensor and a second UAV with a multi-spectral sensor and AgiSoft MetaShape software. Both sensors mapped plant health, capturing plant health with band widths related to each sensor. Ideally the multi-spectral sensors were seen to be more versatile, however the RGB sensor can be useful. The combination of both UAVs created a 3D-rendered model, and the resulting data was useful in determining the potential future areas of erosion and existing areas of high erosion risk. The multi-sensor camera allowed the user to determine micro-features that could potentially become erosional areas in the future as it identified areas with a concentration in water flow. In conclusion, the UAV is a useful spatial tool to monitor, measure and manage soil erosion and gully mapping.
The use of environmental isotopes, soil water measurements and soil water modelling to understand tree water use of an Acacia mearnsii (Black wattle) stand in KwaZulu-Natal.
(2015) Watson, Andrew.; Everson, Colin Stuart.; Clulow, Alistair David.; Bulcock, Hartley Hugh.
In Southern Africa commercial afforestation is an important agricultural activity and accounts for a large portion of the gross agricultural production, However, there are concerns regarding its possible detrimental impact on the hydrological system. Previous research in the Two Streams catchment by Clulow et al. (2011) showed that a commercial forestry species (Acacia mearnsii) was using more water than available through precipitation over a 30-month period (total evaporation was greater than rainfall) and they concluded that the trees were drawing water from another source. In this study, field measurements of stable isotopes of rainfall, soil water, stream water and groundwater were collected and analysed in order to understand the deficit in the water balance identified by Clulow et al. (2011). Experimental apparatus was used to extract isotopes from soil water. Automated rainfall and streamflow samples were used to sample rainfall and stream water (evaporation seals were designed to prevent fractionation). A specific set of criteria was used to program the automated rainfall sampler to better differentiate between event samples. HYDRUS 1-D model outputs of simulated total evaporation and soil water fluxes were verified from total evaporation and soil water measurements at the site. Rainfall varied in isotope signature throughout the year ranging from -150 to -15 permil (δ2H) and -20 to 2 permil (δ18O), these values were largely dependent on rainfall volume. Groundwater isotope composition signature changed only slightly throughout the year ranging from -12 to -5 permil (δ2H) and -4 to -1.5 permil (δ18O), with seasonality being the driving variable. The results from the isotope signatures showed that the main contributor to streamflow (-15 to -1.5 permil (δ2H) and -4.5 to -1.5 permil (δ18O)) was groundwater. Soil isotope signatures varied with depth and season, ranging from -25 to -8 permil (δ2H) and - 1.5 to 4 permil (δ18O). Groundwater signatures were evident on three occasions within the soil horizon (2.0 m and 2.4 m on 23/08/2013 and 1.6 m on 13/0/2013), where water was moved by hydraulic lift or capillary rise and made available for uptake by rooting systems. This was confirmed by Watermark and TDR-100 measurements, where there were upward fluxes of deep soil water during the dry season. HYDRUS-1D results suggested that simulated total evaporation (1052 mm) was similar to measured actual evaporation (1095 mm) during the wet season and dry season. The results conclude that the Acacia mearnsii trees extracted soil water or deep groundwater during the dry season, which allows for continuous growth throughout the year. This supports the conclusion of Clulow et al. 2011 and confirms that commercial forestry could have significant long-term impacts on catchment hydrology, particularly in dry season low flows.
Water-use of commercial bamboo species in KwaZulu-Natal, South Africa.
(2020) Gumede, Mxolisi Percyval.; Clulow, Alistair David.; Everson, Colin Stuart.; Everson, Theresa Mary.
Abstract available in pdf.