Investigation of sediment buffering function of the Gatberg Floodplain Wetland in the upper Tsitsa River Catchment, South Africa
- Pakati, Sibuyisele Sweetness
- Authors: Pakati, Sibuyisele Sweetness
- Date: 2021-10
- Subjects: Sedimentation and deposition South Africa Eastern Cape , Sediment transport South Africa Eastern Cape , Floodplain morphology South Africa Eastern Cape , Wetlands South Africa Eastern Cape , Suspended sediments South Africa Eastern Cape , Floods South Africa Eastern Cape , Fluvial geomorphology South Africa Eastern Cape , Floodplain plants South Africa Eastern Cape , Inundation depth
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190792 , vital:45028
- Description: Floodplain wetlands are important components of river systems that provide various ecosystem services such as sediment buffering. These wide and often expansive storage areas have a substantial impact on downstream water quality by trapping sediment and storing ‘contaminants’ adhered to sediment thus improving water quality. The planned construction of the Ntabelanga and Lalini Dams in the Tsitsa River Catchment has been proposed; however, due to the steep landscapes and erodible soils, this promotes high erosion rates that can potentially reduce the lifespan of the proposed dams. The existing wetlands in the Tsitsa River Catchment have therefore been identified as key sediment buffers that can reduce sediment transport, but the effectiveness of these buffers is poorly researched. This study attempts to investigate the current sediment buffering function of the Gatberg Floodplain Wetland over one wet season (August 2019 to August 2020). Time integrated samplers were installed above and below the wetland to determine relative sediment volume and character coming in and out of the wetland. Five transects were surveyed across the wetland width to evaluate the topography and vegetation characteristics. Surface sediment samples on the floodplain were taken at key morphological features along each transect and along the river longitudinal profile to determine organic content, particle size, and type of stored sediment. Astro turf mats were deployed on targeted transects and on key floodplain features to determine sediment accumulation rates. Field measurements of vegetation parameters (height, density, and stem diameter) were taken to calculate vegetation-induced hydraulic roughness to understand possible sedimentation feedbacks. The relative sediment volume coming into the wetland was greater than that leaving the wetland. This implies that some of the sediment is buffered within the wetland. An approximate proportion of 73% trapping efficiency of the incoming sediment was buffered within the floodplain wetland during the wet season. This accumulated approximately 4 tons within the wetland over the monitoring frame. Bed particle size in the longitudinal profile increased with distance downstream, this was due to localized tributary and hillslope inputs. Inundation depth varied across the floodplain wetland with deeper inundation depths at the head of the wetland than at the bottom; where particle size was larger with an increase in water level depth. This may be linked to both high stream velocities and variability of the floodplain topography. However, the observed trends were inconclusive and uncertain. Stronger correlations with particle size were shown by vegetation roughness (b* = 0.41) and distance from the channel (b* = -0.38). Flood benches and banks had a coarser D50 particle size than back swamps and oxbows. Coarser sediment in flood benches are associated with proximity to the sediment-laden water that experiences abrupt flow velocity changes, while finer material in oxbows are due to minimal flow velocities which reduce with distance from the channel. Finer particles remain in suspension and are carried aloft for longer periods at very low velocities. Therefore, particle size decreased with distance from the channel due to longer travel distances and high surface area relative to weight. Further results showed that finer surface sediment particle size was associated with high vegetation roughness whilst coarser material was associated with low roughness. This was due to vegetation geometry and type or changes in flow velocity and energy. Grassy vegetation induced finer particle size than shrubby vegetation that has a greater line spacing. Furthermore, vegetation roughness varied over the wet season; roughness was highest in late summer and low in early summer. Low roughness was due to fire occurrence in the study area which resulted in a decrease in biomass. Increasing vegetation roughness can be due to increased flood events, and the introduction of non-perennial species; which can increase sediment accumulation rates. Although studies have shown that vegetation density is the most essential factor affecting flow resistance and sedimentation processes; vegetation height and stem diameter for this study area seem to contrast these observations and rather may be the most significant contributing factors in sedimentation. This concluded that vegetation density may not always be the most essential component in sedimentation processes. Sediment particle size was inversely proportional to organic content; finer particle size are more cohesive and more capable of carrying organics. Regions further away from the channel such as oxbows with stable moisture conditions favour plant growth and soil formation thus are susceptible to high organic content. Flood benches are closer to the channel, thus have coarser material and fluctuating moisture conditions that have unstable high water flow velocities. High sediment accumulation rates on flood benches and oxbows is due to high connectivity to sediment-laden water and high hydroperiods or high residence time for sediment accumulation in oxbows. Sediment accumulation rate was shown to be a function of particle size itself (b* = 0.67) rather than the expected vegetation roughness. Although a true representation of sediment accumulation rates in the Gatberg Wetland was limited by the disturbance of astro turf mats by animals and possibly by high flooding events; the wetland can be regarded as a good sediment buffer as some sediment was stored (e.g. up to 48,04 kg/m2 in flood benches) within the wetland over the monitoring period. , Thesis (MSc) -- Faculty of Science, Geography, 2021
- Full Text:
- Authors: Pakati, Sibuyisele Sweetness
- Date: 2021-10
- Subjects: Sedimentation and deposition South Africa Eastern Cape , Sediment transport South Africa Eastern Cape , Floodplain morphology South Africa Eastern Cape , Wetlands South Africa Eastern Cape , Suspended sediments South Africa Eastern Cape , Floods South Africa Eastern Cape , Fluvial geomorphology South Africa Eastern Cape , Floodplain plants South Africa Eastern Cape , Inundation depth
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190792 , vital:45028
- Description: Floodplain wetlands are important components of river systems that provide various ecosystem services such as sediment buffering. These wide and often expansive storage areas have a substantial impact on downstream water quality by trapping sediment and storing ‘contaminants’ adhered to sediment thus improving water quality. The planned construction of the Ntabelanga and Lalini Dams in the Tsitsa River Catchment has been proposed; however, due to the steep landscapes and erodible soils, this promotes high erosion rates that can potentially reduce the lifespan of the proposed dams. The existing wetlands in the Tsitsa River Catchment have therefore been identified as key sediment buffers that can reduce sediment transport, but the effectiveness of these buffers is poorly researched. This study attempts to investigate the current sediment buffering function of the Gatberg Floodplain Wetland over one wet season (August 2019 to August 2020). Time integrated samplers were installed above and below the wetland to determine relative sediment volume and character coming in and out of the wetland. Five transects were surveyed across the wetland width to evaluate the topography and vegetation characteristics. Surface sediment samples on the floodplain were taken at key morphological features along each transect and along the river longitudinal profile to determine organic content, particle size, and type of stored sediment. Astro turf mats were deployed on targeted transects and on key floodplain features to determine sediment accumulation rates. Field measurements of vegetation parameters (height, density, and stem diameter) were taken to calculate vegetation-induced hydraulic roughness to understand possible sedimentation feedbacks. The relative sediment volume coming into the wetland was greater than that leaving the wetland. This implies that some of the sediment is buffered within the wetland. An approximate proportion of 73% trapping efficiency of the incoming sediment was buffered within the floodplain wetland during the wet season. This accumulated approximately 4 tons within the wetland over the monitoring frame. Bed particle size in the longitudinal profile increased with distance downstream, this was due to localized tributary and hillslope inputs. Inundation depth varied across the floodplain wetland with deeper inundation depths at the head of the wetland than at the bottom; where particle size was larger with an increase in water level depth. This may be linked to both high stream velocities and variability of the floodplain topography. However, the observed trends were inconclusive and uncertain. Stronger correlations with particle size were shown by vegetation roughness (b* = 0.41) and distance from the channel (b* = -0.38). Flood benches and banks had a coarser D50 particle size than back swamps and oxbows. Coarser sediment in flood benches are associated with proximity to the sediment-laden water that experiences abrupt flow velocity changes, while finer material in oxbows are due to minimal flow velocities which reduce with distance from the channel. Finer particles remain in suspension and are carried aloft for longer periods at very low velocities. Therefore, particle size decreased with distance from the channel due to longer travel distances and high surface area relative to weight. Further results showed that finer surface sediment particle size was associated with high vegetation roughness whilst coarser material was associated with low roughness. This was due to vegetation geometry and type or changes in flow velocity and energy. Grassy vegetation induced finer particle size than shrubby vegetation that has a greater line spacing. Furthermore, vegetation roughness varied over the wet season; roughness was highest in late summer and low in early summer. Low roughness was due to fire occurrence in the study area which resulted in a decrease in biomass. Increasing vegetation roughness can be due to increased flood events, and the introduction of non-perennial species; which can increase sediment accumulation rates. Although studies have shown that vegetation density is the most essential factor affecting flow resistance and sedimentation processes; vegetation height and stem diameter for this study area seem to contrast these observations and rather may be the most significant contributing factors in sedimentation. This concluded that vegetation density may not always be the most essential component in sedimentation processes. Sediment particle size was inversely proportional to organic content; finer particle size are more cohesive and more capable of carrying organics. Regions further away from the channel such as oxbows with stable moisture conditions favour plant growth and soil formation thus are susceptible to high organic content. Flood benches are closer to the channel, thus have coarser material and fluctuating moisture conditions that have unstable high water flow velocities. High sediment accumulation rates on flood benches and oxbows is due to high connectivity to sediment-laden water and high hydroperiods or high residence time for sediment accumulation in oxbows. Sediment accumulation rate was shown to be a function of particle size itself (b* = 0.67) rather than the expected vegetation roughness. Although a true representation of sediment accumulation rates in the Gatberg Wetland was limited by the disturbance of astro turf mats by animals and possibly by high flooding events; the wetland can be regarded as a good sediment buffer as some sediment was stored (e.g. up to 48,04 kg/m2 in flood benches) within the wetland over the monitoring period. , Thesis (MSc) -- Faculty of Science, Geography, 2021
- Full Text:
An investigation into the fire regimes of the upper Tsitsa River catchment
- Authors: Snyman, Gareth
- Date: 2020
- Subjects: Prescribed burning -- Environmental aspects -- South Africa , Fire ecology -- South Africa , Tsitsa River catchment (South Africa) , Soil erosion -- South Africa , Grasslands -- Management -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145256 , vital:38422
- Description: South African grasslands are rich in flora and fauna and are a dominant vegetation cover in many of the water catchment areas, while providing a multitude of services to local communities and the environment. Fires have been the primary tool used to manage grasslands for livestock production for many years. However, there is debate about how they impact and alter landscapes and there are two schools of thought throughout literature. One argument is that fires are detrimental to landscapes; altering hydrological processes by causing excess soil erosion and changing soil properties. The other opinion is that fires are beneficial to ecosystems; maintaining vegetation structure, preventing bush encroachment, cycling nutrients and allowing for new plant growth. This study focused on the effects of fire regimes on soil properties in order to better understand the role that fire plays in geomorphic processes in the upper Tsitsa River catchment. The catchment falls under two land management types- commercial and communal, with the latter being severely degraded. Fire regimes were determined using a combination of Landsat and MODIS remotely sensed data and testing was carried out on soils exposed to different Fire Return Intervals (FRI). It was found that soils that were exposed to a high fire frequency (1-2-year FRI) exhibited a significantly higher degree of water repellency (p< 0.001) and surface hardness (p< 0.001) than soils that were exposed to a low fire frequency (3-4 year FRI), which indicates increased erosion potential. However, whilst a higher fire frequency resulted in altered soil characteristics, it contributed to landscape degradation as suggested in the literature, and soils are able to return to their previous state in over a short period of time. Further investigation into factors affecting fire regimes found that geology influenced vegetation type, resulting in differences in biomass in the two land management areas. The commercially managed land supported a high biomass, which resulted in a more natural fire regime with frequent fires, whilst the communally managed land supported less biomass. Smaller fuel loads and increased landscape fragmentation through overgrazing and road networks resulted in an altered fire regime with less frequent fires. Although the communally managed land has an altered fire regime, this research suggests that fires are not influencing the severe degradation present in these areas, and this is rather a function of geology and mismanagement of land. Whilst fire and grazing management plans can be implemented to alter the modified fire regime in the communal areas back to its natural state, this would take a long time and an increase in fires would pose a threat to surrounding communities. Overall the fire regimes in the upper Tsitsa River catchment are being altered by human influence and land management type, and whilst fire frequency is negatively altering soil properties, these soils can return to their natural state. The severe land degradation present in the communally managed areas are not a function of fire frequency and rather of geology and land management.
- Full Text:
- Authors: Snyman, Gareth
- Date: 2020
- Subjects: Prescribed burning -- Environmental aspects -- South Africa , Fire ecology -- South Africa , Tsitsa River catchment (South Africa) , Soil erosion -- South Africa , Grasslands -- Management -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145256 , vital:38422
- Description: South African grasslands are rich in flora and fauna and are a dominant vegetation cover in many of the water catchment areas, while providing a multitude of services to local communities and the environment. Fires have been the primary tool used to manage grasslands for livestock production for many years. However, there is debate about how they impact and alter landscapes and there are two schools of thought throughout literature. One argument is that fires are detrimental to landscapes; altering hydrological processes by causing excess soil erosion and changing soil properties. The other opinion is that fires are beneficial to ecosystems; maintaining vegetation structure, preventing bush encroachment, cycling nutrients and allowing for new plant growth. This study focused on the effects of fire regimes on soil properties in order to better understand the role that fire plays in geomorphic processes in the upper Tsitsa River catchment. The catchment falls under two land management types- commercial and communal, with the latter being severely degraded. Fire regimes were determined using a combination of Landsat and MODIS remotely sensed data and testing was carried out on soils exposed to different Fire Return Intervals (FRI). It was found that soils that were exposed to a high fire frequency (1-2-year FRI) exhibited a significantly higher degree of water repellency (p< 0.001) and surface hardness (p< 0.001) than soils that were exposed to a low fire frequency (3-4 year FRI), which indicates increased erosion potential. However, whilst a higher fire frequency resulted in altered soil characteristics, it contributed to landscape degradation as suggested in the literature, and soils are able to return to their previous state in over a short period of time. Further investigation into factors affecting fire regimes found that geology influenced vegetation type, resulting in differences in biomass in the two land management areas. The commercially managed land supported a high biomass, which resulted in a more natural fire regime with frequent fires, whilst the communally managed land supported less biomass. Smaller fuel loads and increased landscape fragmentation through overgrazing and road networks resulted in an altered fire regime with less frequent fires. Although the communally managed land has an altered fire regime, this research suggests that fires are not influencing the severe degradation present in these areas, and this is rather a function of geology and mismanagement of land. Whilst fire and grazing management plans can be implemented to alter the modified fire regime in the communal areas back to its natural state, this would take a long time and an increase in fires would pose a threat to surrounding communities. Overall the fire regimes in the upper Tsitsa River catchment are being altered by human influence and land management type, and whilst fire frequency is negatively altering soil properties, these soils can return to their natural state. The severe land degradation present in the communally managed areas are not a function of fire frequency and rather of geology and land management.
- Full Text:
Seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments, South Africa
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
Developing a citizen technician based approach to suspended sediment monitoring in the Tsitsa River catchment, Eastern Cape, South Africa
- Authors: Bannatyne, Laura Joan
- Date: 2018
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Eastern Cape , Watersheds -- South Africa -- Eastern Cape , Suspended sediments -- South Africa -- Eastern Cape , Suspended sediments -- Monitoring -- Citizen participation , Tsitsa River
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62593 , vital:28211
- Description: Suspended sediment (SS) in channels is spatiotemporally heterogeneous and, over the long term, is known to be moved predominantly by flood flows with return periods of ~1 - 1.5 years. Flood flows in the Tsitsa catchment (Eastern Cape Province, South Africa) are unpredictable, and display a wide range of discharges. Direct, flood-focused SS sampling at sub-catchment scale was required to provide a SS baseline against which to monitor the impact on SS of catchment rehabilitation interventions, to determine the relative contributions of sub-catchments to SS loads and yields at the site of the proposed Ntabelanga Dam wall, and to verify modelled SS baselines, loads and yields. Approaches to SS sampling relying on researcher presence and/or installed equipment to adequately monitor SS through flood flows were precluded by cost, and the physical and socioeconomic conditions in the project area. A citizen technician (CT)-based flood-focused approach to direct SS sampling was developed and implemented. It was assessed in terms of its efficiency and effectiveness, the proficiency of the laboratory analysis methods, and the accuracy of the resulting SS data. A basic laboratory protocol for SSC analysis was developed, but is not the focus of this thesis. Using basic sampling equipment and smartphone-based reporting protocols, local residents at eleven points on the Tsitsa River and its major tributaries were employed as CTs. They were paid to take water samples during daylight hours at sub-daily timestep, with the emphasis on sampling through flood flows. The method was innovative in that it opted for manual sampling against a global trend towards instrumentation. Whilst the management of CTs formed a significant project component, the CTs benefitted directly through remuneration and work experience opportunities. The sampling method was evaluated at four sites from December 2015 - May 2016. The CTs were found to have efficiently and effectively sampled SS through a range of water levels, particularly in the main Tsitsa channel. An acceptable level of proficiency and accuracy was achieved, and many flood events were successfully defined by multiple data points. The method was chiefly limited by the inability of CTs to sample overnight rises and peaks occurring as a result of afternoon thunderstorms, particularly in small tributaries. The laboratory process was responsible for some losses in proficiency and accuracy. Improved laboratory quality control was therefore recommended. The CT-based approach can be adapted to other spatial and temporal scales in other areas, and to other environmental monitoring applications.
- Full Text:
- Authors: Bannatyne, Laura Joan
- Date: 2018
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Eastern Cape , Watersheds -- South Africa -- Eastern Cape , Suspended sediments -- South Africa -- Eastern Cape , Suspended sediments -- Monitoring -- Citizen participation , Tsitsa River
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62593 , vital:28211
- Description: Suspended sediment (SS) in channels is spatiotemporally heterogeneous and, over the long term, is known to be moved predominantly by flood flows with return periods of ~1 - 1.5 years. Flood flows in the Tsitsa catchment (Eastern Cape Province, South Africa) are unpredictable, and display a wide range of discharges. Direct, flood-focused SS sampling at sub-catchment scale was required to provide a SS baseline against which to monitor the impact on SS of catchment rehabilitation interventions, to determine the relative contributions of sub-catchments to SS loads and yields at the site of the proposed Ntabelanga Dam wall, and to verify modelled SS baselines, loads and yields. Approaches to SS sampling relying on researcher presence and/or installed equipment to adequately monitor SS through flood flows were precluded by cost, and the physical and socioeconomic conditions in the project area. A citizen technician (CT)-based flood-focused approach to direct SS sampling was developed and implemented. It was assessed in terms of its efficiency and effectiveness, the proficiency of the laboratory analysis methods, and the accuracy of the resulting SS data. A basic laboratory protocol for SSC analysis was developed, but is not the focus of this thesis. Using basic sampling equipment and smartphone-based reporting protocols, local residents at eleven points on the Tsitsa River and its major tributaries were employed as CTs. They were paid to take water samples during daylight hours at sub-daily timestep, with the emphasis on sampling through flood flows. The method was innovative in that it opted for manual sampling against a global trend towards instrumentation. Whilst the management of CTs formed a significant project component, the CTs benefitted directly through remuneration and work experience opportunities. The sampling method was evaluated at four sites from December 2015 - May 2016. The CTs were found to have efficiently and effectively sampled SS through a range of water levels, particularly in the main Tsitsa channel. An acceptable level of proficiency and accuracy was achieved, and many flood events were successfully defined by multiple data points. The method was chiefly limited by the inability of CTs to sample overnight rises and peaks occurring as a result of afternoon thunderstorms, particularly in small tributaries. The laboratory process was responsible for some losses in proficiency and accuracy. Improved laboratory quality control was therefore recommended. The CT-based approach can be adapted to other spatial and temporal scales in other areas, and to other environmental monitoring applications.
- Full Text:
- «
- ‹
- 1
- ›
- »