Gully erosion as a mechanism for wetland formation: an examination of two contrasting landscapes
- Pulley, Simon, Ellery, William F N, Lagesse, Juliette V, Schlegel, P Philippa, McNamara, Shaun J
- Authors: Pulley, Simon , Ellery, William F N , Lagesse, Juliette V , Schlegel, P Philippa , McNamara, Shaun J
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144410 , vital:38343 , DOI: 10.1002/ldr.2972
- Description: Wetlands occupy broad, gently sloping valleys characterised by net deposition. Consequently, gully incision is viewed as an agent of wetland destruction. However, little attention has been given to the role of gullies in natural wetland formation. This paper determines if gully cutting and filling cycles have led to wetland formation in both an extant eroding wetland and a semi‐arid environment that once supported wetlands. At both sites, the valley fill was investigated to identify infilled gullies, and a 14C date was obtained from the gully fill.
- Full Text:
- Date Issued: 2018
- Authors: Pulley, Simon , Ellery, William F N , Lagesse, Juliette V , Schlegel, P Philippa , McNamara, Shaun J
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144410 , vital:38343 , DOI: 10.1002/ldr.2972
- Description: Wetlands occupy broad, gently sloping valleys characterised by net deposition. Consequently, gully incision is viewed as an agent of wetland destruction. However, little attention has been given to the role of gullies in natural wetland formation. This paper determines if gully cutting and filling cycles have led to wetland formation in both an extant eroding wetland and a semi‐arid environment that once supported wetlands. At both sites, the valley fill was investigated to identify infilled gullies, and a 14C date was obtained from the gully fill.
- Full Text:
- Date Issued: 2018
Epidemic transmission of intestinal schistosomiasis in the seasonal part of the Okavango Delta, Botswana:
- Appleton, C C, Ellery, William F N, Byskov, Jens, Mogkweetsinyana, S S
- Authors: Appleton, C C , Ellery, William F N , Byskov, Jens , Mogkweetsinyana, S S
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144364 , vital:38339 , DOI: 10.1179/136485908X311867
- Description: A well documented epidemic of human intestinal schistosomiasis caused by Schistosoma mansoni occurred at Maun in the seasonal part of the Okavango Delta, Botswana, building from very few cases in the 1950s and early 1960s to a peak prevalence of greater than80% in the 1980s. A retrospective analysis was performed on all available records of the prevalence of S. mansoni in the Maun area and the corresponding flow records of the Thamalakane River. These revealed a statistically significant correlation between prevalence and flow, but only when a lag period was introduced. The correlation was greatest with a lag period of 5–6 years between the rise and fall of discharge and the rise and fall of transmission. Since the hydrological events in the delta follow a cyclical pattern, another epidemic around 2020 appears likely.
- Full Text:
- Date Issued: 2013
- Authors: Appleton, C C , Ellery, William F N , Byskov, Jens , Mogkweetsinyana, S S
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144364 , vital:38339 , DOI: 10.1179/136485908X311867
- Description: A well documented epidemic of human intestinal schistosomiasis caused by Schistosoma mansoni occurred at Maun in the seasonal part of the Okavango Delta, Botswana, building from very few cases in the 1950s and early 1960s to a peak prevalence of greater than80% in the 1980s. A retrospective analysis was performed on all available records of the prevalence of S. mansoni in the Maun area and the corresponding flow records of the Thamalakane River. These revealed a statistically significant correlation between prevalence and flow, but only when a lag period was introduced. The correlation was greatest with a lag period of 5–6 years between the rise and fall of discharge and the rise and fall of transmission. Since the hydrological events in the delta follow a cyclical pattern, another epidemic around 2020 appears likely.
- Full Text:
- Date Issued: 2013
Hydrology, sediment transport dynamics and geomorphology of a variable flow river : the Mfolozi River, South Africa
- Grenfell, Suzanne E, Ellery, William F N
- Authors: Grenfell, Suzanne E , Ellery, William F N
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6632 , http://hdl.handle.net/10962/d1006826
- Description: The co-efficient of variation for inter-annual streamflow of the Mfolozi River is extremely high at 79%. An analysis of flow frequency indicated that streamflow is skewed towards low-flow values, with a number of extremely large flood events occurring as outliers on the histogram. Streamflow variability in the Mfolozi River may be linked to multiple factors including a large catchment size, a seasonal climate of a dry winter and wet summer, evergreen vegetation in the catchment, variable precipitation and the occurrence of regionally pervasive climatic oscillations. This research aimed to address how streamflow variability impacted upon sediment transport and thus, geomorphology. It was found that sediment transport variability occurred at the intra-and inter-annual scale. Analysis of mean monthly sediment concentration and discharge showed a hysteresis effect, such that sediment concentration peaked prior to discharge in the early wet season. During the late wet season, peak discharges often had unexpectedly low sediment concentrations. Furthermore, data suggested the existence of long-term hysteresis that may be related to decadal-scale climatic oscillations that alter sediment availability and stream capacity, resulting in discharge peaking in 2000 and sediment concentration in 2005. However, more data are required to confirm this relationship. Variability in streamflow appears to share a causal relationship with sediment transport variability, as both are linked to variation in precipitation and the resultant impacts on vegetation growth and evapotranspiration rates. The variability of streamflow and sediment transport has implications for stream and floodplain geomorphology, and the hydrology of variable rivers should be considered when interpreting their geomorphology.
- Full Text:
- Date Issued: 2009
- Authors: Grenfell, Suzanne E , Ellery, William F N
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6632 , http://hdl.handle.net/10962/d1006826
- Description: The co-efficient of variation for inter-annual streamflow of the Mfolozi River is extremely high at 79%. An analysis of flow frequency indicated that streamflow is skewed towards low-flow values, with a number of extremely large flood events occurring as outliers on the histogram. Streamflow variability in the Mfolozi River may be linked to multiple factors including a large catchment size, a seasonal climate of a dry winter and wet summer, evergreen vegetation in the catchment, variable precipitation and the occurrence of regionally pervasive climatic oscillations. This research aimed to address how streamflow variability impacted upon sediment transport and thus, geomorphology. It was found that sediment transport variability occurred at the intra-and inter-annual scale. Analysis of mean monthly sediment concentration and discharge showed a hysteresis effect, such that sediment concentration peaked prior to discharge in the early wet season. During the late wet season, peak discharges often had unexpectedly low sediment concentrations. Furthermore, data suggested the existence of long-term hysteresis that may be related to decadal-scale climatic oscillations that alter sediment availability and stream capacity, resulting in discharge peaking in 2000 and sediment concentration in 2005. However, more data are required to confirm this relationship. Variability in streamflow appears to share a causal relationship with sediment transport variability, as both are linked to variation in precipitation and the resultant impacts on vegetation growth and evapotranspiration rates. The variability of streamflow and sediment transport has implications for stream and floodplain geomorphology, and the hydrology of variable rivers should be considered when interpreting their geomorphology.
- Full Text:
- Date Issued: 2009
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