Reproductive biology of ningu, Labeo victorianus (pisces: cyprinidae), in the kagera and Sio rivers, Uganda
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2005
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125864 , vital:35827 , https://doi.10.1007/s10641-004-5564-8
- Description: We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability.
- Full Text:
- Date Issued: 2005
The development of water quality methods within ecological Reserve assessments, and links to environmental flows
- Authors: Palmer, Carolyn G , Rossouw, N , Muller, Nikite W J , Scherman, Patricia A
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , report
- Identifier: http://hdl.handle.net/10962/438033 , vital:73430 , ISBN 0378-4738 , https://wrcwebsite.azurewebsites.net/wp-content/uploads/mdocs/WaterSA_2005_02_1634.pdf
- Description: In the South African National Water Act (NWA, No 36 of 1998), the eco-logical Reserve is defined as the quality and quantity of water required to ensure appropriate protection of water resources, so as to secure ecologically sustainable development and use. Aquatic ecosystems are recognised as the core location of water resources, and although con-siderable progress has been made in developing methods for quantify-ing environmental flow requirements, this paper describes and discuss-es the first agreed method for quantifying environmental water quality requirements in an ecological Reserve assessment. Integration of flow and water quality is emphasised, and is based on the philosophy that environmental flows should be motivated to provide ecologically im-portant flow-related habitat, or geomorphological function, but should not be motivated to solve water quality problems by dilution. Water qual-ity is multivariate, and not all variables can be considered in an ecologi-cal Reserve assessment, but core water quality variables include: sys-tem variables (salts, dissolved oxygen, turbidity, temperature), nutrients (phosphate, nitrite, nitrate) and toxic substances (those listed in the South African Water Quality Guidelines for Aquatic Ecosystems, includ-ing toxic metal ions, toxic organic substances, and/or substances from a chemical inventory of an effluent or discharge). In addition, biological indicator data (eg SASS data), chlorophyll-a (eg phytoplankton and pe-riphyton data) and toxicity test data may be used. For each variable, a concentration range or response is linked to a class within a water re-source classification system, where classes range from minimally to severely modified.
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- Date Issued: 2005
The experiences and needs of HIV/AIDS counsellors at a South African hospital
- Authors: Nulty, Maria , Edwards, David J A
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6269 , http://hdl.handle.net/10962/d1008268
- Description: To increase the availability of HIV/AIDS counselling in South Africa, nurses have been trained to serve as counsellors within hospital services. The aim of the study was to document the experiences and needs of nurse HIV/AIDS counsellors at a small South African hospital (with 279 beds and 10 medical doctors on the staff). The design was a qualitative, multiple-case study. The sample consisted of four nurse counsellors and the co-ordinator of HIV/AIDS services at the hospital. Three semi-structured interviews with the counsellors were used as the basis for case narratives of their experiences. These narratives were in turn subjected to content analysis to determine the range and nature of the concerns identified by the counsellors. The counsellors found their HIV/AIDS counselling work to be emotionally demanding and identified several significant problems. These were related to confidentiality, stigmatisation, motional responses to informing clients of their HIV-positive status, cultural and contextual factors and situational stressors related to the organisation of the work environment. They did not feel sufficiently supported by their work infrastructure. It is recommended that in setting up counselling services of this sort, managers need to be aware of the need for ongoing support in the form of facilitated groups, professional supervision, managerial attention to problems in the working environment, and regular in-service training.
- Full Text:
- Date Issued: 2005
A Unified Architecture For Automatic Software Updates
- Authors: White, Dominic , Irwin, Barry V W
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/428800 , vital:72537 , https://citeseerx.ist.psu.edu/document?repid=rep1type=pdfdoi=6e1cd9269a0c5532faf7a23f82995fcfa39e59bd
- Description: This paper attempts to address the issue of hardening the internal secu-rity of an organisation’s network by easing its patch management. Tradi-tionally security has been modeled on a" hard outer shell" approach, with a firewall protecting the otherwise vulnerable internal network. With the advent of worms using such techniques as social engineering to by-pass the organisational firewall and installing trojans, this approach is no longer sufficient. As a result of these new attacks, emphasis should be placed on improving the security of the internal network. Most research agrees that prompt patching of security vulnerabilities would significantly reduce the vulnerability of these machines. However, this requires sys-tem administrators not only to keep abreast of the flood of patches, but to ensure they are deployed to every machine, in what could be a very large network. These difficulties are worsened by problems the patches themselves often create. This is a difficult task and the failure of system administrators to perform it is echoed in the recent spate of worm at-tacks, with some taking advantage of vulnerabilities for which patches had been released up to six months earlier.
- Full Text:
- Date Issued: 2004
Nuclear translocation of the Hsp70/Hsp90 organizing protein mSTI1 is regulated by cell cycle kinases
- Authors: Longshaw, Victoria M , Chapple, J Paul , Cheetham, Michael E , Blatch, Gregory L
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6488 , http://hdl.handle.net/10962/d1006271 , https://dx.doi.org/10.1242/jcs.00905
- Description: The co-chaperone murine stress-inducible protein 1 (mSTI1), an Hsp70/Hsp90 organizing protein (Hop) homologue, mediates the assembly of the Hsp70/Hsp90 chaperone heterocomplex. The mSTI1 protein can be phosphorylated in vitro by cell cycle kinases proximal to a putative nuclear localization signal (NLS), which substantiated a predicted casein kinase II (CKII)-cdc2 kinase-NLS (CcN) motif at position 180-239 and suggested that mSTI1 might move between the cytoplasm and the nucleus under certain cell cycle conditions. The mechanism responsible for the cellular localization of mSTI1 was probed using NIH3T3 fibroblasts to investigate the localization of endogenous mSTI1 and enhanced green fluorescent protein (EGFP)-tagged mSTI1 mutants. Localization studies on cell lines stably expressing NLS(mSTI1)-EGFP and EGFP demonstrated that the NLS(mSTI1) was able to promote a nuclear localization of EGFP. The mSTI1 protein was exclusively cytoplasmic in most cells under normal conditions but was present in the nucleus of a subpopulation of cells and accumulated in the nucleus following inhibition of nuclear export (leptomycin B treatment). G1/S-phase arrest (using hydroxyurea) and inhibition of cdc2 kinase (using olomoucine) but not inhibition of casein kinase II (using 5,6-dichlorobenzimidazole riboside), increased the proportion of cells with endogenous mSTI1 nuclear staining. mSTI1-EGFP behaved identically to endogenous mSTI1. The functional importance of key residues was tested using modified mSTI1-EGFP proteins. Inactivation and phosphorylation mimicking of potential phosphorylation sites in mSTI1 altered the nuclear translocation. Mimicking of phosphorylation at the mSTI1 CKII phosphorylation site (S189E) promoted nuclear localization of mSTI1-EGFP. Mimicking phosphorylation at the cdc2 kinase phosphorylation site (T198E) promoted cytoplasmic localization of mSTI1-EGFP at the G1/S-phase transition,whereas removal of this site (T198A) promoted the nuclear localization of mSTI1-EGFP under the same conditions. These data provide the first evidence of nuclear import and export of a major Hsp70/Hsp90 co-chaperone and the regulation of this nuclear-cytoplasmic shuttling by cell cycle status and cell cycle kinases.
- Full Text:
- Date Issued: 2004
World view theory and the conceptualisation of space in mathematics education:
- Authors: Schäfer, Marc
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/141052 , vital:37940 , DOI: 10.4102/pythagoras.v0i59.127
- Description: The cornerstone of current education trends that recognise prior knowledge as fundamental to the learning process, is the notion that beliefs and experiences that learners bring to the classroom influence their learning experiences in the classroom (Cobern, Gibson and Underwood, 1999).
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- Date Issued: 2004
Environmental limits to the distribution of Scaevola plumieri along the South African coast
- Authors: Peter, Craig I , Ripley, Bradford S , Robertson, Mark P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6872 , http://hdl.handle.net/10962/d1011617
- Description: Scaevola plumieri is an important pioneer on many tropical and subtropical sand dunes, forming a large perennial subterranean plant with only the tips of the branches emerging above accreting sand. In South Africa it is the dominant pioneer on sandy beaches along the east coast, less abundant on the south coast and absent from the southwest and west coasts. Transpiration rates (E) of S. plumieri are predictably related to atmospheric vapour pressure deficit under a wide range of conditions and can therefore be predicted from measurement of ambient temperature and relative humidity. Scaling measurements of E at the leaf level to the canopy level has been demonstrated previously. Using a geographic information system, digital maps of regional climatic variables were used to calculate digital maps of potential transpiration from mean monthly temperature and relative humidity values, effectively scaling canopy level transpiration rates to a regional level. Monthly potential transpiration was subtracted from the monthly median rainfall to produce a map of mean monthly water balance. Seasonal growth was correlated with seasonal water balance. Localities along the coast with water deficits in summer corresponded with the recorded absence of S. plumieri, which grows and reproduces most actively in the summer months. This suggests that reduced water availability during the summer growth period limits the distribution of S. plumieri along the southwest coast, where water deficits develop in summer. Temperature is also important in limiting the distribution of S. plumieri on the southwest coast of South Africa through its effects on the growth and phenology of the plant.
- Full Text:
- Date Issued: 2003
Threatened plants of the Albany Centre of Floristic Endemism, South Africa
- Authors: Victor, A E , Dold, Anthony P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6555 , http://hdl.handle.net/10962/d1006013
- Description: We present Red List assessments of threatened plants of the Albany Centre of Floristic Endemism in the Eastern Cape province of South Africa. We evaluated the status of taxa using categories and criteria adopted by the World Conservation Union (IUCN) in 1994 and updated in 2001. In total, 126 taxa are threatened with extinction in the Albany Centre, and six are now extinct. A further 22 are listed as Data Deficient. In the past, agriculture has been a severe threat to the survival of rare species in this part of the Eastern Cape; the main threats to the continuing existence of threatened plants in this area are illegal collecting, residential development and urban growth.
- Full Text:
- Date Issued: 2003
Accelerated sludge solubilisation under sulphate reducing conditions: the effect of hydrolytic enzymes on sludge floc size distribution and EPS composition
- Authors: Akhurst, P , Rose, Peter D , Whiteley, Chris G , Pletschke, Brett I
- Date: 2002
- Language: English
- Type: Conference paper
- Identifier: vital:6455 , http://hdl.handle.net/10962/d1010430
- Description: Extracellular polymeric substances (EPS) are the construction materials for microbial aggregates such as biofilms, flocs and sludge, and greatly contribute to the structural integrity of sludge flocs in wastewater treatment processes. The loss of integrity of the sewage sludge floc is believed to be due to enhanced hydrolysis of important structural components such as lignin, protein and cellulose in the sludge floc matrix. The mechanism of enhanced sludge floc fracture, due to the action of enzymes hydrolysing these structural components, remains a key element in our understanding of how the floc integrity in systems utilising a sulphate reducing system is compromised. A range of relatively non-specific exogenous enzymes (ß-glucosidase, cellulase, proteases: trypsin, pronase E and chymotrypsin) were added to a sulphidogenic bioreactor- (containing both sulphate reducing bacteria (SRB) and a methanogenic bacterial system) and a (control) methanogenic bioreactor sample, and the effect of these enzymes on sludge floc size (diameter) distribution and EPS composition was investigated. Sludge samples from the bioreactors were examined under bright field and differential interference contrast light microscopy. Proteolytic and glucohydrolytic activity of the enzymes were monitored using standard enzyme assaying techniques, and Bradford, Somogyi-Nelson, and total carbohydrate assays were performed to establish the composition of the EPS (after extraction with 3% (v/v) glutaraldehyde and Sephacryl S-400 size exclusion chromatography). Sludge flocs present in the sulphidogenic environment of the sulphidogenic bioreactor were found to have smaller diameters than their counterparts present in the methanogenic bioreactor. The addition of hydrolytic (i.e. proteolytic and glycohydrolytic) enzymes resulted in an increased rate of matrix hydrolysis, leading to increased rates of floc fracture and deflocculation. The presence of ß-glucosidase, cellulase, and proteases naturally residing within the sludge floc was confirmed. We propose that the addition of commercially available enzymes may be prohibitively costly on a large scale, and that the activity of the enzymes naturally residing within the floc matrix be optimised or enhanced. As the bulk of the EPS was shown to be composed of mainly polysaccharides, we propose that by increasing the activity of the naturally occurring ß-glucosidases residing within the floc matrix, the process of deflocculation may be enhanced. As sulphide has been shown to increase the activity of this very important key enzyme, we propose that this is one of the contributing factors why sludge solubilisation is accelerated under sulphate reducing conditions.
- Full Text:
- Date Issued: 2002
Pavoclinus caeruleopunctatus, a new species of clinid fish (Perciformes: Clinidae) from South Africa
- Authors: Zsilavecz, Guido , J.L.B. Smith Institute of Ichthyology
- Date: 2001-08
- Subjects: Clinidae -- South Atlantic Ocean -- Classification , Clinidae -- South Africa -- Classification
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/71066 , vital:29774 , Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB)) Periodicals Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB))
- Description: Online version of original print edition of the Special Publication of the J.L.B. Smith Institute of Ichthyology; No. 66 , A new species of clinid fish, Pavoclinns caeruleopunctatus, is described from specimens collected and observed in 6 - 25 m, around the Cape Peninsula, on the southwest coast of South Africa. Pavoclinus caeruleopunctatus is distinguished from similar species by the first 3 dorsal-fin spines forming a moderate crest, a notch between the 3rd and 4th dorsal-fin spines, 1 - 3 soft dorsal rays, an anteriorly rounded head profile, and colour pattern; most characteristic in live specimens are the vivid blue spots in front and behind the eye, and also usually on the flanks.
- Full Text:
- Date Issued: 2001-08
Revisiting nomenclature: 'Early Iron Age', 'First-Millennium Agriculturist', or what?
- Authors: Steele, John
- Date: 2001
- Language: English
- Type: text , Article
- Identifier: http://hdl.handle.net/11260/934 , vital:30067
- Description: As an art historian who has recently become fascinated by First-Millennium Agriculturist ceramics, I have come across several attempts at dealing with an issue of appropriate nomenclature for desigrrating this era. Conceptual frameworks are articulated using words, yet an apparent discomfort with the term Early Iron Age has seemingly not led to a consistently used altemative. I have been wondering about this and, with respect, offer my thoughts on the matter in a hope that debate will be furthered. Hereunder I utilise aspects of the KwaZulu-Natal and Eastem Cape first millennium ceramic sequence to address some significances associated with such artefacts in interpretations of the past, and then discuss some ways in which ideas of particular social contexts are embedded in language. Thereafter introduction of the term Iron Age into South African archaeology is referred to with reference to past and current usage, and advantages/disadvantages of alternatives are suggested.
- Full Text:
- Date Issued: 2001
Spatial aspects of the reproductive and feeding biology of the striped robber, Brycinus lateralis (Pisces: Characidae), in the Okavango Delta, Botswana
- Authors: Booth, Anthony J , McKinlay, Bruce W
- Date: 2001
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446838 , vital:74564 , https://doi.org/10.1080/15627020.2001.11657111
- Description: The Okavango Delta is a vast inland wetland system situated in northern Botswana. High rainfall is received in early summer in the southern Angolan highlands and throughout the Delta with the flood waters reaching the upper riverine floodplain between March and May where it percolates through to the lower drainage rivers between July and September. Aspects of the reproductive and feeding biology of two allopatric populations of the striped robber, Brycinus lateralis, a small characin species inhabiting the northern riverine floodplain and southern drainage rivers, were investigated. Both populations were similar in the biological aspects studied, with the flood cycle having little influence on the timing of reproduction, sexual maturity and dietary composition. Female fish from both populations matured sexually at 57 mm SL, breeding over a protracted period during the warm, summer months. In both populations, the sex ratio was female-dominated at 4.8:1 (riverine floodplain) and 2.2:1 (drainage rivers). The striped robber is an opportunistic micro-carnivore with immature fish feeding predominantly on Daphnia spp. and adults being largely insectivorous.
- Full Text:
- Date Issued: 2001
An estimation of the standing stock and population structure of Upogebia africana (Crustacea: Thalassinidae) in the Knysna Estuary
- Authors: Hodgson, Alan N , Allanson, Brian R , Cretchley, Robyn
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6923 , http://hdl.handle.net/10962/d1011907
- Description: Within the Knysna Estuary Upogebia africana has an extensive distribution from north of Leisure Isle to the Red Bridge, occupying 62% of the available intertidal zone. Six sites were surveyed within the above distributional range. U. africana was found from the high-water level (Spartina zone) to the shallow subtidal zone (to about 1.5 m depth). The density, biomass and population structure of the mud prawns were found to be highly variable within the estuary. Only small animals (carapace length –× = 10.9 mm) were found in the upper estuary at the Red Bridge. Although large animals were present, the Invertebrate Reserve had a low density and biomass of U. africana (– × = 11.7 m–2; 3.9 g.m–2 dry weight). By contrast a relatively inaccessible centre mud bank (Oyster Bank) in the middle reaches of the estuary had much larger populations (–× = 176.5 m–2; 65.3 g.m–2 dry weight). This site is, therefore, a natural mud prawn reserve. Within the intertidal zone, mud prawn density (74–76 m–2) and biomass (26–27 g.m–2 dry weight) was usually greatest in the Spartina and lower Zostera zones. Sex ratios throughout the estuary did not deviate significantly from 1:1.
- Full Text:
- Date Issued: 2000
Incorporating the spatial component of fisheries data into stock assessment models
- Authors: Booth, Anthony J
- Date: 2000
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124800 , vital:35698 , https://doi.10.1006/jmsc.2000.0816
- Description: Fisheries-dependent and independent data have a strong spatial component. These data are also multi-dimensional, making them difficult to visualize and analyze, prompting the use of spatial analysis to facilitate an understanding of their relationships. One aspect of fisheries data that is often ignored is the distribution and abundance of a particular resource and the fishing patterns of its harvesting fisheries. In order to improve management advice, stock assessors need to incorporate the spatial component of these data into an existing assessment framework. This paper presents a three-dimensional visualization of the age-structure and fishery dependent and independent data associated with the sparid fish Pterogymnus laniarius on the Agulhas Bank, South Africa. A spatially-referenced spawner biomass per-recruit model is developed to illustrate the applicability of incorporating spatially referenced information in providing management advice. The model provided evidence that, even on a spatial scale, fishing mortality is significantly correlated to fishing effort. Areas of high levels of spawner biomass are noted, all of which corresponded to those geographic areas with a combination of low fishing effort and high adult biomass.
- Full Text:
- Date Issued: 2000
SASBO Code of ethics
- Authors: SASBO
- Date: 2000
- Subjects: SASBO
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/160565 , vital:40475
- Description: Formed as a trade union in 1916, SASBO's primary objectives are to improve the conditions of service and protect the interests of its members, individually and collectively, in relation to their employers and otherwise, and generally to raise their status. Operating in the South African finance sector, SASBO identifies with the ethics and conventions of finance professionals and has always encouraged sound industrial relations with employers and/or their organisations, with the intention of regulating conflict as peacefully and constructively as possible by endeavouring to settle disputes by conciliatory methods. The union has always been, and continues to be, committed to fair and honest dealings, and integrity, in its interaction with all its stakeholders, this in the fundamental belief that SASBO's operation and business should be conducted honestly, fairly and within the parameters of labour and other laws.
- Full Text:
- Date Issued: 2000
The development of a geomorphological classification system for the longitudinal zonation of South African rivers
- Authors: Rowntree, Kate M , Wadeson, Roy A , O'Keeffe, Jay H
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6722 , http://hdl.handle.net/10962/d1006799
- Description: The recognition of the Reserve by the new South African Water Law poses new challenges for river scientists. The ecological water requirement or environmental flow is recognised by that part of the Reserve known as the ecological Reserve. If the ecological Reserve is to be implemented, it must first be defined and quantified for all river systems subject to water related developments. Standard procedures are being developed through the Resource Directed Measures (RDM) of the Department of Water Affairs and Forestry while monitoring the health of South Africa's rivers is taking place through the National River Health Programme (NRHP). Cost effective methods of developing spatial frameworks for both the RDM and NRHP are required. Concepts of longitudinal river zonation were developed by river ecologists in the 1960s and 1970s to assist in the classification of ecologically uniform stretches of rivers. This paper reviews the different zonation concepts and presents a geomorphological classification of South African river zones that is being applied to the RDM and NRHP. The classification is tested on three rivers, the Sabie, Buffalo and Olifants.
- Full Text: false
- Date Issued: 2000
NUMSA’s Staff Disciplinary Code and Procedure
- Authors: NUMSA
- Date: 1999
- Subjects: NUMSA
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/173722 , vital:42404
- Description: In circumstances in which the breach of a rule or failure to meet a required standard is not serious enough to warrant a final written warning or dismissal, the appropriate Local Chairperson, Regional Secretary or General Secretary may issue a verbal warning or first written warning after discussion with and counselling of the official.
- Full Text:
- Date Issued: 1999
Re-evaluation of Ashton’s types of African cicadas (Homoptera Cicadidae).
- Authors: Villet, Martin H
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/453840 , vital:75291 , https://doi.org/10.1080/03946975.1999.10539389
- Description: ASHTON (1914) described three species of cicada from Africa which were soon placed in synonymy with other species. Re-examination of the type material lead to the following revisions: Platypleura nigromarginata Ashton 1914 is removed from synonymy with Oxypleura quadraticollis (Butler 1874) and placed in the genus Strumoseura n. gen.; P. sikumba Ashton 1914 is confirmed as a junior synonym of Manza basimacula (Walker 1850) along with M. parva Villet 1989 n. syn.; and P. longirostris Ashton 1914 is removed from the synonymy of P. divisa Germar 1834.
- Full Text:
- Date Issued: 1999
Rhodes University Graduation Ceremony 1999
- Authors: Rhodes University
- Date: 1999
- Language: English
- Type: text
- Identifier: vital:8133 , http://hdl.handle.net/10962/d1006778
- Description: Rhodes University 1999 Graduation Ceremonies [at] 1820 Settlers National Monument Friday, 9 April 1999 at 18:00 p.m. [and] 10 April 1999 at 10:30 a.m. , The Installation of Gert Johannes Gerwel as Chancellor of Rhodes University to be followed by a Graduation Ceremony 1820 Settlers National Monument Friday, 9 April 1999 at 10:30 a.m. , Rhodes University 1999 Graduation Ceremony City Hall, East London Friday, 7 May 1999 at 18:00 p.m.
- Full Text:
- Date Issued: 1999
Vegetation controls on channel stability in the Bell River, Eastern Cape, South Africa
- Authors: Rowntree, Kate M , Dollar, Evan S J
- Date: 1999
- Language: English
- Type: Article
- Identifier: vital:6720 , http://hdl.handle.net/10962/d1006796
- Description: Channel instability has occurred in the Bell River in the form of meander cutoffs, a number of which have occurred since 1952. Increased sediment loading from widespread gully erosion in the catchment has been proposed as the trigger for this instability. Willow species of the Salix family, in particular S. caprea, have been planted along the banks in an effort to prevent further channel shifting. This study reports the results of an investigation into the effect of vegetation on channel form and stability over a 17 km stretch of channel. Results indicate that riparian vegetation has significant effects on channel form which have implications for channel stability. Riparian vegetation increases bank stability and reduces channel cross-sectional area, thereby inducing stability at flows less than bankfull. Evidence indicates that narrow stable stretches are associated with relatively high levels of riparian vegetation. Wider, unstable channels are associated with relatively less riparian vegetation. The effectiveness of riparian vegetation relative to bank sediments was investigated. A dense growth of willows was found to have an equivalent effect to banks with a silt-clay ratio of about 70 per cent. The channel narrowing induced by vegetation may contribute to channel shifting at high flows. The reduced channel capacity is thought to result in more frequent overbank flooding which may ultimately lead to channel avulsion. Thus where increased sediment loading is pushing the channel towards instability, vegetation may be effective in imparting local stability, but it is unable to prevent long-term channel shifts, and may rather help to push the system towards more frequent avulsions.
- Full Text:
- Date Issued: 1999