Geomorphological connectivity and sensitivity examined in a recently degraded gravel-bed stream: implications for river-floodplain rehabilitation
- Authors: Powell, Rebecca
- Date: 2017
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/53722 , vital:26313
- Description: The study of river complexity and sensitivity to future human land-use activities and climate change is a fast growing field within the discipline of fluvial geomorphology. Associated with this is a need to improve river rehabilitation and catchment management approach, design and effectiveness. This study aimed to investigate drivers of the recent geomorphological sensitivity of the Baviaanskloof River-floodplain, an upland system in South Africa, by integrating the concepts of geomorphological connectivity and Panarchy. The understanding generated was used to evaluate the approach of the State agency, Working for Wetlands (WfWet), to river-floodplain rehabilitation in the catchment.The concepts of geomorphological connectivity and Panarchy provide useful frameworks for understanding interactions between geomorphological processes and structure across scales of space and time. Geomorphological connectivity explains the degree to which water and sediment is linked in a river landscape, determined by the distribution of erosional and depositional landforms (Brierley et al. 2006; Fryirs et al. 2007a; Fryirs et al. 2007b). Panarchy attempts to explain lagged response to disturbances, non-linear interactions, and sudden shifts in system state, and has been applied largely to ecological systems. Panarchy theory, when combined with the concept of geomorphological connectivity, provides a guiding framework for understanding river complexity in greater depth. The first results chapter of this study investigated river long-term and recent geomorphological history, towards understanding the nature and timing of river geomorphological cycling between erosion and deposition. Optically Stimulated Luminescence dating of alluvial fan and floodplain sedimentary units was conducted, for analysis of river-floodplain long-term history (100s to 1 000s of years). Interviews with 11 local landowners, combined with analysis of historic aerial imagery and river-floodplain topographic surveys, provided a means of describing recent (last few decades) geomorphological dynamics. The results indicated that the Baviaanskloof is naturally a cut- and-fill landscape over scales of several hundred to thousands of years, characterized by the alternation between phases of high fluvial energy and alluvial fan expansion, and low energy conditions associated with floodplain accretion. Recent and widespread river-floodplain degradation was compressed into a short period of approximately 30 years, suggesting that one or more drivers have pushed the system beyond a threshold, resulting in increased water and sediment connectivity. The second results chapter investigated the role of human land-use activities and flooding frequency and magnitude, as drivers of recent river-floodplain degradation. Human impacts were investigated by describing land-use activities for the preceding 80 years, and relating these activities to changes in river-floodplain form and behavior. Temporal trends in flood events of different frequency and magnitude were investigated by analyzing rainfall data, integrated with landowner reports of flood-inducing rainfall magnitudes. The findings indicated that human land-use activities have been an important driver of recent river- floodplain degradation, through the enhancement of water and sediment connectivity across spatial scales of the catchment. Episodic and high magnitude floods synergized with human driven increased connectivity, precipitating stream power and geomorphological threshold breaches, resulting in a shift in river behaviour. The third results chapter investigated the influence of tributary-junction streams and fans on the geomorphological form, behavior and sensitivity of the Baviaanskloof River. Local- scale topographic impacts of tributary fans and streams were described using topographic surveys and geomorphological mapping techniques. Tributary streams form a major control on the behaviour of the river, by influencing the degree of coarse sediment connectivity with the main channel. Although tributary fans buffer the river from disturbances occurring in the wider catchment, they initiate topographic variations along the floodplain, influencing local-scale patterns of deposition and erosion along the river. The main river responds to water and sediment inputs from tributary junction streams by locally adjusting longitudinal slope, maintaining an overall constant slope of 0.0066 m/m. The response of the Baviaanskloof River to tributary junction fans and streams is however variable, and is fashioned by complex interactions between geomorphological and anthropogenic factors. The final two chapters of the thesis evaluate the findings of the study within the context of river-floodplain rehabilitation approaches in South Africa, and within the theoretical, philosophical and methodological context of the research. The first of these two chapters evaluates the approach of the WfWet programme to river-floodplain rehabilitation in the Baviaanskloof. The chapter indicates that the present practice of WfWet is to reinstate a pre-degradation state, which is not suited to the Baviaanskloof River-floodplain, since the river-floodplain has passed a geomorphological threshold, resulting in a new set of interacting processes and landforms. The author presents a conceptual model illustrating the existence of geomorphological adaptive cycles interacting across spatial and temporal scales, thereby attempting to explain a river Panarchy specific to the Baviaanskloof. From this conceptual model, a hierarchical rehabilitation framework, targeting geomorphological processes and structure situated at different spatial and temporal scales of the landscape is suggested. The final chapter discusses the implications of integrating the concepts of geomorphological connectivity and river Panarchy theory in studies of river complexity and sensitivity to geomorphological change. The author suggests that there is scope for further investigation of the application of the two concepts within the discipline of fluvial geomorphology, particularly with regard to developing quantitative approaches to measuring and describing connectivity and Panarchy.
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- Date Issued: 2017
Towards a holistic view of land and water management in the Gamtoos River catchment: applying a political geoecology approach
- Authors: Robb, Breanne Nicola
- Date: 2017
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/7914 , vital:21323
- Description: The Eastern Cape of South Africa is characterised by water scarcity, constraint on usage, and inter-basin transfers. Water from the Gamtoos River catchment supplies water users both within the catchment and outside the catchment boundaries. This requires careful management of water and land to prevent overexploitation. However, management is complex as it is divided among various stakeholders with differing interests. Political geoecology is an approach that has the potential to provide holistic insight into the catchment’s water context. It was proposed to account for spatial patterns underlying interrelationships between resource distribution, human productive activity, and power relations by integrating the fields of political ecology and geoecology. This research was undertaken to further develop political geoecology as an approach for examining human-environment relations in geography through a case study of land and water management in the Gamtoos River catchment and its subcatchments. Distribution of resources and human influences were elucidated through generation of maps. To facilitate spatial analysis, the study area was delineated into catchment zones. Additionally, stakeholders were identified and classified at local, regional, national, and international levels. Power relations between stakeholders were investigated through qualitative content analysis of transcribed semi-structured interviews and survey questionnaires that were administered to 34 research participants (selected through purposive and snowball sampling) directly involved in resource management in the catchment. Findings were spatially interpreted for each of the zones. The source zone was characterised by natural vegetation, steep, rugged topography, limited access ability, and power relations around restoration and conservation interests, which arose most significantly in the Baviaanskloof. The natural recapture zone was characterised by irrigated cultivation in areas of less harsh terrain in the upstream (Baviaanskloof and Kouga) sub-catchments. In the marginal Baviaanskloof, localised power relations over water distribution primarily arose. In the thriving commercial farming context of the Kouga, power relations included a local upstream-downstream legal conflict, competing levels of governance, issues with establishing water users’ associations (WUAs), and lack of adequate implementation of processes by government. Regional power relations are most prominent in the thriving commercial farming context of the overlapping regulated recapture and final use zones in the downstream Gamtoos sub-catchment. The reliance on upstream sub-catchments and tensions with the city of Port Elizabeth over water use are mediated through decisions made at the national level. Non-location specific power relations included indirect influence through energy, markets, and standards organisations, barriers in government preventing successful process implementation, and equity issues (particularly limiting the success of emerging farmers). These results illustrated that resource distribution, human productive activity, and power relations combine to produce unique characteristics in each of the zones in the Gamtoos catchment. The application of political geoecology in this case study situated the approach as useful for examining human- environment relations in geography.
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- Date Issued: 2017