No description available.

Magister Scientiae (Integrated Water Resource Management) / The Klein Berg River catchment is intensely cultivated with orchards, vineyards and wheat, while also ensuring a water supply to the main urban center, Tulbagh, and the two conservation areas (Waterval and Groot Winterhoek). The primary objective of this thesis is to determine channel change over a long and short time period, and to relate these changes to landuse change within the catchment. Assessing stability of a selected reach within the catchment was done on a short term basis with the use of erosion pins and cross profiles, while aerial photographs of over 55 years (acquired during 1942, 1967, 1987 and 1997) which were analysed using Geographic Informations Systems. Rainfall and discharge data, which were available for a period of 49-years were statistically analysed and used to determine trends. Vegetation characteristics were assessed by means of transects within the study reach. The results over the short time period (18 months) indicate noticeable channel change in the form of erosion and deposition within the channel. Bank material composition and riparian invasive alien vegetation play an important role in bank stability. Sand was the dominant grain size of the bank material, and fluvial entrainment occurred during periods of high flow. Woody alien trees prevent the growth of protective ground vegetation, and thus the soil is prone to erosion. Undercutting was also observed with the invasive woody trees, resulting in treefall. Debris dams were also common in the channel and depending on their position in the channel, either cause or prevent bank erosion. Landuse change over the 55-year period illustrated its effects on channel stability. Shrublands within the catchment has been replaced with invasive alien vegetation along the riparian zone, while shrublands along the Obiekwa Mountains, were replaced with cultivated lands. The patterns (shape and size) of lateral and point bars within the study area changed significantly within the 55-year period, which indicates a change in the discharge and sediment dynamics within the catchment. The change in sediment dynamics may be due to agricultural activities and urbanization. The increased trend in rainfall, especially during the winter season within the catchment is also an important catchment control. The study has revealed the integrated nature of variables within the catchment. It is thus recommended that a holistic and integrated approach at a catchment scale is required in the assessment of channel change of a river. / South Africa

No description available.

Alluvial river channels are self-formed by the sediment-laden flow that is supplied to them from upstream and the interactions between this flow and the materials forming the channel bed and banks. Thus, any changes in the volumes of solid and liquid discharge or the resistance of the boundary materials can produce adjustments in the form of river channels over time. These shifts may increase or decrease the capacity of a channel to contain flood flows. However, despite a wealth of studies on the average geometry of river channels across different scales and climatic regimes, there has not yet been a systematic assessment of the rates and controls of trends in channel form. Using a combination of USGS data, including manual field measurements and mean daily streamflow data at hundreds of stream gages, this work is the first attempt to quantify how trends in channel geometry develop over decadal timescales and how they contribute to shifts in flood hazard, in comparison with trends in streamflow. Findings reveal that two-thirds of all channel cross-sections studied exhibit significant trends in channel geometry. The majority of the investigated US river channels are eroding, with widening and deepening trends partially offset by decreases in average flow velocity. Rates of change are principally controlled by the channel size. Although large channels develop larger trends, changes are proportionally greater in small channels in percentage terms. A secondary major control is hydrology: rates of change in channel geometry are heightened by the variability and flashiness of flow regimes. Finally, results show that changing flood frequencies can only be accurately quantified when both hydrologic and geomorphic trends are accounted for, and that flood hazard is significantly increasing across the studied sites. These documented trends in channel geometry, hydraulics, and flood hazard have important implications for the management of alluvial channels, navigation, and riverside infrastructure.

This study examines sediment storage and transfers in gullies of coastal British Columbia, and how logging affects sediment storage and transfers. Both fluvial and debris flow transport of sediment occur in gullies, and the amount of fluvial transport of sediment which occurs will affect the magnitude of a subsequent debris flow. Coarse woody debris (CWD) may affect the storage and transfer of sediment in the gully channel, and logging can affect the supply and type of CWD. To determine whether logging affects storage and transfer of sediment in gullies, sediment budgets were constructed for gullies in four treatment classes: A. Logged, slash full, no recent debris flows : "slash-full (SF)." B. Logged, slash removed, no recent debris flows : "slash-clear (SC)." C. Logged, naturally scoured by debris flows : "torrented (T)." D. Unlogged, naturally loaded with CWD : "unlogged (U)." Each sediment budget had input to the channel, storage in the channel, and output from the channel estimated. Significant differences between treatment types occurred, summarized below. Treatment classes grouped together (in brackets) did not have significant differences. Budget term : Input, greatest→least, Torrented→Slash-full→(Unlogged and Slash-clear). Budget term : Storage, greatest→least, Torrented→Unlogged→Slash-clear. Budget term : Output, greatest→least, Slash-clear→(Torrented and Unlogged)→Slash-full. One objective of the study was to assess the effectiveness and feasibility of cleaning slash from the gully channels. To be effective, cleaning slash must either reduce the magnitude of a debris flow in a treated gully, or else reduce the likelihood of initiation of a debris flow in the treated gully. Removal of slash will reduce the volume of a subsequent debris flow by about 15 percent, simply from the reduction in the amount of CWD. Reduction in sediment stored in the treated channel may reduce the volume of a debris flow by a further 4 percent. There is no evidence that removing slash will decrease the likelihood of initiation of a debris flow.

Headwater streams typically have no fish, owing to steep gradients and impassible barriers; therefore, scientific research and protection measures have been focused on fish bearing streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP) developed a channel classification system which is pertinent to all streams, fishless and fish bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels according to four physical criteria: bed material, gradient, entrenchment, and width. The current study was undertaken to determine the efficacy with which the CSP classification system delineates small, steep streams, on the basis of channel geomorphic units within them, and to examine the benthic macroinvertebrate habitat capability of these geomorphic units. Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were described according to their bed slope and dominant channel-material type and organization. In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped into four CSP channel classes which were compared with respect to the mean relative proportion of class area in geomorphic units. Stratified random benthic samples were extracted from geomorphic units in order to investigate and to compare their habitat capability. "Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport; therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e. bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild slopes. Accordingly, channel classes with opposing bed material and gradient designations exhibited notable differences with respect to relative proportions of geomorphic units while width and entrenchment designations exerted little influence on channel organization. Ultimately, only two of the four CSP classification criteria effectively systematized channels on the basis of channel geomorphic units within them. Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70 individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50 individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition, abundance of invertebrates in channels with ephemeral flow regimes was considerably lower compared to channels with seasonal or perennial flow regimes. Ordination of macroinvertebrate taxa showed that community structure of bedrock cascades and chutes were similar but different from other habitats. Similarly, the benthic macroinvertebrate community structure of channels with ephemeral flow regimes was very distinct.

This study examines sediment storage and transfers in gullies of coastal British Columbia, and how logging affects sediment storage and transfers. Both fluvial and debris flow transport of sediment occur in gullies, and the amount of fluvial transport of sediment which occurs will affect the magnitude of a subsequent debris flow. Coarse woody debris (CWD) may affect the storage and transfer of sediment in the gully channel, and logging can affect the supply and type of CWD. To determine whether logging affects storage and transfer of sediment in gullies, sediment budgets were constructed for gullies in four treatment classes: A. Logged, slash full, no recent debris flows : "slash-full (SF)." B. Logged, slash removed, no recent debris flows : "slash-clear (SC)." C. Logged, naturally scoured by debris flows : "torrented (T)." D. Unlogged, naturally loaded with CWD : "unlogged (U)." Each sediment budget had input to the channel, storage in the channel, and output from the channel estimated. Significant differences between treatment types occurred, summarized below. Treatment classes grouped together (in brackets) did not have significant differences. Budget term : Input, greatest→least, Torrented→Slash-full→(Unlogged and Slash-clear). Budget term : Storage, greatest→least, Torrented→Unlogged→Slash-clear. Budget term : Output, greatest→least, Slash-clear→(Torrented and Unlogged)→Slash-full. One objective of the study was to assess the effectiveness and feasibility of cleaning slash from the gully channels. To be effective, cleaning slash must either reduce the magnitude of a debris flow in a treated gully, or else reduce the likelihood of initiation of a debris flow in the treated gully. Removal of slash will reduce the volume of a subsequent debris flow by about 15 percent, simply from the reduction in the amount of CWD. Reduction in sediment stored in the treated channel may reduce the volume of a debris flow by a further 4 percent. There is no evidence that removing slash will decrease the likelihood of initiation of a debris flow. / Arts, Faculty of / Geography, Department of / Graduate

Headwater streams typically have no fish, owing to steep gradients and impassible barriers; therefore, scientific research and protection measures have been focused on fish bearing streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP) developed a channel classification system which is pertinent to all streams, fishless and fish bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels according to four physical criteria: bed material, gradient, entrenchment, and width. The current study was undertaken to determine the efficacy with which the CSP classification system delineates small, steep streams, on the basis of channel geomorphic units within them, and to examine the benthic macroinvertebrate habitat capability of these geomorphic units. Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were described according to their bed slope and dominant channel-material type and organization. In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped into four CSP channel classes which were compared with respect to the mean relative proportion of class area in geomorphic units. Stratified random benthic samples were extracted from geomorphic units in order to investigate and to compare their habitat capability. "Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport; therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e. bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild slopes. Accordingly, channel classes with opposing bed material and gradient designations exhibited notable differences with respect to relative proportions of geomorphic units while width and entrenchment designations exerted little influence on channel organization. Ultimately, only two of the four CSP classification criteria effectively systematized channels on the basis of channel geomorphic units within them. Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70 individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50 individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition, abundance of invertebrates in channels with ephemeral flow regimes was considerably lower compared to channels with seasonal or perennial flow regimes. Ordination of macroinvertebrate taxa showed that community structure of bedrock cascades and chutes were similar but different from other habitats. Similarly, the benthic macroinvertebrate community structure of channels with ephemeral flow regimes was very distinct. / Arts, Faculty of / Geography, Department of / Graduate

Urban areas experience the loss of natural stream channels through conversion to artificial conveyances. This process tends to target headwater and other low order streams. The purpose of this study is to determine the patterns of stream loss in Denton, Texas, and explore the regulatory structure that manages these streams. Historic and current maps and stream data are used to map Denton's streams and categorize them according to their vertical connectivity as: 1) "intact", streams that are open to the atmosphere and connect to groundwater; 2) "concrete", channelized streams open to the atmosphere but cut off from groundwater; and 3) "buried", streams disconnected from the atmosphere and groundwater. A review of federal, state, and local regulatory codes and interviews with local government officials and other stakeholders elucidates stream management in Denton. Results from these analyses reveal high rates of stream loss in the urban center with low rates overall. The federal Clean Water Act and the local Environmentally Sensitive Areas code serve as the primary protective measures for natural streams. These regulations discourage stream impacts through expensive and complex permitting requirements. However the policies allow minor impacts which may cause cumulative effects. This study aims to inform future policy-making decisions and contribute to the knowledge of the environmental regulation of streams.

The Klein Berg River catchment is intensely cultivated with orchards, vineyards and wheat, while also ensuring a water supply to the main urban center, Tulbagh, and the two conservation areas (Waterval and Groot Winterhoek). The primary objective of this thesis is to determine channel change over a long and short time period, and to relate these changes to landuse change within the catchment. <br /> <br /> Assessing stability of a selected reach within the catchment was done on a short term basis with the use of erosion pins and cross<br /> profiles, while aerial photographs of over 55 years (acquired during 1942, 1967, 1987 and 1997) which were analysed using Geographic Informations Systems. Rainfall and discharge data, which were available for a period of 49-years were statistically analysed and used to determine trends. Vegetation characteristics were assessed by means of transects within the study reach. The results over the short time period (18 months) indicate noticeable channel change in the form of erosion and deposition within the channel. Bank material composition and riparian invasive alien vegetation play an important role in bank stability. Sand was the dominant grain size of the bank material, and fluvial entrainment occurred during periods of high flow. Woody alien trees prevent the growth of protective ground vegetation, and thus the soil is prone to erosion. Undercutting was also observed with the invasive woody trees, resulting in treefall. Debris dams were also common in the channel and depending on their position in the channel, either cause or prevent bank erosion. Landuse change over the 55-year period illustrated its effects on channel stability. Shrublands within the catchment has been replaced with invasive alien vegetation along the riparian zone, while shrublands along the Obiekwa Mountains, were replaced with cultivated lands. The patterns (shape and size) of lateral and point bars within the study area changed significantly within the 55-year period, which indicates a change in the discharge and sediment dynamics within the catchment. The change in sediment dynamics may be due to agricultural activities and urbanization. The increased trend in rainfall, especially during the winter season within the catchment is also an important catchment control. The study has revealed the integrated nature of variables within the catchment. It is thus recommended that a holistic and integrated approach at a catchment scale is required in the assessment of channel change of a river.