Bedload transport is a complicated phenomenon in gravel-bed streams. Several factors account for this complication, including the different hydrologic regime under which different stream types operate and the wide range of particle sizes of channel bed material. Based on the hydrologic regime, there are two common types of gravel-bed streams: perennial and ephemeral. In terms of channel bed material, a gravel bed may have either unimodal or bimodal sediment. This study examines more closely some aspects of bedload transport in gravel-bed streams and proposes explanations based on fluvial mechanics. First, a comparison between perennial and ephemeral gravel-bed streams is conducted. This comparison demonstrates that under a wide range of Shields stresses, the trends exhibited by the bedload transport data of the two stream types collapse into one continuous curve, thus a unified approach is warranted. Second, an empirical bedload transport relation that accounts for the variation in the make-up of the surface material within a wide range of Shields stresses is developed. The accuracy of the relation is tested using available bedload transport data from streams with unimodal sediment. The relation is also compared against other formulae available in the literature that are commonly used for predicting bedload transport in gravel-bed streams. Third, an approach is proposed for transforming the bimodal sediment into two independent unimodal fractions, one for sand and another for gravel. This transformation makes it possible to carry out two separate computations of bedload transport rate using the bedload relation developed in this study for unimodal sediment. The total bedload transport rate is estimated by adding together the two contributions. / Ph. D.

The characteristics of a given stream or river are linked to the material that makes up its channel bed. Usually, a vertical stratification by particle size can be recognized. The presence a coarser surface layer is considered to be one of the most important features of a gravel bed stream. Since this surface layer consists of a distinct population of material, it is necessary to be able to separate it from the underlying material and quantify it distinctly. This is done through surface sampling. Two of the most common adhesive areal sampling techniques, and the subject of the present work, are known as clay and wax sampling. If the material obtained in an areal sample is analyzed as a frequency distribution by weight, it has been shown that the size distribution is biased in favor of the larger particles when compared to the results of a bulk sample. The present research shows that this bias is dependent not only upon the sampling method used to remove the material but also upon the size distribution of the sample itself. Not only are the raw results of areal samples not comparable with volumetric samples, but they are not comparable with other areal samples. Before any comparisons are made among areal samples, it is recommended that the size distribution of each areal sample be first converted into the size distribution that would have resulted from an equivalent volumetric sample. The features and limitations of the gravel simulation model that is used to obtain the necessary conversion formula is also the subject of the present work. In addition, the conversion of both matrix and framework supported gravel mixtures that has been areally sampled with either clay or wax, is addressed. Finally, criteria for approximating the minimum depth required for a volumetric sample is presented. / Master of Science

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

No description available.

Demands on the water resources of South Africa are ever increasing owing to population growth and increased development of urban, peri-urban and rural communities. Problems in terms of water quantity and quality are likely to be experienced during baseflow recessions. It is therefore imperative that water resources managers not only understand these baseflow periods of streamflow, but are able to model them with confidence. Research for this study thus included a comprehensive literature survey of the factors which affect baseflow as well as the approaches that previous studies have utilised to analyse and model baseflow recession. The primary aims of this study were to establish a streamflow database, to construct master recession curves (MRCs) for each catchment under consideration, evaluate the assumption that South African rivers recede exponentially, to determine a representative set of catchment characteristics for use in the baseflow recession analysis, to attempt to explain the MRC trends using these catchment characteristics and to investigate the feasibility of establishing a rule based model for baseflow recession. A streamflow database for South Africa was therefore established. This consisted initially of 202 catchments which were deemed to be recording natural streamflow. MRCs were established for 134 of these catchments. Those MRCs which were established indicate that the majority of South African rivers do not conform to an exponential model of recession. In order to account for the trends defined by the MRCs, catchment area, average catchment slope, drainage density, mean annual precipitation, rainfall concentration, rainfall seasonality, two independent estimates of groundwater recharge and a geological index were calculated for each catchment. Limited success was achieved when the data set was divided into subsets in order to group catchments with similar baseflow recession responses. The geological composition of the catchments appeared to provide the best results in that those trends exhibited by the MRCs could be explained by the types and proportions of the lithologies present. Owing to the lack of readily useable results it was concluded that until further results were forthcoming the development of a rule based model for baseflow recession analysis in South Africa would be premature. The establishment of a readily accessible database containing streamflows and associated catchment characteristics lends itself to future research. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

Measuring the environmental condition of waterways is of interest to river managers, governments and the community. In the State of Victoria, Australia and elsewhere, there is concern that environmental values of streams are declining and that information about the environment, needs to be considered when river management decisions are being made. / This thesis explores the use of environmental indicators as a tool to assist management of rivers. The promise of indicators is that they can turn large amounts of environmental data into simple, timely results and thereby provide an effective means of incorporating this information into river management decisions. It is also suggested that indicators will be useful for measuring the outcomes of management intervention and provide feedback on the effectiveness of strategies. / Can environmental indicators live up to this promise? This thesis examines this question by reviewing indicator systems that have been developed by others and then exploring, in detail, the Index of Stream Conditions (ISC) that is is intended as a tool to assist the management of rivers in Victoria. I argue that environmental indicators have a role at the level of regional waterway management authorities but only if they are closely aligned with managers’ needs. Without consideration of non-technical issues, indicators are unlikely to be used, so it is important to establish a balance between pragmatic constraints and the need for scientific rigour. A procedure to achieve this balance is described in this thesis and was applied to the development of the ISC. Selection of indicators and the choice of indicator frameworks are explored and the value judgements behind the interpretation of indicator scores are examined. / It is also important to consider the accuracy and sensitivity of indicators. Possible objectives for the use of indicators include benchmarking, detecting change and providing information to trigger management intervention. Case studies are used to explore the performance of indicators in practical applications in streams in Victoria in relation to these objectives. Extensive use is made of non-traditional statistical procedures, including bootstrapping, and results are presented that show the likely variance of indicator scores and the relationship between indicator objectives and required sampling effort.

Thesis (D.W.S.)--Institute for Worship Studies, 2007. / Abstract. Includes bibliographical references (leaves 166-171).

Thesis (D.W.S.)--Institute for Worship Studies, 2007. / Abstract. Includes bibliographical references (leaves 166-171).

Thesis (M.Sc. (Geography)) - Rhodes University, 2009.

Many rural communities in arid areas of the world make extensive use of perennial water supplies retained within the sediment of a river channel. This naturally filtered water provides for their basic subsistence. A general term applied to the abstraction of water from river sediment is sand-abstraction. Ephemeral and seasonal rivers primarily drain the dryland regions of the world. These arid regions are typically subject to extensive environmental degradation with a consequent high degree of surface erosion. As a result, many of the rivers have become sand rivers, filled with copious amounts of sediment. Most arid areas are subject to occasional rainstorms and flash floods that immediately drain to waterways and saturate the sediment within the river channel. In larger rivers a perennial supply of water is maintained within the sediment. Despite a perceived potential for this water resource there has been little development of any small-scale technology that is suitable for use at a basic rural level. A research and study programme was instigated to assess fully, the potential of such a resource. Field research was undertaken to characterise typical sand rivers and to assess the water storage and water loss and retention factors within river sediment. A check list for identifying possible sand-abstraction sites was devised. In the process of this study the advantages of storing water in sand was fully appreciated and attention given to the development of initially less suitable sites in serious water deficit areas. Systems for efficient abstraction of water were reviewed and designs formulated for the fabrication of equipment to mechanically draw water from river sediment. A series of well-screens, well-points, infiltration galleries and caissons have been designed and initial tests have been conducted under field conditions. Simple technology handpumps that it was considered could be operated, maintained and repaired by rural communities using locally available materials have been developed in conjunction with the abstraction equipment. In consultation with rural people an analysis was made of the technical and sociological requirements that are considered essential for the sustainability of technology suitable for use by disadvantaged rural communities. Both practical and literature research has indicated the latent possibility of this technology. Interaction has been maintained with four communities throughout the research and development period and contributions and indications received are that there is a need to develop such a water source with an upgraded technology. The conclusion from the work undertaken is that development of the technology is worthwhile and that greater efforts should be made to promote it at a small-scale, rural level. In addition the potential to provide clean water in arid regions from such a lowtechnology application should be drawn to the attention of professional water engineers.