The hydraulic dimensions and planform character of a river channel are very much affected by the channel gradient and the calibre of the bed materials. One of the two major objectives of this study is to analyze these effects on selected reaches along the Bulstrode River, near Victoriaville. / The second objective is to relate the variations in gradient, sediment calibre and channel geometry to the changes in floodplain character along the river valley. / The river is about 85 km long and flows across the Appalachian highlands and foothills in southern Quebec. This study focuses on six alluvial reaches along the river, ranging from 0.7 to 1.5 km in length. The channel gradient ranges from 0.0036 to 0.0001. The decline in gradient is associated with rapid downstream fining from small cobble and gravel-bed in the 'upvalley reaches' to a sand-bedded channel in the 'downvalley' reaches. / The discharge remains fairly constant over the river length, averaging about 140 m$ sp3$/sec. Channel depth, particularly the thalweg depth, increases appreciably in the downstream direction. The channel width decreases appreciably in the downstream direction. The channel capacity varies significantly without a clear pattern in the steeper cobble-gravel bed reaches and generally declines in the more hydraulically efficient, gentler and more hydraulically efficient fine gravel-sand bed downstream reaches. / This study finds that floodplain characteristics vary with specific stream power and within-channel processes, but not in the same manner as suggested in the Nanson and Croke (1992) model. (Abstract shortened by UMI.)

Thesis (Ph. D.)--Rhodes University, 2004. / Title from PDF t.p. (viewed on Apr. 23, 2006). Includes bibliographical references (leaves 222-257).

Philosophiae Doctor - PhD / The Okavango Delta is recognized as one of the famous inland wetlands and its sustainable use is important for socio-economic development of Botswana. The Okavango delta comprises permanent swamps, seasonal swamps, and drylands on islands within the delta and the surrounding areas, sustained by Okavango river inflows from upstream and local rainfall. TheOkavango River splits into several distributary channels within the delta. Areas which are flooded annually vary in response to varying inflows into the delta. Peak inflows into the delta occur during the February to May period. Due to the low gradient over the delta, these inflows move slowly resulting in peak outflows from the delta occurring during the June to August period. The inundated area over the entire delta increases from May until it reaches maximum inAugust and starts to decrease from September, reaching minimum inundated area in the months of December and January. The incoming flood wave into the delta and maximum inundation is out of phase with the local rainfall season.Communities living within and around the delta derive their livelihoods from tourism, hunting, fishing, livestock rearing, and crop production. Crop production is carried out on drylands and within floodplains. Some of the households take advantage of the increase in soil moisture arising from this inundation along floodplains to cultivate their crops as the floods recede. This practice is locally referred to as molapo farming which highly depends on inundation of floodplains. The availability of floodplain inundation highly depends on the magnitude of inflows into the delta and the local rainfall which are highly variable resulting in uncertainty regarding successful crop production, availability of livestock grazing areas, and uncertainty in reliance on the wetlands resources such as fishing. The uncertainty experienced in timing of extreme events which cause flooding of resulting in water reaching areas or floodplains where it is not wanted, and also uncertainity in timing of low flows, therefore water not reaching some parts of the delta.Several hydrological studies have been carried out with the aim of improving the understanding of the spatial and temporal dynamics of flows throughout the delta including predicting areas that are likely to be inundated each year. The significant gap addressed by this research is to improve the understanding of the spatial and temporal influence of magnitude and timing of flows on floodplain inundation. Local rainfall on the delta is highly variable over time and space due to its convective nature. This research also addresses the rainfall temporal and spatial variations and its implications on floodplain inundation. The knowledge about spatial extent and duration of floodplain inundation should assist in predicting each year the viability of molapo farming. Three research site, Shorobe, Tubu and Xobe are selected as case studies to understand the dynamics of floodplain inundation induced either by inflows or local rainfall. Local rainfall during the December to March period enables the crops to reach maturity. The onset of the rainy season is very important in supporting sowing of crop seeds. Local rainfall on the delta varies considerably. Aerial rainfall interpolation shows a change in rainfall magnitudes over space in different rainfall months, i.e different parts of the delta receive different rainfall magnitudes in different months of the rainy season. The spatial variation is mainly associated with the migration of the ITCZ southwards first through East Africa during October andNovember and down over Southern Africa in December to February. The movement of the ITCZ brings rainfall concentration on the northern and eastern parts of the Okavango Delta during December to January and bringing rainfall concentration to the northwestern part of the delta around February. However, rainfall spatial correlation between stations can be poor even within the first 150 km therefore implying neighboring places do not experience floodplain inundation by rainfall at the same time. The poor spatial correlation of rainfall between neighboring stations reflects the erratic nature of rainfall in the Okavango Delta characterised by localized thunderstorms. Change detection shows change points in rainfall which can be associated with ENSO episodes. A change point is identified in 1976 and 1977 which can be associated with the El Nino episodes during those years and two change points identified in 1999 and 2004 which can be associated with the La Nina episodes, therefore rainfall induced floodplain inundation can also be associated with wet and dry ENSO episodes. Rainfall does not show any significant trends except for an increasing trend on 10th percentile of Shakawe rainfall. Rainfall also does not show any cyclic behavior. Rainfall over the Okavango Delta can be divided into three unique homogenious sub-regions; sub-region 1: the northern part following the GEV probability distribution and being the region with highest rainfall amounts; sub-region 2: the lower northern and the outlet parts of the Okavango Delta following the GPA distribution with moderate rainfall; and sub-region 3: the middle part of the delta extending to the western and the eastern fringes of the delta, following the P3 distribution and having the lowest rainfall.The main characteristic that defines the Okavango Delta flows at Mohembo is its cyclic behavior. Three significant cycles are identified, close to 10, 20 and 40 years. No significant trends are identified, only a decreasing trend in minimum flows. Change points are identified in 1979 and 1988 and these can be explained by the existing cyclicity since no major land use changes have taken place in the Okavango River Basin upstream before 1989. The existence of cyclicity in Okavango River flows at Mohembo also explains the periodic wetting and drying of different floodplains in the delta. A long period of low flows was experienced from 1983 until 2003 and floodplain inundation extent was greatly reduced, more especially during the 1993-2003. During the 1993-2003 period, flows could no longer reach Maun Bridge along Thamalakne River, therefore leaving molapo floodplains around Boteti River, Gomoti River and Thaoge River to dry out. The 10 and 40 year return floods are important as they indicate the probability of a flood magnitude which has potential to result in major inundation in the Okavango Delta. Therefore, flood magnitudes with recurrence interval 10 and 40 years have high probability of occurring and can cause major floodplain inundation as they can be above the 2009 flood of 969 m3/s, which was the return of major inundation of Okavango Delta floodplains after a long period of dryness. The Ngoqa-Maunachira distributary channel of the Okavango River receives 32% of flow volumes entering the Okavango Delta at Mohembo. 12 % of the Mohembo flow volumes reach the Jao-Boro distributary whilst 1% is received by the Thaoge distributary. Therefore more inundation is experienced along the Ngoqa-Maunachira system compared to the other two. Only about 2% of the Mohembo flow volumes leave the Okavango Delta through Boteti River. Long term shifting of flow direction amongst reaches along the Okavango Delta distributaries is evident more especially along the Ngoqa-Maunachira River system. This results in shifting of inundation. Sub-surface water respond significantly to local rainfall and inflows with high soil moisture conditions retained at 60 cm and 100 cm below the ground.

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To calculate flow or depth in a waterway, it is necessary to accurately determine the flow resistance. Past research has made considerable progress in predicting the roughness of nonvegetated uniform channels based on both theoretical and experimental investigations. However, to determine the flow resistance associated with vegetated compound flow channels and floodplains, the effects of the vegetation must be considered. Recent advancements have led to greater understanding of the effects of partially submerged uniform vegetation in a waterway. However, to accurately determine flow resistance, it is imperative that the effects of both submerged and partially submerged vegetation be taken into account. It is also critical to account for the effects of multiple species and densities of vegetation throughout the waterway. Extensive testing of both partially submerged and fully submerged vegetation was completed in the laboratory. Multiple species were tested together to represent various ecosystems commonly found in floodplains throughout the country. Results of the testing show that both geometric and biomechanical properties of the plants must be accounted for when determining vegetation resistance. Methods and procedures were developed to quantify these properties. Equations were also developed that provide a basis by which to quantify vegetation resistance. The results of this study were compared to several sets of actual field data. The resistance values predicted by the equations were very close to those measured in the field. Use of the developed equations and procedures now provides those involved in the field of flood control a far more accurate tool by which to predict vegetation resistance than was previously available.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on December 21, 2009). Thesis advisor: Dr. Yingkui (Philip) Li. Includes bibliographical references.

No description available.

No description available.

Aeolian dune interdunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves. This neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole, especially with regard to dune spacing. This project involved the collection of geomorphologically relevant airflow data for four relatively simple transverse dune interdunes. The study locations were chosen in order to sample interdunes with different size and surface type characteristics, the dynamics of which were investigated for when incident flow was normal to the upwind crest. The findings confirm existing models of aeolian dune lee-side flow in terms of flow re-attachment length and recovery attributes. A consistent pattern of increasing near-surface velocity downwind of re-attachment provides a mechanism for interdunes as sand-free features. Where studies for comparison from other aeolian examples are limited, the field-measured turbulence shows the importance of the shear layer as a source of turbulence, and agrees with studies from subaqueous bedforms. The importance of shear stress variability and the possible contribution of turbulence structures to the maintenance of sediment transport at re-attachment where velocity and mean stress is low or negative is also emphasised. At the downwind edge of interdunes, the mean and turbulent velocity properties, and therefore morphodynamics, vary according to the interdune size. In this case, interdune length leads to greater recovery, and a balance exists in this region between the recovering flow at the surface, dissipating wake from above and the obstacle effect of the dune. The flow dynamics are characterised for the different types of interdune observed. Dynamics accordant with the flow response model are seen to characterise the interdune setting with the closest spacing. The occurrence of other “extended” aeolian interdunes with a length well over that for flow separation demanded the development of a new descriptive model to characterise the dynamics therein. In this model, the variation in near-surface flow allowed process zones to be identified through the interdune. The geomorphological significance of the processes dominating each zone are discussed and comparisons are made between the flow response case and the new interdune model from this study