Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Well-planned monitoring of the 2004 Upham Beach nourishment project in west-central Florida collected high-spatial and -temporal resolution field data. Three hurricanes passed by the project soon after nourishment was complete.Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual as pred icted by the typical diffusion models. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges.Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only due to hurricane passage, but also during a winter season. The duration between nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration.The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. The direction of cross-shore transport was governed by wave steepness. Onshore sediment transport occurred during a storm event, in contrast with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as cited in the literature.By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects.

Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2005. / Estuaries are complex water bodies and differ considerably from fluvial river systems. In estuaries the flow reverses regularly due to the tidal currents and flow depths depend primarily on the tides and not the flow. An estuary has two sources of sediment: the river during floods and the ocean that supplies marine sediment through littoral drift which is transported by tidal currents into the estuary. Oversimplified models cannot be used to investigate the hydrodynamics and geomorphology of an estuary due to its complexity. Sedimentation of South African estuaries has created several environmental and social problems. Sediment transport imbalances have been caused by changes in the river catchments such as increased sediment yields and flood peak attenuation due to dam construction. Historically floods used to flush estuaries to maintain the long-term sediment balance in the river-estuary system, but with reduced flood peaks, sediment transport capacities at the estuaries are reduced and flushing efficiency decreased, resulting in marine transport dominating in many estuaries. Two-dimensional (horizontal, 2DH) numerical models have been found to be appropriate tools for studying hydro- and sediment dynamics in SA estuaries. The modelling shows that the sediment balance in the estuary relies on a delicate balance between dominant flood and ebb flows. Although the models performed very well, there are still additional processes to include such as time varying roughness changes and cohesive sediments. For long-term and long reach simulations, onedimensional (or quasi-two-dimensional) models will also be required in future. Mathematical modeling can be used to simulate the flushing of sediments during floods, but attempts should be made to calibrate these models when adequate field data become available in the future. The modelling has shown that floods play a very important part in estuarine sediment transport processes. Physical modelling was undertaken of the breaching of an estuary mouth. The main aim was to illustrate the merits of breaching at higher water levels as well as to investigate the changes in the mouth during breaching. The data obtained from the experiments were used to calibrate and verify a mathematical model. Mathematical modelling of the breaching process at the Klein River estuary confirms what has been observed during numerous breachings in the field, i.e. that breaching at higher water levels and towards the southeast side is more effective. Sediment transport by both waves and currents was investigated. It was found that with increasing wave and stream power, sediment transport rates would increase if both waves and currents travelled in the same direction. In contrast, it seems that with the current direction opposing that of the waves, Hydraulics of Estuarine Sediment Transport Dynamics in South Africa iii greater wave heights resulted in lower sediment transport rates. A new sediment transport equation, based on stream power, wave power, as well as sediment size was calibrated and verified, and compared to the well-known Bijker formula.

Thesis (MEng) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: East London is situated on the south-eastern, Indian Ocean, coast o f South Africa. The sediment transport regime at East London is quite unlike the regimes at other ports in South Africa. A major ocean current (the Agulhas) flows exceptionally close to the coastline in this area, thus significantly affecting nearshore sediment movements. The proximity o f a strong ocean current opposed to the net longshore drift (wave driven transport) creates an anomalous sediment transport regime in comparison with that found at most coastlines throughout the world. Furthermore, the Port o f East London (Figures 1.1 and 1.2) is the only major river harbour in South Africa, which all results in a very intricate pattern o f sediment movement in the area, making it o f particular interest. The aims o f this thesis are to study the littoral sediment transports at East London, achieve a holistic understanding o f this complex sediment transport regime and to quantify the various transport rates as far as possible. The study area includes the coastal zone between the Goda and Nahoon Rivers (Figure 1.3) with the main focus on the Hood Point to Orient Beach area (Figure 1.4). The offshore marine environmental conditions are also considered as they have a strong influence on nearshore currents, waves and sediment transport patterns. The prerequisite to understanding the sediment transport processes is a thorough investigation o f the relevant coastal processes. Thus, an in-depth study is undertaken o f the physical environmental data/information, nearshore processes and coastal dynamics that determine or topography changes, the wave regime, the Agulhas Current, the nearshore current regime, the continental shelf sediment dynamics, sediment characteristics, seabed features, the Buffalo River, the tides, the wind regime, and coastal morphodynamics. The specific contribution of each aspect of the environmental data/information to the qualitative understanding of the overall sediment transport regime is determined, and the various modes of sediment transport in different areas are quantified. All o f this information is then synthesised into an expose' o f the sediment transport regime at East London, as briefly described in the conclusions (Section 5 and Table XI) and illustrated in Figure 4.30: There is a net longshore transport (wave driven) of about 250 000 m3 to 300 000 m3 per year on average from the Foreshore area towards the head of the main breakwater, with the total transport into the main sand trap and entrance channel areas from the south-west estimated at 275 000 m3/year. In the offshore zone, large amounts of sediment are transported downcoast by means of the strong Agulhas Current, which also has a significant influence on nearshore currents and sediment transport in the harbour entrance area. About 75 000 m3/year of sand is transported into the “Bar” area (the seaward part of the entrance channel) from the north-east with downcoast flowing nearshore currents, which is the predominant current direction. The riverine input into the harbour has been estimated at less than 10 000 m3/year of sand. In this thesis, therefore, the sediment transport regime (and sediment transport balance) is derived fo r East London, providing for the first time a holistic understanding o f the complex sediment transport regime. It is recommended that more field data should be collected on specific aspects of this study and that the longer term effects of major weather systems should be investigated further. The numerical wave modelling should be extended and the integration of field measurements and numerical modelling to predict sediment transport and resultant bottom changes should be assessed in detail. Ultimately, the information contained in this thesis should feed into a wider regional investigation, with the aim of drawing up a sediment budget for the entire “regional macro sedimentary cell” of which the present study area forms a part. / AFRIKAANSE OPSOMMING: sedimentvervoer-regime by Oos-Londen is anders as die by ander hawens in Suid-Afrika. ‘n Hoof oseaan-stroom (die Agulhas) vloei besonder naby aan die kus in die gebied en het gevolglik ‘n beduidende impak op sedimentvervoer-patrone in die nabystrandse gebied. Die direkte teenwoordigheid van ‘n sterk diepwater stroom wat teen die netto (golfgedrewe) langsstrandse vervoer inwerk, veroorsaak ‘n ongewone sedimentvervoer-regime in vergelyking met wat algemeen wereldwyd gevind word. Daarbenewens is die Oos-Londenhawe (Figure 1.1 en 1.2) die enigste groot rivier-hawe in Suid-Afrika. A1 die ongewone toestande lei tot ‘n ingewikkelde patroon van sedimentvervoer in die gebied. Die doel van hierdie tesis is om die sedimentvervoerregime by Oos-Londen te bestudeer, ‘n holistiese begrip van die ingewikkelde sedimentvervoerregime te verkry, en om die verskillende komponente van die sedimentvervoer regime so ver as moontlik te kM’antifiseer. Die studiegebied sluit die kusstrook tussen die Goda- en Nahoonriviere in (Figuur 1.3). Daar word egter op die Hoodpunt tot Orientstrand-gebied gefokus (Figuur 1.4). Die diepwater, mariene omgewingstoestande word ook beskou, aangesien hul ook ‘n groot impak op die nabystrandse strome, golwe en sedimentvervoer-patrone het. ‘n Deeglike ondersoek van die toepaslike kusprosesse is ‘n voorvereiste om ‘n goeie begrip van die sedimentvervoer-prosesse op te bou. Gevolglik is ‘n diepgaande ondersoek gedoen na die fisiese omgewingsdata en -inligting, nabystrandse prosesse en kusdinamika wat die sedimentvervoer-regime bepaal of bei'nvloed. Dit het ondersoeke ingesluit na: onderhoudsbaggervolumes, bodemtopografie veranderinge, die golfklimaat, die Agulhasstroom, die nabystrandse stroom-regime, die sedimentdinamika op die kontinentale plaat, sediment eienskappe, die windklimaat, die geaardheid van bodemvorme, die Buffelsrivier, getyaksie, en kus-morfologie. Daar is bepaal wat elke aspek van die omgewingsdata/inligting bydra tot ‘n kwalitatiewe begrip van die algehele sedimentvervoer-regime. Verder is die verskillende komponente van die sedimentvervoer in verskeie gebiede gekwantifiseer. Al hierdie inligting is toe versoen in ‘n beskrywing van die sedimentvervoer-regime by Oos-Londen, soos wat in die gevolgtrekkings (Deel 5 en Tabel XI) gegee word en in Figuur 4.30 geillustreer word: Daar is ‘n gemiddelde netto golfgedrewe langsstrandse vervoer van ongeveer 250 000 m3 tot 300 000 m3 per jaar vanaf die strandgebied suid van die hawe na die punt van die hoof-golfbreker. Die totale beraamde vervoer vanaf die suidweste na die hoofsandvangput en ingangskanaal-gebied is 275 000 m3 per jaar. In die diepsee word groot hoeveelhede sediment langs die kus af vervoer deur die sterk Agulhasstroom, wat ook ‘n beduidende impak het op nabystrandse strome en sedimentvervoer in die haweingangsgebied. Omtrent 75 000 m3 sand word per jaar na die “Bar”-gebied vervoer vanaf die noord-ooste deur nabystrandse strome wat langs die kus af vloei. Dit is ook die oorwegende nabystrandse stroomrigting (uitgesluit die brandersone). Sawafafsetting in die hawegebied afkomstig van die Buffelsrivier word op minder as 10 000 m3 per jaar geskat. Die sedimentvervoer-regime (en sediment-balans) by Oos-Londen word dus afgelei, en vir die eerste keer saamgesnoer in ‘n bree insig van die komplekse sedimentvervoer-regime. Daar word aanbeveel dat meer velddata verkry moet word oor sekere aspekte van hierdie studie en dat die langtermyn-impakte van groot weerstelsels verder ondersoek word. Die wiskundige golf-modellering moet uitgebrei word en die gesamentlike benutting van veldmetings met wiskundige modellering om sedimentvervoere en gevolglike bodemveranderinge te voorspel, moet deeglik ondersoek word. Uiteindelik behoort die inligting vervat in hierdie tesis in te voer in breer streeks-ondersoeke, met die oog daarop om ‘n sediment-begroting vir die “Ooskaapse makro-sedimentvervoer-regime” op te stel.

Riparian areas are valuable resources, particularly in semi-arid areas where water is usually scarce and rapid streamflow responses to runoff are common. Only recently has the importance of in-channel recharge during high streamflow periods ("floods") been recognized in rivers with gaining and losing reaches where recharge processes and flowpaths can be very complex. This dissertation builds upon this recent work by investigating how three factors influence how riparian systems respond to floods over a range of temporal and spatial scales. First, the impact of differences in local hydrogeologic forcings are investigated at the seasonal and 50 meter-reach scales. Second, the significance of flood event size and duration is studied at the multi-year and river (~50 Km) scale. Third, an underlying mechanism behind how changes in bed sediment composition can influence stream-aquifer interactions at the event- and point-scales is developed. Major findings of this work include observations along the Upper San Pedro River of seasonal floodwater storage below moderately gaining reaches and longer-term storage below losing reaches (seasonal to multi-year depending on the nature of the riparian groundwater flow system). The longest and largest floods (with respect to flow volume) dominate floodwater recharge in the Bill Williams River and an apparent flood size and duration threshold exists. This threshold must be met or exceeded in order for individual events to induce observable amounts of recharge that can then influence the amount and composition of later streamflow. This threshold agrees with the process presented here involving preferential mobilization and deposition of fine bed sediment particles--which dictate hydraulic conductivity--during each event that would lead to disproportionately more recharge during large floods. Forecasts of increased precipitation intensity and decreased annual precipitation in some regions, including the southwestern United States, due to changes in the earth's climate are likely to make floods a more important driver of riparian hydrologic processes. Consequently, the work presented here and other process-based studies of how floods influence riparian hydrology and water quality will be useful in making well-informed decisions regarding riparian preservation, management and restoration as human demands and the global climate change in the future.

No description available.

This thesis set out to improve our current understanding specifically of the role of permeability and carbon sources for the metabolic functioning of permeable sands.  Sampling of an intertidal sandy sediment in a shallow estuary over a 1-yr period revealed that permeability, being influenced by natural seasonal changes in biology and environmental conditions, varied temporally.  More specifically, the extracellular polymeric substances in the sediment were proven to substantially contribute to this temporal variability.  Sediment oxygen consumption also demonstrated seasonal variation and could be related to changes in temperature and total organic carbon, but, more importantly, also to permeability. Different carbon (C) sources were shown to influence the time series station but were also identified for other parts of the estuary.  A better understanding of the sedimentary C_org pool and the C_orgundergoing mineralization was furthermore obtained with the novel application of methods developed in the soil sciences comparing the δ¹³C of respired CO₂ to that of available source material and sedimentary C_org.  Overall, the results presented here demonstrate the crucial importance of permeability and carbon sources to metabolic processes and their mediation by biological factors. This thesis highlights the importance of continued research into the complexities of these permeable sands.

This study focuses upon flow hydraulics, sediment transport and riffle-pool maintenance on the River Rede, Northumberland, UK. Analysis of bed structure indicate pools to be coarser than riffles, suggesting these to be zones of maximum tractive force at high flow. Tractive force reversal can be demonstrated using a combination of velocity, shear stress and gravel tracer data, and is therefore advocated as a mechanism for maintaining the riffle-pool form. Three dimensional flow structures are likely to increase the likelihood of reversal in pools situated on bends, which may not always be detected using one-dimensional measures of flow hydraulics. Magnetic tracing and basket trapping techniques were used to provide an insight into rates of movement, accumulation, initial motion criteria and routing, of sand. Sand is transported selectively and is mobilised at between 11-22 Nm⁻². Deposition of sub 2mm material is prevalent on morphological high points (bars/riffle margins), although greatest quantities were routed through morphological lows. Freeze core evidence shows limited intragravel storage. Gravel tracer movements showed evidence of size selective entrainment overall, however hiding effects were also found to be evident at two scales; 30-50mm and 110-140mm (for riffles) and 20- 90mm and 11O-140mm for pool. Slope exponents for log-log relations between scaled grain size (D/D₅₀) versus dimensionless shear stress (Өc) of ≈-0.9 suggest that hiding strongly influences sediment transport. Stream power estimates from pgQs demonstrate a higher threshold for motion for gravel in pools (132 Wm⁻²) compared with riffles (127 Wm⁻²). Differences in initial motion criteria (8e) between riffles and pools were found to be significant (p<0.05), indicating pool sediments to be less mobile than riffle, despite pool sediments being less compact. Reduced mobility of pool bedload sediment results from clasts being sheltered by immobile lag gravel found in the pool. It appears therefore that mobility differences between riffles and pools, related to bed structure, does not explain riffle-pool maintenance on the Rede. Scaled travel distance (L/L₅₀s) for tracers in the reach as a whole showed a convex-up relationship with scaled grain size (D/D₅₀s), demonstrating that for tracer grains progressively coarser than the surrounding D₅₀ surface grains, travel distance drops off rapidly, whereas grains progressively finer than the surrounding clasts, travel further but at a less rapid rate. Furthermore, virtual velocity (V*) of tracer grains showed a positive dependence upon D/D₅₀s. Gravel tracer movement provided important insights into riffle-pool maintenance. Transfer of material through the Rede riffle-pool sequence appeared to be influenced by flow magnitude and duration. For low magnitude high frequency flows below 25% bankfull, intra-unit movement was found to predominate. Medium magnitude and frequency flows (up to 50% bankfull) appeared capable of inter-unit transport; scour from pool troughs and deposition on pool exit slopes I riffle heads, movement of material from riffles to bar edges and from bar to bar. For higher magnitude low frequency flows up to bankfull, there was less scour from pools, and a dominance of bar-to-bar sediment transfer. Limited evidence of sediment routing and deposition in pools suggest these to be scour / sediment source zones only, with supply originating from the bed and outer bank. These data demonstrate the importance of different flow magnitude and frequency in creating / maintaining different areas of the riffle-pool structure.

Mountain watersheds recently burned by wildfire often experience greater amounts of runoff and increased rates of sediment transport relative to similar unburned areas. Given the sedimentation and debris flow threats caused by increases in erosion, more work is needed to better understand the physical mechanisms responsible for the observed increase in sediment transport in burned environments and the time scale over which a heightened geomorphic response can be expected. In this study, we quantified the relative importance of different hillslope erosion mechanisms during two postwildfire rainstorms at a drainage basin in Southern California by combining terrestrial laser scanner-derived maps of topographic change, field measurements, and numerical modeling of overland flow and sediment transport. Numerous debris flows were initiated by runoff at our study area during a long-duration storm of relatively modest intensity. Despite the presence of a well-developed rill network, numerical model results suggest that the majority of eroded hillslope sediment during this long-duration rainstorm was transported by raindrop-induced sediment transport processes, highlighting the importance of raindrop-driven processes in supplying channels with potential debris flow material. We also used the numerical model to explore relationships between postwildfire storm characteristics, vegetation cover, soil infiltration capacity, and the total volume of eroded sediment from a synthetic hillslope for different end-member erosion regimes. This study adds to our understanding of sediment transport in steep, postwildfire landscapes and shows how data from field monitoring can be combined with numerical modeling of sediment transport to isolate the processes leading to increased erosion in burned areas.

Thesis advisor: Noah P. Snyder / Thesis advisor: Gail Kineke / Fluvial terraces form in both erosional and depositional landscapes and are important recorders of land-use, climate, and tectonic history. Terrace morphology consists of a flat surface bounded by valley walls and a steep-sloping scarp adjacent to the river channel. Combining these defining characteristics with high-resolution digital elevation models (DEMs) derived from airborne light detection and ranging (lidar) surveys, several methods have been developed to identify and map terraces. This research introduces a newly developed objective terrace mapping method and compares it with three existing DEM-based techniques to determine which is most applicable over entire watersheds. This work also tests multiple methods that use lidar DEMs to quantify the thickness and volume of fill terrace deposits identified upstream of dam sites. The preliminary application is to the Sheepscot River watershed, Maine, where strath and fill terraces are present and record Pleistocene deglaciation, Holocene eustatic forcing, and Anthropocene land-use change. Terraces were mapped at four former dam sites along the river using four separate methodologies and compared to manually delineated area. The methods tested were: (1) edge detection using MATLAB, (2) feature classification algorithms developed by Wood (1996), (3) spatial relationships between interpreted terraces and surrounding natural topography (Walter et al., 2007), and (4) the TerEx terrace mapping toolbox developed by Stout and Belmont (2013). Thickness and volume estimates of fill sediment were calculated at two of the study sites using three DEM-based models and compared to in situ data collected from soil pits, cut bank exposures, and ground penetrating radar surveys. The results from these comparisons served as the basis for selecting methods to map terraces throughout the watershed and quantify fill sediment upstream of current and historic dam sites. Along the main stem and West Branch of the Sheepscot River, terraces were identified along the longitudinal profile of the river using an algorithm developed by Finnegan and Balco (2013), which computes the elevation frequency distribution at regularly spaced cross-sections normal to the channel, and then mapped using the feature classification (Wood, 1996) method. For terraces upstream of current or historic dam sites, thickness and volume estimates were calculated using the two best performing datum surfaces. If all analyzed terraces are composed of impounded sediment, these DEM-based results suggest that terraces along the main stem and West Branch of the Sheepscot River potentially contain up to 1.5 x 106 m3 of fill. These findings suggest powerful new ways to quickly analyze landscape history over large regions using high-resolution, LiDAR DEMs while relying less heavily on the need for detailed and costly field data collection. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

For the last several decades, beach nourishment has been a widely implemented erosion mitigation strategy along many developed coastlines. Measuring subsequent patterns of erosion and accretion can help elucidate local sediment transport trends, improve time scale predictions of profile equilibration, decrease renourishment intervals, and adjust future engineering design of nourishments. This study evaluates the morphologic evolution of two beach nourishment projects (e.g., characterized as a full and partial nourishment) at the same location in Boca Raton, Florida using time series beach profiles, surface sediment samples, and wave data. More than 85% of sediment volume was retained within the full nourishment six months after project completion, compared to 50% retained eight months after completion of the partial nourishment. Wave energy largely influenced immediate post nourishment change. Profile equilibration was controlled by high-energy events (i.e., hurricanes) for both nourishments. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection