Dissertations / Theses on the topic 'Sediment transport – Champlain, Lake'

Missisquoi Bay, Lake Champlain is a eutrophic, northern shallow freshwater bay that experiences toxic cyanobacteria blooms during the summer months, largely as result of high nutrient (P and N) loading from the agricultural watershed. The sediments, which contain minerals that readily sorb P, can act as a sink or source of water column nutrients. Phosphorus, both inorganic and some organic forms, sorbs to metal oxides at neutral pH in the sediment, thus P release into overlying and pore water can be significantly affected by the reduction and subsequent solubilization of these oxides. This study addresses novel aspects of nutrient cycling in lake sediments as part of a larger study to better understand the link between phosphorus forms, mobility, and cyanobacteria blooms. These aspects include: 1) diel and seasonal sediment redox fluctuations and 2) the role of organic P (Porg) in overall P mobility within sediments as a function of depth and time. Missisquoi Bay sediment porewater redox chemistry was monitored across diel and seasonal cycles over the course of two summers (May-October, 2007 and 2008) by using in-situ voltammetry. Redox chemistry was monitored at the sediment-water interface (SWI) continuously over diel cycles, and the vertical concentration profiles of several key redox species (O2, Mn2+, Fe2+, and FeS(aq)) were obtained from cores collected at different times. The sediments were then analyzed for Total P (TP), Reactive P (RP), Porg, Mn, Fe, Ca, Al, Total Organic C and N. A bloom did not occur in Missisquoi Bay during the summer of 2007, but did in summer of 2008, providing an opportunity to compare the sediment chemistry between non-bloom and bloom conditions. Increasingly anoxic SWI conditions across summer 2008 were observed but the SWI remained oxic for the duration of summer 2007. Significant changes in diel cycle redox chemistry at the SWI were also detected in both summers. Reactive P in the surface sediments decreased across the 2008 season but not in 2007. A strong correlation found between RP and RFe (operationally defined as Fe(III)OOH) suggests that a significant portion of sediment P (30-40%) is closely associated with Fe(III)OOHs, which are susceptible to reduction in anoxic conditions. Phosphorus mobility from the sediment into the water column can be limited by the amount of Fe(III)OOH at the surface, thus P flux from the sediments would be greatest when reducing conditions promote solubilization of these minerals. Completely anoxic surface sediments were only observed during the presence of a bloom, explaining the loss of RP in the surface sediments in 2008 in the late summer. Organic P species represent 18-26% of the P in sediments and the lack of a definite, consistent trend of Porg fractionation across the season suggests that there is variable mobility and degradation of these complex organic compounds on small timescales. The loss of RP from the sediment in 2008 could have contributed to an estimated water column P increase on the order of thousands of μg/L, which in addition to measured increases in NH4+ gradients and subsequent N flux estimates in the upper sediment, could have sustained the bloom for an extended period of time. The relationship between the bloom and reducing sediment conditions suggest that bloom dynamics enhance nutrient release from the sediments, allowing for proliferation and sustainability of the bloom.

A nested three dimensional numerical modeling application was developed to determine the fate of pathogen indicators in Lake Pontchartrain discharged from its tributaries. To accomplish this, Estuarine, coastal and ocean model with sediment (ECOMSED) was implemented to simulate various processes that would determine the fate and transport of fecal coliform bacteria in the lake. The processes included hydrodynamics, waves, sediment transport, and the decay and transport of the fecal coliforms. Wind and tidal effects were accounted along with the freshwater inflows. All the components of the modeling application were calibrated and validated using measured data sets. Field measurements of the conventional water quality parameters and fecal coliform levels were used to calibrate and validate the pathogen indicator transport. The decay of the fecal coliforms was based on the literature and laboratory tests. The sediment transport module was calibrated based on the satellite reflectance data in the lake. The north shore near-field model indicated that the fecal coliform plume can be highly dynamic and sporadic depending on the wind and tide conditions. It also showed that the period of impact due to a storm event on the fecal coliform levels in the lake can be anywhere from 1.5 days for a typical summer event to 4 days for an extreme winter event. The model studies showed that the zone of impact of the stormwater from the river was limited to a few hundred meters from the river mouth. Finally, the modeling framework developed for the north shore was successfully applied to the south shore of Lake Pontchartrain to simulate fate and transport of fecal coliforms discharged through the urban stormwater outfalls.

Thesis (M.S.)--University of New Orleans, 2004.
Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the department of Civil Engineering."--Thesis t.p. Vita. Includes bibliographical references.

This thesis examines the processes of longshore sediment transport in the swash zone of a mixed sand and gravel shoreline, Lake Coleridge, New Zealand. It focuses on the interactions between waves and currents in the swash zone and the resulting sediment transport. No previous study has attempted to concurrently measure wave and current data and longshore sediment transport rates on a mixed sand and gravel lakeshore beach in New Zealand. Many of these beaches, in both the oceanic and lacustrine environments, are in net long-term erosion. It is recognised that longshore sediment transport is a part of this process, but very little knowledge has existed regarding rates of sediment movement and the relationships between waves, currents and swash activity in the foreshore of these beach types. A field programme was designed to measure a comprehensive range of wind, wave, current and morphological variables concurrently with longshore transport. Four electronic instruments were used to measure both waves and currents simultaneously in the offshore, nearshore and swash zone. In the offshore area, an InterOcean S4ADW wave and current meter was installed to record wave height, period, direction and velocity. A WG-30 capacitance wave gauge measured the total water surface variation. A pair of Marsh-McBirney electromagnetic current meters, measuring current directions and velocities were installed in the nearshore and swash zone. Data were sampled for 18 minutes every hour with a Campbell Scientific CR23x data-logger. The wave gauge data was sampled at a rate of 10 Hz (0.1 s) and the two current meters at a rate of 2 Hz (0.5 s). Longshore sediment transport rates were investigated with the use of two traps placed in the nearshore and swash zone to collect sediment transported under wave and swash action. This occurred concurrently with the wave measurements and together yielded over 500 individual hours of high quality time series data. Important new insights were made into lake wave processes in New Zealand's alpine lakes. Measured wave heights averaged 0.20-0.35 m and ranged up to 0.85 m. Wave height was found to be strongly linked to the wind and grew rapidly to increasing wind strength in an exponential fashion. Wave period responded more slowly and required time and distance for the wave length to develop. Overall, there was a narrow band of wave periods with means ranging from 1.43 to 2.33 s. The wave spectrum was found to be more mixed and complicated than had previously been assumed for lake environments. Spectral band width parameters were large, with 95% of the values between 0.75 and 0.90. The wave regime attained the characteristics of a storm wave spectrum. The waves were characteristically steep and capable of obtaining far greater steepness than oceanic wind-waves. Values ranged from 0.010 to 0.074, with an average of 0.051. Waves were able to progress very close to shore without modification and broke in water less than 0.5 m deep. Wave refraction from deep to shallow water only caused wave angles to be altered in the order of 10%. The two main breaker types were spilling and plunging. However, rapid increases in beach slope near the shoreline often caused the waves to plunge immediately landward of the swash zone, leading to a greater proportion of plunging waves. Wave energy attenuation was found to be severe. Measured velocities were some 10 times less at two thirds the water depth beneath the wave. Mean orbital velocities were 0.30 m s⁻¹ in deep water and 0.15 m s⁻¹ in shallow water. The ratio difference between the measured deep water orbital velocities and the nearshore orbital velocities was just under one half (us/uo = 0.58), almost identical to the predicted phase velocity difference by Linear wave theory. In general Linear wave theory was found to provide good approximations of the wave conditions in a small lake environment. The swash zone is an important area of wave dissipation and it defines the limits of sediment transport. The width of the swash zone was found to be controlled by the wave height, which in turn determined the quantity of sediment transported through the swash zone. It ranged in width from 0.05 m to 6.0 m and widened landward in response to increased wave height and lakeward in response the wave length. Slope was found to be an important secondary control on swash zone width. In low energy conditions, swash zone slopes were typically steep. At the onset of wave activity the swash zone becomes scoured by swash activity and the beach slope grades down. An equation was developed, using the wave height and beach slope that provides close estimates of the swash zone width under a wide range of conditions. Run-up heights were calculated using the swash zone width and slope angle. Run-up elevations ranged from 0.01 m to 0.73 m and were strongly related to the wave height and the beach slope. On average, run-up exceeds the deep water wave height by a factor of 1.16H. The highest run-up elevations were found to occur at intermediate slope angles of between 6-8°. Above 8°, the run-up declined in response to beach porosity and lower wave energy conditions. A generalised run-up equation for lake environments has been developed, that takes into account the negative relationship between beach slope and run-up. Swash velocities averaged 0.30 m s⁻¹ but maximum velocities averaged 0.98 m s⁻¹. After wave breaking, swash velocities quickly reduced through dissipation by approximately one half. Swash velocity was strongly linked to wave height and beach slope. Maximum velocities occurred at beach slopes of 5°, where incident swash dominated. At slopes between 6° and 10°, swash velocities were hindered by turbulence, but the relative differences between the swash and backswash flows were negligible. At slope angles above 10° there was a slight asymmetry to the swash/backswash flow velocities due to beach porosity absorbing water at the limits of the swash zone. Three equations were developed for estimating the mean and maximum swash velocity flows. From an analysis of these interactions, a process-response model was developed that formalises the morphodynamic response of the swash zone to wave activity. Longshore sediment transport occurred exclusively in the swash zone, landward of the breaking wave in bedload. The sediments collected in transit were a heterogeneous mix of coarse sands and fine-large gravels. Hourly trapped rates ranged from 0.02 to 214.88 kg hr⁻¹. Numerical methods were developed to convert trapped mass rates in to volumetric rates that use the density and porosity of the sediment. A sediment transport flux curve was developed from measuring the distribution of longshore sediment transport across the swash zone. Using numerical integration, the area under this curve was calculated and an equation written to accurately estimate the total integrated transport rates in the swash zone. The total transport rates ranged from a minimum of 1.10 x 10-5 m³ hr⁻¹ to a maximum of 1.15 m³ hr⁻¹. The mean rate was 7.36 x 10⁻² m³ hr⁻¹. Sediment transport was found to be most strongly controlled by the wave height, period, wave steepness and mean swash velocity. Transport is initiated when waves break at an oblique angle to the shoreline. No relationships could be found between the grain size and transport rates. Instead, the critical threshold velocities of the sediment sizes were almost always exceed in the turbulent conditions under the breaking wave. The highest transport rates were associated with the lowest beach slopes. It was found that this was linked to swash high velocities and wave heights associated with foreshore scouring. An expression was developed to estimate the longshore sediment transport, termed the LEXSED formula, that divides the cube of the wave height and the wave length and multiplies this by the mean swash velocity and the wave approach angle. The expression performs well across a wide range of conditions and the estimates show very good correlations to the empirical data. LEXSED was used to calculate an accurate annual sediment transport budget for the fieldsite beaches. LEXSED was compared to 16 other longshore sediment transport formulas and performed best overall. The underlying principles of the model make its application to other mixed sand and gravel beaches promising.

Approximately 14,500 years ago, Pleistocene Lake Bonneville discharged 4750 km 3 of water over the divide between the closed Bonneville Basin and the watershed of the Snake River. The resulting flood, emanating from the divide at Red Rock Pass, Idaho, followed the present courses of Marsh Creek, the Portneuf River, and the Snake and Columbia Rivers before reaching the Pacific Ocean. For the 1100 kilometers between Red Rock Pass and Lewiston, Idaho, the Bonneville Flood left a spectacular array of flood features that have allowed for geologic reconstruction and quantitative evaluation of many aspects of the flood hydrology, hydraulics, and sediment transport. Geologic evidence of maximum flood stages in conjunction with step-backwater modeling provides for peak discharge estimates and understanding of local hydraulic flow conditions for ten separate reaches along the flood route. Peak discharge was approximately 1.0 million m³•sec⁻¹ at the Lake Bonneville outlet near Red Rock Pass. Downstream, the maximum discharge had attenuated to 0.57-0.62 million m³•sec⁻¹ by arrival at Lewiston. Attenuation was primarily the result of flow storage in the wide alluvial valleys of the western Snake River Plain. The local hydraulic conditions (depth and velocity) of the Bonneville Flood varied significantly within and between the study reaches. The rate of energy expenditure was also highly varied; local calculated stream-power values ranged from less than 10 watts•m² to 100,000 watts•m². Greater than 60% of the total energy loss at peak discharge was expended in a total distance that encompassed less than 10% of the flood route. These spatial variations in local hydraulic conditions were profoundly important in controlling the distribution of flood processes and features. The deposition of tractively-transported cobbles and boulders (measured diameters ranged from less than 10 cm to greater than 10 m) occurred in reaches of decreasing flow energy within quantitatively-definable limits of flow energy. Areas of erosion are more difficult to precisely evaluate; however, they were restricted to reaches of greater stream power. It is likely that cavitation was an important erosional agent in many areas of most intense flow conditions.

Rivers deliver significant macronutrients and sediments to lakes that can vary substantially throughout the year. These nutrient and sediment loadings, exacerbated by winter and spring runoff, impact aquatic ecosystem productivity and drive the formation of harmful algae blooms. The source, extent and magnitude of nutrient and sediment loading can vary drastically due to extreme weather events and hydrologic processes, such as snowmelt or high flow storm events, that dominate during a particular time period, making the temporal component (i.e., time over which the loading is estimated) critical for accurate forecasts. In this work, we developed a data-driven framework that leverages the temporal variability embedded in these complex hydrologic regimes to improve loading estimates. Identifying the "correct" time scale is an important first step for providing accurate estimates of seasonal nutrient and sediment loadings. We use water quality concentration and associated 15-minute discharge data from nine watersheds in Vermont's Lake Champlain Basin to test our proposed framework. Optimal time periods were selected using a hierarchical cluster analysis that uses the slope and intercept coefficients from individual load-discharge regressions to derive improved linear models. These optimized linear models were used to improve estimates of annual and "spring" loadings for total phosphorus, dissolved phosphorus, total nitrogen, and total suspended loads for each of the nine study watersheds. The optimized annual regression model performed ~20% better on average than traditional annual regression models in terms of Nash-Sutcliffe efficiency, and resulted in ~50% higher cumulative load estimates with the largest difference occurring in the "spring". In addition, the largest nutrient and sediment loadings occurred during the "spring" unit of time and were typically more than 40% of the total annual estimated load in a given year. The framework developed here is robust and may be used to analyze other units of time associated with hydrologic regimes of interest provided adequate water quality data exist. This, in turn, may be used to create more targeted and cost-effective management strategies for improved aquatic health in rivers and lakes.

Different magnitude, intensity and timing of precipitation can impact runoff, hillslope erosion and transport of sediment along river channels.  Human activities, such as dam construction and surface mining can also considerably influence transport of sediment and sediment-bound contaminants. Many river basins of the world are currently subject to changes in climate at the same time as pressures from other human activities increase. However, because there are often complex interactions between such multiple drivers of change, it is challenging to understand and quantify contributions of individual drivers, which is needed in predictive modelling of future sediment and contaminant flows. This thesis considers sediment transport in the Lake Baikal basin, which is hydrologically dominated by the transboundary Selenga River of Russia and Mongolia. The Selenga River basin is, for instance, subject to climate change and increasing pressures from mining, but process complexity is reduced by the fact that the river basin is one of few large basins in the world that still is essentially undammed and unregulated. A combination of field measurement campaigns and modelling methods are used in this thesis, with the aim to: (i) identify historical hydroclimatic trends and their possible causes, (ii) analyse the spatial variability of riverine sediment loading in the mining affected areas, and (iii) investigate sediment transport and storage processes within river channels and in river deltas. Results show that, during the period 1938-2009, the annual maximum daily flow in the Selenga River basin has decreased, as well as the annual number of high flow events, whereas the annual minimum daily flow has increased. These changes in discharge characteristics are consistent with expected impacts of basin-scale permafrost thaw. Both field observations and modelling results show that changes in magnitude and number of high-flow events can considerably influence the transport of bed sediment. In addition, the average discharge has decreased in the past 20 years due to an extended drought. Under conditions of low flow, metal-enriched sediment from mining areas was observed to dominate the river water. If discharge will continue to decrease in the Selenga River (or other mining-impacted rivers of the world), further increases in riverine metal concentrations may hence be one of the consequences. Furthermore, under current conditions of extended drought, less sediment may have been distributed over the floodplain wetlands in the Selenga River delta. Present estimates, however, show that sediment can still be transported to, and deposited within, the banks and water bodies located in the backwater zone of the Selenga River delta. This can aid bank and levee stabilization, support the development of wetlands and foster net sedimentation.​
Nederbördens olika magnitud, intensitet och tidpunkt kan påverka ytavrinning, vattenerosion och transport av sediment längs flodkanaler. Mänskliga aktiviteter, som dammkonstruktion och gruvdrift i dagbrott kan också påtagligt påverka transport av sediment och sedimentbundna föroreningar. Många avrinningsområden i världen påverkas för närvarande av klimatförändringar samtidigt som trycket från andra mänskliga aktiviteter ökar. Men eftersom det ofta förekommer komplexa interaktioner mellan sådana multipla orsaker till förändring, är det utmanande att förstå och kvantifiera bidrag från enskilda orsaker, vilket behövs vid prediktiv modellering av framtida sediment- och föroreningsflöden. Denna avhandling behandlar sedimenttransport i Bajkalsjöns tillrinningsområde, som hydrologiskt domineras av den internationella Selengafloden i Ryssland och Mongoliet. Selengaflodens tillrinningsområde är exempelvis påverkat av klimatförändringar och ökat tryck från gruvdrift, men processkomplexiteten reduceras av det faktum att tillrinningsområdet är ett av världens få stora som fortfarande väsentligen saknar dammar och flödesreglering. I denna avhandling används en kombination av fältmätningskampanjer och modelleringsmetoder, i syfte att: (i) identifiera historiska hydroklimattrender och deras möjliga orsaker, (ii) analysera den rumsliga variationen i flodens sedimentbelastning inom de gruvpåverkade områdena, och (iii) undersöka sedimenttransport- och retentionsprocesser inom flodkanaler och i floddeltan. Resultaten visar att det årliga maximala dygnsflödet, liksom det årliga antalet högflödeshändelser, har minskat i Selengafloden under perioden 1938-2009, medan det årliga minimala dygnsflödet har ökat. Dessa förändringar i flödeskaraktäristika överensstämmer med förväntade effekter av storskaligt tinande permafrost. Både fältobservationer och modelleringsresultat visar att förändringar i högflödeshändelsers magnitud och årligt antal kan påverka transporten av bottensediment påtagligt. Dessutom har medelflödet minskat under de senaste 20 åren på grund av långvarig torka. Under lågflöden observerades metallberikat sediment från gruvområdena dominera flodvattnet. Om flödena fortsätter att minska i Selengafloden (eller andra gruvdriftspåverkade floder i världen), kan således ytterligare ökningar av flodvattnens metallkoncentrationer vara en av konsekvenserna. Under den långvariga torka som nu råder mängden sediment som fördelats över våtmarkerna i Selengaflodens delta ha minskat. Sediment beräknas dock fortfarande kunna transporteras till och deponeras inom flodbankar och vattenkroppar i Selengadeltats backwaterområden. Detta kan bidra till stabilisering av bankar och skyddsvallar, stödja våtmarkers utveckling och främja nettosedimentering.
Wielkość, czas trwania oraz intensywność opadów atmosferycznych oddziałuje na charakter odpływu, erozję oraz transport osadów rzecznych. Również ingerencja człowieka w środowisko – np. budowa zapór i zbiorników wodnych, czy górnictwo odkrywkowe – w różnym stopniu może wpływać na transport osadów oraz powiązanych z nimi zanieczyszczeń. Wiele dorzeczy na Ziemi, będących pod wpływem obecnych zmian klimatycznych, jest jednocześnie poddawanych narastającej antropopresji. W celu przewidywania przyszłych zmian w transporcie osadów i powiązanych z nimi zanieczyszczeń, potrzeba dogłębnego zrozumienia i oceny wpływu poszczególnych czynników powodujących te zmiany. Taka analiza jest jednak często utrudniona ze względu na złożone interakcje pomiędzy czynnikami powodującymi zmiany. Niniejsza rozprawa doktorska przedstawia wyniki badań związanych z analizą transportu osadów rzecznych w zlewni jeziora Bajkał, zdominowanej hydrologicznie transgraniczną rzeką Selengą, przepływającą przez tereny Rosji i Mongolii. Zlewnia rzeki Selengi podlega współczesnym zmianom klimatycznym oraz wzrastającej presji związanej z górnictwem. Złożoność procesów hydrologicznych jest jednak w tym wypadku ograniczona, ponieważ zlewnia Selengi jest jednym z nielicznych, względnie dużych dorzeczy na świecie, którego przepływy są – jak dotychczas – naturalne, nieuregulowane przez żadne zapory lub zbiorniki wodne. Dla poszczególnych celów: (i) identyfikacji historycznych trendów hydroklimatycznych i ich przyczyn, (ii) analizy przestrzennych zmian w transporcie osadów rzecznych w części zlewni dotkniętej górnictwem odkrywkowym oraz (iii) badania procesów transportu i magazynowania osadów w korycie i delcie rzeki; zostały w pracy zastosowane hydrometryczne dane pomiarowe, dane pochodzące z badań terenowych oraz metody modelowania. Wyniki badań wskazują na to, że w latach 1938-2009 zmalały roczne przepływy maksymalne oraz liczba wezbrań, podczas gdy w tym samym czasie wzrosły roczne przepływy minimalne. Powyższe zmiany są zgodne z oczekiwanym wpływem rozmarzania wiecznej zmarzliny na ustrój przepływów rzecznych. Analiza danych pomiarowych oraz wyników modelowania wskazują na to, że obecne zmiany dotyczące liczby oraz wielkości wezbrań mogą znacznie wpłynąć na transport osadów dennych w korytach rzek. Dodatkowo, w ciągu ostatnich 20 lat (1995-2014), średnie roczne przepływy znacznie spadły ze względu na przedłużający się okres suszy na terenie zlewni. Analiza danych terenowych pochodzących z obszarów górniczych wykazała, że podczas obniżonych przepływów, w zanieczyszczonych znaczną ilością metali osadach rzecznych, dominuje materiał pochodzący z działalności człowieka (około 80\% transportowanych osadów). Należy zatem przewidywać, że jeśli obecne zmiany w ustroju przepływów w dorzeczu Selengi (lub w innych podobnych dorzeczach na świecie) będą postępować, to ich następstwem może być dalszy wzrost koncentracji zanieczyszczeń (metali pochodzących z obszarów górniczych) rzek. Ponadto, w obecnym okresie obniżonych przepływów, na terenach zalewowych i jeziorach delty rzeki Selengi zatrzymuje się prawdopodobnie mniej osadów. Wyniki badań wskazują jednak na to, że osady rzeczne mogą być wciąż transportowane do brzegów i obszarów wodnych znajdujących się w strefie, w której stany wodne cieków delty są pod wpływem stanów wodnych jeziora Bajkału. Akumulacja materiału w tych częściach delty Selengi może pozytywnie wpływać na stabilizację naturalnych wałów oraz mokradeł i zwiększać sedymentację netto.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

This dissertation addresses hydrodynamics, sediment transport and shoreline erosion within the main pool of Hartwell Lake, a U.S. Army Corps of Engineers reservoir built on the Savannah River, between Anderson, South Carolina, and Hartwell, Georgia, USA. A U.S. Environmental Protection Agency (EPA) Superfund site is located on a tributary of Hartwell Lake because of high concentrations of polychlorinated biphenyls (PCBs) in the lake sediments. PCBs are hydrophobic and typically bond to fine-grained sediments, such as silts and clays. The primary goal of the study was to document, through field measurements, and model, using a 3-D numerical model of flow and sediment transport, the fate of sediments within the main pool of Hartwell Lake. To document forty years of sedimentation within the reservoir, bathymetric survey data were collected in Hartwell Lake during the period, February 10-14, 2003. The bathymetric surveys revealed that deposition was, in places, up to two meters thickness in forty years. During the field campaign, flow velocity measurements were made primarily to provide a check on the magnitude of the velocities predicted by the numerical model used in the study. Shoreline surveys provided data for the modeling procedure for shoreline change. This in turn facilitated specification of the sediment flux into the domain via shoreline erosion. Hartwell Lake is located near the southern terminus of the Appalachian mountain chain in the Piedmont region. Sediments contain high fractions of silt and clay. Hartwell Lake has a shoreline length of 1548 km, and erosion of lake shorelines has been a significant problem for many homeowners. As of September 2002, there were 1123 permitted riprap installations, and 393 permitted retaining walls, for a total of 1516 erosion control structures along the lakeshores (source: USACE Hartwell Office), an indication of the magnitude of the erosion problem. To quantify the erosion rate of the shorelines, an approach that relates erosion rates to wind wave forces was developed. A simplified representation of the shape of beach profiles is employed. Historical shoreline change rates were quantified by comparing available digital aerial photos taken in different years, and the erosion prediction model was calibrated using these computed erosion rates. Sediments derived from shoreline erosion were introduced to the model as an additional source along the model boundary, and the fate of the eroding sediments was investigated via numerical modeling.

Attention to participatory watershed management is increasing across the developing world as soil erosion continues to degrade agricultural land; reservoirs and irrigation infrastructure are clogged with sediment. The realization of the importance of watersheds is crucial for sustainable utilization especially in developing countries where rural livelihoods and economies are highly dependant on the exploitation of natural resources. The Lake Victoria basin is characterized by high population pressures, low productive subsistence agriculture, poor farming methods, loss of soil fertility and deforestation due to demand of fuel wood and charcoal, timber and building materials that are posing serious threat to watersheds. High population density in the basin also means new needs emerge too fast to which rural societies cannot respond in time leading to more area expansion for agricultural land. In spite of positive efforts under the Lake Victoria Basin Commission, there remains a huge gap between policy and institutional framework development at the top level and the actual implementation of actions on the ground to prevent land degradation, soil erosion and decrease sediment load. The study focused on Kagera and Nyando catchments of Lake Victoria Basin and aiming to establish if there exist and the extent to which participatory watershed management has been implemented on the ground to decrease land degradation and sediment load. It therefore provides an insight into watershed management in the Kagera and Nyando catchments by illustrating the link between policy formulation and actual implementation and enforcement.

Ziel dieser Dissertation ist, Wissensdefizite im Bereich der Bioirrigation von Süßwassersedimenten abzubauen. Als Untersuchungsorganismus wurde Chironomus plumosus ausgewählt weil diese weit verbreitete Larve ihre U-förmigen Röhren mit Überstandswasser durchspült und so Nahrung aus dem Wasser filtriert. Um Bioirrigation in Wohnröhren mit einem Durchmesser von ca. 1,7 mm zu untersuchen, wurden geeignete Messmethoden entwickelt, mit denen für das 4. Larvenstadium die Parameter Fließgeschwindigkeit (14,9 mm/s), Pumpzeit (33 min/h) und Pumprate (61 ml/h) gemessen wurden. Bei einer Populationsdichte von 745 Larven/m2 kann somit ein Wasservolumen äquivalent zum Volumen des Müggelsee in Berlin, innerhalb von 5 Tagen durch das Sediment gepumpt werden. Die Positronen-Emissions-Tomographie wurde für die Sedimentanalytik adaptiert und der Transport im Porenwasser analysiert. Mit den Untersuchungen wure gezeigt, dass auch in schlammigen Seesedimenten ein advektiver Transport durch Bioirrigation verursacht wird, der nicht zu vernachlässigen ist. Steigende Temperaturen resultieren aufgrund steigender Fließgeschwindigkeit in einen signifikanten Anstieg der Pumprate sowie der Eintragsrate von Überstandswasser ins Sediment. Ein abfallender Sauerstoffgehalt verlängert die Pumpzeit und führt zu einer sinkenden Fließgeschwindigkeit. Außerdem wird aus den Untersuchungen eine jahreszeitliche Variabilität der Bioirrigation sichtbar, welche unabhängig von konstanten Laborbedingungen auftritt. Mit dem Wasserstrom werden Porenwasserspezies wie SRP in den Wasserkörper abtransportiert, wohingegen SO42- und O2 aus dem Überstandswasser in das Sediment eingetragen werden. Ferner kommt es zur Oxidation von Fe2+ infolgedessen Phosphat im Sediment festgelegt wird, wie mittels P-Fraktionierung gezeigt werden konnte. Mikrobiologische Untersuchungen zeigten, dass Bioirrigation die mikrobielle Abundanz steigert, die Bakteriengemeinschaft verändert und das Potential zur enzymatischen Hydrolyse erhöht.
The aim of this thesis is to fill gaps of knowledge regarding bioirrigation in freshwater sediments. Chironomus plumosus was chosen for the investigations since the filter-feeding larva dwelling in U-shaped burrows is quite common and flushes its burrow with water from the overlying water body. To investigate bioirrigation activity in burrows of approximately 1.7 mm in diameter appropriate measurement techniques were developed. With the methods several parameters were measured for 4th stage of larvae: flow velocity (14.9 mm s-1), pumping time (33 min h-1), and pumping rate (61 ml h-1). Consequently, a water volume equivalent to the volume of Lake Müggelsee in Berlin is pumped through the sediment every 5 days by a population density of 745 larvae m-2. The nuclear medicine imaging technique Positron Emissions Tomography was adapted and used to analyze the transport in the sediment pore water. By means of the experiments, it could be shown that even in muddy lake sediments advection is a relevant transport process and should not be neglected. Rising temperatures result in increased pumping rates and increased influx rates of surface water into the sediment due to increased flow velocities in the burrows. Dropping oxygen concentrations prolong the pumping duration while the flow velocity decreases. Furthermore, experiments show a seasonal variability of bioirrigation which is independent of constant laboratory conditions. Pore water species such as SRP are transported with the water flow into the overlying water body, whereas SO42- and O2 are transported from the overlying water into the sediment. Due to the oxidation of Fe2+, phosphorus is fixed into the sediment, a result confirmed by P-fractionation. Microbiological investigations of the burrow walls demonstrated that the bioirrigation activity enhances the microbial abundance, changes the community structure, and increases the potential of enzymatic hydrolysis.

Aquesta tesi permet adquirir una millor comprensió de la dinàmica dels plomalls hidrotèrmics en l'estany de Banyoles i correlacionar la meteorologia amb els processos de fluïdització que s'hi produeixen. S'han trobat els patrons atmosfèrics que generen els esdeveniments de les fluïditzacions així com la seva freqüència. Això és crucial per a determinar la qualitat de l'aigua de l'estany. S'han trobat inhomogeneïtats espacials tant en el plomall crònic que es desenvolupa en la cubeta B1, com en el plomall episòdic de la cubeta B2. S'ha caracteritzat l'estructura del plomall generat a la cubeta B2 i s'ha comparat amb el desenvolupat a la cubeta B1. Finalment, s'han realitzat simulacions numèriques mitjançant un model numèric: MIT General Circulation Model, en el qual s'ha hagut de fer canvis en les condicions de contorn per a situar la font convectiva al fons de la columna d'aigua. Les simulacions s'han comparat amb els resultats experimentals trobats mitjançant campanyes.
The aim of this thesis is to acquire a better understanding of the dynamics of the hydrothermal plumes in the lake and to gain more insight into the interrelationship between meteorology and fluidization. They have been found the atmospheric patterns that generate the fluidization events, as well as their frequency. This is crucial to determining the water quality of Lake Banyoles. They have been found spatial inhomogeneities of the chronic thermal plume found in B1 and of the episodic thermal plume in B2. The structure of thermal plume in B2 has been characterized and compared to the plume developed in B1. Finally, it has been used a numerical model: MIT General Circulation Model. It has been necessary to modify the boundary conditions moving the buoyancy source from the top of the water surface to the bottom. Results have been compared to experimental data undertaken from the field campaigns.

In North America, the acceleration of the eutrophication of surface waters due to nutrient pollution is still present. Soil studies have not entirely succeeded in linking nutrient and sediment losses to field hydrology because relationships between discharge and dissolved ions/sediments are complicated by a hysteresis effect which has been only described qualitatively. The objective of this thesis was to better understand the effects of hydrology on N, P, and sediment transfer from agricultural and forest soils to surface waters. This was done by developing a technique, called the H index, to quantify the hysteretic behaviour of ion and sediment transport in stream/overland water. The chemical and sediment concentrations in a stream of a forested watershed in the Sierra Nevada during snowmelt and in overland runoff of two agricultural fields during rain events in the Montreal area were examined. In the stream of the forested watershed, H indices for suspended sediment increased (looser hysteresis loop) with the availability of sediments and the lag between peaks in suspended sediment concentrations and discharge. In agricultural fields, nutrient concentrations increased with time during each event with presence of counterclockwise and clockwise hysteresis. The hysteretic behaviour of suspended sediments was not significantly related with either prior soil moisture content or rainfall characteristics. In order to simultaneously monitor P and N in the stream and soils of the forested watershed, a laboratory study was conducted to investigate the efficacy of various mixedbed exchange resins in absorbing dissolved organic and inorganic N and P. Results showed that mixed-bed resin was adequate for characterizing P on a short-time scale but longer exposure periods were required for N. Results from the resin exchange reveal the possibility that the spring time pulse of NOs'-N in stream water was due to the melting of the snowpack.

I conducted a 12-month study of near-shore habitats in Lake Pontchartrain to assess spatiotemporal variation in the abundance of early life stage blue crabs (Callinectes sapidus). Collections were made using a 1 m2 throw trap and data showed that C. sapidus numbers varied over time and among sites. Two recruitment events occurred during the study. During the first recruitment in May-June, C. sapidus entered Lake Pontchartrain via the Inner Harbor Navigational Canal. In September-October, C. sapidus entered the Lake Pontchartrain via the Rigolets and Chef passes. My data suggest that C. sapidus utilize water circulation within the Lake Pontchartrain as a means of transportation throughout the estuary. MODerate-resolution Imaging Spectroradiometer (MODIS) 250 m data were analyzed to gain a large-scale view of suspended sediments patterns within Lake Pontchartrain and quantify water movement. Field sampling along with remote sensing proved to be beneficial when assessing estuarine-wide C. sapidus post-larval dispersal processes.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The Swartvlei estuary and lake system is situated on the southern coast of the Western Cape Province of South Africa and forms part of the core conservation area of the Wilderness National Park. The Swartvlei system comprises two interlinked water bodies, namely Swartvlei Lake and Swartvlei estuary. SANParks have been monitoring this estuary closely over the past two decades, due to its importance to the ecology and to tourism. There are also low-lying properties on the perimeter of the Swartvlei estuary which run the risk of occasional flooding. Two of the major monitoring issues in this estuary system are the water level required for successful mouth breaching, and the influence of the water level on the low-lying properties. This study presents a preliminary analysis of the sediment budget across the Swartvlei estuary mouth. The objective of this study was to identify the various sediment contributory factors and to estimate the quantities that each individually contributed towards the defined sediment budget.
AFRIKAANSE OPSOMMING: Die Swartvlei meer en see monding is geleë aan die kaapse suidkus van Suid- Afrika. Dit vorm deel van die kern bewarings area van die Wilderness Nationale Park. Die Swartvlei sisteem bestaan uit twee verbinde, kern dele nl: Swartvlei meer en estuarium. Vir die afgelope twee dekades is hierdie area onder die noue toesig van SANParke as gevolg van die belangrikheid van die area met betrekking tot toerisme en ekologie. Daar is ook menigde laag liggende eiendomme aan die oewers, wat baie sensitief is vir watervlak stygings. Die optimum water vlakke benodig vir die uitskuring van die gety monding het ook implikasies vir die laag liggende eiendome en vereis noukeurige monitering. ‘n Voorlopige analise van die sediment begroting rondom die gety monding word deur hierdie studie voorgelê.