Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

In this study, incubations of sediments from three Swedish lakes, Parsen, Södra Teden, and Venasjön, were made to examine CH4 production during different temperatures. The incubations took place in two different climate rooms, one with a decreasing temperature and one with an increasing temperature with analyses made on the temperature levels around 10 and 20°C. Samples were taken and analyzed in a gas chromatograph. Results from the incubations ranged from -3,72 μmol m-2 d-1 up to 10,54 μmol m-2 d-1. A Mann Whitney test were made to test the statistical hypothesis if there were any differences in CH4 production between the temperatures. Only Venasjön were significantly different in CH4 production (P=0.01) while Södra Teden and Parsen were non-significant. Discussed points were that the lakes have potential for CH4 production, but there is several factors beside the temperature change that both favors and inhibit the production rates. Södra Teden displayed an individual measurement with a high production rate which suggest a major potential for CH4 production. The study concludes that the temperature effect is not clear in this study due to the lack of significant difference between the temperature levels. It also concludes that we need a bigger understanding of the lakes to be able to draw further conclusions of the results. A final conclusion was that it did not matter whether the sediments were exposed for a temperature increase or a decrease. The study suggested that further research is needed for similar lakes with more samples to enrich the statistical analyses and develop the knowledge about which factors that regulates CH4 production in Swedish freshwater lakes. / I denna studie genomfördes inkubationer av sediment från tre svenska sjöar, Parsen, Södra Teden, och Venasjön i syfte att undersöka CH4 produktion under olika temperaturnivåer. Inkubationerna genomfördes i två olika klimatrum, ett där temperaturen sänktes och ett där temperaturen höjdes. Temperaturperioderna som analyserades var omkring 20°C som den högre nivån och 10°C som den låga nivån. Provtagningar genomfördes och analyserades i en gaskromatograf för att kunna beräkna produktionen av CH4 under de olikatidsperioderna. Analysen gjordes utan att ta hänsyn till vilka prover som hade en sänkt temperatur eller en höjd temperatur. Resultaten från inkubationerna sträckte sig från -3,72 μmol/m-2 d-1 upp till 10,54 μmol/m-2 d-1.Från Södra Teden uppmättes ett enskilt värde som visar på att den sjön har en mycket stor potential för att producera metan. Andra diskuterade punkter är hur kvalitén och mängden organiskt material som och även hur mycket näringsämnen som finns tillgängligt i sjöarnas sediment. En av slutsatserna är att effekten av temperaturförändringen inte är tydlig på grund av bristen på signifikant skillnad mellan de båda temperaturnivåerna. Studien visar också på att vi behöver en större förståelse av sjöarna i sig för att kunna dra ytterligare slutsatser av resultaten. Sist men inte minst så hade det minimal eller ingen betydelse om sedimenten utsattes för en temperaturhöjning eller en temperatursänkning. Studien förslår att ytterligare studier behöver genomföras på liknande sjöar med fler prover för varje sjö för att berika den statistiska analysen och utveckla kunskapen om vilka faktorer som reglerar bildningen av CH4 i svenska sjöar.

Tidal inlets on sandy shorelines separate barrier islands and serve as a conduit for transport of sand and water between embayments and oceans, seas, or other tidally influenced waterbodies. Tides and waves induce currents along the coastline that transport sediment across-shore and alongshore. Coastal managers must optimize barrier-inlet system stability while conserving limited sediment resources, and often base management decisions and engineering design upon geomorphic and numerical models that predict the morphological behavior of tidal inlets on short-to-medium timescales (years to decades). The overall goal of this study was threefold. First, to provide science-based practical guidance for regional sediment management in the vicinity of tidal inlets. Secondly, to enhance the understanding of the temporal and spatial scales of sediment pathways in these regions through numerical simulation of traced sediment transport. And, third, to combine these lessons learned in both regional sediment management and analysis of morphodynamic and sediment bypassing pathways with application to a common practical management practice of inlet shoal mining and adjacent beach placement. The temporal and spatial scales controlling the morphodynamics of barrier-inlet systems were reviewed within a regional sediment management context. Next, the application of regional sediment management methods to case studies of multiple barrier-inlet systems in West-Central Florida led to the development of a decision-support tool for regional sediment management (RSM) as applied to barrier-inlet systems. Connecting multiple barrier islands and inlets at appropriate spatio-temporal scales is critical in developing an appropriately scoped sediment management plan for a barrier-inlet system. Evaluating sediment bypassing capacity and overall inlet morphodynamics can better inform regional sand sharing along barrier-inlet coastlines; particularly where sediment resources are scarce and a close coupling between inlet dredging and beach placement is vital to long-term sustainable management. Continued sea-level rise and anthropogenic activities may intensify the need for investigating longer-term processes and expanding regional planning at a centennial timescale, and are acknowledged as challenging tasks for RSM studies going forward. A regionally focused, multi-inlet study was necessary to improve the management plans for the case study inlets (from north to south): John’s Pass, Blind Pass, Pass-a-Grille Inlet, and Bunces Pass. Key recommendations based on the case studies include: 1) allow the natural sediment bypassing to be re-established at Blind Pass inlet through reduced ebb-tidal delta mining, 2) reduce the interruption to sediment bypassing at John’s Pass and Pass-a-Grille inlets through an improved design of the dredged mining areas located along sediment bypassing pathways, 3) allow for continued natural sediment bypassing at Bunces Pass, and, 4) incorporate the cyclic sediment bypassing through swash-bar attachment into the management plan at Bunces Pass and adjacent barrier-islands. Similar systems in other regions may benefit from the lessons derived in this case study of an adaptively managed multi-inlet system. A numerical model that computes hydrodynamics, sediment transport, and morphodynamics including bed layering was incorporated in this study to analyze sediment transport pathways between littoral sources from adjacent beaches and the geomorphic features of an idealized tidal inlet designed to imitate the John’s Pass tidal inlet in West-central Florida, USA. This study developed a methodology to numerically trace sediment transport, deposition and erosion. This method was applied to investigate sediment-bypassing pathways under varying temporal and spatial scales. The analyses of the adjacent beach’s contribution to tidal inlet sediment bypassing demonstrated variable temporal scales on sediment transport and exchange. High-energy wave events dominated the temporal scale for sand to be transported from the updrift beach to the ebb-tidal delta, whereas cyclical tidal processes had a significant influence on the spatial pattern of exchange between the shoals and channel features of the tidal inlet. The ability to simulate burial and erosion of tracers allowed identification of offshore sedimentation hotspots such as terminal lobe as well as zones of deposition and active transport in shallow water, such as the updrift channel margin linear bar and the downdrift platform of the ebb-tidal delta. The general sediment-bypassing pathway reflected a tidal-driven redistribution following event-driven pulses of wave-induced sediment mobilization. Sediment was transported along the beach during these energetic wave events. Flood- and ebb-tidal currents transported the sediment mobilized by high waves into the inlet channels. This was followed by subsequent gradual redistribution of the deposited channel sediments over the ebb-tidal delta features during fair-weather conditions. The modeling methods were then applied to investigate the sediment pathways and bypassing processes for three validated numerical models of coastal tidal inlets that span a range of forcing conditions. The processes that influence sediment transport along various pathways between the several morphological features of each inlet and its adjacent beaches were examined. The sediment tracing methodology employed in this study allowed for an evaluation of the sediment transport pathways between the various morphologic features of a tidal inlet, as well as their respective processes that drive the exchange of sediments. Characterizing and correlating the sediment pathways between tidal inlet morphologic features can improve the inlet reservoir model, which is a predictive model of inlet shoal volumes based on empirical formulae. The results of this study illustrate the value of including sediment-tracking techniques in simulating sediment bypassing and the potential of this application to inform coastal engineering and design modifications to sediment reservoirs of tidal inlets. And, finally, the spatial patterns of transport and erosion and deposition of traced, littoral source sediment, were investigated using the same modeling framework to evaluate the design of ebb-tidal delta mining on sediment bypassing dynamics of a tidal inlet system based on an idealized model of John’s Pass, Florida. Seven mining areas were simulated with traced sediment sources from the updrift beach, downdrift beach, and adjacent shoals. The tracers’ migration pattern and mining area infilling were analyzed to depict the sediment bypassing pathways and their contributions to mining area infilling. Mining area recovery rates were highest along the channel margin linear bar, and decrease offshore and downdrift. Updrift sand sources contributed more to mining area infilling than downdrift sand sources. The position of the mining area in relation to the updrift or downdrift morphological features dictates whether it will receive primarily updrift- or downdrift-originating littoral sediment from the beach. The source of sedimentation within the mining areas is a combination of inlet-ward transport of beach sediment and nearby shoal sediment. Proximity to the inlet channel determined the degree to which sedimentation had originated from longshore transported beach sediment. This methodology can improve confidence in management decisions concerned with the sand-sharing capacity of barrier-inlet systems in a local and regional context.

As world population increases, coastal areas experience an increase in human occupancy. These community locations come with a greater risk of impacts due to extreme natural events. Tsunami, being one of the most unpredictable and most devastating types of extreme hydrodynamic events, received significant attention over the past decades due to the recent extreme events (2004 Indian Ocean, 2010 Chile, 2011 Japan, 2018 Indonesia). The focus of this thesis is on investigating scour around structures generated by tsunami. Scouring was found to be one of the greatest sources of building damage during the 2011 Tohoku Japan Tsunami and, at the date of the redaction of this thesis, this phenomenon is still little understood by the scientific community. The main objective of this thesis is to study the change in scouring when multiple buildings are constructed in close proximity, as opposed to individual elements such as in the case of all previous studies focussed on tsunami-induced scour. This topic was first investigated by the candidate with the use of a numerical model, FLOW-3D, using the large eddy simulation approach and the Nielsen (1992) bed load sediment transport model. The model results showed a significant increase in scouring when a second building was located along the same transversal plane as the building investigated. Then, three structure arrangements were investigated in a comprehensive physical experiment conducted in the new Dambreak Flume of Hydraulic Laboratory of the University of Ottawa, Canada, to study the effects of (1) upstream constriction, (2) lateral spacing and (3) sheltering on tsunami-induced scour. All three structure arrangements showed a significant effect on tsunami-induced scour. A secondary project was conducted in collaboration with the Technical University of Braunschweig, Germany, and the Leibniz University Hannover, Germany. This large-scale physical experiment, performed in the Large Wave Flume of the Leibniz Institute Hannover, Germany, was used to investigate three different research phenomenon that influence tsunami scouring: (1) the wave drawdown on scour around structures, (2) the evolution of flow eddies and (3) the change in the soil’s pore pressure.

Clean and spiked sediment formulations of various silt sand and clay sand ratios were tested for toxicity using a bioassay that utilizes bioluminescent bacteria Measured toxicities of clean and copper sulfate–spiked sediments were negatively but nonlinearly related with percent silt and percent clay, but no significant relationship existed between measured toxicity and sediment composition for methyl parathion–spiked formulations Results suggest that solid phase sediment bioassays using bioluminescent bacteria may be useful for testing the toxicities of single contaminants in formulated artificial sediments of known particle size composition, and for repeated samples collected from the same site However, extreme caution must be taken when testing sediments of varying composition or which may be differentially contaminated or contain a suite of contaminants.

Recent carbonate sediments from Jamaican north coast fringing reefs display variation in constituent composition, texture, and mineralogy related to their location on the reef. Samples were collected along lines which traversed the back reef and fore reef (0.5m to 70m). The sediment is dominated by highly comminuted coral fragments, plates of the calcareous green alga, Halimeda, coralline algae, and the encrusting Foraminifera, Homotrema rubrum, with lesser amounts of other taxonomic groups (Foraminifera; molluscs; echinoderms). Relative abundances of these biotic components vary between sites. Q-mode cluster analysis indicates that constituent composition can be used to delineate the different reef zones which have been described from analyses of the macrofauna. For most sediment, grain-size frequency distributions indicate that greater than 90% (by weight) of the sample is contained in the interval of 0.125mm to 2.000mm. Mean grain size approaches 0.5mm for most sites with little depth related variation. Sorting, however, becomes progressively poorer from the shallow (5m) fore reef terrace to the upper deep fore reef (70m). X-ray diffraction and insoluble residue analyses indicate that total CaC03 in these sediments is generally greater than 95% by weight. Aragonite is the most abundant carbonate phase, followed by high-Mg calcite , and low-Mg cal cite. Amorphous siliceous sponge spicules and organic matter comprise the remaining non-carbonate fraction of these sands. Significant differences in the proportions of aragonite and high-Mg calcite between fore reef terrace sediments and sediments from other reef zones results from the contribution of high-Mg calcite to fore reef terrace sediments by coralline algae, Foraminifera (principally Homotrema rubrum) and echinoderms, which are relatively less abundant sediment constituents elsewhere on the reef. The 120,000y.b.p.(Sangamon) Falmouth Formation along the north coast of Jamaica displays variability in sedimentological and faunal components analogous to that of back reef and shallow fore reef environments of the modern Jamaican fringing reef system. X-ray analysis of the mineralogy of Falmouth limestones reveals that surface exposures of fore reef grainstones exhibit greater diagenetic alteration than surface exposures of back reef packstones. This indicates variability in diagenetic processes most likely related to original sediment textural characteristics.

No description available.

Sediment oxygen demand (SOD) and nutrients releases from the bottom sediments of a water body are important parameters to be included in studies of water quality processes. Two methods to measure SOD, in situ and at laboratory, were applied at Eckie’s Pond on late spring of 2015. Based upon preliminary results, which showed greater values for the in situ method, some modifications of procedures and equipment were made to improve the measurements. Another set of measurements were made on June of 2016, however their results were not conclusive to establish a correlation between these methodologies. As a result of this research, three standard operating procedures (SOP) have been established to measure SOD at shallow waters, first in situ, second at laboratory, and a third SOP to analyze nutrients and metals by using a spectrophotometer.

The overall objective of this study was to identify trends of sediment nutrients and benthic macro-invertebrates in recreational fishing ponds. The Ekman dredge and the Yabby pump, also were compared for benthic macro-invertebrate sampling effectiveness. Large ranges in the coefficient of variation for Pw (52 – 123.9), C:N (13.4 – 124), density (61.5 – 98.5), and diversity (67 – 142) indicated significant spatial variability within and among ponds. Invertebrate familial diversity was the only variable that did not show any significant temporal variation (H = 4.31, P = 0.230). Results from the gear comparison indicated no differences between the Ekman dredge and Yabby pump (3 pulls); however, showed the Ekman dredge was more effective than the Yabby pump (12 pulls) (Z = -1.796, P = 0.073) indicating potential gear saturation. Although these data supported no discernable patterns between sediment nutrients and macro-invertebrates, it provided an opportunity to detail an operational framework for future studies.

The purpose of this work is to generate a shore profile algorithm to be used in estuaries dominated by fine sediments. Numerical models are continually evolving to enhance the overall accuracy of results. However, the typical shore profile is defined as a vertical wall. This work defines the shore as a nonlinear profile which will provide more realistic models. A variety of shore profile equations were examined and tested against a field site, Weeks Bay, Alabama. The most applicable, an equation by S. C. Lee, was modified in order to calculate the entire shore profile length. The distance from the land-water interface to the depth at which sedimentation is negligible can now be modeled with a single equation. Recommendations for the practical aspect of implementation into a numerical model are also considered.