This study focuses on deposition processes from sediment laden buoyant river plumes in deltaic regions. The goal is to experimentally examine the effects of various physical phenomena influencing the rate at which sediment is removed from the plume. Previous laboratory and field measurements have suggested that, at times, sedimentation can take place at rates higher than that expected from individual particle settling (i.e., C{W}_{s}). Two potential drivers of enhanced sedimentation are flocculation and interfacial instabilities. We experimentally measured the sediment fluxes from each of these processes using two sets of laboratory experiments that investigate two different modes of instability, one driven by sediment settling and one driven by fluid shear. The settling-driven and shear-driven instability sets of experiments were carried out in a stagnant stratification tank and a stratification flume respectively. In both sets, continuous interface monitoring and concentration measurement were made to observe developments of instabilities and their effects on the removal of sediment. Floc size was measured during the experiments using a separate floc camera setup and image analysis routines. Results from the stratification tank experiments suggest that the settling-driven gravitational instabilities do occur in the presence of flocs, and that they can produce sedimentation rates higher than those predicted from floc settling. A simple cylinder based force balance approach adopting the concept of critical Grashof number was used to develop a model for the effective settling velocity under settling-driven instabilities that is a function of sediment concentration in the plume only. Results from the stratification flume experiments show that under shear instabilities, the effective settling velocity is greater than the floc settling velocity, and increases with plume velocity and interface mixing. The difference between effective and floc settling velocity was denoted as the shear-induced settling velocity. This settling rate was found to be a strong function of the Richardson number, and was attributed to mixing processes at the interface. Conceptual and empirical analysis shows that the shear-induced settling velocity is proportional to U{Ri}^{-2}. Following the experiments, analyses were made among contributions of different mechanisms on the total deposition rate, and the locations that the various mechanisms may be active in the length of a plume. This analysis leads to a conceptual discretization of a plume into three zones of sedimentation behavior and Richardson number. The first zone is the supercritical near-field plume with intense interface mixing. Zone two represents the subcritical region where interface mixing still occurs, and zone three is the high Richardson number zone where mixing at the interface is effectively nonexistent. In zones one and two, individual floc settling and shear-induced settling mechanisms play the major roles in removing sediment from the plume. While, shear-induced settling rate was found to be maximum near the river mouth, its share of the total settling rate increases in the crossshore direction, since sand and large particulates deposit near the inlet and only small particles (with relatively low settling velocity) remain as the plume propagates. The third zone, starts when the interfacial mixing diminishes and leaking commences. / Ph. D.

Syftet med detta examensarbete var att bidra med ett alternativ till den nuvarande rengöringsmetoden som används på Wedas bottensugare YT-600. En ersättning av pump och sugmunstycke med en elektrisk driven roterande enhet ska underlätta sedimentupptagningen i bassänger och tunnlar. I nuläget är borstarna som används på sugmunstycket inte tillräckligt effektiva. Den nya lösningen ska kunna bearbeta svårborttaget sediment och annan påväxt. En motor har valts för enheten, motorfästen har konstruerats och design ändringar har genomförts på YT-600s ramverk. Materialval, en marknadsanalys och en SWOT analys har genomförts för att identifiera eventuella förbättringsområden. I ett första skede har konceptgenerering skett för hand därefter har modellen konstruerats på CAD genom Creo Parametric. Beräkningar och simuleringar har genomförts för att kunna identifiera den maximala spänningen som sker på ramverket. Arbetet resulterade i framtagning av en ny lösning för YT-600. En lämplig elmotor har utsetts, motorfästen har konstruerats och en ersättning av pump samt sugmunstycke har genomförts. Därmed har målen för detta arbete uppnåtts. / The purpose of this thesis was to contribute with an alternative to the current cleaning method used on Weda's underwater cleaner YT-600. A replacement of the pump and suction nozzle with an electrically driven rotating unit will facilitate sediment removal in pools and tunnels. At present, the brushes used on the suction nozzle are not efficient enough. The new solution must be able to process sediment that is difficult to remove and other fouling. An engine has been selected for the unit, engine mounts have been designed and design changes have been made to YT-600’s framework. Material selection, a market analysis and a SWOT analysis have been carried out to identify possible areas for improvement. At first, concept generation took place by hand with paper and pen after which the model was constructed on CAD through Creo Parametric. Calculations and simulations have been performed to be able to identify the maximum stress that occurs on the framework. The work resulted in the development of a new solution for YT-600. A suitable electric motor has been appointed, motor mounts have been designed and a replacement of the pump and suction nozzle has been carried out. Thus, the goals for this thesis have been achieved.

This study focused on development of a continuous watershed-scale modelling approach capable of evaluating sediment removal performance of vegetative filter strips (VFS). This was done by integrating the single-event hydrologic and sediment transport model AGNPS with the event-based VFS model (VFSMOD) applying the methodology developed by Sebti and Rudra (2010), and also through the development and incorporation of sub-models capable of describing changes in hydrologic conditions between rainfall events into the integrated models. For modeling purposes, the buffer zone is divided to segments called “buffer cells”. The upstream source area corresponding to each buffer cell and the flow-path connecting the area to the stream are identified, and runoff and sediment generated within each area is simulated for each event applying AGNPS. Using VFSMOD, performance analysis of VFS is conducted for each buffer cell. By applying the developed “continuous simulation” sub-models the hydrologic conditions prior to each event were determined.