Many rivers can shape their path through the landscape with erosion and deposition where the riverbed and riverbanks both shape the direction and energy of the flow. The river flow can erode the riverbanks and create meanders which is when the river creates bends in its path that become increasingly curved. Meanders are affected by natural aspects of the landscape but also by anthropogenic structures like dams. The Rönne river is the largest river in the region of Skåne in southern Sweden and along it is three major dams that act as barriers for fish species. These dams are scheduled to be removed in 2024. To estimate how the Rönne river may react to the removal of these dams, the river’s erosion, deposition, and stream width was studied for the years 1926-1934, 1960, 1970 and 2018. By understanding how the dams have affected the river, it may be possible to argue how the river will change after the dams are removed. Erosion was greatest downstream of the dams but changes to deposition and stream width did not follow the pattern indicative with dams. The dams were not the determining factor and other factors such as land use and surficial geology are more impactful to the morphological changes in the river. Issues with the method and used materials affected and created uncertainty with the results. Improvements and changes are therefore needed for the method and the materials to better determine how the Rönne river is affected by the studied dams.

The aim of this thesis is to devise a method for objective classification of floodplain based on spatially accurate data from UAV that allows identification of the fundamental features of floodplain and channel arising from or affecting by the floods activities. Background research is focused on floodplain forming processes; types of flood on our territory and its geomorphological effects, as well as a brief description unmanned aerial vehicle and their applicability in natural science and the flood. Proposed method was carried out on the test section - a part of meander of Javoří stream in Šumava Mountain - then was tested on complex meander belt of the same stream. Proposed method is based on applicability of standard objective classification. Elementary products from photogrammetric analysis - 2D orthophoto and 3D digital surface model - are used as basic input data. Another aim of theses is to discuss applicability of this method for assessment of fluvial form, its limits and potential development. The results indicated that success of classification will increase significantly the involvement of 3D data to classification, which from standard data from the UAV, despite the lack of absence multispectral bands doing a very valuable source of information for mapping and analysis, for example, the...

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The investigation of the interrelationship of the fluvial morphology and the salinity of the Great Fish River Estuary was performed by the combination of a two-dimensional morphological model and a one dimensional advection dispersion module. Two scenarios were defined for investigation, namely Scenarios A and B. Model bathymetry and grid/network for each model and scenario was compiled from topographical information obtained from aerial photos, SRTM data, LIDAR and 24 measured river cross sections of the area from the river mouth up to 27km upstream of the river mouth. Model boundary conditions were developed from empirical formulas and measured data from the Department of Water and Sanitation (DWS). Both models were calibrated with results obtained during field measurement conducted from 5 – 7 May 2012. Scenario A consisted of a long term 5 year morphological simulation (1 May 2007 to 30 May 2012) with manual mouth closure events for identified river low flow periods. Water levels upstream of the river mouth were extracted from the two-dimensional morphological module and used as the downstream boundary condition of the one-dimensional advection dispersion (salinity) model. For scenario B floods with return periods between 1:2 and 1:100 years were simulated in the morphological model. The resultant bathymetries were then used to compile the network and bathymetry of the one dimensional advection dispersion (salinity) model. The different flood resultant bathymetries were then used with equal boundary conditions (representative of the average flow in the river) in the one dimensional salinity model. The predicted salinity was compared for each bathymetry used. From model results distinct trends were observed. During low flow conditions the estuary basin fills with sediments and during floods the sediments are flushed out of the estuary. Large magnitude floods greatly erode the estuary especially in the middle reach, during floods the tidal inlet experiences overtopping and subsequent erosion, the constriction at the tidal inlet is completely destroyed during larger floods. The estuary mouth in its closed state experiences slight overtopping and the mouth is breached during periods of high river flows. The magnitude of salt intrusion depends mainly on the size (the constriction) of the river mouth (tidal inlet). During periods of mouth closure the average salinity in the estuary decreases, average salinity increases if the tidal inlet area is increased. The extent of salt intrusion is approximately 10 km upstream of the river mouth when the mouth is open and the intrusion length increases during spring tides. / AFRIKAANSE OPSOMMING: Die verwantskap tussen die Groot Vis Rivier Estuarium morfologie en sout toestand is ondersoek deur die kombinasie van ‘n twee dimensionele morfologiese model en ‘n een dimensionele sout model. Twee toestande is gedefinieer vir ondersoek naamlik Scenario A en Scenario B. Die area vanaf die rivier mond tot 27 km stroomop van die rivier mond is deur die modelle gesimuleer. Die gemodeleerde area stem ooreen met die area waar gemete rivier-snit diepte metings beskikbaar was, onbrekende data is aangevul met behulp van lugfotos, LIDAR- en SRTM- data. Die model grens toestande is bepaal met empiriese vereglykings asook gemete data vanaf die Departement Waterwese. Beide numeriese modelle was gekalibreer met veld data verkry vanaf 5 tot 7 Mei 2012. Scenario A het behels ‘n langtermyn 5 jaar morfologiese modellering (1 Mei 2007 tot 30 Mei 2012) met toemond toestande gedurende gedefinieerde rivier vloei toestande. Die watervlakke van die twee dimensionele morfologiese model stroomop van die mond is gebruik as die stroomaf grenstoestand van die een dimnesionele model om die effek van die morfologiese veranderinge te inkorporeer in die sout model. Scenario B het behels die simulering van rivier vloede met herhaal periodes tussen 1:2 en 1:100 jaar in die morfologiese model. Die rivier-bodem vlakke verkry van laasgenoemde simulasiesis toe gebruik in die een dimensionele sout model met dieselfde grenstoestande wat ooreenstem met die gemiddelde toestande in die Groot Vis Rivier. Aangesien die grenstoestande dieselfde was en net die rivier-bodem vlakke gevarieer is, kon die effek van vloede op die souttoestand in die estuarium bepaal word. Uit die model resultate kon duidelike tendense waargeneem word. Gedurende lae rivier vloei toestande is die estuarium gevul met sediment en tydens vloede het die sediment weer ge-erodeer en gedeponeer in die oseaan. Groot vloede veroorsaak baie erosie in die estuarium veral in die middel bereik en by die riviermonding. Indien die vloed groot genoeg is word die riviermond vernouing totaal uitgespoel. Die riviermonding in die geslote staat ondervind effense oorstroming en word oopgespoel indien die rivier vloei groot genoeg is. Die graad van die sout indringing in die estuarium hang hoofsaaklik af van die grootte (die vernouing) van die rivier mond. Gedurende toe mond toestande is die gemiddelde sout vlakke in die estuarium laer, wanner die rivier monding groter raak, word die gemiddelde sout vlakke in die estuarium meer. Die omvang van die sout indringing strek tot ongeveer 10 km stroomop van die rivier mond wanneer die mond oop is en die indringing afstand neem toe gedurende spring getye.

Research of macroinvertebrates is currently an important part of the assessment of stream quality. Basic characteristics influencing macroinvertebrates communities in the streams are elements from the external environment influencing streams, specifically basic geographic parameters of the site, land-use in the catchment and characteristics of the banks. These elements have a considerable influence on effect of the basic parameters in the stream, which are flow, sediment structure, input of organic material and pollution. Research part of the thesis is about the parameters influencing macroinvertebrates communities. Research area of this work includes three different catchments in the upper part of Blanice catchment area near Prachtice. There is one nature stream with forest in it's catchment, stream with a predominantly meadow basin and last stream is characterized by two distinct stretches - a revitalized section and a section with concrete bottom. The subject of this diploma thesis is evaluation of diversity of macroinvertebrates communities in all streams in the research area. Thesis evaluate communities of macroinvertebrate using a wide range of indexes (BMWP score, ASTP index, EPT index a diversity indexes) and compares their diversity by using rank-abundance graph. All results are summarized...

Ce travail s'intéresse aux altérations des systèmes fluviaux et à leur modélisation à une échelle de temps intermédiaire, de l'ordre de quelques décennies, et à l'échelle spatiale de bassins versants étendus et complexes. Une revue de la littérature montre que cette question reste principale chez les géomorphologues. Elle permet de dégager les constantes des différents modèles conceptuels qui ont été développés et en particulier i) la dépendance aux conditions hydrologiques et aux conditions d'alimentation solide, ii) la réaction du système pour s'adapter en cas d'altération de ces conditions, et iii) la propagation de ces perturbations avec une atténuation progressive vers l'aval du bassin versant. Nous avons choisi d'étudier plus particulièrement les perturbations introduites par les aménagements hydroélectriques à l'échelle du bassin versant en développant un modèle conceptuel, basée sur une description volontairement limitée des altérations hydrologiques et d'alimentation solide, et sur la connaissance experte pour la prédiction de l'évolution de la morphologie des rivières alluviales. L'objectif est la détermination des trajectoires d'évolution de variables représentatives de la morphologie de la rivière qui les font évoluer d'un état d'équilibre dynamique à un autre. Nous avons testé ce modèle sur une représentation du bassin versant de l'Isère à l'amont de Grenoble (5818 km2) en intégrant une description du schéma complexe d'aménagements hydroélectriques construits dans la deuxième moitié du XXème siècle. La modélisation donne des résultats cohérents avec les observations du système mais qui sont limitées par les hypothèses fortes d'un équilibre initial du système fluvial et de l'unicité de l'origine des perturbations. En dernière partie, nous ébauché le développement d'un modèle numérique simplifié destiné à prendre en compte la période de transition entre les états d'équilibre dynamique. Ce modèle permet d'évaluer la durée de la période transitoire d'un tronçon de rivière et de valider l'utilisation du concept de débit morphogène qui est fait dans le modèle conceptuel des équilibres dynamiques. Ce modèle permet de simuler la superposition d'altérations mais, dans l'état actuel, il ne permet pas de modéliser la cinétique de la propagation des altérations amont vers l'aval du bassin versant. Mots-clés : morphologie fluviale, bassin versant, régime hydrologique, apports sédimentaires, aménagements hydroélectriques, trajectoires de ajustements, cinétique de évolution du lit. / Abstract This work focuses on the geomorphological dynamics of a river system and the modelling of these changes over a medium time scale (the order of a few decades) and a large watersheds spatial scale (the order of 5000 km2). A literature review shows that this subject is one of the main issues in fluvial geomorphology today. It reveals the constants of different conceptual models that have been developed and in particular i) the dependence of geomorphological dynamics on hydrological flow regime and sediment supply conditions, ii) the ability of the system to adapt, in case of alteration in hydrological flow regime and sediment supply, and iii) the spread of these disturbances with the gradual attenuation of the effect of alteration downstream. In particular, we chose to study the effect of disturbances introduced by hydroelectric structures on the river morphology at the watershed scale by developing a conceptual river morphology model. The model outline was based on a, deliberately limited, description of hydrological regime and -sediment supply alterations, and on expert knowledge to predict the morphological evolution in alluvial rivers. The objective of this work was to determine the direction of evolution trajectories of the river morphology, trough representative variables that evolve from one dynamic equilibrium state to another. We tested the model on a representation of the Isère watershed, upstream of Grenoble, France (5818 km2), incorporating a description of the complex pattern of hydropower structures, built during the second half of the XXth century. The modelled changes in river morphology give results that are consistent with the observations. However, the model is limited by two strong assumptions: i) the initial equilibrium of the system and ii) the synchronisation of the disturbances. In the final section, we described the development of a simplified numerical model which aims to take into account the transient period between the dynamic equilibrium states. This model is used to evaluate the duration of the relaxation period for a river reach and validate the use of the channel-forming discharge concept that was used in the conceptual model. The model simulates the overlay of the disturbances, but in the current state it is not capable of modelling the kinetic propagation of the disturbances downstream into the watershed. fluvial morphology, watershed, hydrological flow regime, sediment supply, hydropower structures