The river morphology (morphé = shape / form and λόγος, lógos = word, doctrine, reason) is a geoscience that deals with the formation and shaping processes of rivers and is a specialty of geomorphology and general river science (potamology). Morphology is the study of surface shapes and geomorphology studies the physical aspects of the earth's surface , it concentrates on the forces and processes that shaped and shape the earth's relief . The river morphology is limited to the redesign of the river bed. The science of river morphology describes the shape, form and structure of the riverbed . The appearance of the rivers and the variety of morphological structures is shaped by the runoff and solid matter dynamics. The change in river morphology takes place in significantly shorter periods of time than that of geomorphology, which is related to geological times.
→ Main article: river bed
Rivers are dynamic and formative parts of the landscape. They are in constant interaction with their surroundings. The river bed and the floodplain are significantly influenced by the runoff and the dependent solids transport. The runoff of the rivers fluctuates over the course of the year. The runoff regime varies both seasonally and due to the geographical location of the respective river section. To run snow and glacial melt and rainfall events to higher outflows. The size of the discharge is a decisive factor in the very complex process of bed formation. Floods change the river morphology significantly, and runoffs full of banks can also modify the river bed. The river bed and the river valley are developed by the alternating current attack. Morphodynamic change processes in the form of erosion and accumulation continuously shape the river bed. Solids such as debris and suspended matter only start moving once they have reached a certain level of drainage. Reaching the critical shear stress leads to the erosion of soil material on the river bed and the bank. These processes are known as bottom and side erosion . The higher-level solid household has a very strong influence on the shape and structure of river beds. The rivers actively shape the relief and shape of their catchment area . At the same time, the appearance of the rivers is also changed by the surrounding area.
The alignment of the rivers is an essential component of the river morphology. It varies depending on the water section due to the different geological and geomorphological conditions. The space in which rivers move is called the pendulum bandwidth . The extent of the migration corridor depends on the runoff, the substrate composition and the longitudinal gradient.
Morphological river types
The morphology of rivers shows a wide range. The different morphological river types range from meandering and calmly flowing lowland rivers to heavily branched rivers to cascading, highly turbulent mountain rivers. The river morphology is determined by the natural spatial characteristics of the catchment area of the river - such as topography , geology , tectonics , vegetation and climate - as well as by the fluvial processes and river geneses that depend on them. Sections of the river are characterized by almost the same natural spatial conditions and they can therefore be assigned to a morphological river type. The morphological river type describes the geometry of the water in the form of longitudinal and transverse profile as well as ground plan . In the classification, the redesign dynamics in the river bed and within the surrounding area also play a role in the event of a flood. In addition to the river bed morphology, the runoff and solid matter dynamics as well as the longitudinal and lateral connectivity (longitudinal continuity and cross-linking between river and floodplain ) are considered in the typification .
The morphology of the rivers can be differentiated into three different types of rivers with elongated, branched and meandering courses based on the shape of the river.
Straight rivers in the geometric sense do not occur in nature. Elongated channels are therefore rivers that have a very small flow development and thus a large stretch. Rivers rarely flow in a straight line for more than ten times their channel width. The stretching of a channel is essentially determined by a steep bed slope or a geomorphologically-related narrowing of the river course through lateral valley slopes. Of course, they occur on hard rocks in valleys of mountains such as the gorge and Kerbtal . The mountain rivers can be found, for example, in alpine regions with steep slopes and with a certain topography. The valley path shuttles from one side of the river to the other. Due to deep and lateral erosion as well as landslides , the alpine rivers have a high solid load.
→ Main article: Intertwined river
Branched rivers arise when the gradient is medium to steep. The solids balance is characterized by transfer processes with high bed load . In ramified rivers, the lack of a limiting shoreline is typical. The bank varies constantly due to the numerous relocation processes. The active flow cross-section is characterized by an enlarged width. The relationship between river width and water depth is large, whereas the relationship between water depth and grain diameter is only small. Numerous channels structure the river bed. The gutters separate irregularly and flow together again. Flood events lead to changes in the channel system. In the course of the relocation dynamics at higher discharges (HQ), mostly vegetationless gravel banks and islands develop between the channels , which are permanently shifted in their position and shape. At these extreme locations, pioneer vegetation can temporarily set in, which is constantly removed by the currents during flood events. There is no fixed valley path.
Winding / meandering rivers
→ Main article: Meander
Winding river stretches are also called river meanders. The river type is characterized by a low ratio between river width and water depth. There is a large relationship between water depth and grain diameter. This type of river forms with a low gradient and a low flow velocity in shallow valley meadows. A single deep channel forms the river bed. The long valley path has been shifted towards the Prallhang (outer bank). River meanders develop freely in their alluvium, and valley meanders develop due to the relief of the terrain.
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