8/16/2023 0 Comments Delta meander river![]() ![]() These mud, silt and sand bed rivers move sediment out to the sea through both river flow and tidal current processes. Rivers flowing into the sea Estuaries and firths In lowland lochs, lake deltas are often built of sands, silts and clays (muds). Rock gorges and waterfalls may form where the river has been able to cut through hard rock sections. As the outside bank of a river bend (above a deep pool) is undercut, sediment is carried downstream, where it may be deposited in a lateral bar or riffle. The channel evolves and migrates across the floodplain in response to the flow path of the channel current (thalweg). These are typically single-channel, sand-bedded rivers that flow over wide, flat floodplains. Rivers crossing the lowlands Meandering rivers Once sediment deposition causes the channel path to become raised above the surrounding land, the river is more likely to switch direction and flow through adjacent lower-lying land. They’re formed as the tributary river switches its channel path every so often over a very long period. Tributary river alluvial fansĪlluvial fans often occur where a side valley river meets a main valley and river. The delta’s shape depends on how much sediment the river or burn carries and how ‘flashy’ its river flow regime. Lake deltasĪ delta often forms where a river enters a loch, as the river flow slows and sediment is dropped into the loch water. If there’s a long time between big floods, the river may gradually rework its gravels and adopt a more meandering path. Channels may form and be abandoned during floods. Scotland has some amazing braided rivers, which have multiple threads of channels that divide and rejoin to form an almost fishnet-style network. Such rivers are most common where there are large amounts of glacially derived sands and gravel deposits to rework – these are often stored in wide straths or valleys as high river terraces. Some have more than one actively migrating channel, and their many reaches can form gravel islands. ![]() Upland Scotland has a great many wide gravel bed rivers. Rivers in glens and straths Wandering gravel bed and braided rivers The steeper the gully, the more likely it is that the burn will carry slurries of rock and water (debris flows). Mountain torrents, especially in steep gullies, deposit these small steep fans of sediment where they meet the valley floor. In many Highland glens, these basins have bedrock-controlled river channels both upstream and downstream of them. Rivers form these small areas of flatter ground where they deposit flood-borne sediment. Many torrents rework the old glacial sediments that plaster Scottish mountainsides, but some erode gullies in vulnerable bedrock. These steep boulder bed burns can move very large rocks in their beds during flash floods. Sub-glacial meltwaters originally carved out many of our deep-sided bedrock channels. Narrow rock chasms, slot gorge channels and freefall waterfalls are steep and often spectacular. Rivers descending the mountains Bedrock reaches, slot gorges and waterfalls Below is a selection of our most typical river types. Such a variety of river types provides Scotland with a great diversity of river habitats and landscapes. ![]()
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