VIEWS: 33 PAGES: 9 POSTED ON: 10/7/2012
Rivers The water cycle Places water can be stored: On the surface as snow or ice In the plants and trees In the lake In the marsh In the grass, on the surface In the soil In the water table In the sea in the clouds Gradient Steep Moderate Gentle Features Rapids, waterfalls Meanders Flood plain, levees ‘V’ shaped valley Drainage Basin: Watershed – Edge of drainage basin, joins high points in basin Source – point at which a river begins Mouth – point at which a river meets the sea, or inland lake Tributary – Stream or small river that leads to a bigger one Confluence – the point at which 2 streams meet River basin – area drained by a single river system (drainage basin) Interfluves – ridge of higher ground that lies between 2 rivers Erosion Processes Hydrolic power: The force of water on the bed and banks. Water force removes material from bed and banks. Particulay strong during floods. Corrasion: The sediment rubs against the bed and banks at times of high flow Corrosion: Rock minerals eg. Calcium carbonate slowley disolve in river water, which is sometime acidic. Attrition: Sediment rub against each other, breaking themselves up and reducing each other to sediment. Transportation Traction: Large boulders roll along the river bed Saltation: Small pebbles are bounced along the river bed as the flow changes Suspension: Finer sand and silt particles are carried along in the flow giving the water a brown appearance Solution: Minerals eg. limestone and chalk are dissolved into the water and carried by the flow, they can’t be seen Upper course features Waterfalls: Falling water and rock particles wear away soft rock The hard rock is undercut as erosion continues Hard rock collapses and if moved by the flow. The waterfall moves backwards Erosion continues and the waterfall continues to move upstream leaving a gorge of recession Interlocking spurs: The river flows a twisting course in between the spurs V-shaped channels and narrow channels, steep gradient and rapids. Middle course features Moderate gradient, almost flood plains widening channels. Meanders. Slip off slope: gentle slope on the inside of a meander River cliff: steep river bank on the outside of a meander Meanders: Ox - bow lake: Semi circular lake formed by a meander being sealed off from the main course of a river. Meander Scar: Dried up ox – bow lake. Lower valley features Flood plain: Wide, flat area either side of the river, in its lower course. It is used for flooding. Bluff: Slope that rises steeply from a rivers valley. Levees: Natural embankments of silt along the banks of the river. The river in flood As the flow looses energy it drops the coarser material by the banks and the finer material further away. The River in Low flow The rivers velocity slows meaning material is deposited on the river bed. After repeated floods The river banks form levees and the river may be raised so that the water is above the level of the flood plain, which can lead to flooding. River Mouth Estuaries: Downed river mouth in a lowland area, because of a rise in the sea level or fall in the land level. Deltas: Often triangular – shaped flat land jutting out into the sea at the mouth of a river. Formed by river deposition, when the velocity of the river drops it deposits its load. If there are no strong sea currents the sediment will stay there. Arcuate Delta: Nile. Egypt Birds Foot or Digiate Delta: Mississippi. USA Estuarine Delta: Elbe. Germany River Management River Management is ways in which the river is controlled. It stops flooding and helps monitor and develop the rivers course. River Wey and Lower Tees Valley: Reservoir – control how much water in is the channel at one time. It also ensures that there is a steady supply of water. Flooding has been decreased due to new advanced flood warnings, embankments, gabions, concrete walls and flood gates. Also building on flood prone land has been discouraged. In the Tees, The Tees Barrage, dredging has been used, and meanders have been cut off. Yarms flood defense: - Reinforced flood walls with gates for access - Earth embankments - Gambions (baskets filled with stones) protects decrease erosion - Fishing platforms, street lighting and replanting to improve the environment. Hard engineering involved large scale engineering works and are usually expensive. Soft engineering schemes cost less, do not have a major impact on the environment, and are thought to be more sustainable. Flood Management Reduces Flooding: Embankments, Flood diversion channels, Flood storage zones, Catchment management, Dams Reduces Damage: Early warning system, Flood proofing, Regulations of building on a flood pain Other: Insurance, Polders River Regimes Discharge is measured in m3 / seconds, called CUMECS. To calculate the discharge you multiply the velocity by the cross section area. The Regime of a river is the variation in the discharge of water carried at different times in the year. Hydrograph Graph showing the discharge of a river at a give point over a period of time. A flood or a storm hydrograph shows how a river responds to one particular storm. Floods Boscastle: Lies on the west coast of Cornwall. 2004 flash floods from the river Valency and Jordan. Biggest rescue operation since WW2. Nobody was killed. Summer means heavy rainfall, which there was in the source of both rivers. There is little woodland near, so no trees could absorb the water. Steep hills near Boscastle. Narrow valleys increased the rivers velocity. 2 streams joined meaning an even bigger volume of water Bangladesh: Reasons: Two very large rivers; Ganges and Brahmaputra meet Very low lying land Monsoon Costal storm surges Deforestation upstream Silting up of riverbeds, decreased capacity Population increased Urban growth increased surface run off River Tees: Uses: Bridging points and larger towns such as Yarn. There are huge mud flats such as Seal Sands, which are important wildlife areas for migratory birds and seals.
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