RIVERS

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RIVERS by Mind Map: RIVERS

1. Energy of river

1.1. Speed

1.1.1. 1.Gradient of the river

1.1.1.1. Steep slope water flowing faster.Gentle slope water flowing slower.

1.1.2. 2.Roughness of the channel

1.1.2.1. Rough channel have rocks protruding out hence more friction when water passes through the obstacles,thus water flow in slower speed.Smooth channel have less rocks and obstacles hence less friction occurs thus water flow in faster speed.

1.1.3. 3.Wetted perimeter of the channel

1.2. Volume

1.2.1. 1.Size of drainage system

1.2.1.1. The bigger the drainage system,there is more surface area for the rain to fall hence the amount of water is large.On the other hand,if the drainage system is small,there will be less surface area and thus small amount of water.

1.2.2. 2.Presence of vegetation

1.2.2.1. If an area is covered with vegetation,there will be more rainwater seeping into the ground,less surface runoff and hence volume of water in the low.On the other hand,if an area is covered with little vegetation,there will be less rainwater seeping into the ground,more surface runoff and thus the volume of water in the river is higher.

1.2.3. 3.Permeability of rocks

1.2.3.1. If the rocks have small pores the water cannot easily pass through,there will be more surface runoff leading to larger volume of water in the river.If the rocks have large pores,water can easily pass through,there will be less surface runoff and therefore smaller volume of water .

1.2.4. 4.Climate

1.2.4.1. Areas with dry climate,usually there will be low volume of water.Areas which experience hot and wet climate,the volume of water in the channel remains high.

2. River processes

2.1. Erosion

2.1.1. CASH 'buy' LV

2.1.2. 1.Corrasion.The grinding of rock fragment carried by the rover against the bed and banks of the river and channel becomes widen and deepen.

2.1.3. 2.Attrition.The rocks collide against one another in the water and the become smaller.

2.1.4. 3.Solution.Water reacts chemically with the soluble minerals in the rocks and dissolves them.

2.1.5. 4.Hydraulic Action.Breaking down of rocks and dissolving dragging them away from the beds and banks by the force of fast running water.The fast moving water enters into the cracks of the worcks and breaks up into smaller pieces.

2.2. Transportation

2.2.1. TS3

2.2.2. 1.Traction.boulders and stones are move downstream by roiling along the river bed by the force of the water.

2.2.3. 2.Saltation.Coarse sand particles are moved downstream in a series of bouncing motion,the get lifted and dropped onto the river bed over and over again.

2.2.4. 3.Solution.Dissolved materials are carried in the water amd are invisible to the naked eye.

2.2.5. 4.Suspension.Clay,slit and fine sand are carried along the river without touching the river bed,they are held in suspension and give the river a murky appearance.

2.3. Deposition

2.3.1. When river energy is low,it cannot erode or transport materials.

2.3.2. When energy of the river is low and when the speed or volume of the river decreases.

3. River Landforms

3.1. Waterfall(upper course)by erosion.A waterfall can form when a river flow from a band of resistant rock to less resistant rock,The less resistant rock that lies downstream will be eroded faster than the resistant rock.The different rate of erosion leads to a change in gradient of the river.Overtime,there will be a sudden steepening of the river bed from the resistant rock,forming a water.Example,such as Niagara River(Between Canada and USA)

3.2. Meanders(Middle and Lower course by erosion,transportation and deposition).Along the outer banks,speed of the water is high as there is less friction.With more speed,energy of the river is high thus leading to erosion.Overtime,the outer banks get undercut and a steep-sided bank,known as river cliff is formed.Erosion occurs on the outer banks of the river,The eroded sediments are transported to the inner bank where they are deposited.Along the inner banks,deposition occurs because the friction is greater.As more sediments is deposited the water becomes shallower at the inner bank and a gentle-slope known as a slip-off slope is formed.

3.3. Floodplain and levees(Lower course,by deposition).When there is heavy rain,the river may overflow its bank and floods the surrounding areas.Once out of the channel,the rover may encounter more friction because of a larger wetted perimeter formed by the large flat low land.The increased friction reduces the energy of the river water and slows down the speed,leading to deposition.The larger and courser materials are carried and deposited at the river banks,these form levees.The smaller and finer materials are carried and deposited further away as they are lighter,the formed floodplains. Repeated floosding causes the fertile alluvial to bulid up on both sides of the river.One example of a floodplain is the Indus Floodplains in Pakistan.

3.4. George(Upper course by erosion).The less resistant rock that lies downstream gets eroded faster.Overtime,when the overhanging resistant rock loses support and collapses the waterfall retreats upstream leading to the formation of a gorge.

3.5. Oxbow lake(Middle and lower course,by erosion and deposition).With constant erosion of the outer bank and deposition of the outer bank and deposition on the inner bank,a meander becomes very sharp, separated by a narrow neck of land.The neck becomes narrower with continued erosion and deposition.Overtime,deposition begins to cut the river from the meander.The rover then flows straight through the channel.Eventually,the meander that is cut off forms an oxbow lake.

3.6. Delta(River mouth,by deposition).As the river approaches the calmer sea water,its speed decreases and deposits its load at the mouth.Layers of different sediments such as sand,slit and clay continue to build up on the sea floor.Overtime,the deposited materials rise above the sea level and a delta is formed.However,they block the path taken by the river to reach the sea.The river branches into smaller rivers called distributaries to find a way around the blockage.Delta at river mouth are formed only if the load deposited in the coast exceeds the amount transported away.Conditions:A lot of sediments being deposited.No large lakes along the river to trap the load.Coastal water is quiet and has few or no strong currents and waves to remove the deposited sediments.

4. River Management

4.1. Re-sectioning.Advantages;Widening and deepen the river channel so that the river can hold more surface runoff from the surrounding area.The river bed and banks maybe smoothened by replacing the soil of the river banks and bed with cement and granite.By doing so,there is less friction between the river bed and banks.Thus,the speed of the river will increase and allow more water to flow away from the area more quickly.Example:Singapore River and Kallang River in Singapore.However,there are also disadvantages:Its destroys the habitats of plants and animals when we line the natural banks of river with concrete surface.With re-sectioning,the river flows faster and has more energy.Sediments will be washed downstream or into the sea and ocean.The increased in sediments will mean that there is less sunlight reaching the riverbed.Thus,the growth of marine life may be affected.

4.2. Re-alignment,the advantages:Straighten river by removing the meanders.this increase speed of river,so the water flow away quickly from the area,the increased in speed causes the river channel to be erode.Thus,it becomes deepen and hold more water.Example:Mississippi River has been shortened by 240km after re-alignment.However there are also disadvantages:It shortens the river course,causing the river to flow over smaller area,shrinking the wetland area.Thus,the habitats of the wetlands are destroyed.Increased speed of the river may result in flooding downstream.Due to channelization upstream,the volume of the water may result on flooding downstream is increased.However,channel downstream cannopt contain the increased flow of water.

4.3. Planting vegetation.The advantages are :Roots of tress and other plants hold the soil together firmly and reduce the amount of sediments being transported into the river,thus the channel does not become shallower,reducing the chances of flood.Vegetation reduces the rate and amount of surface runoff,as water is intercepted by the leaves of the trees and it also infiltrate into the soil.This prevents large amount of water from entering the river at any one time.However,there are also disadvantages:too much vegetation planted along the river is not entirely effective.too much vegetation results in excessive shade and prevents sunlight from reaching the river bed.Aquatic plants are killed and aquatic food chains are affected.

4.4. Bank protection,advantages are:Dykes are walls of sands or concrete they are built along rivers that often overflow.It allows river to hold more water,thereby effective in reducing the chances of floods.Example:In China,dykes have been built for centuries in the lower course in the yellow river.However,there are disadvantages:due to the continuous build up of sediments deposited on the river bed,making the channel shallower.Water level can eventually rises over the dyke walls and causes flooding.Thus,maintenance is needed.

4.5. Building Gabions and revetments it is effective as it are builds to divert the flow of water from the river banks to the centre of the channel.It protects the river banks from being eroded by the force of running water,and it reduces the amount of sediments that enters into the river.There,the river can hold more water and are effective in reducing the chances of floods.Example:In New Passage England.However,it is not entirely effective:as sediments accumulate behind dykes,revetments and gabions.Overtime,river channel becomes shallower as sediments continue to build up.When prolonged rains occurs,the water in the river may overflow these structures and lead to flooding.Structures like Gabion will only last for short period of time between 5 to 10 years,it is also costly to maintain as gabion rust easily because it is made if wire cages.