RiversRevisionppt.ppt

To understand the concept of a systems approach

To understand all of the stages of the Drainage Basin Hydrological Cycle (HC)

Write 250 words to describe whether the HC is and open or closed system and why?

In turn students have 30 seconds each to draw on the board. The finished diagram should be a completed drainage basin/hydrological cycle diagram that the whole class have contributed to.

Questions:Give 2 examples of how humans might influence the hydrological cycle.Create two lists (stores, flows) of the key terms. The hydrological cycle is an example of an open system. What do you think open and closed systems are?Extension sheet.

What might change the Hydrological Cycle?

500words

http://www.grida.no/graphicslib/detail/sea-level-rise-caused-by-the-melting-of-mountain-and-subpolar-glaciers_fccc

http://www.grida.no/graphicslib/detail/population-area-and-economy-affected-by-a-1-m-sea-level-rise-global-and-regional-estimates-based-on-todays-situation_d4fe

http://www.grida.no/graphicslib/detail/estimated-contributions-to-sea-level-rise-1993-2003_9cc9

To understand the characteristics of the drainage basin.

The stores within the drainage basin system have been labelled upon the system diagram for you.You need to add all the following terms onto your blank system diagram and then colour code them to show whether they are an output, store, input or process:throughflow | groundwater flow into deep rocks | infiltration | precipitation | capillary rise back into soil | evaporation and evapotranspiration | overland flow | percolation | channel flow | throughflow and stemflow | baseflow in bedrockDon't forget to add a key!

To understand the characteristics of the drainage basin.

How do the following three choropleth maps link to the idea of a 'water balance'?

The water balance is the relationship between the inputs and outputs of a water system.

Add the following labels to your blank water balance diagram:Total Evapotranspiration Precipitation Water consumption Runoff Groundwater store Unsaturated zone Surface water Dam store Dam capacity Aquifer recharge from channel flow Aquifer discharge to base flow Aquifer recharge from surface water Groundwater Evapotranspiration Non-irrigated land Evapotranspiration Irrigated land Evapotranspiration Evapotranspiration from stores

Using the water balance graph on page 4 of AQA AS Geography as a model produce your own, using the following data for Perth, Western Australia:

Estimate and shade areas of soil water surplus, soil moisture deficit, soil moisture utilization and soil moisture recharge.

Describe your Water Budget graph. 300 words

http://www.slideshare.net/geographyalltheway/geographyallthewaycom-ib-geography-the-bradshaw-model?utm_source=slideshow02&utm_medium=ssemail&utm_campaign=share_slideshow_loggedout

Aims today:

To learn about:Channel EfficiencyThe Hydraulic RadiusThe Graded ProfileX-Sections along a long profile

1. CHANNEL EFFICIENCY

Measure of the ability of a river channel to move water and sediment.

The most efficient channels are generally semicircular in cross-section, and it is this shape that water engineers try to create when altering a river channel to reduce the risk of flooding.

2. THE HYDRAULIC RADIUS

The hydraulic radius is a measure of a river's channel efficiency, and is used by water engineers to assess the likelihood of flooding.

The hydraulic radius of a channel is defined as the ratio of its cross-sectional area to its wetted perimeter.

The greater the hydraulic radius, the greater the efficiency of the channel and the less likely the river is to flood. The highest values occur when channels are deep, narrow, and semi-circular in shape.

3. THE GRADED PROFILE

Contrast the channel shapes and comment on the relative efficiency of the two river cross sections ( 7 marks)

VIDEO LINK

Deltas are depositional landforms that are created from the loading of sediment onto the land as the rivers capacity is reduced. They are dynamic areas that change rapidly due to continual formation and erosion during storm and flood events. Great examples can be found at the Ganges delta in Bangladesh, the Nile Delta in Egypt

As rivers approach the sea they contain high sediment loads and the rivers start to spread out laterally and the velocity is reduced. (Because the sea is a large body of water with a low velocity and the water spreads out).This lateral movement of water reduces hydraulic radius and increases wetted perimeter. (Because the capacity is reduced so sediment is deposited on bed creating undulations).The sediment is deposited and flocculation occurs (where clay sediments join together, gain in mass and sink.)This sedimentation builds up over time and can create small islands which split the channel, similar to braided streams.This can happen again and again until the river consists of a number of smaller streams separated by islands.Sediment is often deposited closer to the sea so builds the delta outwards. These areas are called fore beds, and are highly unstable. They often collapse and cause mass movements within the sea and clouds of sediment known as turbidity currents.

Topset bed: larger and heavy particles due to energy loss.Forest bed: medium sized particles travel slightly further.Bottomset beds: very fine particles travel the furthest.

If sediment is coarse grained, arcuate deltas form. If it is fine grained then birds foot deltas can be created (e.g. Mississippi).A cuspate delta is pointed like a tooth and is shaped by gentle, regular BUT opposing sea currents/ long-shore drift.

Floods can be controlled in many ways:Dams control, store + release waterPumping stations pump water into storesStraighten river allows speed of river to increaseWiden + deepen river so the channel can carry more waterBuild barriers such as concrete embankmentsControl land use Stop people building on the floodplain or plant trees to increase interception

What do you have to consider before building river defences?How often the river floodsHow much each method would costWho would benefit from building defences?How bad is the floodingWho would lose out from defences?Are they good for the environment?

Type of defenceCost

1=low 10=highAppearance

1=natural 10=uglyEnvironment friendliness1=good for env10 = bad for envEffectiveness

1 = very effect10 = not effectTotal score

Higher the score worse the defence typeBuild concentrete flood walls to hold rising watersBuild a dam tohold flood waters backStraighten river so water moves along it quickerBuildearth embankments to stop river floodingWiden and Deepen river so that it can carry more waterPlant more trees that slow down water reaching the riverStop people building on floodplains where flooding is worst

Look at the approaches to flood prevention and complete the sentences below

I think the cheapest project is..because

however, I think is the most expensive project

because. .

The best project for wildlife is

as/because

whereas the project which is best for the rivers appearance is.

because

Bangladesh Government

Distributed money and 400 tonnes of riceRelief supplies of fresh water, water purification tablets and sanitation services providedAid Agencies

Provided Boats to rescue peopleSupplied medicinesSupplied clean drinking waterSet up a medical treatment centreDistributed fodder for livestockDistributed food and plastic sheetingPlanned a rehabilitation programme to repair and construct housing and provide sanitationOther Governments

Gave aid including wheat, money, medicines, water tablets, house repair, sanitation and rehabilitation for farming and fishing

In 1989 the Bangladesh government working with several international agencies and the world bank produced a FLOOD ACTION PLAN (FAP):SHELTERS AND WARNING SYSTEMSBuilt 5000 flood shelters in high risk areasImprove flood forecasting system using satellite and computer technologyPrepare flood disaster management plans which provide early warning and clear, effective instructions as to what people should do before, during and after a floodDAMSBuilding 7 new dams to control river flow and to hold back the monsoon rainwater in reservoirsThe water would be used for irrigation and generating electricity

BANGLADESHMANAGING THE FLOOD LONG TERM contFlood Control12-15 floodwater storage basins to hold floodwater diverted from main rivers Divide the land into compartments and control water flow through a system of channels by sluice gates and water pumpsIn the dry season water can be moved to farming areas requiring irrigationEmbankmentsComplete and strengthen the embankments along all the main river channels to a height of up to 7 metresMore than 7500km of embankments are already in place but repairs, heightening and new building would cost over $6 billionOther controlsPumping water out of the ground in the Himalayas during the dry season to create underground storage for the monsoon rainsReplanting of forest cover in Nepal and Tibet

Debate between HARD and SOFT engineering flood prevention schemes continuesMany oppose the FAP both locally and internationally:

Embankments will trap rainwater and make flooding worse!Dam construction could increase the build up of silt and make flooding worseHow can we provide solutions if we dont really know the causes?These plans are far to expensive!Embankments restrict river access for fishing peopleFlood control systems may damage the environmentHalf a million people will lose their land to reservoirs and embankments!Flood shelters save lives but dont help protect our property and livelihood

DeforestationReduces interception and evapotranspiration, which increases run-off.Possible decrease in channel capacity due to increase in sediment carried.Loss of root systems may cause the soil to erode more rapidly.

UrbanisationHighly impermeable surfaces, such as roads, roofs and pavements.Natural river channels restricted by bridges or roadside facilities.Smooth surfaces drained by a network of drains, gutters and sewers.Some river channels may be straightened, leading to fast delivery of water downstream.

Coastal InfluencesHigh seasonal tides affect areas close to the sea.Storm surges and tropical cyclones can result in high water levels in rivers and low-lying coastal areas.Insufficient planning control allowing high density building along coastlines.

ClimatologicalIntense precipitation reduces infiltration capacity.Sudden increases in temperature can induce snowmelt, which can be made worse if frozen ground exists lower down, thus reducing infiltration rates.Prolonged periods of rainfall produces saturated soil and increases overland flow.

Land Management Techniques/ AgriculturePloughing up and down a slope rather than along the contour increases soil erosion, which increases the rivers load.Drainage systems, ditches and ploughing all reduce the lagtime for the water reaching the river channel.Overgrazing can lead to less vegetation and can also compact the soil, increasing run-off.Planning strategies may allow for building on low lying land prone to flooding.

Nature of the basinInfiltration rate depends on rock and soil type.Shape of the basin, relief/gradient and vegetation cover affects how quickly runoff reaches the channel.

*Discuss and compare with pupils the Yarm example and whether they are seeing individual/community and government responses to the floods.*Continue as before.*Talk through with pupils long term government strategies and how it is more difficult for them to recover compared to Yarm. The floods will just keep on coming.

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RiversRevisionppt.ppt