Presentation on theme: "Rivers. Study Figure 1 which shows the water balance for Birmingham, England. i) Name the months when there is a soil moisture surplus. ii) State one."— Presentation transcript:
Study Figure 1 which shows the water balance for Birmingham, England. i) Name the months when there is a soil moisture surplus. ii) State one of the months when potential evapotranspiration exceeds precipitation the most and by what amount. iii) Give the meaning of soil moisture recharge. 4 marks
Months of January, February, March and December have surplus. 2 marks if all 4;1 mark if three, likely to be January – March. June or July – where evapotranspiration exceeds precipitation by 45-50mm approx. Soil moisture recharge is the replenishment of stores of water used during warmer months when evapotranspiration has exceeded precipitation, when there is a net balance in favour of precipitation, water lost from the soil will be replaced. Maximum 3 on first 2 parts and last part.
Study Figure 2, a satellite image of the Mississippi delta. Draw a labelled sketch plan to show the characteristics of the Mississippi delta. 4 marks
Sketch plan should show recognisable outline of river channels and build – up of land along them, with infilling between those on the right-hand side of plan. Labels likely to include – distributaries, bird’s foot shape of delta, land extending along distributaries, levees, evidence of deposition/shallower water on edges of land, large amounts of sediment present in waters off the developed part of the delta. Allow 1 for sketch and 3 for appropriate labels.
Explain the formation of deltas. 7 marks There are certain conditions that are present which encourage the formation of deltas. The presence of a large amount of sediment is essential – brought down by large rivers. Mississippi transports 450m tonnes per year. The limited removal of this by small range of tides is also significant – thus deltas form in areas such as the Mediterranean, Gulf of Mexico. The presence of relatively calm seas encourages the deposition of material, as does the process of flocculation where the salt present in the water in the sea generates an electrical charge that causes particles to stick together, increasing cohesion and weight and encouraging deposition. There may be reference to the land extending out especially along distributaries and the fact that the largest material is deposited first. This links in with reference to topset, foreset & bottomset beds. Level 1 (Basic) 1-4 marks Begins to explain – ideas separate initially. There is a partial sequence and begins to link ideas at top end. Some use of appropriate terminology present at the higher end. Level 2 (Clear) 5-7 marks Explanation is clear/sequence given. Links between different aspects and interrelated nature is recognised. Appropriate geographical terminology is used
Study Figure 1 which shows a river in the Glens of Antrim, Northern Ireland. Label Figure 1 to describe the characteristics of the landforms shown. 4 marks
The obvious landforms are the waterfall, plunge pool and the associated gorge in the foreground. Allow 1 mark for each of these – maximum 2 for identification. The command word is ‘describe’ so there needs to be more than just recognition of the landforms for further marks. Labels may include reference to the two stages of the descent / the deeper part of the bed just after the descent / the presence of a plunge pool marked by the white water (if not awarded as an identification mark for recognising landform) / the channel occupying the width of the bed in the gorge or narrow channel / the stepped profile of the gorge or narrow channel / the eddying of the water in the gorge / or turbulent flow. Features must be correctly arrowed to be worthy of a mark – arrow must connect with landform / characteristic. 4x1
Explain the formation of the landforms shown in Figure 1. 7 marks The landforms to be explained are the waterfall and the gorge. There is likely to be reference to bands of hard and soft rock that are horizontally arranged, with the hard rock forming a cap rock, underlain by the soft rock. Differential erosion results and the softer rock is eroded faster than the hard rock, creating a steep gradient. There may be reference to specific processes of erosion, such as abrasion and hydraulic action. This causes the undercutting of the soft rock and an overhang develops above the plunge pool and its swirling waters. This ultimately collapses, causing the waterfall to retreat and to leave a narrow, steep-sided valley – the gorge – in its wake. This is the most likely explanation, but there may also be reference to rivers plunging over the edges of plateaus in southern Africa and South America and also to knick point waterfalls. Level 1 (Basic) 1-4 marks Begins to explain the formation of the waterfall/one landform. There is a partial sequence and general reference to process, such as erosion. Some use of appropriate terminology present at the higher end. Level 2 (Clear) 5-7 marks Seeks to explain the sequence of the formation of the landforms – waterfall and gorge. There is some reference to both landforms, although one may be dealt with in greater detail. There will be greater reference to gorge through the level. Sequence is clear and there is reference to specific processes, such as abrasion. Appropriate geographical terminology is used.
Explain one way in which people can cause flooding. 4 marks Reference is likely to be made to deforestation, urbanisation, building on floodplain, farming practices, river management and global warming. One mark for identification of cause. For the cause selected, there should be a clear sequence of the events set in motion that lead to flooding. For example, urbanisation leads to the building of impermeable surfaces that result in increased surface runoff – the fastest transfer of water to the river, thus lag time is reduced and a higher peak results. The development of drains to take away the surface water exacerbates the problem – providing an ideal, obstacle-free route for water to reach the river with subsequent impact on lag time. Building bridges may constrict the flow, encouraging the build-up of water and flooding. The trend for people to concrete over gardens also worsens the problems. 4x1
What is meant by the term ‘magnitude’ of a flood? 2 marks Magnitude refers to the severity of floods. This idea is required for 1 mark. A further mark is for elaboration, with reference to size of area affected, amount of damage done, the fact that it can be used to predict the return period of a flood event of a particular scale in conjunction with frequency. An example may be used to illustrate. 2×1.
Study Figure 1 which shows the predicted return period of flood events for the River Ouse at York. Summarise the information shown in Figure 1. 3 marks
Response should recognise the following elements – there is a general reduction in the frequency of floods as the severity increases. This may be illustrated by reference to any valid figures relating discharge to recurrence interval (up to 2). Further mark(s) are permissible for recognising the clustering of events between 1 and 15 years and the relative infrequency of very small floods (less than 200 cumecs) and very large floods (more than 600 cumecs).
Figure 2 shows potholes; landforms resulting from fluvial erosion. Describe these potholes and explain their formation. (7)
Potholes are circular shaped; cylindrical; vary in depth; some merge with each other; some are exposed above the river level. The water can be seen to be swirling/eddying. This creates a shallow hollow that is deepened by the same process. The water contains some of the load being carried by the river and this hits the base and sides of the hole to both widen and especially deepen it, smoothing the edges (1). This is a particular application of the abrasion process, known as pothole drilling. It is most effective at times of high velocity and discharge. As vertical erosion is the dominant process, potholes tend to form well above base level where potential energy is relatively high. Level 1 (1-4 marks) Describes the landform generally. Begins to explain. Answer may be imbalanced - and clearly emphasise one element. Some use of appropriate terminology present at the higher end. Level 2 (5-7 marks) Description refers partly to the photograph. Response is more balanced. Explanation is clear. Appropriate geographical terminology is used.
Study figure one which is an OS map extract of part of the valley of the River Dee in Dentdale, North YOrkshire Describe the long profile of the River Dee from one of its sources at to the bridge at marks
Concave long profile (1). River begins at approximately m above sea level (1). Descends steeply initially in wood and then flattens towards end of wood (1). On exit, it has dropped to approximately 350m (1). The steep descent continues and the river drops to 250m in approx 2km (near Stone House) (1). Second part of this descent is less steep (1). This trend continues and the next 50m drop is over approx 2km – to confluence with Spice Gill (1). A similar descent is apparent up to where 150m is reached (1). The descent then flattens significantly, falling 10m in next km (1) and at the bridge is approx 135m, 1km further down (1). It is likely that candidates will focus on darker contours at 50m intervals – need map evidence to support points for 4 marks. In general starts steeply and flattens off, without any precise evidence (1) with location (1). Need an overview for 4 marks, i.e. sense of change throughout section. Can credit diagram. Waterfall – as evidence of steep gradient (1). 4 x 1
Contrast the cross profile of the valley occupied by the river at (Dee side house) with that at marks At , the valley is a clear V-shape (1), whilst at , it is a much broader shape (1). The valley floor is narrow occupied by the channel at (1) whilst it is wider at (1) – approx 0.5km between 140m contour (1). Flood plain present here (1) Valley is ushaped (1). Valley sides are relatively steep (in both locations) (1); but are up to the channel in whereas at , they are approx m from channel before ascent begins (1) and the initial gradient is less (1). Separate accounts max 2. 4 x 1
Reference is likely to be made to changes in the dominant processes – from vertical erosion nearer the source to lateral erosion becoming more dominant lower down. Deposition may also be referred to here. There should be understanding of these, why they are dominant in different sections and the impact they have on the valley cross profile. Reference to reasons for this relating to graded profile, the effect of height/gravity in connection with potential energy and the impact of increasing discharge on kinetic energy are valid here. May refer to meander migration in connection with widening the valley. May refer to other factors, such as geology, rejuvenation, glaciation, mass movement, quarries. Level 1 (1-4 marks) Is aware of the changing processes responsible. Begins to explain – in the context of erosion/deposition processes. Some use of appropriate terminology present at the higher end. Level 2 (5-7 marks) Processes responsible are linked clearly to changing shape. Explanation is developed, with reference to underlying reasons – changes in energy, links to graded profile/base level. Appropriate geographical terminology is used. Explain why a river valley changes in its cross profile downstream. 7 marks
Outline the ways in which a river transports its load. 4 marks Traction where large bedload - boulders, cobbles, larger pebbles (1) is rolled along the bottom (1). Only really occurs at high discharge (1). Distance travelled is relatively short - equivalent of 4 channel widths maximum during each period of high flow (1). Saltation where smaller items of bedload - smaller pebbles, gravel, sand (1) bounces/hops along the river bed (1); local changes in flow lead to it being dropped and then picked up again. Suspension where finer sand, silt, clay (1) is carried within the water itself (1). Solution where certain rock types, e.g. chalk, limestone (1) are dissolved (1) in the slightly acidic river water (1). May make reference under what conditions process occurs, where it occurs. 4 x 1; maximum 3 on any one process.
Study Figure 2 which shows part of the Cuckmere River in East Sussex. Describe the landforms shown in Figure 2. (4 marks)
Meanders are the most obvious feature – these are quite sinuous. There is evidence of the build-up of material on the inside bend (to right of photo) forming a gentle slip-off slope. There are levées present following the river’s course. The meanders are surrounded by an extensive flat gently sloping area – the flood plain. The meander belt extends across this. The valley sides (bluffs/river cliffs) rise beyond the extent of the meander belt. Allow 2 marks for identification. There must be reference to at least two landforms. 4x1.
Flooding is important in the formation of some river landforms. With the help of Figure 2, describe the role of flooding in the formation of river landforms. (6 marks) There is likely to be reference to flood plains (shown in Figure 2), ox-bow lakes (the subsequent stage from the meander development present); levées are also permissible as are bluffs and braided streams. Reference should be made to the specific role of flooding in formation, e.g. the development of levées when the river bursts its banks, the subsequent loss of energy and the deposition of material, beginning with the largest first. Subsequent flood events lead to the further buildup of the banks. The finer material is carried further to be deposited on the flood plain, leading to its aggradation. This process may be especially marked in deltas and channels may split, following flooding. There could be recognition that the meander is often cut off during times of flooding resulting in a straight course and the formation of an ox-bow lake. Level 1 (1-4 marks) Identifies landforms at lower end. Describes the formation of landform(s) such as flood plains, ox-bow lakes. May be detail on one or a variety of landforms mentioned. Some reference to flooding will be present at the higher end. Some use of appropriate terminology present at the higher end. Level 2 (5-6 marks) There is mention of two landforms. Description is purposeful – related to flooding specifically. The role of flooding in the formation of at least one landform is clear – link is made. Appropriate geographical terminology is used.
Figure 1 shows the Hjulström curve. Using Figure 1, describe the relationship between velocity and load size for the process of erosion. 4 marks
Very high velocities are needed before the river can erode the largest material (boulders) (1) + 1 for accurate use of evidence. As the size of the load decreases, the speed needed for it to be eroded reduces (1) e.g. smaller pebbles can be eroded at less than 100cm/approximately 80cm per second (1). This relationship is valid until smaller particles of sand are reached (1). For these, silt and clay, the speeds needed to erode this small material rises (1) with speeds in excess of 500cm per second being needed to erode the finest clay (1). 4 x 1 or 2 x (1+1); any combination.
Describe how water reaches a river channel in a drainage basin. 4 marks 2 correct terms = 1 mark. Direct precipitation/channel catch over the river channel (1). Overland flow/surface runoff where water is running over the land surface into the channel (1). Throughflow where water having infiltrated into the soil (1) flows parallel to the surface and into streams (1) above water table/unsaturated zone. Groundwater flow where water that has percolated deeper down into the rock (1) flows parallel to the surface and enters the stream through hydrostatic pressure (1) flows within saturated zone (1). Pipeflow where water follows roots of vegetation (1). May refer to the continuous nature of some of these and relative permanence (1). 4 x 1; maximum 2 marks on any one process.
Shawbury is situated in the drainage basin of the River Severn. Information on rainfall for two separate periods is shown in Figures 1a and 1b Draw sketch hydrographs on Figures 1a and 1b to show the contrasting effects of each of the two rainfall periods on river discharge. 3 marks Suggest reasons for the differences in the shapes of the hydrographs that you have drawn above. 3 marks
Sketch hydrograph for 4/5/ should show much lower peak (1) and longer time lag (1) in contrast to 19/20/21. 2 × 1 for each element. Peak should be much higher (approx 3 times) for third mark or much more steeply rising limb for 19 – 21. If dissimilar start point on Y axis/or does not begin at Y axis – maximum 2. High rainfall total over the two days of 19/20 suggests high intensity which would lead to a steep rising limb (1). The higher amount on the first day would reduce lag time and increase the peak as stores would be fuller (1) saturation or lack of infiltration (1). Rainfall would flow overland (1) so faster transfer (1). Must relate back to hydrographs and make links.
Study Figure 2 which shows an area of deciduous forest. Explain likely effects of the forest on river discharge. 5 marks
The presence of vegetation will slow down the rate at which the water reaches the river, thus increasing the lag-time and reducing peak. This is due to the leaves especially that intercept the rainfall en route to the ground. This delays the progress of the water. Some will reach the ground as stemflow and drip, whilst some may never reach the ground and the river due to evaporation. As the forest is deciduous, the effectiveness of interception will vary, being less apparent during the winter when the leaves have been lost. The trees will also use some of the water to maintain growth and slow the speed at which water gets to the river and so the amount via overland flow and throughflow is much less. Reference to leaf litter soaking up water before infiltration. Level 1 (1 – 3 marks) Outlines the effect of reducing discharge / slowing down response. Begins to explain. Some use of appropriate terminology present at the higher end. Level 2 ( 4 – 5 marks) Explanation is clear / sequence given. More than one effect needed for L2. Refers to the features on photograph, e.g. density of leaf cover. Appropriate geographical terminology is used.
Describe and explain the formation of landforms resulting from rejuvenation. 15 marks A definition of rejuvenation is likely to form part of the answer - a renewal of the river’s energy as a result of a relative fall in base level. This will lead to a return to vertical erosion. It may be a result of a fall in sea level-eustatic change or an increase in the relative height of the land in relation to the sea - due to isostatic uplift (the ‘rebound’ following the end of glaciation) or due to tectonic activity. Landforms - knick point relates to the extent to which the river has created a newly graded profile to adjust to the new base level. It is identified by a break in slope and is usually marked by a waterfall and reflects the process of headward erosion as well as vertical erosion due to the renewed ability to erode vertically. River terraces - are the remains of the former flood plain - now abandoned as the river has eroded too deeply to access it; these may be paired - i.e. at the same level on either side of the channel. This is indicative of rapid down cutting. If it is slower as a result of more gradual uplift, the terraces will be present on different sides of the channel at different levels - unpaired terraces as the river has time to erode laterally. Continued….
Incised meanders - there are two types - entrenched when the cross section is symmetrical and ingrown where the cross profile is asymmetrical. Both result from an increase in the rates of vertical erosion - this is more rapid with entrenched meanders or can be the result of the presence of more resistant rock. With ingrown meanders, vertical erosion is less rapid, allowing some lateral erosion also. Reference to specific examples is not a requirement, but would be one way of enhancing the answer. Level 1 (1-6 marks) Describes at least one landform, two at the top end in general terms - may be definition - like. Begins to explain - will refer to basic processes - vertical erosion. Answer may be imbalanced - may clearly emphasise one element. Some use of appropriae terminology present at the higher end. Generic waterfalls (hard and soft layers of rock). Level 2 (7-12 marks) Description of at least two landforms is more specific and precise. Response is more balanced. Explanation is more focussed and there is a link between erosion and rejuvenation. Appropriate geographical terminology is used. Level 3 (13-15 marks) Clear, purposeful description that links to the process - a recognition of the different types of terraces, meanders. Explanation is clearly linked to the impact of rejuvenation on base level and vertical erosion. l landform d describe e explain 15 marks
Discuss the advantages and disadvantages of hard engineering as a flood management strategy. 15 marks. A definition of hard engineering is likely to form part of the answer. This is where structures are added so that the river channel is directly interfered with so that speed of flow is altered or level of storage is changed. There is often no concern for the environment and the element of control is strong. Specification refers to dams, straightening, building up levées and diversion spillways so reference to some of these is to be expected. Dams e.g. Three Gorges Dam. Advantages – effective at regulating the flow and controlling flooding. Can have an impact on the entire river – depending on size. Disadvantages – schemes are costly; interfere with river processes – deposition encouraged in calm waters behind dam and clearwater erosion after the dam. Reduction in abrasion conversely. Much less discharge downstream. Impact on habitats. Displacement of potentially very large numbers of people. Straightening e.g. Severn. Advantages – as resulting route is shorter it will remove water from area faster; cheaper than dams and quicker to implement. Disadvantages – can cause problems downstream and exacerbate the flood risk there; can interfere with river processes – faster flow increasing erosion; impact on meander development and can damage habitats. Continued….
Levées e.g. Mississippi. Advantages – can increase the capacity of river significantly and so effectively reduce flooding in certain areas. Disadvantages – can result in more severe flooding if levees are breached; water cannot return to river channel prolonging flood event, flood plain cannot develop. Diversion spillways e.g. Jubilee River, Maidenhead / Windsor area on Thames. Advantages – increases the capacity of the river by providing an alternative additional channel, especially during times of high flow; if done appropriately can be sympathetic to the environment and enhance it. Disadvantages – significant cost needed for major schemes; can lead to problems downstream and increase the flood risk. Level 1 (1 – 6 marks) Defines hard engineering. Describes how floods may be managed using hard engineering. Information likely to be generic – Basic advantages/disadvantages. Some use of appropriate terminology present at the higher end. Level 2 ( 7 – 12 marks) Describes hard engineering strategies. Description of how floods may be managed using hard engineering is more specific and precise. Clear link to advantages and/or disadvantages. (may be general references to advantages of dams). Probable imbalance to disadvantages. May relate to case studies. Appropriate geographical terminology is used. Begins to discuss. Level 3 (13 – 15 marks) Precise description of strategies linked to both advantages and disadvantages. (Greater balance) Focus on flooding. Case studies likely to be used in support. Specific terminology is used throughout. Purposeful discussion.
Compare and comment on the social and economic effects of flooding in two contrasting areas of the world. 15 marks Content will depend on case studies used. Flooding may be defined within the answer. There should be clear reference to both economic (those relating to monetary issues – in its broadest sense) and social (those relating to people – their well-being, health). Examples likely to refer to UK, Bangladesh. Economic likely to refer to costs to homeowners, insurance payments, impact on businesses, crops, costs of organising help – to council, government, aid agencies, those involved. Social likely to refer to deaths, homelessness – people displaced and provision for them, impact on state of mind, access to clean water, living conditions. Command is to compare and comment on – so there should be an integral account with similarities/differences drawn out and statement noting scale of similarities/differences, numbers affected, ability to cope, length of time to respond, etc. Continued….
Level 1 (1-6 marks) Describes the social and/or economic effects of flooding. Information likely to be generic – case study named only. Some similarities/differences apparent at top end. Separate accounts. Level 2 (7-12 marks) Description of effects of floods is more specific and precise – begins to distinguish between social and economic or this is implicit. Information relates to case studies – ‘rings true’ – some support. Begins to comment – may be tentative/implicit. May be imbalanced to one area and/or category. Similarities/differences are clear. Level 3 (13-15 marks) Precise similarities/differences of effects of flooding – distinguishes between social and economic effect explicitly. A balanced account – of areas and categories. Case studies are used in support – reference to facts/figures. Comment is explicit and perceptive.
Channel characteristics such as cross profile, wetted perimeter, hydraulic radius, roughness and efficiency change downstream. Describe and explain how channel characteristics change downstream. 15 marks Description should refer to channel characteristics such as cross profile, wetted perimeter, hydraulic radius, roughness and efficiency. There are links between some of these and to velocity, discharge and vertical erosion, lateral erosion and deposition processes. These will form the basis of explanation. Description should identify the changing width, depth and shape of the cross section, the increasing wetted perimeter (but note the impact of boulders near the source), the increasing HR, decreasing roughness and increased efficiency. Continued….
Examples of content include the following: Cross-profile – this refers to the width and the relative depth across the width. The relationship between these two will have a significant impact on the wetted perimeter – the length of the bed and banks in contact with the water. Near the source, this is likely to be small as the river is narrow and shallow, but will increase as the volume of water increases downstream. The relationship between these two characteristics is identified in the hydraulic radius (HR). This divides the cross-sectional area (determined by width × average depth) by the wetted perimeter. This is partly a measure of efficiency as the higher the HR the less water relatively there is in contact with the bed and banks in proportion to that away from them. Thus, there is less friction, greater velocity and greater energy left for erosion, transportation. The roughness of the channel – the extent to which there are large boulders or coarse material along the bed – affects the cross-sectional area, wetted perimeter and hydraulic radius. An increase in roughness will reduce velocity as a result of the need to overcome the increased contact and friction and so the river will be less efficient. Explanation should relate to velocity and discharge and how these change downstream. There may be reference to potential and kinetic energy and the importance of different processes such as vertical erosion near the source, the increasing prevalence of lateral erosion and the dominance of deposition in lower course. Continued….
Level 1 (1-6 marks) Describes channel characteristics and how they change downstream. Description is of individual characteristics. Description is partial – explanation likely to be absent – one-sided. Some use of appropriate terminology present at the higher end. Level 2 (7-12 marks) Description is more complete – begins to see links. Sequence is clear. Explanation begins to be addressed – with reference to process, energy, velocity, discharge. Appropriate geographical terminology is used. Level 3 (13-15 marks) Precise description of changes in channel characteristics. Links are sequential and/or detailed. Explanation is integrated relating to velocity, discharge, energy, process. Appropriate terminology is used throughout.
‘Soft engineering is a better river flood management strategy than hard engineering.’ Discuss this view. 15 marks There is a need to make clear why soft engineering strategies are preferred to hard engineering or vice versa. This is the likely route so there should be reference to the advantages of soft engineering and possibly also the disadvantages of hard engineering. There will probably be some description of the relevant strategies that may be adopted. Alternatively, candidates may disagree with the statement and provide advantages of hard engineering and disadvantages of soft engineering. The final option is to perceive the complementary nature of the two approaches and discuss this aspect. Advantages of soft engineering are likely to refer to its greater sustainability, its limited interference with a natural system, the ability to improve the environment at times and to work with natural systems so that wetlands and habitats may be restored/created, the relative affordability. Disadvantages of hard engineering relate to the extent to which there is change to the natural system and questions over its sustainability – the large scale of building dams and their environmental impact, as well as economic and social costs. Similarly, channelisation means that the flood risk may be increased downstream and habitats destroyed. Continued….
Advantages of hard engineering may relate to their effectiveness, especially in the short term, associated schemes for HEP, irrigation which give other advantages. Disadvantages of soft engineering relate to ineffectiveness in already built-up areas, the fact that flood warnings allow preparation but are not preventing damage from flooding. They will be seen as reducing the scale of risk rather than preventing flooding. The actual content will depend on the specific strategies considered and whether there is exclusive discussion of soft engineering strategies only. There may be reference to case studies – such as River Quaggy, London, Lincolnshire, Oxfordshire (Cherwell), Ouse, Jubilee River Channel, Carlisle, Three Gorges Dam, Colorado etc. Level 1 (Basic) 1-6 marks Identifies soft and/or hard engineering strategies. Refers to simple reasons why soft engineering is better. Some use of appropriate terminology present at the higher end. Coastal flooding response – if relevant, generic aspects. Continued….
Level 2 (Clear) 7-12 marks Describes strategies and advantages and / or disadvantages of soft and / or hard engineering. Begins to discuss why soft engineering strategies are better (or an alternative option). Uses strategies to illustrate points – will illustrate one aspect only or with imbalance e.g. advantages of soft engineering may be discussed with no reference to hard engineering. Case study material may be included in a descriptive way. Appropriate geographical terminology is used. Level 3 (Detailed) marks Clear, purposeful discussion that seeks to put a case for/against soft engineering or is aware of the complementary nature of the strategies. Advantages and disadvantages of soft and hard engineering are discussed. Strategies are effectively used to illustrate concepts. Case studies are used to make points. Specific terminology is used throughout.
Assess the relative importance of physical and human causes of river flooding. 15 marks There may be some discussion of the concept of flooding – which occurs when rivers exceeds bankfull level. There should be a recognition of the physical factors responsible – such as periods of heavy rain, especially when preceded by earlier wet conditions (Tewkesbury, Sheffield etc 2007), the role of snowmelt (Malton 2000 – 01), natural hazards such as Hurricane Katrina in New Orleans or deep depressions in areas such as UK, the part played by impermeable rock, steep slopes, shape and size of drainage basin, drainage density. There should be recognition of how these cause flooding, linked to rates of runoff versus infiltration and causes of rapid runoff. Human causes should also be discussed – with reference to urbanisation – building of impermeable surfaces and then installing drainage systems – deforestation and river management such as straightening, building of levees and dams being the most likely inclusions. Again there should be recognition of the impact of these and reference to how they cause floods. Examples/case studies are not a requirement, but are a useful way of illustrating causes. There should be an assessment of the relative importance that reflects the content of the answer. Continued….
Level 1 (Basic) 1-6 marks Identifies physical causes and/or human causes. Tentative links to how flooding results from e.g. intense rainfall. Information likely to be generic. Some use of appropriate terminology present at the higher end. Level 2 (Clear) 7-12 marks Seeks to explain how physical factors and/or people cause flooding - links to runoff and infiltration are present. There may be imbalance between the two causes. May relate to case studies/illustrate points made. Appropriate geographical terminology is used. Tentative/implicit assessment of relative importance. Level 3 (Detailed) marks Explains clearly how physical factors and people cause flooding – clearly appreciates sequence of events set in motion linked to drainage basin hydrological cycle. There will be balance between the two aspects. May use case studies/detail and purpose in exemplification. Specific terminology is used throughout. Explicit assessment of relative importance – probably suggesting overall importance of physical factors, but made worse by role people play.