What you'll need to know...
KEY CONCEPT - How physical and human factors exacerbate and mitigate flood risk for different places
Hydrograph characteristics (lag time, peak discharge, base flow) and natural influences on hydrographs, including geology and seasonality
How urbanization, deforestation and channel modifications affect flood risk within a drainage basin, including its distribution, frequency and magnitude
Attempts at flood prediction, including changes in weather forecasting and uncertainty in climate modelling
Flood mitigation, including structural measures (dams, afforestation, channel modification and levee strengthening) and planning (personal insurance and flood preparation, and flood warning technology)
• Two contrasting detailed examples of flood mitigation of drainage basins
Hydrograph characteristics (lag time, peak discharge, base flow) and natural influences on hydrographs, including geology and seasonality
How urbanization, deforestation and channel modifications affect flood risk within a drainage basin, including its distribution, frequency and magnitude
Attempts at flood prediction, including changes in weather forecasting and uncertainty in climate modelling
Flood mitigation, including structural measures (dams, afforestation, channel modification and levee strengthening) and planning (personal insurance and flood preparation, and flood warning technology)
• Two contrasting detailed examples of flood mitigation of drainage basins
Starter: Watch this 2023 from The Guardian!
Hydrograph Characteristics...
Hydrographs are important tools for understanding how rivers respond to precipitation and changing environmental conditions over time. Characteristics such as lag time, peak discharge and base flow reveal how quickly water moves through a drainage basin and how flood risk can vary between places. Natural factors including geology, soil type and seasonality strongly influence these patterns by affecting infiltration, storage and runoff. Studying hydrographs helps explain the dynamic relationship between physical processes and flooding, while also highlighting why some environments are more vulnerable to extreme river discharge than others.
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Objective: To describe the characteristics of a hydrograph. Analyse the reasons for spatial and temporal (short term and long term) variations in hydrographs. Starter: Watch the first video to the right hand side. Why doesn't the stream rise as soon as the heavy rain starts? Need to know: There are many key controls that affect drainage basins and ultimately the shape of the resultant flood hydrograph: Basin size Basin Shape Elevation and slope Rock type Rainfall type Rainfall intensity These controls should not be viewed in isolation to one another. It is rare that just one of these control mechanisms would contribute towards a major event in a drainage basin. They should therefore be viewed as an interacting set of factors (systems thinking) that contribute towards the behaviour of the basin. Task 1 - Use this resource from Tutor4u to take focused notes on how basin controls impact on the discharge and flow of a river and ultimately on the features of a flood hydrograph. |
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Task 2 - Go to the GATW site by clicking here and complete the living graph activity.
Task 3 - Take some notes from this site on how human activity can impact on river hydrographs.
Factors affecting flood risk within a drainage basin...
Human activities such as urbanization, deforestation and channel modification can significantly alter the movement of water within a drainage basin and increase flood risk. The removal of vegetation, expansion of impermeable surfaces and engineering of river channels often reduce infiltration and accelerate surface runoff, leading to shorter lag times and higher peak discharge. These changes can influence the distribution, frequency and magnitude of floods across different places and scales. Understanding how human actions interact with physical processes is essential for examining the causes of flooding and the challenges of managing river systems sustainably.
Objective: To discover how urbanization, deforestation and channel modifications affect flood risk within a drainage basin, including its distribution, frequency and magnitude
Task 1 - Watch the three videos below and study the three pieces of information below too. Make notes on the worksheet embedded of the three factors that affect flood risk in terms of its distribution, frequency and magnitude.
Exam Corner - Paper 1 - 10 Marks
Examine the impacts of human activity on river hydrographs. [10]
Attempts at flood prediction...
Attempts to predict flooding rely on advances in weather forecasting, hydrological monitoring and computer modelling to estimate when and where extreme river discharge may occur. Improved satellite technology, real-time data collection and forecasting systems have increased the accuracy of short-term flood warnings in many regions. However, uncertainty remains a major challenge, particularly in climate modelling where changing precipitation patterns, storm intensity and seasonal variability can be difficult to predict. Understanding these uncertainties highlights the complexity of flood management and the challenges of preparing for future environmental change in different places.
Objective: To recognise and be able to evaluate the attempts at flood prediction, including changes in weather forecasting and uncertainty in climate modelling
How Flood Prediction Has Changed
1. Advances in Weather Forecasting:
2. Use of Geographic Information Systems (GIS) and Remote Sensing:
3. Hydrological and Climate Models:
4. Increased Focus on Uncertainty:
5. Community and Policy Integration:
In summary: Flood prediction has become more accurate and data-driven, but uncertainties, especially due to climate change, mean predictions must be used alongside risk management strategies.
1. Advances in Weather Forecasting:
- Improved technology like satellites, radar, and computer models now provide more accurate and timely weather forecasts.
- High-resolution forecasting allows meteorologists to predict localized rainfall events, which are often responsible for flash floods.
- Forecasts can now be updated hourly or in real-time, giving better early warnings.
2. Use of Geographic Information Systems (GIS) and Remote Sensing:
- GIS helps map flood-prone areas and model flood scenarios.
- Remote sensing (from satellites and drones) tracks rainfall, snowmelt, and river levels across large regions quickly.
3. Hydrological and Climate Models:
- Hydrological models simulate how rainfall flows into rivers and causes flooding. These are now more detailed and can include land use, soil type, and urban drainage.
- Climate models are used to assess long-term flood risk under climate change scenarios (e.g. more intense rainfall due to global warming).
4. Increased Focus on Uncertainty:
- Climate modelling has inherent uncertainties due to complex systems and limited historical data.
- Forecasts now often include probability estimates (e.g. a 70% chance of flooding), helping planners and communities understand risks better.
- Scenario planning is used to prepare for multiple possible outcomes.
5. Community and Policy Integration:
- Flood warnings are now often shared through apps, SMS alerts, and social media.
- Governments and international organizations use predictions to improve disaster preparedness and response.
In summary: Flood prediction has become more accurate and data-driven, but uncertainties, especially due to climate change, mean predictions must be used alongside risk management strategies.
Types of uncertainty “there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know.“
Donald Rumsfeld, US Defence Secretary 2001-2006
How does uncertainty arise?
......so we often cannot discriminate between competing models
(Professor Paul Bates, University of Bristol).
- We have incomplete knowledge of the real world - Even our best understanding of processes or the current state of the system may still be wrong
- Time, money and computer power are limited so models are approximations
- We often cannot measure everything we need to know so we often cannot measure everything we need to know
- Even for approximate models we may require further assumptions and all data has error
......so we often cannot discriminate between competing models
(Professor Paul Bates, University of Bristol).
Task 1 - Use the information above and your own research to put together an essay plan to answer the following Paper 1 Option A question:
2 a. Examine the impacts of improved weather forecasting and climate modelling in the prediction of flood events. (10)
2 a. Examine the impacts of improved weather forecasting and climate modelling in the prediction of flood events. (10)
Flood mitigation - Part 1: Structural measures...
Flood mitigation involves a range of strategies designed to reduce the impacts of flooding on people, infrastructure and environments. Structural measures such as dams, afforestation, channel modification and levee strengthening aim to control river discharge and manage the movement of water within drainage basins.
Artificial levee protecting the city of Toulouse from a repeat of the impacts of the 1875 flood.
Objective: To evaluate the success of dams, afforestation, channel modification and levee strengthening as flood mitigation schemes.
Complete this piece of work on the worksheet from the previous section of work.
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Task 1 - Using the embedded Slideshare presentation above as your primary source of information, as well as the three video resources above, evaluate* the success
1. Dams - Use China as your context.
2. afforestation - (Himalayan context here)
3. channel modification
4. levee strengthening - (Toulouse context here)
....as flood mitigation schemes.
Your evaluation should cover the pros, cons, context (place where this happens) and evaluation of each of the four techniques. You should state which type of approach each fits in with (hard or soft).
*Evaluate (AO3): Make an appraisal by weighing up the strengths and limitations
1. Dams - Use China as your context.
2. afforestation - (Himalayan context here)
3. channel modification
4. levee strengthening - (Toulouse context here)
....as flood mitigation schemes.
Your evaluation should cover the pros, cons, context (place where this happens) and evaluation of each of the four techniques. You should state which type of approach each fits in with (hard or soft).
*Evaluate (AO3): Make an appraisal by weighing up the strengths and limitations
Flood mitigation Part 2 - Planning...
Alongside structural measure approaches, planning strategies including flood warning technology, personal insurance and flood preparation help communities improve resilience and reduce vulnerability to flood events. Examining these different responses highlights how physical and human factors interact in the management of flood risk across different places and scales.
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Objective: To evaluate personal insurance, flood preparation and flood warning technology as effective ways of mitigating against floods.
Complete this piece of work on the worksheet from the previous section of work. |
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Task 1 - Take notes on the three ways of mitigating against the flood risk using the note taking framework below.
These are heavily focused on the United Kingdom, a HIC that has seen an increase in severe flood events in recent years partly due to urban sprawl, a reported affordable housing shortage in the South East and subsequent issues with building on flood plains.
Task 2 - Read this 2022 article about the ability of the poorest people in the United Kingdom to afford flood insurance. Pay attention to the section entitled '‘We could be creating flood risk ghettos‘. Make notes on the worksheet.
Fine tuning your Paper 1 skills:
Evaluate the contribution individuals and communities can make towards mitigating their local area’s vulnerability to flooding(10)
These are heavily focused on the United Kingdom, a HIC that has seen an increase in severe flood events in recent years partly due to urban sprawl, a reported affordable housing shortage in the South East and subsequent issues with building on flood plains.
Task 2 - Read this 2022 article about the ability of the poorest people in the United Kingdom to afford flood insurance. Pay attention to the section entitled '‘We could be creating flood risk ghettos‘. Make notes on the worksheet.
Fine tuning your Paper 1 skills:
Evaluate the contribution individuals and communities can make towards mitigating their local area’s vulnerability to flooding(10)
* mark scheme for the question above available in the sample exam pack released by the IB and available on their site. Question 2B - Option A
Managing the Flood Risk - Two contrasting examples
Detailed examples of flood mitigation demonstrate how different places respond to flood risk according to their physical geography, level of development and population pressures. The River Garonne in Toulouse highlights the use of floodplain management, forecasting systems and river monitoring to reduce the impacts of seasonal flooding within an urban environment. In contrast, Tokyo has developed large-scale engineering solutions, including underground flood diversion systems and reinforced channels, to protect one of the world’s largest urban populations from extreme rainfall and river flooding. Comparing these examples reveals how flood mitigation strategies vary between places in response to differing environmental and human challenges.
Case Study 1 - Toulouse and La Garonne (Europe).
Click here to find about more about the history of flooding in Toulouse (in French). Then watch the video above to show what the city is doing to protect a vulnerable population of more than 1.4 million people.
Below, you can see some Google Street View images showing various means of flood protection around the River Garonne in central Toulouse. The first street view on the left hand side shows you a gate that closes across the road called Avenue de la Garonette. To see this gate at work in a recent flood event, click here.
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Many residents living along the River Garonne in Toulouse are unaware of the potential flood risks to their homes. In addition, there is limited understanding of the flood protection measures that are in place to reduce the impacts of a major flood event on the city and its population.
Your task is to produce a short PowerPoint presentation that could be used by the local government of Toulouse to inform and educate the public about how flood risk is managed.
- One slide should include a satellite map of Toulouse with key locations of flood prevention techniques.
- On each subsequent slide, locate one of the flood prevention techniques listed above on the map. There should be a photo to show the technique.
- For each technique, write a short explanation describing:
- how the strategy works
- how it helps to protect vulnerable populations and reduce flood impacts
- how the strategy works
Case Study 2- Tokyo and the tunnel flooding system (Asia)
Task 2 - Watch the video above and complete the activities on the worksheet below.
Exam practice.
With reference to one or more named floodplain, evaluate the costs and benefits of different stream management strategies. (10)
