hydrolgy case studies

1.1 the drainage basin system a good example of water budget graph:

Malaga is on the Costa del Sol in Southern Spain.

There are many farmers who produce fruit and vegetables for the tourist hotels so therefore farmers need a great deal of water for their crops to grow during the summer tourist season

The annual rainfall is over 500mm but very little falls in the summer during the extreme heat

So therefore from June to October there is a soil moisture deficit and evaporation exceeds precipitation.

So therefore in Malaga behind the mountains there is large reservoirs where winter rainfall is stored for use in the summer.

1.3 river channel landforms:

the Nile delta located in Egypt

Deltas are depositional features which form when the a river meets the sea or runs into a lake. When the river meets the sea there is a loss of velocity and therefore this leads to a loss of energy which means that the river deposits its load.

orange river in South Africa is an example of rapids

rapids are common in the upper course of a rive they form at places where the gradient is steep and the river bed is rocky

Niagara falls in Canada

waterfalls form where a horizontal layer of hard rock lies on top of a layer of softer rock in a river valley.

The soft rock underneath is eroded more quickly by the river and gradually a plunge pool develops.

The splashing water and eddy currents in the plunge pool undercut the hard rock layer above. this eventually creates an unsupported overhang of hard rock. The overhang then collapses into the plunge pool. then a waterfall is formed

1.4 the human impact three gorges dam- hard engineering

the three gorges dam is a hydroelectric dam that spans the Yanxi river which is the third largest river in the world.

28,000 people helped to build the dam

more than 4 million people were displaced in order to make room for the dam and its resevoir

Economic impacts:

It cost $25 billion to build

the dam will produce the same amount of electricity as 18 nuclear power stations

enviromental impacts:

there is large problems with water quality and sediment

the resevoir induces earthquakes in the area because of the weight of the water in the dam

more clean air as it saves burning 15 million tonnes of coal a year

the river quaggy- Soft engineering

River Quaggy Restoration, South-East London – Soft Engineering Case Study

Location & Background:

The River Quaggy is a small, urban tributary of the River Ravensbourne, flowing through South-East London, including boroughs such as Lewisham, Greenwich, and Bromley. The river flows through highly urbanised areas, making flood management both essential and challenging.

Since the 1960s, the river had been heavily artificially managed through the construction of culverts, straightened channels, and concrete embankments to reduce flood risk. Much of the river was diverted underground to make space for urban development and transport links. However, this hard engineering approach was seen as environmentally damaging and aesthetically unappealing by local residents.

Public Response & Need for Change:

Local communities and environmental groups voiced concerns about:

  • The loss of natural river environments.

  • Negative impacts on biodiversity, especially species like water voles.

  • Limited public access and amenity value due to the buried river.

There was a strong demand for a sustainable, ecological, and community-focused solution. As a result, a soft engineering restoration project was proposed and implemented, especially focusing on Sutcliffe Park in Greenwich.

Soft Engineering Measures Implemented:

1. River Restoration and Re-naturalisation:

  • The River Quaggy was 'daylighted', meaning it was brought back above ground after decades of being buried.

  • A new meandering channel was cut through Sutcliffe Park, restoring the river’s more natural flow pattern.

  • This improved aesthetic value, public access, and wildlife habitat quality.

2. Creation of a Flood Storage Area:

  • The park itself was re-landscaped and lowered to act as a floodplain. During heavy rainfall, this flood storage area can safely hold excess water.

  • A new artificial lake was created to hold overflow from the river during peak discharge events.

  • These features help attenuate flood peaks and protect surrounding urban areas like Lee Green from flooding.

3. Ecological Enhancements:

  • Wetland vegetation, such as reeds, was planted along the banks to:

    • Stabilise the riverbanks.

    • Reduce the impact of erosion.

    • Provide habitats for birds, amphibians, and insects.

  • The river corridor has become a green space supporting urban biodiversity and ecosystem services.

4. Community Benefits:

  • The restored river and park area offer recreational space for walking, cycling, and leisure.

  • It serves as an educational resource for local schools and environmental awareness.

  • Property values in the area have also seen an increase due to the improved green infrastructure.

Disadvantages and Challenges:

  • Potential River Meandering: If not managed properly, natural meandering of the river could damage park infrastructure or alter the usability of the recreational space.

  • Sediment Deposition: Frequent flooding and sedimentation could lead to raised floodplains, potentially reducing the effectiveness of flood storage over time.

  • Maintenance Needs: Although more sustainable, soft engineering still requires regular maintenance to prevent vegetation overgrowth or blockages.

Evaluation:

The River Quaggy restoration is widely considered a model of successful urban soft engineering, integrating flood risk management, ecological enhancement, and community engagement. While there are limitations, the long-term benefits to biodiversity, sustainability, and urban livability outweigh the risks, especially when compared to the former hard engineering approach.

the Aral sea- Modification to catchment stores and flows (Abstraction)

located in between Kazakhstan and Uzbekistan

the Aral sea began shrinking in the 1960s when the Soviet irrigation schemes took water from the rivers that were feeding the aral sea. This therefore greatly reduced the amount of water reaching the aral sea. By 1994 the shorelines had fallen by 16 metres and the surface area had declined by 50%

As a result Salanity (the amount of salt in the water) began to increase which meant that large amount of fish were killed and salt from the dry seabed had reduced soil fertility.

flooding in Bangladesh 1998

Flooding in Bangladesh, 1998 – Case Study Profile

Geographical Context:

Bangladesh is a densely populated, low-lying country located on the delta of three major rivers: the Ganges, Brahmaputra, and Meghna. Around 60% of the country lies less than 6 metres above sea level, making it highly vulnerable to riverine, flash, and coastal flooding. The country is situated downstream of the Himalayas, where meltwater significantly increases river discharge during the summer.

Causes of Flooding in 1998:

The 1998 floods were among the most severe in Bangladesh's recent history. A combination of physical and human factors contributed to this extreme flood event:

  • Monsoon Rainfall: The region experienced exceptionally heavy monsoon rains from July to September. Rainfall levels were far above average, saturating the ground and increasing runoff into rivers.

  • Himalayan Snowmelt: Meltwater from glaciers in the Himalayas flowed downstream, adding to the already high discharge in the river systems.

  • Confluence of Peak Flows: The three major rivers — Ganges, Brahmaputra, and Meghna — all peaked simultaneously, causing their floodwaters to converge and overwhelm the delta.

  • High Tides and River Backflow: Coastal high tides impeded the seaward flow of rivers, resulting in backflow and increased inland flooding.

  • Deforestation and Poor Drainage: Deforestation in the Himalayan foothills reduced interception and increased surface runoff. Urbanization and poor drainage in cities like Dhaka worsened surface water flooding.

Impacts of the 1998 Flood:

  • Extent and Duration: At its peak, around 50% of the country was submerged under water up to 3 metres deep, with flooding lasting for up to 67 days in some areas.

  • Agricultural Damage:

    • 800,000 hectares of agricultural land were submerged.

    • Significant crop loss, including rice paddies, led to widespread food insecurity and economic hardship.

    • Over 26,000 livestock were killed.

  • Human Impact:

    • Over 1,000 fatalities were reported.

    • More than 25 million people were displaced or affected by floodwaters.

    • Waterborne diseases such as cholera and dysentery spread rapidly due to poor sanitation and contaminated water supplies.

  • Economic Consequences:

    • Extensive damage to infrastructure, including roads, railways, bridges, and embankments.

    • Businesses were forced to shut down, and trade was disrupted.

    • Total economic loss was estimated at over $2 billion.

Coping and Management Strategies:

  • Traditional Adaptations:

    • Many homes and roads in flood-prone rural areas are constructed on raised platforms (plinths) above typical flood levels.

    • Farmers grow flood-resistant rice varieties scuba rice, including deep-water scuba rice that can survive in water up to 1 metre deep and grows as much as 20 cm per day to stay above water.

  • Flood Defences:

    • Over 10,000 km of levees (embankments) have been constructed to protect settlements and farmland.

    • Raised flood shelters are used to provide refuge for people and livestock during flood events.

  • Disaster Management:

    • Government and international NGOs coordinated emergency relief efforts, including the distribution of food, water, and medical supplies.

    • Long-term strategies include the Flood Action Plan (FAP), aimed at improving flood forecasting, early warning systems, and structural defenses.

Evaluation:

While Bangladesh has a high level of resilience and traditional coping strategies, the 1998 floods exposed the limitations of existing infrastructure and the need for more integrated and sustainable flood management. Climate change, population growth, and continued deforestation pose increasing challenges for future flood mitigation.