Geography - GCSE - WJEC - Water

The different processes of erosion:

Hydraulic action - The force of water breaking the bed and banks

Abrasion - The rocks carried by the water smash against the bed and banks.

Attrition - The rocks carried by the river smash into one another.

Corrosion - The wearing away of rocks due to the acid in the water.

The different processes of transportation:

Solution - The dissolved materials carried along by the river

Suspension - The small particles carried along by the river

Saltation - The particles bouncing along the river bed

Traction - The large particles dragged along the river bed by the current

Deposition

• Happens when river loses energy.
• Can not carry material so material is dropped.

Occurs on a river bend, mouth of the river, when river flows onto flat ground or meets the tide.     (All which slow flow)

Meander

• Erosion occurs on the outside of the bend - causes lateral erosion. (sideways erosion)
• Deposition occurs on the inside of the bend.

Formation of a waterfall:

• Water flows over hard rock, onto soft rock.
• Abrasion occurs where the water is flowing over the soft rock.
• This causes the soft rock to erode vertically due to hydrochloric action.
• Forms a plunge pool and undercuts the hard rock due to lateral erosion.
• Hard rock collapses as there isn't enough soft rock to support it underneath.
• This cause the waterfall to retreat.

How a river landform can bring both benefits and costs to people and the environment:

Case Study: Niagara Falls

Tourist attraction - 28 million visitors per year.

Hydroelectricity - generates enough for 3 million homes.

However, habitat destruction and pollution - 28 million visitors need places to stay.

A delta is formed when the river meets the sea. The river loses energy and material is dropped. The river splits into smaller parts and land builds up between them. Over time, vegetation grows on the land forming a delta.

Case Study: The Ganges delta in Bangladesh

Positive impacts

Fertile and good for farming - home to 60 million people who farm crops like rice.

(this leads to farmers earning money and feeding themselves)

Negative impacts

Damages environment - removing vegetation like mangroves.

Ruins a natural habitat for wildlife, tigers, leopards, crocodiles and pythons. - Causes ecological problems - loss of animals >> damage to food chain.

• Steep sided valleys - water flows quickly - river rises rapidly - banks are burst.

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• Lack of vegetation (deforestation) - less waterinterceptedby roots - water flows quickly over surface - makes its way into the channel - rises rapidly - banks are burst.

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• Human development (increase run off as concrete) - does not allow water to infiltrate - water flows straight into the river.

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• Impermeable soil (clay) and rock (granite) - water remains on the surface - does not soak into the ground.

These are factors that could lead to flooding OR influence the lag time.

Flood hydrograph - shows the amount of time it takes for water in a storm to reach the river.  Lag time - the difference in time between peak rainfall and peak discharge of a river.

Case Study: Tewkesbury flood of 2007.

Flooding can damage properties - 800 people had damaged houses.

Houses prices drop due to difficulties with insurance and mortgages.

Businesses and services disrupted.

Mythe Pumping station was flooded cutting water off for several weeks. 

Cost Severn and Trent water £25 million to supply people with emergency water and repair damage.

Environmental damage - flooding farmland and loss of crops.

Widening and deepening the channel to allow more water to flow through the river.

• effective - more water to flow BUT expensive and difficult for large rivers (flow of water may have to be stopped to carry out the work)

Floodwalls or levees to allow water to rise without bursting it's banks

• good - allow river to rise significantly - done cheaply - sidewalks attracting visitors BUT block view of river - involve building on peoples land - levees can create a funnel effect where water flows more quickly down a river increasing flood threat.

Straighten river to speed up the flow thereby removing flood waters 

• Useful for boats - can reduce erosion of the river banks BUT may build on peoples property - problems further down the river - less erosion so less deposition so floodplains and deltas affected. 

Soft engineering allowing a river to flood in some areas which allows vegetation to soak up water

• Create wetlands which benefits plant and wildlife - attract tourists - trees natural looking defence - BUT flooding of farmland or property - trees take a long time to develop which means only a long term solution.