The Ganges Delta

The main two rivers are the Ganges and the Brahmaputra. Distributaries, such as the River Meghna, are tributaries which leave at a delta.

All of the rivers drain into the Bay of Bengal and have created the Sunderbans. These are delta islands created by the millions of tonnes of silt. Cumecs of snow melt and monsoon rains (up to 250cm) result in dynamic changes in the hydrograph and shape of the delta.

Formation of a Delta A delta is a flat triangular low lying area of land at sea level. A delta is a flat triangular low lying area of land at sea level.

Conditions for Conditions for delta delta formation:formation:

1. River with very large load

2. Sea current too low to be able to remove large sediment load.

River erodes rock and soil and the force of the river transports the load downstream towards the sea.

River deposits load as it slows and as it meets the sea, the speed reduces drastically and deposition on the sea bed occurs. Clay and salt undergo a chemical reaction and stick together, so becoming heavy, and sink first, lighter particles are dropped later.

Deposition develops spits and bars with lagoons. Sediments may block a river course and deposition divides the river into several smaller distributaries as water seeks a new route. The lagoons fill with sediment and begin to develop a solid appearance. The deposited material is called alluvium and is very fertile. The distributaries mean that the river spreads out across the delta and the river flows into the bay at many different points.

Over the centuries the Ganges has continued to deposit more sand, silt and clay which has formed the fan shaped platform of the delta. The delta extends seaward as sediments are deposited at the mouth of the river in the Bay of Bengal. Bangladesh is slowly built up and out of the Bay form these deposits. The oldest part of the delta near to the original land is colonised by plants and swamps dry out.

Monsoon Climate of Bangladesh

Low Pressure

High pressure

June 22nd – Summer Solstice

Sun is overhead Tropic of Cancer, meaning low pressure at Cancer (Bangladesh) and high pressure at Capricorn (Australia) . Winds flow from South to North, from high pressure to low pressure, and over the warm seas in-between, cyclones may develop.

September 22nd and March 22nd – equinoxes

The three seasons in monsoon climate are:

1. Dry and cool – October to Feb

2. Dry and hot – March to May

3. Wet and hot – June to October

Low Pressure

High pressure

December 22nd – Winter Solstice

Sun is overhead the Tropic of Capricorn meaning high pressure over Bangladesh and low pressure over Australia. Winds flow from North to South, from high pressure at Cancer to low pressure at Capricorn.

Sun overhead = higher temperatures = air is warmer = air is less dense and can carry moisture = air rises = low pressure created.

Tropical Storms

•Tropical cyclones form when a mass of moist air over a tropical sea is strongly heated by the sun, to over 27 degrees.

•The warm moist air rises rapidly and is replaced at sea level by air being drawn in to the area of low pressure.

•The rising warm air and the in air blowing air swirls around the central area, anticlockwise in the northern hemisphere, clockwise in the southern hemisphere. Winds spin towards land gaining strength and ferocity.

•The rising air forms huge thunderclouds around the central cloudless eye. It is calm in the eye, but winds are violent just outside the eye and weaker as you move further away.

•The storm moves along a storm track until it blows out usually inland from the tropical sea where it formed. It loses energy as it travels over land because there is no supply of warm water to drive the system.

1. Sky starts to cloud over, winds increase, sea choppy

2. Cloud builds up, rain, winds strong, sea rough

3. Tall thunder clouds with heavy rain very strong winds sea rough

4. The eye – clear skies, no cloud, little wind, because it is the only place where air is sinking.

5. Tall thunder clouds again with heavy rain very strong winds, very sea rough

6. Sky clears only a few clouds, winds gentle, seas calm.

29th April 1991

Bangladesh cyclone killed 138,00+ people, and caused $2 billion of

damage. Winds reached 160mph and pressure went as low as

898mb.

Effects of a Tropical Storm Primary effects:Primary effects:

•Winds exceeding 130km/h

•Flooding of villages and farmland due to heavy rain

•Strom surges

•Loss of houses, animals and crops

•People drowned

•Communication links broken

•Contaminated drinking water

Secondary effects:Secondary effects:

•With no communication links, people died because emergency services could not access them.

•Emergency aid cannot reach victims due to lack of communications

•Crops destroyed meaning that people will starve and have no seeds to plant next year.

•Diseases like cholera spread in contaminated water supplies

•No crops and death of cows means no income for families so they cannot afford to repair homes

•Trauma of losing friends and family.

River causes:

•Deforestation of the Himalayan foothills increases the speed of run off and soil erosion. Silt clogs the rivers causing them to overflow their banks.

•Peak flow coincides with the two rivers. Ganges snow melt is in spring and early summer, and monsoon rains are between June and September.

•Brahmaputra snowmelt is spring and early summer, and monsoon rains are May to October. Ground becomes saturated causing rapid surface run off.

90% of people live who live in the country are landless peasants who live by subsistence rice farming on the fertile delta. Delta shifts in floods, meaning land moves, especially in areas around the Sunderbans. This makes Bangladesh one of the poorest countries in the world.

75% of the country is covered by many feet of water during floods, and foreign aid is necessary. 40 million people experience loss and approximately 1 million homes are damaged or destroyed.

Sea causes:

•Tropical cyclones increase the amount of rainfall

•Strong winds and low pressure cause Storm surges. This is when low pressure over an area of sea can cause it to rise by 2m, because water molecules expand. The funnelling effect of the Bay of Bengal in addition to this can cause a rise of 7m in Bangladesh.

Prevention

1. Embankments developed or increased. Reinforcing coastal banks is expensive for a country like Bangladesh.

2. River channels are dredged to clear sediments

3. Artificial dykes put along coast

4. Dams built to control flow of water

5. Young mangrove trees planted on flood embankments to break the force of the tidal waves caused by cyclones.

Flood Preparation

1. Improve satellite weather forecasting to give better predications so that people can remove themselves from danger

2. Raising the mounds that people live on so that they are above the level of the highest flood

3. Build concrete storm shelters so that people are protected

4. Improve structure of roads, and make telephone and power supplies higher above flood level, so they are not affected by water level, and roads mean aid can be easily distributed.

Relief

1. Short term – food, water, shelters

2. Medium term - clean water supplies to stop the spread of diseases like cholera. Establish clean shelter areas

3. Long term - help people to return to their homes, provide them will seeds so they can plant next years’ rice crop, animals to replace lost cattle. This is essential if the area is not to become dependent on foreign aid.

Subsistence Rice Farming in Bangladesh

Farmers in Bangladesh often have large families to support. This results in a high dependency ration, that is, the number of people which a working must support is greater than that of a developed country.

They have small farms, perhaps 1 acre – much smaller than a British farm. They can often loose crops due to floods, and must borrow money in order to buy seeds. They can get caught in the poverty cycle.

Poor farming techniques

Low yield of Food

No surplus to sell

No money for tools or fertiliser or seeds

Little investment

InputsInputs

High temperatures, over 21 degrees throughout year

Rich soils, silt deposited annually by Ganges and its tributaries during monsoon floods

Water buffalo provide manure and are used in preparing paddy fields

Hand labour rather than machinery because of small size of the plots

Labour to build embankments around the padi fields, to build irrigation canals, prepare fields and to plant, weed and harvest the crop.

Processes Processes

Rice planted in nursery beds

When monsoon rains flood padi fields, rice plants are transplanted

Rice harvested

Winter wheat planted

Wheat harvested

Vegetables may be grown

Chickens may be kept

OutputsOutputs

Rice

Vegetables

Chicken (meat and eggs)

Wheat

May: Nursery beds above flood level prepared and manured

June: Rains, rice seeds planted in nurseries. Padi fields manured and ploughed.

July-August: Seedlings transplanted into padi fields

September – October: weeding

November-December: fields drained, rice cut and dried, threshed and winnowed before storage.

January - February: Fields ploughed, 2nd crop planted. Could be rice if enough water, otherwise beans, wheat or peas

March – April: 2nd crop harvested

Advantages of Delta for farming Advantages of Delta for farming and settlementand settlement

•Numerous distributaries supply water for irrigation after monsoon rains have ceased; waterlogged paddy fields are necessary for rice growing

•More than one rice planting is possible, called dual cropping

•Soils are very fertile because river alluvium carried by the Ganges is rich in nutrients derived from land upstream

•Multi cropping, growing more than one crop at the same time, means that cash crops like sugar cane can be grown rather than just subsistence crops.

•Swamp conditions are ideal for rice growing

•Higher, older parts of the delta remain fertile, and is suitable for growing wheat as second crop, because no new alluvium is deposited and therefore is not as fertile.

Disadvantages of Delta for farming and Disadvantages of Delta for farming and settlementsettlement

•Low lying land is susceptible to changes in water levels from sea and river, so land is often flooded

•Soils are easily saturated by heavy prolonged rainfall during monsoon and so land floods easily

•Lack of shelter from violent cyclone winds especially near to coast

•Unconsolidated sands and silts which form the land is easily removed by erosion when the large number of distributaries are flowing at bank full. This results in massive erosion or river banks, and the creation of meanders. The land shifts and is constantly changing shape.

•Rivers frequently change their course as erosion occurs on river bends. Some villages may lose land, others gain it as fresh deposition occurs where water is slower.

•Land is overpopulated because of its productivity

•Rice labour, as well as the farming of jute and sugar cane, is labour intensive so this encourages a high density of population.

The Green Revolution was when it was attempted to introduce technology into farming in Bangladesh, eg, machinery, scientific farming, higher yielding seeds

It was hoped that technology would increase food production so that people could have more food to eat and sell.

Successes

• Increased food production

•Fall in food prices

•HYV grow faster, so an extra crop can be grown

•Yields are more reliable as HYV are disease resistant

•Other crops like vegetables can be grown to add variety to local diet.

•Some commercial cash crops like sugar cane can be grown and sold to raise income levels

•As HYVs are not as tall as traditional varieties they can resist heavy rain and strong winds

•Farmers earnings have increased due to using HYVs, and so farming families have a better standard of living.

Failures

• HYVs need large amounts of fertiliser and pesticides which increase costs and can harm water supplies

•HYVs need a more reliable and controlled source of water. They are more vulnerable to drought or water logging. Irrigation increases costs and can lead to Salinisation.

•HYVs are more susceptible to attacks from pests

•Many of the poorer farmers who do not own the land that they farm cannot afford to buy seeds, tractors and fertiliser, and so have become poorer.

•Mechanisation has increased rural unemployment and migration to towns

•Farming has become less sustainable.

Salinisation is caused by irrigation.

1. Irrigation of water

2. With no drainage, the subsoil becomes waterlogged and water table rises.

3. High temperatures cause rapid evaporation

4. Evaporation of water leaves a white crust of salt

5. Groundwater becomes salty

6. Salt concentrates around the roots of plants, and plants wither.

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Cooperative farmingCooperative farming was an alternative to the green revolution. It allowed farmers to work as a group to: borrow money from the government, sell surplus grain at a better price, gain government loans to buy land, pool resources to buy machinery, build new grain stores, and buy fertilisers cheaply. This gives cooperative farmers a better income than tenant farmers, who cannot afford to buy machinery or fertilisers, who have to borrow money at high interest, and who have to give half of the crop to landowners.

Intermediate Technology – improving production by using methods which are low in cost, use local materials, fulfil a local need, and suit the skills and knowledge of local people. Examples of this include biogas fermentation: when cow dung is fermented and methane is created to cook with.