Wild weather

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Here are some of the ways in which scientists and engineers have worked with people to develop technologies that help with the effects of flooding.

!Floating gardens Floating gardens allow people to grow food on rafts that float when the floods arrive. They do not require large building projects like dams and flood barriers. The floating gardens give them somewhere to grow plants during the wet season that can then be planted out when the dry season comes.

!Floating gardens in Bangladesh are made from rafts of water hyacinth. These plants grow very rapidly in the wet season and are normally seen as weeds!

A mat of bamboo canes holds the water hyacinth plants together. Soil and fertiliser are added on top and then the seeds are planted in small balls of fertiliser directly into the rafts. The seeds germinate and the plants develop into healthy seedlings with a good supply of water. As the water levels fall in the dry season the rafts settle on the ground allowing the farmers to transplant the plants or to leave then where they are to grow.

!!!Dams and dykes Dams can be built to protect the land from seawater flooding. They prevent seawater from flowing upstream to damage fields in low-lying land in Bangladesh. The farmers can plant their seedlings and know that they will not be washed away.

But dams and dykes need large government investment. This takes time and is beyond the means of many poor farmers. The dykes also need maintenance and must be high enough to cope with not just this year’s flooding but also the rising sea levels, due to climate change, that will come in the next 20 years. They also do not protect against flood waters coming down from the rivers draining water from the higher ground.

Flooding and floating

Floating gardens Practical Action

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Although floating gardens have been successful for many people there are some who cannot make use of this farming technique. Some of the landless poor do not have access to areas where the gardens could be set up. Even when areas of water are available they can be some distance away from the household. Another difficulty that can arise is that the raw materials to make the raft may not be available. Gardens are relatively inexpensive to make requiring a small investment in fertiliser and seeds as well as the labour needed to construct them. Other materials such as the aquatic weed for the base of the raft can be obtained locally at no cost. The base of the raft is often made from water hyacinth, which is a common weed in many parts of the world where it clogs up water systems and damages the ecosystems and aquaculture within ponds. It is better to use mature water hyacinth as green water hyacinth will decompose too quickly and the raft will not survive the growing season. If water hyacinth is not available other materials can be used such as paddy straw, nalkhagra – a freshwater wetland tree, and any available organic materials such as azola, coconut straw, bamboo, and old rope. There is no fixed size of raft. Commonly, the rafts are around 8m long and 2m wide and are around 0.6 to 1m deep. The size of the raft can be made to suit the circumstances of the user. If there is a lack of space or if raw materials are in short supply then the rafts can be made smaller. Creating a floating garden The first step to making a floating raft is to collect the water hyacinth. Floating water hyacinth is overlaid with bamboo poles of appropriate length to the size of the raft being constructed and this mass of plant matter is taken to one bank to be worked on. Additional water hyacinth is collected with stick hooks and placed onto the bamboo layer and the thickness of the raft is built up. It is then woven into a buoyant raft. Once the raft’s basic structure has been created the bamboo poles can be pulled out. After around 7 to 10 days more water hyacinth is added to top up the existing structure then a mulch can be added on to the water hyacinth base. Soil, compost and cow dung are added to cover the base of the raft to a depth of around 25cm. The compost is made up from azola, a good nitrogen fixing plant, and other readily available organic matter. Seeds can then be sown. The technique used to improve the seeds’

Figure 4: The floating garden with its earth layer. Photo credit: Practical Action Bangladesh.

Figure 3: The garden begins to take shape. Photo credit: Practical Action Bangladesh.

Floating gardens Practical Action

2

Although floating gardens have been successful for many people there are some who cannot make use of this farming technique. Some of the landless poor do not have access to areas where the gardens could be set up. Even when areas of water are available they can be some distance away from the household. Another difficulty that can arise is that the raw materials to make the raft may not be available. Gardens are relatively inexpensive to make requiring a small investment in fertiliser and seeds as well as the labour needed to construct them. Other materials such as the aquatic weed for the base of the raft can be obtained locally at no cost. The base of the raft is often made from water hyacinth, which is a common weed in many parts of the world where it clogs up water systems and damages the ecosystems and aquaculture within ponds. It is better to use mature water hyacinth as green water hyacinth will decompose too quickly and the raft will not survive the growing season. If water hyacinth is not available other materials can be used such as paddy straw, nalkhagra – a freshwater wetland tree, and any available organic materials such as azola, coconut straw, bamboo, and old rope. There is no fixed size of raft. Commonly, the rafts are around 8m long and 2m wide and are around 0.6 to 1m deep. The size of the raft can be made to suit the circumstances of the user. If there is a lack of space or if raw materials are in short supply then the rafts can be made smaller. Creating a floating garden The first step to making a floating raft is to collect the water hyacinth. Floating water hyacinth is overlaid with bamboo poles of appropriate length to the size of the raft being constructed and this mass of plant matter is taken to one bank to be worked on. Additional water hyacinth is collected with stick hooks and placed onto the bamboo layer and the thickness of the raft is built up. It is then woven into a buoyant raft. Once the raft’s basic structure has been created the bamboo poles can be pulled out. After around 7 to 10 days more water hyacinth is added to top up the existing structure then a mulch can be added on to the water hyacinth base. Soil, compost and cow dung are added to cover the base of the raft to a depth of around 25cm. The compost is made up from azola, a good nitrogen fixing plant, and other readily available organic matter. Seeds can then be sown. The technique used to improve the seeds’

Figure 4: The floating garden with its earth layer. Photo credit: Practical Action Bangladesh.

Figure 3: The garden begins to take shape. Photo credit: Practical Action Bangladesh.

Weaving bamboo and hyacinth to make a raft

Covering the raft with soil, compost and cow dung

Dyke in Bangladesh

Wild weather

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Questions !1. Which flood defence system costs the most to build?

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2. Which system protects against incoming seawater from high sea levels?

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3. Which system would be easier to build quickly?

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4. You are an advisor to the Bangladeshi government on flooding. Which technologies would you suggest they could encourage farmers to use?

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5. You work for an international development organisation that helps people in coastal areas cope with the effects of climate change. Which technologies would you suggest farmers in these regions use and why?

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Flooding and floating

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