In this chapter I am going to describe the retention areas in more detail. They are in valleys like the water catchment areas and are therefore especially along the slopes vulnerable to erosion.
While in the water catchment areas, erosion will be prevented through a re-establishment of the original flora of the Atlantic Rainforest, the retention areas will serve as areas of nutrient exchange (phyto clarification plants, vegetable gardening) and have therefore, to be treated differently.
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In order to raise the percolation capacity of the ground, the off-flow of rainwater has to be slowed down. Especially at peak rainfall times, when the ground is not able to receive all the water, the slowing down devices like trenches and terraces will prevent erosion to happen. Optional on very steep slopes, topsoil has to be applied and secured through coconut fibre nets. These nets can also be used on any other location, where erosion prevention in conjunction with re-forestation will be applied.
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The design of the retention areas is generated through the flow of the water. At the very top of the valleys, all phyto-clarification plants are located, so that a nutrient exchange happens as early as possible (phosphor, nitrate, etc.) They are laid out in terraces, which find their limits in trenches. Right below them, rows of fruit trees should be planted, but in a way, that enough sunlight reaches the ground to enable ground vegetation, on this level, plaited branch barriers create the terraces and prevent the fast off-flow of rainwater. Trenches build the limits of this level. Below this level patches and terraces of vegetable gardens make up the lowest level of the retention areas. Here the patches are elevated with in-between trenches to allow flooding, and in case of rainwater excess, enable the water off-flow without damaging the crops.At the foot of the vegetable gardens an excess water tank can be build to help cover the irrigation demand during drier periods. |
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The functioning of the phyto clarification plants and their role in the nutrient exchange will be explained in detail in the grey and black water chapter.
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Retention areas: erosion prevention and nutrient exchange (373 kByte)
