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Erosion control in the tropics - Part 7

7 Measures to reduce runoff Often technical measures against erosion are not very beneficial in themselves. They should go hand in hand with cultivation methods and good guidance. An important question is whether the farmer himself can pay for the operations and/or execute them. | 7 Measures to reduce runoff Often technical measures against erosion are not very beneficial in themselves. They should go hand in hand with cultivation methods and good guidance. An important question is whether the farmer himself can pay for the operations and or execute them. The purpose of technical measures is to prevent water causing damage. This can be done by making better use of the available water for the crop water conservation and or by controlling the runoff water. These subjects are covered in this chapter. Another way is to develop a drainage system through which the runoff-water is collected and diverged before it reaches the agricultural land. Damage done by the uncontrolled runoff is then avoided. Drainage systems are explained in chapter 8. 7.1 Different levels of measures The catchment area is the area from which the runoff contributes to the discharge at a certain point in a stream or river. The borders of this area are determined by the so-called watersheds the tops of the sur-rouding hills. This means the farther downstream the larger the catchment-area and the larger the flow in the stream. Further the scale determines clearly the extend of the measures to be taken. This seems obvious however it determines a principle aspect of the problem. The number of people involved and therefore the level of cooperation. The people in the flood-prone areas will have most problems whilst the basic measures for prevention have to be taken mostly farther up in the hills. So not only can we distinguish here between different methods but it is also important to consider the level and the scale on which the measures are taken. This can be at farm level slope level or watershed level see figure 20 . 56 Erosion control in the tropics watershed level Figure 20 Catchment areas All measures will need regular maintenance in order to be effective in the long run. Farm level At farm level the starting point is that the land is used according to its potential. This is