There are various techniques to preserve and use harvested rainwater. Canal is one of them. A Canal is a long narrow place that is filled with water and was created by people so that boats could pass through it or to supply fields, crops, etc.., with water.
Water harvesting can best be described as all activities to collect available water resources, temporarily storing excess water for use when required, especially in periods of drought or when no perennial resources are available. The starting point is the collection of natural water resources from rainwater, fog, runoff water, groundwater or even waste water, which otherwise would have escaped.
World water resources are facing dramatic changes as a result of global climate change, high water demands, population growth, industrialisation and urbanisation. As climate change leads to more extreme variations, water harvesting solutions must cope with both extreme rainfall and extreme droughts. Extreme rainfall requires good flood protection and diversion structures. Extreme drought requires large storage capacity and more emphasis on groundwater replenishment. In some cases, droughts last so long that alternative water sources are required, which means that water rationalisation schemes must be developed in advance.
To respond to water scarcity and unequal distribution, new techniques need to be explored and old techniques revisited. Small-scale water harvesting techniques provide a direct solution, especially in rural and drought-prone areas. Local storage of water is increasingly important for ensuring water availability and food security for rural and urban populations, especially in developing countries. This is particularly the case in areas with dry seasons where perennial rivers and fresh groundwater are not available or difficult to reach. In urban areas dam construction, long distance conveyance of water or desalinisation may provide options for ensuring water availability. However, such solutions are generally too costly and complicated for rural water security. Rural populations require low-cost systems that can be constructed, operated and maintained with a high degree of community involvement and autonomy. Water harvesting may reduce the need for deep well drilling or other costly investments in piped water supplies. Water harvesting can also have a positive impact on soil conservation, erosion prevention, groundwater
replenishment and the restoration of ecosystems.
Despite its tremendous potential, water harvesting has not received adequate
recognition from policy makers and engineers. Water harvesting techniques are often considered unsophisticated or ‘traditional’, while water quality is not always guaranteed and unit costs can be high compared to supplies in humid countries. Moreover, these techniques require a high degree of flexibility and adaptation to the local situation. Many NGOs lack the capacity or interest to upscale and institutionalise successful local innovations, and this can contribute to lack of recognition by policy makers.
Most good practices applied by small-scale farmers or development workers are developed by themselves through trial and error, by building on indigenous knowledge, or have resulted from the modified application of ideas introduced from outside. Often, these local innovations go unnoticed. This booklet gives an insight into small-scale water harvesting techniques all over the world. Some may form a good basis for larger scale application.