The fresh water available in the earth is just 3%. Rain is one of the major sources of Freshwater, which we hardly consider preserving. Rainwater harvesting is a technique of collection and storage of rainwater into natural reservoirs or tanks, or the infiltration of surface water into subsurface aquifers (before it is lost as surface runoff). Even we can collect water from fog and dew! In this article we see various methods of Rain water harvesting, how to construct such harvesting facilities and many more info.
The reasons for using rainwater harvesting systems answer three questions:
- What: Rainwater harvesting will improve water supply, food production, and ultimately food security.
- Who: Water insecure households or individuals in rural areas will benefit the most from rainwater harvesting systems.
- How: Since rainwater harvesting leads to water supply which leads to food security, this will greatly contribute to income generation.
|Rainwater Harvesting TECHNOLOGIES|
|Rooftop||In situ||Surface water||Groundwater recharge||Fog and dew|
Rooftop rainwater harvesting
Rainwater harvesting refers to structures like homes or schools, which catch rainwater and store it in underground or above-ground tanks for later use. One way to collect water is rooftop rainwater harvesting, where any suitable roof surface — tiles, metal sheets, plastics, but not grass or palm leaf — can be used to intercept the flow of rainwater in combination with gutters and downpipes (made from wood, bamboo, galvanized iron, or PVC) to provide a household with high-quality drinking water. A rooftop rainwater harvesting system might be a 500 cubic meter underground storage tank, serving a whole community, or it might be just a bucket, standing underneath a roof without a gutter. Rainwater harvesting systems have been used since antiquity, and examples abound in all the great civilizations throughout history.
Rainwater harvesting requires at least an annual rainfall of 100-200 mm. Many places in Latin America have rainfalls of about 500 millimeters per year. It is suitable even when the roof is small. For example a 5 x 6 meters (that is to say 30 square meters) house, with 500 mm annual precipitation, receives a rainfall of 15.000 liters on its roof; this is a sufficient amount for a family formed by 5 members.
|– Possible in almost any climate
– Rainwater generally meets drinking water quality standards, if system is well-designed and maintained
|– Storage is needed to bridge dry periods|
In situ rainwater harvesting
In arid and semi-arid regions, where precipitation is low or infrequent during the dry season, it is necessary to store the maximum amount of rainwater during the wet season for use at a later time, especially for agricultural and domestic water supply. One of the methods frequently used in rainwater harvesting is the storage of rainwater in situ. Topographically low areas are ideal sites for in situ harvesting of rainfall. This technique has been used in the arid and semi-arid regions of northeastern Brazil, Argentina, and Paraguay, primarily for irrigation purposes. The in situ technology consists of making storage available in areas where the water is going to be utilized.
Generally this technology is simple and easy to use. Governmental organizations and the agricultural community generally work together to support and promote the in situ rainwater storage. Educational and information programs should be provided to inform users of the benefits of this technology, and the means of implementing rainwater harvesting while preventing soil loss.
This technology increases water supply for irrigation purposes in arid and semi-arid regions. It promotes improved management practices in the cultivation of corn, cotton, sorghum, and many other crops. It also provides additional water supply for livestock watering and domestic consumption. In situ is applicable to low topographic areas in arid or semi-arid climates.
Extensive use is found in northeastern Brazil, in the Chaco region of Paraguay, and in Argentina. It can be used to augment the water supply for crops, livestock, and domestic use. With the mechanization of agriculture, its use has diminished, but it is still recommended for regions where the volume of rainfall is small and variable. The approach used depends primarily on the availability of equipment, the nature of the agricultural and livestock practices, and the type of soil.
|– This technology requires minimal additional labor.
– It offers flexibility of implementation; furrows can be constructed before or after planting.
– Rainwater harvesting allows better utilization of rainwater for irrigation purposes, particularly in the case of inclined raised beds.
– Rainwater harvesting is compatible with agricultural best management practices, including crop rotation.
– It provides additional flexibility in soil utilization.
– Permeable in situ rainwater harvesting areas can be used as a method of artificially recharging groundwater aquifers.
|– In situ rainwater harvesting cannot be implemented where the slope of the land is greater than 5%.
– It is difficult to implement in rocky soils.
– Areas covered with stones and/or trees need to be cleared before implementation.
– The additional costs incurred in implementing this technology could be a factor for some farmers.
– It requires impermeable soils and low topographic relief in order to be effective.
– The effectiveness of the storage area can be limited by evaporation that tends to occur between rains.
Surface water – general
Rainwater that is not captured directly, used by agriculture, or absorbed into the ground becomes surface water. Surface water harvesting includes all systems that collect and conserve surface runoff after a rainstorm or in intermittent streams, rivers, or wetlands for storage in open ponds and reservoirs. This can provide water for direct household use (treatment is generally required), irrigation, livestock, and aquaculture. Storage can also be the goal of collecting surface water, whether through open reservoirs or direct infiltration to aquifers below ground. Storing water in an aquifer conserves water better as it prevents evaporation, unlike open reservoir systems.
Climate change considerations
Cement made for water collecting structures, in a time of drought, can be made poorly due to less (or polluted) water used in the cement-making process. Higher heat from climate change will increase evaporation rates in reservoirs, or floods may damage infrastructure and increase runoff volumes. These effects and more are listed and tips are given to adapt the water system to climate change conditions.
|Various Types of Surface rainwater harvesting|
Groundwater recharge – general
Groundwater recharge is the enhancement of natural ground water supplies using man-made conveyances such as infiltration basins, trenches, dams, or injection wells. Aquifer storage and recovery (ASR) is a specific type of groundwater recharge practiced with the purpose of both augmenting ground water resources and recovering the water in the future for various uses.
Climate change considerations
- More storage capacity needed to overcome seasonal dry periods and to reduce floods.
- Higher rainfall intensities may exceed infiltration capacities. Create storage, enhanced infiltration or artificial recharge.
- Lower rainfall results in the need for transport and storage of water from other areas.
- Changes in vegetation will cause changes in evapotranspiration, surface runoff, erosion and sediment transport/deposition. This requires water and soil conservation measures, like terracing.
Fog and dew collection
Fog collection (or fog harvesting) is an innovative, environmentally appropriate, socially beneficial and economically viable use of fog, rain and dew as sustainable water resources for people in arid regions of developing countries. Fog is composed of enormous numbers of tiny water droplets. The wind blown droplets can be collected by a plastic mesh. Typical fog harvesting in a well selected desert environment would be 5 liters of water per square meter of mesh per day.
Dew harvesting (or dew collection) is simply taking advantage of water vapor in the atmosphere to harvest clean and potable water through condensation, a passive process that allows water particles to return to the earth in a pure form. Dew harvesting has been practiced by humanity as far back as ancient times, in areas where rainfall and groundwater resources are scarce. When there is any humidity at all in the air and there is a surface that is cool enough to provoke condensation, dew will condense on that surface until the humidity is gone. Vegetation in desert regions have developed modifications that allow them to collect their own humidity from the air, for example, and through efforts of reforestation in desert regions this technology has advanced abundantly around the world.
Courtesy : Akvopedia.org