One sixth of the world's population and one quarter of the land all over the world is affected by desertification (N'Djamena 2002). The United Nations Conference on Environment and Development (UNCED) agenda of 1992, cited in (N'Djamena 2002), states that "in order to reduce poverty in desertification-affected areas, both a cause and consequence of environmental degradation, attempts must be made to restore degraded lands and to provide adequate freshwater resources for consumption by human beings and livestock, as well as for crops."
The aridity of areas is understood in terms of low average precipitation or water availability (N'Djamena 2002). Aridity is mainly a permanent feature and activities in these regions are meant to deal with the constant dryness there. There is a need to harvest the water potential in these areas to meet the demands of drinking water and water needed for irrigation.
The Need for Sustainable Development of Water
The sustainable management of water has become an inevitable issue in the arid regions around the world. In certain parts of the world, the shortage of fresh water led to situations threatening long-term ecological and environmental problems coupled with numerous health issues (Al-Qudah and Abu-Jaber, 2009). In few decades, it will be very evident that the conservation of water resources is one of the most important concerns in various parts of the world (N'Djamena 2002).
As one of the most vital necessities and natural resources, water is indispensable for survival and development. Arid and semi-arid area in different parts of the world experience irregular and insufficient rainfall leading to lack of agriculture and shortage of fresh water. This can lead to desertification and drought that can be catastrophic for agriculture and survival of the humans respectively. In areas like Sahara (N'Djamena 2002), UAE (Murad et al., 2007), Jordan (Al-Qudah and Abu-Jaber, 2009), arid areas of Africa (IHP 2004), Western India (Sharma 1997), Vienna (Froehlich and Yurtsever, 1994), the rainfall is scarce and the dry season dominates for more than 6 months with annual rainfall below five hundred millimetres.
Twenty percent of the world's population does not have access to clean water (N'Djamena 2002). Coping with water requirement may have many socio-economic repercussions. In such situations, it is of dire importance to conserve as much water as possible and look for new resources of water. Solutions are necessary and interventions are required. Apart from meeting the requirements of fresh water needs of the people, there is a need to conserve the water and facilitate irrigation.
Water Management in the Arid Areas
The rapid advancement in science over the years has placed us at a point where we can actively and efficiently deal with desertification and shortage of fresh water in arid areas. The development in water management can be brought in by initiatives from the government and participation of the individuals to create a collaborative effort (Chaichi 2006). Water resource management is a complex exercise and has often failed due to the failure to integrate it in to the global approach of economic development of these areas (N'Djamena 2002).
Water management is associated to a number of problems that may have technical and socio-economic implications. While the technical issue can be sorted out, the socio-economic problems can only be resolved by developing strategies to sustain economic development through water management. Many traditional and modern scientific methods have been used to manage water in the arid areas but no single technique that has not adapted to the socio-economic context of the area has been successful (N'Djamena 2002). There is a need for certain efficient techniques that can work together or individually with a goal of developing the socio-economic status of the area as a whole by water conservation.
Some of the common techniques used in the arid and the semi-arid areas are (N'Djamena 2002):
Artificial Lakes
Micro-catchments
Spreading Bunds
Semi-circular Bunds
Trenches
Contour Earthen Bunds
Contour Ridging
Bench Terracing
Permeable Stone Dams
De-Salination of Water by Solar Energy (El Nashar et al., 2007)
Rainfall Run-off modelling (Sharma 1997)
Two very commonly used techniques are the Micro-catchments and the Contour Earthen Bunds, which are used regularly in most of the countries all over the world to counter desertification and to successfully harvest water.
Micro-Catchments
Micro-catchments are a very common technique employed to conserve fresh water in the arid area in different parts of the world. These consist of two parts: the runoff area and the basin area. The water is balanced using water balance equations of the runoff and the basin area and combined in the water balance of the micro-catchment (Boers et al., 1986). The performance of the system is measured using the water balance. Effective Catchments Water harvesting (MCWH) is very beneficial in the storms when there is sufficient runoff to allow deep infiltration into the profile without any evaporation (Boers et al., 1986). Water is not lost on the surface only, but by deep percolation as well.
Fig 1: Volume of water in infiltration basin as function of water depth. {Retrieved from Boers et al. (1986)}
MCWH is a very viable and useful technique suitable for the arid areas with around 25mm annual rainfall (Boers et al. 1986). The loess soils of these areas form a perfect surface crust. The Micro-catchments do not need extensive engineering activities and are easy to construct. One of the most useful benefits of constructing micro-catchments is that the local population can be involved in the construction to save resources and time.
Fig 2: A comparison of yields and relative benefits of micro-catchment RWH at Kisangara. Results are with and without consideration of the area used as a RPA. {Retrieved from Hatibu et al., 2003}
Fig. 2 gives mean grain yields per unit area cultivated for the different RPA: RRA treatments in a study carried out Hatibu et al. (2003) in southern Kilimanjaro region of Tanzania. An increased yield per unit area cultivated is noticed. On a total system area basis (i.e. including the uncropped catchment), however (line sixth of the table), decreases in production are observed (Hatibu et al., 2003).
Advantages
1. Multi-purpose: The ground water can be used for dry times, when there is a scarcity of runoff water. It can also be used to design watering places at regular intervals distributing the human and animal population according to the carrying capacity of the area, thereby preventing concentrations around wells. "Spacing between these watering points and volumes of water can be designed in accordance with walking distances and sizes of herds" (Boers et al., 1986).
2. Large Scale Production: The production of water can be enough to last for months and can be used for large populations.
3. Ground water is replenished (N'Djamena 2002).
4. Completely adaptable to the local environment (Boers at al., 1986).
Disadvantages
1. Costly - requires huge investments
2. Some upkeep required: Upkeep is required for maintenance.
3. Can harbour water-transmitted diseases. Stagnation of water (N'Djamena 2002).
Contour earthen bunds
Areas that are not suitable due to poor water resources preventing required water distribution can efficiently be irrigated with contour earthen bunds. The farmers block the rivers completely with earthen bunds to supply water to the surrounding paddy fields (Hoshikawa and Kobayashi, 2003). This traditional technique of providing fresh water to the field in the arid regions is very useful but has been ignored since the advent of modern irrigation techniques (Hoshikawa and Kobayashi, 2003).
This technique varies from place to place depending upon the riverbed slope. Contour bunds are used in different parts of the world for soil and water conservation (Hudson 1987). These contour bunds are constructed on grades with ties in the basin and to reduce the damage in case of over-topping, a stone wall is erected on the lower side of the bund (Hudson 1987). This type of water spreading technique is very useful in valleys and depressions; can also be used in lower slopes.
Fig 3: Improved Soil Moisture from Contour Bunds {Retrieved from Hudson (1987)}
Advantages
The groundwater is replenished by using earthen contour bunds (N'Djamena 2002). Deep infiltration of water on lighter soils.
Low cost-per-hectare co-efficient (N'Djamena 2002).
Very easy to build and requires almost no external engineering activities (Hudson 1987).
Disadvantages
Less effective on heavier soils as the infiltration is low (Hudson 1987)
Limited lifespan due to wear and tear of the earthen bund (N'Djamena 2002). Regular upkeep may be required.
No guarantee of a stable yield and there is a danger of damaging the crops in the low plots (Hudson 1987).
Uneven crops and only a small part of the field are cropped in the lower slopes (Hudson 1987).
Conclusion
Each climatic and geographical region supports different water conservation techniques. No one technique can be applicable in all the arid areas of the world. The effective technique must fulfil the criteria of the socio-economic and technical requirements along with the environmental requirements of the place. For long-term conservation and supply of fresh water, low-cost techniques are the most appropriate that can be easily replicated by the local communities. An integrated water development program is required to develop techniques using both traditional and modern methodologies to provide the best results.
Combining different techniques can also be a very useful measure to counter scarcity of fresh water in the arid zones. Moreover, water harvesting techniques need to be aligned with techniques for conservation of water to long term water development of a region.
