Languages:
The source document for this Digest states:
Numerous responses have been put forward to meet the ever-increasing demand for water. In some cases, the response focuses on how to compensate for the natural variability in the hydrological cycle in order to provide a continuously available resource. In other circumstances, the response focuses on overcoming the reduced availability in water quantity or quality that results from human and development impacts, from a demand management perspective.
Most water-short regions of the world with dry climates have long-standing water conservation traditions. These are being maintained or supplemented with demand-management practices. To meet increased demands, water resource management practitioners are augmenting the limited natural water supply with desalination, water reuse, enhanced groundwater recharge and inter-basin transfers.
However, regions with abundant water (tropical and cold climates) are accustomed to water supply schemes and tend to adopt management practices that are particularly adapted to those specific settings. It is often taken for granted that resources will remain relatively abundant and could be readily treated or replaced if polluted; that any disruption in ecosystem balance could be remedied; and that adequate water could be diverted and stored to overcome the inconvenience of seasonal flow variations. However, in these regions, impacts from human development have been more severe than anticipated. Water resources have been diminished in quantity and quality, and ecosystem habitats have become endangered to a point below their resilience levels. As a result, responses are emerging that include some of the same practices in demand management used in dry climates. In both water settings, it is increasingly recognized that maintaining and, where possible, restoring the state of the environment by keeping both aquatic and terrestrial aquatic ecosystems above resilience levels can provide substantial long-term benefits to a region’s water resources.
4a. Environmental flows for preserving ecosystems and increasing water resources
The heightened awareness of the important role played by ecosystems in terms of water resources and sustainability is a result of the recent focus on ‘environmental’ or ‘in-stream’ flows. Dyson et al. (2003) define environmental flows as follows:
- the water regime provided within a river, wetland or coastal zone to maintain ecosystems and their benefits. They provide critical contributions to river health, economic development and poverty alleviation.
The means for maintaining and restoring these flows under multi-use and competing demand situations are increasingly being considered in detail in many nations and basins. In some regions, environmental flow considerations are being integrated into water policy, legislation and regulations, and water management practices. South Africa (1997), Australia (CSIRO, 2004) and several USA states (e.g. Connecticut, Texas), among others, already have broadly encompassing legislation and in-field practices that take into account environmental flows. More research is needed to understand the water volumes, levels and quality needed to keep ecosystems resilient during seasonal variations and periods of climatic stress. Furthermore, a recognized additional challenge is how to introduce and embed this concept in the predominantly engineering-driven water management agencies of many developing countries so that the resilience of their basin- and watershed ecosystem is less at risk (see Chapter 5).
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, p.146
The source document for this Digest states:
Dealing with variability in water runoff in particular has led to centuries-old practices of intercepting, diverting and storing water so that adequate volumes would be available to match the needs and demands of the users.
Rainwater harvesting
Rainwater management, also known as harvesting, is receiving renewed attention as an alternative to or a means of augmenting water sources. Intercepting and collecting rainwater where it falls is a practice that extends back to pre-biblical times (Pereira et al., 2002). It was used 4,000 years ago in Palestine and Greece; in South Asia over the last 8,000 years (Pandey et al., 2003); in ancient Roman residences where cisterns and paved courtyards captured rain that supplemented the city’s supply from aqueducts; and as early as 3000 BC in Baluchistan where farming communities impounded rainwater for irrigation. Recently in India, it has been used extensively to directly recharge groundwater at rates exceeding natural recharge conditions (UNESCO, 2000; Mahnot et al., 2003). Reports from other international organizations focusing on this area5 indicate that eleven recent projects across Delhi resulted in groundwater level increases of from 5 to 10 metres in just two years. In fact, the application of rainwater management in India is likely to be one of the most updated and modern in the world. The site www.rainwaterharvesting.org provides links to cases where rainwater management has been successfully applied in different nations in both urban and rural settings. An advantage of the technique is that its costs are relatively modest and that individual or community programmes can locally develop and manage the required infrastructures (collection devices, basins, storage tanks, surface or below-ground recharge structures or wells). Larger rain harvesting schemes, which intercept runoff using low-height berms or spreading dikes to increase infiltration, have also been introduced in upstream catchments where deforestation has decreased water availability. The various methods of rainwater harvesting that have the potential to satisfy local community and crop demands are described in UNEP (2005).
[5 See
www.irha-h2o.org
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, 4b. Combating natural variability, p.147
The source document for this Digest states:
Diverting surface waters into nearby spreading basins/infiltration lagoons, ditches, recharge pits or injection wells to recharge alluvial or other types of aquifers are techniques used to deal with natural variability in flow, reduce evaporative losses, and obtain better quality water. Water diversion programmes being established around the globe are referred to as ASR (artificial storage and recovery) or MAR (managed aquifer recharge) (see Box 4.6). This practice is being applied in arid and semi-arid locations throughout the Middle East and Mediterranean regions. Runoff in ‘wadis’ (dry riverbeds that only contain water during times of heavy rain) that otherwise would discharge into the sea or evaporate, is collected behind earthen berms following infrequent but heavy rainfall. The water infiltrates into the underlying alluvial gravel thereby remaining available for substantively longer periods without the excessively evaporative losses that would typically occur from surface storage. In wetter areas, diversions into alluvium are used as a means not only to store and maintain groundwater-dependent ecosystems, but also to reduce the treatment needed for the water supplies systems taken from the alluvium further downstream.
BOX 4.6: MANAGEMENT OF AQUIFER RECHARGE (MAR) – AN EXAMPLE FROM VIET NAM
The Binh Thuan province is located along the coastal plain in the lower part of central eastern Viet Nam; its principal city is Phan Tiet, 200 km East of Ho Chi Minh City. The area of the province is approximately 8,000 km2, with a total population of 1 million.
Before 1975, the area was covered by a dense tropical forest, which was cleared to make room for rice fields and resulted in massive desertification. Due to an uneven rainfall distribution and a four-month period (from December to March) of very little precipitation, the area suffers from considerable water shortage during the dry season.
In order to combat desertification, improved practices in ecosystem rehabilitation as well as remediation techniques to restore aquifer systems and groundwater storage capacity are being developed. In particular, these techniques are being used in the Hong Phong sub-district (Bac Binh district), located about 25 km northeast of Phan Tiet, with an area of approximately 300 km2 encompassing three villages.
The geo-hydrological assessment of the area, consisting of a semi-permeable bedrock and porous material (sand dunes) with a thickness of up to 150 m, allows for the use of SAR (storage and aquifer recovery) techniques by redirecting rainfall during the rainy season and making use of the resource during the dry period (December–March).
The project’s implementation by UNESCO is ongoing and the results achieved thus far have allowed for the selection of the site for the Aquifer Recharge Project in the morphological depression of Nuoc Noi, where the aquifer water table is very close to the ground level. The use of the bank filtration technique is already producing satisfactory results as water quality increases. Groundwater can be abstracted and used, after natural filtration, for different purposes (human and agricultural).
Professional associations such as the US National Ground Water Association (US NGWA) and the IAH (International Association of Hydrogeologists) Commission on Managing Aquifer Recharge (MAR)6 in cooperation with UNESCO and other international donors, are actively supporting MAR with applied research, capacity-building and pilot projects. MAR programmes, some including injection of treated wastewaters, are being carried out in both developed and developing countries (e.g. in Australia, China, Germany, Hungary, India, Kenya, Mexico, Oman, Pakistan, the southern Africa region, Switzerland and the US).
[6
www.iah.org/recharge/MAR.html
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
4b. Combating natural
variability, Water Diversions, p.147
The source document for this Digest states:
The construction of dams to create reservoirs has frequently been our response to growing demands for water to provide hydropower, irrigation, potable supplies, fishing and recreation, as well as to lower the impacts and risks to our well-being from high-intensity events such as floods and droughts. These facilities collect natural runoff, frequently quite variable in its location, duration and magnitude, and store it so that its availability is more constant and reliable. Good information on the number and capacity of dams is essential to assess impacts and responses at the local, national and regional levels in order to optimize water resources management, but it is also needed to address issues related to global climate and water availability scenarios (see Chapter 5).
Though the creation of reservoirs enables higher water availability when and where it is needed, the construction of these facilities has had a considerable impact, both positive and negative, on the Earth’s ecosystems and landscapes and has resulted in modifications to the interactions among the components of the hydrological cycle. Despite increased benefits derived from the services reservoirs provide, there is ongoing debate about how to prevent and reduce the social and environmental consequences that come from building dams and creating reservoirs. Following considerable media attention and local actions some practices are changing. Large dam construction rates have slowed, at least temporarily, and there have been advances in the reconsideration of alternatives and design criteria. Some existing dams that no longer provide extensive services have been decommissioned. Lastly, existing reservoir operations and structures have been modified to allow releases. A balance between what enters and what is released is required to have a site’s upstream and downstream hydrological settings and supporting ecosystems sustained. When such a balance is achieved, the results are substantial. There are both added benefits and potential further value to the role of reservoirs in development scenarios.
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, 4b. Combating natural variability, Storing water in
reservoirs, p.148
The source document for this Digest states:
The transfer of water from one river or aquifer basin to another basin has long been used as a way to meet water demands, particularly in arid and semi-arid regions. It occurs often when large populations or, more commonly, agricultural demands have outstripped existing water resources. Even in advanced national development stages, some basins can have surplus water resources while others face shortages. Major long-distance schemes exist in many nations and new ones are in development. Linking the Ganga-Brahmaputra-Meghna system with other rivers in India is part of the solution being offered to counteract extensive recurring droughts and floods. For example, Shao et al. (2003) present the situation in China where there are seven existing major transfers and seven more planned or under consideration. They describe a large-scale south-to-north basin transfer involving the Yangtze and Yellow Rivers’ basins which, when completed, would divert 450 km3/yr. They also point out some of the impacts of such a large scheme. Multi-disciplinary approaches allow evaluation of the feasibility and sustainability of transfer schemes. Global experience has shown that although the transfer of water among basins has been identified as a hydraulically and technically feasible response, before proceeding with such potential changes, broad social and environmental considerations must be taken into account.
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, 4b. Combating natural variability, Transferring water among
basins, p.148
The source document for this Digest states:
Asano and Levine (2004) recently summarized the more important challenges associated with water reclamation and reuse. They noted that the technique of water reuse is being applied in many countries including the United States, Mexico, Germany, Mediterranean and Middle Eastern countries, South Africa, Australia, Japan, China and Singapore. Its increased application is being facilitated by modern wastewater treatment processes, which advanced substantially during the twentieth century. These processes can now effectively remove biodegradable material, nutrients and pathogens so the treated waters have a wide range of potential applications (Table 4.7). On a global scale, non-potable water reuse is currently the dominant means of supplementing supplies for irrigation, industrial cooling, river flows and other applications (Asano, 1998). The reuse of potable waters has been an accepted global practice for centuries. Settlements downstream produced their potable water from rivers and groundwater that had circulated upstream through multiple cycles of withdrawal, treatment and discharge (Steenvorden and Endreny, 2004; Asano and Cotruvo, 2004; GW MATE, 2003). San Diego gets 90 percent of its current municipal water supply from a wholesale water provider but in future that amount will decrease to 60 percent with the supplementary supply coming from reclaimed water and desalination (USGS, 2005). Similar programmes are emerging in many other large urban centres worldwide where there are limited or less readily available freshwater supplies. Similarly, riverbeds or percolation ponds have been used to artificially recharge underlying groundwater aquifers mainly with wastewater.
Table 4.7: Potential applications for reclaimed water
Recent documents from WHO (Aertgeerts and Angelakis, 2003) and the US EPA (2004) address the state-of-the-art aspects and future trends in water use, both of which predict increased development and use of the above-mentioned practice to augment water supply sources in order to meet demands. The WHO guidelines for wastewater reuse first published in 1995 are being updated with a planned release date of 2006 (WHO, 2005). According to water reuse surveys (Lazarova, 2001; Mantovani et al., 2001), the best water reuse projects in terms of economic viability and public acceptance are those that substitute reclaimed water in lieu of potable water for use in irrigation, environmental restoration, cleaning, toilet flushing and industrial uses.
The annual reclaimed water volumes total about 2.2 billion m3, based on 2000 and 2001 figures from the World Bank. Recent projections indicate that Israel, Australia and Tunisia will use reclaimed water to satisfy 25 percent, 11 percent and 10 percent, respectively, of their total water demand within the next few years (Lazarova et al., 2001). In Jordan, reclaimed water volumes are predicted to increase more than four times by 2010 if demands are to be met. By 2012, Spain will need to increase its reclaimed water use by 150 percent and, by 2025, Egypt will need to increase its usage by more than ten times. A number of Middle Eastern countries are planning significant increases in water reuse to meet an ultimate objective of 50 to 70 percent reuse of total wastewater volume. The growing trend of water reuse is not only occurring in water-deficient areas (Mediterranean region, Middle East and Latin America), but also in highly populated countries in temperate regions (Japan, Australia, Canada, north China, Belgium, England and Germany). This method of augmenting natural water sources is becoming an integral component to many water resources management plans and future use policies.
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, 4c. Water reuse, p.148
The source document for this Digest states:
Desalination is used mainly in water-scarce coastal arid and semi-arid areas that are located inland where the only available water source is saline or brackish groundwater. The technology has been well established since the mid-twentieth century and has evolved substantially to meet the increased demands of water-short areas. Awerbuch (2004) and Schiffler (2004) report on the global application of desalination capacity and the most recent advances and challenges. According to the latest statistics in 2002 from IDA (International Desalination Association)7 about 50 percent of global desalination takes place in the Middle East, followed by North America (16 percent), Europe (13 percent), Asia (11 percent) Africa (5 percent) and the Caribbean (3 percent). South America and Australia each account for about 1 percent of the global desalination volume. Globally, the contracted capacity of desalination plants is 34.2 million m3/day converting principally seawater (59 percent) and brackish water (23 percent). In terms of the uses of desalinated water, municipalities are the largest users (63 percent), followed by substantial industry use (25 percent). The cost of producing desalinated water has fallen dramatically in the past two decades. Recently built large-scale plants produce fresh water for US$ 0.45/m3 to US$ 0.50/m3 using reverse osmosis (RO) systems and US$ 0.70/m3 to US$ 1.0/m3 using distillation systems. The energy consumed to drive the conversion is a significant part of the cost and ranges from 4 to 15kWh/m3 depending on factors such as the technique used, the production rate of the facility, and the quality of the equipment (US NRC, 2004).
Much of the conversion is likely to continue to be heavily reliant on fossil fuels with its associated air pollution. The challenge of what to do with the brine waste by-product remains. Today it is disposed of by discharge into the ocean or surface waters, sewage treatment plants, deep-well injection, land application or further evaporation in ponds. Each of these methods has potentially adverse environmental impacts. The cost of concentrate disposal for inland locations often limits its applicability in these locations. Schiffer (2004) recommends the establishment of an internationally agreed-upon environmental assessment methodology for desalination plants to enable the impacts from different facilities to be consistently compared.
Future uses for desalination are emerging and IDA expects that, with increasing demand and the up-scaling of processes, it will continue to be applied for the development of economies in coastal areas to partially meet the demands of recreation and tourism, environmental protection, the military, and irrigated agriculture. One interesting emerging concept proposes combining desalinated water with aquifer storage and recovery (DASR) (Awerbuch, 2004; Pyne and Howard, 2004). This approach has the advantages of allowing storage and recovery of large volumes of water while minimizing facility throughput with lowered operating costs. Stored volumes could be used to meet daily or seasonal peaks in water demands while maintaining a steady desalination rate.
[7 See
www.idadesal.org
Source & ©:
UNESCO,
The United Nations World Water Development Report 2 (2006)
Section 2: Changing Natural Systems,
Chapter 4 (UNESCO
& WMO, with IAEA),
Part 4. Matching Demands to
Supply, 4e. Desalination, p.150
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