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UNESCO G-WADI Workshop on Water Harvesting (cont.)
Workshop Report  |  Papers & Presentations |  Case & Regional Studies |  Participants

Session 2: Environmental and Societal Context

The environmental and societal context of rainwater harvesting was well illustrated by means of 4 presentations covering the Indian subcontinent, the Middle East and the Mediterranean semi-arid region. This session was essential since it exposed the significant role the public plays in first accepting and then integrating rainwater harvesting and managed aquifer recharge techniques within their environments. The session also revealed how crucial it is to understand the natural environment in its holistic way in order to fully exploit the total potential of RWH and MAR techniques and apply them in the most appropriate or ideal locations, adversely impacting the environment in the least way possible.

The water harvesting context in the Indian subcontinent was once again presented by Dr. Anupma Sharma. An overview of the role of societies in the successful implementation of RWH schemes in India, Sri Lanka, Bangladesh and Nepal were given. With the amount of rainfall in the Indian sub continent one would be mistaken that there are no water deficiencies. However the great difference in rainfall variability dictates otherwise. In 1947 the availability of water per capita stood at 6000m3, and in 2006 at 2000m3. These figures are still above the poverty line however the maximum amount of precipitation is only received in a minimal amount of hours. 70% of surface waters and a large proportion of groundwaters are known to be polluted.

Thus the freshwater crisis in this subcontinent has been inflicted by means of the rampant pollution of freshwater resources, inadequate attention, very low prices, uncontrolled boreholes and communities whose work is fragmented. Dug wells are reported to have increased in number from 3 to 9 million and sea water intrusion in coastal areas has become rampant. Rainwater harvesting is thus seen as an alternative source. Around 1-2% of India’s land captures rain providing a total of 950 million people 10 l a day with water!

Several watershed development programmes have been set up to enhance rainwater harvesting practices. Many of these campaigns have an underlying waterwatch motto and enable the rural population, executed by the village governing bodies, to actively participate in the introduction and upkeep of RWH schemes. The role of women is also significant in these campaigns and is encouraged. This often causes a positive snowball effect in small communities as more and more females are encouraged to take an active part in RWH implementation. As a result of these campaigns, water harvesting structures of capacity up to 18000M m3 of water were constructed by the Indian Government in Uttar Pradesh, 2003.

The Bangladesh case presented by Dr. Anupma revealed the benefits harvested rainwater can provide when it comes to providing alternative water to contaminated water supplies. Arsenic contamination is severe in the western and south western parts of Bangladesh. But most buildings are not designed for rainwater harvesting in these areas. Tin roofed houses require modifications through the utilisation of gutters.

In the case of Nepal 67% of the population have access to safe drinking water. Fog water collection is practiced but more importantly was the mention of indiscriminate rainwater harvesting from upstream users. It was pointed out by Dr. Anupma that upstream users have to care for downstream users when harvesting rainwater and therefore there is always a need for research in order to be able to anticipate the impacts by upstream RWH on downstream users.

Further social benefits of RWH were exposed through Dr. Droubi’s succeeding presentation on the use of RWH to alleviate poverty in rural areas. He related the ACSAD experience in the Arab Region. The trend in several Arab countries has been prolonged drought such as that of Cyprus (1991) and Jordan (1998/1999). Dr. Droubi clearly depicted the situation in Syria where average rainfall is about 1000mm in the mountainous areas during the winter months. Summer scarcity means that water is bought expensively. The wadis and terraces in the watershed are used to cultivate wheat. Outcrops of fissured limestone permit rapid recharge.

However poverty is a main characteristic of the area; the elderly are abandoned to make their own living whilst the economically active leave to find work in the city. ACSAD enabled the introduction of a new variety of wheat together with new crops including medicinal plants and fruit trees. Supplementary water sources were also seen to be vital prerequisites to curtail poverty in the area.

Thus modelling for the location of artificial lakes or dams was carried out and a hill reservoir using 1000 micron LDPE sheets for lining was constructed. The end result was a storage lake with a capacity of 7000m3. After creating the lake, water was pumped through 100m polystyrene pipes and tobacco was grown. A picture shown by Dr. Droubi revealed the significant difference between the rainfed and irrigated tobacco grown in the same field. Irrigation doubled the income and the introduced ACSAD varieties improved the local varieties.

Similar projects and outcomes resulted in Shihah, Syria and the Al-Ramaa area in Yemen. Pilot projects were attempted in 4 Arab countries in order to understand and simulate a model on water flow.

RWH in Semi-arid Island Environments
Issues relating to RWH in semi-arid islands followed and was presented by Ms Cardona from the Malta Resources Authority. Her talk explored the potential of small-scale domestic rainwater harvesting on the island of Malta by taking an integrated look at the physical, social, and economic environments. The extent to which domestic rainwater harvesting has been forgotten despite the fact of it being embedded within Malta’s history for centuries was emphasised The case study, based on residential and water professional interviews, examined the cost-effectiveness of RWH technology both at a local and the national scale and teases out the hurdles that have brought about its rejection residential and water professional interviews.

67% of original RWH structures are still used for agricultural and other purposes. From the study it was evident that island characteristics of smallness, contested land and limited space; lack of proper planning and enforcement have instigated the decline in the use of rainwater cisterns. Also a low shadow pricing of water, despite public perception that government water tariffs are high; and a high financial cost of cistern construction have further limited the potential of its widespread application. Increasing reliance on reverse osmosis desalination for water supply often makes RWH the less attractive option. Moreover small scale rainwater harvesting does not at present attract the required attention in order for it to be encouraged nationally.

In conclusion proper planning, enforcement, education and regulation, as well as policy integration seem to be key to unlocking the reluctance of RWH use.

Defining Sustainable Yields for Rainwater Harvesting
Prof. Howard Wheater closed this session by presenting his experiences relating to the definition of sustainable yields for rainwater harvesting. Prof. Wheater stressed at the start of his presentation that thinking about RWH leads to the setting up of methods for harvesting the rain which in turn lead to sustainable issues since a sustainable yield has to be predetermined from the start. Professor Wheater drew the participants’ attention to the need to consider the sustainable yield of rainwater harvesting systems and not just the methods of rainwater collection. In semi-arid and arid areas rainfall collection is not so straightforward because of its extreme variability. Therefore taking mean annual rainfall as an indicator to test the potential of rainwater harvesting in an area is far from being accurate. The intermittancy and interannual variability in rainfall needs to be taken into account.

In arid areas, high evaporation rates means that managed aquifer recharge is the most attractive option for increasing water availability. An example of the investment in recharge dams on the Batinah coastal plain of Northern Oman was given to illustrate this point. Such dams with restricted discharge outlets are able to retain water behind the structure and slow the downstream transmission of stormwater. In this way groundwater recharge is focussed behind and immediately downstream of the dam. In coastal environments the location of these dams can enhance recharge which in turn will combat the problems of saline intrusion in coastal aquifers.

The sustainable yield of these systems must be assessed and this is a complex task due to the spatial variability that exists within surface and groundwater interactions. This is why, as Professor Wheater highlights, there is a need for comprehensive monitoring network of surface and groundwater interactions. Equally important is the consideration of groundwater quality considerations. The few holistic studies that exist are often unavailable to the public sphere since they are unpublished works.

The definition of sustainable yields for managed groundwater recharge was portrayed through the case of a study carried out on a proposed recharge dam in a wadi system in Northern Oman whereby a modelling framework was developed to capture the spatial variability of rainfall, runoff generation and groundwater recharge. A stochastic rainfall generator was developed empirically form the available raingauge network. A specially designed rainfall-runoff model was created to generate the spatial distribution of runoff and flow routing in the wadi channel network. Transmission losses were also taken into account. This model could then be combined with groundwater model to see the groundwater response.

Such a study was deemed important because within the distributed rainfall-runoff model it was possible to explore the response to recharge dams of different sizes and locations, for a number of years of stochastically-generated daily spatial rainfall inputs. In that way the potential yields of alternative designs could be evaluated in a risk-based framework.

Modelling similar to this study is in its embryonic stage, has received little attention and needs to be developed further. Prof Wheater added that such modelling systems could also be linked with Global Climate Model scenarios of future climate, and hence evaluate the response to climate change.

A final important point was related to water quality. Enhanced recharge can improve groundwater quality. On the other hand rising water tables could mobilise naturally anthropogenically-generated pollution. Land use patterns and management effects on rainwater quality would also be needed to be incorporated within the modelling framework. When taken in their total potential these models can provide an extremely effective means of informing policy makers and simultaneously address the concept of integrated water resource management.

 



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