Session 3: Case Studies and Modern Practice
Managed Aquifer Recharge
Mr Ian Gale from the British Geological Survey gave a realistic view of managed aquifer recharge stressing that often MAR is simply seen as a panacea for water supply problems worldwide and that not enough attention is given to the actual evaluation of the effectiveness of such structures. Thus, it was highlighted that MAR should be evaluated in its totality by considering its potential in different climatic, hydrogeological and socio-economic conditions.
This important evaluation of the impacts of MAR structures was depicted using 3 cases whereby 3 research sites in India, were established and monitored. These were Satlasana, Gujarat; the Kolwan Valley, in the Maharashtra state and Kodangipalayam in Tamil Nadu. All 3 sites were representative of different hydrological and socio-environmental characteristics and thus two studies; a physical and socio-economic one were carried out to obtain further understanding of each sites uniqueness. Baseline surveys included geological mapping; the identification of hydrogeologically important features and topographical surveys. Several components such as rainfall, evaporation rates, groundwater levels and surface flows, climate, and sediment flow had to be monitored. In addition to this water samples had to be systematically collected to determine the quality of the water in the local wells in order to assess any possible change in water quality brought about by the MAR structures.
Attention was brought to the fact that the findings of the 3 sites are only preliminary since inter-annnual and annual variability in climate dictates that monitoring over a long-term period is required to obtain a more precise picture. From these initial findings, however, it was brought to the fore, that the effectiveness of each recharge structure in the states was dependent upon rainfall, geology and the actual usage of water abstracted. In the Gujurat case, for instance, actual spilling of the check dam resulted due to the sudden and short duration of the torrential storm. Because of the coarse nature of the sediments in the headwaters of the catchment, rapid infiltration of water to replenish the aquifer resulted. Also, the stream flow was likely to have infiltrated further downstream if taken at a larger scale, thus reducing exposure time to be evaporated.
On the other hand at the Kolwan Valley site, the available storage was a constraint on the amount of additional water that can be recharged since the aquifer was of low storativity. Therefore recharge brought about by the dams has a short transit time since it resurfaces as baseflow. The highest increase in recharge was recorded in the Tamil Nadu site of Kodangipalayan since the aquifer is exploited to such an extent that natural recharge is insufficient to fully replenish the aquifer on an annual basis.
To conclude, MAR proves to be effective at replenishing over-exploited aquifers, and can also be used to control saline intrusion or land subsidence and improve water quality. However it was stressed that it only enhances the volume of groundwater abstracted and can play a role as part of a larger package when it comes to aquifer management, to control abstraction and restore groundwater.
Artificial Recharge in Maharshta, India
Dr. Sunil Jain further contributed to the evaluation of managed aquifer recharge technology through his experience of artificial recharge in an overdeveloped watershed in Maharashtra, India. The watershed under study was the Bhaunak watershed which forms a part of the Tapi alluvial belt located within the basaltic Deccan Traps of Maharashtra State. The multidisciplinary study integrated the science of water, land, topography, and climate, as highlighted previously by Mr. Ian Gale.
Most of the area is cultivated (approximately 70%) and a rapid decline in groundwater levels (on average 1m decline per year) had sparked an interest in aquifer recharge possibilities. The over-abstraction of water is due to over 3000 dugwells and 500 tubewells that have resulted in an extensive overdraft and groundwater imbalance. Various aspects of the study were explained in detail by Dr. Jain in order to reveal the significant role each study played in the final evaluation of the scheme. The morphometrical analysis of the watershed revealed that the value of the drainage density often indicates moderate to high permeability and relief in the watershed. The drainage length and slope are also required to define the number of water conservation structures that could potentially be installed in the mountainous area. The role of geomorphology and geology of the area was also studied in significant depth, giving particular attention to the location of major faults and different strata composition within the basin.
Climatological analysis was permitted through daily rainfall and rainfall intensity analysis, together with other weather components such as temperature, wind velocity, relative humidity and the number of sunshine hours. Soil texture and moisture was also studied in order to identify infiltration rates and thus designate areas ideal for the location of percolation tanks. Soil texture analysis is also deemed essential since this ultimately influences what managed aquifer recharge techniques should be chosen and the actual design of such techniques.
Continuous monitoring of percolation tanks and stream flows enabled the construction of a realistic estimate of the catchment yield in different catchments. It resulted that upstream mountainous stream flow was ideal for artificial recharge due to 2 main reasons - silt free clean water and flow available for a considerable period. Such recharge would augment both the quality and the quantity of water. In the lower catchment, higher silt loads were found, thus being inadequate for recharge due to in unreliability as a source and also because of the possibility of clogging any of the recharge structures with silt.
The construction of lithologs contributed towards the greater understanding of the hydrogeological framework and aquifer geometry of the site. It also permitted the realization that surface spreading techniques of MAR, such as percolation tanks, are not feasible in the part of the basin composed of granular and clay horizons. On the other hand MAR structures such as injection wells and recharge shafts were seen to be more appropriate.
Once the groundwater recharge potential was assessed and an impact assessment considering all types of MAR techniques, together with small scale rainwater harvesting through roof top harvesting, was carried out, a groundwater augmentation plan could be derived. Once again community participation was highlighted to be critical to ensure the success of such measures.
Water Quality Issues and Rainwater Harvesting
Prof Mike Edmunds elaborated on the significance of evaluating the quality of water when considering rainwater harvesting and its effectiveness. Rainwater harvesting can often provide good quality water in areas affected by water pollution and salinity and thus harvested water may provide an improved and safer supply. However quality problems may arise during the collection and actual storage of rainwater. Rainwater that is collected in a roof tank bypasses the natural mineralizing process and thus may be less acceptable for drinking purposes due to its acidity, low mineralization or due to contamination on storage.
The initial rain water chemical signature is derived from the source of water vapour, primarily the oceans, and contains solutes entrained as marine aerosols, atmospheric dust and any impacts of human activity such as forest fires or industrial emissions. This signature changes as soon as rain comes in contact with the ground. This is because of the uptake of solutes and nutrients. Rainwater is slightly acidic and low in dissolved solids, but on entering the soil it rapidly takes up carbon dioxide through microbiological processes. This helps in the dissolving of minerals. If carbonate minerals are present, the water will become close to neutral because of the buffering created by the carbonate-bicarbonate system.
Some published studies revealed that the quality of harvested rain in some developing countries does not meet the drinking-water guideline values since most water is contaminated microbiologically and thus special care has to be taken during the collection and storage of rainwater. Heavy metals and trace organics may also pose problems.
In the case of groundwater recharge, most of the uptake of solutes in the water takes place in the unsaturated zone due to weathering reactions. This process neutralises acidity and mineral dissolution can be enhanced as a result of the high soil pCO2 concentrations. As a result, the main properties of water quality are determined in the top few metres.
The quality of artificially recharged water is superimposed on the natural baseline water quality which may or may not differ from natural recharge. However in semi-arid regions baseline quality needs to be assessed since high quality, relatively modern water from artificial recharge may be superimposed on a baseline of older water containing, for example, higher salinity or high fluoride.
Environmental chemical and isotopic tracers are also often used to help demonstrate recharge pathways of recent rainwater recharge and also confirm the efficiency of managed recharge schemes. Prof. Edmunds mentioned that the most common and simple method was the chloride mass balance (CMB) method to estimate recharge. In this balance the increased salinity (chloride) is proportional to the amount of evapotranspiration and inversely proportional to the amount of recharge (R).
In many semi-arid regions this method has been applied successfully using unsaturated zone profiles, where surface runoff is near-zero. Including surface waters groundwater samples in the CMB approach is more complex but if the sources of Cl are known, an inventory of water inputs and outputs from the catchment or watershed may be involved and the overall efficiency of the recharge scheme should be related to an overall decrease in Cl. It is believed that there is scope for further application of the CMB to estimating the efficiency of rainwater harvesting schemes on condition that appropriate data are collected including that for establishing baseline conditions.
Stable isotopes of oxygen and hydrogen are also potential tracers in evaluating rainwater harvesting. Individual monsoon events may thus have distinct fingerprints that may be traceable into the aquifer. New storms may be distinguishable from previous season’s rainfall which may have undergone evaporation and enrichment in the heavier oxygen isotope (18O). This approach needs testing on research catchments but should lead to better understanding of the recharge efficiency in a well characterised watershed, especially if tested with CMB and WTF methods.
A case study on the quality of rainwater was presented for the state of Rajasthan, India, which is considered to be one of the worst-affected states in terms of high flouride contamination of aquifers. There is a high incidence of dental and skeletal fluorosis in the province. The presented case study showed that in low-rainfall areas with potential fluoride problems such as Rajasthan, it is important to assess the hydrogeological situation very carefully. The generation of high-fluoride groundwaters usually requires considerable residence times in the aquifer. Thus, it is likely that younger, shallow groundwaters, for example those recharged rapidly through check dams and stream channels, may have low fluoride concentrations compared with older groundwater. They may be exploitable by skimming the shallow water table rather than abstraction from deeper penetrating boreholes which mix water of different quality.
High fluoride waters have traditionally been treated by a range of techniques. However, village-scale fluoride removal presents drawbacks in terms of removal efficiency, cost, ethical issues, local availability of materials, chemistry of resultant treated water and disposal of treatment chemicals as well as monitoring the process. The harvesting of rainwater, either directly in cisterns, tanks or by careful collection via small recharge dams, offers a potentially safe and attractive alternative solution in endemic areas.
Professor Edmunds then summarized the main factors relating to quality of collected rain in relation to materials and construction ,including roof materials, roof location, avoidance of matter deposited on roofs and avoiding anaerobic decomposition of organic matter. The chemical and microbiological quality of collected water was then considered and how best to avoid pathogens, trace organics, mosqitos and other contaminants
Costs and Benefits of Rainwater Harvesting in Iran
Further evaluation of the potential and impacts of water harvesting were given by Dr. Sharifi through his recount of experiences and lessons learnt from rainwater harvesting in Iran. The full account of the cost-benefit analysis described by Dr. Sharifi enabled the participants to clearly see what the potentials and limitations of RWH are in a semi-arid and arid environment, as revealed through Iran. Dr. Sharifi described rainwater harvesting as an inexpensive means of mitigating water supply deficiencies. The cost-benefit analysis carried out revealed that RWH is an economic and efficient method since it results in a large return for relatively small investments. What makes its so attractive economically is its simplicity in technology and thus its applicability that is added impetus in encouraging the community to actively participate in RWH promotion and implementation.
When exposing the vast potential Iran has in terms of water resources, Dr. Sharifi gave estimates from a surface flow analysis, a 30-year rainfall analysis and a groundwater balance analysis. All three studies revealed that the potential water from these water resources was highly significant. For surface flow an estimated additional 260Mm3 was calculated. The potential yield of water resources in 646 monitored sub-catchments in wet years was higher than 228 Mm3; whilst the groundwater balance study taken across 3 watersheds in Iran, resulted in an average annual availability of 5 Bm3.
In view of this, the scarcity in water resources in Iran can be attributed to watershed and aquifer mismanagement. It was pointed out that management of these resources could only lead to important soil and water conservation, which in turn will yield a cumulative positive effect on the maintenance of soil nutrients and organic content, as well as the propagation of plants.
Dr. Sharifi also mentioned the utilization of floodwater as an important solution to the shortage of fresh agricultural water. It was argued that this floodwater can best be stored in mountainous areas due to the reduced evaporation losses in such environments. Flood spreading over coarse-grained alluvial fans also enhances agricultural production and forest reclamation. Over 50% of Iran is mountainous, with very low evaporation capacities and also covered in coarse-grained areas, thus providing the capability of storing water and delaying sub-surface flows. It was stated that if 5 rainfall events occur annually and only 1000m3 of water is infiltrated, then the total precipitation in a wet year can be completely accumulated in natural reservoirs.
It was also argued that investing in new dams does not make sense since evaporation rates in open reservoirs in high and dams face problems of sedimentation and pollution, thus increasing costs of maintenance. Also the investment required for each cubic meter of water storage capacity in surface open reservoirs is nowadays 5 to 10 times higher than the capital investment formerly required for similar projects constructed in the past. Moreover in the face of the uncertainties brought about by climate change the estimated storage capacity of these dams cannot be justified due to fluctuating annual precipitation.
Water Harvesting Techniques in the Arab Region
Dr Zakri gave an overview of the diversity in water harvesting techniques in the Arab region, explaining the use of structures in Yemen, Sudan, Libya, Tunisia and Egypt. The main point exposed through Dr Zakri’s presentation was that water harvesting is central to alleviating water scarcity problems in the Arab region. This explains why diverse water harvesting techniques have been widely practiced in the Arab region dating back over 9000 years.
The catchment area in Arab countries is a major criterion for classifying water harvesting systems as follows:
- Micro-catchment water harvesting systems where the catchment area and cultivated area are adjacent. Eg. The Negarim microcatchments and contour bunds are examples of this water harvesting technique.
- Macro-catchment water harvesting systems where the catchment area is located upstream of the cultivated area, permitting the harvesting of overland flow
- Spate irrigation system which depends on harvesting flood water from wadi channels. This type of RWH technique requires a huge catchment.
Dr. Zakri explained a wide range of RWH systems in the Arab world, some of which were further described by Dr. Noman in the subsequent presentation. A full account of the terraced systems in Yemen and spate irrigation systems in Sudan was given, exposing the ingenious technical and engineering capabilities of these seemingly simple but effective techniques and structures. Of particular interest was the description of the Miskat systems, (or Meskat/Jessours in Tunisia), one of the most ancient RWH methods employed. The use of these systems is common in the Arab Maghreb (Tunisia, Morocco and the north-west of Libya in Jebel Nafousa). The Miskat was described to be simply a piece of flat land with a mild slope (3 to 6%) with few or no drainage channels. The land is prepared for rain water harvesting and then water is directed to another piece of land of half its area and located directly below. This parcel of land is called the collector where crops are planted. Water can thus be said, to be stored in the soil horizons. Unfortunately the state of these Miskats has deteriorated because of the intensive agricultural development that took place since the middle of the century.
Two case studies from Egypt were also presented by Dr. Zakri. The first looked at Wadi Watier in south-eastern Sinai. This wadi is characterised by strong flash floods that have put several lives at stake and destroyed several areas which are of historic significance. For this reason 17 retention dams and 5 storage dams have been proposed. The costs of these dams have been calculated to be compensated within a few years after the execution of the proposed control dams.
The second case described the Wadi Ghuweiba, in the Eastern Desert in Egypt. This wadi consists of Eocene limestone outcrops forming a delta. The delta itself is characterized by a gradually sloping irregular surface dissected by fan drainage lines and covered by alluvial deposits, considered as an important source of groundwater in Quaternary sediments that can be withdrawnl by shallow dug wells taking into consideration the sea water intrusion from the Gulf of Suez due to over pumping.
Geoelectrical resistivity sounding was employed to determine the thickness of the layers. From this study it resulted that there two main aquifers in Wadi Ghuweiba area; the upper Quaternary aquifer which can be harvested by drilling wells to a depth of about +150 m, and the Tertiary aquifer which can be harvested by drilling wells of about +450 m.
In order to increase the rate of recharge to the Quaternary aquifer, an artificial recharge system was recommended. Six locations were employed to induce infiltration into the Quaternary aquifer using of instream structures. These structures were series of rechargeable dams which are changing the hydraulic regime of wadi Ghuweiba stream, decreasing flow velocities and encouraging the growth of riparian vegetation..
Review of the Water Harvesting Techniques in Yemen
Dr. Abdulla Noman from the Water and Environment Centre (WEC) of Sana’a University, Yemen gave a comprehensive overview of the various state of the art techniques used in Yemen for using and managing harvested water.
Water collecting catchments are often located away from village cores in order to prevent pollution. Yemen, having historically been one of the oldest civilisations in the Middle East that depended upon agricultural development and thus the main purpose of use of harvested water in cistern structures was for animal watering, drinking and supplementary irrigation. This has permitted Yemen to be self-sufficient in food production for centuries and moreover export its surplus. Changes however, in the lifestyle and consumption patterns of the increasing population has caused the abandonment of terraces and their maintenance and the absence of traditional cooperation among farmers due to both internal and external migration.
Dr. Noman mentioned the production of a local material known as khadad, which was and is still used to cement rainwater cisterns. This material has proven to be of high quality due to its resistance against weather elements and the guarantee of its long lasting quality. Further research on the application and production of this material is required.
The variety of rainwater harvesting systems in Yemen include roof top harvesting whereby water is collected in a dug out structure called a Seqaya. In hilly areas rain is collected on the roof and directed into an underground storage tank through a settling tank used for domestic use. Terracing is also utilised in the mountainous areas whereby terraced fields provide sufficient time for rainwater to intercept the soil, and low-lying contour built rubble walls prevent runoff but simultaneously permit the water to move down slowly from one terrace to the next through the voids between the rocks in the wall. In addition to terracing, ponds for agricultural use are also used. These can be either excavated farm ponds, embankment ponds or excavated-cum-embankment ponds. Cisterns are also used particularly in the mountainous areas of Yemen. These cisterns are usually underground masonry tanks used for drinking and domestic purposes.
Flood water harvesting and spate irrigation is common practice in Yemen. This technique involves the directing of floodwaters in mountainous areas to coastal and foothill areas. In this way spate irrigation is utilised for the production of major crops. Such a traditionally embedded technique is characterised by a water right given to upstream users over downstream users, such that upstream irrigator’s only releases water to downstream users once all the water needs have been satisfied. The irrigator is then obliged to release water to downstream irrigators. Diversion structures used in spate systems are needed to direct large flood waters away from the command area so as not to cause damage. The structures utilised are deflectors or Al-Qaid (low earthen bunds); high earthen bunds (Ogma); drop structures (Al Masaqit) and spillways (Al Masakhil).
Water rights are not consistent in Yemen. This implies administrative difficulty when it comes to keeping track of legitimate users. However a person in each area (known as an Al-Moqadem), a local expert, would know the area and land owners very well and thus aid in the understanding of traditional law of water rights.
Dr. Noman ended his presentation by giving his views on the future role of rainwater harvesting. From the Yemen experience appropriate systems can evolve form traditional know how on water harvesting. It was again emphasised that lessons should be learnt from the shortcomings of previous projects. Worldwide the development in rainwater harvesting technologies has aided the scientific and management community to see such technologies as supplemental water systems and combined system that allow the prolongation of the cropping season or even the possibility of growing a second crop. Rainwater harvesting is also seen to have a dual purpose since the first runoff waters can be used to irrigate cropping areas and excess water can then be stored in some facility for later irrigation use. Rainwater harvesting potential to enhance soil water storage is also essential since the water retention capacity of soils has to be high enough to supply crops with sufficient water, especially in dry environments when rainfall is intermittent.
Lastly the importance of a further need for in depth knowledge on the hydrological, pedological and crop parameters is required so that more efficient models could be developed.
Water Harvesting Experiences in the Indian Subcontinent—The Influence of NGOs
The final group of presentations all struck the same chord—the significance of NGOs in the role they play to encourage rainwater harvesting at the community level.
Ms. Kavarana (CSE Delhi) and Mr. Sharma (Wells for India), both representing highly influential organisations gave insight on how local communities can actually be made to feel a part of the implementation of RWH in their own environments.
A case study of the Aravali Hills Rajasthan India was presented by Mr. Sharma. Wells for India is a UK registered Charity that works with poor communities in Rajasthan, India. The charity supports RWH as a primary intervention in community development. The case studies illustrated that safe potable water availability provided by rainwater harvesting schemes not only improve health and releases time and energy of women, but also improves poor people’s income, education, as well as social and cultural well-being. Increased water availability through small scale water harvesting structures in Nayagaon, Jamun and Nala villages has increased the productivity of crops, fodder and milk production. Local village self-help groups also started playing active roles in the village development issues such as education and health care. The communities are carrying out many activities themselves, enabling to take next step towards better sustainable future.
This work is spread over 11 districts of Rajasthan working with with 22 local non-government organizations (NGOs). Projects are generally based in village clusters in the upland areas of a river basin where resources can be targeted at individual villages. Successful water harvesting intervention in one village often provides the model for adoption and replication in neighbouringneighboring villages.
Results from a 5-year water harvesting project show that RWH is an essential foundation for all other forms of development in a village. Small scale water harvesting work not only helps in increasing water availability but also in enhancing productivity of food grain and fodder and allowing income generation. Local village self-help groups formed in the villages are playing active roles in the village development tackling issues such as health and education. Through water security groups are motivated to carry out a variety of activities, enabling them to take their next step towards better sustainable future.
Rainwater Harvesting in the Cholistan Desert, Pakistan
Dr. Mohammad Kahlown of the Pakistan Council of Research in Water Resources gave an interesting overview of the Pakistani experience on rainwater harvesting initiatives that were created in the Cholistan desert, Pakistan.
About 70 million hectares of Pakistan fall under arid and semi-arid climate including desert land. Cholistan is one of the main deserts covering an area of 2.6 million hectares where water scarcity is the fundamental problem for human and livestock populations as most of the groundwater is highly saline. Rainfall is the only freshwater source, which occurs mostly during the monsoon (July to September). Therefore, rainwater harvesting in the desert has crucial importance.
The Pakistan Council of Research in Water Resources (PCRWR) has been conducting research studies on rainwater harvesting since 1989 in the Cholistan desert by developing catchments through various techniques and constructing ponds with different storage capacities ranging between 3000 and 15000 m3. These ponds have been designed to collect maximum rainwater within the shortest possible time and to minimize seepage and evaporation losses. As a result of successful field research on rainwater harvesting system, PCRWR has developed 92 rainwater harvesting systems on a pilot scale in Cholistan desert. Each system consists of a storage reservoir, energy dissipater, silting basin, lined channel, and network of ditches in the watershed. The storage pond is designed to collect about 15000 m3 of water with a depth of 6 m. Polyethylene sheets (0.127 mm) on the bed and plastering of mortar (3.81 cm) on the sides of the pond was provided to minimize seepage losses. All these pilot activities to harvest rain have brought revolution in the socio-economic uplift of the community. These activities have also saved millions of rupees during the recent drought. Large scale adoption of all these interventions would ultimately help improve the socio-economic conditions of the residents of hyper-arid area of the country.