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Title: Environmental impact assessment for the proposed integrated water resource management project HA. Ihavandhoo
Authors: Sandcays
Keywords: Legislative and regulatory consideration
Project description
Project alternatives
Existing environment
Stakeholder consultation
Impacts and mitigation measures
Environmental monitoring
Issue Date: Nov-2012
Citation: Sandcays. (2012). Environmental impact assessment for the proposed integrated water resource management project HA. Ihavandhoo. Male': Maldives
Abstract: This report discusses the findings of a social and environmental impact study under the proposed integrated water resource management project in Ihavandhoo, Haa Alifu Atoll. The project is proposed by United Nations Office for Project Services (UNOPS). The project is targeted at providing potable water to the community and improving rainwater recharge. Potable water is provided by a combination of rainwater and desalinated water, which is a new and unique project for the Maldives. The recharge well system is even more unique. Consequently, several discussions have been held with the Ministry of Environment (represented by EPA), Ministry of Housing and Infrastructure and UNOPS to discuss the several issues. The issues were re-visited during the scoping meeting, the main issues identified by the EPA being the size of the rainwater tanks and good management of the system to ensure that most of the rainwater is used and desalinated water is depended upon as a supplementary source. EPA also has issues with the proposed recharge wells with the main concern lying in the possibility that the recharge wells may help to cause flooding during storm water. However, the project engineer is quite certain that this was not likely and this was also backed by the EIA Consultant. At present Ihavandhoo does not have a piped water supply system and groundwater is used unanimously for all purposes with the exception of bottled water and rainwater for drinking. Several efforts have been made in the past including the construction of public rainwater tanks with public tapbays, which was later replaced by household rainwater tanks of 2500l at each household for easier access but with some compromise on water quality issues. Rainwater, however, could not be depended upon during long, dry periods during the northeast monsoon. With changing climatic patterns worldwide, rainwater can rarely be depended upon. With lack of space for appropriate rainwater collection facilities combined with groundwater contamination and salinization has been seen to cause various health and environmental problems including water-borne diseases. The dependence on groundwater and untreated rainwater is often a cause for concern. Therefore, an integrated water supply system with sustainable groundwater resource is an immediate need for the people of Ihavandhoo, which has a population of over 2750 people in September 2012. The proposed integrated water supply system is designed for maximal use of rainwater supplemented by desalinated water for an average water demand of 50-70 litres per person per day. Raw water is proposed to be drawn from a borehole with 8’’ casing and pumps to pump the raw water to the treatment plant. The treatment for the water is proposed by using Reverse Osmosis technique. The plant will be run by diesel engine and the possibility of alternative energy options such as solar and wind will be considered. The pure water after treatment is collected in glass or fibre-reinforced plastic tanks of adequate capacity determined for Ihavandhoo to be 1000m3 based on EPA guidelines. The water thus collected is introduced in the network so as to reach all the households, institutional and commercial areas with adequate residual pressure through HDPE pipes. The distribution network is designed for over 35 years while the water tank capacity has been based on 15 years as per Government requirements. The proposed IWRM project also comprises of a mechanism to recharge groundwater using a collection of recharge wells made of concrete that will run along the main roads as well as the island periphery. Direct recharge of groundwater is minimized due to urbanisation as permeability is reduced and infiltration surface is minimized. Therefore, this process is assisted by the use of recharge wells that will direct the excess rainwater from roofs to the groundwater lens. However, it must be noted that these recharge wells are not anticipated to cater for storm water drainage. The sole purpose of these wells is to assist groundwater recharge so that the groundwater lens may be sustainably managed. Environmental impacts were assessed for both the construction and operation phase of the project. Most of the environmental impacts of the project have been identified as positive resulting mainly from easy access to safe water supply, improvements to groundwater quality and resulting reduction in water-borne and water-related diseases and improved health of the population. The socio-economic benefits of the project may be considered to outweigh the negative impacts of the project. There are a few negative impacts of the project including the minor impacts of landuse related to the project and clearing of some mature trees that may be required. The impact of clearing would be compensated by replanting mature trees in other areas of the island and, if necessary, planting additional trees. The impact of brine discharge is also considered minor or negligible especially due to the fact that there is no coral cover in the proposed brine discharge location and good mixing will occur due to currents in the area. Since the pipeline is a pressure system, the pipes will be laid above the water table and no dewatering will be required. Hence, no effect on the groundwater lens. Other minor negative impacts include excavation to lay the water distribution network and brine discharge pipe. One of the impacts of the proposed recharge wells would be space constraints to services on the road and the impact would be mitigated by appropriate planning for locating recharge wells and sewerage manholes as well as other such services. The other impact of the proposed recharge wells would be that there may be clogging of the pipes and such clogging may lead to unnecessary flooding in some areas where clogging occurs, especially in areas easily prone to flooding following rain. However, clogging is expected to occur over the long-term, therefore, it is not possible to do field tests to verify this. It has also been seen that recharge is also not much of a use if pumps are used to draw water from the groundwater aquifer, which leads to rapid salinization of the water lens during the dry period. Recharge of groundwater lens also occurs over a large surface due to rainfall. If we consider the sustainable yield estimated for Ihavandhoo, it can be seen that no amount of recharge will help to overcome the problems related to salinization due to increasing use of pumps. In fact, the Maldives receives well over 2000mm of rainfall, which would be more than sufficient to recharge the aquifer. Yet, the aquifer, similar to a rainwater tank, has its maximum capacity limits and cannot overgrow the impact imposed by high rates of abstraction. Therefore, only sustainable rates of pumping can ensure sustainable management of the aquifer. It has been observed from studies carried out for Malé that freshwater exists in pockets. Where the drawn down effect is high, due to the size of pumps and rate of pumping, there is a tendency for the water lens to become more saline at the location where the drawdown is greater. This draw down or lowering of the water table at the point of abstraction, sometimes referred to as the “coning effect” for the freshwater lens, can only be avoided with the use of appropriate technology such as skimming wells and infiltration galleries. The main mitigation measure for the proposed project would be to identify measures to minimize drawdown on the aquifer including the introduction of skimming wells by improving existing wells and enhancing water conservation techniques. The proposed concept of recharge wells is still at a preliminary stage, therefore, it is proposed that the detailed design takes into consideration the findings of this Environmental Impact Assessment, and consultations with the community and relevant government agencies, especially the EPA. It is inevitable that there would be some negative environmental impacts. However, these are minor compared to the positive effects of the proposed system. Yet, monitoring to ensure the effectiveness of the proposed system would be necessary. Therefore, a monitoring component has been suggested which takes in to consideration, the most important elements that require regular checks. This monitoring component will be adhered to and will allow the assessment of changes due to construction and implementation of the proposed water supply system and aquifer recharge system. Monitoring is specifically focussed on water quality, to include feedwater from the borehole (or other source), collected rainwater, groundwater, product water at designated locations and seawater at brine discharge location (upstream and downstream). Reef or marine ecological monitoring may be considered if the proposed location of the brine discharge or intake is found to be of ecological significance. In conclusion, it appears justified from a technical and environmental point of view, to carry out the proposed project to install and operate a piped water supply scheme using rainwater supplemented by desalinated water. However, the recharge well scheme needs to be further evaluated and possibly replaced by or integrated with an alternative scheme such as converting existing household wells to skimming wells to minimize salinization of the groundwater lens. It is also further recommended to consider one of the three islands under this project as a pilot island for the recharge wells instead of all three islands and Ihavandhoo seems to be the most appropriate since the island is higher in elevation compared to the other two and there is a lesser chance of potential flooding, where there is a concern.
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