Seychelles - La Gogue Water Supply Study
- Référence: P-SC-EA0-003
- Date d’approbation: 08/12/2011
- Date de début: 22/02/2012
- Date d'évaluation: 30/08/2011
- Statut: En coursOnGo
- Agence d'implémentation: WATER AUTHORITY PUBLIC UTILITIES CORPORATION
- Emplacement: MAHE ISLAND, VICTORIA
The study will have two main components:
(i) increasing the storage capacity of La Gogue dam reservoir and
(ii) improvement of the La Gogue distribution system zone. The study will be undertaken in two phases. An abridged TOR is provided Annex 7.
A. Component 1 - Increasing the Storage Capacity of La Gogue Dam Reservoir
The existing La Gogue Dam, completed in 1979, is one of the main water supply reservoirs for the North East Mahé Water Supply System. The Dam is a homogeneous earth fill dam with a maximum height of 35 m from the excavated foundation level and a length of 152 m at the crest. The dam, after being in existence and operation for more than 30 years, it is in a very good condition and is quite safe. The idea to raise the dam wall to increase storage capacity has been under discussion since the 1990s and it has become again a priority in the WDP and is widely seen as a potential solution to contribute to addressing the water shortage.
The proposed feasibility study therefore aims at validate previous assumptions and analysis, and to take the project forward with full scale technical assessment, economic and financial viability study including environmental and social impact assessment. On the basis of feasibility study, the best scenario will be adopted for further detail designs.
B. Component 2 - Improvement of the La Gogue distribution system
The La Gogue distribution area (north east and north west of Mahe) is considered to be a problem area with low pressure zones and the water is travelling long distances from treatment plants to the consumers. The existing system is further characterised by many pumping units with high energy costs. In order to reduce these constraints, a new system is proposed, namely the construction of a new treatment works near the La Gogue reservoir for the treated water to flow by gravity to most areas in the distribution zone. During phase 1 of the study, on the basis of information provided in the WDP and additional information to be secured from the PUC, detailed technical, environmental and social, operational, economic and financial feasibility will be carried out to revalidate the overall feasibility of the system followed by preparations of detail design, cost estimates, tender documents and ESMPs.
The unmet demand for Seychelles is estimated at 40% according to the WDP for 2010. The deficit will continue to increase if further investments are not made timely as recommended inhibiting the economic and social development of the country. It is therefore imperative that the priority activities in the WDP are implemented in a timely and orderly manner. The enhancement of storage at La Gogue dam reservoir is one such activity to ensure water security. The PUC has already embarked on smaller scale improvements to transfer water to the La Gogue dam reservoir. The Salazie and Mount Simpson transfer schemes (4500m3/day capacity) being implemented by the PUC with an outlay of SCR 35 million are typical examples of the efforts to increase availability of water resources. The benefit of such schemes will be much more enhanced with an increase in storage volume. The implementation of this scheme is therefore critical to enhance the capacity of water storage and provide water security to the main island. The storage enhancement scheme will also enable the improvement of the La Gogue distribution system. The WDP shows that the benefits of the new system over the long term is enormous in terms of improving efficiency of the system and reducing operation and maintenance costs. The improvement of the system will see the reduction of pumping stations and shorter distances along the distribution network thus resulting in better control of the residual chlorine contact, better pressure management and leak control. The technical justification described above provides the justification for carrying out the feasibility study and detail designs preparation in order to make the project ready for implementation.
The GOS approved the WDP in June 2011 and immediately embarked on the implementation of the recommendations of plan. The GOS further demonstrated its leadership and political commitment to the implementation of the WDP by organising a donors' conference on 13th September 2011 to mobilise support for the implementation of the WDP. The conference was successful and was attended by government officials, donors including AWF, EIB, BADEA, UNDP, Embassies and other stakeholders. Donors expressed their commitment to strengthen their collaboration with GOS for the implementation of the WDP.
The Bank's CSP gives prominence to infrastructure development vis-à-vis addressing the country's development shortcomings. The CSP prescribes strengthening private sector development and economic competitiveness as its overarching strategic pillar. The pillar is broken up into three separate and complementary sub-components:
(i) Infrastructure development,
(ii) enabling financing and regulatory environment, and
(iii) human capacity development. Within the infrastructure component, deficiencies in communication infrastructure, recurring water supply shortage and limited regional links to main land Africa were recognized as critical bottlenecks. As emphasized in the CSP, the project will contribute to the achievement of the pillar objective by removing water supply constraints for the growing private sector in the tourism which is the mainstay of the economy and other sectors. It will contribute to the enhancement of the competitiveness of Seychelles as a preferred destination in tourism.
The WDP specifically recommends the immediate raising of the height of La Gogue Dam on a priority basis to increase the water storage capacity. According to previous studies and WDP, raising of the height of La Gogue dam by about 5m would alone increase the reliable yield by an average of 3,900m3/day. This additional resource is equivalent to about 50 days of water for the Islands representing 14% of water currently produced. The other alternative considered for storing water was the building of a new dam on the Grand Anse River. However this alternative was dropped due to the environmental concerns and engineering complexities. The raising of the La Gogue dam was therefore deemed the most attractive option due to the amount of fresh water storage to be achieved and the potential for transfer of water from adjacent surplus catchment. The raising of La Gogue dam is therefore a strategic water security enhancement scheme for Seychelles and there is need to further investigate this option to confirm the feasibility of the scheme.
The development of this scheme, if feasible, will further provide the possibility to improve the La Gogue distribution zone with the construction of La Gogue water supply treatment plant (gravity fed system) resulting in net cost saving over longer period from the present energy intensive distribution system in La Gogue area, thereby contributing to the mitigation of climate change. This region is considered to have intermittent supply due to problem of low pressure and long distances from the existing treatment plants at Hermitage and Le Niol. There are 12 pumping stations within this area with high energy costs. In order to reduce these constraints, a new system is proposed, namely the construction of a new treatment works at La Gogue providing supply directly to this distribution zone.
MUTASA Christopher - OWAS2