INFRASTRUCTURE PRELIMINARY PROJECTS - Xai-Xai IDP
5.1.2 Water Demand
The projected demand for water based upon town planning development proposals drawn up by the team at the end of July 1998 is estimated as follows:
Current Water Demand
year 1998 – 400 m3/day
Increasing at 12% per annum for 20 years – year 2018 – 4000 m3/day
Table 12 details the makeup of the projected 20 year water demand at full development. A growth rate of 12% is not unusual in an area of rapid new development starting from a small base as may occur along this coast so planning for a water demand of 4000m3/day in 20 years to 25 years is considered quite reasonable. Projected growth over 20 years was indicated graphically at the Steering Committee meetings and in discussions and was accepted as the basis for staged implementation of the water supply system.
5.1.3 Method of Water Supply to be Adopted
In order to meet this demand and to supply good pressure to proposed development along the coast up to the 60m contour it is necessary to build new reservoirs at a common top water level of 88m close to the areas of consumption. The elevation of 88m has been chosen as top water level as there are a number of sites where reservoirs can conveniently be built at this elevation close to the areas they serve. Placing all the storage at the same level allows interconnection of distribution systems between reservoirs without overflow problems, as well as economical extension of the system over the years. Because the supply of water is from aquifers found in the sand all along this coast the supply to reservoirs can be drawn from wells sited as required next to the reservoirs. Such wells should be carefully sited away from habitations to reduce the possibility of pollution.
A new water distribution system (reticulation) will be required to suit the new higher reservoirs with resulting higher pressures in pipelines. Reservoirs set at 88m top water level also coincide with piping designed to work at this pressure as piping is designed in steps of 30m.
Therefore, all pipes used in any future work should be able to work at 88m (being Class 9 uPVC or Class 18 in fibre cement). Galvanised or steel pipes and fittings subject to corrosion should not be used.
5.1.4 Future Well Reservoirs and Extensions
Additional hydrogeological testing needs to be undertaken to determine the optimum rate of draw off and the spacing of wells so that the existing fresh water aquifers are preserved without intrusion of either salt water or polluted water. The quality of water needs to be tested and monitored. The Department of Public Works has provided the working team with initial hydrogeological data and reports which indicate that each well in the zones of fresh water near the coast can safely supply up to 80 m3/hour. Catchment areas and areas next to wells should also be protected. Six future well sites have been identified, being three each at Xai-Xai and Chongoene, and these should provide sufficient water for the next twenty years.
Between Xai-Xai and Chongoene
Very little development has occurred along the coast between Xai-Xai Beach and Chongoene and the little that has occurred can be supplied from local wells. These should, however, be sited well away from any source of pollution especially septic tanks. We understand from the local doctor that there has already been one case of cholera at Xai-Xai, which could have arisen from drinking from a local well which has been polluted.
At Chongoene itself there is an old well just above the hotel which contains water. It would appear that this well supplied the hotel in the past but it is no longer equipped with pump or motor.