|Water Manual for Refugee Situations (UNHCR, 1992, 160 p.)|
|6. Water sources, their protection and development|
19. Springs are the ideal source of groundwater. Although water from a spring is usually pure at the source and can be piped to storage and distribution points, it may in general be more easily contaminated than water from properly constructed and maintained wells. Care should always be taken to check the true source of the spring water, as some apparent springs may not be related to aquifers but to possible polluted sources which have seeped or flowed into the ground a short distance away. It is essential that the spring water be protected against pollution at the source by means of a simple structure from which the water would fall directly through a pipe to a tank or collection point. Care must also be taken to prevent contamination above the collection point. Subsurface sources of contamination can result from privies, septic tanks, cesspools, and livestock areas. Ordinarily, a distance of 50-100 metres will suffice (if the spring is on the "uphill" side of such sources) to provide adequate protection; many fractured-rock aquifers require particular attention as they are capable of transmitting pollution for much greater distances than loose, granular aquifers.
20. The supply of water from a spring may vary widely with the seasons and will be at its minimum right at the end of the dry seasons or just at the beginning of the rainy season (before newly recharged rainwater has reached the aquifer). Perennial springs drain extensive aquifers, whereas intermittent springs discharge only during portions of the year when sufficient groundwater is recharged to maintain flow.
21. Spring catchment structures should be constructed in simple and practical ways. Their characteristics depend on the topographical situation, the nature of the ground (including the aquifer) and the type and characteristics of the source itself. In view of this, it is important that the design and the direction of construction works to build appropriate spring catchments be the responsibility of experienced technicians. Catchment structures should never interfere with the natural conditions and the flow of the spring, as any such disturbances could mean the alteration or even the disappearance of the spring's yield, as water may try to find another route. They should always provide protection against the spring's pollution from any source; after construction, and when appropriate connections have been made to convey the water to storage or distribution facilities, the structure should be sealed off or covered. The free flow of the water away from the spring must always be guaranteed. Spring catchments have three components:
i) Collection structure. It has two parts: a permeable structure or filter into which the water enters and a barrage to lead the water into the supply pipe which takes it into the inspection chamber. Filters should be large enough to ensure maximum flows without obstruction; a water-tight cover (preferably concrete) should be placed on their top and surface water should be drained away from them. The barrage is built on impermeable ground, to prevent water from bypassing or seeping away from it; its foundation should be cast by excavating directly into the ground to get a water tight structure. Barrages may be built in stone masonry or concrete and should be as high as the impermeable cover on top of the filters.
ii) Water from the barrage is conveyed to the inspection chamber by the supply pipe, whose diameter should be enough to let maximum flows pass (but never smaller than 80 mm). An overflow pipe should always be installed to avoid high water levels behind the barrage which would build up pressure and force water through other ways.
iii) Inspection chamber. These structures should allow easy access to the spring. They should be large enough to allow men to work inside. They are usually calculated as small sedimentation chambers (See 8.16) and should be water tight. Manholes should not be directly above the water. They should be provided with overflows and drains to allow draining off maximum spring flows without interfering with the spring. They are usually built in stone masonry or concrete; the use of wood should be avoided for sanitary reasons.
22. The identification and development of spring catchments suitable for water supply should be undertaken by experienced technicians.