| Water purification, distribution and sewage disposal for Peace Corps volunteers |
|Section 5: Construction techniques|
DEVELOPING THE SOURCE:
Sources which require much development are ground water sources. The development of wells, is covered extensively in the "well construction manual". Constructions in spring development are similar to those for wells.
The quantity of water from a spring can very often be substantially increased by digging out the area around the spring down to an impervious layer to remove silt, decomposed rock, and other rock fragments and mineral matter (usually calcium carbonate) sometimes deposited by the emerging ground water. In doing this, particular care should be taken, especially in fissured limestone areas, to avoid disturbing underground formations to the extent that the spring is deflected in another direction or into other fissures.
Springs in general, and gravity springs in particular, are subject to contamination in the area close to the point of emergence. A thorough sanitary survey should be conducted before development work is initiated. Such a survey should yield information on the origin of the ground water, the nature of the water-bearing strata, the quality of the water, its yield in various seasons of rainfall, the topography and vegetation of the surrounding area, and the presence of possible sources of contamination. To protect the spring, the collection structures should be so located and built as to force surface water to pass through at least 10 ft of soil before reaching the ground water. It is also customary to exclude all animals and habitations from a substantial area (perhaps 100-300 ft), around the collection chamber, and to dig a diversion ditch above and around this to interrupt surface run-off and divert it away from the groundwater collection zone. Springs emerging from solution channels in limestone formations should be carefully investigated and observed, since under such conditions very little, if any, natural filtration takes place in the ground.
Such springs are likely to yield grossly polluted and turbid water soon after heavy rains, and should not be used as a source of domestic supply without a thorough study, including frequent bacteriological examination, and without the provision of corrective measures, such as filtration and/or disinfection. Other protective measures are discussed below.
Springs, especially those which can be piped to the user by gravity, often provide an economical and safe solution to the water-supply problems of rural communities. Fig. 43 show typical methods of collecting water from springs.
The intake may consist of a submerged pipeline used with a submerged crib or a screened bellmouth at the open end. It should be placed well below the water surface since the water is cooler at a greater depth and, also. because of ice formation In cold climates; but it should not be close to the river bottom, in order to avoid sediment and suspended matter moving along there. The intake should also be located some distance from the shore and should be large enough for entrance velocities to be kept to a minimum, preferably less than 6 in. per second. Fig. 43 shows a simple intake structure for small water-supply systems from rivers or lakes.
Reproduced from Hardenbergh W. A. (1952) Water supply and purification, p. 52, by kind permission of international Textbook Co., Seranton, Pa., USA
Intakes from small streams frequently require the construction of small diversion dams. In this manner provision can be made for a sufficient depth of water at all times above the intake pipe; for the settling of suspended matter, thereby reducing the turbidity of the water; and for keeping floating leaves and other debris from obstructing the intake structures. Depending upon circumstances such as the depth of water in the river, location, and degree of permanency of the structure, a floating intake made of empty oil drums held in place by a suitable frame and supporting a flexible inlet hose may be used. Intakes should always be designed to function with a minimum of attendance. More elaborate 'designs are shown in Section 2.