Spring Protection

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Description
Springs occur where water from an underground aquifer flows out of the ground to the surface. The spring can occur where the water flows out of the ground by gravity, or it could be an artesian spring where the water appears at the surface under pressure from a confined aquifer below. The point at which the water reaches the ground surface is known as
Transcript
  Spring protection This Technical Brief looks at spring protection including the catchment area, the immediate area around the spring and the construction of spring boxes. It also highlights two methods of reducing sediments in the water coming from large springs and introduces alternative protection methods to spring boxes. This Technical Brief does not discuss the distribution system between spring box and supply. Springs Springs occur where water from an underground aquifer flows out of the ground to the surface. The spring can occur where the water flows out of the ground by gravity, or it could be an artesian spring where the water appears at the surface under pressure from a confined aquifer below. The point at which the water reaches the ground surface is known as  ‘the eye of the spring’. Spring water can be of good quality microbiologically if the spring is well protected. Spring water can in some areas however, can have the same levels of chemical constituents as other forms of groundwater. In particular this may include high levels of fluoride, or high levels of carbonate hardness in the water, such as found in some areas in Nepal where the Hill regions meet the Terai regions. This can lead to blocking of pipes through encrustation after even a few years of use. Some springs flow all the year around and some springs only flow for part of the year. It is very important when deciding on which spring to protect that local knowledge is used, particularly the knowledge of women and elders, to identify which springs are known to be the most reliable. Effects of natural disasters on springs Natural disasters such as earthquakes, droughts, volcanic eruptions, or landslides can affect springs. Some may move location and others may increase or decrease in yield. Earthquakes may also damage the structures associated with spring protection and the pipelines taking the spring water to villages. This can include the breakage of pipelines.  A reduction of vegetation cover and deforestation also pose risks for the stability of spring sources due to increased erosion and the risk of slope failures. Challenges for spring users in the Caribbean island of Montserrat In 1995 the Caribbean Island of Montserrat faced a volcanic eruption with a series of heavy ash falls. Montserrat’s water supply is reliant on 16 springs. Two of the islands springs, which supplied 35% of the islands water, were on the face most exposed to the volcano. As the volcanic activity worsened the reliance had to be switched to other sources in other parts of the islands. Water catchments were also subject to acid rain and ash fall due to the volcanic activity and there was some concern that movements of joints could lead to the movement of springs and there could also be changes in water quality. (Lashley, D.A, 1997, in House & Reed, 1997) Taking water from an unprotected spring in northern Tanzania Outlet pipe from an ‘open system’ protected spring in a hill district in Nepal OXFAM Technical Brief – Spring protection 1  Superstitions and beliefs surrounding springs There may be local superstitions about springs and care should be taken to consult the communities so that appropriate traditions are followed where necessary and permission sought when upgrading springs. The supernatural power of springs In Midlands Province of Zimbabwe (2006) it was reported that in one area springs are seen as supernatural. This belief was reinforced during the 1992 drought in Southern Africa, as when the shallow wells of the area had mostly dried up, the springs continued to flow. It is believed that if someone undertakes construction near to a spring it will dry up. If this happens special rituals would be needed before the spring could recover.  A protected spring in eastern Zaire being used to supply two large refugee camps   Selecting a spring The selection of springs to protect for emergency water supply should consider the springs’ yield versus the demand, its reliability through the seasons and during years of drought, the quality of the water, vulnerability to landslides and erosion, and who the existing users are and in particular whether they will accept the spring being protected and used for new communities. Wherever possible the springs yield should be measured at the end of the dry season to determine the minimum expected flow. Checks should be made that the spring is not in fact a stream which has passed underground and re-appeared downstream as the water quality is then likely to be poorer. Sometimes water is also taken from a stream which is fed from one or more springs. The problem is that when it rains the water turbidity will have increase which will cause additional problems for treatment, particularly if chlorination without pre-treatment is being undertaken in a camp scenario or a local settlement. Springs can be protected and supply water in the following ways: 1.Simply have a free flowing pipe passing through acatchment structure where water can be directlycollected by users.2.Have a collection chamber with valve chamber and anopen system where the water flows freely through apipe to the users. This system is called an  ‘opensystem’  .3.Have a collection chamber with valve chamber andthen the outlet pipe feeds into a storage reservoirwhere the water is collected over night. This reservoirfeeds through another pipe to a tap. This systemretains as much water as possible and is called a  ‘closed system’  . It is used when the yield is lower inproportion to the demand.4.The second two systems may also have some form of sedimentation tank or filter after the spring box if there are particular problems with solids or turbidity inthe water.  Yields  A flow in excess of 0.1 l/s is sufficient to fill a 20 litre container in just over 3 minutes. From such a spring a useful yield of about 3,000 litres can be expected which is enough water for 150 people @ 20 /p/d, or 200 people at the Sphere standard of 15 l/p/d. If the flow were only at 0.05 l/s then it could supply the same number of people if a storage tank of 1,000 litres capacity was also incorporated into the system. (Ref: WaterAid Technology Notes) Protection principles 1.Protect the catchment area above the spring fromanimals and humans to prevent contamination.2.Constructing a cut off drain above the spring preventscontaminated water from entering or mixing with thespring water.3.No latrines should be located within 30m upstream ordownstream of a spring.4.After cleaning or opening up the area around the eyeof the spring, the spring should be protected withloose stones and gravel and then a soil cover behindthe catchment wall, in addition to possibly also aspring box and a pipe for delivering the water to theusers.5.The area around the spring should be fenced toprevent access by animals, but overflow water shouldbe directed to an area outside the protection zonewhere the animals can take water, particularly inpastoral areas.6.The spring box should be cleaned out on an occasionalbasis.7.The local community and users of the spring should betrained in the correct maintenance of the spring inletand system and in the rationale for the protection of the catchment areas. Local legislation may also beuseful in protecting the catchment area above thespring. Protection of catchment area  A surface water drainage ditch is dug above and around the spring area to divert surface water run off from polluting the source. This should be dug a minimum of 8m OXFAM Technical Brief – Spring protection 2  from the source and ideally further away. The area should then be fenced to keep animals and people out of the area. Earth should also be mounded up against the collection tank walls to divert any surface water away. If the stability of the area around a spring intake works is in doubt or erosion is a risk, then gabions or dry stone masonry can be used to stabilise the area. Ideally an area leaving a minimum distance of 50m above the spring should be left where there is no human habitation and animals are not allowed to graze. Reforesting and the planting of grass and bushes in the area directly above a spring can help to protect the catchment area, to reduce run-off and erosion. Opening up the eye of the spring Opening up the eye of the spring: 1.This must be undertaken with great care as anyform of  ‘back-pressure’   on the water could causeit to change its route and the eye of the spring tomove. Spring water  ‘follows the path of leastresistance’. 2.A temporary drainage channel should beconstructed to ensure that the water can continueflowing during construction and to preventpuddling.3.The area immediately beneath the point of discharge (or seepage area) should be excavateduntil either the horizontal water layer or firm rock are reached.4.The excavation should proceed into the slope untila height of earth above the discharge point is aminimum of 1m. A spring from a rock face requiresminimal excavation, but a spring with widespreadseepage may require an excavation of severalcubic metres.5.For artesian springs the excavation is likely to bevertical into the ground, and this poses additionalproblems for preventing back-pressure. Tworecommended strategies are: a) construct a trencharound the area and locate the intake severalmeters away from the eye of the spring, and b)sink large concrete rings around the eye of thespring as the excavation continues to prevent thesurrounding soil from falling back in to theexcavation hole. The spring may have to be leftrelatively exposed and hence a manhole cover maybe required. The outlet should also be as low aspossible to prevent back-pressure.6.Place loose stones and gravel over the area of theeye of the spring for some initial protection.7.After excavation the spring area should be left for24-48 hours to enable it to stabilise, beforeadditional construction work.(Ref: Neku & Hillman, 1996) If there is more than one spring or seepage point in an area then the excavation may need to be wider or drains or catchment structures and pipes can be constructed to allow the various sources of water to drain into one collection chamber. Protection of a spring catchment (Ref: Jordan, 1984) Constructing the catchment wall or spring box The structure which is required to catch the water from a spring will depend on a number of factors. These include the size of the spring and whether the users will come to the spring or the water will be taken in a pipe to the users.  A number of different designs are shown on the following few pages of this Technical Brief. Construction of retaining wall, catchment dam or cut off wall, spring box and valve chamber 1.A dry stone retaining wall should be built against theexcavated slope. This wall is built using brick sizedstones and both acts as a retaining wall and allows thewater to pass through into the collection areas withminimal sediment.2.A catchment dam or ‘cut-off’ wall with wing walls, isdesigned to catch as much water as possible anddirect it into the collection chamber (see the diagrambelow). It should be constructed in an excavatedtrench of minimum depth 20cm to help ensure thatwater does not seep under the wall.3.The collection chamber and valve chamber are thenconstructed on the downstream side of the catchmentwall and the bottom of the collection chamber shouldbe concreted.4.The overflow pipe from the collection chamber shouldbe lower than the catchment dam wall to preventback-pressure.5.The area behind the catchment dam is filled withstones and gravel to the same level as the catchmentchamber lid, with smaller stones nearer the eye andlarger nearer the wall. Heavy duty sheeting is thenplaced over the catchment area and the edges sealedwith clay. The sheet is then covered with theexcavated soil and then a layer of topsoil. Shallow rootthorny-type vegetation can then be planted to detervandalism and stabilise the soil.(Ref: Neku & Hillman, 1996) OXFAM Technical Brief – Spring protection 3  Spring box with open side (Ref: Water for the World, Technical Note No RWS.1.C.1) Spring box with open bottom (Ref: Water for the World, Technical Note No RWS.1.C.1) Catchment wall, spring box   and valve chamber  (Ref: Neku & Hillman, 1996) OXFAM Technical Brief – Spring protection 4
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