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require that levels are fixed using a surveyor's level. Community members and contractors normally have neither access to a surveyor's level nor the ability to use it, so there is a need to explore alternative ways of fixing levels. Two methods are in fairly common use in Pakistan, and no doubt elsewhere. The first involves the use of a water level, in effect a hose filled with water, to determine differences in level between two points. The second is to use a carpenter's spirit level, together with a straight edge, to determine the fall over a short length. Both these methods have limitations. The water level system can give misleading results unless care is taken to remove all air bubbles from the hose. It is therefore unsuitable for use by untrained workers. The carpenter's level method works reasonably well when falls are good, say greater than about 1 in 200, but it is not certain that it can provide sufficient accuracy when the available fall is limited. |
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In North-east Lahore, the normal practice was for engineers to fix levels on the walls of buildings fronting the lane or street along which a sewer was to run. The trench and invert levels were then tranferred to profiles set over the trench as already described. For community-managed schemes and those implemented by small local authorities with limited resources, it should be possible to develop methods for branch sewers which rely on locally available skills with the engineering input perhaps restricted to fixing the level at one point on the sewer. This will depend on standardized rules for the falls to be provided on branch sewers becoming generally known and accepted. |
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4.3.5
Contract Drawings and Documentation |
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More investigation is required on appropriate contract documentation for small sewer projects. The contracts in North-east Lahore, which included services other than sewerage, typically covered 2030 ha and were for sums in the range Rs15 million to Rs30 million (US$500 000 to US$1 million), were covered by contract documents based on the FIDIC conditions of contract. This represents a large degree of overkill and it is unlikely that either contractors or government officials are aware of much that is in the contract documents. On the other hand, community and municipality contracts are often carried out with an absolute |
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