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manholes are replaced with 'simplified' manholes, cleanouts, or buried boxes (Table 11.3). Simplified manholes are similar to conventional manholes except they are reduced in size from 1.5 m diameter to 0.60.9 m because the need to enter the manholes by maintenance personnel is eliminated due to the shallower depths and to the availability of modern cleaning equipment. They are used only at major junctions. At changes of direction or slope, manholes are replaced by buried boxes or chambers. House connections are adjusted to serve as inspection devices by installing small box under the walkway and connecting it to the sewer with a 45° ell and wye (the jetting hose can be introduced through this box). These changes in the design and use of manholes have been shown to reduce the costs of a sewer system by more than 25 percent. |
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Simplified sewers have proven to be substantially less costly than conventional sewers. In many places, cost savings ranging from 20 to 50 per cent have been reported. In the State of São Paulo, Brazil, the first projects have shown a reduction of construction costs of 30 per cent but after about 8 years of experience, the reduction is estimated to be closer to 40 per cent. Within the City of São Paulo, cost savings over conventional sewerage are reported to be 35 per cent by SABESP, the water and sewerage utility of the State of São Paulo. SABESP estimates construction costs for small towns (excluding costs of treatment and house connections estimated to be about US$40 and 50, respectively) are US$150300 per caput for conventional sewerage and |
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| Table 11.4 Construction costs for selected simplified sewerage projects in Brazila | | City | | | | | | Total cost | | | | | | Cost/metre | | | | | | Cost/caput | | | | | | aCosts in 1988 US$ dollars | | | |
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