The purpose of this paper is to present some of the technical and economic aspects related to the construction of an underground reservoir, currently in progress, for the storage of drinking water to supply the cities of Santos and Sao Vicente, located in the State of Sao Paulo, Brazil. Basically two alternatives are analised to solve the water storage problem, to wit: conventional storage of reinforced Concrete and tunnel excavated in rock. The various factors to be considered for each one of the solutio ns are stated and the conc1usion arrived at is tha t the tunnel storage alternative offers greater advantages from a technical as well as an economic point of view. Some aspects related to construction methods used in tunnel excavation works are also delved into.
The municipalities of Santos and Sao Vicente are communities located on the coast of the State of Sao Paulo, some 70 kilometers away from the city of Sao Paulo, and constitute a sizeable tourist center subject to great population fluctuations. Several alternatives were examined in order to solve the water deficit, one of them being the construction of conventional reinforced concrete reservoirs on hills existing in the target area. However, this solution presented several unfavorable factors, amongst which were the following:
limited availability of adequate locations for the construction of reservoirs, varying from 40 to 50 meters above sea level, near the consumer centers and with not too steep topography;
areas subject to instability where several land slides have already occured, which would consequently require slope stabilization of great cost.
the project is situated on Sta. Tereza hill which has a geological formation which lends itself to exacavation, as well as being located in between the two consumer centers;
the portal areas are situated in uninhabited locales, which makes expropriation much easier;
The number of reservoirs is reduced to only one, however this one has a large storage capacity; consequently both operational and maintenance costs are cut down;
there will be a reduction of the number of areas which must be expropriated, as well as less earthmoving, fewer access roads, less slope stabilization and a shorter extension of inlet, outlet and discharge pipe lines which must be installed;
greater operational flexibility will be obtained with the interconnection of the Santos and Sao Vicente water systems, thereby increasing the dependability of the overa 11 system;
there will be minimal disturbance of the nature of the hill, thus avoiding appreciable alterations in the ecological balance of the existing ecosystem; - the cost of carrying out the job will be much lower than that of a conventional solution.