AN ANALYTICAL SOLUTION FOR DESIGN OF BI-LEVEL DRAINAGE SYSTEMS

The linearized Boussinesq equation has been used to formulate a bounda ry value problem for a bi-level drainage system. The validity of the s olution has been established by comparison with an existing solution a nd field data reported in the literature. The results reveal that the proposed solution can be used in assessing the ground water table beha viour in a bi-level drainage system. The solution has been used to sho w that with increasing time, the location where maximum hydraulic head occurs moves towards the shallow drain. As the maximum hydraulic head approaches the shallow drain, drain discharge of the deeper drain is comparable with drain discharge from a conventional level drain system with double the spacing of the bi-level drains. Moreover, the decreas e in hydraulic head is much slower compared to conventional level drai n system once the hydraulic head approaches the shallow drain. Conside ring several issues that have been put forth as a result of many studi es on horizontal subsurface drainage in India, it is proposed that bi- level drainage could be tried as a means of controlled drainage by app ropriately deciding the depth of the shallow drain. As the proposed eq uation can not explicitly be used for drainage design, a computer prog ramme has been reported to determine the lateral drain spacing. (C) 19 98 Elsevier Science B.V.