The Ganga±Mahawa sub-basin, which has an area of 1280 km 2 forms the western part of the Central Ganga Plain in the Moradabad and Badaun districts of western Uttar Pradesh, India. The Bundelkhand granite forms the basement complex, overlain unconformably by the upper Vindhyan sequence, which is further overlain by the Neogene (Middle and Upper) Siwaliks and ®nally by Quaternary alluvium. Four geomorphological units, the Varanasi older alluvial plain, Aligarh older alluvial plain, terrace zones and the Ganga recent ¯oodplain, abandoned channels, channel scars and meander scars represent various landforms. The hydrogeological crosssections indicate the occurrence of a single aquifer down to 120 m. Some in¯uent seepage from the River Ganga could be seen around Gangeswari, but the rest of the River Ganga is euent.
Groundwater-¯ow modelling was carried out to assess the degree of Ganga river and aquifer interaction. The River Ganga marks the western boundary; boundaries to the northeast and southeast are set as ®xed heads to simulate lateral in¯ow into and out¯ow from the sub-basin respectively. The eastern boundary is simulated as a no-¯ow condition. The Mahawa and Badmar rivers are considered to be euent. The area modelled is covered by a grid of 34 rows  46 columns with three layers, viz., an uncon®ned aquifer, an aquitard which is underlain by a semi-con®ned to con®ned aquifer. The permeability distribution was inferred from morphometric analysis and pumping tests. Natural recharge due to monsoon rainfall forms the main input. The River Ganga stage data at Ahar, Naora and Ramghat has been used for assigning surface water levels and river bed elevations in the model. Abstraction from all existing deep and shallow tube wells has been assigned as output at various cells. A steady state ¯ow simulation was carried out and calibrated against the June 1986 water level; subsequent transient conditions were calibrated up to May 1995. The computed groundwater balance was comparable to that estimated from ®eld investigations. The aquifer modelling study has attempted to integrate all available information and provided a tool that could be used for predictive simulation.