RMZ-M&G 2003, 50 RMZ - Materials and Geoenvironment, Vol 50, No 1, pp 1-4, 2003 1 Scientific paper Drainage problems during construction operations within a burried valley gravel aquifer ALISTAIR ALLEN, DEJAN MILENIC Dept of Geology, University College Cork, Cork, Ireland; E-mail: aallen@uccie Abstract: Dewatering, to a depth of 5 m, of a 400 m 2 excavation in gravels (k f = 687 x 10 -3 msec -1 ) in a buried valley ribbon aquifer in Cork, SW Ireland, during construction of a basement, has proved problematic Drainage required operation of 16 submersible, sump and suction pumps, with a total stated capacity of 400,000 gals/hr (500 l/sec) pumping at maximum capacity Key words: Dewatering; Gravels; Buried Valley Aquifer; Basement Excavation INTRODUCTION Hydrogeological conditions are rarely considered during the design and planning stages of build- ings and other construction projects by architects and civil engineers, even in situations when indi- cations would make it prudent to do so This can have significant consequences, when construction begins and groundwater conditions turn out to be a problem, as it is usually too late to modify the design parameters of the construction once the planning procedure has been completed We describe here the drainage problems encountered in the construction of an Art Museum at University College Cork (UCC), Ireland, located on a riverside site in the floodplain of the River Lee, which flows through Cork city The floodplain overlies a buried valley infilled with gravels with an extremely high hydraulic conductivity THE CONSTRUCTION SITE The construction site is in the lower grounds of UCC main campus, on the south bank of the South Channel of the west to east flowing River Lee a kilometre to the west of Cork city centre (Fig 1) The Lee, consists of two distributary channels 400 m apart, which separate about a kilometre up- stream of the site and reunite about 3 km downstream at the beginning of its estuary It occupies a broad low-lying floodplain approximately half a kilometre wide at this point The construction site is situated about 20 m from the base of a 30 m high limestone scarp, which marks the edge of the floodplain The Lee is tidal within Cork city, and the construction site is at about the tidal limit in the South Channel, with a range of about 15 cm in groundwater levels The Lee floodplain overlies a buried valley, formed 15,000 years ago during the Pleistocene glacia- tion, when sea level fell to -130 m OD, and rivers cut down to the new base level (ALLEN ET AL, 1999) At the end of the glaciation approximately 10,000 years ago, when the ice receded and sea