MODELING RIVER-AQUIFER INTERACTIONS AT THE SPEY ABSTRACTION SCHEME, SCOTLAND - IMPLICATIONS FOR AQUIFER PROTECTION

Groundwater resources in Scotland are receiving increasing attention b ecause of the high costs of surface water treatment and the stringent water quality requirements of the EC Drinking Water Directive. On the River Spey, a unique abstraction scheme has been developed, involving a wellfield comprising 36 production boreholes in the river gravels of the lower catchment. The scheme aims to provide a maximum of 27 000 m (3)/d to meet increasing water demands in northeast Scotland by 2011. This yield is equivalent to one-third of the current total public grou ndwater abstraction in Scotland. This paper describes a steady-state q uasi-three-dimensional numerical model of the Spey river-aquifer syste m which was used in conjunction with a particle tracking program to de lineate travel time related capture zones of the Spey abstraction well field. Three scenarios were simulated: pre-development, current pumpin g rate (16 000 m(3)/d) and projected maximum pumping rate. The pre-dev elopment water budget indicates that 94% of total groundwater inflow i s discharged into the river, whereas the budgets for stressed conditio ns give the percentage of water abstracted from the river as 69% and 7 4% for current and maximum pumping rates respectively. Capture zones o f 50-day (Zone 1) and 400-day (Zone 2) travel time to the wellfield ar e defined for the projected maximum pumping rate. These indicate that the river itself is the primary potential polluting source. However, e xtensive areas of the river floodplain also contribute significantly t o the abstraction, thus certain restrictions on potentially polluting activities are needed. It is concluded that rigorous programmes for mo nitoring water quality both in the river upstream, and within the mode lled catchment are required to protect the Spey Abstraction Scheme.