Modelling river-aquifer interactions at the Spey abstraction scheme, Scotland: Implications for aquifer protection

Groundwater resources in Scotland are receiving increasing attention because 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 groundwater abstraction in Scotland. This paper describes a steady-state quasi-three-dimensional numerical model of the Spey river-aquifer system which was used in conjunction with a particle tracking program to delineate travel time related capture zones of the Spey abstraction wellfield. Three scenarios were simulated: pre-development, current pumping rate (16 000 m(3)/d) and projected maximum pumping rate. The pre-development water budget indicates that 94% of total groundwater inflow is discharged into the river, whereas the budgets for stressed conditions give the percentage of water abstracted from the river as 69% and 74% for current and maximum pumping rates respectively. Capture zones of 50-day (Zone 1) and 400-day (Zone 2) travel time to the wellfield are defined for the projected maximum pumping rate. These indicate that the river itself is the primary potential polluting source. However, extensive areas of the river floodplain also contribute significantly to the abstraction, thus certain restrictions on potentially polluting activities are needed. It is concluded that rigorous programmes for monitoring water quality both in the river upstream, and within the modelled catchment are required to protect the Spey Abstraction Scheme.