Abstract
Abstract. Climate change and land use are rapidly changing the amount and temporal distribution of recharge in northern aquifers. This paper presents a novel method for distributing Monte Carlo simulations of 1-D sandy sediment profile spatially to estimate transient recharge in an unconfined esker aquifer. The modelling approach uses data-based estimates for the most important parameters controlling the total amount (canopy cover) and timing (thickness of the unsaturated zone) of groundwater recharge. Scots pine canopy was parameterized to leaf area index (LAI) using forestry inventory data. Uncertainty in the parameters controlling sediment hydraulic properties and evapotranspiration (ET) was carried over from the Monte Carlo runs to the final recharge estimates. Different mechanisms for lake, soil, and snow evaporation and transpiration were used in the model set-up. Finally, the model output was validated with independent recharge estimates using the water table fluctuation (WTF) method and baseflow estimation. The results indicated that LAI is important in controlling total recharge amount. Soil evaporation (SE) compensated for transpiration for areas with low LAI values, which may be significant in optimal management of forestry and recharge. Different forest management scenarios tested with the model showed differences in annual recharge of up to 100 mm. The uncertainty in recharge estimates arising from the simulation parameters was lower than the interannual variation caused by climate conditions. It proved important to take unsaturated thickness and vegetation cover into account when estimating spatially and temporally distributed recharge in sandy unconfined aquifers.
Highlights
Eskers are permeable, unconfined sand and gravel aquifers (Banerjee, 1975)
It is capable of producing spatially and temporally distributed groundwater recharge values with uncertainty margins, which are generally lacking in recharge estimates, despite understanding of uncertainty related to recharge estimates being potentially crucial for groundwater resource management
The parameter uncertainty defined for the study area was of minor significance compared with interannual variations in the recharge rates introduced by climate variations
Summary
Eskers are permeable, unconfined sand and gravel aquifers (Banerjee, 1975). In addition to water supply, they support groundwater-dependent ecosystems and provide recreational services (Kløve et al, 2011). Esker hydrology is important as eskers and other glaciofluvial aquifer types cover large areas of the north and are among the dominant aquifer types in the boreal zone. Management of these complex aquifers has gained recent attention (Bolduc et al, 2005; Karjalainen et al, 2013; Koundouri et al, 2012; Kurki et al, 2013). The soil surface profile of eskers is complex and highly variable, consisting of kettle holes and sand dunes, resulting in variable thickness of the unsaturated zone (Aartolahti, 1973), a factor which needs to be accounted for in recharge estimation
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