Groundwater discharge from the superficial aquifer into Cockburn Sound Western Australia: estimation by inshore water balance

Abstract

Submarine groundwater discharge (SGD) into Cockburn Sound Western Australia was quantified by applying a distributed groundwater flow model to estimate the inshore aquifer water balance. Spatially averaged SGD along the coast was estimated to be 2.5–4.8 ± 0.9 m³ day⁻¹ m⁻¹. The range in estimated average SGD reflected low and high estimates of average groundwater recharge, which ranged from 0.13 to 0.24 m year⁻¹ (15–28% of average annual rainfall). The error ±0.9 m³ day⁻¹ m⁻¹ was calculated by assuming arbitrary ±20% errors in groundwater pumping and inflow across boundaries. SGD varied spatially along the coastal boundary due to variation in hydraulic connection between the coastal aquifers and ocean, and spatial variability in recharge, transmissivity and pumping. Under assumptions of low and high groundwater recharge, SGD along the coastline varied in the ranges 1.4–4.6 m³ day⁻¹ m⁻¹ and 2.4–7.9 m³ day⁻¹ m⁻¹, respectively.