Hydraulic behaviour and regional impact of a horizontal well in a shallow aquifer: example from the Sefton Coast, northwest England (UK)

Horizontal wells can be utilised for groundwater abstraction in aquifers of limited saturated thickness. One feature that must be considered is the hydraulic head inside the horizontal well, since hydraulic head gradients can be substantial in long wells with relatively small cross-sectional areas. Little experimental evidence is available concerning horizontal wells, but this report describes field data collected for a 300-m long horizontal well in northwest England (UK); the well is curved in plan, in a shallow unconfined aquifer. Conceptual and computational models are presented; they represent regional groundwater flow, convergent groundwater flows towards and into the well, and also hydraulic conditions within the well. Good agreement is achieved between field and modelled values for groundwater heads in the aquifer and for hydraulic heads in the well. The computational model is then used to explore the rates of inflow along the well; the impact on regional groundwater conditions of abstraction from the well is also examined. Finally, a preliminary comparison is made between vertical well points and horizontal wells in shallow aquifers.