Beneficial Aspects of Sea‐Water Intrusion

Abstract

ABSTRACTThe Permo‐Triassic sandstone aquifer of northwest England has been a major source of ground‐water supply since the early 19th century. Between Liverpool and Manchester, ground‐water resource development has led to a considerable lowering of the water level inland and intrusion of sea water from the Mersey Estuary and Manchester Ship Canal. As part of a detailed investigation of resource management, a two‐dimensional finite‐difference flow model was developed to represent aquifer behavior for the period 1840 to 1980. Subsequently, this model was used to predict the effects of implementing various management strategies over a 40‐year period ending 2020.Results indicate that ground‐water withdrawals have exceeded natural replenishment by an average of 100% during the past 50 years. In this time the potentiometric heads have responded remarkably slowly to the flow imbalance, a resilience that is largely attributed to the inflow of sea water at rates only marginally less than recharge from meteoric sources. Careful development of the fresh ground‐water resources has minimized water quality problems along the estuary and ship canal, and the model clearly shows how controlled inflow of saline water can considerably enhance the recovery of fresh ground‐water reserves. Difficulties arise only when excessive exploitation accelerates water quality deterioration. Model calculations indicate that inflow of saline water would continue for over 10 years following complete cessation of fresh ground‐water production.