Recharge of the Upper Chalk aquifer at a site in Hampshire, England: 1. Water balance and unsaturated flow

Abstract

Measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of Upper Chalk at a site in southern England are described. Measured evaporation continued at the Penman potential rate until the soil-moisture deficit reached 175 mm; this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used. The field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed. The mechanisms of water flow through the unsaturated zone of the Chalk are examined and it is shown that at this Upper Chalk site matrix flow is the dominant recharge mechanism.