Analysis of the time series of precipitation and well flow data to determine the sustainable yield of a well pumped at constant head

Abstract

Determining the yield of a production well remains one of the main challenges in hydrogeological studies. Yield estimates are especially challenging when a borehole taps a heterogeneous aquifer, such as those in fissured media. The present study examines a three-year survey of a continuously exploited well, functioning at constant-head. The studied well penetrates fractured rocks formed by locally poorly-karstified Cretaceous limestones with varying degrees of fracturing.The well discharge and precipitation data were analysed using two methods. Cross-correlation and cross-spectral functions were applied to the time series of precipitation and well flow data to investigate the lag time between a rainfall impulse and the corresponding discharge response of a well kept at constant head. The three recession curves of well discharge from the monitoring period were analysed with Maillet and Boussinesq models to investigate the storage volume and parameters regarding the depletion of the aquifer.The cross-correlation and cross-spectral analyses of well dis- charge and precipitation yield a response time of the aquifer to a precipitation input of approximately 30-40 days. The discharge recession curve analyses verify that a well at constant head behaves similar to a spring, therefore the ratio between the exploited resources and those available in the aquifer can be calculated. It results that analysing the discharge of a well functioning at constant head can be a valuable method for simultaneously obtaining data regarding an aquifer’s characteristics and the sustainable yield of a well.