22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Estimating natural gradient groundwater flow direction at multiple depths simultaneously in a bedrock aquifer using fibre optic Active Distributed Temperature Sensing (A-DTS)

27 Sep 2019, 12:15
15m
Multiuse room 3 ()

Multiuse room 3

Oral Topic 5.4 - Innovative approaches for understanding groundwater flow systems Parallel

Speaker

Dr Jonathan Munn (G360 Institute for Groundwater Research, University of Guelph)

Description

A new method to quantify groundwater flow direction at multiple depths simultaneously in a bedrock aquifer is demonstrated. The method utilizes the variable flow rate distribution around a pumping borehole at discrete depths in a bedrock aquifer with natural gradient flow. In such a system, there is generally an increase in flow rate up-gradient, and a decrease in flow rate down-gradient of the pumping well relative to the pre-pumping (natural gradient) conditions. Changes to groundwater flow rates in the aquifer can be detected with fibre optic Active Distributed Temperature Sensing (A-DTS) in multiple boreholes surrounding the pumping borehole, from which, the direction of natural gradient flow can be estimated at many different depths. The method was field tested at the Fractured Rock Observatory on the University of Guelph campus consisting of nine closely spaced boreholes across a 75 x 75 m area drilled to a depth of 73 m below ground surface. Two A-DTS tests were conducted in four observation boreholes under different hydraulic conditions: (1) when all boreholes were sealed with flexible fabric FLUTe liners to measure natural gradient flow rates without pumping, and (2) when the borehole in the centre of the cluster was open and pumped at a constant rate. The observed changes in flow rates at multiple depths were used to estimate the direction of natural gradient flow using a linear regression technique. The A-DTS derived flow direction matches the horizontal hydraulic gradient direction determined from depth-discrete hydraulic head at similar depth intervals. The approach shows excellent potential for efficiently providing both the magnitude and direction of groundwater flow at all depths simultaneously in a suite of boreholes in bedrock aquifers.

Primary authors

Dr Jonathan Munn (G360 Institute for Groundwater Research, University of Guelph) Mr Jonathan Kennel (G360 Institute for Groundwater Research, University of Guelph) Dr Carlos Maldaner (G360 Institute for Groundwater Research, University of Guelph) Mr Thomas Coleman (Silixa LLC) Prof. Beth Parker (G360 Institute for Groundwater Research, University of Guelph)

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