Water seepage investigation using geo-electric streamers

Summary

Seepage from canals and reservoirs can be identified using geo-electric streamers. About 10 kilometres of canal can be surveyed by two people in one day. In electrical conductivity (EC) imagery created, seepage pathways through the substrate reflect the EC of surface water from which seepage was sourced as well as substrate permeability and clay content which enhances EC. Seepage tends not to occur readily through clay and the result, within EC imagery, is generally clear definition of seepage pathways through the substrate. In Australia, canals are typically situated on clayey low flow regime sedimentary deposits where evapotranspiration has concentrated salt in shallow sediment, particularly clays, and seepage has preferentially flushed out this salt resulting in a very clear EC signature regardless of water table depth. In high flow regime environments such as much of New Zealand, seepage pathway anomalies are usually more conductive than the host substrate which is usually cobbles, glacial rock flour and air.

A practical imaging system has been created using a submerged streamer towed behind a floating waterproof equipment capsule housing geo-electric, DGPS, sonar, data logging, and often other instrumentation. The capsule is towed either behind a boat or by two ropes pulled by walkers on each canal bank. Operation is via a wi-fi connection. The capsule is light enough to lift over the numerous obstacles that cross most canals. Imaging is presented in 3D within Google Earth so that water managers can readily handle and use the data.

Key words::

• Seepage
• resistivity
• canals
• channels
• rivers