Seepage meter: Progressing a simple method of directly measuring water flow between surface water and groundwater systems

Many important water issues such as over-allocation, stream salinity and environmental flows are influenced by the interaction between rivers and underlying aquifers. There are many indirect ways of estimating this flux (such as using hydrographs, tracers or geophysics) but the most common direct method is the use of seepage meters. Over recent decades, various modifications have been made to the basic seepage meter to address potential sources of measurement error and to handle operational issues. These aim to reduce the impact of factors such as upward advection of interstitial water (the Bernoulli effect), venturi effects of stream flow on the collection bag, anomalous short-term influx due to bag properties, gas accumulation in the chamber, frictional resistance causing head losses, ineffective seals and capture of shallow throughflow (rather than groundwater). We have attempted to incorporate these improvements in our seepage meter design and development of simple field procedures, which were trialled in two contrasting catchments (Border Rivers and Lower Richmond) in Australia. The field trials had mixed success, highlighting the potential for spurious seepage flux measurements due to these operational issues.