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Hydrogeology

DAAD: Development of Hydrogeophysical Methods to Characterize Water Fluxes in the Vadose Zone of Karstified and Porous Heterogeneous Aquifers

As part of GRaCCE, this project aims to delineate a fractured aquifer using the DTS (Distributed Temperature Sensor) and the ERT (Electrical Resistivity Tomography) instrument and characterize the water flow within the vadose zone in a fractured aquifer. Initial experiments are conducted within a  porous aquifer. Temperature-depth profiles in boreholes will allow calculating the infiltration velocity as a response to daily and seasonal temporal temperature changes. The injection of heated water will then increase the heat signal. 

Project Goals

  • Characterizing infiltration dynamics into karst and porous aquifer using DTS (Distributed Temperature Sensing) technique
  • Utilizing ERT (Electrical Resistivity Tomography) to derive subsurface structures that are relevant for infiltration processes
  • Transfer the developed technique from a porous to a fractured aquifer
© Harmya Sathyan

Distributed Temperature Sensing

The Distributed Temperature Sensor measures different variables along a fiber optic cable. The sensor is composed of two parts where the first is the device that sends a light signal into the fiber optic cable and receives the reflection generated by the rayleigh scattering as the light travels through the fiber optic cable and the second part is the fiber optic cable. If the light is traveling through a fiber optic cable it is being reflected at every point inside the cable. These reflections will travel in the opposite direction as compared to the main direction of the light. These reflections are received by a highly sensitive receiver present at the starting point of the fiber optic cable and measure the temperature.

 

© Harmya Sathyan

Distributed Temperature Sensing (DTS) Instrument

Electrical Resistivity Tomography

Electrical Resistivity Tomography (ERT) allows the analysis of subsurface heterogeneities that influence the infiltration dynamics. One of the most recent advancements in analyzing sediment and hard rock structures is applying the two-dimensional ERT approach. Increasing the electrode spacing gives a greater depth penetration and it provides a 2D contoured section viewing lateral and vertical variations in resistivity. The ERT method is an electrical testing method where current is induced in the ground using two current electrodes. The electrical potential drop is measured is then read using two other electrodes. With the increase in the percent water saturation, the resistivity of the material decreases so the low resistive layers of fault zones suggest the presence of water.

© Chandran et al. (2014)

ERT example from Chandran et al. (2014).

Investigated Field Sites – Hobrechtsfelde and Rüdersdorf

The location Hobrechtsfelde was formerly a Rieselfeld (sewage field). The location consists of 14 wells that are 1-2 meters apart from one another. These wells serve as the hosts for high-resolution pressure and temperature monitoring equipment and are dispersed over a 3-D subsurface area. The location is suited for thermo-tracer tomography experiments and hydraulic tomography studies in three dimensions, and it can host dispersed temperature monitoring systems. To confirm the various hydraulic conditions, a portion of the wells is filtered in an upper, unconfined aquifer and the other portion in a lower, confined aquifer.

East of Berlin, the Rüdersdorf field site is primarily a limestone quarry. It is the key pilot site in GRaCCE for developing using hydrogeophysical techniques to measure and monitor infiltration into the vadose zone with the TDR technique. Therefore, we plan to create several vertical and slanted boreholes at the field site, which will be equipped with TDR bands and fiber optic cables down to a depth of 30m.

© Paul Hepach

Top-down view of the small Hobrechtsfelde site

© Harmya Sathyan

Map of the Rüdersdorf site

© Irina Engelhardt

Example for a highly heterogeneous vadose zone of a porous aquifer

Project Details

Project Coordination

TU Berlin
Coordinator: Prof. Dr. Irina Engelhardt
PhD Student: Harmya Sathyan

Cooperation Partners

UFZ - Helmholtz Centre for Environmental Research

CEMEX

LIAG - Leibniz Institute for Applied Geophysics

Funding

DAAD (Deutscher Akademischer Austauschdienst)