Enhanced Hydrologic Monitoring using Fiber Optics - Implementing Distributed Temperature Sensing to Uncover Flow Paths and Groundwater Interactions in Stormwater Conveyance Structures

Abstract:

The need to construct resilient waterways is of growing importance in the face of extreme weather events and environmental degradation. However, the groundwater dynamics of systems, especially regenerative storm water conveyance systems (RSC), are not yet fully understood. Through technological advancements, the precision and availability of tools for monitoring in-situ parameters have increased dramatically. However, an accurate method for determining water fluxes through retention systems remains uncertain and challenging. For instance, methods like multi-needle heat pulse approaches have demonstrated the ability to make point measurements of water fluxes in the vadose zone; these offer limited viability in the field due to their minuscule sphere of influence and the need to understand flux densities behavior over large spatial scales. We intend to improve this long-standing limitation by instead taking hundreds of simultaneous distributed measurements through an RSC by utilizing fiber-optic distributed temperature sensing (FO-DTS) technology.

The measurement principle relies on the calculation of water flux using heat pulse data generated by supplying a constant current to the shielding of the FO cable. This methodology enables both continuous heating and temperature measurements along the desired length of FO cable, allowing for fluxes to be measured throughout the cross-section of an RSC.

I will be presenting the theoretical background and preliminary results of laboratory and field experiments, and how our data can be used in existing heat pulse models to better understand the coupled heat and water transfer through porous media. Additionally, we will discuss the benefits of this enhanced monitoring approach and its use in evaluating the efficacy of stormwater systems.

Early laboratory tests show potential for FO-DTS uses in applications under field conditions; however, further experimentation is required to fully address the challenges of these methods. Despite these challenges, the long-sought-after ability to accurately measure water flux density would give hydrologists, engineers, and land managers a valuable tool to better understand the processes of infiltration, runoff, and subsurface treatment.