A heat pulse technique for the determination of small‐scale flow directions and flow velocities in the streambed of sand‐bed streams

Abstract

Abstract:The hyporheic zone (HZ) has the capability to eliminate and attenuate nutrients and contaminants in riverine systems. Biogeochemical reactions and the potential elimination of contaminants are strongly controlled by the flow paths and dynamics in the HZ. Nevertheless, an easily applicable method for the field determination of flow patterns in the HZ is still lacking. Therefore, a heat pulse technique, which traces the movement of a short heat pulse in the upper part of the HZ and other sand beds, was developed. Five rods are vertically driven into the sediment of the streambed; one rod with a heater as point source located in about 10-cm sediment depth and four rods with four temperature sensors in 3 cm distance, arranged concentrically with 7 cm diameter around the heating rod. Subsequently, a heat pulse is applied and the resulting breakthrough curves are indicative of flow velocities and flow directions in the streambed. A rough data analysis procedure is also suggested. In addition, laboratory experiments were performed to test the heat pulse technique. These experiments were validated based on coupled numerical modelling of flow and heat transport. First field tests of the method prove that the method is easily applicable under field conditions. These first field tests showed highly complex flow patterns with flow velocities from 1Ð8 to 4Ð9 cm min 1 and flow directions from parallel to surface flow to opposite to surface flow. This suggests the need for a robust method to quantify hyporheic flow patterns in situ.

Active heat pulse sensing of 3-D-flow fields in streambeds

“…Despite the early pioneering work of Lewandowski et al (2011) and Angermann et al (2012b) for the concept of a 3-D active heat pulse sensor to determine flux and direction in the shallow streambed, their studies experienced a number of shortcomings that are related to the design of the instrument and the analysis of the data. This included (1) a limited number of sensors and spatial positions around the heating element; (2) weakness with the sensor sticks wobbling and therefore poorly constrained sensor positions in relation to the heating element; (3) limited constraint on the input functions to the heat transport equation, i.e.…”

“…The distances of the sensors are oriented relative to this new flow vector. The main advantage over previous approaches is that all sensors can be included rather than a single sensor from the array accounting for a single transverse distance (Lewandowski et al, 2011). We then substitute these new dimensions into Eq.…”

“…It builds upon previous studies by Lewandowski et al (2011) and Angermann (2012a, b), who developed an active heat pulse sensor to determine the flow direction and flow velocity in shallow sandy stream environments. In the present study we have developed a more robust field instrument and advanced the analysis of the temperature breakthrough data using the analytical solution of the heat transport equation for a 3-D array.…”

“…The injection of heat as a tracer is not new, with a number of studies using the active temperature-sensing technique to evaluate groundwater flow within wells (Sellwood et al, 2016;Read et al, 2014;Banks et al, 2014), flow in sediments (Greswell et al, 2009;Ballard, 1996;Bakker et al, 2015), surface water-groundwater exchange processes (Kurth et al, 2015) and hyporheic exchange flows in the hyporheic zone (Angermann et al, 2012a, b;Lewandowski et al, 2011).…”

Vertical hydraulic gradient research in hyporheic zone of Beberibe river in Pernambuco State (Brazil)

“…This report is made from the hydrological point of view, using the definition of Lewandowski et al (2011) with the hyporheic zone as the saturated transition zone between surface water and groundwater, being a key terrestrial hydrosphere compartment.…”