TemPro: A Low Cost Temperature Profiling Probe
Looking beneath the streambed
A stream is not limited to the water visible at the surface. Water continuously enters, moves through, and returns from the sediments beneath the channel. This region, known as the hyporheic zone, connects surface water and groundwater and influences stream temperature, nutrient transport, contaminant movement, and ecological functioning.
Despite its importance, hyporheic exchange remains difficult to monitor.
Why Do We Need to Understand the Hyporheic Zone?
How important is the hyporheic zone? ...Can we afford to ignore it?
Beneath the visible stream lies the hyporheic zone—a dynamic region where stream water enters the sediments, mixes with groundwater, and may later return to the channel. Although hidden, it regulates water temperature, provides habitat, increases water residence time, and supports the transformation of nutrients and contaminants. It can promote processes such as nitrate removal, but under unsuitable conditions it may also store and later release pollutants. Ignoring this zone would therefore provide an incomplete understanding of river flow, ecology, and water quality.
Why is hyporheic exchange difficult to quantify, and why will it matter in the future?
Exchange occurs below the streambed, varies over very short distances, and changes with streamflow, groundwater levels, sediment type, and geomorphic features such as boulders, riffles, meanders, and log jams. A measurement at one point may not represent the surrounding reach, while installing instruments can disturb the sediment and alter natural flow paths. Understanding these exchanges will become increasingly important as climate change, droughts, floods, groundwater extraction, nutrient loading, and emerging contaminants place greater pressure on rivers and their natural ability to regulate temperature and water quality.
What methods are available to quantify hyporheic exchange?
Common approaches include piezometers and hydraulic-gradient measurements, seepage meters, salt or dye tracer experiments, environmental and isotope tracers, pore-water chemistry, temperature monitoring, geophysical surveys, and numerical modelling. Each method measures a different component or spatial scale: hydraulic methods indicate flow potential, seepage meters measure local exchange, tracer tests describe reach-scale storage, chemistry reveals transformation, and temperature enables continuous flux estimation. Because no single method provides a complete picture, there is a need for affordable, continuous, multi-depth monitoring systems that can be deployed at several locations—which motivated development of TemPro
So, if there are already so many ways to study hyporheic exchange, why do we need another approach?
The answer lies in the trade-offs. Some methods provide very detailed measurements but only at a few locations. Others cover larger areas but offer only a snapshot in time. Some require repeated field visits, laboratory analysis, or relatively expensive equipment. The figure below brings these trade-offs together by comparing these existing methods in terms of their temporal capability, spatial capability, and relative resource demand, while showing where temperature-based monitoring fits within the broader toolbox for quantifying hyporheic exchange.
Clearly, no single method performs best in every situation. Temperature profiling, however, occupies a particularly useful space: it can capture changes at minute-scale intervals, continue monitoring for weeks or months, and be deployed at multiple depths and locations. In other words, it offers a valuable combination of high temporal resolution, long-term monitoring capability, useful spatial coverage, and relatively lower resource demand.
These advantages made temperature a natural choice for monitoring hyporheic exchange. The next question was simple: can this kind of monitoring be made more affordable, practical, and easier to deploy across multiple locations?
That question is where TemPro begins.
The process occurs beneath the sediment surface, varies over short distances, and often requires several sensors to capture its spatial and temporal behaviour.
Commercial temperature-monitoring systems provide reliable observations, but the cost of deploying several instruments can limit their use in spatially distributed studies.
TemPro was developed to address this challenge.
TemPro is a low-cost, field-deployable temperature profiling system designed to record streambed temperature continuously at multiple depths. The measurements can be used to examine groundwater–surface-water interactions and estimate vertical water flux through streambed sediments.
Explore TemPro
TemPro combines an above-the-stream control and logging unit with a subsurface probe carrying temperature sensors at selected depths.
The interactive explorer below allows you to move through the instrument step by step.
Through the interactive display, visitors can examine:
The complete TemPro instrument
The control and logging enclosure
The battery-management and logging board
The wiring and sensor arrangement
The instrumented probe body
The sensor interface
The waterproof temperature sensor
The perforated protective casing
Each highlighted point opens a closer view and a short description of the selected component.Begin with the complete system and select either the control unit or the probe assembly.
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