HGS RESEARCH HIGHLIGHT – Logjam Characteristics as Drivers of Transient Storage in Headwater Streams
Marshall, A., Zhang, X., Sawyer, A. H., Wohl, E., & Singha, K. (2022). Logjam Characteristics as Drivers of Transient Storage in Headwater Streams. Wiley. https://doi.org/10.1002/essoar.10512058.1
Figure 3: HydroGeoSphere simulated surface water depth (m) and groundwater mean age (log(hour)) for the 8 flume scenarios where the logjam permeability, number of logjams, and/or discharge change.
A new paper by researchers at Colorado State University, Ohio State University and the Colorado School of Mines (available on ESS Open Archive) highlights the impacts that logjams have on the transient storage in streams and rivers. The researchers used a physical flume to test a variety of scenarios and and relied on HydroGeoSphere to elucidate the surface and subsurface flow patterns which contributed to increased transient storage, and changes to hyporheic exchange in areas affected by logjams.
To determine the solute breakthrough and residence times in the physical experiments a sodium chloride tracer was applied, and concentrations were measured throughout. Based on the tracer testing it was concluded that the surface flow paths are more influential for solute transport, and the backwater area behind logjams is where most transient storage takes place. Additionally, they were able to establish that jams that are tightly packed have higher transient storage, and those higher rates of transient storage have the most substantial rate of hyporheic exchange and the greatest duration in the subsurface.
HydroGeoSphere models were used to reproduce six experimental flume tests (and two hypothetical tests) and demonstrated how flow paths would change under different conditions. This study used the groundwater age mass-transport capabilities of HydroGeoSphere to visualize the residence time of groundwater in the hyporheic zone. The new particle tracing capabilities of HGS were also used to calculate mean travel time in the subsurface.
This paper represents an interesting use case for HydroGeoSphere, utilizing several of the lesser-known capabilities of HGS to better understand dynamic flow conditions at a very local scale.
Interested in learning more about HGS research on the hyporheic zone? Check out these other HGS research highlights:
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Abstract:
Logjams in a stream create backwater conditions and locally force water to flow through the streambed, creating zones of transient storage within the surface and subsurface of a stream. We investigate the relative importance of logjam distribution density, logjam permeability, and discharge on transient storage in a simplified experimental channel. We use physical flume experiments in which we inject a salt tracer, monitor fluid conductivity breakthrough curves in surface water, and use breakthrough-curve skew to characterize transient storage. We then develop numerical models in HydroGeoSphere to reveal flow paths through the subsurface (or hyporheic zone) that contribute to some of the longest transient-storage timescales. In both the flume and numerical model, we observe an increase in backwater and hyporheic exchange at logjams. Observed complexities in transient storage behavior may depend largely on surface water flow in the backwater zone. As expected, multiple successive logjams provide more pervasive hyporheic exchange by distributing the head drop at each jam, leading to distributed but shallow flow paths. Decreasing the permeability of a logjam or increasing the discharge both facilitate more surface water storage and elevate the surface water level upstream of a logjam, thus increasing hyporheic exchange. Multiple logjams with low permeability result in the greatest magnitude of transient storage, suggesting that this configuration maximizes solute retention in backwater zones, while hyporheic exchange rates also increase. Understanding how logjam characteristics affect solute transport through both the channel and hyporheic zone has important management implications for rivers in forested, or historically forested, environments.