Restoration increases transient storages in boreal headwater streams

Wohl

2023

Front. Water

Accumulations of wood in rivers can alter three-dimensional connectivity and facilitate channel bifurcations. Bifurcations divide the flow of water and sediment into secondary channels and are a key component of anastomosing rivers. While past studies illustrate the basic scenarios in which bifurcations can occur in anastomosing rivers, understanding of the mechanisms of bifurcations remains limited. We evaluate wood-induced bifurcations across thirteen anastomosing reaches in nine different streams and rivers in the U.S. Rocky Mountains to address conditions that favor different bifurcation types. We hypothesize that (1) wood-induced bifurcations exist as a continuum of different patterns in anastomosing rivers and (2) the position of a river segment along this continuum correlates with the ratio of erosive force to erosional resistance (F/R). We use field data to quantify F/R and compare varying F/R to bifurcation types across sites. Our results support these hypotheses and suggest that bifurcation types exist as a continuum based on F/R. At higher values of F/R, more channel avulsion is occurring and predominantly lateral bifurcations form. At lower values of F/R, banks are more resistant to erosive forces and wood-induced bifurcations are transitional or longitudinal with limited lateral extent. The relationship between F/R and bifurcation types is not linear, but it is progressive. Given the geomorphic and ecological functions associated with large wood and wood-induced channel bifurcations, it becomes important to understand the conditions under which wood accumulations can facilitate different types of bifurcations and the processes involved in these bifurcations. This understanding can inform river corridor restoration designed to enhance the formation of secondary channels, increase lateral and vertical connectivity, and promote an anastomosing planform.

Section: Significance Of Wood-induced Bifurcationsmentioning

confidence: 99%

The continuum of wood-induced channel bifurcations

Wohl

2023

Front. Water

“…Transient storage can be increased by morphologic and geologic features that create spatial heterogeneity in water velocity and drive alternate patterns of downwelling and upwelling along the bed. Examples of such features include bedforms and other variations in channel cross‐sectional geometry (Bencala, 1983; Ensign & Doyle, 2005; Gooseff et al., 2007; J. W. Harvey & Bencala, 1993; Kasahara & Wondzell, 2003), logjams (Ader et al., 2021; Hester & Doyle, 2008; Marttila et al., 2018; Sawyer et al., 2011), and variations in alluvial thickness and grain‐size distribution (J. W. Harvey et al., 1996). Here, we focus on the effects of logjams as an important morphologic element that creates both surface transient storage in the channel (e.g., backwater zones) and subsurface transient storage in porous media (e.g., hyporheic exchange zones).…”

Section: Introductionmentioning

confidence: 99%

“…geometry (Bencala, 1983;Ensign & Doyle, 2005;Gooseff et al, 2007;J. W. Harvey & Bencala, 1993;Kasahara & Wondzell, 2003), logjams (Ader et al, 2021;Hester & Doyle, 2008;Marttila et al, 2018;Sawyer et al, 2011), and variations in alluvial thickness and grain-size distribution (J. W. Harvey et al, 1996). Here, we focus on the effects of logjams as an important morphologic element that creates both surface transient storage in the channel (e.g., backwater zones) and subsurface transient storage in porous media (e.g., hyporheic exchange zones).…”

mentioning

confidence: 99%

Logjam Characteristics as Drivers of Transient Storage in Headwater Streams

Water Resources Research

Zhang

Sawyer

et al. 2023

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 determine breakthrough‐curve skewness to characterize transient storage. We then develop a companion numerical model 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 experiments and numerical simulations, we observe backwater formation and an increase in hyporheic exchange at logjams. Observed complexities in transient storage behavior 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 greater surface water storage and volumetric rate of hyporheic exchange. 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.

“…Transient storage can be generally segregated into surface transient storage-where water flows slowly through recirculation zones and stagnant areas of low velocity-and subsurface transient storage (controlled in part by hyporheic exchange-where stream water flows through the subsurface and returns to the channel). Transient storage has numerous benefits to river corridor ecosystem services and processes including i) increased biogeochemical cycling (Fischer et al, 2005;Battin et al, 2008;Tonina & Buffington, 2009;Harvey & Gooseff, 2015;Marttila et al, 2018); ii) nutrient and pollutant processing (Harvey & Wagnert, 2000;Hall et al, 2002;Ensign & Doyle, 2005;Stewart et al, 2011); iii) increased habitat diversity and thermal refugia (Mulholland et al, 2004;Hester & Gooseff, 2010); and iv) flow attenuation (Herzog et al, 2018). Transient storage can be increased by morphologic and geologic features that create spatial heterogeneity in water velocity and drive alternate patterns of downwelling and upwelling along the bed.…”

Section: Introductionmentioning

confidence: 99%

“…Transient storage can be increased by morphologic and geologic features that create spatial heterogeneity in water velocity and drive alternate patterns of downwelling and upwelling along the bed. Examples of such features include bedforms and other variations in channel cross-sectional geometry (Bencala, 1983;Harvey & Bencala, 1993;Kasahara & Wondzell, 2003;Ensign & Doyle, 2005;Gooseff et al, 2007), logjams (Hester & Doyle, 2008;Sawyer et al, 2011;Marttila et al, 2018;Ader et al, 2021), and variations in alluvial thickness and grain-size distribution (Harvey et al, 1996). Here, we focus on the effects of logjams as an important morphologic element that creates both surface transient storage in the channel (for example, backwater zones) and subsurface transient storage in porous media (for example, hyporheic exchange).…”

Section: Introductionmentioning

confidence: 99%

Logjam Characteristics as Drivers of Transient Storage in Headwater Streams

Zhang

Sawyer

et al. 2022

Preprint

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.