Logjam Research Articles

Impacts of Post‐Fire Debris Flows on Fluvial Morphology and Sediment Transport in a California Central Coast Stream

AbstractPost‐fire debris flows alter impacted fluvial systems, but few studies quantify the magnitude and timing of reach‐scale channel response to these events. In August 2020, the Big Creek watershed along California's central coast burned in the Dolan Fire; in January 2021, an atmospheric river event triggered post‐fire debris flows in steep tributaries to the Big Creek. Here, we characterize the evolution of fluvial morphology and grain size in Big Creek, a cascade and step‐pool channel downstream of tributaries in which post‐fire debris flows initiated, using pre‐ and post‐fire structure from motion (SfM) and airborne lidar surveys. We also make comparisons to Devil's Creek, an adjacent basin which burned but did not experience post‐fire debris flows. We observe grain size fining following debris flows in Big Creek, but the coarsest 40% of the grain size distribution remained essentially unchanged despite reorganization of channel structure. Changes in grain size and elevated post‐fire peak flows account for approximately equal portions of a substantial increase in modeled bedload transport capacity one year post‐fire. In Big Creek, geomorphic recovery is well underway just two years post‐fire. A valley‐spanning log jam, which formed during debris flows, acts as a sediment trap upstream of our Big Creek study reach, and is partially responsible for accelerating recovery processes. In contrast, Devil's Creek exhibited little change in morphology or grain size despite elevated post‐fire peak flows. This period of geomorphic dynamism following the Dolan Fire has complex ecological impacts, notably for the threatened anadromous salmonid spawning habitat in Big Creek.

Understanding how restoration reduces competition for habitat by combining theory, observation, and experiment.

Habitat selection theory enables inferences about species habitat choice across a range of observed population densities. However, it is relatively uncommon to use habitat selection theory in studies of habitat restoration efficacy to understand the effect of restoration on habitat competition. We combined observational density data and resource selection functions to analyze habitat correlations with both habitat selection theory and a mark-recapture experiment to show how habitat restoration can mitigate competition between species with similar habitat preferences. To restore degraded and channelized riverine habitat for juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) engineered log jams (ELJs) have been installed to create pools to enhance growth and rearing. Application of habitat selection theory first showed that both species share a preference for ELJ-treated habitat over unrestored habitat. Linear models showed that steelhead are generalists with respect to depth in unrestored habitat, whereas both species' abundance varies along a depth gradient in ELJ-treated habitat. Selective versus opportunistic use of deep and shallow ELJ pools was density-dependent. We found a range of densities at which a "ghost of competition" exists, where Chinook are selective on deep ELJ-treated pools and steelhead are selective on shallow pools. A mark-recapture experiment confirmed that steelhead limit Chinook movement into unrestored habitat, but this competitive effect vanished in ELJ-treated habitat where selection occurred with respect to pool depth. The experiment, combined with theory, enabled (1) the identification of a mechanism allowing for shared preference of restored habitat and (2) the description of how restoration can mitigate competition.

A conceptual model on the influence of logjam formation on longitudinal and lateral sediment dynamics in forested streams

Large wood (LW) and log jams have important implications for sediment dynamics within river systems. Although many case studies explore this topic, far fewer synthesize these results at the reach and basin scales. In this paper, we present a conceptual model that relates valley setting and landscape history of forested, mountain streams to spatiotemporal patterns of sediment storage and transport via the formation and decay processes of logjams. This conceptual model explores the function of logjams as sediment transport moderators, significantly influencing sediment retention, channel morphology, and lateral and longitudinal connectivity. Detailed wood inventories, channel topographic surveys, and channel morphology from four case studies are used to illustrate the range of channel responses to logjam formation, evolution, and decay in different valley contexts. Valley setting is shown to influence logjam formation and dynamics by determining the mechanisms and timing of sediment and wood recruitment. In steep and narrow (and thus coupled, confined) reaches, colluvial processes are the dominant mechanisms of wood and sediment delivery, and logjams grow vertically as sediment is stored in a wedge behind the jam (longitudinal disconnectivity). In contrast, in unconfined reaches (decoupled hillslopes), wood and sediment recruitment occurs primarily through fluvial processes, and logjams grow laterally as the channel shifts across the valley bottom. These logjams have long lifespans, often over a century, and gradually release sediment as the logjam decomposes. Sediment deposits stabilized by riparian vegetation behind these structures may persist long after logjam decay. This conceptual model is a testable framework and practical tool that offers insight into wood-sediment interaction mechanisms within steep, forested basins.

The importance of retention times in Natural Flood Management interventions

Abstract. The starting point for this study is the simulation study of Metcalfe et al. (2018) which suggested that retention times of the order of 10 h are required for natural flood management storage features to have a maximum effect on large flow peaks. A analysis of the celerity characteristics for some log jams at Tebay Gill, Cumbria (upland UK), suggests that the impacts of storage in slowing the celerities is only of the order of minutes. An analysis of storage-discharge dynamics based on observations at 4 jams reveals that the dynamics of storages can be represented with time constants of between 3 and 213 min, still well short of those required to maximise the effects for larger flood flows. That is not to say that there will not be reduction in flood peaks for smaller events, only that for large events the effects will be limited. A spreadsheet tool for retention times has been developed to help in the design of new schemes that is freely available.

Comment on “Momentum and Energy Predict the Backwater Rise Generated by a Large Wood Jam” by Follett, E., Schalko, I. and Nepf, H.

AbstractFollett et al. (2020a, https://doi.org/10.1029/2020gl089346) developed an analytical model to predict backwater rise by log jams, using the size and packing density of logs and the jam length, as well as river slope and bed roughness. We show that the model formulas can be rewritten using the Froude number instead of river slope and roughness, thus improving their applicability in engineering practice. The equation terms and results of Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) are found to be similar to those of the empirically derived formula by Schalko et al. (2018, https://doi.org/10.1061/(asce)hy.1943‐7900.0001501). However, some differences are identified, calling for further study. Most notably, these distinctions pertain to the effect of accumulation porosity, with additional minor differences in the exponent of the Froude number. Lastly, model implications for some broader applications are explored, showing a methodology to calculate the representative log size for log mixtures, and the expected effect of log orientation on backwater rise.

A high‐resolution inter‐annual framework for exploring hydrological drivers of large wood dynamics

AbstractRivers with alluvial bars store more wood than those without, supplied through channel shifting. However, wood dynamics (arrival or new deposits, departure or entrainment, and stable or immobile pieces) can vary substantially over time in response to critical hydrological drivers that are largely unknown. To evaluate them, we studied the dynamics of large wood pieces and logjams along a 12‐km reach of the lower Allier River using six series of aerial images of variable resolution acquired between 2009 and 2020, during which maximum river discharge fluctuated around the dominant flood discharge (Q1.5) that is potentially the bankfull discharge along this well‐preserved not incised reach. Individual wood departure was best correlated with water levels exceeding dominant flood discharge. The duration of the highest magnitude flood was best correlated with wood depositions, with shorter floods resulting in a higher number of deposits. Finally, most of the wood remained stable when river discharge did not exceed 60% of Q1.5 over a long period of time. Changes in inter‐annual wood budget (reach‐scale) depend on the duration over which discharge exceeded 60% of Q1.5. Hydrological conditions driving jam build‐up and removal were similar to those controlling individual wood piece dynamics. The results suggest that specific hydrological conditions influence the dynamics of large wood and log jams in the Allier River. Understanding the dynamics of large wood and its impact on river morphology is fundamental for successful river management and habitat restoration initiatives.

Impacts of Channel‐Spanning Log Jams on Hyporheic Flow

AbstractIn‐stream wood structures, such as single logs, river steps, and debris dams, are known to drive hyporheic flow, defined as the flow that goes into the subsurface region and then back to the free‐flowing surface water. The hyporheic flow plays an important role in regulating water quality and biogeochemical cycles in rivers. Here, we investigated the impact of a channel‐spanning porous log jam, representing piles of wood logs, on hyporheic flow through a combination of direct visualization and theories. Specifically, we developed a method using refractive index‐matched sediment to directly visualize the hyporheic flow around and below a porous log jam, formed by piles of cylindrical rods, in a laboratory flume. We tracked the velocity of a fluorescent dye moving through the transparent sediment underneath the log jam. In addition, we measured the water surface profile and the spatially varying flow velocity near the log jam. Our results show that the normalized log jam‐induced hyporheic flux remained smaller than 10% at Froude numbers () below 0.06 and increased by a factor of five with increasing at . We combined the mass and momentum conservation equations of surface flow with Darcy's equation to explain the dependency of the log jam‐induced hyporheic flux on . Further, we observed that at , the water surface dropped noticeably and the turbulent kinetic energy increased immediately on the downstream side of the log jam. These findings will facilitate future quantification of hyporheic flow caused by channel‐spanning porous log jams.

Movement behavior and passive dispersal of a reintroduced population of alligator snapping turtles

AbstractMaladaptive movement behavior is a leading cause of failure for reptile reintroductions, thus characterizing movement for translocated populations is important to project success. From 2014–2016 we radio‐tracked 183 immature reintroduced alligator snapping turtles (Macrochelys temminckii) using very high frequency telemetry in a stream in southern Illinois, USA. We assessed environmental, temporal, morphometric, and microhabitat factors influencing movement, including post‐release dispersal from reintroduction sites, movement probability, and step length. We used directional statistics to investigate the effects of precipitation and age on directional movement in the stream. Numerous factors influenced active movement, including ambient temperatures, time since release, use of log jams, turtle size, and age. Precipitation had an age‐biased effect on movement. Directional analyses suggested that movement was largely passive as turtles were swept downstream with increased discharge. Overall, the behavior of reintroduced alligator snapping turtles was similar to that reported in wild populations. Passive downstream transport has implications for reintroduced and natural populations as a force for unintentional emigration in channelized streams under current conditions and future high flow regimes.

Biogeomorphology of Ireland's oldest fossil forest: Plant-sediment and plant-animal interactions recorded in the Late Devonian Harrylock Formation, Co. Wexford

The mid-Palaeozoic was a significant interval in the evolution of plants, during which their biogeomorphic influence on terrestrial landscapes increased dramatically. The products of plant-sediment interactions are well known from Carboniferous strata, but earlier evidence dating to the initial rise of arborescent trees in the Devonian is less common. We present new evidence for early plant-sediment interactions from the Late Devonian (Famennian) Harrylock Formation (County Wexford, Ireland), which hosts standing trees that represent Ireland's earliest known fossil forest. The formation records deposition in fluvial and lacustrine environments, the former of which is here shown to have hosted Earth's earliest known log jam as well as early examples of vegetation-induced sedimentary structures (VISS) and a vegetation-stabilized chute channel. Fossilized driftwood preserved in the lacustrine facies contains the earliest evidence for arthropod(?) borings in large vascular plant debris. Together these early examples show that plant-sediment and plant-animal interactions, frequently recorded in Carboniferous strata, were already in existence by the Devonian and may have been previously underreported in other successions of the same age. The sparse Devonian record of plant-related sedimentary phenomena could be explained by a lesser abundance and/or longevity of such features in landscapes prior to subsequent evolutionary innovations in large vascular plants.

The Cretaceous-Paleogene contact in the Tornillo Group of Big Bend National Park, West Texas, USA

Abstract The Cretaceous-Paleogene (K-Pg) contact interval is constrained by vertebrate fossil sites at seven sites in the Tornillo Group and lies within an 80–100-m stratigraphic section between the top of the Javelina Formation and the base of the “log jam sandstone” marker bed in the Black Peaks Formation. In western exposures of this interval, the highest occurrence of in situ dinosaur specimens and the lowest occurrence of Paleocene mammal specimens are separated by an unusual conglomerate bed. This thin conglomerate bed coincides with the contact between Cretaceous and Paleogene strata and contains reworked Cretaceous fossils. It is superficially similar to conglomerate beds elsewhere attributed to the effects of tsunamis generated by the Chicxulub impact; however, the maximum depositional age of ca. 63 Ma based on detrital zircons indicates that the conglomerate was deposited about three million years after the K-Pg boundary event. Paleocene mammalian fossils from immediately above the conglomerate bed represent a fauna that can be no older than the middle Torrejonian (To2 interval zone). The contact between Cretaceous and Paleocene strata is therefore disconformal and represents a hiatus of at least three million years. A condensed section occurs at the westernmost exposure of the K-Pg contact, where at least 80 m of strata are absent below the conglomerate bed; these strata are present in exposures farther east. This condensed section likely records an erosional event resulting from uplift and deformation of the nearby Terlingua monocline. Although the 80 m of strata below the conglomerate bed are poorly fossiliferous, several clearly in situ dinosaur specimens indicate that this entire interval is Late Cretaceous in age. There is no compelling evidence for preservation of the K-Pg boundary event horizon at any of the seven sites in the Tornillo Group, and so the hiatus represented at the Cretaceous/Paleocene contact here likely also includes some part of latest Cretaceous time. Mammalian specimens from sites in the “log jam sandstone,” ~40 m above the middle Torrejonian sites, represent an early Tiffanian fauna (Ti1 interval zone). Latest Torrejonian (To3) sites have not been recognized, and therefore a second disconformity likely coincides with the base of the “log jam sandstone” marker horizon in the Black Peaks Formation.

Fire and ice: Winter flooding in a Southern Rocky Mountain stream after a wildfire

We observed a low-discharge flooding phenomenon on Little Beaver Creek, a tributary to the Cache la Poudre River in the Southern Rocky Mountains of Colorado, USA. Ice ranging in thickness from a few centimeters to 0.5 m occupied a large volume of the channel, forcing flows out of its banks. On two occasions, multiple consecutive days of uncharacteristically warm weather caused a spike in snowmelt, and bankfull stage was surpassed 60 days before peak runoff. The flow events occurred in late winter, six months after a wildfire had burned a large portion of the watershed at medium-to-high severity. Ash and other organic materials were mobilized during the overbank flows, and we observed evidence of recent ash deposition in the floodplain and high ash concentrations in the channel. During the same time period, camera footage captured the formation and collapse of a large accumulation of ice and snow at a log jam. Because climate change projections and recent observations indicate higher variability in weather patterns, wildfire regime, and precipitation events, winter flooding associated with ice, although not widely documented in small mountain streams, may become more common. Flooding and subsequent deposition of ash and other sediment can disrupt fluvial processes, impair the local biotic community, cause property damage, and impact drinking water sources.

Investigation of Flow Separation Over NACA 24015 and 24021 Airfoils using Flow Injection Method

Few explorations used different stream control techniques to work on the streamlined presentation of different airfoils by postponing the stream partition. In this paper, a complete investigation of NACA 24015 and NACA 24021 airfoils was done in CFD at different approaches for various free stream speeds. CATIA V5 R20 was utilized to make the 2D model of the airfoils and the SST K-e disturbance model was used for CFD investigation. Full investigation is performed on a typical airfoil to comprehend the stream conduct at different point of assaults and admission speeds and the equivalent is accomplished for vented airfoils also by concentrating on the suitability of the log jam surrendering approach.

Driving Utah's Rivers: Working Water in the West

Driving Utah's Rivers: Working Water in the West

Development of a geomorphic monitoring strategy for stage 0 restoration in the South Fork McKenzie River, Oregon, USA

AbstractThe South Fork McKenzie River (SFMR) in western Oregon, USA hosts one of the largest Stage 0 stream restoration projects implemented to date. Stage 0 refers to a multichannel planform with strong hydrologic connectivity to the adjacent floodplain and surface–subsurface connectivity. Stage 0 restoration was implemented on a 900‐m‐long reach of the SFMR by re‐grading the channel and floodplain using 65,000 m3 of sediment to raise the channel bed. Thousands of large logs were added and the ends of some logs were buried in the sediment to provide foundations for future log jams. Our primary objective is to present a monitoring protocol based on randomly located sampling plots. We also analyze results from 2 years of data collection since project implementation. Within each plot, we measured canopy cover, wood volume, flow depth and velocity, organic cover (area covered by coarse and fine organic material), and substrate grain size. We used intracluster correlation coefficients and variance of measured variables to assess heterogeneity at three spatial scales: within plots, between adjacent plots, and across the entire site. Here, we evaluate changes in the first 2 years after restoration (i.e., not pre‐ vs. post‐restoration). We hypothesized that heterogeneity within a plot would decrease as the plot adjusted to local‐scale hydraulics and sediment and particulate material transport. We hypothesized that heterogeneity would increase between adjacent plots and across the entire site. We found that spatial heterogeneity of geomorphic variables decreased within plots. Heterogeneity of organic cover, sediment size, and flow depth increased between adjacent plots, although other variables did not change. Site‐scale heterogeneity decreased for all variables except organic cover and substrate. We interpret the observed geomorphic responses to reflect decreased longitudinal connectivity and increased lateral and vertical connectivity at the restoration site.

“If You Build It…”: Methodological Approaches to Detect Postrestoration Responses in Stream Fishes

Habitat restoration to recover fish populations takes place worldwide, yet studies of its efficacy are fraught with challenges. One difficulty comes from studies of fish responses that are too focused on whether abundance has increased in the restored habitat, limiting the methodology to observational data of fish density. However, many other tools are available for evaluation of restoration. I review a set of conceptually based methods that colleagues and I used to assess restoration efficacy in a model river system to show the strength of considering alternative approaches. Although it was relatively easy to determine that fish are attracted to instream restoration structures (engineered log jams), spatial and temporal variability in the results requires approaches that more closely examine the distinction between increases in density and increases in habitat capacity. Furthermore, I show that efficacy research should be augmented with consideration of behavior, the spatial scale of the post‐restoration studies, the response of life history traits (e.g., growth), and the applicability of habitat selection theory. These detailed studies often, but not always, identify benefits of restoration that go beyond simple observations of fish abundance. They are therefore methods that are worth considering by researchers involved in postrestoration fish monitoring.

Effects of current forest practices on organic matter dynamics in headwater streams at the Trask river watershed, Oregon

Forest management in riparian ecosystems can significantly alter biotic and abiotic processes in streams. Forest harvest without the retention of buffers along small streams can affect organic matter dynamics, and drive instream characteristics like trophic food webs. To investigate the extent to which differing levels of tree retention adjacent to the channel mitigated changes in organic matter dynamics, we examined coarse particulate organic matter delivery, transport, and retention, as well as canopy cover, along small streams with four harvest treatments, both before and after harvest. Our research was part of a larger effort of the Trask River Watershed Study (TRWS) in the northern Oregon Coast Range, which examined the long-term physical, chemical, and biological effects of forest management on aquatic ecosystems at multiple spatial scales. Canopy cover at reference and treatment sites prior to harvest was approximately 91%, but following harvest, mean canopy cover at treatment sites decreased with increasing harvest intensity: 3% decrease after clearcut with buffer, 14% after clearcut with leave trees, and 57% after complete clearcut. Organic matter delivery (i.e., the amount of leaf, needle, wood, reproductive, or miscellaneous litter material) to streams was dominated by leaves and varied seasonally but decreased overall after harvest with complete clearcut. Organic matter transport (i.e., the amount of material netted during a sampling period at the end of each stream reach) values fell within the observed range of reference values at all harvested sites. Organic matter retention (i.e., the amount of material sampled in plots systematically placed along the stream reach) post-harvest was dominated by woody material and was consistent with pre-harvest measurements and reference sites for all the harvested streams. The number of log jams, and the total weight of log jams, increased for all treatments after harvest, although the most dramatic increase in log jam weight (140% increase) was observed for the complete clearcut and clearcut with leave tree sites. On these five sites, our results indicated that while complete clearcutting reduced organic matter delivery, retention of even a small number of trees along these streams appeared to support litter delivery rates after harvesting comparable to before harvest. We acknowledge the limitations of results from single treatment sites; however, our results were generally consistent with studies that had full replication. As part of the Trask River Watershed study, our research adds to the comprehensive effort to understand the ecological significance of riparian buffers and forest harvest in headwater streams.

Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State

Tabor RA, Liermann MC, Gearns HA, Moore ZJ, Lynch KD, Kurko K, Crittenden J, Shoemaker ME. 2022. Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State. Lake Reserv Manage. 38:180–196. We evaluated 4 large restoration projects in south Lake Washington that were designed to improve nearshore habitat for lake-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha). Restoration projects included shoreline modification, substrate enhancement, addition of engineered log jams (ELJs), and nonnatal tributary improvements. For most projects, we used a BACI (before-after-control-impact) study design. Projects were evaluated by determining the nighttime abundance of juvenile Chinook salmon through visual observations (primarily snorkeling with some surface observations in small nonnatal tributaries). Juvenile Chinook salmon are typically concentrated in the south end of the lake near their natal stream, and the project that was the farthest away from the natal stream did not appear to be beneficial, likely because few Chinook salmon were present. The highest observed abundance of juvenile Chinook salmon was associated with ELJs, where the abundance in February to April was typically 2 to 5 times higher than along adjacent, open shorelines. From January to April, juvenile Chinook salmon were usually more abundant in a daylighted nonnatal tributary (i.e., reconfigured from an unusable underground culvert to a more natural stream channel at the surface) than in 2 reference sites. Overall, all 4 project types improved juvenile use of the restored area, with substrate enhancement generally having the weakest response and ELJs the strongest response. Although most restoration projects for salmonids in the Pacific Northwest have focused on lotic systems, our results suggest projects in lentic systems may also be beneficial and should be considered by land-use managers. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2027054 .

Log Jam: Lesson Learned from the Log4Shell Vulnerability

Log Jam: Lesson Learned from the Log4Shell Vulnerability

Structural characteristics of pools in headstream areas

Pools play an important role among stream bed morphologies in mountain streams. They provide habitat and contribute to energy dissipation. However, they have received only marginal attention compared with step structures, and their forms and driving factors, such as stream-channel characteristics and structural characteristics of upstream morphologies, remain unclear. Therefore, the purpose of this study was to determine the structural characteristics of pools, including morphology, size, and deposit conditions, and the factors controlling them. Based on the results of a field survey for a channel length of 9524 m, with 428 reaches and 1302 pools, the correlations between the pool spacing, morphology, size, and deposit conditions of the pool, and controlling factors were investigated for three rock types (granite, rhyolite, and sandstone). The average pool spacing calculated by dividing the interval length of the pool by the channel width was 8.80, 12.87, 4.56, and 16.14 for fall-pool, cascade, step-pool and pool-riffle respectively. This is due to the fact that the target streams are first-order streams with small widths as well as their regional characteristics, that is, few log jams and forced pools. In addition, the depositional depth of the pools varies depending on the geology. The maximum percentage of sediment deposition in the pool was 78%, 33%, and 34% for granite, rhyolite, and sandstone, respectively. Thus, the sedimentation in granite is significantly greater than in the rhyolite and sandstone headstream areas. This is probably due to the discontinuous weathering of granite during which it is broken down into large-sized core stones and fine grains. The difference in the depositional environment of the pools depending on the geology indicates that the biota that use those pools as a habitat may also differ. However, research on the microhabitats of pools is lacked, and research regarding the future perspectives of ecosystems is required.

Development of a CFD model and procedure for flows through in-stream structures

Large wood (LW) has been widely used in river restoration projects due to its ecological benefit. 3D modeling has rarely been conducted. In this study, a 3D modeling procedure is proposed and a new 3D model is developed. The model incorporates advanced CFD techniques and is easy to apply. An engineered log jam (ELJ) is constructed and an experiment is conducted. The data are used to demonstrate the procedure and validate the CFD model. A comparison of the predicted and measured velocity shows that agreement is good with the Nash-Sutcliffe coefficient about 0.4 and index of agreement about 0.85. The model is further applied to a curved channel with ELJ on the outer bank, demonstrating the use of the 3D model to guide the proper representation of ELJs in a 2D model. The 3D model may be used to reveal complex flow patterns generated by LW for ecological benefit analysis.