Surface Sediment Grain Research Articles

A quantitative method to infer lake area changes based on an extensive survey of lake surface sediment grain size across the Inner Mongolia Plateau, and its application to understanding the evolution of Lake Wulanhushao in northern China since 18.59 cal. kyr BP

Grain size is commonly used as a proxy to reconstruct past lake hydrology; however, published research rarely links grain size with modern processes, and uncertainties exist for interpretation. In this paper, we decompose the grain size frequency distributions (GSFD) for 196 lake surface sediments from 61 lakes and 9 reservoirs across the Inner Mongolia Plateau and adjacent areas and divide them into five GSFD components. We statistically analyze the relationship between the GSFD components and influencing variables to determine the taphonomic dynamics and their environmental implications. Within individual lakes, we found that GSFD component 4 (74.00–209.30 μm) and GSFD component 5 (209.30–592.00 μm) dominate near the lake margin and reduce toward the lake center in proportions. By contrast, GSFD component 2 (2.75–15.56 μm) increases toward the lake center. Therefore, the proportions of GSFD component 2, 4, and 5 reflect the relative distance to the lakeshore and allow inferences about lake area changes. We apply this large modern dataset to a sediment core obtained from Lake Wulanhushao (WLHS) on the Inner Mongolia Plateau and link the lake surface sediment-based GSFD components to BEMMA end-members of grain size records to define their environmental implications over the last 18.59 cal. kyrs BP. We found that the Lake WLHS has responded to the orbital and suborbital climate changes since the last deglaciation. Specifically, maximum lake transgression prevailed during the early to middle Holocene (11.70–7.10 cal. kyr BP), medium lake transgression dominated during 17.05–15.80 cal. kyr BP, and weak transgression developed during 14.60–12.90 cal. kyr BP. Maximum lake regressions prevailed before 17.05 cal. kyr BP, during 15.80–14.60 cal. kyr BP and 12.90–11.70 cal. kyr BP. Our reconstructed early Holocene maximum lake area is consistent with regional abiotic proxy-based moisture records, but contrasts with the regional biotic proxy-based moisture records, which reconstruct increasing moisture conditions. Our new method to determine lake area changes will provide valuable data to understand the climate dynamics of northern China.

The Effect of Sediment Supply on Pool‐Riffle Morphology

AbstractDownstream width variations can generate pool‐riffle morphology under experimental conditions, in numerical simulations and natural river channels. The present understanding of how pool‐riffle morphology varies with sediment supply and caliber, however, is insufficient due to the limited range of sediment supply rates explored in previous experiments and the little attention paid to sand supply and sediment size distribution in the laboratory and in the field. We present a model of river morphodynamics that can account for the spatial variability of channel width, and we validate the model with experimental data. Model validation shows how this one‐dimensional model can capture pool‐riffle formation, growth, and equilibration with errors that are comparable with those of other 1D models of river morphodynamics. We then apply the validated model to study the effects of sediment supply rate and caliber on pool‐riffle morphology. Model results show that pool‐riffle morphology is resilient to the range of tested sediment supply (i.e., five‐fold the sediment amount, 41‐fold the sand amount and coarsening the gravel supply). Bed and water surface slopes are sensitive to all types of change of sediment supply, whereas the sensitivity of bed surface sediment grain size varies with the type of change. These findings support prior research emphasizing the role of downstream width variations for the development/maintenance of pool‐riffle morphology and can help in the restoration and recovery of pool‐riffle gravel‐bed rivers.

Sediment controls on the transition from debris flow to fluvial channels in steep mountain ranges

AbstractSteep channel networks commonly show a transition from constant‐gradient colluvial channels associated with debris flow activity to concave‐up fluvial channels downstream. The trade‐off between debris flow and fluvial erosion in steep channels remains unclear, which obscures connections among topography, tectonics, and climate in steep landscapes. Here, we analyze steep debris‐flow‐prone channels across the western United States and observe: (1) similar maximum channel gradients across a range of catchment erosion rates and geologic settings; and (2) lengthening colluvial channels with coarsening sediment cover. Following this compilation, we hypothesize that steep channel gradients are controlled by two competing thresholds of motion for bed‐sediment cover: bed failure by mass‐wasting and fluvial entrainment. We use downstream patterns in discharge, channel geometry, and sediment size to calculate discharges needed to mobilize sediment cover by both mechanisms across channels in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) in southern California. Across steep colluvial channels in both landscapes, decadal discharges are below fluvial entrainment thresholds but above mass‐wasting entrainment thresholds for (median) sediment sizes, consistent with recent debris flows captured by repeat imagery. Colluvial channel gradient is similar despite > 3× contrasts in surface sediment grain size. In concave‐up fluvial channels downstream, decadal discharges exceed fluvial entrainment thresholds, and mass‐wasting is not predicted on lower gradients. In both landscapes, fluvial channels steepen downstream compared to gradients needed to mobilize sediment cover, which we interpret to reflect downstream increases in sediment flux. Coarser sediment supply in the NSJM than the SGM increases fluvial entrainment thresholds, which increases total channel relief in the NSJM by (1) lengthening colluvial channels shaped by debris flows and (2) increasing fluvial channel gradients. Our compilation and downstream analysis show how differing sensitivity of fluvial and debris flow processes to sediment grain size impacts the relative relief of colluvial and fluvial regimes in headwater channel networks.

Changes in the distribution of surface sediment in Pearl River Estuary, 1975–2017, largely due to human activity

In recent decades, the surface sediments in the Pearl River Estuary (PRE), China, have been intensely disturbed by human activities. Data from 1975 to 2017 show that the mean surface sediment grain size in PRE is distributed between 5 and 8 ϕ, while the sorting coefficient of the sediments vary between 0.39 and 4.53, and the skewness is between −0.31 and 0.55. From 1975 to 1994, sandy sediment was mainly distributed near the outlets. However, sandy sediments have been present in the south of the West Shoal and Middle Shoal, and north of Lantau Island, and have had a patchy distribution since the 2000s. From 1975 to 2017, the average total grain size of the surface sediments in PRE changed from 6.4 to 5.3 ϕ, indicating a coarsening trend. This was mainly caused by the sharp reduction in upstream sediment load since the 1980s, as well as channel dredging and sand mining in PRE. On the one hand, the decrease in the sediment load caused an increase in the erosion area, which caused a large amount of fine-grained sediment to be eroded and transported to the open sea. On the other hand, channel dredging and sand mining resulted in coarse-grained sediments in the paleo-sedimentary layer being stirred to the surface, thus making a significant contribution to the coarsening of the average grain size. Channel dredging and sand mining are also the main reasons for the patchy distribution of sediments in PRE. In the future, with further reductions in the sediment load and the persistence of reclamation, channel dredging, and sand mining, the grain size of surface sediments in PRE will continue to show a coarsening trend.

Drainage Area, Bedrock Fracture Spacing, and Weathering Controls on Landscape‐Scale Patterns in Surface Sediment Grain Size

AbstractSediment grain size links sediment production, weathering, and fining from fractured bedrock on hillslopes to river incision and landscape relief. Yet models of sediment grain size delivery to rivers remain unconstrained due to a scarcity of field data. We analyzed how bedrock fracture spacing and hillslope weathering influence landscape‐scale patterns in surface sediment grain size across gradients of erosion rate and hillslope bedrock exposure in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) of California, USA. Using ground‐based structure‐from‐motion photogrammetry models of 50 bedrock cliffs, we showed that fracture density is ~5 times higher in the SGM than the NSJM. 274 point‐count‐surveys of surface sediment grain size measured in the field and from imagery show a drainage area control on sediment grain size, with systematic downslope coarsening on hillslopes and in headwater‐colluvial channels transitioning to downstream fining in fluvial channels. In contrast to prior work and predictions from a hillslope weathering model, grain size does not increase smoothly with increasing erosion rate. For soil‐mantled landscapes, sediment grain size increases with increasing erosion rates; however, once bare bedrock emerges on hillslopes, sediment grain size in both the NSJM and SGM becomes insensitive to further increases in erosion rate and hillslope bedrock exposure, and instead reflects fracture spacing contrasts between the NSJM and SGM. We interpret this threshold behavior to emerge in steep landscapes due to efficient delivery of coarse sediment from bedrock hillslopes to channels and the relative immobility of coarse sediment in fluvial channels.

Effect of water-sediment regulation operation on sediment grain size and nutrient content in the lower Yellow River

The Yellow River (YR) is famous for its high sediment concentration. The Xiaolangdi dam (XLD), the most downstream dam on the mainstream of the YR, plays an integral role in siltation mitigation, flood defence, agriculture, and hydropower generation. To alleviate siltation of the Xiaolangdi Reservoir (XLDR) and riverbed uplift of the lower reaches of the YR and strengthen flood control safety downstream, the XLDR began to implement water-sediment regulation in 2002. Water-sediment regulation (WSR) has significantly changed the hydrological processes, erosion and deposition, and sediment transport in the downstream channel, and the downstream water environmental conditions have also changed. In this study, 10 sections in the Lower Yellow River (LYR, from the XLDR to the Lijin section) and 4 sections in the soft floodplain area were sampled in the field to analyse their surface sediment grain size composition and nutrient content. At the same time, data on the average annual median particle sizes (D50) of channel sediments and suspended particles in 7 typical sections in the LYR from 2004 to 2015 were statistically analysed. The results show that the channel sediment grain size in the LYR decreased along the river course, and the D50 ranged from 0.20 mm in the HYK section to 0.08 mm in the LJ section. Moreover the D50 of the suspended sediment was less than 0.05 mm. The D50 of the channel and suspended sediment were both ranked as follows: non-flood season > flood season > WSR period. After WSR, fine silt particles with diameters of 0.01–0.05 mm were deposited on the soft floodplain. The channel sediment size was mainly coarse particles with diameters of 0.05–0.20 mm due to channel erosion. The suspension of fine silt particles due to flood scouring led to the total organic carbon (TOC) and total nitrogen (TN) absorbed in the particles to also be resuspended in the water. As a result, the TOC and TN contents in the channel sediments decreased by approximately 40% after WSR.

Grain-Size Distribution of Surface Sediments in the Bohai Sea and the Northern Yellow Sea: Sediment Supply and Hydrodynamics

The grain-size distribution of surface sediments in the Bohai Sea (BS) and the northern Yellow Sea (NYS), and its relationship with sediment supply and hydrodynamic environment were investigated based on grain-size compositions of surface sediments and modern sedimentation rates. The results showed that the surface sediments in the BS and the NYS were primarily composed of silty sand and clayey silt with a dominant size of silt. In addition, the Yellow River delivered high amount of water and sediments to the BS, and they are dominated in surface sediments (mainly silt) in the Bohai Bay, the Yellow River mouth, the center of the BS, and the north coast of Shandong Peninsula. The coarse-grained sediments were mainly deposited at the river mouth due to the estuarine filtration and physical sorting. Meanwhile, there was a significant relationship among the modern sedimentation rate, the surface sediment grain size distribution and sediment transport pattern. The areas with coarser surface sediments generally corresponded low sedimentation rates because of strong erosion; whereas the sedimentation rate was relatively high at the place that the surface sediments were fine-grained. Furthermore, the grain-size trend analysis showed that the areas with fine-grained surface sediments such as the mud area in the central BS and the upper Liaodong Bay were the convergent centers of surface sediments, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident.

Spatial heterogeneity of surface sediment grain size and aeolian activity in the gobi desert region of northwest China

Studies have previously discussed characteristics of aeolian activity for different gravel densities on gobi surfaces. However, the significance of the spatial heterogeneity of its surface to sand flow over its surface and to dust emissions from the region has not been clearly demonstrated. This is also the case for spatial variation in the aeolian environment. Accordingly, this study established two observation transects, both through the desert pavement area and the dune field in the gobi desert region of northwest China, to measure surface sediment grain size, wind speed and sand transport along these transects. Results showed that in areas where surface gravel content decreased and mobile sand dunes increased, surface sediments were better sorted and grain-size distribution changed from multimodal to roughly unimodal. Furthermore, sand transport increased significantly and properties of aeolian activity varied markedly within a short distance. This extreme variation in both grain-size parameters and in sand transport indicated that strong spatial heterogeneity exists in the aeolian environment of the study area. Furthermore, dune fields within gobi area are likely the main cause of sand flow over its surface as well as dust emissions from the region itself. The findings in this study have universal applicability in gobi regions with uneven surface properties in other arid areas.

Sediment transport in the nearshore area of Phoenix Island

Based on the measured data, suspended sediment concentration, surface sediment grain size, current and waves, the sediment transport mechanisms and pathways in the Phoenix Island area were analyzed using methods of flux decomposition and Grain Size Trend Analysis (GSTA). The results show that net suspended sediment is mainly transported by average current, Stokes drift, and gravitational circulation. The transport direction of suspended sediment is varying and basically following the direction of residual tidal currents. Surface sediment transport pathways are primarily parallel to the coastline along with two convergent centers. Waves and longshore currents have a significant influence on sediment transport, but the influence is limited due to a steep and deep underwater bank. Tidal current is the main controlling factor for sediment transport, especially in the deep water area. Neither suspended nor surface sediment is transported towards the southwest. The South Shandong Coastal Current (SSCC) has little effect on sediment transport processes in the nearshore area of Phoenix Island.

Transport pathway and depocenter of anthropogenic heavy metals off the Shandong Peninsula, China

Surface sediment grain size as well as the spatial distribution, sources and geochemical baseline levels of heavy metals in the south Shandong Peninsula clinoform were analyzed to determine the transport pathway and main depocenter of anthropogenic heavy metals off the peninsula. Results showed that the surface sediments were primarily silt-sized components, and the fine grain matter mainly originated from the Yellow River and rivers around Laizhou Bay. Heavy metals Cu, Pb, Zn, Cr, and Cd were predominantly from natural sources and their spatial distributions were controlled by grain size; conversely, anthropogenic As (concentration above geochemical baseline level 10.9 mg/kg) was principally derived from human activities, and its transportation from the Yellow River and Laizhou Bay was controlled by the Shandong Coastal Current off the Shandong Peninsula. Furthermore, the anthropogenic As was deposited in three main areas, that is, the Yellow River estuary, Laizhou Bay, and south Shandong Peninsula clinoform.

Grain size distribution at four developmental stages of crescent dunes in the hinterland of the Taklimakan Desert, China

Although scientists have performed many studies on crescent (barchan) dunes in the Taklimakan Desert, few studies reported the changes in grain size at different development stages of crescent dunes. In order to evaluate the changing trends of surface sediment grain size with dune development, we investigated the grain size characteristics at four developmental stages (oval sand pile, shield dune, incipient crescent dune and mature crescent dune) of crescent dunes by measuring the morphology of sand dune and observing the near-surface wind regime. The dunes have developed in a wide inter-dune corridor between high compound longitudinal ridges in China’s Taklimakan Desert. The surface sediments at four developmental stages of the crescent dunes were primarily composed of fine sands, followed by very fine and medium sands. Mean grain sizes ranged from 2.8 to 3.1 φ, with a unimodal distribution. The sands were moderately well-sorted, their distribution varied from platykurtic to very platykurtic, and symmetrical or skewed towards the fine particles. From oval sand piles through shield and incipient crescent dunes to mature crescent dunes, incipient grain size gradually increased, particles became finer, sorting became better, kurtosis and skewness increased. Grain sizes on the surface layer became coarser upwards from the toe of the windward slope and then became finer towards the bottom of the leeward slope. We found that the coarsest particles at different positions at the four developmental stages were different. The coarsest particles were distributed at the top of the oval sand piles and shield dunes, versus at the middle of the windward slope of the incipient and mature crescent dunes. Correlations between the mean grain size and other grain size parameters showed that as mean grain size became finer, sorting became better and kurtosis became wider, but skewness changed only slightly. In addition, grain size variation in the surface sediments correlated with the movement speed of the dunes in the study area. In the open ground among tall-complex longitudinal ridges in the hinterland of the Taklimakan Desert where aeolian environment is characterized by comparatively strong wind and unsaturated sand flow, faster dune movement corresponded to coarser grain size.

Modeling grain size adjustments in the downstream reach following run‐of‐river development

AbstractDisruptions to sediment supply continuity caused by run‐of‐river (RoR) hydropower development have the potential to cause downstream changes in surface sediment grain size which can influence the productivity of salmon habitat. The most common approach to understanding the impacts of RoR hydropower is to study channel changes in the years following project development, but by then, any impacts are manifest and difficult to reverse. Here we use a more proactive approach, focused on predicting impacts in the project planning stage. We use a one‐dimensional morphodynamic model to test the hypothesis that the greatest risk of geomorphic change and impact to salmon habitat from a temporary sediment supply disruption exists where predevelopment sediment supply is high and project design creates substantial sediment storage volume. We focus on the potential impacts in the reach downstream of a powerhouse for a range of development scenarios that are typical of projects developed in the Pacific Northwest and British Columbia. Results indicate that increases in the median bed surface size (D50) are minor if development occurs on low sediment supply streams (<1 mm for supply rates 1 × 10−5 m2 s−1 or lower), and substantial for development on high sediment supply streams (8–30 mm for supply rates between 5.5 × 10−4 and 1 × 10−3 m2 s−1). However, high sediment supply streams recover rapidly to the predevelopment surface D50 (∼1 year) if sediment supply can be reestablished.

Geochemical background and ecological risk of heavy metals in surface sediments from the west Zhoushan Fishing Ground of East China Sea.

Surface sediment grain size as well as the spatial distribution, pollution status, and source identification of heavy metals in the west Zhoushan Fishing Ground (ZFG) of the East China Sea were analyzed to study the geochemical background concentrations of heavy metals and to assess their potential ecological risk. Our results show that surface sediments in the eastern part of study area were mainly composed of sand-sized components. Spatial distributions of heavy metals were mainly controlled by grain size and terrigenous materials, and their concentrations in the coarsest grain sediments formed primarily during the Holocene transgressive period could represent the element background values of our study area. Contamination factor suggests that there was no pollution of Pb, Zn, and Cr generally in our study area and slight pollution of Cu, Cd, and As (especially Cu) at some stations. In addition, ecological harm coefficient indicates that the ecological risk of each heavy metal, except for Cd, at two stations was low as well. These results are consistent with the pollution load index and ecological risk index, which suggest both the overall level of pollution and the overall ecological risk of six studied metals in sediment were relatively low in our study area. Enrichment factor indicates that the heavy metals came mostly from the natural source. Summarily, the quality level of sediment in our study area was relatively good, and heavy metals in sediments could not exert threat to aquatic lives in the ZFG until now.

End member inversion of surface sediment grain size in the South Yellow Sea and its implications for dynamic sedimentary environments

Four end members were inverted from surface sediment grain size data from the South Yellow Sea by using the end member (EM) model. The sediment provenance and hydrodynamic meanings of each EM were discussed based on the frequency and spatial distributions of the EMs. EM1 and EM2 reflect the dynamic transport and sorting processes of the terrigenous sediment, and EM3 and EM4 reflect the modification of relic sand. The ocean front mainly affected transport of relatively coarse terrigenous sediment in the South Yellow Sea, and the fine terrigenous sediments were generally unaffected by the ocean front. Fine sediment could pass through the ocean front and deposit in the central South Yellow Sea under weak tidal condition to form most part of the Central Yellow Sea Mud (CYSM). The CYSM extended toward northwest and southwest. The sediment in the north part of the CYSM mainly consisted of sediment from the Yellow River (Huanghe) in the northwest, and the sediment in the southwest part of CYSM mainly consisted of Subei coastal sediments from both the Yangtze River (Changjiang) and the Yellow River. Compared to the traditional method of sediment grain size analysis, the EM model can determine the EMs and provide better explanations of the sediment provenance and dynamic regional sedimentary environment in the study area.

Sediment partitioning and winnowing in a mixed eolian-marine system (Mauritanian shelf)

Continental shelf systems are highly dynamic sedimentary environments, where sediments from biogenic production as well as from terrigenous sources are redistributed in the shelf depositional system, and partly exported off the shelf to the slope and the deep sea. The Golfe d’Arguin (Mauritania, NW Africa) is dominated by such redistribution processes, involving clastic silt imported as dust from the Sahara desert and biogenic carbonates of marine origin. Indeed, surface-sediment grain size and mineralogy show a clear north–south partitioning of sediment type. Fine material is winnowed from the northern part of the gulf, and transported toward the southern part off the Banc d’Arguin, where coarse silt settles on the outer shelf and upper slope, at least down to 600 m water depth. Particles of the fine silt fraction, estimated in terms of eolian material collected aboard the research vessel, are thought to be exported further offshore as they correspond to grain sizes previously reported from adjacent deep-sea sediments. These findings suggest that the interpretation of dust records from the continental slope and rise off NW Africa must consider reworking and partitioning processes active on the Mauritanian shelf.

Patterns of surface sediment grain size distribution under the influence of varying wave conditions on a mixed sediment beach at Pevensey Bay, southeast England

Surface sediment distributions, derived using a new DGPS based survey technique, are described from three sections of a mixed sediment beach (MSB) at Pevensey Bay, southeast England. Spatial patterns of the distribution and size composition are related to antecedent hydrodynamic conditions and beach topography. Results indicate that higher energy waves produce a beach surface with a relatively homogenous grain size distribution, whilst lower energy waves produce surfaces with a more mixed size distribution. Under storm conditions, a 'type' beach response was recorded, comprised of a fine upper beach face and coarse lower beach face. Management practices, especially beach renourishment, also influence beach surface sediment distribution patterns

BIOGEOMORPHOLOGY OF AN UPPER CHESAPEAKE BAY RIVER-MOUTH TIDAL FRESHWATER MARSH

Field mapping and monitoring of vegetation, sedimentation patterns, substrate characteristics, and geomorphology in the Bush River tributary to upper Chesapeake Bay has been conducted since 1991 to ascertain the process-morphology dynamics in a tidal freshwater marsh. Nine plant associations from 5 distinct marsh habitats were identified by clustering species abundance measurements from 115 quadrats throughout an 84-hectare area. High spatial variability in physical habitat conditions such as summer-average sediment deposition, summer-average organic content, and surface-sediment grain size distributions were explainable using combinations of independent variables, including elevation, plant distributions, and distances to the tidal inlet and an adjacent stream. Sedimentation and vegetation were both observed to show a predictable response to disturbance by animal activity.

Flow properties of turbidity currents in Bute Inlet, British Columbia

ABSTRACTBute Inlet, a fiord along the southwestern coast of British Columbia, Canada, includes a sea‐floor sedimentation system 70 km in length which resembles those developed on some large submarine fans. Turbidity currents originate at the head of the flord on the submerged delta fronts of the Homathko and Southgate rivers. They move downslope for about 30 km within a single large incised channel, spill onto a depositional area termed the channel lobe complex, and finally spread out over a low‐relief distal splay area that passes 55 km downslope into a flat basin floor.During the present study, turbidity currents in Bute Inlet were studied using sea‐floor morphology, bottom sediment distribution, and in‐situ instrument packages. The mean velocities of the most recent flows, estimated from surface sediment grain size, has varied between 100–120 cm s–1 in the incised channel, 20–50 cms–1 in the channel lobe complex, and < 5 cm s–1 on the basin floor. Velocities based on channel morphology are poorly constrained but are in the range of 160‐425 cm s–1 in the upper part of the incised channel and 66 cm s–1 in the lower channel. Calculated flow densities range from 1.049 to 1.028g cm–3.Turbidity flows monitored in 1986 using submerged instrument packages exceeded 32 m in thickness in the upper part of the incised channel, where the maximum measured velocity was 330 cm s–1. At the head of the channel lobe complex the maximum velocity had declined to 75 cm s–1. The density of the monitored flows is estimated at 1.025‐1.03g cm–3. The cored sediments and channel morphology yield estimates of mean flow velocities that are generally greater than those measured by the in‐situ instrument packages and estimated from modern surface sediments. The former suggest past flow velocities up to 500 cm s–1 in the incised channel, about 20 cm s–1 in spillover deposits along the lower part of the incised channel, and 100‐140 cm s–1 in the distal splay. The contrast between the velocities of modern and past flows suggests that past flows may have been considerably larger and more energetic than those presently occurring in Bute Inlet.The size properties of sediments in the monitored turbidity flows suggest a strong vertical size gradient in the suspended load during transport. The surface and cored sediments fine downslope from the channel lobe complex to distal splay area. Distinctive sedimentary sequences are recognized in cores from the spillover lobes, channel lobe complex, distal splay, and basin floor depositional areas. Many individual turbidites grade downslope from massive Ta divisions in the channel lobe complex and probably in the incised channel to Ta divisions overlain by slurried divisions on the distal splay and largely slurried beds on the basin floor. These facies suggest that individual currents commonly evolve from largely cohesionless suspensions in the incised channel and channel lobe complex to dilute cohesive slurries downslope on the distal splay and basin floor. Many flows in Bute Inlet fail to develop a traction state of sedimentation and the resulting turbidites lack well‐developed Tb. Tc, and Td divisions.