Channel Slope Research Articles

Investigation of erosion characteristics of debris flow based on historical cases

Debris flow is one of the most unpredictable geohazards in terms of occurrence and magnitude due to its random nature on flow initiation and changing mass during the flow process. The current approach to calculate erosion and entrainment in debris flow analysis is largely empirical by predetermining and distributing a certain amount of material along its flow path. A rational approach requires detail analysis of flow kinematics in calculating the amount of erosion. However, based on study of several case histories, certain erosional characteristics are found which can be used to calculate changes in the flow mass during the flow process. In this study, a progressive entrainment runout model is used to investigate the erosion characteristics of debris flow and rock avalanche. Four historical cases of debris flow and rock avalanche with long runout distance, steep channel slope, and high travel velocity are being studied. These four cases have some common features but they have different triggering mechanisms, elevation variations and particle size distributions. The results of the analysis show that >50% of erosion occurs in the second half of the flow path. The rate of erosion at the front of the debris is not only dependent on the slope of the flow channel, it also depends on other factors such as the depth of the debris, the velocity of flow and the physical properties of the debris material and the physical characteristics of the flow channel. Most importantly, based on these case studies, it is found that the rate of erosion along the flow channel can be determined based on the velocity, height of the debris and other flow characteristics. The calculated rate of erosion and the amount of entrainment can then be used in debris flow analysis.

Physical habitat in conterminous US streams and rivers, Part 1: Geoclimatic controls and anthropogenic alteration

Anthropogenic alteration of physical habitat structure in streams and rivers is increasingly recognized as a major cause of impairment worldwide. As part of their assessment of the status and trends in the condition of rivers and streams in the U.S., the U.S. Environmental Protection Agency’s (USEPA) National Aquatic Resource Surveys (NARS) quantify and monitor channel size and slope, substrate size and stability, instream habitat complexity and cover, riparian vegetation cover and structure, anthropogenic disturbance activities, and channel-riparian interaction. Like biological assemblages and water chemistry, physical habitat is strongly controlled by natural geoclimatic factors that can obscure or amplify the influence of human activities. We developed a systematic approach to estimate the deviation of observed river and stream physical habitat from that expected in least-disturbed reference conditions. We applied this approach to calculate indices of anthropogenic alteration of three aspects of physical habitat condition in the conterminous U.S. (CONUS): streambed sediment size and stability, riparian vegetation cover, and instream habitat complexity. The precision and responsiveness of these indices led the USEPA to use them to evaluate physical habitat condition in CONUS rivers and streams. The scores of these indices systematically decreased with greater anthropogenic disturbance at river and stream sites in the CONUS and within ecoregions, which we interpret as a response of these physical habitat indices to anthropogenic influences. Although anthropogenic activities negatively influenced all three physical habitat indices in the least-disturbed sites within most ecoregions, natural geoclimatic and geomorphic factors were the dominant influences. For sites over the full range of anthropogenic disturbance, analyses of observed/expected sediment characteristics showed augmented flood flows and basin and riparian agriculture to be the leading predictors of streambed instability and excess fine sediments. Similarly, basin and riparian agriculture and non-agricultural riparian land uses were the leading predictors of reduced riparian vegetation cover complexity in the CONUS and within ecoregions. In turn, these reductions in riparian vegetation cover and complexity, combined with reduced summer low flows, were the leading predictors of instream habitat simplification. We conclude that quantitative measures of physical habitat structure are useful and important indicators of the impacts of human activities on stream and river condition.

Sediment Nourishments to Mitigate Channel Bed Incision in Engineered Rivers

Engineering modifications of rivers, e.g., dams or groynes, often induce long-term riverbed erosion, which can be mitigated with sediment nourishments. Here, we consider nourishments to mitigate channel bed erosion induced by channel narrowing, as opposed to the more common application downstream of dams. Our objective is to assess and quantify how dumping location, grainsize, and volume are important for mitigation efficacy. Our results show that erosion can be mitigated if nourishments change the sediment flux such that the corresponding equilibrium channel slope is increased. This is achieved by coarsening the sediment flux throughout the reach, increasing magnitude of the sediment flux, or both. Flux is coarsened via additions of sediment at or coarser than the bed surface and nourished sediment should be distributed throughout the incising reach. The second option is nourishing a large volume of relatively fine sediment to increase the equilibrium channel slope. Additions of fine sediment in small volumes decrease the equilibrium channel slope and enhance erosion, because the fine sediment flux makes the gravel more mobile.

Paleoenvironmental and paleodepositional architecture of SAMO field in Niger-Delta Basin of Nigeria using seismic and well log data

The use of Seismic data and well log data within the context of sequence stratigraphy is a valuable tool for the recognition of ancient cycles and sequences because they reflect information on the different processes that deposit sediments in different palaeoenvironment. An integrated geophysical well log data and seismic data from our wells within the SAMO field have been utilized to delineate the upper Miocene-Pliocene depositional environment parts of the Niger-Delta Basin. Identification of the different lithologies and depositional environment present in the penetrated borehole was achieved using gamma ray log. This enables the establishment of different rock units in the well from the gamma ray log values and signatures. Three succession signatures which include; the bell, cylindrical and the funnel being more prominent were identified from the log motifs in the different sand bodies attenuated in the wells from the field. The mapped sequences generated Low stand System Tracts (LST) progradational, Trangressive System Tracts (TST) retrogradational and High stand System Tract (HST) aggradational packages. All these reflect the depositional systems that dominated the different phases as a result of base level changes. Furthermore, values quantified from the logs revealed that porosity and permeability are more prominent in places where sand bodies accumulated in the slope channel setting indicative of slope-fills and turbidity fans. This deep-sea channels and switch complex fault system suggest good hydrocarbon bearing potential associated with the distal Niger-Delta province. Also a good quality reservoir was inferred from the sands of both LST and HST while the shale of the TST could serve as a good reservoir.

Study of Inundation Management on Tertiary Drainage Channels in Keputih Tegal Surabaya City

In the case of heavy rain, several places in Surabaya are still submerged. The Keputih Tegal region is one of them. The Jalan Keputih Tegal channel is a tertiary drainage channel that drains into a secondary drainage channel on Jalan Raya Keputih before emptying into the Wonokromo river. The flood on Jalan Keputih Tegal occurred at a depth of 20 cm. The drainage channel on Jalan Keputih Tegal is the subject of this study, and the data utilized are secondary data in the form of rainfall data collected from the Public Works Department of Highways Surabaya and the SDMP (Surabaya Drainage Master Plan) map obtained from BAPPEKO Surabaya. The dimensions of the channel are 1.5 x 1.5 m with a capacity of 0.9 m3/s based on the flood flow from the CA region and the drainage system of the Keputih Tegal channel, which is impacted by the height of the secondary channel MAB. The channel's proportions allow for both flood discharge and backwater discharge. With a flow velocity of 0.4 m/s, the channel slope is planned to be 0.04 percent. This condition exceeds the allowed speed criteria for concrete channels, which are 1.5 m/s.

Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

AbstractRiparian vegetation plays a crucial role in determining the flow behaviour in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though real field vegetation distribution is non‐uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. This paper attempts to address this issue through laboratory studies as it was not explored properly. Flow properties like velocity, Reynolds shear stress, turbulence intensities, and turbulent kinetic energy behave differently in heterogeneous vegetated channel compared with the homogeneous vegetated channel. These flow properties in the slopes and main channel section are more pronounced for uniformly distributed vegetation than non‐uniform distribution. The multi‐layered/varying vegetation height showed higher velocity, turbulent intensity, and turbulent kinetic energy than single‐layered/constant vegetation height on slopes and main channel sections. Integral scales (Taylor and Euler) analysis showed greater magnitude for uniform multi‐layered vegetation than non‐uniform multi‐layered vegetation. Further, the study of octant analysis reveals that internal outward and internal inward interaction events dominate the slope floodplain interaction section, which is not seen in no‐vegetation cases. These studies give a better perspective to understand flow in heterogenous vegetation and move closer to real field scenarios.

Hydrodynamic Process of Partial and en Masse Dam Failure Induced Debris Flows

Because of landslides, seismic events, and/or unregulated human activities, a massive amount of loose solid materials are sometimes deposited at the confluence between the branch valley and stem stream, or blocked at the lateral channel contraction section in a river channel. Immersion of these granular materials in naturally-generated reservoirs tend to cause mass failure and even induce debris flow. However, the majority of previous studies primarily focused on post-event processes (i.e. flow hydraulics such as flood flow hydrographs, sediment transport or erosion, and river morphological changes) following dam failure. In this study, our attention is restricted to hydro-sediment dynamic processes that control unconsolidated dam failure as well as subsequent debris flow. This objective is achieved by conducting a series of experiments in a tilting flume and selecting the overtopping flows, vertical grading configurations, dam heights, and channel gradients as causative factors responsible for chain disaster in the form of dam failure and debris flow. We found that all experimental dams are either subject to partial failure through a gradual breach development or suddenly collapsed in en masse failure mode, debris flows induced by partial dam failures are likely to take place in the conditions of low overtopping flow and shallow channel slope. On the contrary, debris flows originated from en masse dam failures are shown to develop well in the opposite conditions. Also, the critical shear stresses for sediment entrainment under en masse dam failure cases are generally higher if compared with partial dam-failure equivalents. Moreover, the relative proportion of clear water to erodible solid materials is also related to dam failure mode, which will eventually determine debris-flow properties. These findings have strong implications for predicting and mitigating natural disasters of these kinds usually encountered in nature.

Quantitative Seismic Geomorphology of Four Different Types of the Continental Slope Channel Complexes in the Canterbury Basin, New Zealand

Modern marine seismic reflection data have allowed for the study of the morphology of submarine channels in a 3D perspective. This study presents a quantitative analysis of continental slope channel complexes morphology within the Canterbury Basin (New Zealand). It aims to characterize the morphology and seismic facies of submarine channels to better understand their formative sedimentary processes, paleoenvironment, and petroleum prospectivity. Submarine channel morphometric parameters are measured at 150 m intervals perpendicular to the axis of channels complexes. Based on the morphology analysis of erosional surfaces and seismic facies of channel complexes filling deposits, four types of continental slope channel complexes are found in the study area. These are vertical migrating channels, lateral migrating channels, V-shaped channels, and U-shaped channels. Furthermore, our work shows that channel morphometry varies over distances of 0.1 to 14 km in this continental slope system. These changes indicate a combination of submarine gravity flow process and channel wall collapse responsible for the development of continental slope channel complexes. Regionally, the evolution of the channels indicated less significant regional plate movement. This quantitative seismic geomorphology approach of characterizing submarine channels system has broader applications for better interpretation of paleoenvironment and petroleum prospectivity within frontier basins.

River response to mining-induced subsidence

Land subsidence is a phenomenon commonly associated with water withdrawal and mining. In river valleys it increases the risk of flooding, which is usually reduced by channel alignment and raising of flood dykes. In this work, we describe the natural, advanced processes of sedimentation and channel adjustment to ground level changes in the Chechło River reach within an about 30-year-old subsidence basin in southern Poland. Physicochemical properties of sediments, channel geometry and its changes over a 5-year period have been analyzed. These sediments of the ponded depression differ markedly from the laminated overbank deposits of the unaffected river reach in respect of their stratigraphy and accretion rate. Formation of a levee is the characteristic feature of the ponded reach. The levee deposits are silt-dominated and highly organic and overlay thick sandy strata. The ponded parts of the basin outside the levee zone are characterized by slow deposition of fine grained organic sediments. A local increase in a channel slope induces relatively intensive erosion at the knickpoint and the formation of sediment wave on the channel at the downstream end of the pond. These changes are associated with a rapid increase of the Width/Depth ratio. The sediment wave has a tendency to disperse in place due to channel downcutting and the formation of the over 100 m-long downstream reach with the geometry similar to that observed in unaffected river reaches. These investigations indicate that even small subsidence ponds can exist in a highly dynamic fluvial environment for decades before they disappear. They can enrich the local habitat and landscape for long enough to be important for biodiversity in regions heavily impacted by human activity. Decisions regarding the restoration of subsided lands should be site-specific and preceded by considerations for achieving the best possible benefits instead of mandatory liquidation of subsidence depressions.

Extreme Learning Machine model for assessment of stream health using the Qualitative Habitat Evaluation Index

Abstract The Extreme Learning Machine (ELM) approach was used to predict stream health with a Qualitative Habitat Evaluation Index (QHEI), and watershed metrics. A dataset of 112 sites in Ontario, Canada with their Hilsenhoff Biotic Index (HBI) and richness values was used in the development of two ELM models. Each model used 70 and 30% of the dataset for training and testing respectively. The models show a great fit with Root Mean Square Error (RMSE)=0.12 and 0.33 for HBI and richness test models, respectively. Then, features elimination based on ELM coefficients and coefficient of variation showed a slight increase in the models' RMSE to reach 0.09 and 0.33 correspondingly. Accordingly, this high predictability of the models in this research provide better insights into which factors influence HBI or richness, and suggests that ELM has a better architecture than other machine learning models and ANN to learn complex non-linear relationships. Also, sensitivity analysis expressed channel slope as the most affecting stream-health parameter for stream health.

Dynamic response of debris flows impacting curved joint check dams

The dynamic impact force of debris flow on dams with a curved upstream face curved was investigated using laboratory experiments and a theoretical approach. Equations describing the impact force and maximum run-up height were derived. The experiments and theoretical considerations reveal that the impact force and maximum run-up height are mainly controlled by the Froude number (Fr) reduced by the cosine of the channel slope angle (cosα). Both the impact force and the maximum run-up height have a quadratic relation with the modified Froude number (Fr/(cosα)0.5). The experimental data and the results of the theoretical approach are in good agreement, indicating that the theoretical approach can be used in practical applications. It is concluded that the comparison between the curved-joint dam and the more conventional sharp-joint dam shows no differences in the maximum impact force and run-up height for the same modified Froude number. With the sharp-joint dam, the peak values of the impact force are reached more quickly than with the curved-joint dam.

생태적 수질정화시설로서 댐 저수지 인공습지의 구조 적정성 평가방안

Many constructed wetlands have been installed in dam reservoirs nationwide for ecological purification of watershed pollutants, but aging and reduced efficiency are becoming issues. To improve the management of constructed wetlands, an objective evaluation of structural suitability is required. This study evaluated 39 constructed wetlands of 15 dams. First, through fogus group interview(FGI), survey analysis, and analytic hierarchy process(AHP), eight evaluation items in the physical and vegetative aspects were selected and the evaluation criteria applied with weights were prepared. Second, as a result of the structural suitability evaluation, the average score of the overall constructed wetlands was 80.8, with 10 sites rated as ‘good grade(91~100)’, 22 sites rated as ‘normal grade(71~90)’ and 7 sites rated as ‘poor grade(70 or less)’. The average score of physical structure evaluation was 52.6, with 14 sites rated as ‘good’, 21 sites as ‘normal’ and 4 sites as ‘poor’. The suitability of location was good level in most constructed wetlands, but the water supply system, depth of water, ratio of length-to-width, and slope of flow channel were evaluated as ‘normal’ or less in constructed wetlands of 50% or more. Therefore, it was found that overall improvement was necessary for stable flow supply and flow improvement in the constructed wetland. The average score of vegetative structure evaluation was 28.2, and about 84% of them were identified as ‘normal’ or lower. As a result of analyzing the Spearman’s correlation coefficient between the physical structure evaluation score and the vegetation structure evaluation score, there was a significant correlation(<italic>r</italic> = 0.728, <italic>p</italic> &lt; 0.001), and it was found that each evaluation factor also influences each other. As a result of the case review of 6 constructed wetlands, the appropriateness of the evaluation results was confirmed, and it was found that the location, flow rate supply, and type of wetland had a great influence on the efficiency and operation of the wetland. Through this study, it will be possible to derive structural weaknesses of constructed wetlands in dam reservoirs as a nature-based solution, to prepare types and practical alternatives for improved management of each constructed wetland in the future, and to contribute to enhancing various environmental functions.

STUDY OF CATCHMENT AREA AND DIMENSIONAL DESIGN OF HAUL ROAD OPEN CHANNEL AT PT. LINTAS ARTHA, SORONG CITY, WEST PAPUA PROVINCE

Lintas Artha is a mining company with an open mining system where its activities are directly related to the outside air. Topographical conditions in the form of a plateau which has a height of ± 44m-62m above sea level (dpl). The mining location is on a hill, so the weather is very uncertain. Influencing mining activities, the company needs to pay attention to the proper drainage system to prevent or control water entering the mining location from rainwater and runoff. Therefore, a technical study of the flow system on the haul road will be carried out. Based on the calculation, it is found that the area of the rain catchment area is 24,400 km2, the dimensions of the open channel in the haul road area have a channel bottom width of 1m, a water guard height of 0.6m, a channel slope of 60°. Then we get a trapezoidal channel that can flow a discharge of 33.33m3/second.

A Field Study on the Lithological Influence on the Interaction Between Weathering and Abrasion Processes in Bedrock Rivers

AbstractLithology is an important control on the efficiency of bedrock incision and thus the pace of landscape evolution. Rock strength is commonly considered the limiting lithologic factor that resists erosion. Yet, rock strength is a dynamic property that oscillates during advection of rock to the channel surface as damaging processes weaken rock and erosion exposes fresh rock. We approach the problem by investigating damage on bedrock surfaces that vary by the frequency they are eroded in channels of different lithologies. Our data set includes measurements of channel slope and width to characterize channel morphology, and Schmidt hammer rebound, P wave velocity, slake durability, and porosity to characterize the mechanical properties of channel surfaces. The average damage accumulation rate of lithologies ranges over 41% of the mean. We find a range of damage patterns among the different lithologies. Local surface damage increases with erosion frequency in channels comprised of coarse‐grained bedrock but decreases with erosion frequency in channels comprised of fine‐grained bedrock. We interpret these patterns to develop from lithological influences on weathering, abrasion, and the threshold of damage to erosion. The cross‐channel damage patterns between channel floors and margins are well correlated with stream power demonstrating links between microstructural rock properties, reach‐scale morphology, and landscape‐scale processes. We conclude that the morphodynamics of bedrock channels are sensitive to the lithological influences on the direction and magnitude of feedback in the coevolution of bedform morphology and the mechanical properties of the surface.

Giant pockmark-initiated deep-water slope channel complexes

Giant pockmark-initiated deep-water slope channel complexes

The influence of sediment supply on the stratigraphic evolution of an ancient passive margin deep-marine slope channel system, Windermere Supergroup, British Columbia, Canada

ABSTRACTAt the Castle Creek study area a superbly exposed continental-slope channel-complex set of the Isaac Formation termed ICC1 crops out. ICC1 is 220 m thick and exposed over 5 km parallel to bedding and consists of four vertically stacked channel complexes—lower channel complex (LC), and three upper channel complexes (termed UC1–UC3). Based on differences in lithological and textural makeup, and stratal trends, two styles of channel fill and stacking pattern are recognized—disorganized stack of bottom-up channel fills (LC, UC1, and UC2), and organized lateral-offset stack of laterally accreting channel fills (UC3). Bottom-up channel fills show an upward and axis-to-margin fining and thinning, and were filled by poorly sorted, density-stratified flows. In contrast, channel fills of UC3 exhibit negligible upward and lateral fining and thinning and were filled by flows enriched in coarse and very coarse sand and were only negligibly stratified in their lower part. Accordingly, the lower, depositionally important part of the flow had a plug-like density profile with limited overspill that caused circulation patterns in channel bends to resemble those in rivers. Notably, the grain-size makeup of late-stage channel fills of UC3 indicates a change in the makeup of the sediment supply, namely grain size and sorting. Note that this systematic upward change in sediment texture and channel type is observed in most (5 of 8) Isaac slope channel-complex sets at the Castle Creek study area. These changes reflect a change from hinterland- to shelf-dominated sediment supply interpreted to be associated with a long-term rise of relative sea level that progressively expanded continental-shelf accommodation and retention of coarse relict and palimpsest sediment. During short-term relative sea-level falls this increasingly voluminous source of coarse, moderately well-sorted siliciclastic and minor carbonate sediment eventually came to dominate the supply of coarse sediment to the shelf edge, and in turn, controlled the character of turbidity currents that remobilized sediment farther down the continental slope and possibly onto the basin floor.

Dredging transforms the seafloor and enhances functional diversity in urban seascapes

Landscape modification alters the condition of ecosystems and the complexity of terrain, with consequences for animal assemblages and ecosystem functioning. In coastal seascapes, dredging is routine practice for extracting sediments and maintaining navigation channels worldwide. Dredging modifies processes and assemblages by favouring species with wide trophic niches, diverse habitat requirements and tolerances to dredge-related eutrophication and sedimentation. Dredging also transforms the three-dimensional features of the seafloor, but the functional consequences of these terrain changes remain unclear. We investigated the effects of terrain modification on the functional diversity of fish assemblages in natural and dredged estuaries to examine whether dredging programs could be optimised to minimise impacts on ecological functioning. Fish assemblages were surveyed with baited remote underwater video stations and variation in functional niche space was described using species traits to calculate metrics that index functional diversity. Terrain variation was quantified with nine complementary surface metrics including depth, aspect, curvature, slope and roughness extracted from sonar-derived bathymetry maps. Functional diversity was, surprisingly, higher in dredged estuaries, which supported more generalist species with wider functional niches, and from lower trophic levels, than natural estuaries. These positive effects of dredging on functional diversity were, however, spatially restricted and were linked to both the area and orientation of terrain modification. Functional diversity was highest in urban estuaries where dredged channels were small (i.e. <1% of the estuary), and where channel slopes were orientated towards the poles (i.e. 171–189°), promoting both terrain variation and light penetration in urban estuaries. Our findings highlight previously unrecognised functional consequences of terrain modification that can easily be incorporated into dredging programs. We demonstrate that restricting the spatial extent of dredging operations and the orientation of dredged channel slopes, wherever this is practical, could help to limit impacts on ecosystem functioning and productivity in urban seascapes.

ERRATUM: Morphologic signatures of autogenic waterfalls: A case study in the San Gabriel Mountains, California

The published version of this paper contains two typos: The last sentence of the first paragraph of the “CRITERIA FOR AUTOGENIC WATERFALL IDENTIFICATION” section (p. 248) contained a typo, and should read “For constant Qs/Qsc, cyclic step theory predicts that step spacing and step height will decrease with increasing channel slope (S) (Izumi et al., 2017).” The last sentence of the last paragraph of the “Waterfall Metric Measurements” section (p. 250) should read “We also examined the along-channel waterfall distribution by calculating the fraction of total upstream distance XL/LR, where XL is the distance, and LR is the channel length from outlet to channel head.” These typos do not change the results, conclusions, or implications of the paper, and we note them in this erratum for clarity.

Influence of Boulders on Channel Width and Slope: Theory and Field Application

Influence of Boulders on Channel Width and Slope: Theory and Field Application

Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. This study uses data from three bottom-mounted mooring arrays to show seasonal variability and local forcing for the currents moving into and out of the Dotson ice shelf cavity. A southward flow of warm, salty water had maximum current velocities along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. The inflow correlated with the local ocean surface stress curl. At the western slope, meltwater outflows followed the warm influx along the eastern slope with a ~2–3 month delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to significantly control the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.