Channel Evolution Model Research Articles

Fluvial geomorphic evolution and stream fish community trajectories in the Bayou Pierre, Mississippi, U.S.A.

Abstract Human activities have often altered sediment dynamics in rivers, leading to aquatic habitat degradation. The dominant paradigm in fish–sediment interactions focuses on excessive fine sediments as indicators of habitat and water quality degradation. In contrast, geomorphologists have provided frameworks linking altered sediment dynamics to much broader and more complex changes to channel morphology and stream habitats across spatial scales. In this paper we use an interdisciplinary approach with historical and contemporary channel morphology and fish community datasets to examine how altered sediment dynamics have affected stream fish community evolution in the Bayou Pierre, Mississippi, U.S.A. Erosional process regimes have advanced upstream consistent with models of knickpoint propagation and channel evolution, leaving most of the catchment in a state of increased sediment transport and local sediment deficits. Fish communities in modern samples have less α and β diversity and fewer habitat specialist taxa than in historical samples. Whole‐community analysis via non‐metric multidimensional scaling found a strong gradient of homogenisation towards a fauna comprised of small‐bodied taxa adapted to large rivers. Comparisons of community and geomorphic change on this gradient found that reaches that transitioned between process regimes had more community change, and that local habitat factors relating to advanced channel evolution were strongly positively related to total community change. These results demonstrate that a catchment‐scale geomorphic analysis provided a strong tool for understanding fish community change on a decadal scale. Our findings further demonstrate concordant ecological responses to a complex sequence of disturbances and suggest that a broader view of sediment dynamics offers a rich toolkit for ecological analyses.

Multi-decadal changes in river morphology in an urbanizing watershed: Highland Creek, Toronto, Canada

Urban land development causes significant changes to river channel form and function. Outcomes are strongly conditioned by local circumstances although responses such as channel enlargement and incision are common but are highly variable in extent and detectability. Many case studies focus on small watersheds (or short reaches) and before-after conditions, and direct causation and temporal trajectories of change are not well known but often presumed to be a single step change and response. Well-documented examples in fully-urban, larger watersheds are rare, and rarer still are cases covering the full trajectory from pre-urban to fully urban land cover with accompanying data on the direct drivers of change such as discharge and stream power. Highland Creek, Toronto, has a drainage area of 102 km2 and between the early 1950s and 2000s underwent a land cover change from agricultural to completely urban in very low relief terrain with channels in narrow valleys incised locally into glacial sediments. Streamflow monitoring, land cover data and aerial photography over this seven-decade period, along with a calibrated runoff model and digital elevation data, give a complete picture over multiple epochs of the causes and changes in fluvial hydrology and geomorphology. The complete transformation of the flow regime, along with channel straightening and steepening, resulted in increases in average stream power (total and specific) of the order of ten and six times, respectively. The channel is now exceptionally energetic with maximum total and specific stream power for 2-year flood approaching 5000 Wm−1 and 300 Wm−2, respectively. The semi-alluvial and supply-limited character of the channels is also influential. Channel response is variable along the 20–25 km of channel measured and is notably different between the sub-watersheds, related to timing of development and its intersection with engineering intervention, and changing conceptions of the channel over time. In places the channel widened by a factor of four or five and changed from high sinuosity meanders to wide, bar-chute morphology, consistent with regime expectations for gravel-bed channels. In other places the process of urbanization has involved progressive engineering of the channel to convey stormwater (channelized), protect infrastructure and mitigate erosion, so that responses in these reaches are much more restricted and fluvial functions such as bend and bar development have been eliminated. Substantial channel transformation can be seen to have occurred episodically resulting from two major flood events as well as the increases in magnitude and frequency of peak flows, which limit post-flood recovery. Urbanization effects and consequences have developed gradually over a long period, rather than in a single urbanization step change, and they do not match simple models of channel evolution. In many ways urbanization of the river is ongoing, particularly in the form of geomorphically-referenced design of the channels as a response to damage from large floods and overall institutional watershed planning. The ongoing urbanization story of Highland Creek illustrates some extreme effects of urbanization as well as the complexity and contingency of response to the physical and institutional processes influencing the trajectory of urban river evolution.

MmWave Beam Tracking With Spatial Information Based on Extended Kalman Filter

Beam tracking is essential to compensate for beam misalignment and reduce the training overhead in millimeter wave (mmWave) systems. In high mobility scenarios, beam tracking can be implemented with the spatial information of the user equipment (UE) to avoid huge training overhead. However, there are estimation errors of spatial information in practical systems, which may lead to beam misalignment and performance degradation. In this letter, we propose a beam tracking algorithm to improve the tracking accuracy by combining spatial information and beam training. We first propose a novel channel evolution model based on the spatial information under the line-of-sight (LOS) condition. Then we consider the estimation error and modify the model accordingly. Based on the model, the extended Kalman filter (EKF) algorithm is utilized to track the beams at both ends. We also propose a novel training beam design to mitigate the non-linearity of measurement function and improve the tracking accuracy. Finally, simulation results validate the performance of the proposed algorithm.

Whittle Index Based Age-of-Information Aware Scheduling for Markovian Channels

The focus of this work is on minimizing the time average of the weighted sum of the Age-of-Information in a multi-sensor system in the setting where all sensors report their measurements to a central monitoring station using a shared communication channel. We consider multiple information settings including complete CSI/delayed CSI/no CSI and two stochastic channel evolution models, i.e., i.i.d. channels and Markovian channels. In all settings considered, we prove the indexability of the scheduling problem. In addition, we compute the Whittle Index in closed form for some of the settings. Indexability for Markovian channels for the objective of minimizing AoI is a key contribution of this work. Further, under i.i.d. channels, we propose a novel efficient implementation for the Whittle Index-based policy. We use simulations to show that Whittle Index-based scheduling policies either outperform or match the performance of the state-of-the-art policies for all the settings considered.

A method to detect abrupt shifts in river channel position using a Landsat‐derived water occurrence record

AbstractThe lateral migration of river channels is an important control on the evolution of alluvial fans, deltas, and floodplains. Lateral migration consists of both gradual riverbank migration and abrupt shifts in location due to avulsions or cutoffs. Methods exist to measure bank migration, but abrupt shifts in position are rarely considered or are not emphasized. Here we describe a new method using Landsat‐derived water occurrence images that primarily focuses on detecting when a channel has abruptly shifted position, either from avulsion or cutoff. The method does not assume any a priori model of channel geometry or evolution. Within a given area of interest, binary channel images created from the fluvial water occurrence record are stacked through time. Then a channel shift intensity, , is created by estimating the number of possible ending times for fluvial water voxels (a point in three‐dimensional space) in the stacked occurrence record. The number of possible end‐times for fluvial water voxels within a given region of the occurrence record reveals the likelihood that a reach of a river underwent an abrupt channel shift during the observation period. We present the results of this analysis for a 194 481 km2 region of the Amazonian basin. Follow‐up validation found three avulsions and 270 cutoffs within regions identified by this method. We show that areas above a threshold contain an avulsion or cutoff with high probability. This highlights the method's potential to detect and quantify abrupt channel shifts at the basin scale. The method also successfully distinguishes between abrupt channel movement and complex braiding behaviour. As this method is applicable to any binary water‐masked time series images, future applications of this method have the potential to provide insight into the controls and spatial variance of avulsions and cutoffs across a variety of scales.

Tracking geomorphic changes after suburban development with a high density of green stormwater infrastructure practices in Montgomery County, Maryland

Stream morphology is affected by changes on the surrounding landscape. Understanding the effects of urbanization on stream morphology is a critical factor for land managers to maintain and improve vulnerable stream corridors in urbanizing landscapes. Stormwater practices are used in urban landscapes to manage runoff volumes and peak flows, potentially mitigating alterations to the flow regime that drive changes in channel morphology. However, there remains a paucity of long-term studies assessing watershed-scale relationships between urbanization and effects on stream morphology where green stormwater infrastructure exists in high densities. This paper evaluates the geomorphic changes across four headwater catchments in the Chesapeake Bay Watershed over the course of >10 yr and relates these changes to urban development. Annual cross-sectional surveys conducted from 2002 to 2019 in one forested catchment, one agricultural catchment, and two treatment catchments were used to understand the relationship between urbanization and changes in stream morphology. Six cross-sectional geomorphic metrics were calculated and compared with development timelines and high flow events. A channel evolution model was then used to understand the status of morphologic stability at sites within the study. Results suggest downstream environments in developing areas are more impacted during early phases of suburban construction. Channel change during construction could be a result of sediment and erosion control efforts' limitations on preventing and controlling overland sediment mobilization or of increased discharge causing widening and thus bank-derived sediment to move to the streambed. Results demonstrate that geomorphic metrics are highly variable within a small area and are not always accurate representations of broader landscape changes but rather of the more localized environment at a specific stream segment. Despite a high density of stormwater management facilities in urban catchments, substantial alterations to cross sections were found at multiple locations in each catchment including the controls.

Evaluating the geomorphic channel response to beaver dam analog installation using unoccupied aerial vehicles

AbstractBeaver dam analogs (BDAs) are a stream restoration technique that is rapidly gaining popularity in the western United States. These low‐cost, stream‐spanning structures, designed after natural beaver dams, are being installed to confer the ecologic, hydrologic, and geomorphic benefits of beaver dams in streams that are often too degraded to provide suitable beaver habitat. BDAs are intended to slow streamflow, reduce the erosive power of the stream, and promote aggradation, making them attractive restoration tools in incised channels. Despite increasing adoption of BDAs, few studies to date have monitored the impacts of BDAs on channel form. Here, we examine the geomorphic changes that occurred within the first year of restoration efforts in Wyoming using high‐resolution visible light orthomosaics and elevation data collected with unoccupied aerial vehicles (UAVs). By leveraging the advantages of rapidly acquired images from UAV surveys with recent advancements in structure‐from‐motion photogrammetry, we constructed centimeter‐scale digital elevation models (DEMs) of the restoration reach and an upstream control reach. Through DEM differencing, we identified areas of enhanced erosion and deposition near the BDAs, suggesting BDA installation initiated a unique geomorphic response in the channel. Both reaches were characterized by net erosion during the first year of restoration efforts. While erosion around the BDAs may seem counter to the long‐term goal of BDA‐induced aggradation, short‐term net erosion is consistent with high precipitation during the study and with theoretical channel evolution models of beaver‐related stream restoration that predict initial channel widening and erosion before net deposition. To better understand the impacts of BDAs on channel morphology and restoration efforts in the western United States, it is imperative that we consistently assess the effects of beaver‐inspired restoration projects across a range of hydrologic and geomorphic settings and that we continue this monitoring in the future.

On the channel tracking under uncertain state model for multiuser massive MIMO in high-rate Internet-of-Things

The significant advancement of the internet-of-things has led to a dramatic increase in the number of moving or motionless devices that are connected to the cellular network. For handling such a great number of devices, 5G networks make use of massive MIMO technology. By considering a dynamic model for all channels variation of devices, joint channel estimation and tracking of all devices are studied regardless of the transmission or non-transmission of pilot by each device in the massive MIMO system. The channel predicting and updating is contingent upon the channel evolution model. This evolution does not necessarily follow a predetermined or fixed model. In this paper, the Recursive Least Squares (RLS) tracker and the Interacting Multiple-Mode (IMM) tracker are developed for tracking these channels. In addition, the autoregressive (AR) coefficients are obtained theoretically for all channels between devices and BS antennas by considering an AR model as an approximation of the channel model between a device and a BS antenna. Consequently, the optimal noise covariance of channel state is obtained adaptively online by means of these coefficients. Furthermore, exponential stability and error bound of the IMM tracker as well as the asymptotic stability of the RLS tracker are derived. Finally, the performance of the introduced trackers is assessed through simulations, and the reduced sum-rate of massive MIMO systems is shown under the effect of time-varying channel.

Analytical One‐Dimensional Conceptual Model of Channel Evolution After Dam Removal Based on Diffusion Framework

AbstractIn assessing the removal of dams, it is important to consider the degree to which these efforts could affect channel evolution. A number of previous studies have analyzed the problem of channel evolution using frameworks based on the diffusion equation. In this study, we adopted a similar analytical framework to examine one‐dimensional channel evolution within an infinite channel following dam removal. The Fourier transform is used to obtain an analytical solution which is further used to determine the volume of sediment and position of knickpoints. Analytical results obtained using the proposed models were compared with experiment results reported by Cantelli et al. (2004), https://doi.org/10.1029/2003wr002940 and in‐situ data related to the Balin dam break in Taiwan. We determined that the rate of sediment volume change is proportional to in the early period and in the intermediate period, before eventually decreasing to nearly zero. The proposed solution also makes it possible to derive qualitative and quantitative predictions pertaining to bed elevation, sediment volume, and knickpoint positions.

Toward Entrainment Thresholds in Fluvial Plucking

AbstractPlucking of blocks is an important, but understudied component of erosion in steep bedrock rivers. With the goal of developing realistic entrainment thresholds for use in bedrock channel evolution models, we re‐formulate the block entrainment problem. We derive the force and torque balances representing sliding and toppling of blocks occupying backward‐facing steps in the channel floor. We employ a computational fluid dynamics package to calculate the pressures and shear stresses on all faces of such a block, therefore explicitly representing the horizontally directed drag force and vertically directed lift force. We find that the pressure difference between the upstream and downstream block faces can significantly impact the force and torque balances. At typical flows, downstream pressure becomes ∼1%–2% lower than total upstream pressure, reflecting the reduction in fluid pressures in the recirculation zone. This pressure difference scales with the block Reynolds number squared and dramatically increases if the block protrudes above the plane of the upstream ledge. The resulting net downstream‐directed force both adds to the forces promoting sliding and provides a torque about the lower downstream corner of the block. Armed with the full set of forces on a block, we explore the roles of block geometry, flow velocity and depth, toppling pivot point location, and bed slope in facilitating sliding and toppling. Incorporating the small pressure difference between upstream and downstream faces greatly lowers the threshold for plucking, and suggests that blocks on river channel floors should move at lower and hence more frequent discharges than previously thought.

RSS-Based Channel Estimation for IRS-Aided Wireless Energy Transfer System

Although intelligent reflecting surface (IRS) is regarded as a promising solution to enhance the efficiency of wireless energy transfer (WET), the acquiring of channel state information is a crucial challenge for the system in which a training sequence for channel estimation is sent by low-power Internet-of-Things (IoT) devices. In this article, an IRS-aided multidevice WET system is considered. To overcome the limitation in channel estimation, we propose a received power-based channel estimation scheme that can be easily implemented and scalable in wirelessly empowered IoT devices. Specifically, at every single time slot, each device measures the received power of a randomly generated radio-frequency signal and feeds it back to the transmitter. We formulate a channel estimation problem to use the history of received power measurements based on the maximum-likelihood estimation using the phase retrieval framework and temporal channel evolution model. Moreover, we propose an algorithm that can be employed to obtain the stationary solution for the channel estimation problem, which is based on the inexact block coordinate descent method. We also perform algorithm modification to deal with the special case in which the transmitter-IRS channel is available. The simulation results show that the performance of the proposed algorithm approaches the upper bound as the channel slowly changes, although the proposed channel estimation protocol requires only one scalar value feedback.

Suburban stream erosion rates in northern Kentucky exceed reference channels by an order of magnitude and follow predictable trajectories of channel evolution

This paper documents ranges of streambed and bank erosion observed across suburban northern Kentucky via time-series surveys at 61 stream monitoring sites from the last ~10 yr. Average erosion rates in streams draining undeveloped watersheds (<5% total impervious area, TIA) were nominal: 0.5 cm/yr of incision (range of −5.8 to 11 cm/yr) and 1.0 cm/yr of widening (range of −58 to 20 cm/yr). By contrast, streams draining developed watersheds (>5% TIA) averaged 1.5 cm/yr of incision (range of −9.2 to 36 cm/yr) and 9.4 cm/yr of widening (range of −11 to 61 cm/yr). The suburban streams also followed predictable patterns of evolution consistent with the “classic” Channel Evolution Model (CEM) of Schumm et al. (1984), with the initial incision period (Stage 2) coinciding with bed coarsening followed by widening (Stage 3). Out of 45 sites draining >5% TIA, only four were in a state of dynamic equilibrium (Stage 1), two of which were attributable to stabilization via stream restoration and another was attributable to an upstream stormwater retrofit that substantially restricted erosive discharges. The other stable suburban site drained a watershed that was only 6.5% TIA and was just upstream of a reach undergoing incision and headcutting, implying that it would likely be experiencing incision (Stage 2) soon. Although the suburban sites spanned a gradient of development age and extent, >90% fell into unstable CEM categories (Stages 2 through 4), with only one site exhibiting features emblematic of potential geomorphic recovery (Stage 4 trending to Stage 5), attributable to an upstream stormwater retrofit. This case study underscores the predictable nature of long-term channel instability in gravel/cobble streams draining conventionally-developed suburban watersheds in support of more mechanistically based stormwater management strategies tailored to prevent the geomorphic degradation commonly associated with the urban stream syndrome.

Analytical Model of Navigable Channel Evolution in Ice Conditions

Analytical Model of Navigable Channel Evolution in Ice Conditions

Self‐Affine Fractal Spatial and Temporal Variability of the San Pedro River, Southern Arizona

AbstractPrevailing mathematical models of alluvial channel evolution generate smooth, idealized longitudinal profiles. Alluvial channel longitudinal profiles in nature, however, have substantial multiscale spatial and temporal variability. In this paper we quantify the spatial and temporal hydrologic and geomorphic variability of a 90‐km‐long reach of the San Pedro River (San Pedro River) in southeastern Arizona and compare that variability to numerical models designed specifically to honor the spatial and temporal variability of alluvial channel systems in nature. A key motivation of this work is the power law frequency size distribution of wet and dry reaches observed in the San Pedro River. We demonstrate that such a distribution is consistent with self‐affine fractal variations of the depth to bedrock and the channel longitudinal profile. At large spatial scales, spatial variations in depth to bedrock control the accommodation space for groundwater, which, in turn, controls spatial variations in surface water discharge. At small spatial scales, the longitudinal profile controls spatial variations in surface water discharge by changing the distance between the channel bed and the water table. These results underscore the complex spatiotemporal behavior of dryland alluvial rivers and the tight coupling that is possible between hydrologic and geomorphic processes in such systems.

A process‐based approach to restoring depositional river valleys to Stage 0, an anastomosing channel network

AbstractStream restoration approaches most often quantify habitat degradation, and therefore recovery objectives, on aquatic habitat metrics based on a narrow range of species needs (e.g., salmon and trout), as well as channel evolution models and channel design tools biased toward single‐threaded, and “sediment‐balanced” channel patterns. Although this strategy enhances perceived habitat needs, it often fails to properly identify the underlying geomorphological and ecological processes limiting species recovery and ecosystem restoration. In this paper, a unique process‐based approach to restoration that strives to restore degraded stream, river, or meadow systems to the premanipulated condition is presented. The proposed relatively simple Geomorphic Grade Line (GGL) design method is based on Geographic Information System (GIS) and field‐based analyses and the development of design maps using relative elevation models that expose the relic predisturbance valley surface. Several case studies are presented to both describe the development of the GGL method and to illustrate how the GGL method of evaluating valley surfaces has been applied to Stage 0 restoration design. The paper also summarizes the wide applicability of the GGL method, the advantages and limitations of the method, and key considerations for future designers of Stage 0 systems anywhere in the world. By presenting this ongoing Stage 0 restoration work, the authors hope to inspire other practitioners to embrace the restoration of dynamism and diversity through restoring the processes that create multifaceted river systems that provide long‐term resiliency, meta‐stability, larger and more complex and diverse habitats, and optimal ecosystem benefits.

Evaluating the effects of urbanization age on the morphology of low-order urban streams in the U.S. southern Piedmont

ABSTRACTWe used space-for-time substitution, correlation, and regression analyses to study the effects of urbanization age on stream channel variables from 19 low-order urban watersheds in the southern Piedmont of the United States. The results are used to address questions regarding which variables are most responsive to urbanization age, the duration of response relative to system size, and changes in adjustment rate over time. Few morphological variables were found to be well correlated with metrics of urbanization age. The maximum-width/maximum-depth ratio (Wmax/Dmax) exhibited the best correlations to multiple metrics of urbanization age, with all correlations positive. A dearth of young urbanization ages in our dataset makes mathematically derived response times and end states for Wmax/Dmax highly uncertain. Inferences from the age range that is better represented suggest that the period of major response has occurred within the first three decades following urbanization. Subsequently, gradual increase in Wmax/Dmax appears to continue over 40 or more years. Response of channel form to urbanization and time elapsed in these low-order Piedmont streams is constrained by the presence of resistant bedrock below streambeds, a circumstance addressed by recent channel evolution models.

Iterative Search Algorithm to Maximize System Capacity in Time-Varying MIMO DAS

In this paper, an iterative search algorithm to maximize system capacity in a time-varying MIMO distributed antenna system (DAS) is proposed. A common DAS model is employed, in which the transmit antennas are distributively located and the receiver can move arbitrarily in the region. Due to the small-scale fading effect and the receiver movement, the transmitters and receiver cannot obtain accurate channel state information (CSI) or optimize the system capacity. Therefore, we present a time-varying MIMO DAS model and corresponding channel evolution model to predict the time-varying channel. With the channel evolution model, the proposed iterative search algorithm can calculate the precoding matrix, and an iterative search process is employed to determine the optimal precoding matrix from a precoding matrix set. Meanwhile, error analysis show the error on the instantaneous mutual information with the proposed algorithm has a close relationship with the element number of the precoding matrix set and small-scale fading evolution coefficient. We also propose a non-uniform power allocation strategy which can improve the system capacity. Simulation results are presented to verity the analysis above and demonstrate the performance of system capacity with the proposed iterative search algorithm.

Channel Evolution Models as Predictors of Sediment Yield

AbstractThis paper recounts our predictions of channel evolution of the Black Vermillion River (BVR) and sediment yields associated with the evolutionary sequence. Channel design parameters allowed for the prediction of stable channel form and coincident sediment yields. Measured erosion rates and basin‐specific bank erosion curves aided in prediction of the stream channel succession time frame. This understanding is critical in determining how and when to mitigate a myriad of instability consequences. The BVR drains approximately 1,062 km2 in the glaciated region of Northeast Kansas. Once tallgrass prairie, the basin has been modified extensively for agricultural production. As such, channelization has shortened the river by nearly 26 km from pre‐European dimensions; shortening combined with the construction of numerous flow‐through structures have produced dramatic impacts on discharge and sediment dynamics. Nine stream reaches were established within three main tributaries of the BVR in 2007. Reaches averaged 490 m in length, were surveyed, and assessed for channel stability, while resurveys were conducted annually through 2010 to monitor change. This work illustrates the association of current stream state, in‐channel sediment contributions, and prediction of future erosion rates based on stream evolution informed by multiple models. Our findings suggest greater and more rapid sedimentation of a federal reservoir than has been predicted using standard sediment prediction methods.

Bottom morphology in the Song Hau distributary channel, Mekong River Delta, Vietnam

Field studies in the Song Hau distributary of the Mekong Delta in Vietnam conducted at high (Sept.-Oct 2014) and low (March 2015) Mekong River discharge are utilized to examine channel bottom morphology and links with sediment transport in the system. Multibeam bathymetric mapping surveys over the entire channel complex in the lower 80km of the distributary channel, and over 12- to 24-h tidal periods at six transect locations in the reach are used to characterize bottom type and change on seasonal and tidal timescales, supplemented by bottom sampling. The results of this study indicate that the largest proportion of channel floor (up to 80% of the total area) is composed of substratum outcrops of relict sediment units deposited during the progradation of the delta in the last 3.5ka. These take the form of outcrops that are either (1) steep-sided, tabular channel floor, (2) steep-sided sidewall, or (3) relatively flat channel floor. Flatter outcrops of channel floor substratum are identified by the presence of sedimentary furrows (<0.5m deep) incised into the channel bottom that are exposed at high discharge and oriented along channel and laterally continuous for kilometers. These furrows are persistent in location and extent across tidal cycles and appear to be incised into relict units, sometimes with a thin surficial layer of modern sediment observable in bottom grabs. The extent of substratum exposure, greater than that observed previously in low tidal energy systems like the Mississippi River, may relate both to a relatively low sand supply from the catchment, and/or to an efficient transfer of both sand and mud through this tidally energetic channel. Sand bottom areas forming dunes, comprise about 19% of the channel floor over the study area and are generally less than a few meters thick except on bar extensions of mid-channel islands. Both sandy and substratum areas are mantled by soft muds 0.25–1m thick during low discharge in the estuarine section of the study area. This mud mantling appears to be a key control on bottom sourcing of sand to suspension. An understanding of channel bottom morphology, particularly mobility and erodibility of sediments, is valuable for setting up morphodynamic models of channel evolution that can be used to test system response to anthropogenic alterations in the catchment and rising sea levels.

Application of the Stream Evolution Model to a Volcanically Disturbed River: The North Fork Toutle River, Washington State, USA

AbstractIn this study, a recently revised version of the channel evolution model, named the Stream Evolution Model (SEM), was applied to the upper North Fork Toutle River disrupted by the deposition of a 2.5‐km3 debris avalanche during the catastrophic eruption of Mount St. Helens in 1980. The results show that, in the first few years following the eruption, upstream channel reaches generally incised, evolving in SEM Stage 4 (i.e. degradation and widening), while downstream reaches aggraded, evolving in Stage 5 (i.e. aggradation and widening). However, starting in the late‐1980s, this simple pattern was disrupted by incision in the downstream reaches, which seemed to propagate upstream. Since the 1990s, lateral channel adjustments have become predominant as rates of vertical adjustment have slowed and river valley top widths relaxed to asymptotic values. Spatial and temporal sequences of channel evolution have tended to follow the sequences of stages expected according to the SEM, although these sequences have been frequently disrupted by renewed incision, secondary cycles of adjustment and the impacts of local geologic, geomorphic and hydraulic conditions. Within the quasi‐full SEM cycles, stages 4 and 5 were sometimes repeated, while stage 6 (quasi‐equilibrium) was sometimes omitted, and stage 8 (anabranching) only occurred in the downstream braided/anabranching reaches. According to the SEM, degradation, widening and lateral activity (stages 4 and 7) are forecast to continue until transverse valley profiles and channel planforms stabilize and floodplain and terrace surfaces are fully colonized by vegetation. Copyright © 2017 John Wiley &amp; Sons, Ltd.