(Dis)Connectivity in catchment sediment cascades: a fresh look at the sediment delivery problem

The concept of the sediment delivery problem was introduced into the literature in 1983 by Des Walling. This concept describes how only a fraction of sediment eroded within a catchment will reach the basin outlet and be represented as sediment yield, and that sediment storage mechanisms operating within a catchment explain this discrepancy. Since this paper was published, geomorphologists have been examining in great detail the fate of sediment eroded from the landsurface, and the pathways and timeframes of sediment transport and storage in catchments. However, to fully understand the internal dynamics of sediment flux requires a ‘fresh look at the sediment delivery problem’. A framework is required that can incorporate the various processes involved in sediment movement from source areas through a basin to its outlet, and can take account of the spatial distribution of, and timeframes over which, these processes operate. This paper presents a conceptual framework for analysis of catchment (dis)connectivity that incorporates both spatial and temporal variability in the operation of the sediment cascade. This approach examines where blockages occur to disrupt these longitudinal, lateral and vertical linkages in catchments. Depending on the position of blockages (termed buffers, barriers and blankets), and their sediment residence time, various parts of a catchment may be actively contributing sediment to the sediment cascade and be switched on, or inactive and switched off. This paper discusses how such a framework can be used to model response times to disturbance and explain the manifestation of geomorphic change in catchments. The paper then highlights challenges geomorphologists face in applying such a framework to understand the internal dynamics of the catchment sediment cascades, and forecast how environmental change might affect the operation of sediment fluxes into the future. Copyright © 2012 John Wiley & Sons, Ltd.     

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley,SEQ, Australia

The nature of catchment‐scale sediment (dis)connectivity is the primary influence on sediment delivery to trunk streams and controls the particle size distribution of channel bed sediments. Here, we examine the distribution of major sediment buffers (floodplains, terraces, alluvial fans, trapped tributary fills), barriers (weirs), and effective catchment area (i.e. sediment contributing area) to characterize the potential for coarse sediment (dis)connectivity in 20 tributaries of Lockyer Creek, in the Lockyer Valley, SEQ. We then analyse the distribution of trunk stream sedimentary links to determine how certain tributaries or disconnecting features (buffers and barriers) influence downstream patterns of bed sediment fining along Lockyer Creek. We find that buffering increases downstream in the Lockyer Valley, and that tributary position and shape influence the space available for sediment buffering. Correspondingly, the spatial extent of sediment buffers impacts the distribution of effective catchment area, which influences the sedimentological significance of individual tributaries. Tributary sediment connectivity, the extent of overbank flows (floodwater zones), and weir locations all exert an additional influence on the distribution of sediment links along the trunk stream. These controls are related to the physiographic and climatic setting of the Lockyer Valley, and anthropogenic influences in this system. We conclude that controls on sediment connectivity and bed load sediment characteristics are highly variable between catchments, and that sediment (dis)connectivity merits equal consideration with tributary basin/channel size when determining controls on tributary–trunk stream relationships and channel sediment regime. Copyright © 2017 John Wiley & Sons, Ltd.     

‘Out with the Old?’ Why coarse spatial datasets are still useful for catchment‐scale investigations of sediment (dis)connectivity

The increasing popularity of remote sensing techniques has created numerous options for researchers seeking spatial datasets, especially digital elevation models (DEMs), for geomorphic investigations. This yields an important question regarding what DEM resolution is most appropriate when answering questions of geomorphic significance. The highest possible resolution is not always the best choice for a particular research aim, and DEM resolution should be tailored to fit both the scale of investigation and the simplicity/complexity of modelling processes applied to the dataset. We find that DEM resolution has a significant effect on a simple model of bed load sediment connectivity in the Lockyer Valley, Queensland. We apply a simple bed load transport threshold to catchment DEMs at three different resolutions – 1 m, 5 m, and 25 m. We find that using a 1 m resolution DEM generates numerous disconnections along tributary channel networks that underestimates the sediment contributing area, i.e. effective catchment area (ECA), of seven tributary basins of Lockyer Creek. Utilizing a coarser (lower‐resolution) DEM helps eliminate erroneous disconnections, but can reduce the detail of stream network definition. We find that the 25 m resolution DEM provides the best measure of ECA for comparing sediment connectivity between tributary catchments. The utility of simple models and coarse‐resolution datasets is important for undertaking large, catchment‐scale geomorphic investigations. As catchment‐scale investigations are becoming increasingly entwined with river management and rehabilitation efforts, scientists need not embrace an ‘out with the old’ philosophy. Simple models and coarse‐resolution datasets can help better integrate geomorphic research with management strategies and provide inexpensive and quick first‐order insights into catchment‐scale processes that can help focus future management efforts. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of ENSO events on sediment production in a large coastal basin in northern Peru

Although the importance of ENSO on hydrological anomalies has been recognized, variations in sediment fluxes caused by these extreme events are poorly documented. The effect of ENSO is not limited to changes in sediment mobilization. Since ENSO events can affect terrestrial ecosystems, they may have important effects on sediment production and transport in river basins over time spans that are longer than the duration of the event itself. The Catamayo‐Chira basin is an interesting casestudy for investigating these geomorphic implications. The objectives were: (i) to study the effect of ENSO on stream flow and sediment yields in the basin, (ii) to investigate if ENSO events affect sediment yields in the post‐ENSO period and (iii) to understand which factors control the ENSO and post‐ENSO basin response. During strong negative ENSO periods, mean annual stream flow discharge at the inlet of the Poechos reservoir in the lower basin was 5.4 times higher than normal annual discharges, while average sediment fluxes exceeded those of normal years by a factor of about 11. In two heavily affected periods, 45.9% of the total sediment yield in the 29 years observation period was generated. Sediment fluxes in the post‐ENSO period are lower than expected, which proves post‐ENSO event dynamics are significantly different from pre‐event dynamics. Our analysis indicates the increase of vegetation growth in the lower basin is not the main reason explaining considerable sediment flux decrease in post‐ENSO periods. During strong ENSO events, sediment in alluvial stores in the lower part of the basin is removed due to enlarging and deepening of channels. In post‐ENSO periods, normal discharges and persisting sediment supplies from the middle/upper basin lead to river aggradation and storage of large amounts of sediment in alluvial plains. The decrease in sediment export will last for several years until the equilibrium is re‐established. Copyright © 2011 John Wiley & Sons, Ltd.     

Modelling localized sources of sediment in mountain catchments for provenance studies

A hydrology–sediment modelling framework based on the model Topkapi-ETH combined with basin geomorphic mapping is used to investigate the role of localized sediment sources in a mountain river basin (Kleine Emme, Switzerland). The periodic sediment mobilization from incised areas and landslides by hillslope runoff and river discharge is simulated in addition to overland flow erosion to quantify their contributions to suspended sediment fluxes. The framework simulates the suspended sediment load provenance at the outlet and its temporal dynamics, by routing fine sediment along topographically driven pathways from the distinct sediment sources to the outlet. We show that accounting for localized sediment sources substantially improves the modelling of observed sediment concentrations and loads at the outlet compared to overland flow erosion alone. We demonstrate that the modelled river basin can shift between channel-process and hillslope-process dominant behaviour depending on the model parameter describing gully competence on landslide surfaces. The simulations in which channel processes dominate were found to be more consistent with observations, and with two independent validations in the Kleine Emme, by topographic analysis of surface roughness and by sediment tracing with ¹⁰ Be concentrations. This research shows that spatially explicit modelling can be used to infer the dominant sediment production process in a river basin, to inform and optimize sediment sampling strategies for denudation rate estimates, and in general to support sediment provenance studies. © 2020 John Wiley & Sons, Ltd.     

Spatial and temporal patterns of sediment storage over 45 years in Carnation Creek,BC, a previously glaciated mountain catchment

The movement of sediment through mountain river networks remains difficult to predict, as processes beyond streamflow and particle size are responsible for the entrainment and transport of bedload sediment. In deglaciated catchments, additional complexity arises from glacial impacts on landscape organization. Research to date indicates that the quantity of sediment stored in the channel is an important component of sediment transport in systems which alternate between supply and transport limited states, but limited long-term field data exist which can capture storage-transfer dynamics over a timescale encompassing episodic supply typical of mountain streams. We use a 45-year dataset with annual and decadal-scale data on sediment storage, channel morphology, and wood loading to investigate the spatial and temporal organization of storage in Carnation Creek, a previously glaciated 11 km² catchment on Vancouver Island, British Columbia. Sediment is supplied episodically to the channel, including additions from debris flows in the early 1980s just upstream of the studied channel region. Analyzing the spatial and temporal organization of sediment storage along 3.0 km of channel mainstem reveals a characteristic storage wavelength similar to the annual bedload particle travel distance. Over time, two scales of variation in storage are observed: small-scale fluctuation of 3–10 years corresponding to local erosional and depositional processes, and larger scale response over 25–35 years related to supply of sediment from hillslopes. Complex relationships between storage and sediment transfer (i.e., annual change in storage) are identified, with decadal-scale hysteresis present in storage-transfer relations in sites influenced by hillslope sediment and logjams. We propose a conceptual model linking landscape organization to temporal variability in storage and to storage–export cycles. Collectively, our results reaffirm the importance of storage to sediment transport and channel morphology, and highlight the complexity of storage–transport interactions. © 2019 John Wiley & Sons, Ltd.     

Sediment transport at the network scale and its link to channel morphology in the braided Vjosa River system

In this article we apply the CASCADE network-scale sediment connectivity model to the Vjosa River in Albania. The Vjosa is one of the last unimpaired braided rivers in Europe and, at the same time, a data scarce environment, which limits our ability to model how this pristine river might respond to future human disturbance. To initialize the model, we use remotely sensed data and modeled hydrology from a regional model. We perform a reach-by-reach optimization of surface grain size distribution (GSD) and bedload transport capacity to ensure equilibrium conditions throughout the network. In order to account for the various sources of uncertainty in the calculation of transport capacity, we performed a global sensitivity analysis. The modeled GSD distributions generated by the sensitivity analysis generally match the six GSDs measured at different locations within the network. The modeled bedload sediment fluxes increase systematically downstream, and annual fluxes at the outlet of the Vjosa are well within an order of magnitude of fluxes derived from previous estimates of the annual suspended sediment load. We then use the modeled sediment fluxes as input to a set of theoretically derived functions that successfully discriminate between multi-thread and single-thread channel patterns. This finding provides additional validation of the model results by showing a clear connection between modeled sediment concentrations and observed river morphology. Finally, we observe that a reduction in sediment flux of about 50% (e.g., due to dams) would likely cause existing braided reaches to shift toward single thread morphology. The proposed method is widely applicable and opens a new avenue for application of network-scale sediment models that aid in the exploration of river stability to changes in water and sediment fluxes.     

Reworking of basin fill deposits along a tributary of the upper Yellow River: Implications for changes to landscape connectivity

Recent emphasis on sediment connectivity in the literature highlights the need for quantitative baseline studies on the patterns and distribution of sediment stores to facilitate understanding of how sediment moves through the landscape at various temporal and spatial scales. This study evaluates the distribution and make‐up of sediment stores within the dramatically incised landscapes of the upper Yellow River, where basin fill deposits up to 1200 m in depth have been extensively reworked following incision by the Yellow River. Field and GIS analyses highlight the discontinuous distribution of sediment stores in Garang catchment, a 236 km² tributary of the upper Yellow River. Volumetric estimates of sediment storage were obtained through a combination of field mapping, GPR transects, and GIS analyses. Sediment stores cover 20% of the Garang catchment, with an estimated volume of 474.0 × 10⁶ m³, and inferred residence times from OSL and ¹⁴C dating of 10³–10⁴ years. Fans and terraces reworked from basin fill deposits, and associated cut and fill terrace features, are the dominant forms of sediment storage (~90% of total). A space‐for‐time argument is used to assess stages of basin infilling and subsequent landscape responses to incision, outlining a dramatic example of changes to sediment dynamics and connectivity relationships within the upper Yellow River. Sediments within the upper catchment lie above the regional basin fill level, offering a glimpse of pre‐incisional conditions. This contrasts markedly with the enduring influence of basin incisional history seen within the middle catchment, and the contemporary landscapes of the lower catchment where nearly all available sediment has been excavated from the basin and the landscape effectively operates under post‐incisional conditions. The need to contextualise catchment‐scale studies in terms of landscape history is emphasised. Copyright © 2017 John Wiley & Sons, Ltd.     

基于连通性指数(IC)的近30年鄱阳湖流域水系结构与水文连通演变评估

由于气候变化和人类活动等多重影响,流域河湖水系格局与连通程度发生了显著变化,进而引发洪涝灾害等一系列水资源问题。本文以鄱阳湖流域为研究区,基于Google Earth Engine(GEE)提取1989—2020年5期水系数据,采用图论方法构建水系评价体系,定量分析该地区近30年来水系格局和结构连通性的时空演变特征,并结合该时期地形、土地利用和归一化植被指数(NDVI)等数据,利用连通性指数(index of connectivity,IC)评估功能连通性的动态变化,进而探讨水文连通与径流量和输沙量的联系。结果表明,近30年来鄱阳湖流域水系结构趋于复杂化,主要体现在流域北部。除干流外,其他等级河流的数量和长度均有所增加,其中Ⅲ级河流最为明显。河网密度、水面率、河网复杂度和发育系数均呈增加趋势,2000年后的变化率约为2000年前的两倍。水系连通环度、节点连接率和水系连通度总体增加,结构连通性呈好转趋势且变化幅度较小。功能连通分析表明,近30年来大部分流域IC减少,流域下游靠近主河道的平坦地区IC较高,上游远离河道的植被密集区域IC较低。此外,IC与年径流量和输沙量表现为显著的正相关性(...     

The effect of forestry drainage operations on upland sediment yields: A study of two peat-covered catchments

The suspended sediment yields of two adjacent, paired, catchments on blanket peat in mid-Wales were compared before and after preafforestation drainage works. Catchment A was ploughed whilst an adjacent catchment (B) was left unploughed. After eight months Catchment B was also ploughed. The ploughing strategy in both catchments was designed to minimize sediment loss. However, suspended sediment loss increased 2·5 times following ploughing in Catchment A, whilst no such increase occurred at this time in Catchment B. Subsequently, suspended sediment yields in Catchment B increased 4·8 times after it was ploughed. Organic sediment was lost mainly from furrow sides, and erosion pins showed maximum ground recession in summer, due to peat wastage. Summer desiccation prepared sediment for transport, and organic suspended sediment loads were highest in the autumn. Sediment loads were limited by vegetation colonization and some reduction in sediment loss was due to the presence of unploughed strips adjacent to stream courses.     

Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model

Abstract

Rainfall–runoff induced soil erosion causes important environmental degradation by reducing soil fertility and impacting on water availability as a consequence of sediment deposition in surface reservoirs used for water supply, particularly in semi-arid areas. However, erosion models developed on experimental plots cannot be directly applied to estimate sediment yield at the catchment scale, since sediment redistribution is also controlled by the transport conditions along the landscape. In particular, representation of landscape connectivity relating to sediment transfer from upslope areas to the river network is required. In this study, the WASA-SED model is used to assess the spatial and temporal patterns of water and sediment connectivity for a semi-arid meso-scale catchment (933 km²) in Brazil. It is shown how spatial and temporal patterns of sediment connectivity within the catchment change as a function of landscape and event characteristics. This explains the nonlinear catchment response in terms of sediment yield at the outlet.

Citation Medeiros, P. H. A., Güntner, A., Francke, T., Mamede, G. L. & de Araújo, J. C. (2010) Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model. Hydrol. Sci. J. 55(4), 636–648.     

A suburban sediment budget: Coarse-grained sediment flux through hillslopes,stormwater systems and streams

Sediment in urban stormwater systems creates a significant maintenance burden, while a lack of coarse-grained bed sediment in streams limits their ecological value and geomorphic resilience. Gravel substrates, for example, provide benthic habitat yet are often scoured from the channel bed only to end up in a detention basin or treatment wetland. This dual problem of both ‘too much’ and ‘too little’ coarse-grained sediment reflects a watershed sediment budget that is profoundly altered. We developed a conceptual urban coarse-grained (>0.5 mm) sediment budget across three domains: hillslopes (urban land surfaces), the built stormwater network and stream channels. We then quantified key sources, sinks and storages for a suburban case study, using a combination of hillslope and in-channel monitoring, and interrogation of local government records. Around 36% of the sediment supplied to the stormwater network reached the catchment outlet, a level of sediment delivery much higher than observed in similar-sized natural catchments. The remainder was deposited in the sediment cascade and either stored, or extracted and removed from the catchment (e.g. material deposited in sediment ponds and gross pollutant traps). Conventional urban drainage networks are characterized by high hillslope sediment supply and low storage, resulting in efficient sediment delivery. Channel erosion, deposition in (and extraction from) pipes and channels, and floodplain deposition are small compared to sediment transport through the cascade. An understanding of the sediment budget of urban headwater catchments can provide stormwater and waterway managers with the information they need to address specific sediment problems such as sedimentation in stormwater assets and geomorphic recovery of urban streams. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Influence of storm-related sediment storage on the sediment delivery from tributary catchments in the upper Waipaoa River,New Zealand

Although much is known about overall sediment delivery ratios for catchments as components of sediment production and sediment yield, little is known about the component of temporary sediment storage. Sediment delivery ratios focused on the influence of storm-related sediment storage are measured at Matakonekone and Oil Springs tributaries of the Waipaoa River basin, east coast of New Zealand. The terrace deposits of both tributaries show abundant evidence of storm-related sedimentation, especially sediment delivered from Cyclone Bola, a 50 year return rainfall event which occurred in 1988. The sediment delivery ratio is calculated by dividing the volume of sediment transported from a tributary to the main stream by the volume of sediment generated at erosion sites in the tributary catchment. Because the sediment delivery volume is unknown, it can be calculated as the difference between sediment generation volume and sediment storage volume in the channel reach of the tributary. The volume of sediment generated from erosion sites in each tributary catchment was calculated from measurements made on aerial photographs dating from 1960 (1:44 000) and 1988 (1:27 000). The volume of sediment stored in the tributary can be calculated from measurements of cross-sections located along the tributary channel, which are accompanied by terrace deposits dated by counting annual growth rings of trees on terrace surfaces. Sediment delivery ratios are 0·93 for both Matakonekone catchment and Oil Springs catchment. Results indicate that Oil Springs catchment has contributed more than twice the volume of sediment to the Waipaoa River than the Matakonekone catchment (2·75 × 10⁶ m³ vs 1·22 × 10⁶ m³). Although large volumes of sediment are initially deposited during floods, subsequent smaller flows scour away much of these deposits. The sediment scouring rate from storage is 1·25 × 10⁴ m³ a⁻¹ for Matakonekone stream and 0·83 × 10⁴ m³ a⁻¹ for Oil Springs stream. Matakonekone and Oil Springs channels respond to extreme storms by instantaneously aggrading, then gradually excavating the temporarily stored sediment. Results from Matakonekone and Oil Springs streams suggest a mechanism by which event recurrence interval can strongly influence the magnitude of a geomorphic change. Matakonekone stream with its higher stream power is expected to excavate sediment deposits more rapidly and allow more rapid re-establishment of storage capacity. Copyright © 1999 John Wiley & Sons, Ltd.     

The influence of landscape connectivity and landslide dynamics upon channel adjustments and sediment flux in the Liwu Basin,Taiwan

Catchment‐scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as Taiwan. This study uses historical aerial photographs, flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the Liwu Basin. Recurrent earthquakes and typhoon events trigger frequent landslide activity, channel adjustment and sediment reworking in this system. Spatial variability in magnitude–frequency relations of hillslope‐valley floor (lateral) and upstream–downstream (longitudinal) connectivity during the study period are shown to reflect annual reworking in source and accumulation zones, while partly‐confined valleys in the mid‐catchment area trap sediment behind landslide‐induced dams that are formed and breached on an approximately decadal basis. This promotes partial longitudinal connectivity in these areas. Landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images. Although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the Liwu Basin, residence times for sediment storage are very short in this highly‐connected river system, where confined valley settings extend virtually to the coast. Copyright © 2014 John Wiley & Sons, Ltd.     

Regionalizing mean annual flow and daily flow variability for basin‐scale sediment and nutrient modelling

River discharges vary strongly through time and space, and quantifying this variability is fundamental to understanding and modelling river processes. The river basin is increasingly being used as the unit for natural resource planning and management; to facilitate this, basin‐scale models of material supply and transport are being developed. For many basin‐scale planning activities, detailed rainfall‐runoff modelling is neither necessary nor tractable, and models that capture spatial patterns of material supply and transport averaged over decades are sufficient. Nevertheless, the data to describe the spatial variability of river discharge across large basins for use in such models are often limited, and hence models to predict river discharge at the basin scale are required. We describe models for predicting mean annual flow and a non‐dimensional measure of daily flow variability for every river reach within a drainage network. The models use sparse river gauging data, modelled grid surfaces of mean annual rainfall and mean annual potential evapotranspiration, and a network accumulation algorithm. We demonstrate the parameterization and application of the models using data for the Murrumbidgee basin, in southeast Australia, and describe the use of these predictions in modelling sediment transport through the river network. The regionalizations described contain less uncertainty, and are more sensitive to observed spatial variations in runoff, than regionalizations based on catchment area and rainfall alone. Copyright © 2006 John Wiley & Sons, Ltd.     

Geomorphic controls on floodplain sediment and soil organic carbon storage in a Scottish mountain river

River floodplains constitute an important element in the terrestrial sediment and organic carbon cycle and store variable amounts of carbon and sediment depending on a complex interplay of internal and external driving forces. Quantifying the storage in floodplains is crucial to understand their role in the sediment and carbon cascades. Unfortunately, quantitative data on floodplain storage are limited, especially at larger spatial scales. Rivers in the Scottish Highlands can provide a special case to study alluvial sediment and carbon dynamics because of the dominance of peatlands throughout the landscape, but the alluvial history of the region remains poorly understood. In this study, the floodplain sediment and soil organic carbon storage is quantified for the mountainous headwaters of the River Dee in eastern Scotland (663 km²), based on a coring dataset of 78 floodplain cross-sections. Whereas the mineral sediment storage is dominated by wandering gravel-bed river sections, most of the soil organic carbon storage can be found in anastomosing and meandering sections. The total storage for the Upper Dee catchment can be estimated at 5.2 Mt or 2306.5 Mg ha^-1 of mineral sediment and 0.7 Mt or 323.3 Mg C ha^-1 of soil organic carbon, which is in line with other studies on temperate river systems. Statistical analysis indicates that the storage is mostly related to the floodplain slope and the geomorphic floodplain type, which incorporates the characteristic stream power, channel morphology and the deposit type. Mapping of the geomorphic floodplain type using a simple classification scheme shows to be a powerful tool in studying the total storage and local variability of mineral sediment and soil organic carbon in floodplains. © 2019 John Wiley & Sons, Ltd.     

Modelling particle residence times in agricultural river basins using a sediment budget model and fallout radionuclide tracers

Contemporary patterns in river basin sediment dynamics have been widely investigated but the timescales associated with current sediment delivery processes have received much less attention. Furthermore, no studies have quantified the effect of recent land use change on the residence or travel times of sediment transported through river basins. Such information is crucial for understanding contemporary river basin function and responses to natural and anthropogenic disturbances or management interventions. To address this need, we adopt a process‐based modelling approach to quantify changes in spatial patterns and residence times of suspended sediment in response to recent agricultural land cover change. The sediment budget model SedNet was coupled with a mass balance model of particle residence times based on atmospheric and fluvial fluxes of three fallout radionuclide tracers (⁷Be, excess ²¹⁰Pb and ¹³⁷Cs). Mean annual fluxes of suspended sediment were simulated in seven river basins (38–920 km²) in south‐west England for three land cover surveys (1990, 2000 and 2007). Suspended sediment flux increased across the basins from 0.5–15 to 1.4–37 kt y^‐1 in response to increasing arable land area between consecutive surveys. The residence time model divided basins into slow (upper surface soil) and rapid (river channel and connected hillslope sediment source area) transport compartments. Estimated theoretical residence times in the slow compartment decreased from 13–48 to 5.6–14 ky with the increase in basin sediment exports. In contrast, the short residence times for the rapid compartment increased from 185–256 to 260–368 d as the modelled connected source area expanded with increasing sediment supply from more arable land. The increase in sediment residence time was considered to correspond to longer sediment travel distances linked to larger connected source areas. This novel coupled modelling approach provides unique insight into river basin responses to recent environmental change not otherwise available from conventional measurement techniques. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

An approach for measuring confinement and assessing the influence of valley setting on river forms and processes

Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although there are various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lacking and/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearly define forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement are differentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and share the same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this framework to examples from Australia, United States and New Zealand, showing how this framework can be applied across the spectrum of river diversity. This method can help to inform interpretations of reach‐scale river behaviour, highlighting the role of antecedent controls on contemporary forms and processes. Clear definitions of confinement are shown to support catchment‐scale analysis of river patterns along longitudinal profiles, and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments (e.g. process zone distribution, lateral sediment inputs and (dis)connectivity). Copyright © 2015 John Wiley & Sons, Ltd.     

Development of ST:REAM: a reach‐based stream power balance approach for predicting alluvial river channel adjustment

River channel sediment dynamics are important in integrated catchment management because changes in channel morphology resulting from sediment transfer have important implications for many river functions. However, application of existing approaches that account for catchment‐scale sediment dynamics has been limited, largely due to the difficulty in obtaining data necessary to support them. It is within this context that this study develops a new, reach‐based, stream power balance approach for predicting river channel adjustment. The new approach, named ST:REAM (sediment transport: reach equilibrium assessment method), is based upon calculations of unit bed area stream power (ω) derived from remotely sensed slope, width and discharge datasets. ST:REAM applies a zonation algorithm to values of ω that are spaced every 50 m along the catchment network in order to divide the branches of the network up into relatively homogenous reaches. ST:REAM then compares each reach's ω value with the ω of its upstream neighbour in order to predict whether or not the reach is likely to be either erosion dominated or deposition dominated. The paper describes the application of ST:REAM to the River Taff in South Wales, UK. This test study demonstrated that ST:REAM can be rapidly applied using remotely sensed data that are available across many river catchments and that ST:REAM correctly predicted the status of 87.5% of sites within the Taff catchment that field observations had defined as being either erosion or deposition dominated. However, there are currently a number of factors that limit the usefulness of ST:REAM, including inconsistent performance and the need for additional, resource intensive, data to be collected to both calibrate the model and aid interpretation of its results. Copyright © 2014 John Wiley & Sons, Ltd.     

Parsimonious sediment transport equations based on Bagnold's stream power approach

It is increasingly recognized that effective river management requires a catchment scale approach. Sediment transport processes are relevant to a number of river functions but quantifying sediment fluxes at network scales is hampered by the difficulty of measuring the variables required for most sediment transport equations (e.g. shear stress, velocity, and flow depth). We develop new bedload and total load sediment transport equations based on specific stream power. These equations use data that are relatively easy to collect or estimate throughout stream networks using remote sensing and other available data: slope, discharge, channel width, and grain size. The new equations are parsimonious yet have similar accuracy to other, more established, alternatives. We further confirm previous findings that the dimensionless critical specific stream power for incipient particle motion is generally consistent across datasets, and that the uncertainty in this parameter has only a minor impact on calculated sediment transport rates. Finally, we test the new bedload transport equation by applying it in a simple channel incision model. Our model results are in close agreement to flume observations and can predict incision rates more accurately than a more complicated morphodynamic model. These new sediment transport equations are well suited for use at stream network scales, allowing quantification of this important process for river management applications. Copyright © 2017 John Wiley & Sons, Ltd.