Modelling of sediment dynamics in a laboratory‐scale experimental catchment

The variability of hillslope form and function is examined experimentally using a simple model catchment in which most landscape development parameters are either known or controlled. It is demonstrated that there is considerable variability in sediment output from similar catchments, subjected to the same hydrological processes, and for which the initial hillslope profiles are the same. The results demonstrate that, in the case of catchments with a linear initial hillslope profile, the sediment output is initially high but reduces through time, whereas for a concave initial profile the sediment output was smaller and relatively constant. Concave hillslope profiles also displayed reduced sediment output when compared with linear slopes with the same overall slope. Using this experimental model catchment data, the SIBERIA landscape evolution model was tested for its ability to predict temporal sediment transport. When calibrated for the rainfall and erodible material, SIBERIA is able to simulate mean temporal sediment output for the experimental catchment over a range of hillslope profiles and rainfall intensities. SIBERIA is also able to match the hillslope profile of the experimental catchments. The results of the study provide confidence in the ability of SIBERIA to predict temporal sediment output. The experimental and modelling data also demonstrate that, even with all geomorphic and hydrological variables being known and/or controlled, there is still a need for long‐term stream gauging to obtain reliable assessments of field catchment hydrology and sediment transport. Copyright © 2005 John Wiley & Sons, Ltd.     

Gully catchments as a sediment sink,not just a source: Results from a long‐term (~12 500 year) sediment budget

Sediment delivery from hillslopes to trunk streams represents a significant pathway of mass transfer in the landscape, with a large fraction facilitated by gully systems. The internal gully geomorphic dynamics represent a considerable gap in many landscape and empirical erosion models, therefore a better understanding of these processes over longer timescales (10–10⁴ years) is needed. This study analyses the sediment mass balance and storage dynamics within a headwater gully catchment in central Europe over the last ~12 500 years. Human induced erosion resulted in hillslope erosion rates ~2.3 times higher than under naturally de‐vegetated conditions (during the Younger Dryas), however the total sediment inputs to the gully system (and therefore gully aggradation), were similar. Net gully storage has consistently increased to become the second largest term in the sediment budget after hillslope erosion (storage is ~45% and ~73% of inputs during two separate erosion and aggradation cycles). In terms of the depletion of gully sediment storage, the sediment mass balance shows that export beyond the gully fan was not significant until the last ~500 years, due to reduced gully fan accommodation space. The significance of storage effects on the gully sediment mass balance, particularly the export terms, means that it would be difficult to determine the influences of human impact and/or climatic changes from floodplain or lake sedimentary archives alone and that the sediment budgets of the headwater catchments from which they drain are more likely to provide these mechanistic links. Copyright © 2015 John Wiley & Sons, Ltd.     

(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.     

Spatial patterns of sediment delivery to valley floors: sensitivity to sediment transport capacity and hillslope hydrology relations

There is considerable interest in large‐scale spatial patterns of sediment transport in catchments, and this topic is often approached using terrain‐based modelling. In such models topography influences the discharge of overland flow and its sediment transport capacity. The sediment transport capacity of overland flow is commonly expressed as a power function of slope and discharge (i.e. q_s=k₁q^βS^γ). The relationship between discharge and contributing area can also be expressed as a power function. Several reviews reveal a limited range of values for the two exponents β and γ. In this paper we examine the sensitivity of catchment‐scale patterns of sediment delivery to valley floors to a range of sediment transport capacity and hillslope hydrology parameterizations, using two catchments on the southern tablelands of New South Wales. The results indicate that, over the limited range of β and γ identified within the literature, sediment deliveries to valley floors across the two catchments are similar for all but one of five sediment transport capacity relationships. The patterns are dominated by the trend in slope through each catchment. The sensitivity to hillslope hydrology of predicted sediment delivery patterns is strong in the catchment with systematic variation in unit hillslope area, and weak in the catchment for which there are no systematic trends in unit hillslope area. We believe there is less experimental evidence to restrict choice of hillslope hydrology parameters than there is for sediment transport capacity. Copyright © 2001 John Wiley & Sons, Ltd.     

Scale variation of post‐glacial sediment yield in Chilliwack Valley,British Columbia

The Holocene volumetric sediment budget is estimated for coarse textured sediments (sand and gravel) in a large, formerly glaciated valley in southwest British Columbia. Erosion is estimated by compiling volumetric loss estimated in digital elevation models (DEMs) of gullied topography and by applying a non‐linear diffusion model on planar, undissected hillslopes. Estimates of steepland yield are based on estimates of post‐glacial deposition volumes in fans, cones and deltas at the outlets of low‐order tributary catchments. Erosion of post‐glacial fans and tributary valley fills is estimated by reconstructing formerly continuous surfaces. Results are classed by catchment order and compared across scales of contributing area, revealing declining specific sediment yield (in m³ km^?2 a^?1) with catchment area for the smaller tributaries (<10 km²) and increasing specific sediment yield for larger tributaries and Chilliwack Valley itself. Approximately 60% of mobilized sediment is redeposited in first‐ to third‐order catchments, with lesser proportions stored at the outlets of higher order catchments. A simple network routing model emphasizes the significant sediment flux contributions from colluvium, drift blankets and gullies in steeper terrain. As this material is deposited at junctions within the lower drainage network, an increasing proportion of material is derived from remnant valley fills and para‐glacial fans in the major valleys. Yield from lower‐order, steepland catchments tends to remain in storage, indefinitely sequestered on footslopes. These observations have implications for modelling the post‐glacial sediment balance amongst catchments of varying size. After 10⁴ years, the system remains in disequilibrium. The critical linkage lies between low‐order, hillslope catchments (相似文献   

Pathways of runoff and sediment transfer in small agricultural catchments

Simultaneous field monitoring of runoff and suspended sediment loads from a 30 ha, artificially‐drained, mixed‐agricultural catchment in Herefordshire, UK indicates field drains are the dominant pathway for the transfer of runoff and sediment to the stream. Surface runoff pathways draining 6·2% of the catchment area transported around 1% of the catchment sediment load, while subsurface runoff in field drains draining 26·5% of the catchment transported around 24% of the sediment load. The explanations offered here for the dominance of drainflow—the spatial limitation of surface runoff generation and low hillslope‐stream connectivity of surface runoff compared with subsurface runoff—are also likely to apply to other artificially‐drained lowland agricultural catchments in the UK. These catchments are usually on poorly‐drained soils, and land management can have a considerable effect on the operation of runoff pathways and the transfer of sediment from hillslope to stream. As a result, subsurface inputs may also dominate sediment transfers in other underdrained catchments. The focus on sediment and pollutant losses via surface runoff pathways means that pollution inputs from subsurface, preferential pathways have been unfairly neglected, and it may be more important to focus on subsurface sediment and sediment‐associated pollution inputs for mitigation rather than inputs from surface pathways. Copyright © 2009 John Wiley & Sons, Ltd.     

Changes to sediment sources following wildfire in a forested upland catchment,southeastern Australia

Few investigations link post‐fire changes to sediment sources and erosion processes with sediment yield response at the catchment scale. This linkage is essential if downstream impacts on sediment transport after fire are to be understood in the context of fire effects across different forest environments. In this study, we quantify changing source contributions to fine sediment (<63 µm) exported from a eucalypt forest catchment (136 ha) burnt by wildfire. The study catchment is one of a pair of research catchments located in the East Kiewa River valley in southeastern Australia that have been the subject of a research program investigating wildfire effects on runoff, erosion, and catchment sediment/nutrient exports. This previous research provided the opportunity to couple insights gained from a range of measurement techniques with the application of fallout radionuclides ¹³⁷Cs and ²¹⁰Pb_ex to trace sediment sources. It was found that hillslope surface erosion dominated exports throughout the 3·5‐year post‐fire measurement period. During this time there was a pronounced decline in the proportional surface contribution from close to 100% in the first six months to 58% in the fourth year after fire. Over the study period, hillslope surface sources accounted for 93% of the fine sediment yield from the burnt catchment. The largest decline in the hillslope contribution occurred between the first and second years after fire, which corresponded with the previously reported large decline in sediment yield, breakdown of water repellency in burnt soils, substantial reduction in hillslope erodibility, and rapid surface vegetation recovery. Coupling the information on sediment sources with hillslope process measurements indicated that only a small proportion of slopes contributed sediment to the catchment outlet, with material derived from near‐channel areas dominating the post‐fire catchment sediment yield response. Copyright © 2011 John Wiley & Sons, Ltd.     

Using 137Cs measurements to establish catchment sediment budgets and explore scale effects

Growing awareness of the wider environmental significance of fine sediment transport by rivers and associated sediment problems linked to sediment–water quality interactions, nutrient and contaminant transfer, and the degradation of aquatic habitats has resulted in the need for an improved understanding of the mobilization and transfer of sediment in catchments to support the development of effective sediment management strategies. The sediment budget provides a key integrating concept for assembling information on the internal functioning of a catchment in terms of its sediment dynamics by providing information on the mobilization, transfer, storage and output of sediment. One key feature of a catchment sediment budget is the relationship between the sediment yield at the catchment outlet and rates of sediment mobilization and transfer within the catchment, which is commonly represented by the sediment delivery ratio. To date, most attempts to derive estimates of this ratio have been based on a comparison of the measured sediment yield from a catchment with an estimate of the erosion occurring within the catchment, derived from an erosion prediction procedure, such as the Universal Soil Loss Equation (USLE) or its revised version, RUSLE. There is a need to obtain more direct and spatially distributed evidence of the erosion rates occurring within a catchment and to characterize the links between sediment mobilization, transfer, storage and output more explicitly. In this context, fallout radionuclides have proved particularly useful as sediment tracers. This paper reports the results of a study aimed at exploring the use of caesium‐137 (¹³⁷Cs) measurements to establish sediment budgets for three catchments of different sizes and contrasting land use located in Calabria, southern Italy. Long‐term measurements of sediment output were available for the catchments, and, by using the estimates of gross and net rates of soil loss within the catchments provided by ¹³⁷Cs measurements, it was possible to establish the key components of the sediment budget for each catchment. By documenting the sediment budgets of three catchments of different sizes, the study provides a basis for exploring the effects of scale on catchment sediment budgets and, in particular, the increasing importance of catchment storage as the size of the catchment increases. The results of this study demonstrate a reduction in the sediment delivery ratio from 98 to 2% as catchment area increases from 1·47 ha to 31·2 km². Copyright © 2010 John Wiley & Sons, Ltd.     

Optimization strategies for sediment reduction practices on roads in steep,forested terrain

Many forested steeplands in the western United States display a legacy of disturbances due to timber harvest, mining or wildfires, for example. Such disturbances have caused accelerated hillslope erosion, leading to increased sedimentation in fish‐bearing streams. Several restoration techniques have been implemented to address these problems in mountain catchments, many of which involve the removal of abandoned roads and re‐establishing drainage networks across road prisms. With limited restoration funds to be applied across large catchments, land managers are faced with deciding which areas and problems should be treated first, and by which technique, in order to design the most effective and cost‐effective sediment reduction strategy. Currently most restoration is conducted on a site‐specific scale according to uniform treatment policies. To create catchment‐scale policies for restoration, we developed two optimization models – dynamic programming and genetic algorithms – to determine the most cost‐effective treatment level for roads and stream crossings in a pilot study basin with approximately 700 road segments and crossings. These models considered the trade‐offs between the cost and effectiveness of different restoration strategies to minimize the predicted erosion from all forest roads within a catchment, while meeting a specified budget constraint. The optimal sediment reduction strategies developed by these models performed much better than two strategies of uniform erosion control which are commonly applied to road erosion problems by land managers, with sediment savings increased by an additional 48 to 80 per cent. These optimization models can be used to formulate the most cost‐effective restoration policy for sediment reduction on a catchment scale. Thus, cost savings can be applied to further restoration work within the catchment. Nevertheless, the models are based on erosion rates measured on past restoration sites, and need to be updated as additional monitoring studies evaluate long‐term basin response to erosion control treatments. Copyright © 2006 John Wiley & Sons, Ltd.     

Vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain area

Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short‐term (1–15 years) sediment deposition and gully stabilization. In well‐vegetated gully systems ( ≥ 30% of ground vegetation cover), 0.035 m³ m^–1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short‐term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd.     

Delayed delivery from the sediment factory: modeling the impact of catchment response time to tectonics on sediment flux and fluvio‐deltaic stratigraphy

The sediment flux from a catchment is driven by tectonics and climate but is moderated by the geomorphic response of the landscape system to changes in these two boundary conditions. Consequently, catchment response time and the non‐linear behavior of landscapes in response to boundary condition change control the downstream propagation of climatic or tectonic perturbations from catchments to neighboring basins. In order to investigate the impact of catchment response time on sediment flux, we integrated a spatially‐lumped numerical model PaCMod, with new routines simulating the evolution of landscape morphology and erosion rates under tectonic and climatic forcing. We subsequently applied the model to reconstruct the sediment flux from a tectonically perturbed catchment in central Italy. Finally, we coupled our model to DeltaSim, a process‐response model simulating fluvio‐deltaic stratigraphy, and investigated the impact of catchment response time on stratigraphy, using both synthetic scenarios and a real world system (Fucino Basin, central Italy). Our results demonstrate that the differential response of geomorphic elements to tectonic and climatic changes induces a complex sediment flux signal, and produces characteristic stratigraphic architectures and shoreline trajectories. Copyright © 2014 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.     

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.     

Proglacial sediment dynamics from daily to seasonal scales in a glaciated Alpine catchment (Bossons glacier,Mont Blanc massif,France)

The sediment yields of Alpine catchments are commonly determined from streamload measurements made some distance downstream from glaciers. However, this approach indiscriminately integrates erosion processes occurring in both the glacial and proglacial areas. A specific method is required to ascertain the respective inputs from (i) subglacial and supraglacial sediments, (ii) proglacial hillslopes and (iii) proglacial alluvial areas or sandurs. This issue is addressed here by combining high‐resolution monitoring (2 min) of suspended sediment concentrations at different locations within a catchment with discharge gauging and precipitation data. This methodological framework is applied to two proglacial streams draining the Bossons glacier (Mont Blanc massif, France): the Bossons and Crosette streams. For the Bossons stream, discharge and suspended load data were acquired from June to October 2013 at 1.15 and 1.5 km from the glacial terminus, respectively upstream and downstream from a small valley sandur. These hydro‐sedimentary data are compared with the Crosette stream dataset acquired at the outlet of the Bossons glacier subglacial drainage system. A fourfold analysis focusing on seasonal changes in streamload and discharge, multilinear regression modelling, evaluation of the sandur flux balance and probabilistic uncertainty assessment is used to determine the catchment sediment budget and to explain the proglacial sediment dynamics. The seasonal fluctuation of the sediment signal observed is related to the gradual closing of the subglacial drainage network and to the role of the proglacial area in the sediment cascade: the proglacial hillslopes appear to be disconnected from the main channel and the valley sandur acts as a hydrodynamic sediment buffer both daily and seasonally. Our findings show that an understanding of proglacial sediment dynamics can help in evaluating paraglacial adjustment and subglacial erosion processes. Copyright © 2017 John Wiley & Sons, Ltd.     

Distributed empirical algorithms to estimate catchment scale sediment connectivity and yield in a subtropical region

The intensity of soil loss and sediment delivery, representing hydrologic and geomorphic processes within a catchment, accelerates with rapid changes in land cover and rainfall events. An underlying component of sustainable management of water resources is an understanding of spatial and temporal variability and the adverse influences of regional parameters involved in generating sediment following widespread changes in land cover. A calibrated algorithm of soil loss coupled with a sediment delivery ratio (SDR) was applied in raster data layers to improve the capability of a combined model to estimate annual variability in sediment yields related to changes in vegetation cover identified by analyses of SPOT imagery. Four catchments in Kangaroo River State forest were assessed for annual changes in sediment yields. Two catchments were selectively logged in 2007, while the two other sites remained undisturbed. Results of SDR estimates indicated that only a small proportion of total eroded sediment from hillslopes is transported to catchment outlets. Larger SDR values were estimated in regions close to catchment outlets, and the SDR reduced sharply on hillslopes further than 200–300 m from these areas. Estimated sediment yield increased by up to 30% two years after land cover change (logging) in 2009 when more storm events were recorded, despite the moderate density of vegetation cover in 2009 having almost recovered to its initial pre‐logging (2005) condition. Rainfall had the most significant influence on streamflow and sediment delivery in all catchments, with steeply sloping areas contributing large amounts of sediment during moderate and high rainfall years in 2007 and 2009. It is concluded that the current scenario of single‐tree selection logging utilized in the study area is an acceptable and environmentally sound land management strategy for preservation of soil and water resources. Copyright © 2013 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.     

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.     

Storage,properties and seasonal variations in fine‐grained bed sediment within the main channel and headwaters of the River Sanginjoki,Finland

Lowland catchments in Finland are intensively managed, promoting erosion and sedimentation that negatively affects aquatic environments. This study quantified fine‐grained bed sediment in the main channel and upstream headwaters of the River Sanginjoki (399.93 km²) catchment, Northern Finland, using remobilization sediment sampling during the ice‐free period (May 2010–December 2011). Average bed sediment storage in river was 1332 g m^?2. Storage and seasonal variations were greater in small headwater areas (total bed sediment storage mean 1527 g m^?2, range 122–6700 g m^?2 at individual sites; storage of organic sediment: mean 414 g m^?2, range 27–3159 g m^?2) than in the main channel (total bed sediment storage: mean 1137 g m^?2, range 61–4945 g m^?2); storage of organic sediment: mean 329 g m^?2, range 13–1938 g m^?2). Average reach‐specific bed sediment storage increased from downstream to upstream tributaries. In main channel reaches, mean specific storage was 8.73 t km^?1, and mean specific storage of organic sediment 2.45 t km^?1, whereas in tributaries, it was 126.94 and 34.05 t km^?1, respectively. Total fine‐grained bed sediment storage averaged 563 t in the main channel and 6831 t in the catchment. The proportion of mean organic matter at individual sites was 15–47% and organic carbon 4–455 g C m^?2, with both being highest in small headwater tributaries. Main channel bed sediment storage comprised 52% of mean annual suspended sediment flux and stored organic carbon comprised 7% of mean annual total organic carbon load. This indicates the importance of small headwater brooks for temporary within‐catchment storage of bed sediment and organic carbon and the significance of fine‐grained sediment stored in channels for the suspended sediment budget of boreal lowland rivers. Copyright © 2013 John Wiley & Sons, Ltd.     

Debris-flow-dominated sediment transport through a channel network after wildfire

Field studies that investigate sediment transport between debris-flow-producing headwaters and rivers are uncommon, particularly in forested settings, where debris flows are infrequent and opportunities for collecting data are limited. This study quantifies the volume and composition of sediment deposited in the arterial channel network of a 14-km² catchment (Washington Creek) that connects small, burned and debris-flow-producing headwaters (<1 km²) with the Ovens River in SE Australia. We construct a sediment budget by combining new data on deposition with a sediment delivery model for post-fire debris flows. Data on deposits were plotted alongside the slope–area curve to examine links between processes, catchment morphometry and geomorphic process domains. The results show that large deposits are concentrated in the proximity of three major channel junctions, which correspond to breaks in channel slope. Hyperconcentrated flows are more prominent towards the catchment outlet, where the slope–area curve indicates a transition from debris flow to fluvial domains. This shift corresponds to a change in efficiency of the flow, determined from the ratio of median grain size to channel slope. Our sediment budget suggests a total sediment efflux from Washington Creek catchment of 61 × 10³ m³. There are similar contributions from hillslopes (43 ± 14 × 10³ m³), first to third stream order channel (35 ± 12 × 10³ m³) and the arterial fourth to fifth stream order channel (31 ± 17 × 10³ m³) to the total volume of erosion. Deposition (39 ± 17 × 10³ m³) within the arterial channel was higher than erosion (31 ± 17 × 10³ m³), which means a net sediment gain of about 8 × 10³ m³ in the arterial channel. The ratio of total deposition to total erosion was 0.44. For fines <63 μm, this ratio was much smaller (0.11), which means that fines are preferentially exported. This has important implications for suspended sediment and water quality in downstream rivers. © 2019 John Wiley & Sons, Ltd.     

Lithological controls on hillslope sediment supply: insights from landslide activity and grain size distributions

The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically‐active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of ~2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop‐scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long‐term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. Copyright © 2017 John Wiley & Sons, Ltd.