Valley Length Research Articles

Spatial patterns of valley network erosion on early Mars

Fluvial valley networks are a key record of the geomorphic effects of past liquid water on the surface of Mars. Most valley networks formed early in Mars history (>3.5 Ga) during a period of increased surface water availability, and these landforms may preserve information on the nature and spatial heterogeneity of the ancient martian hydroclimate. Here we present work to constrain patterns of valley network geometry (length, depth, and volume), and assess how these factors are related to topography and landscape position. We find that valley depth is most strongly controlled by regional slope and landscape relief, with deeper valleys on steeper/higher relief terrains, likely driven by a slope control on the rate of fluvial erosion. In contrast, total valley length and volume are most controlled by slope orientation, with larger values on north-draining slopes, which we suggest is related to more efficient fluvial integration (i.e., inter-connection of valleys) on such slopes. At lower elevations and towards terminal basins (northern plains and Hellas), valley depth increases, while total valley length and volume decrease, consistent with the geometry expected as a branching valley system converges downstream into fewer, larger valleys. Finally, we show that patterns of total valley length and eroded volume peak about a previously proposed paleo-latitude band on a pre-Tharsis-driven true polar wander Mars. Valley depth increases from paleo-south to paleo-north in this pre-true polar wander framework, consistent with valley network development in a paleo-north direction. This is potentially consistent with syn/pre-Tharsis growth and true polar wander valley network incision; however, this signal is not unique and may be amplified by patterns of post-valley network incision resurfacing.

Effects of process‐based floodplain restoration on aquatic macroinvertebrate production and community structure

AbstractRecent stream restoration approaches, such as Stage 0 restoration, aim to restore natural processes to regain lost ecosystem functions, but project implementation can also represent a reach‐scale disturbance. Assumed outcomes of these restoration actions, like greater biological productivity, are rarely evaluated. In this study, we examined the short‐term effects of Stage 0 floodplain restoration on the secondary production of aquatic macroinvertebrate communities in the South Fork McKenzie River, Oregon, 1–2 years following project implementation. We seasonally sampled macroinvertebrates from benthic and submerged wood surfaces in the restored reach, and two unrestored reference reaches located upstream, to estimate annual secondary production. Macroinvertebrate production estimates were 3× lower on a per‐meter‐squared basis in the restored reach than in the upstream unrestored reference reaches (9764 vs. 29,636 mg DM/m2/yr). However, because there was 4.5‐times greater wetted area available in the restored reach, overall macroinvertebrate production per unit of valley length was 3.4× higher in the restored reach than in unrestored reference reaches (2744 vs. 802 kg DM/km). Additionally, the mosaic of aquatic habitats created via restoration (main‐channel, side‐channel, and wetted forest habitats) supported a diversity of macroinvertebrate assemblages both within and among reaches. Our findings suggest Stage 0 project implementation, which can include dewatering and filling incised channels, may reduce aquatic macroinvertebrate production on a per‐unit‐area basis for at least 1 or 2 years following restoration. However, this short‐term disturbance effect may be offset by channel aggradation and widening, which can provide a more wetted area for macroinvertebrate production and may support greater macroinvertebrate community diversity. Future studies are needed to examine the longer term (2–10 years) aquatic macroinvertebrate response to Stage 0 restoration, and the impacts of shifting resource availability on stream fishes.

Validation of Computational Fluid Dynamics Approach of Lateral Velocity Profile Due to Curvature Effect on Floodplain Levee of Two-stage Meandering Channel

Rivers play an integral part in the sustenance of life on earth. The river or natural channel’s sinuous nature causes erosion of its outer wall and silt deposition on its inner wall. These changes in the terrain make it vital to design the meandering compound channel. Levees, both straight and meandering, can be constructed on both sides of the channel to guard the surrounding lands. For doubly meandering levee alignment, the momentum transfer between the main channel and the adjoining floodplains affects the velocity distribution across the channel cross-section. So, hydraulic engineers must investigate this complex flow phenomenon in the case of a doubly meandering compound channel. This study investigates the flow in meandering compound channels using numerical and physical modelling, both of which are important in understanding non-uniform flow and its behaviour. As a result, a research is presented on the sharing of velocity over the cross section of the main channel and the floodplains of meandering compound channels. The geometry of meandering compound channels, having straight as well as sinuous floodplain levees, is chosen for this study. Unlike the experimental models, numerical hydraulic models are remarkably economical. So, in this research, the numerical hydraulic model is adopted to determine the different flow characteristics of compound meandering channels. In this paper, a complete three-dimensional and two-phase Computational Fluid Dynamics (CFD) model of the meandering compound channels is analyzed making use of the RNG K-ɛ turbulence model as well as Volume of Fluid (VOF) methodology. A comparison study between numerical results and experimental results are represented, considering the two different experimental data of compound meandering channel having the main channel meandered with sinuosity (ratio of channel length to the down valley length) of 1.37 and were flanked by straight floodplains as well as meandering floodplains having sinuosity 1.06 on both sides. By error analysis, it is observed that the numerical results agree with that of the experimental ones.

Discordance analysis on a high-resolution valley network map of Mars: Assessing the effects of scale on the conformity of valley orientation and surface slope direction

Fluvial valleys incised into planetary surfaces display morphologies, geometries and orientations that can be used to understand their controlling processes. Comparisons between valley orientations and topographic surface slope direction have been used to understand how Martian surfaces have evolved (Luo and Stepinski, 2012; Black et al., 2017); however, new insights from terrestrial studies have revealed that the slope needs to be defined on a scale commensurate with the length of valley (Lipp and Roberts, 2020). We propose and test a new map-based framework for interpreting the difference between Martian valley orientation and surface slope direction (discordance) at varying spatial scales. Valleys and inverted channels were manually mapped in a latitudinal strip from pole to pole between 20°E–20°W using High/Super Resolution Stereo Colour Imager images (15 to 25 m per pixel). The orientation of incisional valleys, associated with fluvial activity, were compared with topographic slope direction at varying scales (463 m, 1 km, 10 km and 50 km). High-resolution mapping resulted in ~1.5 times the density (0.02 km/km2 on average) of the previous valley map (Hynek et al., 2010), which raises the possibility that water volumes necessary to carve valleys were greater than previously thought. The distribution of valleys is similar to previous valley maps, however there are areas where valleys were identified that have previously remained undetected in low resolution images. The scale over which one compares valley orientation to surface slope direction has a clear effect on the apparent conformity between Martian valley orientation and topographic slope direction, with smaller valleys conforming more closely with smaller scale topography. To account for scale we perform discordance analysis with the spatial scale of surface slope direction varying based on valley length. When scale is accounted for, there is a greater conformity between valley orientation and surface slope direction, however only ~38% of valleys display conformity, indicating other sources of high discordance. We find that the source of the high values of discordance are likely a result of a combination of valley immaturity, attesting to the arid nature of the Late Noachian – Early Hesperian climate, but also the palaeolake outburst and, possible, subglacial origin of some valley networks. Considering a large proportion of valleys do not display conformity with topography, we suggest that a discordance analysis of the kind reported here is an important preliminary to any hydrodynamic analysis that relies on topographic information.

Tectonic Control of the Nanggulan Formation Based on Morphometric Analysis in Kulon Progo, Indonesia

DOI:10.17014/ijog.9.2.147-157Outcrop of Nanggulan Formation, surrounded by Old Andesite Formation (OAF) in the eastern part of Kulon Progo Dome, is very limited. Tectonic control is interpreted as a contributing factor. Tectonic activity can be shown by a morphometric aspect. The research purpose was to calculate the valley floor - valley height ratio, stream gradient index, and drainage density of Nanggulan and Old Andesite Formations. The method used is field survey and Shuttle Radar Topography Mission analysis. The field survey focused on Clumprit, Klepu, and Kalisonggo Rivers. The total number of valley segments for the Nanggulan Formation is 223 with the valley length of 4.62 km, while OAF is 101 with a valley length of 3.55 km. SRTM analysis showed that the valley segment in OAF was 55, and valley length was 1.48 km. The valley floor - valley height ratio measured in the Nanggulan Formation is ten valleys and OAF is eight valleys. In Nanggulan Formation, the valley floor - valley height ratio value is from 1.00 to 5.46 (low uplift), whilst in OAF, the results vary: as 1.35 to 4.58 (low uplift), 0.59 (medium uplift), and 0.43 (high uplift). The stream gradient index value of the Nanggulan Formation is 460.47 (medium tectonic), while OAF is 723.84 (high tectonic). The drainage density value of the Nanggulan Formation is 10.35 km/km2 (very smooth landscape texture) and OAF is 10.35 km/km2 (somewhat smooth landscape texture). Morphometry proves that Nanggulan Formation tectonic activity is more active, causing the Nanggulan Formation to be exposed to the surface.

Deformation characterization of oil and gas pipeline by ACM technique based on SSA-BP neural network model

Accurate and quantitative characterization of deformation in oil and gas pipelines is essential. This paper proposed a novel ACM (alternating current magnetization) based technique to detect the deformation of oil and gas pipelines. Numerical simulations and experiments reveal the relationships between the deformation factors (height, length, tilt angle) and the detected waveform signals. Meanwhile, the peak value, integral area, first-order differential peak and valley value, peak and valley length of the waveform signals are selected as the features. In addition, a BP neural network model optimized by SSA (sparrow search algorithm) was introduced to identify the deformation of the pipelines. The results show that the waveform signals corresponding to the deformation due to external stress and corrosion are distributed in the mountain peak and basin shape, respectively. With features as input, the proposed SSA-BPalgorithm can efficiently characterize the deformation within the mean relative error of 10%.

The importance of lake breach floods for valley incision on early Mars.

The surface environment of early Mars had an active hydrologic cycle, including flowing liquid water that carved river valleys1-3 and filled lake basins4-6. Over 200 of these lake basins filled with sufficient water to breach the confining topography4,6, causing catastrophic flooding and incision of outlet canyons7-10. Much past work has recognized the local importance of lake breach floods on Mars for rapidly incising large valleys7-12; however, on a global scale, valley systems have often been interpreted as recording more persistent fluvial erosion linked to a distributed Martian hydrologic cycle1-3,13-16. Here, we demonstrate the global importance of lake breach flooding, and find that it was responsible for eroding at least 24% of the volume of incised valleys on early Mars, despite representing only approximately 3% of total valley length. We conclude that lake breach floods were a major geomorphic process responsible for valley incision on early Mars, which in turn influenced the topographic form of many Martian valley systems and the broader landscape evolution of the cratered highlands. Our results indicate that the importance of lake breach floods should be considered when reconstructing the formative conditions for Martian valley systems.

Semi-automatic terrain slope unit division method based on human–computer interaction

A slope is the fundamental element of a landslide. Conducting a high-precision geohazard survey and a slope-based evaluation is important for geohazard prevention and mitigation and useful for governments in terms of improving the precision and the efficiency of geohazard management. The efficient and accurate division of slope units is the precondition of improving the accuracy and automation of a slope-based geohazard evaluation. This study introduces a semi-automatic slope unit division method that mainly includes automatic division using the geographic information system technology, followed by the revision and refinement of results by experienced professionals. Three major steps are involved in this method: 1) searching and eliminating the disturbing effect areas that could result from the disturbance of the micro-landform during the automatic division process; 2) determining the slope unit density by disclosing the relationship between the valley length and the threshold by fitting the trend with the power function; and 3) experienced professionals would perform the revision and refinement of the results generated from the previous steps to ensure that the slope unit division results meet the requirements of the slope-based evaluation. The field verification indicates that the slope units generated by the presented method are sufficient to support a slope-based evaluation on a scale of 1:10,000. The method can save considerable time and effort, which could, otherwise, be consumed during the conventional slope unit division process.

Effects of wind and rain on the motion of the high-voltage conductor in a simplified valley terrain

Due to the funneling effects of valley terrain, intensified wind and rain may cause conductor galloping, line breaking, insulator flashover and even tower collapses. Researchers are mainly concerned about the distribution of wind velocities within valley terrains, and very few of them studied the characteristics of wind-driven rain and its effects the motion of the suspended high-voltage conductor. The objective of this paper is to investigate the characteristics of wind and rain in a simplified valley and their effects on the motion of the high-voltage conductor. The distribution of wind velocities in the simplified valley is computed by computational fluid dynamics method (CFD), of which the results demonstrate that the valley length has a stronger effect on wind velocity compared to flat terrain, and the maximum speed-up amplitude of wind velocity reaches 67% which apparently higher than 10% specified in Codes of GB 50545-2010. Meanwhile, the velocities and the trajectories of raindrops are calculated with finite difference method, and the results show that raindrops’ velocities in the valley terrain increase rapidly than that of in the flat terrain. Then an analytical model based on the finite element method is proposed to study the effects of wind and rain on the motion of the high-voltage conductor suspended over the simplified valley, and the results show that the maximum percentage of vibration amplitude by rain-wind loads relative to wind loads can reach to 8% (in-plane) and 19% (out-of-plane). Therefore, wind and rain in the valley terrain obviously different from that of in the flat terrain and should be give more attention in the design and operation of transmission lines.

Aerial and terrestrial-based monitoring of channel erosion, headcutting, and sinuosity.

Headcuts are points of accelerated channel erosion that frequently have ecological consequences. A particularly large and dynamic headcut in southwest Wyoming has affected natural and anthropogenic resources for decades. To better understand and address this issue, we undertook a review of the headcut's upstream retreat, followed by photogrammetric monitoring of the present condition for erosion monitoring. Aerial photography shows the Bitter Creek headcut retreated > 200m upstream in 68years (1948-2016) at ~ 1.4myear-1. Following installation of a concrete slab structure inthe mid-1970s, headcut retreat slowed to ~ 0.5myear-1. Channel sinuosity downstream of the headcut is greater than upstream, which we attribute to the presence of the headcut, given that there are no major changes in valley geometry, geology, or soils through this reach. Both aerial and terrestrial-based image platforms were used to collect stereo imagery and create 3D photogrammetric models of the headcut in 2016. From these two models, we measured soil loss downstream of the headcut at ~ 126m3m-1 valley length. Since 1954, soil loss within the channel has been ~ 98m3year-1 or ~871tha-1year-1since then. Models created from aerial- and terrestrial-based images differed in volumetric estimates by 2%, indicating that either method could be used for this type of monitoring. The ground-based imagery model showed more detail, especially on vertical and overhanging surfaces, while the aerial imagery model produced a more realistic orthomosaic and efficiently covered a larger area. Ground-based image acquisition took longer and was more costly per unit area, but is an efficient method for small project areas, or areas where aerial imagery cannot be safely or practically acquired. Historical imagery and photogrammetric modeling proved very useful in elucidating stream dynamics associated with this large, dynamic headcut.

The characteristics of valley phase as predictor of the forthcoming solar cycle

Is Solar Cycle 24 anomalous? How do we predict the main features of a forthcoming cycle? In order to reply such questions, this work partitions quantitatively each cycle into valley, ascend, peak, and descend phases, statistically investigate the correlations between valley phase and the forthcoming cycle. We find that the preceding valley phase may dominate and can be predictor of the forthcoming cycle: (1) The growth rate in ascend phase strongly negatively correlates to valley length and strongly positively correlates to cycle maximum. (2) The cycle maximum strongly negatively correlates to valley length, and strongly positively correlates to cycle minimum. (3) The cycle period strongly negatively correlates to the valley variation. Based on these correlations, we conclude that the solar cycle 24 is a relatively weak and long cycle which is obviously weaker than Cycle 23. The similarity analysis also presents the similar result. The Cycle 25 is also inferred possibly to be a weak cycle. These results can help us understanding the physical processes of solar cycles.

The loss of large wood affects rocky mountain trout populations

AbstractWestern U.S. rivers are currently influenced by legacy effects of reduced large wood (LW) loading and retention that has substantially reduced in‐stream habitat complexity. Large wood is typically associated with streams in undisturbed old‐growth forest and in the correct geomorphic context can drastically alter stream and valley habitat complexity. Streams withLWare typically multichannel and depositional, while streams lackingLW, due to relatively recent wildfire or logging (<200 years ago), are usually single channelled and erosional. We compared population biomass and individual growth rates of Brook TroutSalvelinus fontinalisin streams across a gradient of wood volumes. At both the square metre and valley length scales, standing stock biomass of aquatic invertebrates was the best predictor of trout biomass. However, at the valley scale, the number of pools was important in predicting trout biomass in combination with standing stock biomass of aquatic invertebrates. Individual growth rates of age‐1 Brook Trout were negatively affected by increasing density; however, growth rates for the largest and smallest individuals at each site were unaffected by density. Our results suggest the pool habitat created byLWacts synergistically with prey availability to dramatically increase trout populations. However, in streams lacking LW, negative effects of detrimental land use practices have persisted >100 years, suggesting that recovering lost animal production in mountain stream networks will only occur at decadal to century time scales.

Predictive Dynamics of Channel Pattern Changing Trends at Arial Khan River (1977-2018), Bangladesh

Arial Khan River is right bank distributary of Ganges-Padma River systems flowing southwest region of Bangladesh. It is morphologically very dynamic meandering river: where the delta-building process is more active than other distributaries of Ganges-Brahmaputra-Meghna (GBM) River basin. This study analyzes, morphological variables- channel length, valley length, channel area and channel patterns of Arial Khan River. A major portion of this river divided into 8 reaches from starting point Faridpur to outlet point Barisal district in order to measure channel pattern changing trends. For the proper accomplishment of the findings section of this research, time-series satellite images (Landsat MMS, Landsat TM, Landsat ETM+ and OLI) of the year 1977 to 2018 has been taken for delineation of the morphological parameters using GIS and RS techniques. In this research, sinuosity ratio index technique has been applied to analyze the morphological parameter- channel pattern and its changing trends. From the satellite images analysis results over time span, it is observed that significant morphological changes have been occurred in the river length, valley length, river area and its channel patterns. Likewise, the hydro-morphological parameters of this river (e.g., discharge, flow velocity, the river depth, width and pattern) also significantly changed due to combined massive sediment deposition from Ganges-Padma and Brahmaputra-Jamuna River systems. These hydro-morphological changes increased flood hazard vulnerability, bank erosion and sand carpeting; which badly impacted on ecological diversity, agriculture system, rural settlements and transportation networks.

The thermally driven diurnal wind system of the Adige Valley in the Italian Alps

The Adige Valley is one of the major corridors connecting the Po Plain with the inner Alps. A series of permanent weather stations and one wind profiler provide regular monitoring of air temperature, atmospheric pressure, global solar radiation, wind speed and direction over the 140 km valley length and in the adjacent plain. Data from these stations are analyzed for a subset of days on which weather conditions favoured full development of diurnal valley winds in the period 2012–2014. The analysis highlights typical features in the alternating patterns of diurnal up‐valley winds and nocturnal down‐valley winds. In particular, the wind intensity depends linearly on the along‐valley pressure gradient, supporting the concept of a quasi‐steady balance between the pressure gradient and surface friction. Also, in agreement with previous investigations, the amplitude of the surface pressure cycle increases in the up‐valley direction, causing the reversal of the horizontal pressure gradient twice per day. In contrast, no appreciable along‐valley variation in the diurnal temperature range is found. The analysis of surface temperature and pressure measurements suggests that the larger pressure perturbations found far into the valley are caused by the increased depth of the atmospheric layer subject to heating and cooling. Local inhomogeneities in the valley cross‐section, in particular in the vicinity of a large basin, cause temperature and pressure perturbations that are strong enough to alter the typical cycle of down‐ and up‐valley winds. Similarly, local wind convergence over the major cities during the night is explained in terms of the urban heat island effect.

GDBC: A tool for generating global-scale distributed basin morphometry

In response to the vital role of geomorphological analysis in natural hazards study, geomorphology, distributed hydrology and other related disciplines, we present the first global basin morphometric product of 30 characteristics, 9 archived elementary including stream order, stream number, stream length, basin relief, basin length, basin perimeter, maximal flow length, down valley length and overland flow length, and 21 derivable from these elementary morphometric characteristics. Characteristics of basins discharging to every grid-cell of the global earth surface are generated at 30 arcsec resolution from the remotely sensed HydroSHEDS dataset. This product does not exist in previous literature because tree-structural grid-cells bring large computational redundancy to basin delineation and thus computing basin characteristics. To generate this product within a reasonable timeframe, we introduce in this paper an efficient framework to reduce the algorithm complexity to linear, O(N). We have presented a few geomorphologic findings using the generated product.

Interactions Between the Nighttime Valley-Wind System and a Developing Cold-Air Pool

The Weather Research and Forecast numerical model is used to characterize the influence of a thermally-driven down-valley flow on a developing cold-air pool in an idealized alpine valley decoupled from the atmosphere above. Results for a three-dimensional (3D) valley, which allows for the formation of a down-valley flow, and for a two-dimensional (2D) valley, where the formation of a down-valley flow is inhibited, are analyzed and compared. A key result is that advection leads to a net cooling in the 2D valley and to a warming in the 3D valley, once the down-valley flow is fully developed. This difference stems from the suppression of the slope-flow induced upward motions over the valley centre in the 3D valley. As a result, the downslope flows develop a cross-valley circulation within the cold-air pool, the growth of the cold-air pool is reduced and the valley atmosphere is generally warmer than in the 2D valley. A quasi-steady state is reached for which the divergence of the down-valley flow along the valley is balanced by the convergence of the downslope flows at the top of the cold-air pool, with no net contribution of subsiding motions far from the slope layer. More precisely, the inflow of air at the top of the cold-air pool is found to be driven by an interplay between the return flow from the plain region and subsidence over the plateaux. Finally, the mechanisms that control the structure of the cold-air pool and its evolution are found to be independent of the valley length as soon as the quasi-steady state is reached and the down-valley flow is fully developed.

Climatic variations and geomorphology of the Indus River valley, between Nimo and Batalik, Ladakh (NW Trans Himalayas) during Late Quaternary

The Indus River valley is tectonically unstable, exhibiting complex topography, landscape relief, and varied sedimentation. The major geomorphic landforms are alluvial fans, debris cones, fluvio-lacustrine deposits, scree, and talus cones. In the present work, a transect between Nimo and Batalik along the river was studied to consider the geomorphological landform evolution during the Quaternary based on the distribution of the sediments along the valley. Mass movements, catastrophic land sliding and tectonic activity transported material from steep slopes to valley bottoms which were responsible for forming lakes (preserved as thick piles of fine sediment), while the outburst floods redistributed sediment down valley. Three phases of lake formation are recorded in the 136 km stretch – ∼35,000–26,000 BP (Lamayuru palaeolake); 17,000–13,000 BP (Rizong palaeolake) occupying 35 km of the valley length, and 14,000–5000 BP (Khalsi–Saspol palaeolake) 55 km in length and having the highest lake levels. The lake formation is attributed to deglaciation after the Last Glacial maximum (LGM) and Holocene warming. Tectonic activity (seismites) are concentrated only at 10 and 6 ka.

Spatial and temporal variations in incised valley systems from the Durban continental shelf, KwaZulu-Natal, South Africa

Abstract The evolution of several incised valley systems from the KwaZulu-Natal shelf is compared over time. These represent the shelf extension of the collective Durban Harbour drainage system, and the Mgeni, Mhlanga, and Mdloti Rivers. Two main ages of incision are apparent; early Santonian (Cretaceous), and late Pleistocene/Holocene. The early valleys formed by tectonic controls, namely phases of higher frequency base level fall superimposed on lower frequency, higher order transgression. The results are complex networks of stacked compound valleys that have been exploited by some of the younger networks formed by glacio-eustatic fall prior to the last glacial maximum (LGM) of ~ 18 Ka BP. The valley fills have evolved from high energy basal fluvial deposits, low-energy central basin fines, mixed-energy estuarine mouth plug deposits, clay-rich flood deposits through capping sandy shoreface deposits. The earliest fills are dominated by central basin deposits and were underfilled as a result of low gradient and limited sediment supply. The more recent late Pleistocene/Holocene fills have significantly thicker fluvial deposits as a result of increased gradient and stream competence during the later stages of valley and shelf evolution. The youngest valleys show a situation of differential evolution along the valley length due to varying rates of sea level rise in the Holocene. Initial rapid sea level rise caused drowning and overstepping of the outer segment of the incised valley, whereas slower rates of sea level rise in the late Holocene caused shoreface ravinement of the inner-mid segments of the valley. This differential exposure to accommodation has resulted in a sedimentological partitioning between tide-dominated facies in the outer valley segment and river-dominated facies in the inner segment (cf. Cooper, 2001 ).

Exploring changes in the spatial distribution of stream baseflow generation during a seasonal recession

Relating watershed structure to streamflow generation is a primary focus of hydrology. However, comparisons of longitudinal variability in stream discharge with adjacent valley structure have been rare, resulting in poor understanding of the distribution of the hydrologic mechanisms that cause variability in streamflow generation along valleys. This study explores detailed surveys of stream base flow across a gauged, 23 km2 mountain watershed. Research objectives were (1) to relate spatial variability in base flow to fundamental elements of watershed structure, primarily topographic contributing area, and (2) to assess temporal changes in the spatial patterns of those relationships during a seasonal base flow recession. We analyzed spatiotemporal variability in base flow using (1) summer hydrographs at the study watershed outlet and 5 subwatershed outlets and (2) longitudinal series of discharge measurements every ∼100 m along the streams of the 3 largest subwatersheds (1200 to 2600 m in valley length), repeated 2 to 3 times during base flow recession. Reaches within valley segments of 300 to 1200 m in length tended to demonstrate similar streamflow generation characteristics. Locations of transitions between these segments were consistent throughout the recession, and tended to be collocated with abrupt longitudinal transitions in valley slope or hillslope‐riparian characteristics. Both within and among subwatersheds, correlation between the spatial distributions of streamflow and topographic contributing area decreased during the recession, suggesting a general decrease in the influence of topography on stream base flow contributions. As topographic controls on base flow evidently decreased, multiple aspects of subsurface structure were likely to have gained influence.

Quantification of alluvial sediment storage in contrasting environments: Methodology and error estimation

Abstract Floodplains are an important sediment sink in many temperate catchments during the Holocene, especially where anthropogenic land use had a dominant influence on the landscape. As such, the quantification of Holocene floodplain deposits plays an important role in the global interest in continent-ocean transfers of sediments. In this study the total Holocene floodplain deposition was quantified for three contrasting catchments in Belgium, characterized by a different fluvial architecture and Holocene deposits thickness. Several methods were used to delineate the floodplain, and combined with different amounts of field data in Monte Carlo type simulations. The results show that the method used to delineate the floodplains is responsible for the largest uncertainties on the results, while the number of used field data has less influence. Based on the results of this study, ca one cross-section each 30 km valley length, combined with at least 5 corings per cross-section, should yield a reliable quantification of catchment wide floodplain deposition. The results show that inter- and intra-catchment variability in floodplain deposition varies largely between the studied catchments. Based on the available data, spatial patterns of floodplain sediment storage can be explained by a combination of sediment delivery to the fluvial system and the sediment transport capacity of the fluvial system, which depends on floodplain slope and runoff discharge peaks.