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Drainage Network (drainage + network)
Selected AbstractsRiver spacing and drainage network growth in widening mountain rangesBASIN RESEARCH, Issue 3 2006Sébastien Castelltort ABSTRACT Drainage networks in linear mountain ranges always display a particular geometrical organisation whereby the spacing between the major drainage basins is on average equal to half the mountain width (distance from the mountain front to the main drainage divide), independent of climate and tectonics. This relationship is valid for mountains having different widths and is thus usually thought to be maintained by drainage reorganisation during mountain belt widening. However, such large-scale systematic drainage reorganisation has never been evidenced. In this paper, we suggest an alternative explanation, namely that the observed drainage basin relationships are an inherent property of dendritic river networks and that these relationships are established on the undissected, lowland margins outside mountain ranges and are progressively incorporated and quenched into uplifted topography during range widening. Thus, we suggest that the large-scale geometry of drainage networks in mountain ranges is mainly antecedent to erosion. We propose a model in which the large-scale drainage geometry is controlled mainly by the geometrical properties of the undissected surfaces (in particular, the ratio of the regional slope to the local slope related to roughness) over which rivers are flowing before uplift, and is therefore independent of climate and tectonics. [source] Network-scale dynamics of grain-size sorting: implications for downstream fining, stream-profile concavity, and drainage basin morphologyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2004Nicole M. Gasparini Abstract We explore the link between channel-bed texture and river basin concavity in equilibrium catchments using a numerical landscape evolution model. Theory from homogeneous sediment transport predicts that river basin concavity directly increases with bed sediment size. If the effective grain size on a river bed governs its concavity, then natural phenomena such as grain-size sorting and channel armouring should be linked to concavity. We examine this hypothesis by allowing the bed sediment texture to evolve in a transport-limited regime using a two grain-size mixture of sand and gravel. Downstream ,ning through selective particle erosion is produced in equilibrium. As the channel-bed texture adjusts downstream so does the local slope. Our model predicts that it is not the texture of the original sediment mixture that governs basin concavity. Rather, concavity is linked to the texture of the sorted surface layer. Two different textural regimes are produced in the experiments: a transitional regime where the mobility of sand and gravel changes with channel-bed texture, and a sand-dominated region where the mobility of sand and gravel is constant. The concavity of these regions varies depending on the median gravel- or sand-grain size, erosion rate, and precipitation rate. The results highlight the importance of adjustments in both surface texture and slope in natural rivers in response to changes in ,uvial and sediment inputs throughout a drainage network. This adjustment can only be captured numerically using multiple grain sizes or empirical downstream ,ning rules. Copyright © 2004 John Wiley & Sons, Ltd. [source] Gully-head erosion processes on a semi-arid valley floor in Kenya: a case study into temporal variation and sediment budgetingEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2001D. J. Oostwoud Wijdenes Abstract A three year monitoring programme of gully-head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully-head erosion on the low-angled alluvio-lacustrine Njemps Flats in semi-arid Baringo District, Kenya. This paper discusses the factors controlling the large observed spatial and temporal variation in gully-head retreat rates, ranging from 0 to 15 m a,1. The selected gullies differed in planform and in runoff-contributing catchment area but soil material and land use were similar. The data were analysed at event and annual timescales. The results show that at annual timescale rainfall amount appears to be a good indicator of gully-head retreat, while at storm-event timescale rainfall distribution has to be taken into account. A model is proposed, including only rainfall (P) and the number of dry days (DD) between storms: which explains 56 per cent of the variation in retreat rate of the single-headed gully of Lam1. A detailed sediment budget has been established for Lam1 and its runoff-contributing area (RCA). By measuring sediment input from the RCA, the sediment output by channelized flow and linear retreat of the gully head for nine storms, it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period (DD) between storms. Sediment input from the RCA was usually the largest component for the smaller storms. The erosion of the gully head occurred as a direct effect of runoff falling over the edge (GHwaterfall) and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation (GHmass/storage). The latter component (GHmass/storage) was usually much larger that the former (GHwaterfall). The sediment output from the gully was strongly related to the runoff volume while the linear retreat, because of its complex behaviour, was not. Overall, the results show that the annual retreat is the optimal timescale to predict retreat patterns. More detailed knowledge about relevant processes and interactions is necessary if gully-head erosion is to be included in event-based soil erosion models. Copyright © 2001 John Wiley & Sons, Ltd. [source] Improvement of the hydrological component of an urban soil,vegetation,atmosphere,transfer modelHYDROLOGICAL PROCESSES, Issue 16 2007A. Lemonsu Abstract A numerical study was conducted on the Rezé suburban catchment (Nantes, France) to evaluate the hydrological component of the town energy balance (TEB) scheme, which simulates in a coupled way the water and energy balances for the urban covers. The catchment is a residential area where hydrological data were continuously collected from 1993 to 1998 by the Laboratoire Central des Ponts et Chaussées (LCPC), notably the runoff in the stormwater drainage network. A 6-year simulation with the TEB and interaction soil,biosphere,atmosphere (ISBA) schemes in off-line mode enabled the comparison of modelled and observed runoff. Some weaknesses of the TEB were uncovered and led to improved parameterization of water exchanges: (1) calibration of the maximum capacity of the rainfall interception reservoir on roads and roofs and (2) inclusion of water infiltration through the roads, according to a simple formulation. The calibration of this water flux gives results that are consistent with direct measurements of water infiltration performed on the Rezé site and from the literature. The new parameterization produces better runoff in terms of timing and magnitude, which are comparable to those obtained by the LCPC with other hydrological models. It shows also the impact of the water infiltration through the roads, corresponding to a water transfer from the TEB to ISBA, on the water balance: the water contents of road, roof and soil reservoirs being modified, the evaporation from artificial surfaces decreases, while the evapotranspiration from natural covers increases. Through the evaporative flux, such a modification of the water balance induces large repercussions on the surface energy balance. Copyright © 2007 John Wiley & Sons, Ltd. [source] A network-index-based version of TOPMODEL for use with high-resolution digital topographic dataHYDROLOGICAL PROCESSES, Issue 1 2004S. N. Lane Abstract This paper describes the preliminary development of a network-index approach to modify and to extend the classic TOPMODEL. Application of the basic Beven and Kirkby form of TOPMODEL to high-resolution (2·0 m) laser altimetric data (based upon the UK Environment Agency's light detection and ranging (LIDAR) system) to a 13·8 km2 catchment in an upland environment identified many saturated areas that remained unconnected from the drainage network even during an extreme flood event. This is shown to be a particular problem with using high-resolution topographic data, especially over large appreciable areas. To deal with the hydrological consequences of disconnected areas, we present a simple network index modification in which saturated areas are only considered to contribute when the topographic index indicates continuous saturation through the length of a flow path to the point where the path becomes a stream. This is combined with an enhanced method for dealing with the problem of pits and hollows, which is shown to become more acute with higher resolution topographic data. The paper concludes by noting the implications of the research as presented for both methodological and substantive research that is currently under way. Copyright © 2004 John Wiley & Sons, Ltd. [source] Evidence for seasonal subglacial outburst events at a polythermal glacier, Finsterwalderbreen, SvalbardHYDROLOGICAL PROCESSES, Issue 12 2001J. L. Wadham Bulk runoff and meteorological data suggest the occurrence of two meltwater outburst events at Finsterwalderbreen, Svalbard, during the 1995 and 1999 melt seasons. Increased bulk meltwater concentrations of Cl, during the outbursts indicate the release of snowmelt from storage. Bulk meltwater hydrochemical data and suspended sediment concentrations suggest that this snowmelt accessed a chemical weathering environment characterized by high rock:water ratios and long rock,water contact times. This is consistent with a subglacial origin. The trigger for both the 1995 and 1999 outbursts is believed to be high rates of surface meltwater production and the oversupply of meltwater to areas of the glacier bed that were at the pressure melting point, but which were unconnected to the main subglacial drainage network. An increase in subglacial water pressure to above the overburden pressure lead to the forcing of a hydrological connection between the expanding subglacial reservoir and the ice-marginal channelized system. The purging of ice blocks from the glacier during the outbursts may indicate the breach of an ice dam during connection. Although subglacial meltwater issued continually from the glacier terminus via a subglacial upwelling during both melt seasons, field observations showed outburst meltwaters were released solely via an ice-marginal channel. It is possible that outburst events are a seasonal phenomenon at this glacier and reflect the periodic drainage of meltwaters from the same subglacial reservoir from year to year. However, the location of this reservoir is uncertain. A 100 m high bedrock ridge traverses the glacier 6·5 km from its terminus. The overdeepened area up-glacier from this is the most probable site for subglacial meltwater accumulation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Water Resources Modeling of the Ganges-Brahmaputra-Meghna River Basins Using Satellite Remote Sensing Data,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2009Bushra Nishat Nishat, Bushra and S.M. Mahbubur Rahman, 2009. Water Resources Modeling of the Ganges-Brahmaputra-Meghna River Basins Using Satellite Remote Sensing Data. Journal of the American Water Resources Association (JAWRA) 45(6):1313-1327. Abstract:, Large-scale water resources modeling can provide useful insights on future water availability scenarios for downstream nations in anticipation of proposed upstream water resources projects in large international river basins (IRBs). However, model set up can be challenging due to the large amounts of data requirement on both static states (soils, vegetation, topography, drainage network, etc.) and dynamic variables (rainfall, streamflow, soil moisture, evapotranspiration, etc.) over the basin from multiple nations and data collection agencies. Under such circumstances, satellite remote sensing provides a more pragmatic and convenient alternative because of the vantage of space and easy availability from a single data platform. In this paper, we demonstrate a modeling effort to set up a water resources management model, MIKE BASIN, over the Ganges, Brahmaputra, and Meghna (GBM) river basins. The model is set up with the objective of providing Bangladesh, the lowermost riparian nation in the GBM basins, a framework for assessing proposed water diversion scenarios in the upstream transboundary regions of India and deriving quantitative impacts on water availability. Using an array of satellite remote sensing data on topography, vegetation, and rainfall from the transboundary regions, we demonstrate that it is possible to calibrate MIKE BASIN to a satisfactory level and predict streamflow in the Ganges and Brahmaputra rivers at the entry points of Bangladesh at relevant scales of water resources management. Simulated runoff for the Ganges and Brahmaputra rivers follow the trends in the rated discharge for the calibration period. However, monthly flow volume differs from the actual rated flow by (,) 8% to (+) 20% in the Ganges basin, by (,) 15 to (+) 12% in the Brahmaputra basin, and by (,) 15 to (+) 19% in the Meghna basin. Our large-scale modeling initiative is generic enough for other downstream nations in IRBs to adopt for their own modeling needs. [source] EFFECT OF ORIENTATION OF SPATIALLY DISTRIBUTED CURVE NUMBERS IN RUNOFF CALCULATIONS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2000Glenn E. Moglen ABSTRACT: The NRCS curve number approach to runoff estimation has traditionally been to average or "lump" spatial variability into a single number for purposes of expediency and simplicity in calculations. In contrast, the weighted runoff curve number approach, which handles each individual pixel within the watershed separately, tends to result in larger estimates of runoff than the lumped approach. This work proposes further enhancements that consider not only spatial variability, but also the orientation of this variability with respect to the flow aggregation pattern of the drainage network. Results show that the proposed enhancements lead to much reduced estimates of runoff production. A revised model that considers overland flow lengths, consistent with existing NRCS concepts is proposed, which leads to only mildly reduced runoff estimates. Although more physically-based, this revised model, which accounts directly for spatially distributed curve numbers and flow aggregation, leads to essentially the same results as the original, lumped runoff model when applied to three study watersheds. Philosophical issues and implications concerning the appropriateness of attempting to disaggregate lumped models are discussed. [source] Stream order controls geomorphic heterogeneity and plant distribution in a savanna landscapeAUSTRAL ECOLOGY, Issue 2 2009LESEGO KHOMO Abstract We posed the question: does viewing a savanna as a network of streams linked to a matrix of terrestrial hillslopes provide a useful framework to research and understand plant distribution in these landscapes? Our study area, the Phugwane River network, lies in the semi-arid savanna of Kruger National Park, South Africa. We examined changes in hillslope geomorphology from first-, third- and fifth-order hillslopes with regression equations. The distribution of geomorphic boundaries was enumerated by moving window analysis and the relationship between geomorphology and plant distribution was explored through ordination. First-order hillslopes had a simple geomorphology, fewer geomorphic boundaries and a relatively homogeneous plant assemblage. By contrast, fifth-order hillslopes were more complex in geomorphology, with more boundaries and a relatively heterogeneous vegetation pattern. Stream order classification of a savanna drainage network resulted in landscape units distinguishable by geomorphology, geomorphic boundaries and vegetation pattern. Therefore, the drainage network is a useful template to expose and organize the complexity in savanna landscapes into easily managed and researched units. This perspective should inform a shift from single-scale phytosociological views of homogeneous vegetation units towards multi-scale conceptualizations of savannas as water dependent ecosystems. [source] Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analysesBASIN RESEARCH, Issue 2 2004W. Vétel The Turkana rifted zone in northern Kenya is a long-lived and polyphased rift system where the lack of well-marked rift morphology makes it difficult to identify the zone of active deformation. A high-density river network is exceptionally well developed over the study area and shows evidence of drainage anomalies that suggest recent fault-induced movements at various scales. Correlation of surface drainage anomalies with Landsat remote sensing and deep seismic reflection data permits to characterize the deep geometry of the inferred fault structures. Seismic stratigraphy further allows distinction between the inherited (Oligocene,Pliocene) and the newly formed (<3.7 Ma) origin of the recent deformation. Evidence for neotectonics are observed (1) along a large-scale transverse (EW) fault rooted at depth along a steep basement discontinuity (Turkwell), (2) along a rift-parallel (NS) fault zone probably emplaced during the Pliocene,Pleistocene and currently bounding the Napedet volcanic plateau to the west and (3) over a round-shaped uplifted zone caused by positive inversion tectonics (Kalabata). The major contribution of this work is the recognition of a broad (80 km wide) zone of recent/active extensional deformation in the Turkana Rift in contrast with the narrow (20 km wide) N10°E-trending axial trough forming the Suguta valley to the south, and the Chew Bahir faulted basin to the north. These along-strike variations in structural style are partly controlled by the occurrence of rejuvenated Oligocene,Miocene rift faults and long-lived transverse discontinuities in the Turkana Rift area. More generally, this study has implications for the use of river drainage network about recent/active extensional domains with subdued topography and slow deformation rate. [source] Drainage patterns and tectonic forcing: a model study for the Swiss AlpsBASIN RESEARCH, Issue 2 2001A. Kühni ABSTRACT A linear surface process model is used to examine the effect of different patterns of rock uplift on the evolution of the drainage network of the Swiss Alps. An asymmetric pattern of tectonic forcing simulates a phase of rapid retrothrusting in the south of the Swiss Alps (,Lepontine'-type uplift). A domal pattern of tectonic forcing in the north of the model orogen simulates the phase of the formation of the ,Aar massif', an external basement uplift in the frontal part of the orogenic wedge (,Aar'-type uplift). Model runs using the ,Lepontine'-type uplift pattern result in a model mountain chain with a water divide in the zone of maximum uplift and orogen-normal rivers. Model runs examining the effect of ,Lepontine'-type uplift followed by ,Aar'-type uplift show that the initially formed orogen-normal river system and the water divide are both very stable and hardly affected by the additional uplift. This indifference to changes in tectonic forcing is mainly due to the requirement of a high model erosion capacity for the river systems in order to reproduce the exhumation data (high-grade rocks in the south of the Swiss Alps point to removal of a wedge-shaped nappe stack with a maximum thickness of about 25 km). The model behaviour is in agreement with the ancestral drainage pattern of the Alps in Oligocene and Miocene times and with the modern pattern observed in the Coast Range of British Columbia; in both cases river incision occurred across a zone of rapid uplift in the lower course of the rivers. The model behaviour does not, however, explain the modern drainage pattern in the Alps with its orogen-parallel rivers. When the model system is forced to develop two locally independent main water divides (simultaneous ,Lepontine'- and ,Aar'-type uplift), a zone of reduced erosional potential forms between the two divides. As a consequence, the divides approach each other and eventually merge. The new water divide remains fixed in space independent of the two persisting uplift maxima. The model results suggest that spatial and temporal changes in tectonic forcing alone cannot produce the change from the orogen-normal drainage pattern of the Swiss Alps in Oligocene,Miocene times to the orogen-parallel drainage observed in the Swiss Alps today. [source] Modern and ancient fluvial megafans in the foreland basin system of the central Andes, southern Bolivia: implications for drainage network evolution in fold-thrust beltsBASIN RESEARCH, Issue 1 2001B. K. Horton ABSTRACT Fluvial megafans chronicle the evolution of large mountainous drainage networks, providing a record of erosional denudation in adjacent mountain belts. An actualistic investigation of the development of fluvial megafans is presented here by comparing active fluvial megafans in the proximal foreland basin of the central Andes to Tertiary foreland-basin deposits exposed in the interior of the mountain belt. Modern fluvial megafans of the Chaco Plain of southern Bolivia are large (5800,22 600 km2), fan-shaped masses of dominantly sand and mud deposited by major transverse rivers (Rio Grande, Rio Parapeti, and Rio Pilcomayo) emanating from the central Andes. The rivers exit the mountain belt and debouch onto the low-relief Chaco Plain at fixed points along the mountain front. On each fluvial megafan, the presently active channel is straight in plan view and dominated by deposition of mid-channel and bank-attached sand bars. Overbank areas are characterized by crevasse-splay and paludal deposition with minor soil development. However, overbank areas also contain numerous relicts of recently abandoned divergent channels, suggesting a long-term distributary drainage pattern and frequent channel avulsions. The position of the primary channel on each megafan is highly unstable over short time scales. Fluvial megafans of the Chaco Plain provide a modern analogue for a coarsening-upward, > 2-km-thick succession of Tertiary strata exposed along the Camargo syncline in the Eastern Cordillera of the central Andean fold-thrust belt, about 200 km west of the modern megafans. Lithofacies of the mid-Tertiary Camargo Formation include: (1) large channel and small channel deposits interpreted, respectively, as the main river stem on the proximal megafan and distributary channels on the distal megafan; and (2) crevasse-splay, paludal and palaeosol deposits attributed to sedimentation in overbank areas. A reversal in palaeocurrents in the lowermost Camargo succession and an overall upward coarsening and thickening trend are best explained by progradation of a fluvial megafan during eastward advance of the fold-thrust belt. In addition, the present-day drainage network in this area of the Eastern Cordillera is focused into a single outlet point that coincides with the location of the coarsest and thickest strata of the Camargo succession. Thus, the modern drainage network may be inherited from an ancestral mid-Tertiary drainage network. Persistence and expansion of Andean drainage networks provides the basis for a geometric model of the evolution of drainage networks in advancing fold-thrust belts and the origin and development of fluvial megafans. The model suggests that fluvial megafans may only develop once a drainage network has reached a particular size, roughly 104 km2, a value based on a review of active fluvial megafans that would be affected by the tectonic, climatic and geomorphologic processes operating in a given mountain belt. Furthermore, once a drainage network has achieved this critical size, the river may have sufficient stream power to prove relatively insensitive to possible geometric changes imparted by growing frontal structures in the fold-thrust belt. [source] Response of the Rhine,Meuse fluvial system to Saalian ice-sheet dynamicsBOREAS, Issue 3 2008FREEK S. BUSSCHERS A new reconstruction of the interaction between the Saalian Drente glaciation ice margin and the Rhine,Meuse fluvial system is presented based on a sedimentary analysis of continuous core material, archived data and a section in an ice-pushed ridge. Optically Stimulated Luminescence (OSL) was applied to obtain independent age control on these sediments and to establish a first absolute chronology for palaeogeographical events prior to and during the glaciation. We identified several Rhine and Meuse river courses that were active before the Drente glaciation (MIS 11-7). The Drente glaciation ice advance into The Netherlands (OSL-dated to fall within MIS 6) led to major re-arrangement of this drainage network. The invading ice sheet overrode existing fluvial morphology and forced the Rhine,Meuse system into a proglacial position. During deglaciation, the Rhine shifted into a basin in the formerly glaciated area, while the Meuse remained south of the former ice limit, a configuration that persisted throughout most of the Eemian and Weichselian periods. An enigmatic high position of proglacial fluvial units and their subsequent dissection during deglaciation by the Meuse may partially be explained by glacio-isostatic rebound of the area, but primarily reflects a phase of high base level related to a temporary proglacial lake in the southern North Sea area, with lake levels approximating modern sea levels. Our reconstruction indicates that full ,opening' of the Dover Strait and lowering of the Southern Bight, enabling interglacial marine exchange between the English Channel and the North Sea, is to be attributed to events during the end of MIS 6. [source] Cost-effective Targeting of Riparian BuffersCANADIAN JOURNAL OF AGRICULTURAL ECONOMICS, Issue 1 2004Wanhong Yang This paper develops an integrated economic, hydrologic and GIS modeling framework to examine the cost-effective targeting of land retirement for establishing riparian buffers in agricultural watersheds. Previous studies have examined the efficiency of targeting large land parcels for retirement or targeting management practices such as conservation tillage but have not considered narrow variable buffer strips. An empirical application of the framework in the Canagagigue Creek watershed in Ontario shows that average and marginal costs of sediment abatement increase at an increasing rate as the environmental goal becomes more stringent. The locations of the buffer strips vary across the watershed and are not necessarily located on those sites with greatest slope or those adjacent to visible streams. Cost effectiveness is further increased if the targeting is extended to allow for the width of the buffer strip to vary by location rather than assume a uniform width. The modeling results have important policy implications for the design of conservation stewardship programs such as setting appropriate environmental health goals based on marginal abatement costs relative to marginal benefits, and setting physical characteristics of the riparian buffers for selection along the drainage network in targeted sub-catchments. L'auteur propose un modèle intégrant l'économie, l'hydrologie et les SIG pour déterminer l'efficacité du choix des terres retirées de la production en vue de l'aménagement de zones tampon dans les bassins hydrographiques agricoles. D'autres auteurs se sont déjà penchés sur l'efficacité du retrait de vastes parcelles de la production ou sur certaines pratiques de gestion environnementales comme le non-travail du sol, sans toutefois s'intéresser aux étroites bandes tampon aux propriétés variables. L'application empirique du modèle au bassin du ruisseau Canagagigue, en Ontario, révèle que les coûts moyens et marginaux des mesures de lutte contre la sédimentation augmentent à un taux croissant quand l'objectif environnemental se fait de plus en plus rigoureux. L'emplacement des bandes tampon varie le long du bassin hydrographique et ces derniéres ne se situent pas nécessairement là où la pente est la plus raide ni à proximité des cours d'eau visibles. Le rendement augmente quand on laisse la largeur de la bande tampon varier en fonction de l'endroit, au lieu de présumer une largeur uniforme. Les résultats de la modélisation revêtent une grande importance pour l'élaboration de politiques relatives aux programmes de conservation et d'intendance comme l'établissement d'objectifs de protection de l'environnement fondés sur une comparaison des coûts et des avantages marginaux des mesures de lutte, et le choix de zones riveraines tampon selon leurs caracteristiques physiques dans le réseau de drainage des zones de captage secondaires. [source] Stream geomorphology in a mountain lake district: hydraulic geometry, sediment sources and sinks, and downstream lake effectsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2007C. D. Arp Abstract Lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels. Lakes in the Sawtooth Mountains, Idaho, USA, were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions. First, we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake. To expand on these observations and understand the role of glacial legacy, we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes, meadows (filled lakes), and no past or present lakes. Downstream hydraulic geometry relationships were weak for both the single catchment and regionally. Our data show that downstream patterns in sediment size, channel shape, sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources (hillslopes and tributaries) and sediment sinks (lakes). Stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size, where outlets are wide and shallow with coarse sediment, and inlets are narrow and deep with finer sediment. Meadow outlets and lake outlets show similarities in the coarse-sediment fraction and channel capacity, but meadow outlets have a smaller fine-sediment fraction and nearly mobile sediment. Estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2,4 km downstream, but full recovery may not be reached within 20 km downstream. These results suggest that sediment sinks, such as lakes, in addition to sources, such as tributaries, are important local controls on mountain drainage networks. Copyright © 2006 John Wiley & Sons, Ltd. [source] Predator,prey interactions in river networks: comparing shrimp spatial refugia in two drainage basinsFRESHWATER BIOLOGY, Issue 3 2009ALAN P. COVICH Summary 1.,Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2.,We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3.,We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998,2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4.,Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5.,The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6.,Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking. [source] An inverse cascade model for self-organized complexity and natural hazardsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005Gleb Yakovlev SUMMARY The concept of self-organized complexity evolved from the scaling behaviour of several cellular automata models, examples include the sandpile, slider-block and forest-fire models. Each of these systems has a large number of degrees of freedom and shows a power-law frequency-area distribution of avalanches with N,A,, and ,, 1. Actual landslides, earthquakes and forest fires exhibit a similar behaviour. This behaviour can be attributed to an inverse cascade of metastable regions. The metastable regions grow by coalescence which is self-similar and gives power-law scaling. Avalanches sample the distribution of smaller clusters and, at the same time, remove the largest clusters. In this paper we build on earlier work (Gabrielov et al.) and show that the coalescence of clusters in the inverse cascade is identical to the formation of fractal drainage networks. This is shown analytically and demonstrated using simulations of the forest-fire model. [source] A box scheme for transcritical flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2002T. C. Johnson Abstract The accurate computer simulation of river and pipe flow is of great importance in the design of urban drainage networks. The use of implicit numerical schemes allows the time step to be chosen on the basis of accuracy rather than stability, offering a potential computational saving over explicit methods. The highly successful Box Scheme is an implicit method which can be used to model a wide range of subcritical and supercritical flows. However, care must be taken over the modelling of transcritical flows since, unless the correct internal boundary conditions are imposed, the scheme becomes unstable. The necessity of accurately tracking all the critical interfaces and treating them accordingly can be algorithmically complex and in practice the underlying mathematical model is often modified to ensure that the flow remains essentially subcritical. Such a modification however inevitably leads to additional errors and incorrect qualitative behaviour can be observed. In this paper we show how the technique of ,residual distribution' can be successfully implemented in order to accurately model unsteady transcritical flow without the need to know a priori which regions of the computational domain correspond to subcritical and supercritical flow. When used in conjunction with a form of artificial smoothing, the resulting method generates very high resolution results even for transcritical problems involving shocks, as can be seen in the numerical results. Copyright © 2002 John Wiley & Sons, Ltd. [source] Investigating the surface process response to fault interaction and linkage using a numerical modelling approachBASIN RESEARCH, Issue 3 2006P.A. Cowie ABSTRACT In order to better understand the evolution of rift-related topography and sedimentation, we present the results of a numerical modelling study in which elevation changes generated by extensional fault propagation, interaction and linkage are used to drive a landscape evolution model. Drainage network development, landsliding and sediment accumulation in response to faulting are calculated using CASCADE, a numerical model developed by Braun and Sambridge, and the results are compared with field examples. We first show theoretically how the ,fluvial length scale', Lf, in the fluvial incision algorithm can be related to the erodibility of the substrate and can be varied to mimic a range of river behaviour between detachment-limited (DL) and transport-limited (TL) end-member models for river incision. We also present new hydraulic geometry data from an extensional setting which show that channel width does not scale with drainage area where a channel incises through an area of active footwall uplift. We include this information in the coupled model, initially for a single value of Lf, and use it to demonstrate how fault interaction controls the location of the main drainage divide and thus the size of the footwall catchments that develop along an evolving basin-bounding normal fault. We show how erosion by landsliding and fluvial incision varies as the footwall area grows and quantify the volume, source area, and timing of sediment input to the hanging-wall basin through time. We also demonstrate how fault growth imposes a geometrical control on the scaling of river discharge with downstream distance within the footwall catchments, thus influencing the incision rate of rivers that drain into the hanging-wall basin. Whether these rivers continue to flow into the basin after the basin-bounding fault becomes fully linked strongly depends on the value of Lf. We show that such rivers are more likely to maintain their course if they are close to the TL end member (small Lf); as a river becomes progressively more under supplied, i.e. the DL end member (large Lf), it is more likely to be deflected or dammed by the growing fault. These model results are compared quantitatively with real drainage networks from mainland Greece, the Italian Apennines and eastern California. Finally, we infer the calibre of sediments entering the hanging-wall basin by integrating measurements of erosion rate across the growing footwall with the variation in surface processes in space and time. Combining this information with the observed structural control of sediment entry points into individual hanging-wall depocentres we develop a greater understanding of facies changes associated with the rift-initiation to rift-climax transition previously recognised in syn-rift stratigraphy. [source] River spacing and drainage network growth in widening mountain rangesBASIN RESEARCH, Issue 3 2006Sébastien Castelltort ABSTRACT Drainage networks in linear mountain ranges always display a particular geometrical organisation whereby the spacing between the major drainage basins is on average equal to half the mountain width (distance from the mountain front to the main drainage divide), independent of climate and tectonics. This relationship is valid for mountains having different widths and is thus usually thought to be maintained by drainage reorganisation during mountain belt widening. However, such large-scale systematic drainage reorganisation has never been evidenced. In this paper, we suggest an alternative explanation, namely that the observed drainage basin relationships are an inherent property of dendritic river networks and that these relationships are established on the undissected, lowland margins outside mountain ranges and are progressively incorporated and quenched into uplifted topography during range widening. Thus, we suggest that the large-scale geometry of drainage networks in mountain ranges is mainly antecedent to erosion. We propose a model in which the large-scale drainage geometry is controlled mainly by the geometrical properties of the undissected surfaces (in particular, the ratio of the regional slope to the local slope related to roughness) over which rivers are flowing before uplift, and is therefore independent of climate and tectonics. [source] Modern and ancient fluvial megafans in the foreland basin system of the central Andes, southern Bolivia: implications for drainage network evolution in fold-thrust beltsBASIN RESEARCH, Issue 1 2001B. K. Horton ABSTRACT Fluvial megafans chronicle the evolution of large mountainous drainage networks, providing a record of erosional denudation in adjacent mountain belts. An actualistic investigation of the development of fluvial megafans is presented here by comparing active fluvial megafans in the proximal foreland basin of the central Andes to Tertiary foreland-basin deposits exposed in the interior of the mountain belt. Modern fluvial megafans of the Chaco Plain of southern Bolivia are large (5800,22 600 km2), fan-shaped masses of dominantly sand and mud deposited by major transverse rivers (Rio Grande, Rio Parapeti, and Rio Pilcomayo) emanating from the central Andes. The rivers exit the mountain belt and debouch onto the low-relief Chaco Plain at fixed points along the mountain front. On each fluvial megafan, the presently active channel is straight in plan view and dominated by deposition of mid-channel and bank-attached sand bars. Overbank areas are characterized by crevasse-splay and paludal deposition with minor soil development. However, overbank areas also contain numerous relicts of recently abandoned divergent channels, suggesting a long-term distributary drainage pattern and frequent channel avulsions. The position of the primary channel on each megafan is highly unstable over short time scales. Fluvial megafans of the Chaco Plain provide a modern analogue for a coarsening-upward, > 2-km-thick succession of Tertiary strata exposed along the Camargo syncline in the Eastern Cordillera of the central Andean fold-thrust belt, about 200 km west of the modern megafans. Lithofacies of the mid-Tertiary Camargo Formation include: (1) large channel and small channel deposits interpreted, respectively, as the main river stem on the proximal megafan and distributary channels on the distal megafan; and (2) crevasse-splay, paludal and palaeosol deposits attributed to sedimentation in overbank areas. A reversal in palaeocurrents in the lowermost Camargo succession and an overall upward coarsening and thickening trend are best explained by progradation of a fluvial megafan during eastward advance of the fold-thrust belt. In addition, the present-day drainage network in this area of the Eastern Cordillera is focused into a single outlet point that coincides with the location of the coarsest and thickest strata of the Camargo succession. Thus, the modern drainage network may be inherited from an ancestral mid-Tertiary drainage network. Persistence and expansion of Andean drainage networks provides the basis for a geometric model of the evolution of drainage networks in advancing fold-thrust belts and the origin and development of fluvial megafans. The model suggests that fluvial megafans may only develop once a drainage network has reached a particular size, roughly 104 km2, a value based on a review of active fluvial megafans that would be affected by the tectonic, climatic and geomorphologic processes operating in a given mountain belt. Furthermore, once a drainage network has achieved this critical size, the river may have sufficient stream power to prove relatively insensitive to possible geometric changes imparted by growing frontal structures in the fold-thrust belt. [source] | ||||||||||||||||