Channel Network Structure Research Articles

Development and application of a catchment similarity index for subsurface flow

In this study, we develop a similarity parameter to describe shallow subsurface hydrological response of small catchments on the basis of the hillslope‐Péclet number. This new similarity parameter, named the catchment‐Péclet (caPe) number, provides a theoretical framework to compare the relative hydrologic response derived from shallow subsurface flow of small catchments on the basis of geomorphic properties. Using 400,000 synthetically derived catchments to model catchment‐scale characteristic response functions (CRFs), we see good agreement between the synthetic and theoretical relationships relating the caPe number to the first two dimensionless moments of the CRF of small catchments. Working with real‐world data, however, requires the estimation of hydrologic parameters and delineation of hillslopes to apply the caPe number. Allowing for uncertainty in the estimation of hydrologic parameters and in the definition of the extent of the channel network, the caPe number is able to recreate the observed moments of an approximate catchment‐scale CRF for four small catchments ranging in size from 0.025 to 880 ha in two distinct climatic and geologic settings. By using physics to underpin the link between landscape and hydrological response, the caPe number creates a functional relationship between hydraulic theory and a catchment's pedogeomorphological structure. While this study is limited to small headwater catchments, it lays the groundwork for a catchment‐scale similarity parameter that could be expanded to larger scales where channel network structure and storage become more important.

Effect of AAc-GA content on swelling behaviors of temperature-sensitive PNIPAAm-based hydrogels

A series of temperature-sensitive poly (NIPAAm-co-AAc-GA) hydrogels were synthesized by the copolymerization of glycyrrhetinic acid with vinyl monomer (AAc-GA) and N-isopropylacrylamide (NIPAAm) in N, N-dimethylformamide (DMF). Since GA has the specific binding capacity to asialoglycoprotein receptors on the membrane of hepatocyte, the hydrogel with GA could be expected as good candidate for hepatic cell culture. The results showed that macroporous and channel network structure was formed in the hydrogel matrix. With increasing the AAc-GA content, the swelling ratios of hydrogels and lower critical solution temperature (LCST) increased because of the hydrophilic group of AAc-GA and the macroporous structure. In addition, the prepared hydrogels could respond quickly to temperature and exhibited good reversible temperature-responsive characteristics.

Dynamics of the Selenga river network and delta structure

The results of investigations for the Selenga river basin and delta are presented. The causes for the changes in the channel network structure are considered. The study revealed tendencies of erosion activity and plane deformations within the delta. An analysis is made of the distribution of water flow rate and sediment loads for the channel network, based on field measurements and existing research material.

Diels-Alder Cycloaddition of Cyclopentadiene with Ethylacrylate Catalyzed by Mesoporous Al-MCM-48 and Al-MCM-41 Catalysts

In the present work, Diels-Alder reaction of cyclopentadiene with ethylacrylate has been carried out by using two types of mesoporous solid acid catalysts (Al-MCM-41, Al-MCM-48) with different pore structures. The specific topology of Al-MCM-48 (cubic Ia3d structure composed of two independent 3-D channel systems) exhibit higher activity and stereo-control than those of Al-MCM-41 (hexagonal packing of 1-D channels). The physical properties of Al-MCM-48 catalyst, such as high accessibility of reactants to the acid sites, spatial confinement in the nanoscopic reactors, and 3-D channel network structure that are effective adsorption and diffusion of reactants, play a crucial role in the present study.

Chiral Spherical Molecule Constructed from Aromatic Amides: Facile Synthesis and Highly Ordered Network Structure in the Crystal

A novel chiral spherical molecule composed of aromatic amide was synthesized in short steps. The molecule is constructed from four benzene rings connected by six amide bonds and has multiple functionalizable points and an asymmetric structure. The racemic spherical molecule constructed channel network structures in the crystalline state.

Channel network scaling laws in submarine basins

[1] Fluvial drainage basin area is often related to channel length and local slope through power law relationships and the relatively small range of exponents observed in these relationships is thought to result from physical mechanisms. Proposed mechanisms assume that the observed correlation between drainage area and fluid discharge is caused by precipitation. Using high resolution DEMs of channelized continental slope settings offshore Monterey, CA and Brunei Darussalam we extracted submarine channel profiles and drainage area statistics from five basins. In-situ and remote observations suggest discharge in these oceanic settings is determined by boundary conditions at the shelf-edge. In spite of substantial differences in environment and physical process, the data yield submarine scaling exponents within the range of terrestrial (fluvial) observations. The convergence in scaling relationships from two very different settings supports theoretical arguments that channel network structure results from the aggregation of random walks.

A catchment-scale model of mountain stream channel morphologies in southeast Australia

The position of mountain streams high in the channel network and their proportional dominance mean that channel modifications and adjustments within these systems will have important implications for downstream processes and linkages. This study develops an analysis framework for examining the catchment-scale distribution of reach morphologies, and the relationship among reach type, catchment lithology and flow competence in southeast Australian mountain streams. The analysis framework is applied to three catchments which have contrasting proportions of the two dominant lithologies of the region, Devonian granites and Ordovician metasediments. The model successfully delineated 68% of reach types, and the resultant spatial maps allowed the effects of stream network position and catchment specific controls on channel morphology to be evaluated. Maximum lengths of the majority of reach morphology types were in second-order streams and the maximum number of morphology types (six) was present in third-order streams, with dramatic reductions in reach type variability as the network expands. The position of catchment lithology within the channel network structure was recognized as more important than the aerial extent of a particular lithology on the distribution and abundance of reach morphologies. The model provides an important tool in the management of channel networks for the protection or restoration of ecological diversity, by identifying river segments and tributaries with high morphological diversity.

Do gravel bed river size distributions record channel network structure?

Bed load sediment particles supplied to channels by hillslopes are reduced in size by abrasion during downstream transport. The branching structure of the channel network creates a distribution of downstream travel distances to a given reach of river and thus may strongly influence the grain size distribution of the long‐term bed load flux through that reach. Here we investigate this hypothesis, using mass conservation and the Sternberg exponential decay equation for particle abrasion, to predict bed material variability at multiple scales for both natural and artificial drainage networks. We assume that over a sufficiently long timescale, no net deposition occurs and that grains less than 2 mm are swept away in suspension. We find that abrasion during fluvial transport has a surprisingly small effect on the bed load sediment grain size distribution, for the simple case of spatially uniform supply of poorly sorted hillslope sediments. This occurs because at any point in the channel network, local resupply offsets the size reduction of material transported from upstream. Thus river bed material may essentially mirror the coarse component of the size distribution of hillslope sediment supply. Furthermore, there is a predictable distance downstream at which the bed load grain size distribution reaches a steady state. In the absence of net deposition due to selective transport, large‐scale variability in bed material, such as downstream fining, must then be due primarily to spatial gradients in hillslope sediment production and transport characteristics. A second key finding is that average bed load flux will tend to stabilize at a constant value, independent of upstream drainage area, once the rate of silt production by bed load abrasion per unit travel distance is equal to the rate of coarse sediment supply per unit channel length (q). Bed load flux equilibrates over a distance that scales with the inverse of the fining coefficient in the abrasion rate law (α) and can be approximated simply as q/3α. Thus the efficiency of particle abrasion sets a fundamental length scale, shorter for weaker rocks and longer for harder rocks, which controls the expression in the river bed of variability in sediment supply. We explore the role of the abrasion length scale in modulating the influence of sediment supply variability in a number of channel network contexts, including individual tributary junctions, a sequence of tributary inputs along a main stem channel, and variable basin shapes and network architecture as expressed by the width function. These findings highlight the need for both data and theory that can be used to predict the grain size distributions supplied to channels by hillslopes.

Feasible optimality of vegetation patterns in river basins

We examine mechanisms leading to organization of vegetation patterns within the channel network structure of a semi‐arid New Mexico river basin under the controlling influence of water stress. We compare the actual pattern of water stress within the basin to patterns resulting from two algorithms of local stress optimization which proceed from an initial fully random vegetation distribution. Here we show that the distribution of vegetation and basin water stress derived from an algorithm that maintains local optimization within the network flow path exhibits considerably better agreement with the actual distribution than one that ignores the network structure of the basin. These results suggest the pattern of actual vegetation observed within the basin corresponds to a condition of feasible optimality in which organization is constrained by the stochastic nature of local interactions mediated by the network configuration. The principles of such organization have important consequences regarding the interaction between land cover change and hydrological dynamics in river basins, as well as the biogeographical evolution of landscapes.

Fractal Dimension of the Channel Network Structure of Selenga River Delta

Specific features of the geomorphology and hydrology of Selenga River delta are considered. Fractal theory is used to evaluate the fractal dimension of the river delta as a branched structure. The fractal dimension of the planar pattern of the Selenga and Volga deltas are evaluated for the first time using three independent methods. The obtained values are 1.38 and 1.72, respectively.

A novel poly- l-lactic acid scaffold that possesses a macroporous structure and a branching/joining three-dimensional flow channel network: its fabrication and application to perfusion culture of human hepatoma Hep G2 cells

In the development of large internal organ equivalents for use in humans, the organs themselves must be reorganized based on three-dimensional (3D) fabrication of biodegradable polymer scaffolds. To this end, appropriate design of the 3D structure—particularly with respect to the arrangement of a 3D flow channel network and macroporous structures for cell immobilization—is critical. In the present work, we therefore presented a new scaffold design based on a regular tetrahedron whose edge is 3.0 mm as a unit composing the entire shape and the 3D flow channel network of the scaffold. Such an advanced scaffold successfully fabricated through repeated layering/micromachining of macroporous PLLA/NH 4HCO 3 salt particle composite sheets followed by salt leaching and gas forming. This reliable production of a flow channel network over scaffolds is more promising than existing 3D microfabrication processes in which such networks are produced indirectly in the spaces remaining after fabrication. A preliminary short-term perfusion culture of Hep G2 cells demonstrated that, even in a small scaffold with a small volume of around 1.3 cm 3, such a 3D flow channel arrangement is necessary to allow the cells to grow and function. Although the current dimensions of the design unit were not ideal, the basic design concept presented in this study shows great promise for use in the engineering of a large human organ equivalent.

Channel Network Structure and the Product Assortment Function

Although business networks provide value for many of their participants, the ability of network systems to perform product assortment functions is unclear. After raising several related research questions about network structure and product matching, this paper reviews some conceptual foundations of the network approach. In particular, the paper reviews and develops the distinction between network positions and distribution functions. It then assesses the functions performed within channel network structures in several published case studies. Some of these network structures exhibit low densities and closely resemble rather conventional vertical supply systems. It appears, though, that such more vertical networks perform a speculative matching function for product assortments when supply and demand are heterogeneous and volatile. Under more rigid and stable conditions, vertical networks may engage in product customisation to postpone product form. Horizontal networks (when they exist), may facilitate product standardisation and thus may contribute to beneficial diversities in supply.

A connection between topographically driven runoff generation and channel network structure

Runoff generation can be modelled using a topographic wetness index; the fraction of the catchment where the wetness index exceeds some threshold is assumed to be saturated. We show that distributions of a topographic index can share a common form across many catchments, particularly for sufficiently large catchments. This leads us to speculate that the topographic structure of drainage networks provides a unifying theme for runoff generation. We identify those catchments which share the common distribution of topographic index, and label them “organized.” Visual examination of maps of this index and of subcatchment area indicates that the organized catchments are those which have a “proper” network: The branching structure provides an orderly increase in subcatchment area as one proceeds downstream. We consider that the presence of a “properly” branched network is the essence of “organization.” It has previously been observed that catchments can have a power law distribution of subcatchment area: our data show that the distributions of wetness index and subcatchment area are closely connected for catchments with a well‐developed channel network. Since the distribution of subcatchment area is a signature of the channel network, this permits the reparameterization of runoff generation models using channel network properties. As a result, the runoff generation model is a truly a catchment‐scale model and can no longer be disaggregated to the point scale. This view of catchment response is closely related to the representative elementary area concept, where catchment response is “simple” for sufficiently large catchments and depends only on catchment‐scale phenomena.

Automated channel ordering and node indexing for raster channel networks

A numerical algorithm is proposed for automated interpretation of channel networks from raster images, indexing of network nodes, and ordering of channels by the Strahler method. Channel ordering and node indexing is fundamental to the automation of flow-routing management in distributed hydrologic models and morphometric evaluation of channel-network structure. The node index numbers can also serve to link network nodes to corresponding tabulated attributes of network channels. The proposed algorithm uses a two-step approach: first, the raster image of the network is interpreted and a channel attribute table is created; second, the network nodes are indexed based only on the network connectivity information contained in the channel attribute table. The use of attribute information in the second step eliminates a repeat of the time consuming cell-by-cell interpretations of the network raster image. In addition to the general case of nodes with two upstream inflows, the algorithm also handles complex nodes (nodes with more than two upstream inflows) which are rare under natural conditions, but more frequent in raster networks. The final product of the presented algorithm is a table of channel orders and node indices derived from raster images of channel networks.

Fractal analyses of tree-like channel networks from digital elevation model data

Digital elevation models (DEMs) are generally used to automatically map the channel network and to delineate subbasins. The most common approach to extract a channel network from DEMs consists of specifying a threshold area S which is the minimum area required to drain to a point for a channel to form. This threshold area is usually specified arbitrarily, although it is recognized that different threshold areas will result in substantially different channel networks for the same basin. In this paper, we study the effect of S (that is also the scale of observation) on the morphometric properties (external and internal links, length of drainage paths, mainstream length) and scaling properties (such as Horton's and Strahler's laws, and fractal dimension). Three basins, located in southern France, were extensively studied. The results indicate that morphometric properties vary considerably with S, and thus values reported without their associated S should be used in hydrologic analysis with caution. Then, the fractal geometry is used to take into account the dependence of measured values on observation scales, which is not possible with classical hydrological indexes. The use of fractals allows, first, to point out self-similarity in the structure of channel networks and then to quantify the tree-like organization. New catchment shape indexes, independent of the observation scale S, are defined. These indexes are useful for comparing catchments and for measuring the irregularity level of the channel network.

On scaling exponents of spatial peak flows from rainfall and river network geometry

The hypothesis of statistical self-similarity, or scaling invariance, in the spatial variability of rainfall, channel network structures and floods has been supported by recent advances in data analyses. This hypothesis is used here to calculate the statistical scaling exponents of peak river flows using a random cascade model of spatial rainfall intensities and the Peano basin as an idealized model of a river basin. The ‘maximum contributing set’ approximately determines the magnitudes of peak flows in a self-similar manner in different subbasins of the Peano basin. For an instantaneously applied random, spatially uniform rainfall, the Hausdorff dimension of the maximum contributing set appear, as the statistical simple scaling exponent of peak flows. This result is generalized to an instantaneously applied cascade rainfall, and it is shown to give rise to statistical multiscaling in peak flows. The multiscaling exponent of peak flows is computed and interpreted as a Hausdorff dimension of a fractal set supporting rainfall intensity on the maximum contributing set of the Peano basin. Potential implications of this interpretation are illustrated using the regional food frequency analysis of the Appalachian flood data in the United States and a rainfall data set from the tropical Atlantic ocean. It is argued that the hypothesis of self-similarity identifies a powerful theoretical framework which can unify a statistical theory of regional flood frequency with important empirical features of topographic, rainfall and flood data sets and distributed rainfall-landform-runoff relationships.

Spatial variability in flood estimation for large catchments: the exploitation of channel network structure

Abstract A methodology for incorporating spatial variability into a unithydrograph type flood estimation procedure is presented. The method centres on the use of a network width function, which describes the spatial disposition of channels within a catchment, a two-parameter routing function, and a hillslope response function. The spatial variability is expressed in terms of weights applied to the network width function. The method is illustrated with respect to both soil type, as described by the winter rain acceptance potential, and total event rainfall in seven events on the River Thames at Cookham, UK.

Study on Runoff from Small Basin with Ideal Channel Network

Meteorological radars have covered almost the Japanese archipelago. The information from these radar systems consists of mesh data. The size of each mesh is approximately 3km*3km. It is very important to estimate the runoff from these small basins to use the information from radar system. In this paper, the effects of variations of channel network structure on flood peak magnitude are investigated using simulated stream networks for the small basins. Numerical experiments are carried out to explore the relationship between the hydrograph and the channel network structure. It is concluded that the duration of rainfall input plays an important role.

Frequency Distributions of Stream Link Lengths and the Development of Channel Networks

A number of hypotheses concerning the evolution of stream channel networks have been advanced, with the object of accounting for the observed properties of distributions of channel link lengths. This paper comments on the validity of earlier investigations, and on current hypotheses of network growth. Data from a time-controlled series of drainage networks and the results of a computer simulation experiment are presented and employed to generate a new hypothesis to account for the observed distributions of link lengths. This hypothesis suggests that the structure of channel networks may be accounted for without the need to invoke the major post-bifurcation channel "adjustments" of previous models.

Quantitative characterization of channel network structure

The most commonly used quantitative parameters for characterizing channel networks are derived from a Horton analysis (bifurcation ratios, stream length ratios, and so forth). Although these parameters give useful information about individual networks, they are generally ineffective in distinguishing differences in network structure due to lithologic controls and degree of maturity. As Shreve has noted, this failure is due in part to the random nature of network topology and link lengths and in part to the fact that the Horton analysis tends to average out many of the details that characterize such differences. Parameters derived from considerations of statistical geometric similarity, on the other hand, are relatively successful in characterizing network structure. For a simple example, let le and li be the mean exterior and interior link lengths, respectively, and ae and ai be the means of the associated drainage areas. Four dimensionless parameters that can be constructed from this set are λ = le/li α = ae/ai Ke = le2/ae and Ki = li2/ai. Data on λ, α, Ke and Ki for natural networks drawn from different geologic populations indicate that these quantities are effective in detecting differences due to varying lithology and degree of maturity.