River Network Structure Research Articles

River network structure shapes interannual feedbacks between adult sea lamprey migration and larval habitation

Adult sea lampreys ( Petromyzon marinus) migrating upstream to spawn follow a pheromone released by instream larvae. The size (i.e. flow) of a tributary dilutes the concentration of this pheromone, such that the downstream propagation pattern of larval pheromone must be influenced by patterns in the relative sizes and numbers of confluent tributaries. We developed an individual-based model to explicitly test the resulting hypothesis that river network structure influences the migration decisions of adult lampreys following the larval pheromone, and in turn the distribution of larvae. First, we initialized the model using randomly generated river networks, and found a strong positive relationship between network diameter and larval aggregation. Larvae aggregated over time, and the degree and rate of this aggregation depended on network diameter. Second, we initialized the model using a river network based on the Muskegon River, Michigan, and compared model-generated larval distribution to available field survey data. We found a significant correlation between model-generated larval abundance and field-measured larval densities ( r 2 = 0.54; p < 0.0001). We also found an inverse relationship between subwatershed area and the degree to which path-dependent effects influenced larval abundance in that subwatershed. Our results overall suggest that larval distribution across a watershed results from a system of context-dependent interannual feedbacks shaped by network structure and the past migratory and spawning behavior of adults.

Dispersion mechanisms and the effect of parameter uncertainty on hydrologic response in urban catchments

The link between river network structure and hydrologic response for natural watersheds has been the subject of ongoing research for the past 30 years. In this paper we investigate the link between sewer network structure and hydrologic response in urban catchments. It has been shown in natural watersheds that there are dispersion mechanisms that contribute to the impulse response function of the catchment: hydrodynamic dispersion, geomorphologic dispersion, and hydrodynamic dispersion. We introduce a fourth dispersion mechanism, intrastate dispersion, which accounts for the variance in conduit (e.g., slope, length, diameter, etc.) and overland region input parameters (e.g., slope, area, imperviousness, etc.) within an order. This dispersion mechanism is found to be the second largest contributor to the total dispersion in the urban catchments analyzed, contributing less than hydrodynamic dispersion but more than kinematic and geomorphologic dispersion. This is primarily a result of the shorter network travel times observed in urban catchment. The dispersion mechanisms are incorporated in the Illinois Urban Hydrologic Model, which is a recently developed probabilistic approach for predicting the hydrologic response in highly urbanized catchments. Furthermore, an analysis is performed to help better understand the uncertainty in the predicted hydrologic response that is introduced by spatial variation in conduit and overland input parameters. It is identified that conduit slope and length are the greatest sources of uncertainty in the predicted direct runoff hydrograph for the CDS‐51 catchment in the village of Dolton, Illinois, and the CDS‐36 catchment in the city of Chicago, Illinois.

Automated upscaling of river networks for macroscale hydrological modeling

We developed a hierarchical dominant river tracing (DRT) algorithm for automated extraction and spatial upscaling of basin flow directions and river networks using fine‐scale hydrography inputs (e.g., flow direction, river networks, and flow accumulation). In contrast with previous upscaling methods, the DRT algorithm utilizes information on global and local drainage patterns from baseline fine‐scale hydrography to determine upscaled flow directions and other critical variables including upscaled basin area, basin shape, and river lengths. The DRT algorithm preserves the original baseline hierarchical drainage structure by tracing each entire flow path from headwater to river mouth at fine scale while prioritizing successively higher order basins and rivers for tracing. We applied the algorithm to produce a series of global hydrography data sets from 1/16° to 2° spatial scales in two geographic projections (WGS84 and Lambert azimuthal equal area). The DRT results were evaluated against other alternative upscaling methods and hydrography data sets for continental U.S. and global domains. These results show favorable DRT upscaling performance in preserving baseline fine‐scale river network information including: (1) improved, automated extraction of flow directions and river networks at any spatial scale without the need for manual correction; (2) consistency of river network, basin shape, basin area, river length, and basin internal drainage structure between upscaled and baseline fine‐scale hydrography; and (3) performance largely independent of spatial scale, geographic region, and projection. The results of this study include an initial set of DRT upscaled global hydrography maps derived from HYDRO1K baseline fine‐scale hydrography inputs; these digital data are available online for public access at ftp://ftp.ntsg.umt.edu/pub/data/DRT/.

Metacommunity theory as a multispecies, multiscale framework for studying the influence of river network structure on riverine communities and ecosystems

Explaining the mechanisms underlying patterns of species diversity and composition in riverine networks is challenging. Historically, community ecologists have conceived of communities as largely isolated entities and have focused on local environmental factors and interspecific interactions as the major forces determining species composition. However, stream ecologists have long embraced a multiscale approach to studying riverine ecosystems and have studied both local factors and larger-scale regional factors, such as dispersal and disturbance. River networks exhibit a dendritic spatial structure that can constrain aquatic organisms when their dispersal is influenced by or confined to the river network. We contend that the principles of metacommunity theory would help stream ecologists to understand how the complex spatial structure of river networks mediates the relative influences of local and regional control on species composition. From a basic ecological perspective, the concept is attractive because new evidence suggests that the importance of regional processes (dispersal) depends on spatial structure of habitat and on connection to the regional species pool. The role of local factors relative to regional factors will vary with spatial position in a river network. From an applied perspective, the long-standing view in ecology that local community composition is an indicator of habitat quality may not be uniformly applicable across a river network, but the strength of such bioassessment approaches probably will depend on spatial position in the network. The principles of metacommunity theory are broadly applicable across taxa and systems but seem of particular consequence to stream ecology given the unique spatial structure of riverine systems. By explicitly embracing processes at multiple spatial scales, metacommunity theory provides a foundation on which to build a richer understanding of stream communities.

Flooding-induced landscape changes along dendritic stream networks and implications for wildlife habitat

Severe low frequency natural disturbances along stream networks can substantially alter urban and rural landscapes and impact habitat and population dynamics of wildlife species. In 1978, severe flooding along the North Prong of the Medina River significantly altered the habitat for the Rio Grande wild turkey and may have contributed to the decreased abundance of this species observed during recent decades in the southeastern Edwards Plateau, TX, USA. The objective of our study was to examine the changes in landscape structure caused by this flooding event and their potential impact on wild turkey habitat. Aerial photography from 1972, 1984, and 1995 was used to quantify habitat changes in riparian zones and adjacent bottomlands along the Medina River. We documented substantial reductions in habitat suitability and connectivity caused by the flooding, followed by a partial recovery over 17 years. Analysis using patch-level metrics in conjunction with class-level metrics, provided insights to the pattern and possible mechanisms of the landscape changes. Habitat along higher-order streams was most affected, reducing not only the suitable habitat locally, but also the habitat connectivity throughout the riparian network. This loss of connectivity rendered numerous habitat patches along lower-order streams unavailable to Rio Grande wild turkeys as this species depends on riparian corridors for dispersal and movement among habitat patches. Our results illustrate the critical importance of multiple-scale analysis based on hierarchical dendritic structures of river networks when assessing habitat changes and their impact on populations of terrestrial wildlife species dependent on riparian habitats in semi-arid landscapes.

Effects of colonization asymmetries on metapopulation persistence

Ocean currents, prevailing winds, and the hierarchical structures of river networks are known to create asymmetries in re-colonization between habitat patches. The impacts of such asymmetries on metapopulation persistence are seldom considered, especially rarely in theoretical studies. Considering three classical models (the island, the stepping stone and the distance-dependent model), we explore how metapopulation persistence is affected by (i) asymmetry in dispersal strength, in which the colonization rate between two patches differs in direction, and (ii) asymmetry in connectivity, in which the overall colonization pattern displays asymmetry (circulating or dendritic networks). Viability can be drastically reduced when directional bias in dispersal strength is higher than 25%. Re-colonization patterns that allow for strong local connectivity provide the highest persistence compared to systems that allow circulation. Finally, asymmetry has relatively weak effects when metapopulations maintain strong general connectivity.

Transport on river networks: A dynamic tree approach

This study is motivated by problems related to environmental transport on river networks. We establish statistical properties of a flow along a directed branching network and suggest its compact parameterization. The downstream network transport is treated as a particular case of nearest neighbor hierarchical aggregation with respect to the metric induced by the branching structure of the river network. We describe the static geometric structure of a drainage network by a tree, referred to as the static tree, and introduce an associated dynamic tree that describes the transport along the static tree. It is well known that the static branching structure of river networks can be described by self‐similar trees; we demonstrate that the corresponding dynamic trees are also self‐similar, albeit with different self‐similarity parameters. We report an unexpected phase transition in the dynamics of three river networks (one from California and two from Italy), demonstrate the universal features of this transition, and seek to interpret it in hydrological terms.

Hortonian scaling and effect of cutoffs on statistics of self‐affine river networks

The planar structure of river networks exhibits fractal properties. In particular, available data indicate a tendency for drainage areas A to be distributed according to a power law; their boundaries and main channels to form self‐affine curves; the characteristic lengths of drainage areas to be independently self‐affine in the one‐dimensional space Z of total channel length, rendering the network elongated (and anisotropic); the inverse network density A/Z to be either constant or self‐affine in Z, depending on whether or not the network fills the two‐dimensional space of A; and (as found in a recent study) areas of given size, vegetative cover, and mean steady state soil moisture, weighted by their flow distance from the basin outlet, to be self‐affine in the one‐dimensional space of this distance. Various theoretical and semiempirical relationships have been proposed among exponents defining some of these and other scale dependencies. Expressions have been proposed for ensemble moments of A and some length measures associated with finite size river basins. We present a new model that views any self‐affine basin property, Y(X), as belonging to an infinite hierarchy of mutually uncorrelated, statistically homogeneous random functions defined on elementary subbasins, each of which is characterized by a unique integral (spatial correlation) scale λ. We cite a mathematically rigorous hydrologic rationale for our model and use it in conjunction with published scaling relations to obtain the probability density function of λ; to derive analytical expressions for ensemble analogs of Horton's scaling laws; to deduce from them that streams of any Horton‐Strahler order ω are associated with integral scales λω ≤ λ ≤ λω+1, where the ratio λω+1/λω is a constant independent of ω; to develop analytical expressions relating statistical moments of Y(X) to arbitrary lower and upper cutoff scales that may (but need not) be taken to represent data support and maximum watershed size; to describe ways of estimating the corresponding parameters; and to provide a theoretical basis for the heretofore unexplained observation that self‐affine amplitude fluctuations of basin boundaries and main channels (as measured by their variance), having a common Hurst exponent, are larger in the former than in the latter.

Deriving a global river network map and its sub-grid topographic characteristics from a fine-resolution flow direction map

Abstract. This paper proposes an improved method for converting a fine-resolution flow direction map into a coarse-resolution river network map for use in global river routing models. The proposed method attempts to preserve the river network structure of an original fine-resolution map in the upscaling procedure, as this has not been achieved with previous upscaling methods. We describe an improved method in which a downstream cell can be flexibly located on any cell in the river network map. The improved method preserves the river network structure of the original flow direction map and allows automated construction of river network maps at any resolution. Automated construction of a river network map is helpful for attaching sub-grid topographic information, such as realistic river meanderings and drainage boundaries, onto the upscaled river network map. The advantages of the proposed method are expected to enhance the ability of global river routing models by providing ways to more precisely represent surface water storage and movement.

Effects of intersite dependence of nested catchment structures on probabilistic regional envelope curves

Abstract. This study analyses the intersite dependence of nested catchment structures by modelling cross-correlations for pairs of nested and unnested catchments separately. Probabilistic regional envelope curves are utilised to derive regional flood quantiles for 89 catchments located in Saxony, in the Southeast of Germany. The study area has a nested structure and the intersite correlation is much stronger for nested pairs of catchments than for unnested ones. Pooling groups of sites (regions) are constructed based on several candidate sets of catchment descriptors using the Region of Influence method. Probabilistic regional envelope curves are derived on the basis of flood flows observed within the pooling groups. Their estimated recurrence intervals are based on the number of effective sample years of data (i.e. equivalent number of uncorrelated data). The evaluation of the effective sample years of data requires the modelling of intersite dependence. We perform this globally, using a cross-correlation function for the whole study area as well as by using two different cross-correlation functions, one for nested pairs and another for unnested pairs. In the majority of the cases, these two modelling approaches yield significantly different estimates for the effective sample years of data, and therefore also for the recurrence intervals. The reduction of the recurrence interval when using two different cross-correlation functions is larger for larger pooling groups and for pooling groups with a higher fraction of nested catchments. A separation into nested and unnested pairs of catchments gives a more realistic representation of the characteristic river network structure and improves the estimation of regional information content. Hence, applying two different cross-correlation functions is recommended.

Erosion on a line

An erosion model is proposed to calculate erosion rates for plane-strain models in which the Earth's surface is represented on a line. The fundamentals of river erosion networks are captured by two principles, Hack's Law, which describes the drainage area structure of river network and a stream-power erosion law, which describes the rate of incision of a river. For a simple morphology of parallel transverse rivers with rectangular drainage basins, this allows the earth's surface to be parameterized by two heights: the trunk stream channel height and the interfluvial ridge height. The resulting expressions are solved for the simple cases of constant uplift rate and a constant mean slope as occurs in critical wedge problems. In the latter case, the uplift rate is variable and changes in space so that the trunk channel elevation and the interfluvial ridge elevation average to maintain a constant mean slope. A general, numerical solution is presented for application to any numerical model with arbitrary surface velocity, variable rock erodibility and precipitation. This algorithm is coupled to a plane-strain, plastic-deformation model to demonstrate the utility of the model.

Aspects in the evolution of the hydrographical network from the Lower Siret Plain reflected in cartographic materials

Situated in the north-eastern part of the Romanian Plain, Lower Siret Plain is known in literature as one of the youngest and lowest regions of Romania. It is also currently an important area of subsidence, responsible for the convergence of the main rivers flowing from the Carpathian’s and Sub-Carpathian’s Curvature to Siret, the main drainage axis. Following these issues and also due to some human intervention, river beds have suffered over the years many amendments, reflected in the detail geomorphology of the region (dead river beds, abandoned banks, oxbows etc.) and, the most recent, in the cartographic materials. All natural transformations of the river network structure were mainly related to the alluvial contribution of the tributaries with Carpathian and Sub-Carpathian origin, which continuously raised the right part of Siret’s alluvial plain, forcing the river to move eastward and finally determining the recalibration of the entire network. Traces of such an important and recent river bed dynamics are still visible today and are indirectly confirmed by historical documents. These indicate that in some areas, the lower parts of the main rivers are very young. Article examines how the available cartographic materials report recent dynamics of the main rivers of Lower Siret Plain and can explain the age of the present river pattern. Among the conclusions is that the maps made by the end of the seventeenth century and early-twentieth century reflects little of that time geographical realities, that, so far, the Siret river had abandoned its old bed located west of the current and named on various maps - Siretel (Little Siret). In this abandoned river bed continued to flow all the rivers of the SubCarpathian bend, except Buzau river, until the middle of the eighteenth century, when some areas were clogged and tributary rivers have had to extend their lower courses to the new Siret. Thus, the current configuration of the hydrographic network seems to date, with few exceptions,from the first half of the nineteenth century.

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.

Macroinvertebrate diversity in headwater streams: a review

Summary1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the ‘health’ of whole river networks.2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid‐order streams.4. When stream systems are viewed as networks at the landscape‐scale, α‐diversity may be low in individual headwater streams but high β‐diversity among headwater streams within catchments and among catchments may generate high γ‐diversity.5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β‐diversity among headwater streams both within and among catchments.6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.

Neutral metacommunity models predict fish diversity patterns in Mississippi–Missouri basin

River networks, seen as ecological corridors featuring connected and hierarchical dendritic landscapes for animals and plants, present unique challenges and opportunities for testing biogeographical theories and macroecological laws. Although local and basin-scale differences in riverine fish diversity have been analysed as functions of energy availability and habitat heterogeneity, scale-dependent environmental conditions and river discharge, a model that predicts a comprehensive set of system-wide diversity patterns has been hard to find. Here we show that fish diversity patterns throughout the Mississippi-Missouri River System are well described by a neutral metacommunity model coupled with an appropriate habitat capacity distribution and dispersal kernel. River network structure acts as an effective template for characterizing spatial attributes of fish biodiversity. We show that estimates of average dispersal behaviour and habitat capacities, objectively calculated from average runoff production, yield reliable predictions of large-scale spatial biodiversity patterns in riverine systems. The success of the neutral theory in two-dimensional forest ecosystems and here in dendritic riverine ecosystems suggests the possible application of neutral metacommunity models in a diverse suite of ecosystems. This framework offers direct linkage from large-scale forcing, such as global climate change, to biodiversity patterns.

Patterns of vegetation biodiversity: The roles of dispersal directionality and river network structure

This paper investigates the importance of dispersal directionality and river network structure to biodiversity patterns. Our model results suggest that dispersal directionality plays a crucial role in determining biodiversity patterns, even more so than dispersal rates. Dispersal directionality heterogenizes the spatial distribution of abundance, which results in higher extinction rates of rare species and higher β diversity. It induces a few species with very high abundances at the expense of many species with intermediate abundances, thereby lowering α and γ diversities. The river network structure also increases β diversity, i.e., more heterogeneous ecosystems, in comparison to typical two-dimensional landscapes. We find that the interplay between the dispersal directionality and network topology has important consequences on relative species abundance patterns and the distribution of α diversity.

Inevitable self-similar topology of binary trees and their diverse hierarchical density

Self-similar topology, which can be characterized as power law size distribution, has been found in diverse tree networks ranging from river networks to taxonomic trees. In this study, we find that the statistical self-similar topology is an inevitable consequence of any full binary tree organization. We show this by coding a binary tree as a unique bifurcation string. This coding scheme allows us to investigate trees over the realm from deterministic to entirely random trees. To obtain partial random trees, partial random perturbation is added to the deterministic trees by an operator similar to that used in genetic algorithms. Our analysis shows that the hierarchical density of binary trees is more diverse than has been described in earlier studies. We find that the connectivity structure of river networks is far from strict self-similar trees. On the other hand, organization of some social networks is close to deterministic supercritical trees.

River networks and ecological corridors: Reactive transport on fractals, migration fronts, hydrochory

Moving from a recent quantitative model of the US colonization in the 19th century that relies on analytical and numerical results of reactive‐diffusive transport on fractal river networks, this paper considers its generalization to include an embedded flow direction which biases transport. We explore the properties of biased reaction‐dispersal models, in which the reaction rates are described by a logistic equation. The relevance of the work is related to the prediction of the role of hydrologic controls on invasion processes (of species, populations, propagules, or infective agents, depending on the specifics of reaction and transport) occurring in river basins. Exact solutions are obtained along with general numerical solutions, which are applied to fractal constructs like Peano basins and real rivers. We also explore similarities and departures from different one‐dimensional invasion models where a bias is added to both the diffusion and the telegraph equations, considering their respective ecological insight. We find that the geometrical constraints imposed by the fractal networks imply strong corrections on the speed of traveling fronts that can be enhanced or smoothed by the bias. Applications to real river networks show that the chief morphological parameters affecting the front speed are those characterizing the node‐to‐node distances measured along the network structure. The spatial density and number of reactive sites thus prove to be a vital hydrologic control on invasions. We argue that our solutions, currently tied to the validity of the logistic growth, might be relevant to the general study of species' spreading along ecological corridors defined by the river network structure.

A neutral metapopulation model of biodiversity in river networks

In this paper, we develop a stochastic, discrete, structured metapopulation model to explore the dynamics and patterns of biodiversity of riparian vegetation. In the model, individual plants spread along a branched network via directional dispersal and undergo neutral ecological drift. Simulation results suggest that in comparison to 2-D landscapes with non-directional dispersal, river networks with directional dispersal have lower local ( α ) and overall ( γ ) diversities, but higher between-community ( β ) diversity, implying that riparian species are distributed in a more localized pattern and more vulnerable to local extinction. The relative abundance patterns also change, such that higher percentages of species are in low-abundance, or rare, classes, accompanied by concave rank-abundance curves. In contrast to existing theories, the results suggest that in river networks, increased directional dispersal reduces α diversity. These altered patterns and trends result from the combined effects of directionality of dispersal and river network structure, whose relative importance is in need of continuing study. In addition, riparian communities obeying neutral dynamics seem to exhibit abrupt changes where large tributaries confluence; this pattern may provide a signature to identify types of interspecific dynamics in river networks.

Allometric relationships between traveltime channel networks, convex hulls, and convexity measures

The channel network (S) is a nonconvex set, while its basin [C(S)] is convex. We remove open‐end points of the channel connectivity network iteratively to generate a traveltime sequence of networks (Sn). The convex hulls of these traveltime networks provide an interesting topological quantity, which has not been noted thus far. We compute lengths of shrinking traveltime networks L(Sn) and areas of corresponding convex hulls C(Sn), the ratios of which provide convexity measures CM(Sn) of traveltime networks. A statistically significant scaling relationship is found for a model network in the form L(Sn) ∼ A[C(Sn)]0.57. From the plots of the lengths of these traveltime networks and the areas of their corresponding convex hulls as functions of convexity measures, new power law relations are derived. Such relations for a model network are CM(Sn) ∼ and CM(Sn) ∼ . In addition to the model study, these relations for networks derived from seven subbasins of Cameron Highlands region of Peninsular Malaysia are provided. Further studies are needed on a large number of channel networks of distinct sizes and topologies to understand the relationships of these new exponents with other scaling exponents that define the scaling structure of river networks.