Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

The Ecology of Interfaces: Riparian Zones

Two features characterize all natural communities. First, they are dynamic systems. The densities and age-structures of populations change with time, as do the relative abundances of species; local extinctions are commonplace (37). For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated (36). The idea that equilibrium is rarely achieved on the local scale was expressed decades ago by a number of forest ecologists (e.g. 10 1, 168). One might even argue that continued application of the concept of climax to natural systems is simply an exercise in metaphysics (41). While this view may seem extreme, major climatic shifts often recur at time intervals shorter than that required for a community to reach competitive equilibrium or alter the geographical distributions of species (6, 21, 43, 76, 92). Climatic variation of this kind influences ecological patterns over large areas, sometimes encompassing entire continents. Other agents of temporal change in natural communities operate over a wide range of smaller spatial scales (47, 242). Second, natural communities are spatially heterogeneous. This statement is true at any scale of resolution (242), but it is especially apparent on what is commonly referred to as the regional scale. (By region I mean an area that potentially encompasses more than one colonizable patch.) Across any land or seascape, one observes a mosaic of patches identified by spatial discontinuities in the distributions of populations (153, 159, 161, 231, 239, 240). Closer examination often reveals a smaller-scale patchwork of same-aged individuals (e.g. 85-87, 101, 146, 199,204,217-220,235,246). Discrete patch boundaries sometimes reflect species-specific responses to

The Role of Disturbance in Natural Communities

Architectural-Element Analysis: A New Method of Facies Analysis Applied to Fluvial Deposits

A classification system for natural rivers is presented in which a morphological arrangement of stream characteristics is organized into relatively homogeneous stream types. This paper describes morphologically similar stream reaches that are divided into 7 major stream type categories that differ in entrenchment, gradient, width/depth ratio, and sinuosity in various landforms. Within each major category are six additional types delineated by dominate channel materials from bedrock to silt/clay along a continuum of gradient ranges. Recent stream type data used to further define classification interrelationships were derived from 450 rivers throughout the U.S, Canada, and New Zealand. Data used in the development of this classification involved a great diversity of hydro-physiographic/geomorphic provinces from small to large rivers and in catchments from headwater streams in the mountains to the coastal plains. A stream hierarchical inventory system is presented which utilizes the stream classification system. Examples for use of this stream classification system for engineering, fish habitat enhancement, restoration and water resource management applications are presented. Specific examples of these applications include hydraulic geometry relations, sediment supply/availability, fish habitat structure evaluation, flow resistance, critical shear stress estimates, shear stress/velocity relations, streambank erodibility potential, management interpretations, sequences of morphological evolution, and river restoration principles.

https://www.cpp.edu/~marshall/rs414/RS414_Readings/Rosgen_94_Classification_of_Natural_Rivers.pdf

A classification of natural rivers

Summary
Fluvial landforms and deposits provide one of the most readily studied Quaternary continental records, and alluvial strata represent an important component in most ancient continental interior and continental margin successions. Moreover, studies of the long-term dynamics of fluvial systems and their responses to external or ‘allogenic' controls, can play important roles in research concerning both global change and sequence-stratigraphy, as well as in studies of the dynamic interactions between tectonic activity and surface processes. These themes were energized in the final decades of the twentieth century, and may become increasingly important in the first decades of this millennium.

This review paper provides a historical perspective on the development of ideas in the fields of geomorphology/Quaternary geology vs. sedimentary geology, and then summarizes key processes that operate to produce alluvial stratigraphic records over time-scales of 103−106 years. Of particular interest are changes in discharge regimes, sediment supply and sediment storage en route from source terrains to sedimentary basins, as well as changes in sea-level and the concept of accommodation. Late Quaternary stratigraphic records from the Loire (France), Mississippi (USA), Colorado (Texas, USA) and Rhine–Meuse (The Netherlands) Rivers are used to illustrate the influences of climate change on continental interior rivers, as well as the influence of interacting climate and sea-level change on continental margin systems.

The paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea-level change. At present, empirical field-based research on fluvial response to climate and sea-level change lags behind: (a) the global change community's understanding of the magnitude and frequency of climate and sea-level change; (b) the sequence-stratigraphic community's desire to interpret climate and, especially, sea-level change as forcing mechanisms; and (c) the modelling community's ability to generate numerical and physical models of surface processes and their stratigraphic results. A major challenge for the future is to catch up, which will require the development of more detailed and sophisticated Quaternary stratigraphic, sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings. There is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter (102−103 years) and longer (104−106 years) time-scales than has commonly been the case to date, as well as in larger river systems, from source to sink. Studies of Quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre-Quaternary rock record.

Fluvial responses to climate and sea‐level change: a review and look forward

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1989&context=smhpapers

A genetic classification of floodplains

Anabranching rivers consist of multiple channels separated by vegetated semi-permanent alluvial islands excised from existing floodplain or formed by within-channel or deltaic accretion. These rivers occupy a wide range of environments from low to high energy, however, their existence has never been adequately explained. They occur concurrently with other types of channel pattern, although specific requirements include a flood-dominated flow regime and banks that are resistant to erosion, with some systems characterized by mechanisms to block or constrict channels, thereby triggering avulsion. The fundamental advantage of an anabranching river is that, by constructing a semi-permanent system of multiple channels, it can concentrate stream flow and maximize bed-sediment transport (work per unit area of the bed) under conditions where there is little or no opportunity to increase gradient. On the basis of stream energy, sediment size and morphological characteristics, six types of anabranching river are recognized; types 1–3 are lower energy and types 4–6 are higher energy systems. Type 1 are cohesive sediment rivers (commonly termed anastomosing) with low w/d ratio channels that exhibit little or no lateral migration. They are divisible into three subtypes based on vegetative and sedimentary environment. Type 2 are sand-dominated, island-forming rivers, and type 3 are mixed-load laterally active meandering rivers. Type 4 are sand-dominated, ridge-forming rivers characterized by long, parallel, channel-dividing ridges. Type 5 are gravel-dominated, laterally active systems that interface between meandering and braiding in mountainous regions. Type 6 are gravel-dominated, stable systems that occur as non-migrating channels in small, relatively steep basins. Anabranching rivers represent a relatively uncommon but widespread and distinctive group that, because of particular sedimentary, energy-gradient and other hydraulic conditions, operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges.

Anabranching rivers: their cause, character and classification

Dendrochronological surveys on ten point-bar complexes on the Beatton River, northeast British Columbia, provide the basis for measurement of lateral migration and incision during the last 250 yr. The rate of channel-bend migration reaches a maximum value where the ratio radius of channel curvature to stream width ( r m / w m ) approximates 3.0. The rate of channel migration rapidly declines for bends with values of r m / w m greater or less than 3.0. In addition, the spacing of flood-plain ridges ( d ) increases with increasing rates of bend migration. Equations for predicting the migration rate ( M , meters/year) on the study reach take the form:

(see pdf for equation)

The Character of Channel Migration on the Beatton River, Northeast British Columbia, Canada

This paper describes flood plains formed episodically by vertical accretion along high-energy, laterally stable channels, in southeastern Australia. Overbank deposition gradually builds a flood plain of fine-textured alluvium over a period of hundreds or thousands of years, following which catastrophic erosion by a single large flood, or a series of more moderate floods, strips the flood plain to a basal lag deposit from which it slowly reforms. This periodic destruction appears due to the progressive development of large levee banks and flood-plain surfaces of highly variable relief. As the levees and flood plain grow, overbank flow is gradually displaced from the broad flood plain into the main channel and flood-plain backchannels, with a resulting concentration of erosional energy. Eventually, high flows greatly exceed erosional thresholds, and wholesale scour of the channel boundary and flood plain occurs. Vertical-accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals, even along the same river. Some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime. The almost random but catastrophic nature of this flood-plain erosion means that sediment supply and transport are highly variable and probably impossible to predict. This model of flood-plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial, coarsegrained, traction-load flood plains along high-energy rivers in narrow gorges to extensive low-gradient flood plains in which alluvial stratigraphy is dominated by fine-grained overbank deposition.

Episodes of vertical accretion and catastrophic stripping: A model of disequilibrium flood-plain development

This study examines the morphology, sedimentology and genesis of the point bars and floodplain of the Beatton River. The formation of point bars occurs in distinct stages. An initial point bar platform composed mainly of coarse sediment is formed adjacent to the convex bank of a migrating meander bend, and is the base on which develops a single scroll bar of fine traction and suspended load. With continued sedimentation, the scroll bar grows, eventually supporting vegetation and becoming a floodplain ridge. Scroll bars form with greatest size and frequency in rapidly migrating bends, and the shape of the meander bend appears to determine both the location of the initial bar deposit, and its direction of growth up or downstream. Approximately one-half of the floodplain sediment is derived from suspended load, and the initiation of a scroll bar appears to be due to excessive deposition of suspended load in a zone of flow separation over a point bar platform. The critical flow condition for the initiation of a scroll bar does not occur with the same recurrence interval on different shaped meander bends, however, the average recurrence interval within the study reach is approximately every 30 years. Sedimentation rates on point bars and on the floodplain indicate two relatively distinct stages of floodplain alluviation. The most rapid is for surfaces less than 50 years old, although sediment accumulation still persists on surfaces up to 250 years in age. Although frequently flooded, surfaces older than this accumulate very little sediment. Despite 2–3 m of overbank deposition, the amplitude of floodplain ridges is maintained by secondary currents which sweep sediment from the swales towards the ridge crests.

Gerald C. Nanson

Papers

A genetic classification of floodplains

Anabranching rivers: their cause, character and classification

The Character of Channel Migration on the Beatton River, Northeast British Columbia, Canada

Episodes of vertical accretion and catastrophic stripping: A model of disequilibrium flood-plain development

Point bar and floodplain formation of the meandering Beatton River, northeastern British Columbia, Canada