Tools in Fluvial Geomorphology

G. Mathias Kondolf, Hervé Piégay

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781118648575
• Edition: 2
• Topic: Sciences physiques
• Subtopic: Géologie et sciences de la Terre

Fluvial Geomorphology studies the biophysical processes acting in rivers, and the sediment patterns and landforms resulting from them. It is a discipline of synthesis, with roots in geology, geography, and river engineering, and with strong interactions with allied fields such as ecology, engineering and landscape architecture. This book comprehensively reviews tools used in fluvial geomorphology, at a level suitable to guide the selection of research methods for a given question. Presenting an integrated approach to the interdisciplinary nature of the subject, it provides guidance for researchers and professionals on the tools available to answer questions on river restoration and management. Thoroughly updated since the first edition in 2003 by experts in their subfields, the book presents state-of-the-art tools that have revolutionized fluvial geomorphology in recent decades, such as physical and numerical modelling, remote sensing and GIS, new field techniques, advances in dating, tracking and sourcing, statistical approaches as well as more traditional methods such as the systems framework, stratigraphic analysis, form and flow characterisation and historical analysis. This book:

• Covers five main types of geomorphological questions and their associated tools: historical framework; spatial framework; chemical, physical and biological methods; analysis of processes and forms; and future understanding framework.
• Provides guidance on advantages and limitations of different tools for different applications, data sources, equipment and supplies needed, and case studies illustrating their application in an integrated perspective.

It is an essential resource for researchers and professional geomorphologists, hydrologists, geologists, engineers, planners, and ecologists concerned with river management, conservation and restoration. It is a useful supplementary textbook for upper level undergraduate and graduate courses in Geography, Geology, Environmental Science, Civil and Environmental Engineering, and interdisciplinary courses in river management and restoration.

Section V

Analysis of Processes and Forms: Water and Sediment Interactions

Chapter 11
Channel form and adjustment: characterization, measurement, interpretation and analysis

Andrew Simon¹, Janine Castro² and Massimo Rinaldi³

¹Cardno ENTRIX, Oxford, MS, USA

²US Fish and Wildlife Service, Portland, OR, USA

³Università degli Studi di Firenze, Florence, Italy

11.1 Introduction

Channel form, or morphology, has long been recognized as a diagnostic tool in evaluating fluvial landforms. Since Davis (1909) conceptualized the temporal aspect of channel and drainage basin evolution in the ‘cycle of erosion’, geographers, geologists and geomorphologists have used channel form as a parameter in the classification, analysis and prediction of fluvial response. Davis's view of fluvial landscapes was simplistic but, in combination with the detailed measurements of channel forms and processes in the studies by Gilbert (1914), we can envision these works as representing opposite approaches by which to direct future work. Davis's work represents large-scale, qualitative assessments of channel form by which inferences about smaller scale processes were advanced. Conversely, Gilbert's work represents the use of quantitative measurements by which inferences about larger scale processes were advanced. The implied links between channel form and process have been central in understanding fluvial geomorphology and, as such, have been the topic of many textbooks (e.g. Leopold et al. 1964; Morisawa 1968; Gregory and Walling 1973; Schumm 1977; Richards 1982; Knighton 1998).

Channel form includes aspects of the shape of a stream in profile, cross-section and planform. Profile characteristics include channel-bed gradient and valley slope and features such as pools, riffles and cascades. Cross-sectional characteristics include channel width and depth and features such as the bed, bars, banks, floodplains and terraces. Planform characteristics include sinuosity, meander wavelength and belt width and features such as meanders, braids and abandoned channels. Channel form measurements and descriptions can be used in combination with other attributes of a stream system, such as riparian vegetation and character of the boundary sediments, to infer dominant trends in channel processes and response (Simon and Hupp 1986; Simon 1989a; Montgomery and Buffington 1997; Elliott et al. 1999). However, using gross channel form in isolation to quantitatively predict channel behaviour, such as channel adjustments, system disturbances or rates of sediment transport, without rigorous analysis of channel processes is unsound (Miller and Ritter 1996). Hence the key to using channel form in the analysis of fluvial landforms must be based on either (i) measurements of parameters that aid in quantifying channel processes, such as flow hydraulics, sediment transport and bank stability, or (ii) observations of diagnostic characteristics that provide information on active channel processes. In turn, measurements should either directly or indirectly lead to analysis of those forces acting on the channel boundary and those forces resisting entrainment of boundary sediments. Change in channel form is a matter of the applied forces overcoming resistance.

The purpose of this chapter is to provide a synthetic overview of available techniques, methods and parameters for characterizing and measuring channel forms and analysing and interpreting changes over time. Hence the chapter is organized into two major components, characterization and measurement, followed by analysis and interpretation. Synthetic review of analysis of channel changes, including measurement of some of the parameters that aid in quantifying channel processes responsible for morphological changes, is also included.

Because of the broad scope of this chapter, it is not possible to address specifically all channel form measurement and analysis techniques; however, there are several other chapters that focus on specific components, including: Chapter 4, Using historical data in fluvial geomorphology; Chapter 6, Analysis of aerial photography and other remotely sensed data for fluvial geomorphology and river science; Chapter 13, Measuring bed sediment; and Chapter 15, Sediment transport.

11.2 Characterization and measurement

Characterization and measurement of channel form provide information for river classification and studies on past and future channel changes. Following the basic tripartive division of channel patterns provided by Leopold and Wolman (1957) of braided, meandering and straight, various morphological classifications have been developed (e.g. Schumm 1977, 1981; Church 1992; Thorne 1997; Montgomery and Buffington 1997; Fuller et al. 2013; see also Chapter 7). For the scope of this chapter, an initial distinction is drawn between bedrock and alluvial channels. Channels formed in bedrock have a discontinuous or thin alluvial cover and cannot substantially widen, lower or shift their bed without eroding bedrock (Turowski et al. 2008), whereas channels formed in sediment that can be eroded, transported and deposited by the flow can be classified as alluvial or ‘self-formed’ (Thorne 1997). Alluvial channels adjust their form to the driving variables (i.e. water and sediment flow) and their interactions with the boundary characteristics, whereas forms and dimensions of bedrock channels are controlled by geological and structural factors.

Alluvial rivers display a wide spectrum of channel forms and morphological units on a variety of landforms, such as alluvial fans, confined alluvial valleys and wide alluvial valleys, that can be identified and classified during stream reconnaissance. They include bed morphology (i.e. cascade, step-pool, plane bed, riffle-pool, dune ripples) (Montgomery and Buffington 1997; Halwas and Church 2002), mid-channel or bank-attached sedimentary features (such as various types of bars, islands, benches, berms) (Brierley and Fryirs 2005) and fluvial forms in the alluvial plain (floodplain, terraces, secondary or abandoned channel...