A Field Guide to British Rivers. George Heritage

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Figure 1.4 Typical heavily modified upland system, straightened, walled, and dredged. The Upper Whit Beck at Low Lorton.

Examples of naturally functioning fluvial systems are few and far between, existing only as small fragments developing because of a lack of system management. Nevertheless, these reaches offer valuable insights into how our rivers and floodplains would function when unconstrained, acting as exemplars against which we should be judging our present systems. On lowland rivers, the propensity appears to be one of the development of a low‐gradient stable multiple channel river network well connected to intervening areas of floodplain (Figure 1.5). The recovery of such areas appears strongly influenced by vegetation which acts as the precursor to sediment deposition and consolidation and creates high levels of local morphologic, hydrologic, and hydraulic diversity. Development of such systems remains highly restricted, but their form and functionality, even at a local scale, offers clear indications of how many lowland systems should look and behave.

Upland systems appear to be naturalising most strongly through in‐channel feature re‐development leading to enhanced local bank erosion and lateral reworking of floodplain sediment, which on many rivers has created a well‐connected narrow inset floodplain (Figure 1.6). On more energetic systems, the loss of constraints on channel movement has seen the development of strong active meandering systems (Figure 1.7), or wandering channel networks (Figure 1.8), both of which offer considerably higher morphologic, hydrologic, and hydraulic diversity over their previously managed state.

1.5 Purpose of This Book

This book aims to highlight the true form and function of watercourses and valley bottom areas using examples from the British Isles on which the authors have worked, either individually or together, over the last three decades. The intention is to encourage the reader to view fluvial systems, and their potential for management and restoration in a new light using examples of functional river types. The book will act as a guide to recognising these river types, and Chapter 2 serves to illustrate and widen understanding of their classification into different functional types based on character and complexity. In Chapter 3, we illustrate the morphological unit makeup of, and drivers and processes behind, each river type through a comprehensive photographic guide, and review the current research understanding of their form and function through a focussed review of published studies. Whilst we include examples of the science from outside the British Isles, these studies all focus on temperate rivers, and all examples of functional river types used are from the United Kingdom. Of great value to the river scientist is the ability to infer fluvial processes and probable directions of fluvial change from the current morphology of the system, and in Chapter 4, we provide a guide to “reading” rivers, describing key watercourse indicators that help in this task. Finally in Chapter 5, we provide some thoughts regarding sensitive and appropriate management for British rivers going forward.

Figure 1.5 Semi‐natural multi‐channel network on the River Narr.

Figure 1.6 Laterally migrating active channel on the River Mallart, Syre, northern Scotland.

Figure 1.7 Active reach of the River Glen at Kirknewton, Northumberland, showing bank erosion and bar formation.

Figure 1.8 Wandering reach of the River South Esk, Scotland, showing sediment deposition and temporary storage.

2 River Types: A Brief Overview

      2.1 Introduction

      The pattern and features of any watercourse are influenced by the river type and its sediment load, as well as by the environment through which the stream flows (its catchment). Furthermore, the form of a channel both influences and reflects the processes active in the stream system. As such, the classification of channel form can help those concerned with rivers to understand the hydraulic and sediment processes acting on a watercourse and how the physical nature of the watercourse modifies local processes (Rosgen 1994). An appropriate river typology is thus a valuable tool when trying to understand and work with a watercourse and can facilitate interventions in rivers and across floodplains which work with current and restored processes to provide sustainable systems for the future. This short chapter reviews a wide variety of classifications developed for rivers.

2.2 Classification

      River and floodplain systems exist СКАЧАТЬ