traditional engineering methods, physical consequences and alternative practices

Abstract

The effect of humans on rivers and river channels has been widespread throughout the period of habitation of this planet. Water supply and land drainage schemes were implemented as early as 3200 BC (Drower, 1954) whilst in Britain river regulation was widely used by Domesday (Cole, 1976). Concern for the human impact on rivers has been expressed in an abundance of research papers and since about 1970 the geomorphological study of river channels has been increasingly concerned with channel adjustments which are significant in relation to practical problems (e.g. Hails, 1977;Schumm, 1977;Gregory, 1979a). This has arisen because of the extensive distribution and in many cases the intensive nature of environmental problems and because of the realization that geomorphologists can extend the understanding of complexities of fluvial systems.At least four components of applied research related to river channels can be identified. First there is a need to establish the ways in which river channel stability has been affected by a range of impacts and at this stage it is necessary to identify the various types of effects that particular structures or changes could have. Although the direct effects of engineering structures have been acknowledged by engineers for many years the more widespread effects of these structures were less well appreciated. For example, the potential occurrence of scour immediately below dams had to be allowed for at the design stage and equations were developed to predict scour in relation to local environmental and hydraulic conditions (e.g. Komura and Simons, 1967). However, the downstream effects of dams were less immediately obvious but geomorphological research during the last decade has revealed a series of effects which can persist for very considerable distances below dams.A second component has been to investigate the magnitude and spatial extent of the effects which can be identified along individual river channels and this has produced valuable results. For example, below reservoirs in Britain channel capacities may be reduced to as little as 0.31 times those expected (Petts, 1980) whilst the effects of the Aswan High Dam on the channel morphology persist downstream for 965 km (Kashef, 1981). More recently a third component has emerged as it has been realized that there is a range of strategies available for the management of channel adjustment effects. The need for practical application has been advocated at Apollo Group -UOP on February 7, 2015 ppg.sagepub.com Downloaded from

How Wetlands Affect Floods

“…water movement through small pore spaces in a fine textured soil, or rough geometry and debris obstructed river channels; Lin 2010; Thomas and Nisbet 2012) while other pathways enable rapid transfers of water downstream and may increase the size of the flood and reduce its lag time (e.g. overland flow generation or uniform, unobstructed river channels; Burt 1996;Brookes 1985). These processes can be divided into two main groups: (1) the movement of water from precipitation through or over the land surface to the river; and (2) the movement of water along the river channel.…”

Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge

“…Such changes cause the channel to adjust to a new equilibrium, or sometimes a state of disequilibrium (Brookes 1988;Knighton 1998;Surian and Rinaldi 2003). Straightened reaches usually experience an increase in shear stress and the capacity to transport bed material, leading to erosion and degradation of the channel bed, destruction of pool-riffle variability, and increased sedimentation and flooding downstream (Yearke 1971;Brookes 1985;Wyzga 2001;but see Petts 1984;Dietrich and others 1989;Talbot and Lapointe 2002). Although much of the channel work was conducted in rapids, most pristine rapids in the Swedish rivers were relatively gently-sloping with plenty of fine material available in sections with less turbulent flow, such as in backwaters and downstream of boulders.…”

Riparian proper functioning condition assessment to improve watershed management for water quality

“…Leopold et al (1964) (Brookes 1985;Simon and Rinaldi 2006). These alterations can significantly increase erosion and sediment discharge (figures 1, 2, and 3) (Simon 1989;Simon and Rinaldi 2006;Hupp et al 2009;Florsheim et al 2011).…”