CPY Document

,. - vasting debris regardless of GIDMDRPHDlDGY he impacts on Geomorphology 31 (1999) 229-245 earch. Equally ELSEVIER s of channels rts to enhance nto considera- bris contribu- wasting as a Fluvial geomorphology and river engineering: future roles woody debris utilizing a fluvial hydro systems framework David 1. Gilvear * Department of Environmental Science, University of Stirling, Scotland, FK94LA, UK ironmental Ethics Received I May 1997; received in revised form 30 June 1997; accepted 15 July 1997 gun. Unpublished metric analysis of . Band 46, 67-77. Abstract , L. , 1982. Con- basins. Sediment River engineering is coming under increasing public scrutiny given failures to prevent flood hazards and economic and ,sins. U. S. Forest environmental concerns. This paper reviews the contribution that fluvial geomorphology can make in the future to river engineering. In paricular, it highlights the need for fluvial geomorphology to be an integral par in engineering projects, that . Integrated flood implementation, and post-project appraisal stages of engineering projects. It should be bservation Maga- is, to be integral to the planning, proactive rather than reactive. Areas in which geomorphologists wil increasingly be able to complement engineers in river , 3- management include risk and environmental impact assessment, floodplain planning, river audits, determnation of instream curring on a Mc- flow needs, river restoration, and design of ecologically acceptable channels and structures. There are four key contributions d MS thesis, De- that fluvial geomorphology can make to the engineering profession with regard to river and floodplain management: 'ersity. ation to geology. 1. to promote recognition of lateral, vertical, and downstream connectivity in the fluvial system and the inter-relationships xtland, OR, dated between river planform, profile, and cross-section; 2. to stress the importance of understanding fluvial history and chronology over a range of time scales, and recognizing the elected landslides significance of both palaeo and active landforms and deposits as indicators of levels of landscape stabilty; 'gon. Unpublished 3. to highlight the sensitivity of geomorphic systems to environmental disturbances and change, especially when close to gon State Univer- geomorphic thesholds, ard the dynamcs of the natural systems; and 4. to demonstrate the importance of landforms and processes in controllng and defining fluvial biotopes and to thus promote ecologically acceptable engineering. Challenges facing fluvial geomorphology include: gaining full acceptance by the engineering profession; widespread utilization of new technologies including GPS, GIS , image analysis of satellite and airborne remote sensing data computer-based hydraulic modeling and geophysical technques; dovetailing engineering approaches to the study of river channels which emphasize reach-scale flow resistance, shear stresses, and material strength with catchment scale geomorphic approaches , empirical predictions, bed and bank processes, landform evolution, and magnitude-frequency concepts; * Fax: +44- 1786-467843. E-mail address: djglCistir.ac.uk(DJ. Gilvear). 0169-555X/99/$ - see front matter 1999 Elsevier Science B.V. All rights reserved. PIT: SOI69- 555X(99)00086- 230 D.J Gilvear 1 Geomorphology 31 (1999) 229-245 producing accepted river channel typologies; fundamental research aimed at producing more reliable deterministic for prediction of bed and bank stability and bedload transport; and collaboration with aquatic biologists to determineequations the role and importance of geomorphologically and hydraulically defined habitats. (Q 1999 Elsevier Science B. V. All rights reserved Keywords: fluvial; geomorphology; river engineering; risk assessment; environmental impact; river restoration 1. Introduction In addition , the recent interest in geomorphology stems from the desire to minimize flood damage A few decades ago, the relationship between flu- , the vial geomorphology and river requirement to reduce environmental degradation as engineering was un- a result of river engineering schemes (Hey, clear. Engineering involved the use of straight trape- 1996), a move toward restoring ' sterile ' channelized zoidal channels, impoundments, embankents, and a river range of training Strctures to control rivers and their channel reaches to ecologically valuable and aesthet- flow. Little consideration was given to ically pleasing watercourses (e. , Larson, 1996), and downstream concern with regard to the response of river channels environmental impacts, and when engineering struc- to climate change scenarios (Gilvear and Black tures failed, it was normally explained by ' design flood exceedance rather than that the 1999). dynamics of A number of areas in which fluvial the geomorphic system had not been taken into geomorphol- account. At the same time ogy is directly relevant to river engineering and , geomorphology was gen- management are shown in Table 1. More erally concerned with landscape evolution over generally, timescales that seemed inappropriate to the realm of application of a geomorphological approach involving the following the engineer, and fluvial geomorphology was in its principles would be beneficial to infancy. Over the last few decades river engineering. , however, the disciplines have been on converging paths. Indeed by 1988 a book had been published entitled Fluvial Principle 1. The river channel functions as a three- Processes In River Engineering (Chang, 1988). A dimensional form with longitudinal , transverse more recent ilustration of convergence is that fluvial , and vertical dimensions involving changes in morphol- geomorphologists have recently published a guide- ogy and fluxes of water and sediment. book for the US Ary Corps of Engineers (Thome et aI. , 1997). Perhaps the most important develop- ment over the last decade has been geomorpholo- Principle 2. The river system functions in response to water and sediment gists' move from undertakng relevant or applicable inputs from the upstream catchment. research (Gregory, 1985; Hooke, 1988) to studies in which outcomes are put into practice (e. , Brookes 1992, 1995). An indication that geomorphology can Principle 3. The size, shape, and planform of a river contribute to engineering has been its success in normally varies through time, but the dynamics of assessing the feasibility of using engineering to natural channel adjustment varies between and along tame' the mighty Brahmaputra in Bangladesh (e. rivers. Thome et aI. , 1993). The change in the relationship between fluvial geomorphology and engineering has resulted in par Principle 4. The geomorphic stability of a river from a trend toward process studies, increased pro- system can be upset by such activities as river fessionalism among geomorphologists, greater quan- training, removing riparian vegetation, land use, and tification, adoption of common methodologies and climatic change. The sensitivity of river channels to tools (i. , computer-based hydraulic modeling, re- change varies between and along rivers. mote sensing, GIS, GPS , etc. ) (Cornelius et aI. 1994), and the requirements of geomorphologists to seek funding for their studies from research councils. Principle 5. Fluvial landforms , substrates , and processes define habitats for biota while vegetation and D.J. Gilvear 1 Geomorphology 31 (1999) 229-245 231 :rministic equations ) determine the role ects of fluvial geomorphology with direct relevance to river engineering (number of key areas taken from Brookes, 1995) All rights reserved. Connectivity within the fluvial hydrosystem and environmental impact field techniques and surveys enabling sediment sources to be traced ( Quantitati ( StUdies of the downstream impacts on ri:,er ch nel mo y of ri,:er regulation, channelisation, and river training sedIment YIeld predIctIOn II relatIOn to land use change ( Preliminar equations for catchment (e.g., agriculture, mining, deforestation and urbanisation), and assessment of the impact of change on the downstream fluvial system l geomorphology Historical legacy, chronology and channel adjustments 100d damage, the ( StUdies of channel process (e. , bed and bank erosion and bedload and suspended sediment transport rates) al degradation as ( Examination of the role of importance of floodplain stratigraphy on channel adjustment ~s (Hey, 1996), a ( Quantificatio of rates and modes of sediment movement within the fluvial system :hannelized river ( StUdies of past channel adjustment in relation to climatic and anthropogenic change table and aesthet- Landscape sensitivity arson, 1996), and ( Qualitative and quantitative field techniques and modellng to identify instabilty of river channels ( Analysis of river channel cross-sections and planform to predict future change ( The influence of large flood events, land use changes and climate changes vear and Black Eco-geomorphology vial geomorphol- ( Appraisal and design of mitigation and enhancement measures and restoration projects ( Determination of instream flow requirements engineering and ( Fluvial auditing and river channel typologies More generally, approach involv- Headings within text. be beneficial to woody debris play an important role in determning headwaters to mouth via the concept of downstream fluvial processes. hydraulic geometr. This unidirectional approach has resulted in an understanding of longitudinal connec- Rather than looking back and examining the link- :tions as a three- tivity in the river system, with upstream

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