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Floodplain processes
Journal of
Hydrology ELSEVIER
Journal of Hydrology 204 (1998) 301-303
Book Review
Floodplain Processes, by M.G. Anderson, D.E. Walling and P.D. Bates, John Wiley and Sons, Chichester, U.K. 658(+iv)pp, ISBN 0-471-96679-7, Hardback, £75.00.
Floodplain Processes incorporates chapters based on geomorphology, hydraulics and hydrology, with links to concerns of ecology and the human occupation of floodplains. The chapters are invited contributions from leading academics that provide the volume with far more coherence than is usually the case for themed conference proceedings. Also, the chapters are substantial reviews, which is a blessing if, like me, you get frustrated by intriguing conferencepaper titles which turn out to be only six sides in length as chapters. The book is split into four topic sections following a lead chapter which is a genuine attempt by the editors to explain the purpose and relevance of their text. The first section, on Floodplain Evolution, contains detailed summaries of floodplain development in planform (Howard) and cross-section (Brown) sandwiching a chapter by Marriott explaining an experiment into floodplain sediment transport. Howard's chapter complements and extends his 1992 review (Howard, 1992) with an account of prospects for modelling across a range of floodplain types. He focuses particularly on floodplain development in meandering streams (20 pp) and highlights the importance of meander kinematics alongside water and sediment transport processes. Brown traces processes of floodplain evolution relative to past environmental change, including a summary of techniques available for interpreting floodplain change. He then provides a generalised development history of north-western European floodplains highlighting the integral role of vegetation in floodplain development during the 0022-1694/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved 1°11 S 0 0 2 2 - 1 6 9 4 ( 9 7 ) 0 0 1 1 8 - 2
early to mid-Holocene period. Marriott links James' (1985) overbank sedimentation model to Crane's (1982) model of alluvial architecture as a starting point in deriving more realistic models of floodplain stratigraphic development, a theme that is returned to in the third section. The second section, on Floodplain Flows, incorporates 6 of the 19 chapters and focuses primarily on flow hydraulics. For hydrologists, it is noteworthy that several chapters recognise that hydrological variability has greater practical significance for accurate modelling than developing more sophisticated hydraulic models. This is stated by Knight and Shiono and Romanowicz et al. while Bates et al., provide an illustration whereby the zero flux floodplain boundaries are relaxed and floodplain flow is coupled with models of hillslope hydrology and floodplain infiltration. Hydrological concerns are not, of course, an excuse for ignoring study of detailed processes and Younis foresees future models based on predictions of real turbulence using Reynolds stress transport factors. One current constraint is that we cannot yet compute a fine enough mesh to model true turbulence (Hervouet and Van Haren). Mesh resolution is a second major theme in these chapters. Bates et al. note that higher mesh resolution is useful in avoiding topographic filtering effects, especially as related to inundation boundaries. Romanowicz et aL examine the issue further on the basis that, as a distributed problem, inundation boundaries require a distributed solution - - the GLUE (generalised likelihood uncertainty estimation) approach is detailed. One practical aspect of current modelling constraints is that, through their data efficiency, one-dimensional models of floodplain flows may have greater longevity than might otherwise be expected. In this respect, 1-D models which segment channel and floodplain flows
302
Book Review
using simple roughness characterisation before a final global correction seem most appropriate (Knight and Shiono; Sellin and Willetts). The section on Floodplain Sediment Transport and Water Quality covers a wide variety of issues. Falconer and Chen address the issues of modelling of flow, sediment transport and water quality in tidal floodplains focusing on Poole Harbour, UK, re-emphasising many issues from the previous section. The following two chapters link strongly to the first section of the text: Walling et al. review the importance of overbank processes in floodplain formation and illustrate the role of microtopography and complex diffusion effects stemming from the difference between "effective" and "ultimate" suspended sediment transport dynamics. Macklin considers the dynamics of heavy metals as indicators of channel metamorphosis, as tracers and as indicators of rapid environmental change wherein processes of remobilisation are a major headache for environmental protection policies. Burt and Haycock's review of floodplains as transitional zones focuses on the efficacy of floodplain buffer zones as sinks for nitrogen and phosphorus. The consequence of potentially complex subsurface hydrology imparted by floodplain architecture and valley slope requires solutions in which buffer zones are linked to the risk of pollutant production. This requires strategic planning of the whole drainage basin and links neatly to the final section. The final section, on Floodplain Management, is characterised by a hydroecological theme centred on the benefits of the "flood pulse" in ensuring floodplain integrity. Petts considers this theme explicitly arguing the case for the flood pulse in maintaining river corridor patch diversity especially in large floodplain rivers. In relation to semi-arid/arid areas, Jolly notes that natural floodplains may be the only " w e t " area (if PE>Rf) and will have a disproportionate ecological importance. Therefore, the impact of river regulation may be especially severe and episodic flooding is critical to dilute soil salinisation caused by the perennial flow of regulated rivers. For river restoration, Brookes argues that, where land ownership problems can be overcome, restoring the flood pulse may provide the basis for cost-effective, largescale river restoration. Finding multiple advantages to the flood pulse is important as both Petts and Richards et al. conclude that a vegetation-only basis for
restoring the flood pulse is unlikely to be costeffective. Richards et al. demonstrate how a combination of field monitoring, laboratory experiments and numerical modelling of riparian vegetation may be used to optimise locations for establishing vegetation in conjunction with local geomorphological characteristics. However, the prospects for more ecocentric approaches to floodplain planning and management in various countries receive a fairly downbeat conclusion from Penning-Rowsell and Tunstall, with the prevailing view still based on a simple reduction of flood damage. Maybe, as argued in several of the chapters, additional hydrological information may form the basis for more informed and rational floodplain management. In truth, Floodplain Processes may offer nothing new in the chapters covering the discipline(s) with which you are familiar (except, perhaps, in their context). However, supposing that most readers are not fully-versed in developments in each discipline, the book provides an accessible entry to floodplainrelated issues in neighbouring disciplines. For hydrologists, I would isolate the calls for hydrological data, the issue of mesh scale and microtopography and the importance of the flood pulse as central concerns. It may be that these concerns are met, as suggested in the introductory chapter, through development in "representative elementary area" modelling. The quality of individual chapters and the coherence achieved by the editors make the text eminently suitable reading for practising river managers, postgraduates and final year undergraduates. If in doubt about its suitably, skim read the excellent introductory chapter prior to purchase. Whilst I suspect that disciplinary specialists may have some reservations about the topics highlighted from their own particular specialism, this book stands as a benchmark text from which to gauge current knowledge in a new multidisciplinary (and maybe, someday, inter-disciplinary) field of study. Hopefully, it will date quickly because then we will have made progress.
1. References
Crane, R.C., 1982. A computermodel for the architecture of avulsion controlled suites. Unpublished PhD thesis, University of Reading.
Book Review
Howard, A.D., 1992. Modelling channel migration and floodplain development in meandering streams. In: Carling, P.A., Peas, G.E. (Eds.), Lowland Floodplain Rivers. Chichester, John Wiley and Sons, pp. 142.
303
James, C.S., 1985. Sediment transfer to overbank sections. Journal of Hydraulic Research 23, 435452. PETER DOWNS (University of Nottingham, UK) 1997 E l s e v i e r S c i e n c e B.V.
Hydrology ELSEVIER
Journal of Hydrology 204 (1998) 301-303
Book Review
Floodplain Processes, by M.G. Anderson, D.E. Walling and P.D. Bates, John Wiley and Sons, Chichester, U.K. 658(+iv)pp, ISBN 0-471-96679-7, Hardback, £75.00.
Floodplain Processes incorporates chapters based on geomorphology, hydraulics and hydrology, with links to concerns of ecology and the human occupation of floodplains. The chapters are invited contributions from leading academics that provide the volume with far more coherence than is usually the case for themed conference proceedings. Also, the chapters are substantial reviews, which is a blessing if, like me, you get frustrated by intriguing conferencepaper titles which turn out to be only six sides in length as chapters. The book is split into four topic sections following a lead chapter which is a genuine attempt by the editors to explain the purpose and relevance of their text. The first section, on Floodplain Evolution, contains detailed summaries of floodplain development in planform (Howard) and cross-section (Brown) sandwiching a chapter by Marriott explaining an experiment into floodplain sediment transport. Howard's chapter complements and extends his 1992 review (Howard, 1992) with an account of prospects for modelling across a range of floodplain types. He focuses particularly on floodplain development in meandering streams (20 pp) and highlights the importance of meander kinematics alongside water and sediment transport processes. Brown traces processes of floodplain evolution relative to past environmental change, including a summary of techniques available for interpreting floodplain change. He then provides a generalised development history of north-western European floodplains highlighting the integral role of vegetation in floodplain development during the 0022-1694/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved 1°11 S 0 0 2 2 - 1 6 9 4 ( 9 7 ) 0 0 1 1 8 - 2
early to mid-Holocene period. Marriott links James' (1985) overbank sedimentation model to Crane's (1982) model of alluvial architecture as a starting point in deriving more realistic models of floodplain stratigraphic development, a theme that is returned to in the third section. The second section, on Floodplain Flows, incorporates 6 of the 19 chapters and focuses primarily on flow hydraulics. For hydrologists, it is noteworthy that several chapters recognise that hydrological variability has greater practical significance for accurate modelling than developing more sophisticated hydraulic models. This is stated by Knight and Shiono and Romanowicz et al. while Bates et al., provide an illustration whereby the zero flux floodplain boundaries are relaxed and floodplain flow is coupled with models of hillslope hydrology and floodplain infiltration. Hydrological concerns are not, of course, an excuse for ignoring study of detailed processes and Younis foresees future models based on predictions of real turbulence using Reynolds stress transport factors. One current constraint is that we cannot yet compute a fine enough mesh to model true turbulence (Hervouet and Van Haren). Mesh resolution is a second major theme in these chapters. Bates et al. note that higher mesh resolution is useful in avoiding topographic filtering effects, especially as related to inundation boundaries. Romanowicz et aL examine the issue further on the basis that, as a distributed problem, inundation boundaries require a distributed solution - - the GLUE (generalised likelihood uncertainty estimation) approach is detailed. One practical aspect of current modelling constraints is that, through their data efficiency, one-dimensional models of floodplain flows may have greater longevity than might otherwise be expected. In this respect, 1-D models which segment channel and floodplain flows
302
Book Review
using simple roughness characterisation before a final global correction seem most appropriate (Knight and Shiono; Sellin and Willetts). The section on Floodplain Sediment Transport and Water Quality covers a wide variety of issues. Falconer and Chen address the issues of modelling of flow, sediment transport and water quality in tidal floodplains focusing on Poole Harbour, UK, re-emphasising many issues from the previous section. The following two chapters link strongly to the first section of the text: Walling et al. review the importance of overbank processes in floodplain formation and illustrate the role of microtopography and complex diffusion effects stemming from the difference between "effective" and "ultimate" suspended sediment transport dynamics. Macklin considers the dynamics of heavy metals as indicators of channel metamorphosis, as tracers and as indicators of rapid environmental change wherein processes of remobilisation are a major headache for environmental protection policies. Burt and Haycock's review of floodplains as transitional zones focuses on the efficacy of floodplain buffer zones as sinks for nitrogen and phosphorus. The consequence of potentially complex subsurface hydrology imparted by floodplain architecture and valley slope requires solutions in which buffer zones are linked to the risk of pollutant production. This requires strategic planning of the whole drainage basin and links neatly to the final section. The final section, on Floodplain Management, is characterised by a hydroecological theme centred on the benefits of the "flood pulse" in ensuring floodplain integrity. Petts considers this theme explicitly arguing the case for the flood pulse in maintaining river corridor patch diversity especially in large floodplain rivers. In relation to semi-arid/arid areas, Jolly notes that natural floodplains may be the only " w e t " area (if PE>Rf) and will have a disproportionate ecological importance. Therefore, the impact of river regulation may be especially severe and episodic flooding is critical to dilute soil salinisation caused by the perennial flow of regulated rivers. For river restoration, Brookes argues that, where land ownership problems can be overcome, restoring the flood pulse may provide the basis for cost-effective, largescale river restoration. Finding multiple advantages to the flood pulse is important as both Petts and Richards et al. conclude that a vegetation-only basis for
restoring the flood pulse is unlikely to be costeffective. Richards et al. demonstrate how a combination of field monitoring, laboratory experiments and numerical modelling of riparian vegetation may be used to optimise locations for establishing vegetation in conjunction with local geomorphological characteristics. However, the prospects for more ecocentric approaches to floodplain planning and management in various countries receive a fairly downbeat conclusion from Penning-Rowsell and Tunstall, with the prevailing view still based on a simple reduction of flood damage. Maybe, as argued in several of the chapters, additional hydrological information may form the basis for more informed and rational floodplain management. In truth, Floodplain Processes may offer nothing new in the chapters covering the discipline(s) with which you are familiar (except, perhaps, in their context). However, supposing that most readers are not fully-versed in developments in each discipline, the book provides an accessible entry to floodplainrelated issues in neighbouring disciplines. For hydrologists, I would isolate the calls for hydrological data, the issue of mesh scale and microtopography and the importance of the flood pulse as central concerns. It may be that these concerns are met, as suggested in the introductory chapter, through development in "representative elementary area" modelling. The quality of individual chapters and the coherence achieved by the editors make the text eminently suitable reading for practising river managers, postgraduates and final year undergraduates. If in doubt about its suitably, skim read the excellent introductory chapter prior to purchase. Whilst I suspect that disciplinary specialists may have some reservations about the topics highlighted from their own particular specialism, this book stands as a benchmark text from which to gauge current knowledge in a new multidisciplinary (and maybe, someday, inter-disciplinary) field of study. Hopefully, it will date quickly because then we will have made progress.
1. References
Crane, R.C., 1982. A computermodel for the architecture of avulsion controlled suites. Unpublished PhD thesis, University of Reading.
Book Review
Howard, A.D., 1992. Modelling channel migration and floodplain development in meandering streams. In: Carling, P.A., Peas, G.E. (Eds.), Lowland Floodplain Rivers. Chichester, John Wiley and Sons, pp. 142.
303
James, C.S., 1985. Sediment transfer to overbank sections. Journal of Hydraulic Research 23, 435452. PETER DOWNS (University of Nottingham, UK) 1997 E l s e v i e r S c i e n c e B.V.