The following are summaries of papers published in other parts of ICE Proceedings during 2003 that readers of Water Management may find of interest. You can get copies of individual papers emailed or posted to you for £5 or faxed to you for £2 a per page from the ICE library (telephone +44 (0) 20 7665 2251; fax +44 (0) 20 7976 7610; e-mail library@ice.org.uk). In all cases you need to complete a copy request form which can be downloaded from the ICE website at www.ice.org.uk. Summaries of all papers in ICE journals are also freely available and fully searchable at the ‘journals on-line’section of the ICE website at www.ice.org.uk.
The use of ‘managed retreat’ in coastal engineering
N. J. Cooper
Proceedings of the Institution of Civil Engineers—Engineering Sustainability, 156, No. 2, June, 101–110
‘Managed retreat’ involves the deliberate breaching, removal or landward relocation of an existing tidal defence or coastal protection structure. Its use in coastal engineering is unquestionably controversial. Despite this, changes over the last decade in the approach to coastal engineering in England and Wales have ensured that consideration is given to managed retreat (together with other potential solutions) along all coastal frontages. Furthermore, where managed retreat is identified as the most technically justified, economically viable and environmentally acceptable option, it is now more frequently being selected as the preferred engineering approach to addressing coastal management problems. This paper discusses the role of managed retreat in coastal engineering, identifies the physical and technical situations to which managed retreat is best suited, describes general implementation techniques and methods for optimising scheme designs, and identifies reasons for the relatively conservative uptake of managed retreat in the UK to date. One such reason is identified as a lack of guidance concerning methods for assessing, during feasibility studies, the potential impacts associated with managed retreat schemes. The paper addresses this issue directly by additionally presenting a case study of two proposed managed retreat schemes located within the Tamar estuary in Cornwall, south-west England. The paper concludes that, in order to increase future uptake of managed retreat in the UK, there is a need for an improved mechanism for freeing up land to enable retreat to occur. This could include both improved compensatory remuneration for land and property owners, to make the managed retreat option more favourable, and improved links between coastal engineering and development control, to ensure that the potential for managed retreat is not negated by future land-use developments.
The effects of pumping on the energy potential of a tidal power barrage
T. L. Shaw and M. J. Watson
Proceedings of the Institution of Civil Engineers—Engineering Sustainability, 156, No. 2, June, 111–117
Low head, doubly-regulated (Kaplan) axial flow turbines are well suited to working in reverse as pumps. For good efficiency in both operations, the generating and pumping heads must be complementary. The Rance tidal power scheme in Brittany has been carrying out matched generating and pumping operations to good effect since it was commissioned in 1966. Some simplifications to the range of operations performed at Rance have been identified. There is also potential for these operations to be extended, in particular to make greater use of pumping now that energy storage promises to become a more important function of electricity network operation. The results of the studies reported here explore this opportunity, together with its associated benefit of allowing the timing of generation from the enhanced resource to be varied to best suit that of energy demands.
Flexible power generation from the tides
T. L. Shaw and M. J. Watson
Proceedings of the Institution of Civil Engineers—Engineering Sustainability, 156, No. 2, June, 119–123
The predictable, regular reversal of the tides makes this an important renewable energy resource, one which is large, technically well proven and reliable if exploited by applying the conventional principles of hydroelectric power. The basic operating principles of tidal power stations were explored in depth in many studies carried out throughout the twentieth century. With few exceptions, a basic premise was to maximise energy output. Less attention was given to identifying the design and operating procedures needed to maximise aggregated energy value, it presumably being assumed that the latter followed the former. The studies reported in this paper are based on the now strongly established commercial trend for electricity to be marketed competitively, having regard for such factors as time of day and guarantee of use. Consumer technologies have taken advantage of the differential tariff structures which have emerged and will continue to evolve, and this in turn is being reflected in the composition of the supply industry. The much-valued versatility of hydro generation applies equally to tidal power plant. The opportunities for a tidal barrage to be operated flexibly, having regard for fundamental resource constraints, are set out, though without regard for tariff structures because these will depend on the particular network conditions in which any project will operate. The studies have been carried out in the context of a Severn Estuary barrage.
Briefing: Sustainable coastal defence
H. R. Payne
Proceedings of the Institution of Civil Engineers—Engineering Sustainability, 156, No. 3, September, 135–137
With the threat of rising sea levels and more frequent and intense storms, coastal defence is being considered on a more strategic basis. This aims to enable coastal change to occur as naturally as possible while sustaining both coastal habitats and those developments on the coast for which such a location is necessary. There will inevitably be some compromises but decisions will be made on a much more rigorous basis than in the past. This note outlines the methods being employed and directs the reader to more detailed guidance.
Designing sustainable estuarine intertidal habitats
N. I. Pontee
Proceedings of the Institution of Civil Engineers—Engineering Sustainability, 156, No. 3, September, 157–167
The creation of intertidal habitats, especially in estuary areas, has become increasingly popular in the UK over the last ten years. The complexities of artificially creating sustainable natural habitats means that the design of schemes requires an appreciation of a number of interrelated parameters. Morphological considerations are particularly important and include the site elevation, gradient and presence or absence of creek networks. Other important design considerations relate to hydraulic factors such as the exposure to wave action and tidal currents, the tidal prism and the inundation period. Relevant hydrological factors encompass aspects of water quality such as salinity and pollutant levels. Sedimentological considerations comprise sediment supply, particle size, consolidation rates, organic content, sediment chemistry and sediment quality. Since natural habitats are dynamic features, this paper also describes the tools available for investigating the short- and long-term evolution and stability of proposed schemes. Over the long term these tools include the analysis of historical charts, photographs and maps; the use of regime theory and various empirical relationships. Over the shorter term numerical modelling of tides, waves and sediment transport can be used. The scale of assessment and the approaches which are adopted are likely to be influenced by the size of the scheme and the number of associated issues. However, the complexity of processes within estuary systems means that it is often beneficial to use a range of techniques and synthesise the results to reduce uncertainties.
Eigen buckling of cylindrical shells in offshore structures: influence of geometry, loading and end conditions
B. F. Ronalds and R. Pinna
Proceedings of the Institution of Civil Engineers—Structures and Buildings, 156, No. 2, May, 183–191
Shell eigen buckling behaviour is investigated for combined axial and lateral pressure loading and with various end conditions. In addition to the more common pinned (P) and clamped (C) end conditions, particular emphasis is placed on shells where one or both of the ends are free (F). The physical behaviour in different geometry ranges is used to develop simple, approximate eigenvalue formulae, which are verified against the predictions of linear shell buckling theory using the method of variations. The different end conditions are treated through multipliers to the well-known pin-ended (P–P) case. It is found that, for practical geometries, P–F shells are very much weaker than C–F shells due to the lack of warping restraint. The results have application to the design of suction caisson foundations for offshore platforms.
