Sampling-based flood risk analysis for fluvial dike systems

A dike system of moderate size has a large number of potential system states, and the loading imposed on the system is inherently random. If the system should fail, in one of its many potential failure modes, the topography of UK floodplains is usually such that hydrodynamic modelling of flood inundation is required to generate realistic estimates of flood depth and hence damage. To do so for all possible failure states may require 1,000s of computationally expensive inundation simulations. A risk-based sampling technique is proposed in order to reduce the computational resources required to estimate flood risk. The approach is novel in that the loading and dike system states (obtained using a simplified reliability analysis) are sampled according to the contribution that a given region of the space of basic variables makes to risk. The methodology is demonstrated in a strategic flood risk assessment for the city of Burton-upon-Trent in the UK. 5,000 inundation model simulations were run although it was shown that the flood risk estimate converged adequately after approximately half this number. The case study demonstrates that, amongst other factors, risk is a complex function of loadings, dike resistance, floodplain topography and the spatial distribution of floodplain assets. The application of this approach allows flood risk managers to obtain an improved understanding of the flooding system, its vulnerabilities and the most efficient means of allocating resource to improve performance. It may also be used to test how the system may respond to future external perturbations.     

Evolution of the Mount Woods Inlier, northern Gawler Craton, Southern Australia: an integrated structural and aeromagnetic analysis

Structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships. This approach is used to constrain the geometry and evolution of the sparsely exposed Mount Woods Inlier in the northern Gawler Craton. The Mount Woods Inlier records a history of poly-phase deformation, high-temperature metamorphism, and syn- and post-orogenic magmatism between ca. 1736 and 1584 Ma. The earliest deformation involved isoclinal folding, and the development of bedding parallel and axial planar gneissic foliation (S₁). This was accompanied by high-temperature, upper amphibolite to granulite facies metamorphism at ca. 1736 Ma. During subsequent north–south shortening (D₂), open to isoclinal south–southeast-oriented F₂ folds developed as the Palaeoproterozoic successions of the inlier were thrust over the Archaean nuclei of the Gawler Craton. The syn-D₂ Engenina Adamellite was emplaced at ca. 1692 Ma. The post-D₂ history involved shear zone development and localised folding, exhumation of metamorphic rocks, and deposition of clastic sediments prior to the emplacement of the ca. 1584 Ma Granite Balta Suite. The Mount Woods Inlier is interpreted as the northern continuation of the Kimban Orogen.     

Evaluation of Lidar and Medium Scale Photogrammetry for Detecting Soft-Cliff Coastal Change

Lidar and photogrammetry have both been evaluated for detecting shortterm coastal change using the Black Ven mudslide, Dorset as a case study. A lidar-generated digital elevation model (DEM) was obtained and initially compared with a DEM generated using available 1:7500 scale aerial photography and automated digital photogrammetry. The quality of these two data sets was assessed using a third DEM, derived using a total station and conventional ground survey methods. The vertical accuracies (rms error) of the lidar and photogrammetry were 0.26m and 0.43m respectively, although both data sets displayed a tendency to generate heights slightly lower than the elevation of the terrain surface. The quality of the two data sets was then assessed with respect to local slope angle. The accuracy of photogrammetrically derived elevations varied with slope and more so than in the case of lidar
From these basic tests, lidar has proved to be more accurate than photogrammetry for soft-cliff. monitoring. Further research is required to establish whether this trend is applicable to other data sets and specifically for photogrammetric data acquired using larger scale imagery     

Penetrative convection in rapidly rotating flows: preliminary results from numerical simulation

Turbulent convection forced by a surface heat flux into a stably stratified region is a feature of both the atmospheric and oceanic planetary boundary layers. Of particular interest is the interface between the convective layer and the stable stratification, where the entrainment of fluid into the convective layer by penetrating plumes may lead to a reverse buoyancy flux, and an enhancement of the stable stratification. Whereas in the atmosphere the influence of rotation on this penetrative convection is negligible, oceanic convection may be subjected to lower Rossby numbers and hence greater rotational influence. To isolate the effects of rotation, we present three numerical solutions for turbulent penetrative convection, characterised by different rotation rates, with all other parameters being held constant. Our results indicate that at lower Rossby numbers the lateral scale of the plumes is reduced, whereas the vertical vorticity of the plumes is much enhanced. Vertical transports of buoyancy and kinetic energy across the convective layer are reduced, leading to less efficient penetration at the interface with the stratified layer, and hence less reverse buoyancy flux in this region.     

Properties of New Coordinates for the General Three-Body Problem

This is an analysis of the features of the new coordinate system given by the principal axes of inertia, as determined by Euler angles, and twodistances related to the inertia principal moments and an auxiliar angleas coordinates, for studying the general three-body problem, interactingthrough gravitational forces.The reduction of order is performed in these new coordinates by using the angular velocity vector or the Euler angles.The Eulerian case of collinear motion is revisited from our own perspective.The value of the auxiliar angle is computed for the Sun–Earth–Moon system.     

Characterization of periodic variations in the GPS satellite clocks

The clock products of the International Global Navigation Satellite Systems (GNSS) Service (IGS) are used to characterize the timing performance of the GPS satellites. Using 5-min and 30-s observational samples and focusing only on the sub-daily regime, approximate power-law stochastic processes are found. The Block IIA Rb and Cs clocks obey predominantly random walk phase (or white frequency) noise processes. The Rb clocks are up to nearly an order of magnitude more stable and show a flicker phase noise component over intervals shorter than about 100 s. Due to the onboard Time Keeping System in the newer Block IIR and IIR-M satellites, their Rb clocks behave in a more complex way: as an apparent random walk phase process up to about 100 s and then changing to flicker phase up to a few thousand seconds. Superposed on this random background, periodic signals have been detected in all clock types at four harmonic frequencies, n × (2.0029 ± 0.0005) cycles per day (24 h coordinated universal time or UTC), for n = 1, 2, 3, and 4. The equivalent fundamental period is 11.9826 ± 0.0030 h, which surprisingly differs from the reported mean GPS orbital period of 11.9659 ± 0.0007 h by 60 ± 11 s. We cannot account for this apparent discrepancy but note that a clear relationship between the periodic signals and the orbital dynamics is evidenced for some satellites by modulations of the spectral amplitudes with eclipse season. All four harmonics are much smaller for the IIR and IIR-M satellites than for the older blocks. Awareness of the periodic variations can be used to improve the clock modeling, including for interpolation of tabulated IGS products for higher-rate GPS positioning and for predictions in real-time applications. This is especially true for high-accuracy uses, but could also benefit the standard GPS operational products. The observed stochastic properties of each satellite clock type are used to estimate the growth of interpolation and prediction errors with time interval.     

Reviews of recent Australian publications

AUSTRALIA: A GEOGRAPHY. Volume 1: The Natural Environment edited by D. N. Jeans. 18 × 25 cm, viii and 347 pages. Sydney University Press: Sydney 1986 (ISBN 0 424 00114 4) $A55.00 (hard); (ISBN 0 424 00124 1) $A32.50 (soft).

Western Australia. Departments of Education and Lands and Survey (1979) Western Australia: an atlas of human endeavour, 1829–1979, Government Printer, Perth.

ATLAS OF SOUTH AUSTRALIA edited by T. Griffin and M. McCaskill. 28 × 40 cm, xiv and 134 pages. South Australian Government Printing Division and Wakefield Press on behalf of the South Australian Jubilee 150 Board: Adelaide 1986 (ISBN 0 7243 46880) $A55.00 (hard).

URBAN AUSTRALIA: Planning Issues and Policies edited by S. Hamnett and R. Bunker. 16 × 24 cm, 192 pages. Nelson Wadsworth: Melbourne 1987 (ISBN 0 17 007166 9) $A29.95 (hard).

AUSTRALIAN URBAN DEVELOPMENT AND INTERNATIONAL FINANCE CAPITAL (Working Paper No. 31) by M. T. Daly. 21 × 30 cm, viii and 39 pages. Transnational Corporations Research Project, University of Sydney 1985 (ISBN 0 908470 66 5) $A5.00 (soft).

TRANSNATIONAL CAPITAL AND URBANIZATION IN JAPAN (Research Monograph No. 25) by M. Douglass. 21 × 30 cm, viii and 42 pages. Transnational Corporations Research Project, University of Sydney 1987 (ISBN 0 908470 74 6) $A10.00 (soft).

MELBOURNE WESTERN REGION: Industrial Sites Atlas by Melbourne Western Region Joint Working Group. 45 × 32 cm, 40 pages. Melbourne Western Region Joint Working Group: Melbourne 1984 $A20.00 (soft).

MINE INFRASTRUCTURE AND ECONOMIC DEVELOPMENT IN NORTHERN AUSTRALIA by C. O'Faircheallaigh. 18 × 25 cm, vi and 87 pages. North Australia Research Unit, Australian National University: Darwin 1987 (ISBN 0 7315 0043 1) $A10.00 (soft).

AUSTRALIA'S CHANGING POPULATION: Trends and Implications by G. Hugo. 16 × 24 cm, x and 354 pages. Oxford University Press: Melbourne 1986 (ISBN 0 19 554680 6) $A40.00 (hard).

WOMEN OVER SIXTY: A Study of the Housing, Economic and Social Circumstances of Older Women (Publication No. 130) by L. Coleman and S. Watson. 17 × 24 cm, v and 89 pages. Australian Institute of Urban Studies: Canberra 1987 (ISBN 0 86419 112 X).

THE MANNING VALLEY: Landscape and Settlement 1824–1900 by W. K. Birrell. 21 × 29 cm, xvi and 280 pages. Jacaranda: Milton, Qld, 1987 (ISBN 0 7016 2170 2) $A29.95 (hard).

ISSUES IN THE MANAGEMENT OF AUSTRALIA'S WATER RESOURCES by J. J. Pigram. 15 × 23 cm, xvi and 331 pages. Longman Cheshire: Melbourne 1986 (ISBN 0 582 71139 8) $A24.95 (soft).

PROSPECTS FOR HARDWOOD FORESTS (Monograph No. 19) edited by J. Dargavel and G. Sheldon. 16 × 23 cm, xv and 334 pages. Centre for Resource and Environmental Studies, Australian National University, Canberra 1987 (ISBN 0 86740 226 1) $A19.95 plus $A5.00 post and packing (soft).

FOREST SOILS AND NUTRIENT CYCLES by P. M. Attiwill and G. W. Leeper. 15 × 22 cm, x and 202 pages. Melbourne University Press: Melbourne 1987 (ISBN 0 522 84315 8) $A29.90 (hard).

AUSTRALIAN SOILS: The Human Impact edited by J. S. Russell and R. F. Isbell. 26 × 18 cm, xi and 522 pages. University of Queensland Press: St Lucia 1986 (ISBN 0 7022 1968 1) $A50.00 (hard).

THE AUSTRALIAN SUMMER MONSOON, TELECONNECTIONS, AND FLOODING IN THE LAKE EYRE BASIN (South Australian Geographical Papers No. 2) by R. J. Allen. 18 × 25 cm, 47 pages. Royal Geographical Society of Australasia (South Australian Branch): Adelaide 1985 (ISBN 0 909112 09 6).     

Heat Flux in the Coastal Zone

Various difficulties with application of Monin–Obukhov similarity theory are surveyed including the influence of growing waves, advection and internal boundary-layer development. These complications are normally important with offshore flow. The transfer coefficient for heat is computed from eddy correlation data taken at a mast two kilometres off the Danish coast in RASEX. For these coastal zone data, the thermal roughness length shows no well-defined relation to the momentum roughness length or roughness Reynolds number, in contrast to previous theories. The variation of the momentum roughness length is dominated by wave state. In contrast, the thermal roughness length shows significant dependence on wave state only for small values of wave age where the mixing is apparently enhanced by wave breaking. The development of thin internal boundary layers with offshore flow substantially reduces the heat transfer and thermal roughness length but has no obvious influence on momentum roughness length. A new formulation of the thermal roughness length based on the internal boundary-layer depth is calibrated to the RASEX data. For the very stable case, the turbulence is mainly detached from the surface and existing formulations do not apply.As an alternative to adjusting the thermal roughness length, the transfer coefficient is related directly to the stability and the internal boundary-layer depth. This avoids specification of roughness lengths resulting from the usual integration of the non-dimensional temperature function. The resulting stability function is simpler than previous ones and satisfies free convection similarity theory without introduction of the gustiness factor. The internal boundary layer also influences the moisture transfer coefficient.