Three‐dimensional gravity‐current flow within a subaqueous bend: Spatial evolution and force balance variations

The nature of three‐dimensional flow in submarine channel bends is poorly understood, largely due to the absence of detailed data from natural channels. Herein, data from density‐driven flows in a large reservoir on the Huanghe (Yellow) River are presented showing the spatio‐temporal variation of flow around a subaqueous bend. The data demonstrate for the first time that reversed helical flow, relative to that found in river channel bends, can occur from the centrifugal forcing of flow, even when the Coriolis force acts in the opposite direction. The data also suggest that reversed helical flow fields in submarine channels may be more frequent than currently estimated, notably for bends where Coriolis and centrifugal forces combine in the same direction. In addition, this study provides the first field evidence suggesting that sinuous submarine channels can exhibit an asymmetry in helical flow orientation between left and right‐turning bends, which will have major implications for the morphodynamics of submarine channels, their resultant patterns of sedimentation and, ultimately, the distribution of depositional units across submarine fan systems.     

Sub-daily alias and draconitic errors in the IGS orbits

Harmonic signals with a fundamental period near the GPS draconitic year (351.2 days) and overtones up to at least the sixth multiple have been observed in the power spectra of nearly all products of the International GNSS Service (IGS), including station position time series, apparent geocenter motions, orbit jumps between successive days, and midnight discontinuities in earth orientation parameter (EOP) rates. Two main mechanisms have been suggested for the harmonics: mismodeling of orbit dynamics and aliasing of near-sidereal local station multipath effects. Others have studied the propagation of local multipath errors into draconitic position variations, but orbit-related processes have been less examined. We elaborate our earlier analysis of GPS day-boundary orbit discontinuities where we observed some draconitic features as well as prominent spectral bands near 29-, 14-, 9-, and 7-day periods. Finer structures within the sub-seasonal bands fall close to the expected alias frequencies for 24-h sampling of sub-daily EOP tide lines but do not coincide precisely. While once-per-revolution empirical orbit parameters should strongly absorb any sub-daily EOP tide errors due to near-resonance of their respective periods, the observed differences require explanation. This has been done by simulating EOP tidal errors and checking their impact on a long series of estimated daily GPS orbits and EOPs. Indeed, simulated tidal aliases are found to be very similar to the observed IGS orbital features in the sub-seasonal bands. Moreover and unexpectedly, some low draconitic harmonics were also produced, potentially a source for the widespread errors in most IGS products. The results from this study are further evidence for the need of an improved sub-daily EOP tide model.     

Flood-tide Delta Morphological Change at the Gippsland Lakes Artificial Entrance,Australia (1889–2009)

Analysis of historical survey and navigation charts, aerial imagery, and digital hydro-data (representing a time-series of 1889–2009) allows the morphological evolution of a flood-tide delta at the artificial entrance to the Gippsland Lakes (Victoria, Australia) to be visualised and quantified. Analysis shows that flood-tide delta growth has imposed progressively greater demands upon port managers for publicly funded maintenance dredging. This flood-tide delta growth corresponds with a progressive diminution of Gippsland Lakes catchment river discharge volumes, and dampening of flow variability, due to both regional precipitation pattern changes and changes in catchment water resource allocation. Future climate change predictions for the Gippsland Lakes catchment and coastal area suggest both further decreases in catchment river discharge, and changing sediment flux along this sector of the Ninety Mile Beach. Thus, scope for flood-tide delta nourishment will probably increase, as will the demand for mitigation of the inevitable effects upon entrance channel navigability. Information derived from the analysis of time-series bathymetry used for this study offers baseline information in support of stakeholder consensus building regarding options for maintaining navigability. Analysis points to the merit of considering (and testing via morphological modelling) alternative options for navigation channel maintenance than those in present practice. We argue that the circumstances prevailing at the artificial entrance call for consideration of engineered configuration changes practised elsewhere by entrance managers faced with similar issues.     

Gypsy Architecture: Houses of the Roma in Eastern Europe

Why is Ortley Beach, New Jersey, known as Superstorm Sandy's ground zero? This article employs qualitative vulnerability analysis to understand why vulnerability of second homes in Ortley Beach resulted in dune failure and slow rebuilding after Sandy. The second-home owners who largely make up the community in Ortley Beach are identified as the key vulnerable group. This group's lack of political representation and financial compensation after Sandy increased house damage and slowed rebuilding. Identifying the level of vulnerability of the majority group in a location is paramount to understanding how the community recovers from a disaster. Such identification can also aid in preparing communities, especially for types of disasters they have not yet encountered.     

Book reviews

APPLIED GEOGRAPHY: Issues, Questions and Concerns (Geo Journal Library Vol. 15) edited by M. S. Kenzer. 16 × 24 cm, x and 210 pages. Kluwer: Dordrecht 1989 (ISBN 0 7923 04381).

WINE AND THE VINE: An Historical Geography of Viticulture and the Wine Trade by T. Unwin. 16 × 24 cm, xvi and 409 pages. Routledge: London 1991 (ISBN 0 415 13120 6) $A155.00 (hard); distributed by The Law Book Co.

WATERFRONT SYDNEY 1860–1920 by G. Aplin and J. Storey. 26 × 18 cm. 144 pages. Allen & Unwin: Sydney 1991 (first published 1984) (ISBN 1 86373 098 2) $A24.95 (soft).

Australian Geographer 23 (2), November 1992

INDUSTRIAL LOCATION: Principles and Policies (Second Edition) by K. Chapman and D. F. Walker. 15 × 23 cm, xiii and 322 pages. Basil Black‐well: Oxford 1991 (ISBN 0 631 16789 7) $A39.95 (soft).

INTERNATIONALISATION OF AUSTRALIA'S SERVICE INDUSTRIES by J. V. Langdale. 17 × 25 cm, iv and 373 pages. Australian Government Publishing Service, for Department of Industry, Technology and Commerce: Canberra 1991 (ISBN 0 644 13841 6).

TOURISM AND GOLD IN KAKADU: The Impact of Current and Potential Natural Resource Use on the Northern Territory Economy by B. Knapman, O. Stanley and J. Lea. 21 × 29 cm, vi and 49 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1179 4).

ABORIGINAL AUSTRALIA AND THE ‘NEW FEDERALISM’ INITIATIVE (Discussion Paper No. 2) by G. J. Crough. 14 × 21 cm, 42 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1325 8).

AUSTRALIAN NATIONHOOD AND OUTBACK INDIGENOUS PEOPLES (Discussion Paper No. 1) by P. Jull. 14 × 21 cm, 38 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1309 6).

MIGRATION AND DEVELOPMENT IN THE SOUTH PACIFIC (Pacific Research Monograph No. 24) edited by J. Connell. 17 × 25 cm, xii and 199 pages. National Centre for Development Studies, Australian National University: Canberra 1990 (ISBN 0 07315 0668 5) $A25.00 (soft).

POPIULESIN BLONG HONIARA: Olketa Popiulesin Map Blong 1986 Sensis. HONIARA: 1986 Census Atlas (Statistics Office Occasional Paper No. 4 / Board of Development Studies Monograph No. 1) by A.C. Walsh. 21 × 29 cm, vii and 95 pages. Department of Statistics: Honiara and Board of Development Studies, Massey University: Palmerston North 1990 (ISSN 0114 8834) $NZ34.00 in New Zealand, $NZ38.00 elsewhere (soft).

DOI MOI: Vietnam's Renovation Policy and Performance (Political and Social Change Monograph No. 14) edited by D. K. Forbes, T. H. Hull, D. G. Marr and B. Brogan. 15 × 22 cm, xiv and 263 pages. Department of Political and Social Change, Australian National University: Canberra 1991 (ISBN 0 7315 1303 7).     

North Atlantic atmospheric circulation and surface wind in the Northeast of the Iberian Peninsula: uncertainty and long term downscaled variability

The variability and predictability of the surface wind field at the regional scale is explored over a complex terrain region in the northeastern Iberian Peninsula by means of a downscaling technique based on Canonical Correlation Analysis. More than a decade of observations (1992–2005) allows for calibrating and validating a statistical method that elicits the main associations between the large scale atmospheric circulation over the North Atlantic and Mediterranean areas and the regional wind field. In an initial step the downscaling model is designed by selecting parameter values from practise. To a large extent, the variability of the wind at monthly timescales is found to be governed by the large scale circulation modulated by the particular orographic features of the area. The sensitivity of the downscaling methodology to the selection of the model parameter values is explored, in a second step, by performing a systematic sampling of the parameters space, avoiding a heuristic selection. This provides a metric for the uncertainty associated with the various possible model configurations. The uncertainties associated with the model configuration are considerably dependent on the spatial variability of the wind. While the sampling of the parameters space in the model set up moderately impact estimations during the calibration period, the regional wind variability is very sensitive to the parameters selection at longer timescales. This fact illustrates that downscaling exercises based on a single configuration of parameters should be interpreted with extreme caution. The downscaling model is used to extend the estimations several centuries to the past using long datasets of sea level pressure, thereby illustrating the large temporal variability of the regional wind field from interannual to multicentennial timescales. The analysis does not evidence long term trends throughout the twentieth century, however anomalous episodes of high/low wind speeds are identified.     

Interrelations between socio-economic development and environmental quality: a simulation integrating system dynamics models with GIS

System dynamics (SD) theory has long been deployed in modeling complex non-linear interrelationships but, so far it has not been common to do the kind of modeling in support of bringing environmental sustainability policies to practice. This is largely because the challenge of including spatial data has not yet been well met. Potential for adoption of SD and GIS methods in combination is exemplified with the results of a decision-support exercise designed for simulation and prediction of the dynamic inter-relationships between socio-economic development and environmental quality for the “Wen, Pi, Du” county in Sichuan province, southwestern China.     

Comparison of heat and bromide as ground water tracers near streams

Heat and bromide were compared as tracers for examining stream/ground water exchanges along the middle reaches of the Santa Clara River, California, during a 10-hour surface water sodium bromide injection test. Three cross sections that comprise six shallow (<1 m) piezometers were installed at the upper, middle, and lower sections of a 17 km long study reach, to monitor temperatures and bromide concentrations in the shallow ground water beneath the stream. A heat and ground water transport simulation model and a closely related solute and ground water transport simulation model were matched up for comparison of simulated and observed temperatures and bromide concentrations in the streambed. Vertical, one-dimensional simulations of sediment temperature were fitted to observed temperature results, to yield apparent streambed hydraulic conductivities in each cross section. The temperature-based hydraulic conductivities were assigned to a solute and ground water transport model to predict sediment bromide concentrations, during the sodium bromide injection test. Vertical, one-dimensional simulations of bromide concentrations in the sediments yielded a good match to the observed bromide concentrations, without adjustment of any model parameters except solute dispersivities. This indicates that, for the spatial and temporal scales examined on the Santa Clara River, the use of heat and bromide as tracers provide comparable information with respect to apparent hydraulic conductivities and fluxes for sediments near streams. In other settings, caution should be used due to differences in the nature of conservative (bromide) versus nonconservative (heat) tracers, particularly when preferential flowpaths are present.