3 84 BOOK REVIEWS

HYDRODYNAMICS OF ESTUARIES edited by Bjorn Kjerfve, VOL I1 Estuarine Case Studies, CRC Press, 1988. No. of pages: 125.

In the second of the pair of volumes devoted to exploring the dynamics and physical processes active in estuaries Kjerfve has drawn together accounts of estuar- ies from each of the major morphological categories and from a variety of geographical locations. Five of the contributions concentrate on N. American estuaries, principally the Chesapeake Bay, St. Lawrence, Mobile Bay, The Laguna Madre of Texas and the complex Pujet Sound fjordic network. One reviews estuaries of tropical Northern Australia and one the Seine estuary of France. The remaining two chapters examine the impact of dredging upon problems of water circulation and the packages of instruments and data handling systems currently employed in monitoring inshore waters in Australia.

In the opening chapter Carter and Pritchard summar- ize a wealth of data from the microtidal Chesapeake Bay and its many tributary estuaries. The collation provides information on the cotidal conditions, tidal amplitude variations, the residual currents, mixing, water tempera- tures and average salinity in spring, summer, autumn and winter. Most of the facts are familiar, and, although text- figure captions often leave much to be desired, the assembling of the information, together with instructive comments on the implications of various features in relation to environmental considerations and conse- quences of human activity around the shores makes this a very useful opening to the work.

The interconnecting network of fjordic basins of the Pujet Sound and the contrasting currents in different segments of the system provide problems for the assess- ment of residence times of the different water bodies. Ebbesmeyer, Word, and Barnes indicate that the internal recycling of pollutants may become so prolonged that it can take years for effluents discharged into some parts of the system to be released through the 100 km long Juan de Fuca Strait and into the Pacific. The more dynamic Main and Southern basins have well mixed waters, but those of the Whidbey and Hood Canal basins move more slowly and normally exhibit stratified conditions. Most of the water mixing occurs in the narrows between the basins. Many of the individual physical dynamics and biological features show fluctuations on time scales of days, months and years. Water management practices need to be designed from a whole system viewpoint rather than on a purely local basis.

The hydrography of the hypersaline 400 km long, but generally shallow, Laguna Madre of Texas has changed with the opening of the Intracoastal Waterway, per- mitting water exchanges with Corpus Christi Bay. Quasi- periodic salinity variations at 4-5 month intervals show peaks exceeding 60 ppt in the interior of Laguna Madre, only 40 km from the interconnection. In an examination of the tidal and freshwater inputs Smith demonstrates that low frequency meteorological forcing is important in the lagoon-shelf exchanges. Normally renewal of marine input occurs on fortnightly and seasonal time scales.

The Alabama and Tombigbee Rivers supply freshwater to the 984 km Mobile Bay area, which rarely exceeds 5 m in depth. Despite the shallowness of the waters, the very low tidal ranges (max. 0.8 m) permit strong salinity- induced stratification. Although winds may disrupt the summer stratification, Schroeder and Wiseman demon- strate a repeated association of stratification with reduc- tions of near-bottom dissolved oxygen levels, and result- ant stress to the biota. Hypoxic conditions in the central and northern areas of the bay are responsible for ‘jubilees’ which are shoreward mass-migration of estuarine or- ganisms such as flounders, eels, and crabs. Details of historic ‘jubilees’ and the accompanying hydrographic and meteorological conditions are given in a nicely documented account.

The importance of evaporation and evapotranspira- tion in driving the baroclinic circulation of tropical estuaries, notably the Alligator River and Norman River systems in Northern Australia is stressed in the chapter by Wolanski. Some 30 km off the Alligator River mouth is a zone of high salinity water separating the estuary from the waters of the Arafura Sea. Using a simple box model Wolanski demonstrates that in the dry season the S. Alligator River waters are effectively trapped within the estuary and salinity rises due to evaporation. Salinity enhancement by ebbing waters draining marginal salt pans is known in the Norman River estuary, and evapo- transpiration in mangrove swamps also enhances salt concentrations in the waters of minor drainage channels in the Coral Creek area.

The St. Lawrence Estuary waters are well mixed to- wards the head, and mixing decreases seaward, with stratified waters in the lower estuary. Advection and diffusion are both important in the upper estuary but advective salt transfer dominates the seaward reaches. According to El-Sabh two circulation forms are present, one consisting of a series of transverse gyres separated by fronts and the second separates the colder, deeper, more saline, southern waters from those of the northern shore. The impacts of factors such as spring-neap cycles, fresh- water discharge, topography, and meteorological forcing are examined. The tables and clear diagrams are sup- plemented by useful thermal infrared HCMM satellite images from summer and autumn.

The Seine macrotidal estuary of Northern France has tides and depths of similar magnitude. The landward modification of the tidal curve and relatively low fresh- water inputs provide an estuary dominated by marine dynamics. In a very useful summary Saloman documents the effects of man in confining the water to a single channel and thereby restricting saltwater intrusion, sep- arating the freshwater discharges to one side of the embayment. Reference to tidal curves, current residual patterns, suspension concentration, and sediment dis- charges provides interesting background to the disequili- brated system now attempting to establish a stable regime.

The impact of human intervention through dredging forms the basis of the contribution from Maynard Nicols, who refers to engineering studies in which proposed modifications are modelled physically or numerically

BOOK REVIEWS 385

before being carried out. Changes of tidal effects are examined from the Delaware, Lune and Seine estuaries and effects of changing estuarine circulation outlined in the Savannah Harbour, the South Pass of the Mississippi, and in the Thames River.

No modern work on estuarine or coastal systems is complete without a description of an instrument package. Imberger and Chapman provide details of devices dealing with meteorological monitoring, mini-loggers, remote profiters, portable data aquisition systems, vehicles, and data processors. Technical specifications and examples of out from equipment used by the Australian group are provided.

This second volume serves a useful purpose of gathering together diverse physical factors controlling the

behaviour of estuarine waters world wide. Above all it provides detailed references to the specific water bodies and frequently to investigations not widely available through the international journals. The companion vol- ume examines the principles of estuarine oceanography, and this work supplements it with useful examples and case histories of hydrographic factors in action. The combined works provide a fine basis for anyone seeking to produce an up to date course on estuarine systems with clear separation of principles and apposite case histories.

JOHN MCMANUS University of St Andrews

DESERT SEDIMENTS: ANCIENT AND MODERN, L. E. Frostick and I. Reid (Eds), Geol. SOC. Special Publ. No. 35, Blackwell Scientific Publishers, Oxford, 1987. No. of pages: XI+401. Price S45.00.

The flow of books emanating from conferences is not abating. Special Publication No. 35 of the Geological Society of London contains 24 papers by 46 authors, from the May 1986 meeting of the Geological Society in London. The meeting aimed at bringing together workers on ancient and modern deserts. Though only four of the 24 papers deal with ancient sediments, the range of topics treated is wide, from small distance grain size change on linear dunes to rippled landforms on Mars. Some authors present a conceptual formulation or state-of-art position of their research; others report results of specific research topics.

In the introduction Glennie inexplicably states, in a confusedly constructed sentence, that only 4 % of deserts is covered by sand dunes, whereas the commonly quoted Sgure is about 20%. In this book, topics on eolian sands and dust, the traditional desert sediments, comprise about half of the volume. In addition, special attention is given to fluvially produced clastic sediments (seven pa- pers) commonly covering only about 6 to 8 % of desert landscapes, including badlands, fans, wadis and sebkhas, which have been somewhat neglected in previous com- pilations and books. Only one paper (B. P. J. Williams et ul.) deals with cold deserts, and one reports laboratory experiments (Whalley et ul.). Two papers deal with chem- ical sediments and none with the surficial alteration products and soils of desert plateaus and plains, though weathering processes are briefly tackled in some of the papers.

Three papers deal with grain size data and their environmental interpretation. Thomas finds SEM images useful but the Folk and Ward parameters essentially inadequate to distinguish between aeolian and associated environments in a regional context of the Kalahari. On the other hand, Livingstone shows that careful detailed sampling can identify measurable differences across a

single linear dune. In line with the Danish Aarhus group, the Sheffield group (Flenley et a/.) also promotes the log- hyperbolic distribution of grain sizes and has some harsh words to say about the graphical probability plots on theoretical grounds, considering them misleading when the distribution is not strictly unimodal. Their study provides a limited set of data showing that log-hyperbolic or the more easily calculated log skew Laplace model (3 parameters instead of 4) can recognize mixed grain size populations. Essentially they argue that a log-log histo- gram, as already advocated long ago by Bagnold, is a better plot than a cumulative log-probability plot on which linear segments are usually interpreted as due to specific transport processes. One cannot but wonder whether the wider application of log-hyperbolic distribu- tions will bring about a true advance in the recognition and characterization of various mixed sedimentary en- vironments, which at present seem most in need of better interpretation.

It seems significant to point out that none of the three papers dealing with interpreting environments of ancient dune sands used grain size data in the interpretations of their origin, but only bedform and internal structures to characterize them. So perhaps, like our unquestional ability to analyze for dozens of chemical elements which only in special cases are used in environmental interpreta- tions, the ability to 'read' and understand the ancient or modern desert landscapes and their sediments will only rarely be improved by using the more elaborate grain size statistics, though log-histograms should be used more widely.

In the field of desert fluviatile processes, advances in understanding the basic processes of sediment produc- tion and redistribution seem more tangible and some are reported here. Schick and co-workers' concept of vertical exchange of coarse bedload in desert streams is a signific- ant contribution to the understanding of ancient con- glomerates and as an interpretative tool for paleohydro- logy. Frostick and Reid's general model of sedimentation in rift basins fills a definite gap in existing sedimentation models. Several additional papers which treat fluviatile