WOODY DEBRIS ON THE MAINLAND SHELF OFF VENTURA, SOUTHERN CALIFORNIA

Land plant debris occurs in appreciable quantities in the shelf sediments off Ventura, southern California. Concentrations range from less than 2 g (wet weight)/1 (less than 250 g/m²) to 53 g/1 (10,662 g/m²). The highest values are found near the outer edge of the shelf.     

REVISITING RIO DE JANEIRO AND SÃO PAULO*

ABSTRACT. Contrasting models of urban development characterize the historical-geographical evolution of Brazil's two leading cities, viewed in an updating of the seminal 1933 article by Preston James. Native to Rio de Janeiro is a distinctive Luso-Brazilian style of irregular coastal urbanization, whereas SÃo Paulo displays a more uniform, modern type of inland commercial-industrial expansion. Even as Rio de Janeiro and SÃo Paulo sprawl today to form a virtual megalopolis in southeastern Brazil, they retain distinguishing roles in the national city system. Both metropolises are experiencing increasing functional decentralization and socioeconomic polarization, but in their own characteristic fashions. Generalized models of “Latin American city structure” are of limited value, unless they take into account such significant historical-geographical variations in urban form.     

GLOBAL AND LOCAL CHANGE ON THE PORT‐CITY WATERFRONT*

ABSTRACT. Successful waterfront redevelopment requires an understanding of global processes and an appreciation of the distinctiveness of port‐city locations. Waterfront revitalization occurs at the problematic and controversial interface between port function and the broader urban environment. It reflects varied forces and trends, involves community attitudes and environmental sensitivities, and influences transport evolution and urban change. The revitalization phenomenon is examined using community attitudes in Canada and urban regeneration in East Africa to illustrate retrospective and prospective dimensions.     

PIPEFLOW CONTRIBUTING AREAS AND RUNOFF RESPONSE

Links that have been established between the characteristic responses of hillslope drainage processes and the size of drainage catchments enable valuable extrapolations and comparisons to be made, both within and beyond the range of the field data. To date, flow through natural soil pipes has not been included in these investigations. A methodology is offered for achieving this and the first such analyses of field data on pipeflow. The results indicate that pipeflow responses follow trends which are broadly similar to other hillslope drainage processes and are intermediate between throughflow and saturation overland flow. © 1997 by John Wiley & Sons, Ltd.     

High-temperature 'clockwise'P-T paths and melting in the development of regional migmatites: an example from southern Brittany, France

The Southern Brittany Migmatite Belt (SBMB), which evolved through the metamorphic peak between c. 400 Ma and c. . 370 Ma ago, consists of a heterogeneous suite of high-grade gneisses and anatectic migmatites, both metatexites and diatexites. Rare garnet-cordierite gneiss layers record evidence of an early prograde P-T path. In these rocks, growth-zoned garnet cores and a sequence of included mineral assemblages in garnet, from core to rim, of Qtz + Ilm + Ky, Pl + Ky + St + Rt + Bt and Pl + Sil + St + Rt + Bt constrain a prograde evolution during which the reactions Ilm + Ky + Qtz→ Aim + Rt, Ms + Chl→ St + Bt + Qtz + V and St + Qtz→ Grt + Sil + V were crossed. Parts of this prograde evolution are preserved as inclusion assemblages in garnet in all other rock types. In all rock types, garnet has reverse zoned rims, and garnet replacement by cordierite and/or biotite and plagioclase suggests the following reactions have occurred: Grt + Sil + Qtz→ Crd → Hc ± Ilm, Bt + Sil + Qtz → Crd ± Hc → Ilm → Kfs + V and (Na + Ca + K + Ti) + Grt → Bt + Pl + Qtz. Microstructural analysis of reaction textures in conjunction with a petrogenetic grid has enabled the construction of a tightly constrained 'clockwise' P–T path for the SBMB. The high-temperature part of the path has a steep dT/dP slope characteristic of near isothermal decompression. It is proposed that the P-T path followed by the SBMB is the result of the inversion, by overthrusting, of a back-arc basin and that such a tectonic setting may be applicable to other high-temperature migmatite terranes. The near isothermal decompression is at least partly driven by the upward (diapiric) movement of the diatexite/anatectic granite core of the SBMB.     

Short-wave aerosol radiative efficiency over the global oceans derived from satellite data

Using 5 yr (December 2000–November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency ( E_τ ) of aerosols during the morning Terra satellite overpass time over the global oceans (60°N–60°S). We calculate E_τ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes. Over the 5 yr, the global mean instantaneous E_τ between the methods is remarkably consistent and within 5 W m⁻²τ⁻¹ with a mean value of –70 W m⁻²τ⁻¹. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of <3 W m⁻²τ⁻¹. These differences are largely due to assumptions in aerosol models and definition of clear sky backgrounds. Independent assessments of aerosol radiative effects from different satellite sensors and methods are extremely valuable and should be used to verify numerical modelling simulations.     

NICKPOINT RECESSION IN KARST TERRAINS: AN EXAMPLE FROM THE BUCHAN KARST,SOUTHEASTERN AUSTRALIA

Nickpoint recession in the Buchan karst, southeastern Australia, has resulted in the formation of an underground meander cut-off system in the Murrindal River valley. Three nickpoints have been stranded in the surface channel abandoned by the subterranean piracy, and these can be correlated with river terraces and epiphreatic cave passages in the nearby Buchan River valley. The presence of palaeomagnetically reversed sediments in the youngest cave passage in the Buchan valley implies that the topographically lowest nickpoint in the Murrindal valley is more than 730 ka old, and the other nickpoints are probably several million years old. The nickpoints are occasionally active during floods, but the diversion of most surface flow underground has slowed down their retreat to the extent that they have been effectively stationary for several million years. Underground nickpoint migration has been by both incision within major phreatic conduits and their abandonment for lower-level passages. The nickpoints are all present in the upstream part of the cave system, but have not migrated past the sink in the river channel, despite the long period of time available for this to happen. The sink is characterized by collapsed limestone blocks; these filter out the coarse bedload from the river channel. As a result, erosion within the cave passages is dominantly solutional and therefore slower than in the surface channel, where it is mostly mechanical. In addition, to transmit a drop in base level the cave system requires the removal of a larger volume of rock than for the surface migration of a nickpoint, because any roof collapse material in the subsurface system must be removed. These factors have slowed the migration of the base-level changes through the subsurface system, and may be a general feature in caves that have diffuse sinks as their main inputs.     

Risk assessment and drought management in the Thames basin

Abstract

A risk assessment procedure is described for use in managing a system of pumped-storage reservoirs in the Thames basin during a drought. Historical daily rainfall sequences are used as equi-probable scenarios of future rainfall. These are transformed to flow, reservoir level, and demand restriction sequences through the use of rainfall-runoff and water resource system models. The risk assessment information required is then obtained through a statistical analysis of these sequences. A novel technique is presented for incorporating monthly rainfall forecasts, presented as probabilities of rainfall being above average, average, or below average, into the risk assessment scheme. Information on current hydrological conditions is incorporated in the procedure through the use of recently observed natural flows to adjust the internal state variables of a conceptual rainfall-runoff model to achieve agreement between observed and model flow. The overall procedure is accommodated within a decision support system for drought management which is implemented on a microcomputer and makes extensive use of interactive menus, forms and colour graphic displays. A key feature of the system is the maintenance of an up-to-date archive of hydrometric data which is achieved through a real-time communication link with a second computer dedicated to real-time data acquisition via telemetry. Monitoring the reliability of the water resource system during droughts is made a quick and easy task, and the effect of a change in the operating policy on system reliability can be readily assessed. The information obtained provides valuable support for tactical decision-making within the overall long-term operating strategy.