The topography of a catchment has a major impact on the hydrological, geomorphological. and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered. K E Y WORDS Basin topography Digital elevation models Terrain analysis Hydrologic models -6087/9and diversity within landscapes. A number of hydrologically-based, topographically-derived indices appear to be particularly powerful and useful for determining this susceptibility to hazard (Moore and Nieber, 1989). Many geographic information systems and resource inventory systems are being developed storing topographic information as primary data for use in analysing water resource and biological problems. This paper reviews the availability of digital elevation data and its accuracy, digital representation of topography, analysis of the digital data for hydrological, geomorphological, and biological applications, and describes some models that make use of digital representations of topography. We use examples from Australia and the United States of America in our discussions because of our familiarity with hydrologic research and practice in these two countries. DIGITAL ELEVATION MODELSA Digital Elevation Model (DEM) is an ordered array of numbers that represents the spatial distribution of elevations above some arbitrary datum in a landscape. I t may consist of elevations sampled at discrete points or the average elevation over a specified segment of the landscape, although in most cases it is the former. DEMs are a subset of Digital Terrain Models (DTMs) which can be defined as ordered arrays of numbers that represent the spatial distribution of terrain attributes.The acquisition. storage, and presentation of topographic information is an area of active research.Generally, raw elevation data in the form of stereo photographs or field surveys, and the equipment to process these data, are not readily available to potential end users of a DEM. Therefore, most users must rely on published topographic maps or DEMs produced by government agencies such as the United States Geological Survey (U.S.G.S.) or the Australian Surveying and Land Information Group (AUSLIG-formerl...

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We describe a green fluorescent protein (GFP)-based assay for investigating membrane traffic on the secretory pathway in plants. Expression of AtRab1b(N121I), predicted to be a dominant inhibitory mutant of the Arabidopsis Rab GTPase AtRab1b, resulted in accumulation of a secreted GFP marker in an intracellular reticulate compartment reminiscent of the endoplasmic reticulum. This accumulation was alleviated by coexpressing wild-type AtRab1b but not AtRab8c. When a Golgi-targeted and N-glycosylated variant of GFP was coexpressed with AtRab1b(N121I), the variant also accumulated in a reticulate network and an endoglycosidase H-sensitive population appeared. Unexpectedly, expression of AtRab1b(N121I), but not of the wild-type AtRab1b, resulted in a reduction or cessation of vectorial Golgi movement, an effect that was reversed by coexpression of the wild type. We conclude that AtRab1b function is required for transport from the endoplasmic reticulum to the Golgi apparatus and suggest that this process may be coupled to the control of Golgi movement.

The length‐slope factor in the universal soil loss equation (USLE) is a purely empirical relationship that was derived from an extensive data base. A physically based length‐slope factor was independently derived in this paper by using unit stream power theory to describe the erosion processes associated with sheet and rill flow on hill‐slopes. It was shown that the two length‐slope factors are equivalent. Therefore, the USLE length‐slope factor is a measure of the sediment transport capacity of runoff from the landscape, but fails to fully account for the hydrological processes that affect runoff and erosion. The strength of the theoretically derived length‐slope factor is that it explicitly accounts for the dual phenomena of catchment convergence and rilling. The empirically derived factor can not account for changes in either surface flow or erosion processes, nor slope geometry, and this may explain why the values derived for other factors in the USLE, especially soil erodibilities, have been found to be inconsistent.

Abstract. Explicit and quantitative models for the spatial prediction of soil and landscape attributes are required for environmental modelling and management. In this study, advances in the spatial representation of hydrological and geomorphological processes using terrain analysis techniques are integrated with the development of a field sampling and soil-landscape model building strategy. Statistical models are developed using relationships between terrain attributes (plan curvature. compound topographic index, upslope mean plan curvature) and soil attributes (A horizon depth, Solum depth, E horizon presencelabsence) in an area with uniform geology and geomorphic history. These techniques seem to provide appropriate methodologies for spatial prediction and understanding soil landscape processes.