Previous studies of channel morphological change have often relied upon sparse spatial and temporal data-sets, resulting in a degree of uncertainty in their conclusions. Furthermore, previous methodologies have been unable to quantify small-scale changes in channels composed of sand and fine gravel due to inadequate data density. This study reports the use of a high-resolution 3D laser scanner (LMS-Z210) in the assessment of erosion and deposition volumes in the proglacial zone of Glacier du Ferpècle and Mont Miné, Switzerland. Highresolution (> > > > >500 points/m 2 ) data obtained across a 5881 m 2 area of braid plain during the early part of the melt-water season permitted digital elevation models (DEMs) of bar surfaces and channels to be produced. The approach negates the need for complex surface interpolation algorithms required in surveys with lower point density, e.g. those obtained from global positioning systems or total stations. Furthermore, the technique has the advantage of being able to cover a large area over a comparatively short time period. Laser scanner returns revealed high vertical precision, ± ± ± ± ±0·02 m, for dry bar surfaces; however, submerged areas (< < < < <0·2 m depth) returned lower precision, with a range of − − − − −0·15 to + + + + +0·06 m. To account for this, different levels of detection (LoD) were applied to the dry and wet parts of the study reach during DEM subtraction. Subtraction of successive DEMs revealed two short depositional episodes over the ten-day study, with erosion dominating in between. Three episodes of avulsion were identified, two of which appeared to be triggered by constriction avulsion, whilst the other was initiated by bar-edge erosion. Transient lobes and sediment sheets could also be identified at the downstream end of the reach, as could lobe progradation. Relatively minor, but common, changes in channel morphology could also be detected, such as bar edge accretion, bank erosion and chute development. In an analysis of the effects of survey frequency upon volumes calculated following DEM subtraction, daily surveys were found to increase erosion volumes by 67 per cent and deposition volumes by 14 per cent when compared with an 8-day survey interval.

Abstract. Two prominent conceptual frameworks, environmental gradients and patch hierarchies, are used in combination to describe vegetation patterns along a riparian corridor in a semi‐arid South African system. We adopt both approaches, since riparian corridors are characterized by both strong environmental gradients above, away from and along the river, as well as a mosaic of patches in the geomorphology at multiple hierarchical scales. Constrained and unconstrained ordinations were used to determine the variability in vegetation pattern accounted for by the gradient and the geomorphic patch hierarchy data sets. The gradient data set consisted of vertical, lateral and longitudinal dimensions of the macro‐channel, while the patch hierarchy data set consisted of substratum type, morphological unit and channel type. Elevation up the macro‐channel bank, of the gradient data set, explained the main variation in vegetation pattern, and alluded to overriding processes of flooding frequency and water availability as determinants of vegetation pattern. Along the fluvially dynamic macro‐channel floor (lower elevation range), patchiness at the scale of the morphological unit best explained vegetation pattern. This relationship with morphological units suggests that the formation of well developed alluvial bars, and the degree of bedrock influence are important processes. The nested hierarchical framework used provided a good basis for identifying scale specific pattern in a relational manner. In systems characterized by strong environmental gradients as well as a patch mosaic at different spatial and temporal scales, the combined use of both perspectives to develop a fuller understanding of vegetation pattern is imperative and is encouraged.

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Sediment budgeting procedures based on analysis of three-dimensional morphological change provide a useful mechanism by which rates and patterns of fluvial sediment erosion, transfer and deposition can be monitored. This paper presents results from an annual sediment budgeting programme established in a 1-km long piedmont reach of the gravel-bed River Coquet in Northumberland, northern England. The study reach has a locally braided channel planform and has experienced lateral instability over at least the past 150 years. Annual sediment budgets for 1997–1998 and 1998–1999 have been based on tacheometric survey of: (i) 15 monumented channel cross-profiles; and (ii) channel margins and gravel-bar morphology. Survey data have been analysed for each discrete morphological unit (differentiating channel and complex bar assemblages) within 17 sub-reaches of the study reach using Arc/Info™ GIS. The morphological sediment budgeting techniques used to generate these reach-scale budgets may be particularly valuable in unstable gravel-bed rivers due to the inherent difficulties in measuring bed-load transport. The results show considerable variability in rates and patterns of within-reach sediment transfer between the successive surveys. The channel at Holystone is characterized by substantial within-reach sediment transfer, with minimal net export downstream. This behaviour appears to be characteristic of UK gravel-bed piedmont rivers.

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Terrestrial photogrammetry enables rapid survey to be undertaken in the fluvial environment, a crucial factor when assessing highly dynamic features. In addition, it permits the generation of terrain surfaces at a level of detail which, given equal time constraints in the field, far exceeds the detail permitted by conventional tacheometric survey. This study details the levels of accuracy that can be achieved using the RolleiMetric Close-range Digital Workstation (CDW) photogrammetric survey technique on a variety of low relief fluvial geomorphic features (lateral, point and mid-channel bars) ranging from 10 m 2 to 100 m 2 . The CDW software processes image data from an array of photographs and establishes a set of three-dimensional co-ordinates for the photographed object. The accuracies achieved across all bar surfaces were well within the resolution defined by the maximum size of the gravel on the bar surface (mean errors were between 0·026 and 0·057 m). The use of CDW photogrammetry does not require experienced personnel; however, care must be taken during the survey to minimize edge effects and to ensure that target density is sufficient to produce a terrain model that is accurate to within the limits of the surface sediment size. Guidance on target density as a function of terrain roughness is given to aid the user. A methodology is suggested that will allow CDW to be incorporated into sediment budgeting techniques, improving the level of achievable accuracy.