Developments in monitoring and modelling small‐scale river bed topography

Abstract

Recent research in fluvial geomorphology has emphasized the spatially distributed feedbacks amongst river channel topography, flow hydraulics and sediment transport. Although understanding of the behaviour of dynamic river channels has been increased markedly through detailed within-channel process studies, less attention has been given to the accurate monitoring and terrain modelling of river channel form using three-dimensional measurements. However, such information is useful in two distinct senses. Firstly, it is one of the necessary boundary conditions for a physically based, deterministic modelling approach in which three-dimensional topography and river discharge drive within-channel flow hydraulics and ultimately spatial patterns of erosion and deposition and therefore channel change. Secondly, research has shown that an alternative means of estimating the medium-term bedload transport rate can be based upon monitoring spatial patterns of erosion and deposition within the river channel. This paper presents a detailed assessment of the distributed monitoring and terrain modelling of river bed topography using a technique that combines rigorous analytical photogrammetry with rapid ground survey. The availability of increasingly sophisticated terrain modelling packages developed for civil engineering application allows the representation of topographic information as a landform surface. Intercomparison of landform surfaces allows visualization and quantification of spatial patterns of erosion and deposition. A detailed assessment is undertaken of the quality of the morphological information acquired. This allow some general comments to be made concerning the use of more traditional methods to monitor and represent small-scale river channel morphology.

Towards a protocol for laser scanning in fluvial geomorphology

“…Data may now be rapidly acquired and processed at a density sufficient to represent the surface at the grain scale estimated at between 4000 and 10 000 points m −2 by Lane et al (1994). The issue of point distribution and potential operator bias is also rendered obsolete as a dense cloud of meshed data points ensures that a surface is sampled many times.…”

“…As a result, new insights are being offered into fluvial dynamics utilizing three-dimensional DEMs of the riverine environment (e.g. Lane et al, 1994;Milne and Sear, 1997;Heritage et al, 1998;Brasington et al, 2000;Fuller et al, 2005). Many of these studies continue to suffer area or resolution limitations due to a trade-off between spatial coverage and morphologic detail captured ( Figure 1): techniques such as terrestrial photogrammetry produce dense accurate morphometric data but aerial coverage is restricted; aerial photogrammetry offers increased spatial coverage but reduced elevation accuracy; EDM theodolite surveys suffer from long collecting times resulting in reduced data density if large areas are surveyed (Figure 1).…”

9 Modelling river-bank-erosion processes and mass failure mechanisms: progress towards fully coupled simulations

“…Recently, techniques such as digital photogrammetry and laser scanning (e.g., Lane et al, 1994;Barker et al, 1997;Nagihara et al, 2004) can provide the opportunity to define river bank topography at unprecedented spatial resolution (surveys with point densities of ca. 10 7 points across a bank face are readily obtainable using terrestrial laser scanning) and accuracy (72 mm).…”

Investigating the geomorphological potential of freely available and accessible structure‐from‐motion photogrammetry using a smartphone

“…Initially, these developments focused upon constructing digital elevation models (DEMs) or digital terrain models (DTMs) using both photogrammetric (e.g. Lane et al, 1994;Barker et al, 1997;Lane et al, 1999;Lane, 2000) and differential global positioning system (dGPS) (e.g. Fix and Burt, 1995;Brasington et al, 2000) data.…”