Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step–pool channel

Abstract

High-resolution tacheometric field surveying was integrated with computer-assisted drafting to visualize and contrast three-dimensional bed and water surface digital elevation models (DEMs) for submerged and unsubmerged hydraulic jump regions in a bedrock step-pool channel. Measurements were conducted for two discharge conditions. Since previous applications of three-dimensional field mapping and digital elevation modelling of stream channels have been limited to smoothly contiguous gravel-bedded systems, surveying was optimized by topographic setting and scaled to localized bed and water surface discontinuities. Traces and visualizations of the jump regions indicated that dichotomous decimetre shifts in water surface topography occurred for both jump regions from lower to higher discharges. Systematic removal of the survey points and DEM differencing indicated that point densities of ten points per square metre, in conjunction with a survey structure targeting grade breaks of 0·3-0·5 m, were required to capture decimetre form variations of the natural jump regions. The DEMs highlight the importance of recognizing the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels.

Accounting for uncertainty in DEMs from repeat topographic surveys: improved sediment budgets

“…The average kernel point density (pt ρ) was on the order of 0·3 points m −2 (based on a 5 × 5 rectangular moving window; see Table I). A 2-3 m grid-based sampling scheme was adopted across the entire reach, with feature-stratifi ed infi lling in areas of greater topographic complexity to capture bar-scale morphological features (Valle and Pasternack, 2005). In general, this results in high point density in areas of topographic complexity and low point density in topographically simple areas.…”

Channel Representation in Physically Based Models Coupling Groundwater and Surface Water: Pitfalls and How to Avoid Them

“…This approach seeks to reduce the number of measurements while favoring some spatial uniformity of elevation errors (Merwade et al 2008;Heritage et al 2009). In complex terrains, a useful approach is a triangular sampling pattern scaled to surface discontinuities, which can be efficiently converted to the numerical mesh (Vallé and Pasternack 2006).…”

Influence of survey strategy and interpolation model on DEM quality

“…While in fluvial geomorphology, TINs (e.g. Butler et al, 1998;Brasington et al, 2000;Vallé and Pasternack, 2006;Milan et al, 2007;Rumsby et al, 2008;) or kriging (Fuller et al, 2003a;Nicholas, 2003) are the most common interpolation algorithms used, Fuller and Hutchinson (2007) in a comparison found TINs to be more reliable. Furthermore, the solution of TINs can be computationally efficient and well suited to discontinuous shapes (such as ridges), and breaks of slope (Moore et al, 1991).…”