Breaklines and point measuring density in modeling earth surface processes

Abrupt changes in terrain elevation are called breaklines. When simulating earth surface processes breaklines are important structure elements and should be recorded as realistically as possible. They can appear as embankments, dams, walls, building outlines and the like.

The density of measuring points nearby breaklines must be sufficiently high, while the number of measuring points can be lower in less structured areas. With triangulation and the use of Thiessen Polygons, varying demands concerning point density can be considered. This procedure supports effective integration of measuring points within the modeling environment.

A basis for identifying areas with higher or lower requirements of elevation measurements are curvature information from digital terrain models. In SAGA GIS the module Slope, Aspect, Curvature is a great option for generating curvature rasters. For the given purpose the profile curvature is needed, which depicts vertical elevation changes (convex and concave segments along a terrain cross-section).

Different types of breaklines in a lowland fluvial environment.
Different types of breaklines in a lowland fluvial environment.

The resulting curvature information serves as spatial template for the initial point cloud, in order to perform data thinning with different intensities within the area of interest. In case of hydrodynamic modeling of a creek besides its embankments, road embankments, locally confined dams or embankment lines of smaller ditches appear as typical breaklines. These areas therefore require higher measuring point densities.

Despite the usage of high resolution airborne laserscanning data, usually not all hydraulically relevant breaklines can be detected by this technique. This accounts for example for narrow dams and protection units or – in case of even higher quality standards – curbsides. For these kind of objects it is necessary to use conventional, precise surveying devices (DGPS, tachymeter, etc.) or possibly drone-based laser scanners in the near future.