The application of geomorphic indices in terrain analysis for ground engineering practice

- Geomorphic indices are applied to freely available DEM data.
- Develops understanding of hillslope and rivers response to tectonics, climatic and land use change.
- Identify engineering constraints/geohazards related to gully, badland formation and landsliding.

Terrain analysis studies for long linear engineering projects provide critical engineering geological and geomorphological data that inform project design options, route selection and construction methodologies. This paper introduces the use of geomorphic indices alongside methods of aerial photograph interpretation and remote sensing in the desk study phase of engineering terrain evaluations in the identification of landscape changes and geohazards in active tectonic regions. Three geomorphic indices (hypsometry, river long profile analysis and stream-length gradient index) are applied to freely available DEM data in order to develop the qualitative and quantitative (relative to study area) understanding of how the hillslope and river systems respond to the effects of tectonic activity and climate change. A hypothetical pre-feasibility study corridor (10 km width) located in the Sorbas Basin (SE Spain) is used to develop the methods of application, which could represent a proposed rail, road or pipeline routing. The results of the scaled indices approach, from catchment to reach (i.e. section of uninterrupted river channel) investigations, indicate a variable response of landscape processes. 'Active' erosional conditions are found in the central and northern limits of the basin relating to a known zone of tectonic deformation, the Infierno-Marchalico Lineament, and also to the effects of a river capture-related base-level lowering. 'Active' conditions are typically linked to an increased occurrence of landslides and badland formation. 'Stable' conditions are more common in the west and east of the basin where drainage channels are effectively coupled to base level. The combined results of geomorphic indices and aerial photograph interpretation are used in the identification of engineering constraints and geohazards as related to gully development, badland formation and the formation of landslides. A simple geohazard constraints map is produced which demonstrates ground related hazard to the wider project team and can be used to target field investigations and further inform construction methodologies and limitations.