Scales and similarities in runoff processes with respect to geomorphometry

Numerous investigations using various techniques have been carried out towards a more detailed understanding of relationships and interactions between catchment morphometry and rainfall-runoff processes. Recently, this research question has become more relevant through the need for hydrologic computer models simulating the water balance of large areas. Moreover, advances in the analysis of landform morphometry through the availability of high resolution Digital Elevation Models (DEMs) and powerful Geo-Information Systems (GIS) enhance research efforts within this topic.

In this study several computer techniques and models were applied to investigate the effects of geomorphometry on rainfall-runoff processes at different scales. The sensitivity of dynamic hydrologic processes to comparatively static boundary conditions requires different methods for modelling, analysis and visualisation of different kinds of data. Therefore an approach integrating several geocomputational concepts, including spatial analysis of different types of geo-data, static modelling of spatial structures, dynamic 4D-modelling of hydrologic processes and statistical techniques was chosen.

Geomorphometric analysis of the research areas was carried out with GIS packages (including Arc/Info and GRASS), special purpose software and self developed tools. Soil-morphometry relationships were modelled within a GIS environment. Hydrologic models (SAKE and TOPMODEL) were used to simulate rainfall runoff processes. Statistical tools and sensitivity analysis were applied to gain an insight into the hydrologic significance of geomorphometric properties.

The results demonstrate the importance of small parts of the catchment area, which are related to low slope angles, low flow lengths and concavities. The spatial distribution of soil types has a significant relationship to the modelled runoff. Spatial distributions of soil types are partly related to morphometry and can be captured by means of soil - morphometry models. Further results show that catchments which differ significantly in morphometry show different runoff responses and different hydrologic sensitivity to changes in boundary conditions. A crude derivation of geomorphometric - hydrologic landform types could be reached. Therefore geomorphometric classifications of catchment types could be a promising method to support large scale hydrologic modelling. Models describing soil distribution in relation to geomorphometry could assist regionalisation of spatial heterogeneity and structure of soil parameters relevant in hydrologic modelling. Moreover, quantification of geomorphometric catchment structure, e.g. in terms of contributing areas, is needed to describe significant geomorphometric catchment characteristics.