GIS Applications to Investigate the Linkage between Geomorphological Catchment Characteristics and Response Time: A Case Study in Four Climatological Regions, South Africa

Ockert J Gericke

doi:10.3390/w11051072

Abstract

In flood hydrology, geomorphological catchment characteristics serve as fundamental input to inform decisions related to design flood estimation and regionalization. Typically, site-specific geomorphological catchment characteristics are used for regionalization, while flood statistics are used to test the homogeneity of the identified regions. This paper presents the application and comparison of Geographical Information Systems (GIS) modelling tools for the estimation of catchment characteristics to provide an enhanced understanding of the linkage between geomorphological catchment characteristics and response time. It was evident that catchment response variability is not exclusively related to catchment area, but rather associated with the increasing spatial–temporal heterogeneity of other catchment characteristics as the catchment scale increases. In general, catchment and channel geomorphology overruled the impact that catchment variables might have on the response time and resulting runoff. Shorter response times and higher peak flows were evident in similar-sized catchments characterized by lower shape factors, circularity ratios, and shorter centroid distances and associated higher elongation ratios, drainage densities and steeper slopes. The GIS applications not only enabled the inclusion of a more diverse selection of catchment characteristics as opposed to when manual methods are used, but the high degree of association between the different GIS-based methods also confirmed their preferential use.

Highlights

Geomorphological catchment characteristics serve as fundamental input to inform decisions related to design flood estimation and hydrological regionalization
It is evident from these tables that catchment area influences both the volume of runoff and catchment response time, i.e., an increase in catchment area is associated with increases in both the volume of runoff and response time
The use of specialized Geographical Information Systems (GIS) spatial modelling tools and conventional equations in conjunction with standard GIS tools resulted in comprehensive and comparable catchment parameter estimations, which contributed towards the better understanding of the linkage between geomorphological catchment characteristics and response time

Summary

Introduction

Geomorphological catchment characteristics serve as fundamental input to inform decisions related to design flood estimation and hydrological regionalization. The main objective of regionalization in flood hydrology is to improve and augment the accuracy of design flood estimates at gauged and ungauged sites, which is normally reflected by the Goodness-of-Fit (GOF). The two most difficult aspects of any regionalization process are [2,3]: (i) to establish whether regionalization is required, and (ii) to identify and establish the number of homogeneous hydrological regions required. Geomorphological catchment characteristics at specific sites are used for regionalization, while flood statistics (e.g., L-moment ratios and other statistical measures from observed rainfall-runoff data) are used to test the homogeneity of the identified regions. Geomorphological catchment characteristics and the accurate estimation thereof are essential to both

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