Abstract
Abstract. The aim of the paper is to apply an object-based geomorphometric procedure to define the runoff contribution areas and support a hydro-geomorphological analysis of a 3 km2 Mediterranean research catchment (southern Italy). Daily and sub-hourly discharge and electrical conductivity data were collected and recorded during a 3-year monitoring activity. Hydro-chemograph analyses carried out on these data revealed a strong seasonal hydrological response in the catchment that differed from the stormflow events that occur in the wet periods and in dry periods. This analysis enabled us to define the hydro-chemograph signatures related to increasing flood magnitude, which progressively involves various runoff components (baseflow, subsurface flow and surficial flow) and an increasing contributing area to discharge. Field surveys and water table/discharge measurements carried out during a selected storm event enabled us to identify and map specific runoff source areas with homogeneous geomorphological units previously defined as hydro-geomorphotypes (spring points, diffuse seepage along the main channel, seepage along the riparian corridors, diffuse outflow from hillslope taluses and concentrate sapping from colluvial hollows). Following the procedures previously proposed and used by authors for object-based geomorphological mapping, a hydro-geomorphologically oriented segmentation and classification was performed with the eCognition (Trimble, Inc.) package. The best agreement with the expert-based geomorphological mapping was obtained with weighted plan curvature at different-sized windows. By combining the hydro-chemical analysis and object-based hydro-geomorphotype map, the variability of the contribution areas was graphically modeled for the selected event, which occurred during the wet season, by using the log values of flow accumulation that better fit the contribution areas. The results allow us to identify the runoff component on hydro-chemographs for each time step and calculate a specific discharge contribution from each hydro-geomorphotype. This kind of approach could be useful when applied to similar, rainfall-dominated, forested and no-karst catchments in the Mediterranean eco-region.
Highlights
In order to gain a better understanding of hydrology, it is essential to study the complex interactions and linkages between watershed components, such as drainage network, riparian corridors, headwaters, hillslopes and aquifers and related processes operating at multiple scales (National Research Council, 1999)
Hydrologists have carried out numerous studies on catchment and hillslope hydrology in order to define when, how and where runoff is produced and how it progressively increases along the drainage network
Hydrologists generally agree that following rainfall, new-event water components are added to the old, pre-event water components through various hydrological mechanisms that are generally referred to as baseflow components that are derived
Summary
In order to gain a better understanding of hydrology, it is essential to study the complex interactions and linkages between watershed components, such as drainage network, riparian corridors, headwaters, hillslopes and aquifers and related processes operating at multiple scales (National Research Council, 1999). The most common general concept that explains the above-mentioned hysteretic behavior is the variable source area (VSA) concept This concept was originally proposed by Hewlett (1961) and later adopted by other authors (Dunne and Black, 1970; Dunne and Leopold, 1978; Huang and Laften, 1996; Vander Kwaak and Loague, 2001; Zollweg et al, 1995, Pionke et al, 1996). The “hydro-geomorphic paradigm” was proposed by Sidle et al (2000) in order to discriminate the VSA hydrologic sources and pathways, which refers to the connected hydrogeomorphic components of the catchments (hollow, hillslope and riparian corridor). Based on the up-to-date and shared theoretical geomorphometric background (Baatz and Schäpe, 2000; Dragut and Blaschke, 2006; van Asselen and Seijmonsbergen, 2006; Anders et al, 2011; Dragut et al, 2013, 2014; Eisank et al, 2014), this proposal is currently under experimental calibration as an effective, object-based geomorphometric procedure for spatial individuation, objective delimitation and automatic recognition of the hydrogeomorphotypes from the perspective of an object-based distributed hydrological modeling (Cuomo et al, 2012)
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