Hydrometric and tracer-based assessment of time-variable groundwater contributions to stormflow in a small tropical catchment
Abstract
Runoff generation in surficial flowpath dominated catchments is still poorly understood. Several mechanisms have been described that explain the occurrence of surficial flowpaths, among them are infiltration excess overland flow (OF), saturation excess OF and return flow. Overland flow due to saturation excess has been described as one dominant flowpath contributing to stormflow even in forested catchments of Amazonia. However, the nature of the processes generating saturation OF and in the end stormflow remains unclear. Understanding these processes is vital in the context of forest cover conversion and the impacts on the hydrological and nutrient cycles. Several methods exist to assess flowpaths and runoff generation processes based on hydrometric and tracer data and model approaches. However, often conflicting results were found in terms of, for example, groundwater contributions to stormflow using different methods. This study is designed to tackle the conflicting findings of baseflow / groundwater contribution to stormflow at a pasture site that is dominated by saturation OF and take a closer look at the exact mechanisms that produce stormflow on an event basis. We used a combination of hydrometric and tracer data, a traditional end member mixing analysis (EMMA) and a conceptual flow-tracer model, to show the time variability of runoff generation and mixing processes and the influence on groundwater contribution to stormflow. We selected conservative tracers and performed EMMA to identify potential end members that contribute to runoff. Rainfall, a shallow (soil water) and a deeper subsurface (groundwater) source were identified as end members and used to develop a simple, lumped conceptual model to simulate stormflow and solute dynamics during 3 rain events representing two different seasons. End member contributions were calculated using both approaches. Our results indicate that baseflow represented by groundwater is minimal during event peak flows but increases during the recession of the hydrograph. We further show that the selection of the method may have a significant impact on the estimation of stormflow contributions of different hydrological components, e.g. such as groundwater.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H21G1138B
- Keywords:
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- 1860 HYDROLOGY Streamflow;
- 1850 HYDROLOGY Overland flow