Analysis of storm hydrograph and flow pathways using a three-component hydrograph separation model

128

133

Abstract. The mechanisms allowing the rapid release of stored water to streams are poorly understood. Here we use a tile-drained field site to combine macroporous soils at the hillslope scale with the advantage of at least partly controlled lower boundary conditions. We performed a series of three irrigation experiments combining hydrometric measurements with stable isotope and bromide tracers to better understand macropore-matrix interactions and stored water release processes at the hillslope scale. Stable isotope concentrations were monitored in the irrigation water, the tile-drain discharge and the soil water before and after the experiment. Bromide was measured every 5-15 min in the tile-drain hydrograph. Different initial conditions for each experiment were used to examine how these influenced flow and transport. Different amounts of irrigation water were necessary to increase tile-drain discharge above the baseflow level. Hydrograph separation based on bromide data revealed that irrigation water contributions to peak tile-drain discharge were on the order of 20 %. Oxygen-18 and deuterium data were consistent with the bromide data and showed that pre-event soil water contributed significantly to the tile-drain event flow. However, the isotopic composition of soil water converged towards the isotopic composition of irrigation water through the course of the experiment. Mixing calculations revealed that by the end of the irrigation experiments 20 % of the soil water in the entire profile was irrigation water. The isotopic data showed that the pre-event water in the tile drain was mobilized in 20-40 cm soil depth where the macroporematrix interaction leads to an initiation of macropore flow after a moisture threshold is exceeded.

Section: On the Importance Of Our Findings For Catchment-scale Hydrogmentioning

confidence: 80%

Macropore flow of old water revisited: experimental insights from a tile-drained hillslope

Klaus

Zehe

Elsner

et al. 2013

128

133

“…The following equations define a three-component separation (modified after Ogunkoya and Jenkins, 1993):…”

Section: Hydrograph Separationmentioning

confidence: 99%

“…The method is based on several assumptions, which are described in the literature (e.g. Ogunkoya and Jenkins, 1993). Note, however, that the method is only applicable if the components are chemically distinguishable and if tracers are conservative or their fluctuations measurable.…”

Section: Hydrograph Separationmentioning

confidence: 99%

A three-component hydrograph separation based on geochemical tracers in a tropical mountainous headwater catchment in northern Thailand

Hugenschmidt

Ingwersen

Sangchan

et al. 2014

Abstract. Land-use change in the mountainous parts of northern Thailand is reflected by an increased application of agrochemicals, which may be lost to surface and groundwater. The close relation between flow paths and contaminant transport within hydrological systems requires recognizing and understanding the dominant hydrological processes. To date, the vast majority of studies on runoff generation have been conducted in temperate regions. Tropical regions suffer from a general lack of data, and little is known about runoff generation processes. To fill this knowledge gap, a three-component hydrograph separation based on geochemical tracers was carried out in a steep, remote and monsoondominated study site (7 km 2 ) in northern Thailand. Silica and electrical conductivity (EC) were identified as useful tracers and were applied to calculate the fractions of groundwater (similar to pre-event water), shallow subsurface flow and surface runoff on stormflow. K + was a useful indicator for surface runoff dynamics, and Ca 2+ provided insights into groundwater behaviour. Nevertheless, neither measure was applicable for the quantification of runoff components. Cl − and further parameters (e.g. Na + , K + , and Mg 2+ ) were also not helpful for flow path identification, nor were their concentrations distinguishable among the components.Groundwater contributed the largest fractions to stormflow (62-80 %) throughout all events, followed by shallow subsurface flow (17-36 %) and surface runoff (2-13 %). Our results provide important insights into the dynamics of the runoff processes in the study area and may be used to assess the transport pattern of contaminants (i.e. agrochemicals) here.

“…Most studies in the humid tropics revealed that lateral processes -mainly subsurface stormflow (interflow) -are predominant in tropical forest ecosystems. In West Africa, only a few studies concerning hydrological processes -particularly in Nigeria and the Ivory Coast-were carried out (Jeje et al, 1986;Ogunkoya and Jenkins, 1993;Chevallier and Planchon, 1993;van de Giesen et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Physically-based modelling of hydrological processes in a tropical headwater catchment (West Africa) – process representation and multi-criteria validation

Giertz

Diekkrüger

Steup

2006

Abstract. The aim of the study was to test the applicability of a physically-based model to simulate the hydrological processes in a headwater catchment in Benin. Field investigations in the catchment have shown that lateral processes such as surface runoff and interflow are most important. Therefore, the 1-D SVAT-model SIMULAT was modified to a semi-distributed hillslope version (SIMULAT-H). Based on a good database, the model was evaluated in a multi-criteria validation using discharge, discharge components and soil moisture data. For the validation of discharge, good results were achieved for dry and wet years. The main differences were observable in the beginning of the rainy season. A comparison of the discharge components determined by hydro-chemical measurements with the simulation revealed that the model simulated the ratio of groundwater fluxes and fast runoff components correctly. For the validation of the discharge components of single events, larger differences were observable, which was partly caused by uncertainties in the precipitation data. The representation of the soil moisture dynamics by the model was good for the top soil layer. For deeper soil horizons, which are characterized by higher gravel content, the differences between simulated and measured soil moisture were larger.A good agreement of simulation results and field investigations was achieved for the runoff generation processes. Interflow is the predominant process on the upper and the middle slopes, while at the bottom of the hillslope groundwater recharge and -during the rainy season -saturated overland flow are important processes.