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

Abstract

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.

Water resources trends in Middle East and North Africa towards 2050

“…country level, would be studied using the same methodology (e.g. Giertz et al, 2006). The second line of research to be undertaken is an analysis on potential adaptation strategies and costs of these adaptations using the developed framework (e.g.…”

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

“…The dominance of groundwater as a main contributor to stormflow generation in a temperate study area was postulated, for example, by Sklash et al (1976) and has been further consolidated by subsequent studies (e.g. Peters and Ratcliffe, 1998;Hoeg et al, 2000;Uhlenbrook and Hoeg, 2003).Whereas studies on runoff generation processes in temperate regions are plentiful, Giertz et al (2006) stress a lack of studies within tropical regions. Chuan (2003) also notes a general lack of data on runoff generation processes in tropical regions, which applies especially for Southeast Asia.…”

Interplay of riparian forest and groundwater in the hillslope hydrology of Sudanian West Africa (northern Benin)

“…Its lower part is bordered by a 20 m-wide riparian forest which represents about 5 % of the hillslope length. According to the World Reference Base (IUSS Working Group WRB, 2006), the soils are mainly lixisols on crests and mid-slopes, plinthosols with or without outcrops of hardpan at the slope bottom and thin sandy soils overlying a thick clayey horizon in the bas-fonds (Faure, 1977;Giertz and Diekkrüger, 2003). The French word bas-fonds denotes a tropical, seasonally waterlogged, linear depression in the headwater zones of rivers, frequently without any marked stream channel, and predominantly covered by grass species (Giertz and Diekkrüger, 2003;Séguis et al, 2011b).…”

“…These waterlogged headwater zones are very common in the region and are considered to play a major role in the hydrological regimes in Africa (Balek and Perry, 1973;Bullock, 1992;Giertz and Diekkrüger, 2003;Séguis et al, 2011a) but this assumption remains disputed (for a review, see von der Heyden, 2004). In our area, these bas-fonds, mainly covered with grass, have no riparian vegetation (for reasons unknown to the authors) which, according to our study, can explain the occurrence of exfiltration downslope and consequently generate streamflow.…”

“…For one, by taking into account hillslope processes (overland flow and interflow) in an enhanced 1-D SoilVegetation-Atmosphere Transfer (SVAT) model, Giertz et al (2006) correctly simulated the streamflow of the 16.5 km 2 Aguima catchment (Benin). In the same area, but on a larger scale, Le Lay et al (2008) used a TopModel approach (Beven and Kirkby, 1979) based on shallow hydrological processes to simulate discharges.…”