Modélisation hydrologique stochastique d'un bassin affecté par des changements d'occupation: cas du Merguellil en Tunisie centrale /Hydrological stochastic modelling of a basin affected by land-use changes: case of the Merguellil basin in central Tunisia

Abstract

Résumé Le bassin du Merguellil ayant été l'objet de nombreux aménagements de conservation des eaux et des sols (CES), une étude de l'impact de ceux-ci par une modélisation hydrologique a été effectuée. Le modèle MODCOU qui simule à la fois les écoulements de surface et souterrains a été utilisé. Les aménagements CES ont été pris en compte à travers une paramétrisation de la fonction de production. Le calage du modèle a été effectué par une approche stochastique multicritères sur plusieurs sites d'observations. Les résultats montrent que l'évapotranspiration réelle constitue la plus grande composante du système superficiel et que le système souterrain est largement déficitaire. Les sorties de ce dernier ont été estimées à quatre fois supérieures aux entrées. Il a enfin été montré l'amélioration de la représentativité du modèle apportée par la prise en compte des aménagements CES au moyen de paramètres spécifiques attribués à la fonction de production.Mots clefs aquifères; bassin versant; changement d'occupation du sol; modèle couplé eaux de surface-eaux souterraines; ressources en eau; Tunisie centrale Hydrological stochastic modelling of a basin affected by land-use changes: case of the Merguellil basin in central TunisiaAbstract Several works in the area of water and soil conservation (WWSC) have been implemented in the Merguellil basin. In order to test their efficiency, an impact study of these works was carried out by hydrological modelling. The MODCOU model, which simulates both surface and underground flow at the same time, was used. The WWSC were considered through a parameterization of the production function. The calibration of the model was carried out with a multi-objective stochastic approach on several observation sites. The results show that the actual evapotranspiration is the largest component of the surface system. The groundwater system is largely overdrawn with outputs estimated to be four times higher than the inputs. This study has shown the improvement in model representativeness by assigning specific parameters to the production functions of the WWSC zones.

Is Climate or Direct Human Influence Responsible for Discharge Decrease in the Tunisian Merguellil Basin?

“…The expansion of water and soil conservation management has led to a marked decrease in runoff in the Merguellil watershed [41]. Many investigations have focused on the variability of runoff coefficient (e.g., [79][80][81]). In this regard, by analyzing 114 comparable events over the period 1989-2010, Ogilvie et al [82] estimated a 40% reduction in the runoff coefficient following the expansion of water and soil conservation practices since 1996 with a decrease of 25% in annual flow at the basin outlet.…”

Surface water monitoring in small water bodies: potential and limits of multi-sensor Landsat time series

“…Water availability in small reservoirs is constrained by design capacities but determined by site-specific hydrological dynamics regulated by both natural (climate, topography, geology, geomorphology, pedology) and human factors (maintenance, leaks, withdrawals, releases). Studies based on hydrological measurements and geochemical analyses have identified the water balance of small reservoirs (Gay, 2004;Grunberger et al, 2004;Lacombe, 2007;Li and Gowing, 2005;Nyssen et al, 2010) but highlighted multiple modelling uncertainties due to evaporation, groundwater flows, high spatial rainfall variability, and human management (Li and Gowing, 2005;Grunberger et al, 2004;Lacombe, 2007;Leduc et al, 2007;Kingumbi et al, 2007). Rainfall-runoff modelling of gauged small reservoirs in Tunisia notably failed to exceed R 2 = 0.5 (Lacombe, 2007) and difficulties are greater in ungauged catchments (Cudennec et al, 2005).…”

“…Low spatial resolution sensors such as MODIS (Moderate Resolution Imaging Spectroradiometer, 250 m) and AVHRR (Advanced Very High Resolution Radiometer, 1.1 km), providing daily coverage of the globe, notably facilitated the assessment and monitoring of large wetlands (Guo et al, 2017), including the Niger Inner Delta (Mahé et al, 2011;Seiler et al, 2009;Ogilvie et al, 2015;Bergé-Nguyen and Crétaux, 2015), the Okavango Delta (Wolski and Murray-Hudson, 2008;Gumbricht et al, 2004), the Tana Delta (Leauthaud et al, 2013), or the Mekong Delta (Kuenzer et al, 2015;Sakamoto et al, 2007), large rivers such as the Amazon (Martinez and Le Toan, 2007;Alsdorf et al, 2007), and large lakes notably in eastern Africa (Swenson and Wahr, 2009;Ouma and Tateishi, 2006) and China (Ma et al, 2007;Qi et al, 2009). These sensors have also been used for global assessments (Prigent et al, 2007;Papa et al, 2010;Klein et al, 2015), but their low spatial resolutions remain inadequate for small reservoirs, as a single MODIS pixel corresponds to an area of 6.25 ha.…”

Surface water monitoring in small water bodies: potential and limits of multi-sensor Landsat time series

“…5 Water availability in small reservoirs is constrained by design capacities but determined by site-specific hydrological dynamics regulated by both natural (climate, topography, geology, geomorphology, pedology), and human factors (maintenance, leaks, withdrawals, releases). Studies based on hydrological measurements and geochemical analyses have identified the water balance of small reservoirs (Gay, 2004;Grunberger et al, 2004;Lacombe, 2007;Li and Gowing, 2005;Nyssen et al, 2010) but highlighted multiple modelling uncertainties due to evaporation, groundwater flows, high spatial rainfall variability and 10 human management (Li and Gowing, 2005;Grunberger et al, 2004;Lacombe, 2007;Leduc et al, 2007;Kingumbi et al, 2007). Rainfall-runoff modelling of gauged small reservoirs in Tunisia notably failed to exceed R 2 = 0.5 (Lacombe, 2007) and difficulties are greater in ungauged catchments (Cudennec et al, 2005).…”