Abstract. The Lake Chad basin, located in the centre of northern Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential evapotranspiration. Groundwater is an essential source for drinking-water supply, as well as for agriculture and groundwater-related ecosystems. Thus, assessment of groundwater recharge is very important although also difficult because of the strong effects of evaporation and transpiration, as well as the limited available data. A simple, generalized approach, which requires only limited field data, freely available remote sensing data, and well-established concepts and models, is tested for assessing groundwater recharge in the southern part of the basin. This work uses the FAO dual-Kc concept to estimate E and T coefficients at six locations that differ in soil texture, climate, and vegetation conditions. Measured values of soil water content and chloride concentrations along vertical soil profiles together with different scenarios for E and T partitioning and a Bayesian calibration approach are used to numerically simulate water flow and chloride transport using Hydrus-1D. Average groundwater recharge rates and the associated model uncertainty at the six locations are assessed for the 2003–2016 time period. Annual groundwater recharge varies between 6 and 93 mm and depends strongly on soil texture and related water retention and on vegetation. Interannual variability of groundwater recharge is generally greater than the uncertainty of the simulated groundwater recharge.

Depression-focused recharge

Groundwater model

Soil texture

10.5194/hess-27-3601-2023

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Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones

Journal of Contaminant Hydrology (2014)

Christoph Neukum A. Braun Rafig Azzam

Silver nanoparticle

10.1016/j.jconhyd.2014.05.012

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Citations (13)

Erratum zu: Integration der bodenkundlichen Filter- und Pufferfunktion in die hydrogeologische Vulnerabilitätsbewertung

Grundwasser (2015)

Tobias Wirsing Christoph Neukum Nico Goldscheider Matthias Maier

10.1007/s00767-015-0297-5

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Soil water balance in the Lake Chad Basin using stable water isotopes and chloride of soil profiles

Isotopes in Environmental and Health Studies (2019)

Daniel Okubay Tewolde Paul Koeniger Matthias Beyer Christoph Neukum Maike Gröschke

The Lake Chad Basin (LCB) is an endorheic transboundary catchment highly vulnerable to drought. For effective groundwater management, recharge areas need identification and replenishment quantification. At present, little research exploring unsaturated zone water flow processes and groundwater recharge are available. In this study, 12 vertical soil profiles were analysed for stable water isotopes and chloride concentration to estimate evaporation and groundwater renewal. Most δ18O and δ2H isotope profiles reveal typical arid environment patterns, with maximum enrichment at depths between 2.5 and 20 cm and depletion towards the surface (atmospheric influence) and depth (mixing and diffusion). Average annual dry season evaporation rates in Salamat and Waza Logone range from 5 to 30 mm, in Bahr el Ghazal and Northern Lake Chad from 14 to 23 mm. According to the chloride mass balance (CMB), the average annual recharge rate is estimated between 3 and 163 mm in Salamat and Waza Logone and less than 1 mm in Bahr el Ghazal and Northern Lake Chad. Based on the CMB results, potential recharge sites were identified, while estimated soil evaporation corresponds to plant water use at the initial growing stage, which is an important component in irrigation water management.

10.1080/10256016.2019.1647194

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Consideraciones sobre el funcionamiento hidrogeológico y la vulnerabilidad a la contaminación de la Sierra de las Nieves (Málaga) a partir de un ensayo de trazador en condiciones de estiaje

Geogaceta (2004)

Bartolomé Andreo Navarro Iñaki Vadillo Pérez Francisco Carrasco Cantos Christoph Neukum Pablo Jiménez‐Gavilán

A tracer test during low-flow conditions was carried out in the karstic aquifer of Sierra de las Nieves (Malaga) in order to assess its hydrogeological functioning and vulnerability to contamination. Two kilogrammes of Eosine were injected in an active siphon located in the Sima del Aire cave shaft (-640 m) at the end of August 2003. The springs were sampled until November 2003. For more than 50 days, the tracer was not detected at any of the springs. After several rainfall events in October 2003, a signal was observed in the two Rio Grande springs. The first arrival of Eosine appears before the increase of spring discharge and the dilution effect of the most important rainfalls (86 mm, October 25th). The calculated groundwater velocities (below 4 m/hour) are not representative of the dry period because rainfall forced the Eosine transport. However, they give an idea about the long residence time if a contamination event occurs during low-flow conditions.

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