Development of a quantitative transport-time-based groundwater vulnerability model for non-point-source pollution in karst aquifers: a conceptual approach and example from the Tanour and Rasoun spring catchment, north-western Jordan | Développement d’un modèle de vulnérabilité quantitative des eaux souterraines basée sur le temps de transport pour des pollutions diffuses d’aquifères karstiques: une approche conceptuelle et un exemple sur le bassin d’alimentation des sources de Tanour et Rasoun, nourd-ouest de la Jordanie Desarrollo de un modelo cuantitativo de vulnerabilidad de las aguas subterráneas a la contaminación de una fuente no puntual en los acuíferos cársticos basado en el tiempo de transporte: un enfoque conceptual y un ejemplo de la Cuenca del manantial de Tanour y Rasoun, en el noroeste de Jordania 喀斯特含水层中非点源污染的基于运移时间的地下水脆弱性定量化模型开发:约旦西北部Tanour和Rasoun泉水流域的概念方法和案例 O desenvolvimento de um modelo quantitativo de vulnerabilidade das águas subterrâneas em aquíferos cársticos, baseado no tempo de transporte de uma fonte de poluição não pontual: uma abordagem conceitual, e o exemplo da bacia hidrográfica de Tanour e Rasoun, noroeste da Jordânia
2020
Hamdan, Ibraheem | Ptak, Thomas | Wiegand, Bettina | Sauter, Martin
A quantitative transport-time-based vulnerability assessment approach for non-point-source pollution using a spatially distributed geographic information system (GIS)-generated topographic model was developed for the karst aquifer system feeding the Tanour and Rasoun springs in NW Jordan. The approach implies the assessment of the groundwater residence times in different compartments of the karst system, i.e. the epikarst, the vadose zone and the phreatic system. Groundwater transport times within the epikarst zone were determined by employing two main variables: (1) the length of the flow path, and (2) the transport velocity between the assumed point of subsurface infiltration into the soil and the location for the actual groundwater recharge at the ephemeral streams. Sub-horizontal lateral flow is assumed for the epikarst. The base-flow recession curve method was employed to estimate the effective, average and catchment-wide transmissivity of the epikarst. Based on the calculated transmissivity, three different hydraulic conductivity values were assumed to assess the effect of the unknown average saturated thickness of the epikarst. The developed method was validated by independent measurements of the transport-time-based on the δ¹⁸O breakthrough signal in the spring catchment discharge, following a recharge event. The transport-time distribution map, calculated based on flow-path length towards the streams and average solute transport velocity, shows high correlation with the catchment-averaged stable isotopes’ breakthrough curves. Because of the intensive karstification below the stream bed, residence times in the vadose and the phreatic zones can be assumed to be negligible compared to the transport times in the epikarst.
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