Amaël Poulain

Assessment of groundwater recharge processes through karst vadose zone by cave percolation monitoring

Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behaviour because it is the place where most contamination takes place. In this work, an in situ experimental approach was performed to identify and quantify flow and storage processes occurring in karst vadose zone. Cave percolation monitoring and dye tracing were used to investigate unsaturated zone hydrological processes. Two flow components (diffuse and quick) were identified and, respectively, account for 66% and 34% of the recharge. Quickflow was found to be the result of bypass phenomenon in vadose zone related to water saturation. We identify the role of epikarst as a shunting area, most of the storage in the vadose zone occurring via the diffuse flow component in low permeability zones. Relationship between rainfall intensity and transit velocity was demonstrated, with 5 times higher velocities for the quick recharge mode than the diffuse mode. Modelling approach with KarstMod software allowed to simulate the hybrid recharge through vadose zone and shows promising chances to properly assess the recharge processes in karst aquifer based on simple physical models.

Surface to Cave Dye Tracing: Lessons Learned from the Belgian Karst

vadose zone between the surface and the cave by mean of dyes and drip-water monitoring. These methods enable us to discover information about groundwater dynamic. A maximum velocity of around 10 meters/ hour was calculated in absence of rainfall and without significant flush during the injection of the dye. A multimodal breakthrough curve was recorded in the percolation water, the tracer being remobilized by every rainfall event during more than 120 days. The dye tracked the reaction of the percolation to rainfall events at the surface. Separation and analysis of the different peaks and their related rainfall events revealed a clear trend. The higher the rainfall intensity, the faster the reaction of the percolation. The effect of the rainfall gives infiltration velocities from 10 to 55 m/h for the higher rainfall intensities. Additionally, the dye tracing allowed us to compare the effect of snowmelt and Abstract The vadose zone (unsaturated) of karst aquifers is critical for several reasons. (1) It is the main pathway for karst groundwater recharge from the surface to the phreatic zone (saturated), (2) it forms the transition zone between surface human activities (potential contamination) and the groundwater resource, and (3) it gives a support for karst fauna and flora through its hydrogeological dynamic. The hydrogeological functions of the vadose zone are of growing interest for these reasons but, also, because this highly heterogeneous media is still poorly understood by hydrogeologists and karst researchers.

Double-peaked breakthrough curves as a consequence of solute transport through underground lakes: a case study of the Furfooz karst system, Belgium

The existence of double-peaked breakthrough curves (BTC), which are the result of the transport of a dye tracer through underground lakes, is reported. Investigations were undertaken on the Furfooz karst system in southern Belgium. In this system, the River Lesse sinks partially into a swallow hole. The water follows a solitary conduit leading to an underground lake that is directly connected to a second underground lake. Double-peaked BTCs were detected in the resurgent water, downstream of this second lake. The report first describes field data (tracer tests in various hydrologic conditions) which point towards the double peak being linked to a nonlinear process that originates within the lakes. Complementary investigations within the lakes show a complex behavior of the dye tracer related to a specific hydrodynamic feature that leads to the separation of the solute plume. A conceptual model of the solute transport within the lakes is proposed. This model emphasizes the physical effect of the lakes on the dye flow-through process.RésuméOn rapporte l’existence de courbes de restitution à double pics (CR), résultant du transport d’un traceur artificiel (colorant) dans des lacs souterrains. Des études ont été menées sur le système karstique de Furfooz dans le Sud de la Belgique. Dans ce système, la rivière Lesse s’infiltre partiellement dans une perte. L’eau s’écoule au sein d’un conduit unique menant à un lac souterrain qui est directement connecté à un deuxième lac souterrain. Les CR à double pics ont été détectées dans une résurgence, située en aval de ce deuxième lac. Cet article décrit d’abord les données de terrain (essais de traçage dans des conditions hydrologiques diverses) qui indiquent que le double pic est lié à un processus non linéaire qui prend son origine au sein des lacs. Des études complémentaires au niveau des lacs montrent un comportement complexe du traceur artificiel associé à une hydrodynamique spécifique conduisant à la séparation du panache du soluté. Un modèle conceptuel du transport de soluté au sein des lacs est proposé. Ce modèle met l’accent sur l’effet physique des lacs sur les processus de transport du traceur artificiel.ResumenSe informa acerca de la existencia de curvas de avance de doble pico (BTC), que son el resultado del transporte de un trazador de colorantes a través de lagos subterráneos. Se realizaron investigaciones sobre el sistema karst de Furfooz en el sur de Bélgica. En este sistema, el río Lesse se hunde parcialmente en pozos kársticos. El agua sigue un conducto único que conduce a un lago subterráneo que está conectado directamente a un segundo lago subterráneo. Se detectaron BTCs de doble pico en el agua resurgente, aguas abajo de este segundo lago. El artículo describe primero los datos de campo (pruebas de trazabilidad en diversas condiciones hidrológicas) que apuntan hacia el doble pico vinculado a un proceso no lineal que se origina dentro de los lagos. Las investigaciones complementarias dentro de los lagos muestran un comportamiento complejo del trazador de colorantes relacionado con una característica hidrodinámica específica que conduce a la separación de la pluma de soluto. Se propone un modelo conceptual del transporte de soluto dentro de los lagos. Este modelo enfatiza el efecto físico de los lagos en el proceso de flujo del colorante.摘要报道了双峰突破曲线(BTC)的存在,这是通过地下湖运输染料示踪剂的结果。对比利时南部的Furfooz岩溶系统进行了调查。在这个系统中,River Lesse部分地陷入了一个燕窝。水沿着一条通向直接连接到第二个地下湖泊的地下湖的独立导管。在第二湖下游的复水中检测到双峰BTC。本文首先描述了现场数据(各种水文条件下的示踪剂测试),其指向与峰值起源于湖泊内的非线性过程相关联的双峰。湖中的互补调查显示了染料示踪剂与导致溶质羽流分离的特定流体动力特征相关的复杂行为。提出了湖泊内溶质运输的概念模型。该模型强调了湖泊对染料流通过程的物理效应。ResumoApresenta-se a existência de curvas de identificação de pico duplo como resultado do transporte de um traçador corante através de lagoas subterrâneas. As investigações foram realizadas no sistema cárstico de Furfooz ao sul da Bélgica. Neste sistema o Rio Lesse desaparece parcialmente dentro de uma cavidade rasa. A água segue por um conduto isolado em direção a uma lagoa subterrânea que está diretamente conectada a uma segunda lagoa subterrânea. Curvas de identificação de pico duplo foram detectadas em ressurgências, a jusante da segunda lagoa. O artigo explica em primeiro lugar os dados de campo (testes com traçadores em diversas condições hidrogeológicas) que apontam para o pico duplo associado a um processo não linear que se origina dentro das lagoas. Investigações complementarias dentro das lagoas mostram um comportamento complexo do traçador corante, relacionado a uma característica hidrodinâmica específica que condiciona a separação da pluma de soluto. É proposto um modelo conceitual do transporte de soluto dentro das lagoas. Este modelo enfatiza o efeito físico das lagoas no processo de fluxo do corante.

Transmissive and Capacitive Behavior of the Unsaturated Zone in Devonian Limestones, Implications for the Functioning of the Epikarstic Aquifer: An Introduction

The hydrogeological behavior of the unsaturated zone in karst limestones is far to be completely understood. However, this part of aquifer systems is the most important for the vulnerability of drinking water resources. In Wallonia, the majority of tap water is provided by Devonian and Carboniferous limestones, which consist of highly karstified and fractured formations. The purpose of this research was to apply an experimental approach in order to assess the functioning of the unsaturated part of karst systems. We choose to follow two drip sites within the Han-sur-Lesse cave system (Rochefort, Belgium), the actual dataset covers the 2008–2013 period and the recording device is still active. We also conduct dye tracer experiment (uranin) from the surface with a fluorometer into the cave coupled with a drip collector. In this paper, we present the contextualization of the study site, the experimental methodology, and the first results.

Hydrogeological Dynamic Variability in the Lomme Karst System (Belgium) as Evidenced by Tracer Tests Results (KARAG Project)

Introduction Karst areas represent an important part of the Belgian territory, especially in the south (Wallonia) where Paleozoic limestones (Carboniferous and Devonian) have extensive cave development. A report established in 2011 stated that groundwater coming from those limestones represents 53% of the total water volume extracted from Walloon aquifers (200 million cubic meters; SPW-DGO3, 2014). In addition, Belgium is a densely populated country with heavy agricultural and industrial development. Many human activities represent a threat for the karst media especially in terms of water quality.