Alain Francés

Integrating MRS data with hydrologic model - Carrizal Catchment (Spain)

Magnetic resonance sounding (MRS) provides quantitative hydrogeological information on hydrostratigraphy and hydraulic parameters of subsurface (e.g. flow and storage property of aquifers) that can be integrated in distributed hydrologic models. The hydraulic parameters are typically obtained by pumping tests. In this study, we propose an MRS integration method based on optimizing MRS estimates of aquifer hydraulic parameters through hydrologic model calibration. The proposed MRS integration method was applied in the 73 km2 Carrizal Catchment in Spain, characterized by a shallow unconfined aquifer with an unknown aquifer bottom. 12 MRS survey results were inverted with Samovar 11.3, schematized and integrated in the transient, distributed, coupled, hydrologic, MARMITES-MODFLOW model. As the aquifer bottom was unknown, the aquifer was schematized into one unconfined layer of uniform thickness. For that layer, MRS estimators of specific yield and transmissivity/hydraulic conductivity were calculated as weighted averages of the inverted MRS layers. The MRS integration with hydrologic model was carried out by introducing multipliers of specific yield and transmissivity/hydraulic conductivity that were optimized during transient model calibration using 11 time-series piezometric observation points. The optimized multipliers were 1.0 for specific yield and 3.5*10-9 for hydraulic conductivity. These multipliers were used, and can be used in future MRS investigations in the Carrizal Catchment (and/or adjacent area with similar hydrogeological conditions), to convert MRS survey results into aquifer hydraulic parameters. The proposed method of MRS data integration in the hydrologic model of Carrizal Catchment not only allowed us to calibrate the model but also to confirm the functional capability of MRS in quantitative groundwater assessment. Most importantly however, it demonstrated that if pumping tests are not available, the use of MRS integrated in distributed coupled hydrological models, or even in standalone groundwater models, provides a valuable aquifer parameterization alternative.

Contributions of hydrogeophysics to the hydrogeological conceptual model of the Albufeira-Ribeira de Quarteira coastal aquifer in Algarve, Portugal

Geoelectrical and electromagnetic (time and frequency domains) hydrogeophysical methods were applied and jointly interpreted together with auxiliary information such as regional piezometric maps, borehole lithological logs and offshore data. The objective was to retrieve the structure and geometry of the Albufeira-Ribeira de Quarteira coastal aquifer system (Algarve, Portugal) and to upgrade the current hydrogeological conceptual model. The results allowed for the detection of the freshwater–saltwater interface along the coastline and identification of the water-bearing layers and aquitards and their hydraulic relationships. An explanation for the location of the inter- and subtidal fresh groundwater discharge is also presented and a new modeling unit is proposed for groundwater flow modeling. Limitations of the used hydrogeophysical methods are indicated and recommendations are made for follow-up studies.RésuméLes méthodes hydrogéophysiques de type géoélectrique et électromagnétique (domaines temporel et spatial) ont été appliquées et conjointement interprétées en utilisant comme information auxiliaire des surfaces de piézométrie régionale, des logs lithologiques de forage et des données de la plate-forme littorale. L’objectif était d’obtenir la structure et la géométrie du système aquifère côtier Albufeira-Ribeira de Quarteira (Algarve, Portugal) et de réviser l’actuel modèle conceptuel hydrogéologique. Les résultats ont permis de détecter l’interface eau douce-eau salée le long du littoral, de différencier niveaux aquifères et aquitards et d’établir leurs relations hydrauliques. Une explication de la localisation des décharges d’eau souterraine douce dans la zone inter- et subtidale est avancée et une nouvelle unité de modélisation de l’écoulement d’eau souterraine est proposée. Les limitations des méthodes hydrogéophysiques utilisées sont indiquées et des recommandations sont faites pour les études à venir.ResumenSe aplicaron métodos hidrogeofísicos geoeléctricos y electromagnéticos (en los dominios del tiempo y frecuencia) y se interpretaron en forma conjunta con información auxiliar, tales como mapas piezométricos regionales, registros litológicos de pozos y datos offshore. El objetivo fue recuperar la estructura y geometría del sistema acuífero costero Albufeira-Ribeira de Quarteira (Algarve, Portugal) y actualizar el actual modelo hidrogeológico conceptual. Los resultados permitieron la detección de una interfaz agua dulce-agua salada a lo largo de la línea costera y la identificación de las capas, acuíferos y acuitardos y sus relaciones hidráulicas. Se presenta también una explicación para la ubicación de la descarga de agua dulce subterránea inter y submareal y se propone una nueva unidad de modelado para el modelación de flujo de agua subterránea. Se indican las limitaciones de los métodos hidrogeofísicos utilizados y se hacen recomendaciones para los estudios de seguimiento.摘要应用了地电和电磁(时间和频率范围)水文地球物理方法并跟根据诸如区域测压图、钻孔岩性记录和近海资料等辅助信息对此进行了解译。目标就是获取(葡萄牙阿尔加维)Albufeira-Ribeira de Quarteira沿海含水层的结构和几何形状,对目前的水文地质概念模型进行升级。依赖获得的结果能检测到沿海岸线的淡水-咸水界面,识别出含水层和隔水层及其水力关系。还论述了交互的和潮下的地下淡水补给位置,为地下水流模拟提出了新的模拟单元。指出了所用水文地球物理方法的局限性,为后续研究提出了建议。ResumoOs métodos hidrogeofísicos geoelétricos e eletromagnéticos (domínios de tempo e de frequência) foram aplicados e conjuntamente interpretados utilizando como informação auxiliar mapas piezométricos regionais, logs litológicos de sondagens e dados da plataforma costeira. O objectivo foi obter a estrutura e a geometria do sistema aquífero costeiro Albufeira-Ribeira de Quarteira (Algarve, Portugal) e actualizar o modelo hidrogeológico conceptual. Os resultados permitiram detectar a interface água doce-água salina ao longo da cost, identificar as camadas aquíferas e aquitardas e definir as suas relações hidráulicas. Uma explicação para a localização das descargas de água doce subterrânea inter- e subtidais é avançada e uma nova unidade de modelação do fluxo de água subterrânea é proposta. As limitações dos métodos hidrogeofísicos utilizados foram indicadas e recomendações foram feitas para futuros estudos.