Impact of lateral variations of geologic facies on water resources in homogeneous basins: example of tertiary plateaus in the Paris Basin

Abstract

Spatial disparity of run-off conditions during low-water period in homogeneous watersheds depends on the degree of incision of valleys, but may also be influenced by a structural partitioning or some lateral variations in the aquifer lithology. For small basins (area <300 km 2 ), often hydrometrically unsupervised, campaigns of serial flow measurements, gauging, conductivity and temperature are achieved. The Ardre basin, localised in the Tertiary formations of the Paris Basin is used as a workshop basin. Results validated by hydrological and physico-chemical profiles show increased hydrological yields in the basin which correspond to the increase in the thickness of aquifers and their porosity. These lateral variations of facies and of aquifer thicknesses are related to Eocene sedimentary conditions (Lutetian) for homogeneous basins, which explain the spatial disparity of water resources.

Relationships between fluvial evolution and karstification related to climatic, tectonic and eustatic forcing in temperate regions

“…In the Eastern Paris Basin, epigenetic speleogenesis and fluvial incision is linked to the structural framework of the basin and entrenchment of the main valley into the alternating marl and limestone strata (Losson, 2003;Devos et al, 2009Devos et al, , 2015. The main feature is the position of the river with regard to the water table.…”

“…When perched rivers are entrenched into limestone above the saturated zone, infiltration occurs into and under the valley from local or allochtonous flows (Jaillet, 2000;Losson, 2003;Devos et al, 2009Devos et al, , 2015; Figure 4A level a). 2) When the surface river channel is in contact with the water table of the saturated zone, the lack of hydraulic gradient induces a ghost rock process around the fractures of the valley floor (Quinif, 2010, Devos et al, 2011Figure. When the surface river channel is strongly entrenched into the limestone substratum, and drains the flooded karst zone, a thin piezometric horizon develops ( Figure 4A level c).…”

“…2) When the surface river channel is in contact with the water table of the saturated zone, the lack of hydraulic gradient induces a ghost rock process around the fractures of the valley floor (Quinif, 2010, Devos et al, 2011Figure. When the surface river channel is strongly entrenched into the limestone substratum, and drains the flooded karst zone, a thin piezometric horizon develops ( Figure 4A level c). 4) If fluvial incision occurs in the marls or clays situated below the saturated zone, the perched karstified zone is disconnected from the river (Figure 4A level d) and the flooded zone drains into low flow springs (Devos et al, 2015). However, as shown in Figure 4B, it is important to remember that the faulted tectonic basement can produce structural and aquifer compartments which control the hydraulic gradient between aquifers and rivers (Devos et al, 2007).This can have major impacts on the hydrological and geomorphological connectivity, between karst and subaerial fluvial drainage networks.…”

“…Underground streams adjust to falling base level by incising new passages. However, there is evidence that per descensum speleogenesis also depends on the timing of valley incision, as well as geological factors such as (i) the degree of bedrock karstification (Abel et al, 2002), (ii) alternating pervious and impervious strata causing perched karsts (Devos et al, 2015, Figure 4A level a) and iii) underground karstic flows towards a lower elevation river in a neighbouring hydrographic basin or in the downstream position of the same river (Losson, 2003). As a consequence, numerous interactions between fluvial evolution and karstification can exist.…”

Multiple-step numerical modeling to assist aquifer characterization: a case study from the south of Brazil

“…Knowledge about this environment is gained through observation and interpretation of data that are collected using various techniques from the land surface or underground (Chaminé et al 2015). The surface data include variations in the topographic relief (Lee et al 2002;Montgomery and Brandon 2002), lithology (Dewandel et al 2006;Kühni and Pfiffner 2001), soil texture (Skempton 1953), vegetation (Eberhardt and Latham 2000), characteristics of surface-water bodies and temporal changes of river flow (Harrington et al 2013;Devos et al 2015). The underground data may refer to the spatial variations in lithology, grain-size distribution, fractures and karst features (i.e.…”