Spatial and temporal variability of groundwater dynamics in a sub-Mediterranean mountain catchment

Abstract

Abstract:The temporal and spatial dynamics of groundwater was investigated in a small catchment in the Spanish Pyrenees, which was extensively used for agriculture in the past. Analysis of the water table fluctuations at five locations over a 6-year period demonstrated that the groundwater dynamics had a marked seasonal cycle involving a wetting-up period that commenced with the first autumn rainfall events, a saturation period during winter and spring and a drying-down period from the end of spring until the end of the summer. The length of the saturation period showed great interannual variability, which was mainly influenced by the rainfall and evapotranspiration characteristics. There was marked spatial variability in the water table, especially during the wetting-up period, which could be related to differences in slope and drainage area, geomorphology, soil properties and local topography. Areas contributing to runoff generation were identified within the catchment by field mapping of moisture conditions. Areas contributing to infiltration excess runoff were correlated with former cultivated fields affected by severe sheetwash erosion. Areas contributing to saturation excess runoff were characterized by a marked spatial dynamics associated with catchment wetness conditions. The saturation spatial pattern, which was partially related to the topographic index, was very patchy throughout the catchment, suggesting the influence of other factors associated with past agricultural activities, including changes in local topography and soil properties. The relationship between water table levels and stream flow was weak, especially during the wetting-up period, suggesting little connection between ground water and the hydrological response, at least at some locations. The results suggest that in drier and human-disturbed environments, such as sub-Mediterranean mountains, saturation patterns cannot be represented only by the general topography of the catchment. They also suggest that groundwater storage and runoff is not a succession of steady-state flow conditions, as assumed in most hydrological models.

Catchment based hydrology under post farmland abandonment scenarios

“…the baseflow at the start of the flood event and antecedent rainfall) García-Ruiz et al, 2008;Llorente-Adán et al, 2015;Nadal-Romero et al, 2016) (table 4). This was confirmed in Arnás and San Salvador by Lana-Renault et al (2014a) and , who showed that streamflow discharge in these catchments was strongly related to the dynamics of the water table. Rainfall in Arnás and Araguás_Afforestation also influenced the stormflow, but to a lesser extent than preceding moisture conditions.…”

“…Long-term monitoring of these catchments has provided useful hydrogeomorphological information, enabling study of the factors that explain their hydrological and sedimentological responses Seeger et al, 2004;García-Ruiz et al, 2005;Serrano-Muela et al, 2008;Llorente-Adán et al, 2015;Nadal-Romero et al, 2016), their water and sediment sources (González et al 1997;Lana-Renault and Regüés 2009;Butzen et al, 2011;Lana-Renault et al, 2014a), the dynamics of the groundwater table Lana-Renault et al, 2014a), translocation and stemflow processes (SerranoMuela et al, 2012) and the hydrological properties of their soils (Seeger and Ries, 2008;Regüés et al, 2012Regüés et al, , 2017Serrano-Muela et al, 2014). These findings have enhanced knowledge of the runoff generation processes operating in these catchments under different rainfall and moisture conditions , 2014cSerrano-Muela et al, 2008;Nadal-Romero et al, 2016).…”

Characteristics and controls of variability in soil moisture and groundwater in a headwater catchment

“…If groundwater rises into upper soil layers, large increases in soil matrix porosity or macropores may "cap" water table levels, as additional water is quickly transported to the stream (Haught and Meerveld, 2011). Lana-Renault et al (2014) found in a Mediterranean catchment that patterns of near-surface saturation and transient water tables were affected not only by topography, but also by soil properties and previous agricultural land use. The riparian zone facilitates mixing between soil water and groundwater, and tracers, temperature, electrical conductivity, flow gauging and head differences may all be used to quantify the interactions (Unland et al, 2013).…”

Los efectos geoecológicos del cambio global en el Pirineo Central español: una revisión a distintas escalas espaciales y temporales

“…Lana-Renault et al (2007a, 2014b y Lana-Renault (2011) comprobaron, no obstante, que esas áreas varían mucho en extensión según la época del año, según las características de cada evento lluvioso y en función del estado del nivel freático. El patrón espacial de saturación del suelo, que está parcialmente relacionado con el índice topográfico, es muy heterogéneo debido a la influencia de las actividades agrícolas del pasado.…”

“…Las relaciones entre los niveles de la capa freática y el caudal son bastante débiles, especialmente durante la fase de recarga, lo que sugiere que en este tipo de ambiente todavía predominan, bajo determinadas condiciones, procesos de escorrentía hortoniana. Por otra parte, esta escasa relación también indica que hasta que la cuenca no alcanza un cierto umbral de humedad, la respuesta del caudal no es importante (Lana-Renault et al, 2007b, 2014b. Durante la estación fría y la primavera, con una notable extensión de los suelos saturados o muy húmedos, toda la cuenca está en condiciones de contribuir con agua y sedimento, de manera que la concentración de este último se diluye entre caudales muy elevados.…”