Water percolation process studies in a Mediterranean karst area

Abstract

Abstract:To investigate processes of water percolation, the drip response of stalactites in a karstic cave below a 143 m 2 sprinkling plot was measured. The experiment was conducted in Mount Carmel, Israel, at the end of the dry season and intended to simulate a series of two high-intensity storms on dry and wet soils. In addition to hydrometric measurements (soil moisture, surface runoff, stalactite dripping rates), two types of tracers (electrical conductivity and bromide) were used to study recharge processes, water origin and mixing inside a 28-m vadose zone. Results suggested that slow, continuous percolation through the rock matrix is of minor importance and that percolating water follows a complicated pattern including vertical and horizontal flow directions. While bromide tracing allowed identification of quick direct flow paths at all drips with maximum flow velocities of 4Ð3 m/h, mixing analysis suggested that major water fractions were mobilized by piston flow, pushing out water stored in the unsaturated zone above the cave. Under dry preconditions, 80 mm of artificial rainfall applied in less than 7 h was not enough to initiate significant downward water percolation. Most water was required to fill uppermost soil and rock storages. Under wet preconditions during the second day sprinkling, higher water contents in soils and karst cavities facilitated piston flow effects and a more intense response of the cave drips. Results indicate that in Mediterranean karst regions, filling of the unsaturated zone, including soil and rock storages, is an important precondition for the onset of significant water percolation and recharge. This results in a higher seasonal threshold for water percolation than for the generation of surface runoff.

Recharge estimation and soil moisture dynamics in a Mediterranean, semi-arid karst region

“…150 mm for the shallow and 240 mm for the deep soil moisture plots. Cave drip studies in the region Lange et al, 2010;Sheffer et al, 2011) measured similar thresholds for the initiation of percolation through the epikarst (100-220 mm).…”

“…However, these studies treat karst systems as units, including both the unsaturated and the saturated zones, and are limited in temporal and spatial resolution. Studies on cave drips (Gregory et al, 2009;Arbel et al, 2010;Lange et al, 2010) provided insights into the deeper unsaturated zone in terms of water storage, spatial variability of percolation and flow paths. Their data was also used to incorporate variability in recharge modelling (Hartmann et al, 2012).…”

Role of epikarst in near-surface hydrological processes in a soil mantled subtropical dolomite karst slope: implications of field rainfall simulation experiments

“…Results from Lange et al . () indicate that filling of the soil and rock storages is an important precondition for significant water percolation onset and recharge. Therefore, the thickness and permeability of both soil and epikarst are considered as key parameters in karst groundwater vulnerability assessment models (Daly et al ., ; Vías et al ., ).…”

Mixing of water in a carbonate aquifer, southern Italy, analysed through stable isotope investigations

“…Thus, the types of vadose flow (preferential or fracture fed; matrix or seepage fed; Baker & Brundson, 2003) were not directly investigated, contrary to other studies (eg. Baker et al, 1997;Genty & Deflandre, 1998;Baker et al, 2000;Kaufman et al, 2003;Tooth & Fairchild, 2003;Spötl et al, 2005;Karmann et al, 2007;McDonald & Drysdale, 2007;Lange et al, 2010). The role of the unsaturated zone (thickness ranging from 27 to 62 meters during the observation period) was analysed based on observations made within the groundwater profile in a purpose-drilled well.…”