Field-based groundwater recharge and leakage estimations in a semi-arid Eastern Mediterranean karst catchment, Wadi Natuf, West Bank

Abstract

15Groundwater recharge processes in semi-arid climates are highly sensitive to spatial and temporal variability (event precipitation). However, in previous research, the spatial distribution of recharge has received relatively little attention. This study differentiates recharge according to the following spatial characteristics: a) soil type and soil condition, b) land forms such as relief, vegetation and land use, 20and c) lithology and hydrogeological characteristics of the subsurface rock formation. For the first time, this paper analyses and quantifies the specific recharge in the different individual rock formations of the Western Aquifer Basin (WAB). The WAB is a large transboundary karst aquifer that stretches from sub-humid to semi-arid climates from the recharge area in the West Bank Mountains to the Mediterranean Coast. The assessment is based on actual field data, including soil moisture and 25spring discharge in Wadi Natuf, a 103 km 2 large sub-catchment in the West Bank slopes and mountain region, i.e. the recharge area of the WAB. A parsimonious soil moisture balance model was set up to calculate daily recharge rates from daily precipitation and evapotranspiration records over an extended period of 7 years (2003/04-2009/10). Unlike in most comparable studies, the simple but solid parsimonious soil moisture and percolation 30 model and the budget calculations were based on actual quantitative field-observations, in contrast to the generally applied model fitting and inverse calibration. The model's daily deep percolation rates were compared with soil moisture field-data and in addition, by comparing major event recharge depths with daily spring discharge response. This combination of modelling and intensive field measurements, comprising eight different soil mois-35 ture measurement stations in six different litho-facies formations allowed identifying and quantifying the recharge characteristics of each formation at high spatial resolution, which is a first in the Western Aquifer.We found that recharge varies widely at the spatial dimension, ranging between 0 % and almost 60 % of annual rainfall. The spatially variable long-term average recharge coefficients were applied to other 40 outcropping formations by a ranking procedure taking into account each of the three above spatial characteristics (landform, soil and geology). In addition to the recharge analysis, special emphasis was paid to the examination of the role of perched leaky aquifers positioned between the main regional Upper and Lower Aquifers. The particular geometry of the local aquifers, i.e. hills with well-defined aquifers, leaky aquitard bases and there-45 fore well-defined catchment areas, allowed the quantification of the flow budget. By measuring and budgeting spring group discharge of each leaky sub-aquifer, for the first time also leakage coefficients could be calculated empirically. The methodology of this study is also applicable to comparable catchments and aquifers outside the region. The resulting mean annual recharge coeff...

Using a Distributed Recharge Model to Quantify Recharge Processes in a Semi-Arid Karst Catchment: An Example from Wadi Natuf, West Bank

“…There is a large number of springs (around 130 [19]) in the catchment, with an estimated LTA flow of 0.5 Mm 3 •a −1 (~1400 m 3 •d −1 ). The majority issue around Beitillu [28] (Figure 1) where 101 springs discharge for part of the year. The springs are small, localized components of the groundwater system issuing from perched aquifers and are of mainly good groundwater quality [29].…”

Identification and quantification of leakage into the carbonate aquifer by using non- isotopic environmental tracers and hydro-chemical modeling

“…Leakage area delineation in multi-aquifer systems is one of the most challenging topics of regional hydrogeological studies. Existing methods for this purpose include the use of natural environmental tracers, mostly isotopes and chloride (Anker, 2003 Kleinig et al, 2015); and balance calculations (Walton, 1960;Ruhl et al, 2002;Anker, 2007;Messerschmid et al, 2018; Kunchao Lei et al, 2020). The best review of methods for aquifer connectivity determination is given in the report of CIESC (Harrington et al, 2014).…”