Partitioning groundwater recharge between rainfall infiltration and irrigation return flow using stable isotopes: The Crau aquifer

Abstract

This study reports an assessment of the water budget of the Crau aquifer (Southern France), which is poorly referenced in the literature. Anthropogenically controlled by a traditional irrigation practice, this alluvial type aquifer requires a robust quantification of the groundwater mass balance in order to establish sustainable water management in the region. In view of the high isotopic contrast between exogenous irrigation waters and local precipitations, stable isotopes of water can be used as conservative tracers to deduce their contributions to the surface recharge. Extensive groundwater sampling was performed to obtain d18O and d2H over the whole aquifer. Based on a new piezometric contour map, combined with an updated aquifer geometry, the isotopic data were implemented in a geostatistical approach to produce a conceptual equivalent homogeneous reservoir. This makes it possible to implement a parsimonious water and isotope mass-balance mixing model. The isotopic compositions of the two end-members were assessed, and the quantification of groundwater flows was then used to calculate the two recharge fluxes (natural and irrigation). Nearly at steady-state, the set of isotopic data treated by geostatistics gave a recharge by irrigation of 4.92 ± 0.89 m 3 s À1 , i.e. 1109 ± 202 mm yr À1 , and a natural recharge of 2.19 ± 0.85 m 3 s À1 , i.e. 128 ± 50 mm yr À1. Thus, 69 ± 9% of the surface recharge is caused by irrigation return flow. This study constitutes a straightforward and independent approach to assess groundwater surface recharges including uncertainties and will help to constrain future transient groundwater models of the Crau aquifer.

Avaliação de multiabordagem da distribuição espacial do rendimento específico: aplicação no aquífero da planície do Crau, França

“…Subjected only to natural recharge, P29B yields 116 mm year −1 of mean recharge using an average value of 16.38 m asl for the water level (over 12 years). The subtraction yields 1,223 mm year −1 of recharge by irrigation return flow and 116 mm year −1 of natural recharge, which is consistent with the values obtained by previous studies using geochemical tracers at the aquifer scale (Seraphin et al 2016; i.e. 1,109 ± 202 mm year −1 of recharge by irrigation return flow, and 128 ± 50 mm year −1 of natural recharge), and local scale (Vallet-Coulomb et al 2017; i.e.…”

“…This process amplifies the water level rise, especially in the case of a very shallow water table with an unsaturated zone thickness of less than 1 m (Weeks 2002). Since, according to the digital elevation model (GO-13 2009) and the 2013 piezometric map (Seraphin et al 2016), the average unsaturated zone thickness of the Crau aquifer is greater than 6 m, this process can be neglected; moreover, all the piezometers used in this study present unsaturated zone thicknesses greater than 1 m.…”

“…The right-hand side of Eq. (14) can be computed using the fluxes independently obtained using a stable isotope-mixing model (Seraphin et al 2016). According to this study, for the 7-month time period considered here, the recharge by irrigation return flow (R i ) and the natural recharge (R n ) were 4.92 ± 0.89 and 1.17 ± 0.50 m 3 s −1 , respectively.…”

Prospects for Improving Gravity-Fed Surface Irrigation Systems in Mediterranean European Contexts

“…In addition, the water 'losses' along the unlined water conveyance and distribution systems represent a possibility for aquifer recharge management [92]. Interestingly, a recent study by Seraphin et al [93] found that using isotopes for tracing the contributions to the groundwater recharge of the Cru aquifer in France, showing that about 69% ± 9% of the surface recharge is caused by irrigation return flow i.e., from specific irrigation practices and the presence of unlined canals. Moreover, many assumptions suggest that the quality of water that flow in the gravity-fed surface irrigation canals is comparable with that in the feeding rivers.…”

Using bromide data tracer and HYDRUS‐1D to estimate groundwater recharge and evapotranspiration under film‐mulched drip irrigation in an arid Inland Basin, Northwest China

“…Most of these methods also have limited success in semi-arid and arid areas, if the lithology varies significantly over space (Chand et al, 2004;Singh et al, 2019). Tracer tests can provide information about soil-water movement (Yang & Fu, 2017) and they are considered to give more reliable estimates of GR (Huang et al, 2020;Seraphin et al, 2016;Wang et al, 2008;Zagana et al, 2007). ET can be evaluated by mapping the vertical movement of tracer concentration peaks in arid and semi-arid areas with shallow water table depths (Huo, 2015;Huo et al, 2020;Wang et al, 2020).…”