Abstract: Abstract Sloping coastal aquifers in reality are ubiquitous and well documented. Steady state sharp-interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the Dupuit-Forchheimer approximation. Specifically, analytical solutions based on the constant-flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone. Analytical solutions for the constant-head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant-flux inland boundary. It is found that for the constant-flux inland boundary, the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types, despite that the geometry of the bottom confining layer determines the location of the interface tip. This is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary, so the shape of the bed below the interface is irrelevant to the interface position. Moreover, developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable-density flow numerical modeling. Analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer.

Abstract: In order to identify the origin of the salinity and formation of saline plumes in the central part of the Mediterranean coastal aquifer of Israel, we determined the elemental and boron, strontium, and oxygen isotopic compositions of fresh and brackish groundwater (C1 up to 1500 mg/L). We distinguish between two key anthropogenic sources: (1) sewage effluents used for irrigation with high Na/C1, SO4/C1, and B/C1 ratios and low Br/C1 ratios relative to seawater ratios, low ;5•B values (0-10%o) and high ;5•80 values (>-4%0); and (2) imported water from the Sea of Galilee that is artificially
recharged tothe aquifer with high Br/C1 (3 x 10 -3) and ;5•80 values (-1%o) and a low 87Sr/86Sr ratio of 0.70753. The brackish groundwater from the saline plumes have relatively low Na/C1 ratios (0.5-0.8) and high Ca/Mg, Mg/C1, and Ca/(SO 4 q- HCO3) (> l) ratios relative to seawater ratios; marine SO4/C1 and Br/C1 ratios;5•B values of 24.8-49.9%0; 18 87 86 ;50 of -2.95%0 to -4.73%0; and Sr/ Sr ratios of 0.708275-0.708532. The composition of most of the investigated groundwater from the saline plumes differs from those of the 87 86 anthropogenic sources, imported water, fresh uncontaminated groundwater (Sr/ Sr of 0.70866, ;5•B of 20-30%o), and saline water from the adjacent Eocene aquitard. Only in ß 18 areas of artificial recharge does local groundwater have high Br/C1 and ;50 values that are typical to the Sea of Galilee. The linear relationships between chloride and most of the ions, including Band Sr, the relatively high ;5•B (>30%0) and low ;5•80 (<-4%0) values, and the chemical signature of the saline plumes (e.g., marine Br/C1 and SO4/C1 ratios), suggest that (1) mixing processes control the chemical composition of the brackish water within the aquifer, and (2) the saline postulated end-member has a chemical composition that resembles modified seawater with a marine and higher ;5•B values, and a 87Sr/86Sr ratio of <0.7083. We propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw-down of the overlying fresh groundwater.