Random Field Approach to Seawater Intrusion in Heterogeneous Coastal Aquifers: Unconditional Simulations and Statistical Analysis Ahmad Al-Bitar 1 and Rachid Ababou 1 1 Institut de Mécanique des Fluides de Toulouse, Allée Camille Soula, 31400 Toulouse, France. 1 Introduction and summary Seawater intrusion in coastal aquifers is a growing concern in mediterranean re- gions, due to over-population and over-exploitation of coastal groundwater re- sources. Under these circumstances, it is essential to model the extent of seawater intrusion and to locate the saltwater-freshwater interface taking into account het- erogeneity and parameter uncertainty. There are different ways to couple salt transport and freshwater flow in groundwater models. We choose here the verti- cally integrated sharp interface approach, with two immiscible fluid regions (freshwater and seawater). We use this model to analyze the effects of aquifer variability on the saltwater wedge in plane view, based on large numerical simula- tions of 2D seawater intrusion in randomly heterogeneous unconfined aquifers. 2 Groundwater flow equations with seawater intrusion We consider an unconfined coastal aquifer with an impervious bedrock at z = Z INF (x,y) and a fresh water table of elevation z = Z S (x,y). In addition, because we use a plane flow model, the vertically averaged freshwater hydraulic head H(x,y) coincides with the free surface elevation, i.e. : H(x,y)≈Z S (x,y). In this 2D framework, all variables and parameters are spatially distributed in (x,y). A sche- matic representation of the coastal aquifer and its salt wedge is shown in Fig. 1. We assume that seawater and freshwater are separated by a sharp interface. More precisely, we rely on the Ghyben-Herzberg approximation(s), that is: • the seawater and freshwater fluids are assumed immiscible (sharp interface); • the subsurface seawater wedge is assumed quasi-hydrostatic; • the freshwater is assumed vertically hydrostatic (negligible vertical velocities). AL-BITAR A., R. ABABOU, 2005: “Random Field Approach to Seawater Intrusion in Heterogeneous Coastal Aquifers : Unconditional Simulations and Statistical Analysis”. In : Geostatistics for Environ. Applications, Renard P., Demougeot-Renard H., Froidevaux R. (eds.), Springer Verlag (2005). Pre-Print