ABSTRACT
The evolution of the interface between salt and fresh water in underground aquifers can be modelled by the equation () https://www.w3.org/1998/Math/MathML"> ρ ( x ) u t = d i v ( u ( 1 − u ) ∇ u for ( x , t ) ∈ ℝ N × ℝ + , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203755518/fbcb5fb2-fbc4-4b15-ab17-e703fd7c937e/content/eq446.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
