Providing the majority of runoff into the Laptev Sea, the Lena River and its associated delta have become an indicator for recent and future environmental change in the Arctic Region. However, a detailed examination on the hydrodynamics over complex topography in the delta region and its interaction with the estuary has been missing. This study aims to fill this gap by a series of high-resolution numerical simulations based on a state-of-the-arts Discontinous Galerkin (DG) regional 3D ocean model, UTBEST3D, under different discharge conditions. The first task is to tune the numerical model and reproduce the velocity regimes and discharge distributions in different major sub-channels in the delta. The second task is to scrutinise the potential flooding area due to ocean surface waves, river runoff and the coupling of these.