Use the Domain Properties node to set the bottom topography and material properties.

The Bottom height (SI unit: m) is defined as a user defined expression. It can depend on the geometry coordinates, but it is expected to be constant in time. The default is set to 0 m.

The default Density ρ (SI unit: kg/m3) is taken User defined. Enter a different value or expression. The default is 1000 kg/m3. The density can also be set From material. In that case, select the Material to use. By default, the material used is the Domain material. This corresponds to the material currently applied to the domain in question.