The ability to have the UPPER_THRESHOLD and LOWER_THRESHOLD of inlets set automatically, relative to the WATER_LEVEL of the enclosing water level area. I.e. the UPPER_THRESHOLD is WATER_LEVEL + X, relative to datum, and the LOWER_THRESHOLD is WATER_LEVEL + Y, relative to datum, where X and Y are individually user-configurable. The current situation is that the UPPER_THRESHOLD’s value and the LOWER_THRESHOLD’s value are always the upper and lower threshold height relative to datum. If a user wants to relate the upper and/or lower threshold height to the water level, they have to do so manually. In the requested situation the user can eighter set either threshold in absolute terms, as is currently the case, or the user can opt to have the upper or lower threshold (or both) set to a value relative to the WATER_LEVEL attribute of the enclosing water level area.