Ability to set pump upper threshold relative to water level

The ability to have the UPPER_THRESHOLD of pumps 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, where X is user-configurable. The current situation is that the UPPER_THRESHOLD’s value is always the upper threshold height relative to date. If a user wants to relate the upper threshold height to the water level, they have to do so manually. In the requested situation the user can eighter set the height in absolute terms, as is currently the case, or the user can opt to have the upper threshold set to a value relative to the WATER_LEVEL attribute of the enclosing water level area.