Departure seperation here is delegated to tower via a simple to understand formula we have nicknamed the suduko charts.
There are 4 bands of performance based lines. We use 2 and a half miles in-trail for aircraft in the same group, 1 and a half for anything slower following a Boeing or Airbus, Runway length following observation of preceeding a/c turning 30 degrees, observation of a turn on radar where the blip has cleared the departure track, "adequate seperation" where one (or more ) of the a/c are on a visual departure, preceeding aircraft above 4000ft (4500ft where the 2nd is faster) plus since we have to protect the missed approach when wx below circling (for a category, or all categories) there is a chart of required distances the departure has to be rolling by depending on what performance band the departure (and the arriving) a/c is in. Typically 4-7nm, up to 12 nm eg; for a Seneca departing ahead of a Boeing on final.
There are permutations which vary depending on the particular SID flown, the radar performance on the day, and the presence of tailwind on approach. So worst case scenario when we have to consult 2 seperate calculations on 2 seperate charts, (x4) decide whether a shortcut can be achieved by changing a SID, re-calculate the revised spacing, by the time it's been decided that it might work, it's too late. It's all very efficient.