The time-area method dates from the research of Ross in 1922. Networked urban drainage adoptions of the procedure however only date back to 1963. This computerised program known as the TRRL Method was developed by the UK Transport and Road Research Laboratory (TRRL), described by Watkins (1963).
In the US Terstriep and Stall (1974) further developed the method to include pervious runoff. In South Africa Watson (1981) made a number of additional changes particularly to the way infiltration was estimated. Between 1982 and 1986 O’Loughlin (1988) using Watson’s model as a basis carried out extensive changes once again to formulate a computerised package known as ILSAX. The sub-catchment runoff estimating procedure still utilises the basic time-area method to estimate both pervious and impervious portion of runoff.