2/09/2021 TIME-AREA METHOD The time-area method of flood estimation was proposed by an Australian named Ross in 1921. In essence, the time-area method is an extension of the Rational Method taking into account the travel time of surface runoff to the catchment outlet from different parts of the catchment or subcatchment. 1 TIME-AREA METHOD The basic approach is the subdivision of a catchment (or subcatchment) into a number of areas based on the time of travel from that region to the catchment (or subcatchment) outlet. The application usually requires determination of isochrones. 2 1
2/09/2021 TIME-AREA METHOD An isochrone can be defined as an imaginary line joining points within a catchment from where the influence of rainfall influences flow at the catchment outlet at the same time . 3 TIME-AREA METHOD The concept of travel times is illustrated in the figure. In this example, the distance between the isochrones is At. kochone Ihugging M towel tme to'outet = 4 2
2/09/2021 TIME-AREA METHOD 50 45 404 3.0 Arca Are 20 20 10 1.0 The result of considering the isochrones is a time-area diagram. An example of the time-area diagram is illustrated. As illustrated, the time-area diagram is a bar chart of the area between pairs of isochrones. 0.0 + 1 3 4 5 5 COMPUTATIONAL ALGORITHM There are two basic computational algorithms that have been applied with the time area method. The first of these is based on the surface runoff being the difference between the rainfall and the infiltration losses while the second is based on the surface runoff being a coefficient times the rainfall intensity. 6 3