The relation of hydrographs of runoff to size and character of drainage‐basins

In a previous paper entitled “stream‐flow from rainfall by unit method” (Eng. News‐Record, April 7, 1932), the writer defined a unit graph as the hydrograph of runoff from a given area, due to a one‐inch runoff‐depth applied in one day or in any other convenient unit of time. A procedure for deriving the unit graph from observed rainfall‐ and runoff‐records was presented. After the unit graph has been derived a runoff‐record for the given area, for any rain or series of rains, may be computed by a simple summation process. Figure 1, from the aforesaid paper, graphically illustrates the summation process and it will not be described further here.