Lambert, A.O., Reed, D.W. 1986. Rainfall/runoff and channel routing using the ISO-function method. HOMS component J12.1.08, Institute of Hydrology/World Meteorological Organization, 22 pp.
These notes have been written to describe, for HOMS, the principles upon which ISO-functions are based, with particular reference to their use for real-time flood forecasting; equations are given for both linear and non-linear routing in terms of hydrograph (rate of flow) forecasts, volume of runoff forecasts, and accuracy of forecasts for errors in various input values.
Elements of similarity between ISO-models and storage function (HOMS component J05.1.02)/transfer function/unit hydrograph methods are pointed out. Attention is drawn to the importance of determining the translation lag L (introduced as a pure time delay in the routing process); once this single parameter has been determined (even approximately) for any given catchment area, the relative importance of measured and future rainfalls in flood forecasts can be easily determined.
The reader of these notes will soon realise that ISO-functions do not offer one fixed model, but rather a generalised flexible simple approach to hydrological modelling which is capable of being adapted to a wide variety of different hydrological situations.