RN-15 : Use of catchment characteristics for unit hydrograph derivation

Abstract

A lack of meteorological and hydrological data is one of the greatest obstacles to accurate estimation of design flood or volumes of runoff. The hydrologist is usually faced with the problem of having few rainfall measuring sites and even fewer stream flow measuring stations in the basins under study. Techniques are therefore required for predicting or forecasting the peak flow rate and/or volume of runoff for events or situations of interest that do not rely on historical records. In this situation the methods, which consider the catchment and storm characteristics for design flood -and/or volume runoff estimation are most appropriate. As unit hydrograph is one of the widely used techniques for design flood and/or volume of runoff computations, therefore, one will always be concerned with the unit hydrograph derivation using catchment and storm characteristics.

The description of the physical characteristics of a catchment is not easily formulated. The physical structure of the surface runoff pattern is open to view, and there are certain similarities in the land form, which have evolved under similar geologic and climatic conditions. These similarities make it possible to quantify some of the parameters and standardise terminology related with various aspects of the catchment characteristics.

In this report, the parameters suggested by many investigators to describe the different aspects of catchment and storm characteristics, such as (i) linear aspect of channel system ii) areal aspect of the catchment;(iii) relief aspect of the catchment and channel networks;(iv) forest and agricultural land use changes, (v) urbanization and (vi) storm characteristics etc., have been discussed. Some typical catchment characteristic parameters have also been identified, which will be useful to derive the unit hydrograph for the catchment. Further, the procedures used by different investigators to evaluate different catchment characteristic parameters from toposheets have been described and discussed. The catchment characteristics considered for developing the synthetic unit hydrograph for different Indian basins have also been reviewed.