Use of Catchment Physiographic Factors in Selection of Design Storm and its Effect on Floods Estimated for Ungauged Catchments

Abstract

Reliable estimation of high and low flow events in rivers or streams at any ungauged watershed location are essential for making strategic and informed decisions. This is required when the civil works such as flood protection works, and design of hydraulic structures are being planned on river stretches. Wherever data is not available on rivers/ streams, hydrological models (empirical, conceptual and/or probabilistic) act as important tools to establish baseline characteristics for determining the longterm impacts. In the present study, river protection works are planned on river Sirsa and its tributaries for which observed flood records are not available. As the protection works depend on the intensity of flood at the location of interest, flood estimation assumes vital role. Thus, a systematic analysis of catchment factors followed by estimation of design storm duration and design storm depth from the extreme value analysis of daily rainfall is carried out. The selection of storm depths for the design storm durations was carried out for desired return periods for catchments through a physiographic analysis. Evaluation of flood estimate is made with hydrologic analysis where scanty data made available for the study. A typical case of time compensation for the storm depth estimation adopted for flood estimation along the Sirsa river stretch is presented to depict the hydrologic time scale effects of rainfall on runoff