Sensitivity analysis of hydrological parameters on flood hydrograph – A research report by National Institute of Hydrology

In this study, Clark’s model has been used for derivation of one-hour unit hydrograph for a catchment. The design flood estimate has been obtained using the calibrated parameters of the Clark model together with the time-area diagram corresponding to a 48-hour design storm, which has been temporally distributed and critically sequenced as a single bell, giving due consideration to the ordinates of the unit hydrograph.

Sensitivity of the design flood estimate has also been studied considering the different scenarios viz.

• Varying the design unit hydrograph characteristics
• Considering the design storm as one bell, two bells and four bells for the 48-hour storm, and
• Varying the design loss rate

An objective methodology has been suggested and applied for estimation of design unit hydrograph parameters after increasing the peak of the average unit hydrograph to account for the hydraulic conditions of the channel and the catchment for the extreme flooding situations. The design flood peak is not much sensitive to the change in the design loss rate.

The following conclusions can be drawn from the study –

• The unit hydrograph derived using the Clark model together with other design parameters has been used for estimation of design flood hydrograph.
• An objective methodology has been suggested and applied for estimation of design unit hydrograph parameters after increasing the peak of the average unit hydrograph to cater to the hydraulic conditions of the channel and the catchment for extreme flooding situations, which would occur due to the occurrence of design flood. 
• The sensitivity runs taken considering the various design storm patterns show that design flood estimates are very much dependent on the temporal distribution and the critical sequencing of the PMP values.

Download the report here: