DAMBRK FLOOD WAVE ANALYSIS CONSIDERING HYSTERESIS

Abstract

In open channel flows, a rating curve is a fundamental tool for converting measured stages to corresponding discharges. It, therefore, provides vital information, i.e. discharge, for almost all hydrological studies. The rating curves can be either single-valued or double-valued. The former correspond to steady state stage-discharge relationship, and the latter to looped or hysteretic rating curves. In both hydrological research and practice, the latter have received relatively much less attention than the former, which are most commonly used. In this study, the hydraulics of an artificial channel constructed in laboratory was studied in the perspective of looped or hysteretic rating curves generated at several cross-sections using the results of National Weather Service (NWS) dam break flood forecasting (DAMBRK) model which is widely used for the flood wave propagation. To visualize the effect and response of channel and the effect of sudden or gradual opening of the gate on flood wave propagation, the study was carried out for three cases: slow, intermediate, and sudden gate operation. The sudden and gradual openings of the gate help to generate the waves of dynamic and diffusion/kinematic waves, respectively. The routing results due to DAMBRK model were compared with those observed at the same sections. The plots of discharge, stage and looped rating curves matched fairly well, indicating satisfactory DAMBRK model application. The above analysis was further carried out in the perspective of non-dimensional hysteresis that represents the area encompassed by the non-dimensional stage-discharge curve and closely relates with the characteristics of a flood wave (celerity, wave number, phase difference and attenuation) and energy loss occurring at a site during the passage of a flood wave. Based on the hysteresis criteria, the waves were identified as kinematic/diffusion/dynamic. Notably, the wave identified as a dynamic wave when routed through diffusion method of routing through the iii channel valley showed significant deviation, and vice versa, indicating the efficacy of hysteresis-based criteria in wave description. Furthermore, a hypothetical study was also carried out to see the impacts of flow and channel characteristics on flood wave propagation.