Author(s): Ameer Hasan Al-Jubouri and Zainab Kareem Al-Bayati

Abstract: The present study investigates the hydraulic performance of compound open channels under unsteady flow conditions using a combination of laboratory experiments and numerical simulations. Compound channels, comprising a main channel flanked by floodplains, exhibit complex flow behavior due to lateral momentum exchange, variable resistance, and transient storage effects during flood events. Traditional steady-flow analyses often fail to capture these dynamics, leading to inaccuracies in predicting stage-discharge relationships, conveyance, and energy losses. In this research, an experimental flume was constructed with adjustable floodplain roughness and slope to replicate realistic riverine conditions. Flow data were collected under both steady and unsteady regimes, with discharge, stage, and velocity profiles recorded using electromagnetic and acoustic Doppler instruments. The unsteady flow simulations were conducted using the Saint-Venant equations, incorporating dynamic momentum transfer coefficients calibrated against experimental measurements. Statistical tools, including root mean square error (RMSE) and Nash-Sutcliffe efficiency (NSE), were applied to evaluate model accuracy. The unsteady flow model outperformed the steady-state approach, yielding lower RMSE values, higher NSE scores, and more accurate hydrograph reproduction. Results revealed pronounced hysteretic behavior between the rising and falling limbs of flood hydrographs, driven by time-dependent shear redistribution and lateral mixing across floodplains. Wider floodplains and higher roughness contrasts amplified unsteady effects, emphasizing the inadequacy of steady-state resistance assumptions. The study concludes that integrating unsteady flow principles into hydraulic modeling enhances prediction accuracy for flood routing, sediment transport, and river training design. Practical recommendations are proposed to incorporate dynamic resistance calibration and transient modeling approaches into modern flood management and river engineering practices to improve the reliability of hydraulic assessments and infrastructure resilience under variable hydrological conditions.

Pages: 49-53 | Views: 6 | Downloads: 4

Download Full Article: Click Here