An improved subgrid channel model with upwind-form artificial diffusion for river hydrodynamics and floodplain inundation simulation

Abstract

Abstract. An accurate estimation of river channel conveyance capacity and the water exchange at the river–floodplain interfaces is pivotal for flood modelling. However, in large-scale models limited grid resolution often means that small-scale river channel features cannot be well-represented in traditional 1D and 2D schemes. As a result instability over river and floodplain boundaries can occur, and flow connectivity, which has a strong control on the floodplain hydraulics, is not well-approximated. A subgrid channel (SGC) model based on the local inertial form of the shallow water equations, which allows utilization of approximated subgrid-scale bathymetric information while performing very efficient computations, has been proposed as a solution, and it has been widely applied to calculate the wetting and drying dynamics in river–floodplain systems at regional scales. Unfortunately, SGC approaches to date have not included the latest developments in numerical solutions of the local inertial equations, and the original solution scheme was reported to suffer from numerical instability in low-friction regions such as urban areas. In this paper, for the first time, we implement a newly developed diffusion and explicit adaptive weighting factor in the SGC model. Adaptive artificial diffusion is explicitly included in the form of an upwind solution scheme based on the local flow status to improve the numerical flux estimation. A structured sequence of numerical experiments is performed, and the results confirm that the new SGC model improved the model performance in terms of water level and inundation extent, especially in urban areas where the Manning parameter is less than 0.03 m-1/3 s. By not compromising computational efficiency, this improved SGC model is a compelling alternative for river–floodplain modelling, particularly in large-scale applications.

Impact of Soil Moisture Dynamics and Precipitation Pattern on UK Urban Pluvial Flood Hazards Under Climate Change

“…Therefore, a UK future flood hazard assessment framework under global warming is proposed. A physics-based flood inundation model LISFLOOD-FP (Bates et al, 2010;Neal et al, 2012;Rong et al, 2023) which explicitly incorporates the flood-driving factors is further developed, with a separately configured water balance model and an integrated Green-Ampt infiltration model accounting for changing soil moisture and antecedent conditions. Characteristics of flood-producing rainfall events and their corresponding consequences in a warmer world are analyzed.…”

“…For each rainfall event, the maximum water depth in each individual grid during the computation is acquired, which is used to assess the flood hazard. A detailed description of the hybrid 1D-2D surface water flood model can be found in Bates et al (2010), Neal et al (2012), and Rong et al (2023).…”

“…This is because when IDF curves are extended from point scales to areas they necessarily only represent spatially uniform rainfall and not the full spatial signatures of an ensemble of rainfall events. To address both these issues, here a physics-based flood inundation model (LISFLOOD-FP) which explicitly incorporates the multiple spatial information sources of changes in flood-driving factors is further developed (Bates et al, 2010;Neal et al, 2012;Rong et al, 2023;Sampson et al, 2015), to account for changing soil moisture and antecedent conditions. Together with 12 ensemble members of UKCP Local climate data at the hourly and kilometer scale, a scenario-based framework for future flood hazard assessment is proposed.…”

Experimental Study on the Buffering Effects of Urban Trees Group in Dike-Break Floods

“…The dike-break wave propagates approximately in an elliptical shape within the flood-prone area, centered around the breach. Furthermore, the flood propagation time and peak velocity vary significantly across flood-prone areas with different roughness coefficients 9,10 . Specifically, when urban street blocks serve as flood-prone areas during dike-break floods, the floodwater takes on complex flow patterns consisting of shock waves and reflected waves due to the intricate nature of residential areas.…”

Experimental study on the buffering effects of urban trees group in dike-break floods

“…The dike-break wave propagates approximately in an elliptical shape within the flood-prone area, centered around the breach. Furthermore, the flood propagation time and peak velocity vary significantly across flood-prone areas with different roughness coefficients 9 , 10 . Specifically, when urban street serve as flood-prone areas during dike-break floods, the floodwater takes on complex flow patterns consisting of shock waves and reflected waves due to the intricate nature of residential areas.…”