Effect of water-sediment regulation and its impact on coastline and suspended sediment concentration in Yellow River Estuary

Implementation of the water-sediment regulation(WSR) scheme, mainly focused on solving the sedimentation problems of reservoirs and the lower reaches of the Yellow River, has inevitably influenced the sediment distribution and coastal morphology of the Yellow River Estuary.Using coastline delineation and suspended sediment concentration(SSC) retrieval methods, this study investigated water and sediment changes,identified detailed inter-annual and intra-annual variations of the coastline and SSC in the normal period(NP: 1986-2001, before and after the flood season) and WSR period(WSRP: 2002-2013, before and after WSR). The results indicate that(1) the sedimentation in the low reaches of the Yellow River turned into erosion from 2002 onward;(2) the inter-annual coastline changes could be divided into an accretion stage(1986-1996), a slow erosion stage(1996-2002), and a slow accretion stage(2002-2013);(3) an intra-annual coastline extension occurred in the river mouth in most years of the WSRP; and(4) the mean intra-annual accretion area was 0.789 km^2 in the NP and 4.73 km2 in the WSRP,and the mean SSC increased from 238 mg/L to 293 mg/L in the NP and from 192 mg/L to 264 mg/L in the WSRP.

An efficient dynamic uniform Cartesian grid system for inundation modeling

A dynamic uniform Cartesian grid system was developed in order to reduce the computational time in inundation simulation using a Godunov-type finite volume scheme. The reduction is achieved by excluding redundant dry cells, which cannot be effectively avoided with a conventional Cartesian uniform grid system, as the wet area is unknown before computation. The new grid system expands dynamically with wetting, through addition of new cells according to moving wet-dry fronts. The new grid system is straightforward in implementation. Its application in a field-scale flood simulation shows that the new grid system is able to produce the same results as the conventional grid, but the computational efficiency is fairly improved.

Preface for special section on flood modeling and resilience

Climate change has led to increased frequency, intensity,and duration of extreme weather events, e.g., intense rainfall,heat waves, droughts, and storm surges, worsened byrapid population growth and urbanization at the global scale.Evidence can be found in the exceptional number of unprecedentedweather extremes and the resulting naturalhazards, especially flooding, as seen in the last few decades.For example, the UK has experienced numerous storms andsevere floods in the last decade, particularly in 2007, 2012,and 2015, with 2012 being recorded as the second wettest year in the UK and the wettest ever in England. These events have resulted in lives lost and tremendous economic damage. The UK is not alone. Similarly unusual weather events have been reported across the globe. In China,different types of flooding threaten 1/10 of the country's total area, millions of hectares of farmland, and over 100 large cities, making it one of the most vulnerable countries to flooding.

A graphics processing unit-based robust numerical model for solute transport driven by torrential flow condition

Solute transport simulations are important in water pollution events.This paper introduces a finite volume Godunovtype model for solving a 4×4 matrix form of the hyperbolic conservation laws consisting of 2D shallow water equations and transport equations.The model adopts the Harten-Lax-van Leer-contact(HLLC)-approximate Riemann solution to calculate the cell interface fluxes.It can deal well with the changes in the dry and wet interfaces in an actual complex terrain,and it has a strong shock-wave capturing ability.Using monotonic upstream-centred scheme for conservation laws(MUSCL)linear reconstruction with finite slope and the Runge-Kutta time integration method can achieve second-order accuracy.At the same time,the introduction of graphics processing unit(GPU)-accelerated computing technology greatly increases the computing speed.The model is validated against multiple benchmarks,and the results are in good agreement with analytical solutions and other published numerical predictions.The third test case uses the GPU and central processing unit(CPU)calculation models which take 3.865 s and 13.865 s,respectively,indicating that the GPU calculation model can increase the calculation speed by 3.6 times.In the fourth test case,comparing the numerical model calculated by GPU with the traditional numerical model calculated by CPU,the calculation efficiencies of the numerical model calculated by GPU under different resolution grids are 9.8–44.6 times higher than those by CPU.Therefore,it has better potential than previous models for large-scale simulation of solute transport in water pollution incidents.It can provide a reliable theoretical basis and strong data support in the rapid assessment and early warning of water pollution accidents.