A new one-dimensional numerical model for unsteady hydraulics of sediments in rivers
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A new one‑dimensional numerical model for unsteady hydraulics of sediments in rivers Eman AlQasimi1 · Tew‑Fik Mahdi1 Received: 20 April 2020 / Accepted: 29 July 2020 © Springer Nature Switzerland AG 2020
Abstract This paper presents the model UMHYSER-1D (Unsteady Model for the HYdraulics of SEdiments in Rivers 1-D), a onedimensional hydromorphodynamic model capable of representing water surface profiles in a single river or a multiriver network, with different flow regimes considering cohesive or non-cohesive sediment transport. It has both steady and unsteady flow and sediment modules. For steady gradually varied flows, UMHYSER-1D uses the standard step method to solve the energy equation and the “NewC” scheme for the de St Venant equations. For sediment transport, UMHYSER1D uses two methods: for long-term simulation, the unsteady terms of the sediment transport continuity equation are ignored, and a non-equilibrium sediment transport method is used. For short-term simulation, the convection–diffusion equation, with a source term arising from sediment erosion/deposition is solved using the fractional step method. The equation without the source term is solved with an implicit finite-volume method, then the equation with source term is solved. Internal boundary conditions, such as time-stage tables, rating curves, weirs, bridges, and gates are simulated. Incorporated is the active layer concept, which allows selective erosion, enabling the simulation of bed armoring. Noncohesive sediment transport equations and cohesive sediment physical processes are applied to calculate the sediment deposition and erosion. Finally, UMHYSER-1D empirically accounts for bed geometry adjustments by using a relationship between erosion width and flow rate, an angle of repose condition for bank stability and three minimization theories. The presented validation and application cases show UMHYSER-1D’s capabilities and predicts its promising role in solving complex, real engineering cases. Keywords One-dimensional model · UMHYSER-1D · Fractional step method implicit finite-volume method · Unsteady sediment transport · Bed geometry adjustment · Minimization theories
1 Introduction Numerical modeling is widely used in river engineering studies. Determining the risk zone caused by floods [1], investigations of river morphology changes [2, 3], stream restoration projects and sediment deposition studies [4, 5] are some examples of river engineering problems involving numerical modeling. Several numerical models were developed during the last decades, spanning from the simplest ones to more complex solvers. The less complicated
ones are the one-dimensional (1D) models. Some do not consider riverbed erosion, such as FLDWAVE [6], by solving unsteady flow equations, while others are developed for mobile riverbeds such as GSTARS [7] or MHYSER [2] using the flow quasi-steadiness hypothesis. Others more complicated, were developed and still under improvement such as the one by El Kadi and Paquier [8], CONCEPTS [5], SRH-1D [9], CCHE1D [10], MIKE
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