Riverine Modeling with AdH
Rivers are lotic systems that are generally dominated by flows, which are usually uni-directional in response to gravity. Rivers typically flow towards an ocean, lake, sea, or into another river. The physical structure of the river changes as it travels from the headwaters to its outlet. This flow path is termed the stream corridor. Moving from upstream to downstream, the stream corridor changes from the headwaters zone, defined by steep slopes resulting in erosion, to the transfer zone, defined as a milder slope where smaller stream merge, to finally the depositional zone where the gradient flattens and sediment deposits. When smaller rivers, termed "stream" "brook", "beck", "crick", or "creek", converge, stream order increases. As the stream order changes so does the behavior of the river and its planform, i.e. single thread versus braided. Each change and transition represents a new and different challenge. Thus, understanding and capturing the complexity of the system is imperative for the proper application of tools for river management and engineering.
Historically, river modeling has been performed with one-dimensional (1D) models. Here the cross-sections are defined and the back water profile is calculated. Though useful for a multitude of river engineering issues, there are an equal number of issues where a 1D model is insufficient. Multi-dimensional modeling (2D or 3D) can allow for more accurate predictions of flood discharges, inundation times, flood wave propagation, and travel times. Inundation times are especially important for shallow water habitat management. Additionally, sedimentation is an important part of river modeling. As the river progresses through the corridor, the transport behavior changes along with the shape of a river. One typical example is a river flowing a bend. As flow moves around the bend, it will erode the outer bank and deposit on the interior bank, creating a constant morphodynamic change along the waterway. This lateral transport behavior is impossible to simulate in a 1D model. Furthermore, human interference has led to the construction of levees and hardened channels to limit geomorphic changes. Though these measures improve navigation and flood control, they also provide additional challenges in properly understanding the effect of human interference.
AdH can simulate flow in rivers for a steady flow condition or for a hydrograph where the flow and water surface elevation change with time. River flood applications or levee breaches can be performed due to AdH's ability to wet and/or dry sections of the model domain. The bendway correction, or vorticity, component of the code is necessary to compute accurate cross-channel velocity patterns and allows the 2D depth averaged model to accurately represent these 3D helical flow features. The vorticity component is also extremely important for accurate sediment transport and morphodynamic evolution of the river.
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