A Unified Sediment Transport Formulation for Coastal Inlet Application

Abstract

Abstract:The Coastal Inlets Research Program (CIRP) is developing predictive numerical models for simulating the waves, currents, sediment transport, and morphology change at and around coastal inlets. Water motion at a coastal inlet is a combination of quasi-steady currents such as river flow, tidal current, wind-generated current, and seiching, and of oscillatory flows generated by surface waves. Waves can also create quasisteady currents, and the waves can be breaking or non-breaking, greatly changing potential for sediment transport. These flows act in arbitrary combinations with different magnitudes and directions to mobilize and transport sediment. Reliable prediction of morphology change requires accurate predictive formulas for sediment transport rates that smoothly match in the various regimes of water motion. This report describes results of a research effort conducted to develop unified sediment transport rate predictive formulas for application in the coastal inlet environment. The formulas were calibrated with a wide range of available measurements compiled from the laboratory and field and then implemented in the CIRP's Coastal Modeling System. Emphasis of the study was on reliable predictions over a wide range of input conditions. All relevant physical processes were incorporated to obtain greatest generality, including: (1) bed load and suspended load, (2) waves and currents, (3) breaking and non-breaking waves, (4) bottom slope, (5) initiation of motion, (6) asymmetric wave velocity, and (7) arbitrary angle between waves and current. A large database on sediment transport measurements made in the laboratory and the field was compiled to test different aspects of the formulation over the widest possible range of conditions. Other phenomena or mechanisms may also be of importance, such as the phase lag between water and sediment motion or the influence of bed forms. Modifications to the general formulation are derived to take these phenomena into account. The performance of the new transport formulation was compared to several popular existing predictive formulas, and the new formulation yielded the overall best predictions among the formulas investigated. Results of this report are thus considered to represent a significant and operational step toward a unified formulation for sediment transport at coastal inlets and the nearshore where transport of non-cohesive sediment is common.

Dredging Optimization of an Inlet System for Adjacent Shore Protection Projects Using CMS and Gencade

“…CMS-Flow is a finite-volume, depth-averaged model that can calculate water surface elevation, flow velocity, sediment transport (Camenen and Larson 2007), and morphology change (Sanchez et al 2011). CMS-Wave calculates spectral wave propagation including refraction, diffraction, reflection, shoaling, and breaking, and also provides wave information for the sediment transport formulae ( Figure 6).…”

An Integrated Numerical Model for the Design of Coastal Protection Structures

“…Different model concepts are being presently used for the prediction of each one, which range from empirical transport formulae to more sophisticated bottom boundary layer models. In the present work, bed load transport (q b ) is estimated with a quasi-steady, semi-empirical formulation, developed by Camenen, and Larson [19,20] for an oscillatory flow combined with a superimposed current under an arbitrary angle:…”

“…where θ cw,on and θ cw,off are the mean values of the instantaneous Shields parameter over the two half "periods" T wc (crest-onshore) and T wt (trough-offshore), α pl,b is a coefficient for the phase-lag effects [19], and α α is a coefficient for the acceleration effects [39]. The Shields parameter θ cw is defined by:…”

“…where h is the total mean depth, C is the depth-averaged volumetric sediment concentration, c R is the reference concentration at the bottom [19], w s is the sediment fall velocity, and β d is a coefficient calculated based on [20] by:…”

“…The model consists of three main modules that simulate: linear wave propagation (i.e., WAVE_L), wave-induced circulation (i.e., WICIR), and sediment transport along with bed morphology evolution (i.e., SEDTR). The model is capable of simulating the presence of various types of structures (vertical structures; groins and groin systems; emerged, submerged, and floating breakwaters) and includes a novel approach for the representation of swash zone hydrodynamics, while sediment transport is modelled based on the formula proposed by Camenen and Larson [19,20]. The model is tested against experimental data to study the effect of representative coastal protection structures [21,22], and-given the good agreement between calculated results and measured data-is afterwards applied to a real case study of a coastal engineering project in North Greece (combination of submerged breakwaters and beach nourishment).…”