Journal of Waterway, Port, Coastal, and Ocean Engineering

Longshore‐sediment transport rates for the south Indian coast from Allur to Cochin and for Sri Lanka are estimated from ship‐reported wave data (1968–86). Annual gross sediment transport rate is high (1.5 to $2.0\times {10}^6{m}^3$) along the coasts of north Tamil Nadu and south Kerala and is less (0.5 to $1.0\times {10}^6{m}^3$) along the south Tamil Nadu and Sri Lankan coasts. The annual net transport is southerly along the west coast of India and predominantly northerly along the east coast except near Durgarajupatnam in Andhra Pradesh. Coasts near Tharangampadi, Karaikal, Nagore, Tuticorin, Virapandianpatinam, and Manakkodam in India and Kuchchaveli, Betticola, Pottuvil, Chilaw, and Negombo in Sri Lanka appear to be nodal drift points, with an equal volume of transport in either direction annually.

A new mathematical formulation is established for two‐dimensional (plan view) unsteady water flow, sediment transport, and bed evolution in natural watercourses such as reservoirs, estuaries, and coastal waters, where depth averaging is appropriate. Sediment mixtures in natural watercourses are represented through a suitable, and unlimited, number of discrete size classes, any of which may be subject to either suspended‐load or bedload transport (or both) depending on prevailing local hydraulic conditions. Governing equations for water and sediment are transformed (completely) into curvilinear coordinates and then depth‐averaged, when appropriate. The system of governing sediment equations at a computational point is solved in a new implicit, finite‐difference, fully coupled manner. Furthermore, the sediment equations are coupled with the water flow in an iterative manner in order to account for the feedback between the flow field and changes in both bed elevation and bed‐surface size distribution. The mathematical formulation and associated numerical solution, incorporated into the new MOBED2 computational code, are tested through simulation of mobile‐bed dynamics in the Cor‐alville Reservoir on the Iowa River, Iowa. Initial proof‐of‐concept tests confirm the feasibility of the new approach by reproducing the proper qualitative behavior of the overall modeling concept.

A bootstrap resampling approach is developed for extremal analysis of measured and hindcast ocean‐wave data for use in design, construction, operations, and maintenance of coastal structures. The resampling method produces estimates for the extrapolation bias associated with competing extreme‐probability models. A goodness‐of‐fit statistic for the extremal type 1 model is also developed. The bias estimates and goodness‐of‐fit statistic are used in selecting an appropriate probability model for a given record of extreme significant wave heights. The method is shown to provide information about model selection that is not available from present extremal analysis methodology, and may help prevent significant un‐derprediction of extremes that can occur with conventional approaches. Examples using both hindcast and measured wave data are presented to demonstrate application of the methods developed in this paper.

Linearized shallow water wave theory is utilized to investigate the interaction of surface waves with a rectangular pit of finite dimensions in water of otherwise uniform depth. The fluid domain is divided into two regions: an interior region whose boundary consists of the projection of the outline of the pit and an exterior region consisting of the remainder of the fluid domain. Application of Green's second identity utilizing an appropriate Green's function in each region leads to a pair of simultaneous integral equations for the velocity potential and its normal derivative at the imaginary fluid interface between the two regions. These integral equations may then be discretized and the resulting systems of algebraic equations solved by standard matrix techniques. Utilizing the values of the velocity potential and its derivative on the imaginary fluid boundary, a reapplication of Green's identity allows the potential at any point in the fluid to be determined. Based on this solution technique, numerical results are presented that illustrate the influence of the various pit characteristics on the wave field for several example geometries.

The heights of water waves propagating over fluid‐mud bottom can be significantly reduced due to the viscous energy dissipation occurring in the mud bottom. In some cases, exceptionally high rates of attenuation are possible whereby waves are almost completely damped within several wavelengths. This phenomenon has been observed both in field investigation and in laboratory experimentation. In this paper, the viscous damping of cnoidal waves progressing over fluid‐mud seabeds is investigated, in which fluid mud is assumed to be a viscous fluid. The theoretical model adopted here is a two‐layer viscous fluid model modified with three boundary layers at the water‐mud interface and at the rigid bottom beneath mud layer. Viscosities of both water and fluid mud are taken into consideration. For a nonlinear shallow wave progressing over a viscous mud bed, the first‐order analytical solutions are derived for the velocity distributions in boundary layers and for the attenuation rate of wave heights with distance. The attenuation coefficients are larger than those predicted on the basis of linear shallow wave theory, and unlike the case of linear shallow waves, they are not independent of wave height. The viscous damping of solitary and sinusoidal waves, which are two extreme cases of cnoidal wave, are also discussed according to the present solution.

Tidal inlets present a major barrier to the longshore littoral drift, particularly when they have been improved for navigation by dredged channel and/or jetties. This paper discusses improvements of present procedures of bypassing and backpassing. Bypassing is transfer parallel to shore, backpassing is transfer perpendicular to shore from the ocean, bay, or lagoon. It is now possible to improve available bypassing techniques by much larger traps to intercept the littoral drift toward the inlet from all directions. The same equipment used for transfers can be applied for maintenance of the navigation channel. With present technology, too much material is lost to the ocean and to bay shoals. It may be recovered by the use of the same technology as for bypassing. We are in the process of developing greatly improved bypassing and backpassing technologies combining conventional dredge pumps and fluidization pumps or jet pumps. Better shallow-water and dredge-barge equipment is needed and will undoubtedly become available from dredging industries overseas and in the United States.