enhancement, the best means of preventing the shoaling of nearby harbor waters by material 

 eroded from this beach is to revet the beach face. To perserve the beach, an inharbor wave 

 baffle or fence may be required between the navigation channel and the beach to control 

 the sediment migration. Another control is to effectively implement a slow-speed zone in 

 the reach of channel opposite the beach. If the beach is only for recreational purposes, it 

 should be located at the inner end of a basin where boat -wake waves are seldom generated, 

 provided that the water quality in that location is adequate. In this location, the beach 

 would also help to reduce surge oscillations in the basin. 



b. River Discharge. Harbors in off-river basins are subject to shoaling because of 

 sediment deposition in the quiet water area and by eddy currents that may be created by 

 the entrance configuration and the flowing water in the river. Although shoaling can not be 

 prevented, it is often reduced by proper entrance design. Along the Colorado River, for 

 example, the banks are friable and sandy, without much cohesive property. The river 

 silt -load increases rapidly with slight increases in flow velocity; the suspended material is 

 coarser than normal, and it settles out rapidly in the quiet waters of the entrance channel to 

 any off -river basin. The best solution is to provide a flat area on the downstream lip of the 

 entrance from which a dragline can excavate deposits from the bottom of the entrance 

 channel and cast them into the river downstream from the entrance (Fig. 15). The entrance 

 must be kept narrow to permit such an operation, and a training dike off the upstream lip is 

 helpful in reducing the deposits. 



c. Nearby Water Area Structures. Structures in the water area outside the harbor 

 entrance may also cause harbor shoaling, especially along shorehnes where littoral transport 

 is a problem. An example is a groin or jetty located in an area that is normally downdrift 

 from a harbor entrance. This type of structure tends to impound or stockpile sediment 

 under normal conditions. However, on those occasions when waves approach from the 

 opposite direction and cause a reversal of direction of littoral transport, some of this sand 

 may be transported back into the entrance and cause shoaling. Relatedly, periodic 

 maintenance operations of another harbor located updrift from the problem harbor may 

 result in large quanities of sand being transported downcoast toward it. Beach-fill operations 

 along the nearby coast may increase the transport rate of material into the harbor entrance. 



On rivers, any structure upstream or across from the harbor may alter the current flow 

 and cause excessive shoaUng at the harbor site. Current-deflecting dikes, bridge piers, and 

 pile-supported structures are examples of manmade works that may affect the shoaling 

 characteristics of the river at the site. Bank reahnements and erosion-control works 

 undertaken after a harbor has been built may have a profound effect on the harbor. Thus, it 

 is important first to consult with controlling authorities about any plans for future 

 construction or corrective works near the site, or upstream from it, before harbor 

 construction on any river. Such information should be considered in the siting and design of 

 the harbor. 



d. Redistribution of Bottom Materials. In some water areas, the shifting of bottom 

 materials by natural processes poses a severe threat to any harbor built along the margins of 



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