292 caldwell. SEDIMENTATION IN HARBORS [Ch. 16 



vania; Sacramento, California; Mainz (on the Rhine), Germany; 

 Budapest (on the Danube), Hungary; and Chungking (on the Yang- 

 tze) , China. For the most part, fresh-water streams keep the silts and 

 clays moving, and the sedimentation problem becomes one of sand. 

 Such harbor sites are usually selected initially where a deep pool exists 

 in the bottom contours of the river rather than in one of the crossing 

 or bar areas. However, the meandering tendencies of the river beds, 

 the shifting in the bar locations with varying flows in the river, dredg- 

 ing to increase navigable depth, or attempts to expand the harbor be- 

 yond the limits of the pool frequently result in the creation of a shoal- 

 ing problem in the harbor. 



Solutions of the problem have been for the most part confined to: 



(1) Dredging to remove the sediment. 



(2) Partially enclosing the harbor area with training walls and 

 dikes. This sometimes results in the silting of the harbor by the de- 

 posit of silt and clay in the dead-water area created. The channel 

 from the river to the harbor also continues to be subject to shoaling. 



(3) Use of training walls to divert sand-laden bottom waters past 

 the harbor and allowing only the sand-free top water to enter the 

 harbor. This procedure can have the same results as (2) unless care 

 is taken to maintain sufficient flow to flush the harbor. 



(4) Diverting the river to another course to by-pass the harbor. 

 This in effect makes the harbor an off-channel harbor, which is dis- 

 cussed below. 



(5) Construction of locks and dams in the river channel, thereby 

 increasing depths in the harbor area. 



In order to avoid, lessen, or eliminate shoaling in harbors of this 

 type, it would appear that a better understanding is needed of the 

 following: (a) the laws governing the meandering of rivers; (6) the 

 laws governing the movement of sand by flowing waters, including a 

 study of the action when the flow is bifurcated by a dike or train- 

 ing wall; (c) the laws governing the intermixing of river and harbor 

 waters, which results in the silting action described in (2) above; 

 (d) the laws relating to non-silting velocities as related to (3) above. 



OFF-RIVER HARBORS 



Many river harbors are essentially landlocked in that the harbor is 

 not in the river channel proper and is connected with the channel only 

 by the navigation access channel. Such harbors are usually stag- 



