made in a place that is normally dry but can be flooded (either at high tide 

 or by removing a gate) for towing the mattress to its final location. The 

 mattress is then loaded with stones and sunk into place. It is then covered 

 with stones as needed to resist the expected currents. Examples of fascine 

 mattresses are shown in Figure 78. Finer material is placed on the bottom 

 of the mattress where it contacts the sand and coarser material is on top to 

 support the stones. These mattresses will deteriorate rapidly if left where 

 they would receive periodic wetting. Therefore, they will only work where 

 they are completely submerged all the time. Where damage by marine borers 

 is expected, preservative treatment could be applied but the cost of treatment 

 may indicate that some other material be used (Van Bendegon and Zanen, 1960) . 



(5) Submerged Screens. Submerged screens for current control can 

 be made of "wattles" (flexible branches woven around posts) as shown in 

 Figure 79 or can be made by combining stones and small poles (or bamboo) 

 into cribs. The cribs are formed by forming a lattice work of poles to form 

 a cage (crib) and filling it with stones for stability. Figure 80 shows 

 some crib types . 



(6) Piers and Wharves. Piers and wharves may be made entirely of 

 wood construction with incidental use of metal fastenings and rock for slope 

 protection. Piles, pile caps, stringers and decking would all be treated 

 and placed as discussed in earlier paragraphs of this section. These wood 

 members can also be used in conjunction with other materials, such as con- 

 crete piles . 



Mooring dolphins and fender piles for piers and wharves are frequently 

 made of wood to take advantage of the energy absorbing property of wood even 

 when the remainder of the structure is of some other material such as 

 concrete. 



(7) Sand Fences . Fences made of brush have proved more effective than 

 fences made of boards in building sand dunes on the Outer Banks of North 

 Carolina (Savage, 1963). In this installation, brush was held upright 

 between pairs of wood plank rails as shown in Figure 81. The filtering 

 action of the brush apparently trapped more sand than the wind deflection 

 action of wood slats. 



279 



