(d) Winds. Prevailing northwest winds from November through March at speeds 

 up to 12 knots; varying in direction through remainder of year, but not as strong. 



(e) Storm Surge and Tides. 



Mean tidal range, 4.1 feet above MLW 

 Spring tidal range, 4.9 feet above MLW 

 Mean tide level, 2.1 feet above MLW 

 Extreme high tide, 5.4 feet above MLW 

 Extreme low tide, —1.1 below MLW 



(f) Littoral Transport. Littoral transport has reached a stable condition with 

 little scour or accretion taking place. 



(g) Water Depth at Structure. Harbor of Refuge, 10 to 70 feet; Breakwater 

 Harbor, 3 to 23 feet. 



(h) Ice Conditions. Thin ice forms on Delaware River in early December; heavier 

 ice from January to March. Tidal currents and heavy traffic of large ocean vessels generally 

 keeps ice broken. 



(i) Bottom Conditions. Stable sandy bottom in Harbor of Refuge ; shifting silty 

 bottom in Breakwater Harbor (Fig. 25). 



(5) Structural Features (Figs. 26 and 27). Stone for the old breakwater was dumped 

 on the bay bottom in a mound averaging 160 feet wide, with side slopes about 45°. In 1833, 

 at the end of five construction seasons, contemporary reports show 75 percent of the 

 breakwater length laid with levels varying from 15 feet above sea bottom to 5 feet above 

 higher water, plus an even greater part of the ice breaker. Work continued intermittently 

 until 1839, when 2,586 Uneal feet had been constructed against the 3,600 feet as designed. 

 In 1869 the construction was finally brought to design height of 14 feet above MLW with a 

 width at the crest of 22 feet. 



The Gap was finally closed from 1882 to 1898 by dumping stone for lower sections, and 

 placing upper stone by derrick barge. An earUer plan had called for a timber bridge and 

 railroad track which was finally discarded for the rubble-mound section. 



The outer breakwater, completed in 1901, was constructed basically to the same cross 

 section as the Gap, with a length of 8,040 feet at low water, and 7,950 feet at the crest. The 

 seaward side, brought up first, afforded protection for work on the harbor side, and 

 permitted settlement of the lower parts before topping off the seaward face. 



(6) Design Data. There are few reliable records to indicate the criteria followed in 

 the original design. The inner breakwater was the first of its type in the Western 

 Hemisphere, but there were precedents in Europe at Cherbourg, Plymouth, and Kingstown. 

 Some records indicate that the irmer breakwater was an exact duplicate of the one at 

 Cherbourg, and therefore, greatly over-designed. Recommendations were made at one point 

 to continue construction with the use of stone, wliich could be safely removed from the old 

 breakwater, although reducing its cross section by as much as 50 percent. 



52 



