MODEL STUDY CF WAVE SET -UP INDUCED BY HURRICANE 

 WAVES AT NARRAGANSETT PIER, RHODE ISLAND 



by 



John C. Fairchild, Engineer 

 Research Division, Beach Erosion Board 



Introduction 



In compliance with a request from the U. S. Army Engineer Division, 

 New England, certain model tests to determine wave set-up (super- 

 elevation of the water surface over normal surge elevation due to onshore 

 mass transport by wave action alone) at Narragansett Pier, Rhode Island 

 have been performed at the Beach Erosion Board laboratory. It was 

 recognized that onshore wind action tends to pile up the waters at the 

 shore; it was desired to learn if wave action alone acts to give an addi- 

 tional rise, or set-up, of the average water level when the waves are 

 dissipated as breakers. 



Purpose 



The purpose of the tests was to determine: (1) if the wave set-up 

 would occur on a model beach scaled to the average offshore profile at 

 Narragansett Pier, and (2) if wave set-up were in evidence, to evaluate 

 the amount of still water level rise (wave set-up) caused by selected 

 conditions of water depth and wave characteristics. Also, estimates of 

 any significant wave run-up were desired in conjunction with the wave 

 set-up tests. This information was desired as a possible explanation 

 of an observed difference of about 3 feet in maximum water level eleva- 

 tions for "the 1938 hurricane for the relatively exposed area of Narra- 

 gansett Pier, where wave action was dissipated as surf, and the calmer 

 waters off Newport. From considerations of surge distribution and wind 

 set-up alone, it was generally assumed that these two levels would be 

 identical, however the 3-foot difference had been noted. Should wave 

 set-up be identified as a partial cause of this difference, it would have 

 important connotations for determining design and danger criteria in 

 many areas subject to storm waves. 



Selection of Profiles for Model Scale Tests 



It was desired to simulate in the model wave tank the average off- 

 shore profile at Narragansett Pier to as large a scale as tank dimensions 

 would permit. In keeping with this requirement and the wind directions 

 from the isotach charts of the hurricane of September 21, 1938 (Figure 

 1)* eight Drofiles (two oriented in the wind directions from each of four 



♦obtained from Membrsmdum HUR 7-4, March 1, 1956, Hydrometeorological 

 Section, U. S. Weather Bureau, Subject; "Wind Over Narragansett and 

 Buzzard's Bay in Hurricane of September 21, 1938 for Aid in Consider- 

 ation of Design Hurricane". 



