HYDROGRAPHY OF THE MARINE WATERS 11 



given wind are not available. From the United States Coast Pilot (1936) it 

 is noted that the wind-driven water may range about 2 feet above and below 

 normal in the open sounds, and the funneling of this water, such as may occur 

 at Washington up the Pamlico River or at New Bern up the Neuse River 

 behind an easterly wind, may give tides 3 or 4 feet above normal. 



Obviously the net seaward flow through the sounds is positively correlated 

 with river discharge. Direct rainfall on the sounds is to be added to this effect 

 and evaporation from the sounds subtracted. The Corps of Engineers (1935) 

 attempted to compile figures that would indicate these net results. The basic 

 source of data used is not indicated and I have been unable to learn of this 

 through correspondence. If, as is quite possible, the discharge was taken from 

 so-called downstream gaging stations, the data are of a sort that I have 

 deliberately avoided using for this purpose. Such stations are placed well 

 upstream from sea level and tidal influences; consequently actual discharge 

 may be greatly modified over the remaining miles from rainfall, evaporation, 

 and transpiration from the vegetation. With this reservation, it is interesting 

 to consider the figures obtained by the Engineers. The stated daily discharge 

 into Albemarle, Pamlico, and Core sounds is 44,464 acre-feet. The daily 

 evaporation given (from figures on Lake Michie, Durham, North Carolina) 

 is 25,392 acre-feet. In the report the authors subtracted evaporation from 

 discharge without mentioning rainfall on the sounds, and reported a daily 

 net of 19,072 acre-feet to flow into the ocean. This would be a relatively minor 

 item in sounds that total 1,648,000 acres (Table 2 shows that on October 11, 

 1932, the net seaward flow through Oregon Inlet alone was greater than this) . 



Of course freshets and seasonal highs and lows in river discharge, all of 

 which are discussed below in the section on Salinity and Nutrient Salts, 

 directly affect circulation in the sounds and generally cause the greatest sea- 

 ward flow to occur in the early spring. The discussion of salinity also 

 mentions density stratification, a factor which may cause shoreward counter- 

 currents along the bottom. 



It is commonly stated that there are no lunar tides in the North Carolina 

 sounds except at the inlets (Table 3) which, of course, irriplies a general lack 

 of tidal currents. The sounds are too small to have an appreciable tide 

 generated within; ^ consequently what tide there is must issue from the 

 ocean by way of the inlets. Such tidal effects are rapidly dampened with 

 distance from these inlets as is clearly illustrated in Figure 3, which compares 

 simultaneous gage readings inside Oregon Inlet, at Fort Raleigh 15 miles to 

 the north on Roanoke Island, and at Munden Point in northern Currituck 

 Sound, an additional 48 miles away. It follows that near inlets, currents 

 would be more regular and stronger than elsewhere within the sounds. Many 



S. In Lake Superior, for example, there is a tide of about 2 inches (Stewart, 1945). 



