theoretically, it represents the path of the slick after 30 days. The "x" 

 surrounded by the circle represents the location of the Avgo Mevohant . The 

 boxed- in area represents the limits of the slick after 30 days or as other- 

 wise specified. The limits of the slick were provided by R. Griggs of the 

 U.S. Coast Guard. Each "x" along the path represents the end of a 5-day 

 period. 



There are two different sets of Monte Carlo plots. One set (Figures 

 VII- 24 andVII-25) depicts five separate Monte Carlo trajectories. Each 

 position of the leading edge of the spill is plotted every 2 hours for 30 

 days. The second, Figures VII-26 through VII-29 and figure 2-14, depicts a 

 point for each 200 trajectories after 5, 10, 20, and 30 days. The area with 

 the highest concentration of points indicates the most probable position of 

 the leading edge. The limits of the observed slick have been added to each 

 plot to aid in evaluating the accuracy of the predictions. 



Discussion 



The U.S. Naval Weather Service wind data for the Quonset region indi- 

 cates that westerly and northwesterly winds predominate. This yields a 

 general eastsoutheast movement of the oil slick. The trajectories calculated 

 follow the direction of the actual slick until the 25 to 30 day period. At 

 that time, the trajectories continue on their east-southeast path while the 

 slick assumes an almost due east heading. This occurs near 68 °N longitude 

 and 38°W latitude. According to Sverdrup, Johnson, and Fleming (1942), the 

 Gulf Stream in the New England Atlantic area is located between 68° and 60 °N 

 longitude and 37° and 41°W latitude and flows in an east-northeast direction 

 at a speed of approximately 1 knot. Due to yearly changes and meanders, it 

 is difficult to locate the Gulf Stream at any one time. Since only tidal 

 currents are used in the models, this would explain the inaccuracy of the 

 trajectories after 20 to 25 days. The addition of a strong east-northeast 

 current when the slick reached the Gulf Stream would give more accurate long- 

 term results. 



Subsurface Currents 



R. Gordon, M. Spaulding, P. Cornillon, and R. Halm of the Department of 

 Ocean Engineering at the University of Rhode Island generated a model which 

 predicted the subsurface drift of Avgo Merchant oil. Directions of the 

 monthly mean bottom velocity vectors for December and January in the spill 

 area (Bumpus, 1973) as reported by the Bureau of Land Management (1976) in 

 thesis draft Environmental Impact Statement for the North Atlantic Region 

 were used along with estimates for maximum speed in the area (taken as 3.0 

 nautical miles per day throughout) as model input. A particle injected at 

 the spill location (41°0'N, 69°30'W) was advected using the closet bottom 

 velocity vector. A time step of 1 day was used. 



Figure 2-15 shows the trajectory of a particle injected in the vicinity 

 of the spill location (41.0°N latitude, 69.5°W longitude) near the bottom. 

 The spill location is identified by a square (d) and subsequent positions at 

 daily intervals are denoted by crosses (X) . The bottom movement at first 

 proceeds towards the southwest and after approximately 5 days heads west. 



61 



