Theoretical Downflow Flow in "River Channel" in Southern Staten Island

In the attached map, I used the GRASS 6.4.1 hydrology program to construct the hypothetical river flow based on elevation for southern Staten Island.  I brought in the "Carve" program that used the Staten Island Rapid Transit right of way as a base.  The artificial channel follows the Staten Island Railway for a small section and then goes to along Seguine Avenue.  The narrow thin black bars is the theoretical water flow direction.  The program seems to have done this for even the higher elevations as well.  This is just an experiment and is not done by a professional environmental person.  The areas of interest, which is the flood channels along the SIRT and Seguine Avenue and vicinity is penciled in red.  Notice that the flood flow pattern for Seguine Avenue is from east to west and not north to south.  Since there are more flood flow bars on the Seguine Avenue than on the southern Staten Island RR right of way, I believe the Seguine Avenue corridor is a stronger flood flow victim than SIRT.  The SIRT flood flow is also from west to east.  Correction:  The GRASS 6.4.1 program here creates a vector showing downhill flow on the surface.  Since Hurricane Sandy was a sea surge event and not mainly a rain event, the flooding that occured was due to a sea surge and  a downhill water flow mapmay not explain that much, particularly any theoretical flooding along the right of way of the Staten Island Rapid Transit line and Seguine Avenue.  Notice that the flow along Seguine Avenue is west to east.