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Thursday, November 15, 2012

Theoretical Downhill Flood Flow in Southern Brooklyn and Sea Beach Line Open Cut

In the map below, I used GRASS 6.4.1 to bring in the "carve" file of river channels produced earlier based on the street elevation.  Remember in an earlier post, the program predicted a river flow along the open cut of the Sea Beach Line (N) between 86th Street and Avenue U.  Using this as a basis, I constructed a water flow diagram for southern Brooklyn.  What is surprising is that the water flow in the penciled area, along the open cut of the Sea Beach Line is from west to east and not south to north from the Coney Island Creek as expected.  Also notice that the horizontal flow near the Sea Beach Line is along the western side of the open cut.  I do not know if GRASS is incorrect in this projection or if I made a mistake in the settings. Notice the water flow in Coney Island where there was extensive flooding.  Correction:  The GRASS 6.4.1 hydrology program here creates a vector showing downhill flow on the surface elevation.  Since Hurricane Sandy was mainly a sea surge event and not a rain event. the minor downhill flow on the surface would not explain the flooding of the Sea Beach Line.  For this reason, the vector direction is perpendicular to the Sea Beach open cut.  The vectors do not show the direction of the sea surge.

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