NYCkayaker The Yonkers spill

[Graeme Birchall]

Greetings;

I know that the story is old news, but I thought I'd comment on the 
recent Yonkers sewerage spill.  But before I begin, it much easier to 
get a grip on a problem like this if one crunches the data in metric. 
For those who have forgotten, below are the basics:

   There are 1,000 liters (volume) in 1 cubic meter
   There are 1,000 meters (distance) in 1 kilometer

According to the reports, the sewerage spill was 4,000,000 gallons. 
This equals 15,000,000 liters, which equals 15,000 cubic meters.  The 
Tappan Zee is approximately 20km long and 1km wide, and has a 1 meter 
tide range.  This means that during every tide approximately 20,000,000 
cubic meters of water move in and out of the Tappan Zee.  The amount of 
sewerage spilled thus equals 0.07% of the water moving in and out in a 
single tide cycle.

There are of course other factors to consider:  On the plus side, there 
is much more water in the Tappan Zee than that which goes in and out 
with each tide cycle.  And there have been approximately ten tide cycles 
since the spill.  On the negative side, the spilled sewerage probably 
did not disperse evenly, and a lot of the water in the Hudson near 
Yonkers simply sloshes back and forwards with the tides.

Graeme

Graeme Birchall