Really? I suggest that you take a look at the photo series posted by mosquitobite above:
http://www.kodakgallery.com/Slideshow.jsp?mode=fromshare&Uc=14ewb3ap.b147fdut&Uy=nyvoby&Ux=1
There is a two swathe of dry land with thousands upon thousands of buildings. Go in the other direction for miles and miles (not shown), and you would still be walking across dry land with buildings and supplies.
Now, I am not defending the cops on the bridge, all I am saying is that there were plenty of supplies within the several hundred square miles of both the Dome and Convention Center and it was completely dry land!!!
Look closely at the concentration of buildings, warehouses, skyscrappers, shipping containers, ect... Are you honestly going to say that there were more supplies across the bridge?