the arch where the canal went under the three-way intersection at the heart of derry 's downtown area was full almost to the top ; main street , canal street , and the foot of up-mile hill were impassable except by foot , and those who splashed and hurried their way toward the sandbagging operation felt the very streets beneath their feet trembling with the frenzied flow of the water , the way a turnpike overpass will tremble when big trucks pass each other .