Make that mostly arched the flood. It's been raining a lot here lately (picture from a couple weeks ago). If it had been raining like that in 1775, Lt. Col. Smith's regulars would have to have asked for transport from the Royal Navy. But once at Concord, there wouldn't have been much resistance - the largest contingent of Minutemen came from neighboring Sudbury, and the Sudbury River would have been impassable.
As it was, His Majesty's 10th Regiment of Foot had to fight its way back to Boston. Even reinforced, it was a near thing, and Lt. Col. (later Major General) Smith was wounded in the withdrawal. Given how outnumbered the Red Coats were (2 and a half to one), and how the Red Coats had left Boston with insufficient ammunition for a prolonged engagement, they did very well indeed to arrive under the protective guns of the fleet in one piece. The Colonists blockaded the British at the narrow peninsula that connected Beacon Hill to the mainland (back in the day before land fill and Fenway Park), and it was on.
By the rude bridge that arched the flood
Their flag to April's breeze unfurled
Here once the embattled farmers stood
And fired the shot heard round the world.- Ralph Waldo Emerson