The mist burns off of a cozy Sunday morning as I sit, watching a flock of geese trade honks with a train. They’re preening in the calm water above the first drop of the Manchester Whitewater Park, and occasionally a brave one floats down the chute before flapping back up to its friends. Tucked between industrial buildings and Main Street, the park is already humming with cyclists, dog walkers and photographers doing portrait shoots. The structured banks of ochre boulders look amazingly inviting, and upstream, a to...