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from Geography of the Blackstone Valley
The average dam in the Blackstone Valley was only about
nine feet tall. Even small dams were important for mill owners.
Building a dam causes the water in the river to rise until it flows
over the dam as a waterfall. The rising water created reservoirs or
mill ponds that allowed mills to operate their water wheels
almost all year long. They provided a steady source of water even
in times of drought.
The Blackstone River drops about 440 feet over its 46-mile
length. That's an average drop of about 9 % feet per mile. This
drop is important. Water weighs 8.34 pounds per gallon. It is the
weight, not the speed of the water that pushed the water wheels
that powered the mills. The series of drops along the Blackstone
over multiple rapids and waterfalls, made it perfect for the
construction of water-powered mills.
The geography and geology of the Valley made this relatively
small and seemingly ordinary New England River the birthplace
of the American Industrial Revolution. Eventually it won the
nickname of "America's Hardest Working River."
(from "Geography of the Blackstone Valley" by National Park Service)
What was the relationship between the Blackstone River's drop
of 440-feet over its 46-mile length and the river's usefulness for
industry?
1. The drop created reservoirs of water that helped power
the mills all year long.
2. The drop increased the speed of the water that gave the
mills power to operate.
3. The drop balanced the weight of the water with the speed
of the water to power the mills.
4. The drop produced the water weight needed to turn the
wheels that powered the mills.