The average volume is 6,731 cubic feet per second, making it one of the largest waterfalls by volume in Washington State. The maximum recorded volume, 49,000 cubic feet per second, was measured on May 31, 1894. Shortly after the falls were discovered and the city founded, the falls were harnessed for hydropower and irrigation. http://www.world-waterfalls.com/waterfall.php?num=164
Here's a picture of how the falls look today.
When I was attending law school in Spokane in the early 1970s, some guy decided to go over the falls in a self-built barrel. It was against the law, but somehow word got out that he was attempting it. He went over part of the falls, but then got stuck in a whirlpool. I don't remember his name, but I sort of recall that the police arrived. Not too far upstream in 1974, President Richard Nixon appeared at the opening ceremonies for "Expo '74," a world's fair on the site of the falls. He didn't bring a barrel, but stayed on the shore that day. Surely, the Watergate mess was starting to breathe down his neck.
The following information comes from http://www.cabinetmagazine.org/issues/19/turner.php
Carlisle Graham, a barrel maker from Philadelphia, was the first person to dream up the crazy idea of going over Niagara Falls in a barrel. Here's a picture of Graham next to the barrel he'd built himself for the stunt. It was seven feet tall, and he'd painted it red.
Graham climbed into his barrel several times in 1886 and rode around in the rapids at the bottom of Niagara Falls. He promised to go over the falls at some later date. Then, in 1889, he showed up in a saloon, excited and wet, claiming to have just escaped death by finally going over the falls in his barrel. His claims were shortly exposed as a fabricated hoax.
In 1901, Annie Edson Taylor became the first human being to actually attempt the treacherous trip over Niagara Falls in a barrel. She was a destitute former dance teacher who reasoned that if she died in the attempt she would avoid living as a pauper, but if she survived she would be showered in riches. Surprisingly she survived, injured. But her manager ran off with her barrel and sold it and pocketed the money.
I suggest you read the excellent article at the above link. It details the injuries daredevils suffered going over Niagara Falls in the years since. And here's a fascinating article about Alfred Irvin Faussett, from which the following information comes. It's a good read-- http://www.historylink.org/index.cfm?DisplayPage=output.cfm&file_id=8567
Alfred Irvin Faussett (1879-1948) was a logger and waterfall-jumping daredevil from Monroe, Washington. In the 1920s he built canoes and other craft in which he successfully tumbled down waterfalls in Washington, Oregon, and Idaho. In 1926, he successfully went over the 104-foot Sunset Falls on the Skykomish River (Washington) and lived to tell about it. Encouraged, he then made plans to go over Niagara Falls and Snoqualmie Falls (Washington).
In 1927, Al Faussett attempted to go over the 186-foot Spokane Falls, but had to be rescued after just getting past the first of the two rapids. It was reported that he had sustained a moderate concussion of the brain, numerous contusions of the head and body, and possibly internal injuries. While he "shot" a number of waterfalls in the Northwest, Faussett never did go over Niagara or Snoqualmie Falls. He was denied permission to shoot Snoqualmie and was served a restraining order by Puget Sound Power and Light Company when he approached the rim of the falls. In frustration, he pushed his empty self-built boat into the river and watched it go over the rapids. "Unhappy when out of the limelight, in his 50s Al Faussett sought attention through boxing and as a professional ring man and trainer. . . Thwarted in hopes for Niagara for over 20 years, he was building a boat for that attempt in his house right before he died. Relatives later had to remove part of a wall to get the canoe out."
Al Faussett was 68 when he died in 1948-- the year I was born in Spokane! Hmmmm . . . Maybe somebody will yet build a barrel and successfully shoot Spokane Falls.