It would seem to me that a decimal, or perhaps two has been misplaced as to the power production. To generate just 1 KW at 18" of head will require roughly 1 horsepower which is 33,000 ft-lbs/minute.
That equals about 4,000 gallons/min.....This stream looks like 200/gpm at best. Certainly not 4,000.

HH McDonald PE, BSME