Of course, the main influence on streamflow is precipitation runoff in the watershed. Rainfall causes rivers to rise, and a river can even rise if it only rains very far up in the watershed-remember that water that falls in a watershed will eventually drain by the outflow point.
One US gallon of water weighs 133.526464 ounces. The calculations for that answer are below: 1 gallon = 8.345404 pounds 1 pound = 16 ounces 8.345404 X 16 = 133.526464.
Here's a way to remember the weight of 1 gallon of water. A cup of water is 8 fluid ounces or 1/2 pound. So 2 cups in a pint and 2 pints in a quart and 4 quarts in a gallon so a gallon is 128 fluid ounces or 8 pounds. Well I just looked it up and 8.35 pounds is correct. I guess a fluid ounce is not an ounce of water.