Calculate the flow of the stream during your release day event. Approx. 5-7 students can be involved at a time: one recorder, one person to keep time on phone or stopwatch, two people to measure the stream stretch, one to drop the ping pong ball (or water bottle as explained in the video below) at the top of the stretch, two at the end of the stretch to catch the ping pong ball.
Discussion: Ask how students think that humans can impact how a stream responds to precipitation. For example, land use around the stream, such as over-grazing by animals and removal of riparian areas, will increase surface runoff because the natural filter (plants in the riparian zone) are replaced by grass or erosion which can cause a high increase in water and even lead to flooding. Conversely, if humans are using or pumping water from the stream, a decrease in flow can cause higher water temperatures which results in low levels of oxygen which can harm insect or fish populations. Changes in flow are also a natural result of weather patterns.