by David Murphy
Creek and stream flooding can occur relatively quickly after a steady rain event begins, although it's most common after one or two recent storms have already crossed a given region.
How does it happen? Steady rain initially soaks into the ground through a myriad of tiny cracks and crevices in the earth. But once those openings fill up with water, the remaining rainfall has nowhere to go but downhill, over the top of the land. Eventually, this run-off finds its way into creeks and streams which can not hold the extra water. Water levels rise until the waterways overflow their banks. In our area, this type of flooding is common, especially in Southeastern Pennsylvania where the hilly terrain easily channels water into streams.
Creek and stream flooding can be deceptive as water levels do not always rise at the same rates, nor at the same locations from storm to storm. The intensity and exact location of flooding often depends on where the heaviest rainfall is occurring and that can be difficult to forecast. Flooding may also grow worse along certain portions of waterways from year-to-year, depending on how much development is occurring upstream. Additional roads, parking lots and buildings generate additional run-off---and a heightened chance of flooding downstream.
In general, people who live near creeks and streams learn to monitor broadcast media and online flood gauges during large rain events, to see whether their local waterway is rising to dangerous levels. A link to flood gauges for our area are available on 6abc.com and are usually moved to the front page of the website when flooding is occurring.
Flooding along creeks and streams is not only destructive, it can be dangerous. Swollen waterways contain deceptive currents. Even a small depth of rushing water is capable of knocking pedestrians off their feet or sweeping an automobile into deeper water.