Well - Hurricane Irene certainly produced lots of stormwater for us to observe! A quick look at the USGS gage at Graterford illustrates how quickly Irene poured through the valley and the amount of water that followed with Hurricane Lee. Many felt like we had been hit with twin tsunamis!
Given the amount of water passing through the watershed and the rate at which the Perkiomen rose, we were happy to learn that there were few local injuries resulting from the flooding. One of the primary reasons we did not have more damage was the large areas of preserved and undeveloped floodplains that exist throughout the watershed! It is great that we are talking about rain gardens and rain gardens will do their part to help reduce flood waters but maintaining undeveloped and naturally vegetated floodplains for all creeks, large or small, is a critical action that communities can take to protect themselves against flooding. Levees, dams and floodwalls may protect limited areas but they do not reduce flood volumes and only serve to push floodwater elsewhere. Floodplains on the other hand, allow flood waters to spread out, slow down and begin soaking onto the ground.
Irene came blowing through the Perkiomen Valley late on Saturday, August 27. By Sunday morning, the PWC headquarters in Schwenksville had become an island! We were surrounded by a brown, raging Perkiomen Creek that infiltrated our building as well as the brand new rain garden. Records indicate that our stone bank barn was probably in place as early as the mid 1800's and was part of larger operations associated with the Pennypacker Mills conplex and the mill that once stood in Red Fox Park. Because it was originally a barn, flooding was probably not considered too much of a problem. (The photo below was taken from the middle of the Rt 73 bridge over the Perkiomen at Schwenksville, looking toward Skippack. )
Well, times have changed and so has the expectation of high water conditions associated with our changing climate. A Union of Concerned Scientists Report for Pennsylvania (http://www.ucsusa.org/global_warming/science_and_impacts/impacts/climate-change-pa.html) suggests that we can expect more storms like Irene in the coming years. These larger, more dramatic storms will interrupt longer periods of drought-like conditions and extremely high temperatures. Sounds an awfully lot like most of 2011 so far!
The one bit of good news for the PWC was that our brand new rain garden was not damaged. The photo below was taken Monday morning, August 29, after much of the floodwater had receded. We do not think the rain garden was totally under water but we could tell that lots of water had passed through the area or had swirled around close to the garden during the storm. But it had absorbed a great deal, the plants were all still in place and there was no standing water by Monday. Pretty amazing!
The PWC is still catching up on our regular work as we clean-up and plan for repairs at our headquarters so we hope to get back to the blog with more details about planning your rain garden project before long. Please check back soon for the details.
In the meantime, contact your local municipal offices to learn about your local floodplain regulations. Municipalities should have floodplain maps on hand and should be able to tell you about the ordinances controlling what can be constructed in a designated floodplain. Development within the floodplain is controlled at the municipal level so it is up to all of us to make sure our elected officials take precautions to keep floodplains clear of structures and naturally vegetated. The two photos below are of the large floodplain at the Graterford bridge in Perkiomen Township. The Creek is actually behind the photographer! Imagine if condos or a shopping center had been constructed in that meadow.
Instead of more flood damage, this floodplain allowed large volumes of water to spread out and slow down, possibly saving structures and people downstream. We will need more open spaces like these, in addition to more rain gardens and bioswales, to accomodate the changing conditions coming our way.
We will be back soon with details about planning your rain garden - stay dry!