Why aren't the swales mowed neatly?

Much of the trail is flanked by shallow ditches called swales.  Most of the swales along the trail are filled with vegetation, generally grasses mixed with other plants. The swales function to slow down rainwater and they also act as filters to reduce the sediment and pollutants in the water. 

Sometimes people think that not mowing the swales is a sign of neglect.  But it's done to help the creek stay cleaner.  Remember, much of the water that goes into Vine Creek starts by falling on a roadway, parking lot or other impervious surface. There is a lot to filter out.  So the more vegetation present in the swales, the more filtration they can accomplish. 

The movie at the left shows stormwater coming into a swale from Trevor Lane and Llandrillo Road during a moderate rainstorm; note that the water is cloudy with all the sediments, oils, and other substances that were on the streets. All these things are detrimental to the insects, fish, amphibians and other animals that live in the creek further downstream. The more time that the water can spend in a grassy swale like this, the cleaner it will be when it enters the creek at Bala Cynwyd Park and finally at Barmouth.

At the very end of the video, note how the water at the bottom of the screen is much clearer and slower moving.  That water came down a long swale before joining with the untreated stormwater. 

There is more information about the Vine Creek watershed in other parts of this website.