This post is more of a rant, born of frustration over a situation (all too common) that affects this little forest fragment. When it comes to storm water, out of sight means out of mind. The useless old culvert pipe in the pic above once drained the area of Creason Park’s maintenance barn. The pipe was long ago undercut by the torrent of storm water that gushes from the culvert above it. Among the misfortunes of this forest – being situated on one side below a large area of pavement and parking lots that pour stormwater down its steep slopes with every heavy rain.
This culvert goes under Sheridan Ave. on the southern edge of the forest. It’s a major artery for stormwater as you can see from the deep gully below it. If someone living uphill from you tried to drain their property in such a way onto your land, you’d be outraged. But apparently when stormwater regularly rips through a “natural area”, including a state nature preserve, it’s ok. After all it’s just trees and dirt, nothing important.
Of course there is flooding everywhere lately due to a very intense rain event. The main focus, understandably, is on damage to homes and structures. But the cause is the same – too many impervious surfaces causing high speed runoff and preventing infiltration of water into the soil. Trees and urban forests are often touted as past of the solution; however this little forest can’t soak it up as fast as it pours in.
The pics in this post will document the movement of water that originates from from 2 “point source” locations – culverts that drain good sized areas of pavement in Joe Creason park. It’s an unfortunate fact of topography that the forest slopes down so steeply here, leading to a high velocity surge of stormwater that travels well into the heart of the forest carrying pollutants, invasive plant seeds and eroded soil.
Debris lodging in the drainage has slowed the flow and collected a fresh deposit of soil behind it.
Over time the gullies get deeper, leaving old trees perched with exposed roots.
One of the more damaging aspects of rapid water movement through the forest has been the facilitation of Wintercreeper, Euonymus fortunei, invasion. The seeds of this plant appear to be highly adapted to dispersal by water, and most infestations first began in areas of soil deposition. Additionally, small portions that break off the trailing vines during flood events are carried to new locations.
The mound of soil in the pic above has been deposited at the base of a drainage, where it levels out to the floodplain and water movement slows. This is a prime site for infestations of Wintercreeper to start.
What might appear to be a pretty stream is actually a stormwater channel that moves rapidly over the forest floor, scouring vegetation as it goes. Invasive plant removal in this area has exacerbated the soil damage, another reason restoration planting is so important.
So what can be done, if anything? The place to start would be at the source of the stormwater. Though it’s very unlikely to happen, the construction of retention basins and bioswales at the top of the hill could soak up a lot of runoff. Once it’s moving down the hill, there’s only the hope of locking up more soil by planting species with “grabby” roots – River Oats, Chasmanthium latifolium, and Virginia Wild Rye, Elymus virginicus, are excellent for erosion control. And general replanting of shrubs and trees lost to the Emerald Ash Borer and invasive plant removal is an ongoing process.
Much of this forest is floodplain, so the presence of standing water is to be expected. But the damaging, high velocity movement of stormwater is a newer phenomenon. It’s one more challenge of maintaining this little fragment of forest surrounded by the city.