Swale
We had a real downpour yesterday.
Every time we get a good rainstorm like that, we get a little water feature in our front yard. Storm water runoff on my street isn’t handled by the standard suburban curb-and-gutter arrangement. Instead, we have swales. These are shallow grassy ditches on either side of the street. These ditches run down the length of the street, delivering it to a large storm drain at the end of the block. A nice solid deluge will turn my swale into a little river.
Swales were undoubtedly the cheapest way to build runoff controls back in the day. They are also incredibly simple to maintain. Each property owner treats the swale as part of the front lawn, and collectively the entire block keeps the swale mown.
Surprisingly, swales aren’t just cheap, they are more environmentally sound than standard curb-and-gutter. Around here, the entire name of the game for storm water control is to slow it down and keep it as silt-free as possible. Ideally, pond it up so that it sinks in and doesn’t run off at all. This reduces both the nutrient load and the sediment load of water flowing into the Chesapeake Bay. In particular, slowing the runoff helps prevent local streams from scouring out their beds (and depositing that material downstream) during heavy downpours.
Swales do a better job of all of that than impervious concrete curb-and-gutter. The grassy sides of the swale both absorb water and slow it down. Better, each little driveway culvert bottlenecks the flow of water, forcing it to back up in the swale. With enough rain this transforms the ditch into a string of little linear ponds.
I calculate that during a hard rain, my hundred feet of front-yard swale temporarily holds about 250 cubic feet of water. Rounding up, that’s about 2000 gallons. Or more than three times the capacity of all of my rain barrels combined (Post G21-043). That may sound like a lot, but in terms of runoff, it’s not. That 250 cubic feet amounts to about a quarter-inch of rain in my yard. So that temporary storage doesn’t make a huge difference. But it’s a lot better than nothing, which is what you get with curb-and-gutter.
Not so swale.
Which is why I was dismayed to look at my swale during this last rainstorm. I expected to see what I normally see, which is a curb-side ditch filled with clear rainwater. Instead, it was filled with water that was carrying a lot of mud along with it.
We have a big commercial construction project going on at the end of the street, so I decided to take a stroll and see whether this was coming off that construction site.
It was most definitely coming from somewhere upstream of my yard. Below, like the confluence of the Mississippi and Missouri rivers, the clear runoff from my lot was met by totally silt-laden runoff from further up the block.
And that silt-laden water meant that the swale was oh-so-efficiently carrying all that silt down to the storm sewer at the end of the block. Like so, looking downhill.
Actually, I had no problem figuring out where the muddy water was entering the swale. My next-door-neighbor has some sort of sump pump arrangement to solve a drainage problem in his back yard. That was more-or-less producing a mud fountain.
So, case closed, right? The mud in the water had nothing to do with the commercial construction just around the corner in the photo above. The mud was coming out of my next door neighbor’s back yard. Literally being pumped into the swale.
But this seemed odd as a) he’s a pretty reasonable guy, b) he has a very nicely manicured back yard, and c) he put that new drainage in some time back.
It was then that I recalled the semi-permanent state of construction at the house that’s just uphill of his.
Source: Google Street View.
And sure enough. Below, there’s another view of our decorative neighborhood porta-pottie, in the rain, with a telltale trace of mud in the swale water.
Walking back, I finally spotted the main issue. I guess they’ve moved on to the next phase of their permanent home addition project. So a chunk of their back yard appears to have been stripped down to the bare soil. That seems like a new development. That bare soil then runs off as sheet erosion and gets picked up by the next guy’s pump-and-drainage system. And that’s what’s filling the swale with silty water.
For new construction, my town and county rigorously enforce rules about putting up barriers to keep muddy runoff out of the storm sewers. That’s the first thing that goes up on a new-home construction site, and the last thing to come down.
But here? I don’t know if this guy just didn’t bother with the permits, whether those barriers aren’t required on additions/remodels, or whether it’s just not enforced.
And, unlike my immediate next-door-neighbor, who is both reasonable and a nice guy, my extremely limited interaction with this neighbor immediately set off looney-tunes alarm bells. I vaguely recall my wife getting some un-prompted statement that Obama was going to fry in hell for all eternity due to his being a Moslem and something-something-something-there-goes-the-neighborhood/country. I’ve tried to repress it, but I clearly recall that it pegged the needle on the crazy-meter.
So I don’t think a little pep talk about the Chesapeake Bay is going to do me a lot of good here. I’m not quite sure what to do about it, if anything. All I know for sure is that it has taken the joy out of watching my swale after a heavy rain.
