Today I was asked by a junior engineer, (EIT) if we had any details of a level spreader design. I told them, “Sure, we’ve got a typical detail, but I wouldn’t use it”. Of course an answer like that tends to raise more questions, (intentionally in this case!), so I dug out some of my notes that I’ve collected, and thought it might be useful to the world, if I published them here, I’m going to write them up in metric and modify them from my experience, so it’ll take a couple of days, but anyway, here’s the story.
Generally, engineers look for the lowest cost solution to themselves, like a typical detail or a cookie-cutter design template. Not bad in many situations, but you’ve got to know when you can apply the simple rules, and when you’re likely to need more detail. So what I’m going to say will probably annoy a lot of those type of engineers…
The design of a level spreader is a direct product of the downstream filter strip design requirements.
“Hang on, filter strip? You never mentioned a filter strip!”
(Yes this is a real conversation)
“Yeah mate, you’ve got to do something with the water after the level spreader, you know, run it through some vegetation or something.”
“Oh, like a treatment train or something”
“Exactly, now let me explain…”
First of all I explained that a level spreader isn’t the best solution for just wanting to discharge runoff with no regard for stormwater quality. It is however a great solution, site dependant of course, for discharging to a section of land dedicated for surface runoff filtration, i.e through grasses. IT is an environmentally friendly feature that falls under the class of Water Sensitive Urban Design.
So how can we best apply level spreaders in subdivision and road design? Glad you asked, that will be the subject of my next technical post – Stay tuned.
Image used courtesy of NCSU-BAE.