So they just built a HUGE new ramp for a pedestrian bridge over the interstate. They’ve been working on this for over a year. It has opened up recently.
I have exactly zero construction experience and the within 20 seconds of walking this ramp I stated “There is no l[COLOR=black][FONT=Trebuchet MS]egitimate drainage path.” [/FONT][/COLOR]
So the State (or its contractor) built a concrete, 350-foot long, 10-foot wide, twisted ramp for a pedestrian bridge and it does not have a single drainage path besides flowing all the way down to the end of the ramp.
Imagine my shock and surprise when I noticed the end of the bridge is starting to show some major erosion issues. For example, the once-buried electrical wires that provide power for the ramp’s lighting must cross through the air to span a newly formed erosion gully.
[COLOR=black][FONT=Trebuchet MS]Is there a reason why they did this? Isn’t proper drainage of large impermeable objects construction 101? What am I missing?[/FONT][/COLOR]
Sadly, accommodation for bicycles and pedestrians all too often, in all too many places seems to be considered with disdain, and that is when it is considered at all. Sheer WAG but I am guessing they use these things as a starter projects for the new kids in the engineering office.
A MUP I use regularly has similar issues. There is no drainage for the bridge itself where it crosses the freeway, but the way it was set up, and with the prevailing winds, it poured water onto one of the traffic lanes. So they added angle iron “curbs” to force the water to run off the ends instead. One approach has a low spot that stands with 4" of water for about a week after each rain, and the other end has about a 20% grade.
You’ve obviously not worked with a large department of engineers.
Think of them as almost as clever and creative as computer majors, be we can recode, recompile and reload our “oops” moments. That’s a bit harder with concrete. Or someone in consruction embellished the design withut asking the engineers.
My guess is someone took an existing design and added curbs, or decided it would be faster and easier to pour concrete railing than install a more flimsy metal railing.
We had some engineer design an anchor pad for our long distance wireless connection antenna. This had to go on the top of a very tall bulding, so it was easier to pour it with hooks built in and fly it up than haul all the concrete materials up a ladder. The helicopter barely lifted what should have been an easy load - we found somewhere along the line, someone had ignored my boss’s design, and forgot about the helicopter, the whole point of pouring it on ground level. What should have been a 4-inch pad was 8 inches and almost at the helo’s weight limit.
Well, yeah, but wouldn’t adding a gutter with drains at set distances, all eventually feeding into a storm sewer (or at least some sort of drainage field, directed away from the structural components) be almost a given?
The question is, was it deliberate? they considered drainage and said “nah, forget it.” (Unlikely).
Did they just think “not a problem!”? When it’s raining that bad, nobody will be walking on the bridge anyway.
Was it an oversight, slipped their mind? “Oh shoot, forgot about drainage!”
Was it a design modification with unintended consequences? Add curbs but forget to leave occasional drains?
Unaware that the power of the resulting flood would cause as much damage as it did?
Faliure to follow through with the rest? Is the gully at the walkway exit to the bridge where there was supposed to be concrete sidewalk, or off to the side where they assumed the grass was sufficient to stem the tide?
All you can do is ask the designers and hope for a straight answer…
closed drainage on the bridge could get blocked and cause deterioration of the structure and high maintenance. open gutters inside the bridge would be hazards to walker and riders on the bridge. outside open gutters or drains above the road would be a hazard to drivers.
maybe letting the surface handle the water is best, though with ample drainage at the ends would be needed.
My guess is this. The engineer decided since no pedestrian would ever be out when it’s raining, the water running across the structure wouldn’t be a problem, and there’s a good path for the water to drain off the structure so the structure’s not at risk.
From then on, in the words of Tom Lehrer channeling Wernher Von Braun, “It’s not my department” where the water comes down.
I mean, they hired him to design the structure, not make a drainage plan for the entire site, right?