Storm drains / inlets / catch basins / etc.

[Mr. Matté]

One thing that I used to notice a lot when I used to go on trips down south versus what's around NJ is that the storm drains down there tend to be more of just an opening in the curb with the bulk of the structure behind the curb and under grass whereas around here the structure is contained within the road and consists of a grate and possibly a metal curb piece. Now that I'm sort of in the business of designing such structures, I've wondered what the reasons are behind the various DOTs' choice to typically pick one over the other (or both). Does anyone have any insight into their own DOT's decision?

I also kind of want to make this a general storm drain megathread, so another point I want to make is to comment about my state's insistence on using one specific type of grate. They are typically manufactured by Campbell Foundry, based out of Harrison, NJ, with the current typical design being six rows of eight openings, though there are still way too many instances of the "stream flow" grate that eats up bicycle tires. Other manufacturers (such as East Jordan Iron Works in Michigan and US Foundry in Florida(?)) make similar grates with the same dimensions of the Campbell so we can approve their use when the contractor submits it but I wonder if there's any other states with a "quasi-monopoly" on such features.

Final comment on my initial post is just an interesting video if you've never seen it before: In Minneapolis, after a large storm event in 1999, the water in the sewer went through some funky hydrodynamics and led to this sight along I-35W:
https://www.youtube.com/watch?v=DcnH3pZJQrw

[GCrites]

This is a massively important part of highway engineering that even roadgeeks don't think about much.

[Jardine]

JFC !!

It was like Krakatoa !!!!

[DaBigE]

I don't have the slightest clue on the history of the decision-making, but it seems as though 99% of the inlet and manhole structures spec'd and installed around Wisconsin come from Neenah Foundry.

[Pete from Boston]

I don't have the slightest clue on the history of the decision-making, but it seems as though 99% of the inlet and manhole structures spec'd and installed around Wisconsin come from Neenah Foundry.

Quite a lot of them in the Northeast have come from there as well.  However, India has taken a lot of that business in recent years.

What impresses me around here is the longevity of a lot of the castings in the road. It is quite common, for example, to see manhole covers here bearing the initials of the Boston Elevated Railway, which has not existed since the 40s, or local sanitary or drainage systems with years stamped on them from the 1890s and before.

[triplemultiplex]

Final comment on my initial post is just an interesting video if you've never seen it before: In Minneapolis, after a large storm event in 1999, the water in the sewer went through some funky hydrodynamics and led to this sight along I-35W:

That happens when you have a surge of water from multiple pipes converging on a section that is too narrow to handle all the water all at once.  Especially when the grade is steep, the pressure of all that water will cause the flow to back up rapidly and shoot out of manhole covers.  In cities with combined sewers, this will also happen in people's homes if they don't have one-way valves on drains in basements.  Imagine a fountain of shitwater bellowing from a toilet or floor drain.  Not a pretty sight.

It may sound like a design flaw and if it happens frequently, then it is.  But we can only design pipes to handle so much water over so much time without it becoming cost prohibitive.  Most systems are designed with a 100 year recurrence interval event in mind.  That's the storm you have a 1 percent chance of getting every year.  If something larger hits, it will overtax those 100-year systems.

When I lived in Milwaukee in 2010, we got one of those rare storms with rainfall rates way in excess of what the sewer system could handle and there were many instances of sewer fountains across the city.

I retained a lot of information about flowing water from college.  I had a few classes on the subject and I can probably still ballpark how much volume a storm water detention pond needs to hold or how large a culvert pipe should be to avoid problems.  And don't get me started about how flowing water moves sediment around or the infiltration capacity of different soil types.

[noelbotevera]

Rural roads could use this too. I actually live in a rural neighborhood about 2 miles south of Chambersburg, and we used to take US 11 to Loop Road to Tallow Hill Road to PA 995. All three do not have storm drains or anything to drain water, so on Loop Road one night, due to the lack of anything to drain the water, the road got overflowed because of a creek block upstream (it wasn't raining).

[jeffandnicole]

One thing that I used to notice a lot when I used to go on trips down south versus what's around NJ is that the storm drains down there tend to be more of just an opening in the curb with the bulk of the structure behind the curb and under grass whereas around here the structure is contained within the road and consists of a grate and possibly a metal curb piece. Now that I'm sort of in the business of designing such structures, I've wondered what the reasons are behind the various DOTs' choice to typically pick one over the other (or both). Does anyone have any insight into their own DOT's decision?

Just like most other aspects of road/highway design (bridges, traffic lights, etc), drainage inlet designs and productss tend to be what the state prefers to use.  There can be other influences within the state, such as NJ's DEP (Dept. of Environmental Protection).  There's a whole host of calculations that go into water flows and such, and those drainage inlets and underground pipes have to be configured to allow such a flow.

In most road paving projects, NJ is switching to bicycle-safe drain covers, specifically to deal with those bike-tire eating covers from by-gone eras of road building.

[2Co5_14]

The Urban Drainage Design Manual (Hydraulic Engineering Circular #22) published by the Federal Highway Admin. is one of the main guides that many states use (including my state-Georgia) to design storm drain systems.  States also tend to have their own guides, as well as specific design standards for the types of drainage structures that are most prevalent in their state.

https://www.fhwa.dot.gov/engineering/hydraulics/pubs/10009/10009.pdf

The following is an excerpt from the guide that explains the difference between the major types of inlets:

4.4.1 Inlet Types

Storm drain inlets are used to collect runoff and discharge it to an underground storm drainage system. Inlets are typically located in gutter sections, paved medians, and roadside and median ditches. Inlets used for the drainage of highway surfaces can be divided into the following four classes:

1. Grate inlets
2. Curb-opening inlets
3. Slotted inlets
4. Combination inlets

Grate inlets consist of an opening in the gutter or ditch covered by a grate. Curb-opening inlets are vertical openings in the curb covered by a top slab. Slotted inlets consist of a pipe cut along the longitudinal axis with bars perpendicular to the opening to maintain the slotted opening. Combination inlets consist of both a curb-opening inlet and a grate inlet placed in a side-by-side configuration, but the curb opening may be located in part upstream of the grate. Figure 4-4 illustrates each class of inlets. Slotted drains may also be used with grates and each type of inlet may be installed with or without a depression of the gutter.

4.4.2 Characteristics and Uses of Inlets

Grate inlets, as a class, perform satisfactorily over a wide range of gutter grades. Grate inlets generally lose capacity with increase in grade, but to a lesser degree than curb opening inlets. The principal advantage of grate inlets is that they are installed along the roadway where the water is flowing. Their principal disadvantage is that they may be clogged by floating trash or debris. For safety reasons, preference should be given to grate inlets where out-of-control vehicles might be involved. Additionally, where bicycle traffic occurs, grates should be bicycle safe.

Curb-opening inlets are most effective on flatter slopes, in sags, and with flows which typically carry significant amounts of floating debris. The interception capacity of curb-opening inlets decreases as the gutter grade steepens. Consequently, the use of curb-opening inlets is recommended in sags and on grades less than 3%. Of course, they are bicycle safe as well.

Combination inlets provide the advantages of both curb opening and grate inlets. This combination results in a high capacity inlet which offers the advantages of both grate and curb-opening inlets. When the curb opening precedes the grate in a "Sweeper" configuration, the curb-opening inlet acts as a trash interceptor during the initial phases of a storm. Used in a sag configuration, the sweeper inlet can have a curb opening on both sides of the grate.

Slotted drain inlets can be used in areas where it is desirable to intercept sheet flow before it crosses onto a section of roadway. Their principal advantage is their ability to intercept flow over a wide section. However, slotted inlets are very susceptible to clogging from sediments and debris, and are not recommended for use in environments where significant sediment or debris loads may be present. Slotted inlets on a longitudinal grade do have the same hydraulic capacity as curb openings when debris is not a factor.