Other than height, is there any particular reason to use two smaller culverts side by side instead of one larger? A property I work at occasionally has a double 3' steel culvert and it seems like there are always sticks and debris partially blocking them. Also they are starting to rust out. Based on my calculations, a single 5' should flow as much water as the two 3' and be much less of a stick trap.
Not that I know of. Whoever put in the double pipe probably had it laying around and wanted to use it up. If height is a problem, you should be able to find a steel pipe supplier who can make an oval pipe.
A lot of people ran the double culverts because either the single culvert wasn’t enough for springtime or the 2 smaller culverts were cheaper than one big one. A driveway I did 20 years ago for a guy, upgraded from an 8” to a 12” and I told him that wouldn’t be enough as the 8” got completely washed out. He no listena to my suggestion a so I had to go back the next spring an add another 12”.
Two is almost always worse than 1. They make squash pipes, elliptical and box culverts to avoid using two pipes. To size a pipe, you really need to look at the drainage area going to the pipe. The ground cover has a huge impact on flow rates and how much water actually gets to the pipe.
When the water level gets down to 6" or so, the two pipe arrangement will flow more water faster. Also, there are many instances where you have a situation where you don't want 5' of water held back by the pipe, and you need that much to achieve the same flow as the double 3'.
I avoid double culverts if at all possible, they constantly plug up when debris gets caught in the middle. I've started using the oval or arched culverts in applications where I need a lot of flow but don't have enough height. Concrete box culverts are also a good option, but spendy.
Do they make oval culverts in plastic?
I wish they would stop making plastic culverts period
Why?
I prefer the HDPE culverts. Last forever and their ribbing and connections are much easier to work with. I certainly have never heard of an oval HDPE culvert but have certainly installed a few, when space is limited. Just use the hoe and some good gravel to bed it and collapse it a little, being careful of bedding and compaction.
AFAIK they do not. However, our local place that makes the metal ones offers them in three coating grades: standard galvanized, galvanized + aluminized, and galvanized + aluminized + black tar like coating on the bottom half. The latter are supposed to have a 100yr lifespan. I usually buy the mid-grade ones, they seem to last considerably longer than the standard from what I've seen. All that said, I do use the black plastic double wall culverts where I can, just a lot easier to work with.
You guys that use plastic must never have grass fires.
How does pricing compare between steel and plastic?
Correct.
HDPE pipes are better for alot of reasons as long as its the double wall pipes. The single wall ones aren't worth much. The corrugated metal pipes are ok as long as the conditions aren't abrasive or acidic. I have not see elliptical or squash HDPE pipes Never had a grass fire here. Its usually to stinking wet to worry about those. We typically have to worry more about pump arounds for the amount of water we deal with to make sure we can work in the trenches.
Can’t remember the last time I saw a grass fire. They way they are building around here, won’t hardly be any lawns left, never mind fields.
The guys that use steel must not have road salt.
I can’t count how many galvanized culverts I have changed out at the end of peoples driveways for town ditches. The town claims right of way but are nowhere to be found, when the culvert rust out and homeowners start cutting their tires on the open culverts. The skunks love collapsed culverts.