LBrown59
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How big of a ditch does it take to handle a 15 inch culvert ?
HOW BIGA ?
- Thread starter LBrown59
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Dougryan
Bronze Member
Is this a trick question? 
schmism
Super Member
ummm no,
depends on your culvert type, and how much cover you need over you culvert based on how much weight you want to carry.
you also need to identify the ditch slope, ditch side slopes, and ditch material (as it affects your flow rates)
depends on your culvert type, and how much cover you need over you culvert based on how much weight you want to carry.
you also need to identify the ditch slope, ditch side slopes, and ditch material (as it affects your flow rates)
AndyM
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LBrown59 said:
More than 15 inches.
AndyM
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LBrown59 said:
It gives you seat time, doesn't it?
Thomas
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Morning LB. Where the water enters culvert even w/the bottom of the stream etc.. also add a slight down wards pitch....wide enough to pack fill w/BH or tamp.
RobS
Super Member
It almost seems as though the question is backwards. You might want to ask "How big a culvert to I need for my ditch?". Around here, the county determines culvert needs for all driveways across roadside ditches. Even if yours isn't a roadside ditch, the county might be a good source of expertise.
ovrszd
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This is definitely a loaded question with so many variables that we could discuss it for a week!!! First being, what is your intent???
I would estimate that I've installed 400 culverts in my life, varying in size from 15" to 72". For the 30" and smaller I use double wall plastic. For bigger sizes I use galvanized steel. Double wall Plastic has larger corrugations and will not wash out as bad, plus plastic lasts thru my lifetime. In Missouri galavanized steel has a lifespan of about 12 years depending on location before it rusts out.
For dirt cover, it takes very little if it's installed in a hard packed roadbed. A plastic 15" culvert will survive with 6" of cover with daily traffic. My driveway culvert has about 4" of cover and has been there 25 years.
If you are controlling water without it running over the roadbed, you have to determine acres of drainage, degree of slope of drainage and type of soil cover of drainage area. If it's open fields with considerable slope you better have considerable freeboard above the culvert to catch and hold the runoff until the rain slows and it can catch up. If it's basically flat land with grass cover which will slow down the runoff, less freeboard is needed. Either way I build a catch basin at the input end to give the culvert some tolerance for flash floods.
I avoid putting in a culvert with slope. I just want enough slope that it's a few inches lower at the output end, just enough so water doesn't stand in the culvert. Over the years I discovered that culverts put in with a radical slope from input to output ends have a tendency to "leak" water down the outside of the culvert and eventually wash it out. Especially if using galvanized culvert with small corrugation. That's why I like plastic with larger corrugation.
If you want to significantly increase the flow capacity of a culvert, angle cut the ends, both ends, at 45 degree angle if possible. If the input end of a culvert is straight cut, it cannot fill and run to maximum capacity. If you need to check this, go out when you are getting heavy rain and look at the output end of a culvert with a flooded input end. The output end will be running about 70% full. If you angle cut the input you are increasing the intake capacity which will allow the culvert to run full.
Some DO NOTs. DO NOT use smooth plastic pipe as it will wash out easier if you are installing in a steep drainage area.
DO NOT use single walled, corrugated black plastic pipe like is used for terrace drainage. It has a very small crush limit and if buried shallow in a travelled roadway will eventually collapse.
DO NOT allow weeds, grass and/or brush to grow up around the input end, this reduces the capacity.
DO NOT burn the roadbank with a plastic culvert installed unless you are there to watch it. That black plastic pipe will burn like crazy. I've saw them completely burn out and just leave a hole in the dirt with a pile of melted plastic in the bottom. Really upsets the road crew if it's a county/township road.
I'm sure I've missed some great ideas and maybe someone can add them.
I would estimate that I've installed 400 culverts in my life, varying in size from 15" to 72". For the 30" and smaller I use double wall plastic. For bigger sizes I use galvanized steel. Double wall Plastic has larger corrugations and will not wash out as bad, plus plastic lasts thru my lifetime. In Missouri galavanized steel has a lifespan of about 12 years depending on location before it rusts out.
For dirt cover, it takes very little if it's installed in a hard packed roadbed. A plastic 15" culvert will survive with 6" of cover with daily traffic. My driveway culvert has about 4" of cover and has been there 25 years.
If you are controlling water without it running over the roadbed, you have to determine acres of drainage, degree of slope of drainage and type of soil cover of drainage area. If it's open fields with considerable slope you better have considerable freeboard above the culvert to catch and hold the runoff until the rain slows and it can catch up. If it's basically flat land with grass cover which will slow down the runoff, less freeboard is needed. Either way I build a catch basin at the input end to give the culvert some tolerance for flash floods.
I avoid putting in a culvert with slope. I just want enough slope that it's a few inches lower at the output end, just enough so water doesn't stand in the culvert. Over the years I discovered that culverts put in with a radical slope from input to output ends have a tendency to "leak" water down the outside of the culvert and eventually wash it out. Especially if using galvanized culvert with small corrugation. That's why I like plastic with larger corrugation.
If you want to significantly increase the flow capacity of a culvert, angle cut the ends, both ends, at 45 degree angle if possible. If the input end of a culvert is straight cut, it cannot fill and run to maximum capacity. If you need to check this, go out when you are getting heavy rain and look at the output end of a culvert with a flooded input end. The output end will be running about 70% full. If you angle cut the input you are increasing the intake capacity which will allow the culvert to run full.
Some DO NOTs. DO NOT use smooth plastic pipe as it will wash out easier if you are installing in a steep drainage area.
DO NOT use single walled, corrugated black plastic pipe like is used for terrace drainage. It has a very small crush limit and if buried shallow in a travelled roadway will eventually collapse.
DO NOT allow weeds, grass and/or brush to grow up around the input end, this reduces the capacity.
DO NOT burn the roadbank with a plastic culvert installed unless you are there to watch it. That black plastic pipe will burn like crazy. I've saw them completely burn out and just leave a hole in the dirt with a pile of melted plastic in the bottom. Really upsets the road crew if it's a county/township road.
I'm sure I've missed some great ideas and maybe someone can add them.