For you grading guru's which would you go with for general culverts? The Black vs. gray slickwall culverts are what I'm referring to. I see the gray is somewhat less expensive. Thanks in advance.

Pretty easy to Google the properties of each and compare.

We use the black slick wall HDPE exclusively.

I had 2 new ones put in at one of my propertys probably 15 years ago. county had a deal they put them in if you bought them from the county price included a load of gravel. was about what materials would have cost so I jumped on it. I wanter a larger( tired of unblocking it) in diameter and length ( wanted 2 cars wide wife driving) on the main entrance and added a 2nd drive as well for access to the back of property.

choice was black plastic and galvanized. County said both had pros and cons I went with one of each as an experiment. can't tell a difference yet.

A side note about culverts, installing aprons on both ends of a culvert will increase culvert flow capacity by 30 %

The HDPE (black) culverts are very easy to catch fire and will burn completely out in a matter of a few minutes. If we have a wildfire or sometimes even a control burn where we have the HDPE pipes we end up having to replace culverts. We have started using HDPP (grey), they are supposed to be more fire resistant, but to my knowledge we haven’t had any fires where we have installed them yet so don’t really know if they are any better.

Fire is why most here have gone back to steel or cement.

MAin reason I'm asking is since Helene, our 100' culvert ( 5 sticks) over flows only during hard rains. I believe there is a rock or stick catching silt somewhere in the midst. I thought about trying the tire and cable trick, but a 100' feet is a long way for a lot to happen. Originally it was 2 metal corrugated 24". The neighbors added 3 more sticks over the years to fill in the ditch. I bought an excavator after helene and thought I would go ahead and replace them. FEMA and the county both said they MAY be able to help but may be a couple of years. I thought I may go ahead and get 5 sticks of the HDPP. There local for $4-450 a stalk. The black seems more flexible, but the gray seems less expensive, by a good bit. Thanks for the advice.

The corrugated smooth wall is nice for if you ever have to dig it back up or reset it
Hard to do with galvanized without it bending.

Ol dad

All sections are corrugated metal. So I look forward to replacing them with the smooth wall. Hopefully won't have to worry the rest of my life. I have been told, smooth wall 24" moves water better than corrugated.

Yes smooth wall will move more water than corrugated, like others said if fire is an issue go galvanized. A squashed galvanized will take more water than a round. Cover over pipe and weight of vehicles is a consideration, if little cover go with squashed galvanized. Either way bed the pipe properly and it will take more weight.