DIY Bridge

[garymartin63965]

I have a fry creek that runs across my driveway. After heavy rains the water runs through & will get up to 3-4’ deep and might run 60-70’ wide. I want to hire a dozer to come and clean the creek bed up (push gravel to the banks and straighten the run a bit. After that I would like to install two 36” HDPE culvert pipes. The plan is to trench out a footing on the upstream side 24” deep under the culverts, pour concrete in the trench, pour 12” of concrete on each side of the culverts as well as between them. Use 3/4” minus to fill any voids in the driveway and ‘level’ it out. After that I’ll pour a 6” concrete slab on top with #3 rebar 12”OC. The upstream side would be concrete (to keep the water from getting under the bridge) & footings would be on each end of the slab. This is the only access I have to my house & property and it would need to be able to stand up to occasional heavy traffic. ( concrete trucks, logging trucks, triple axle trailers & such) Will in work? Am I going overboard, do I need more ‘fill’ over the culvert. TIA for your help.I will try and post an example of the bridge I thinking of.
garymartin63965

 

[2manyrocks]

Over time, it seems to me that culverts concentrate the flow of water when there's a lot of it. This can erode the stream bed downstream and/or erode the banks downstream.

It also seems like it is too easy to undersize culverts, either by underestimating the volume of seasonal water flows or by getting surprised by those occasional gully washing rainfalls.

I have no skill at estimating water volume and culvert sizes myself.

The last one of these that got built nearby seemed to have intentionally been built with a dip in the middle to allow any excess water to run over the top of it.

 

[4570Man]

I’m not a storm water engineer but your described flow of 4ft deep or even 1 ft deep 60 foot wide is drastically more than 2 36” culverts could handle. For a volume of water that large I think an actual bridge would be better. Assuming the 70 foot wide is a typo and you meant 70 inches that’s still too much water to fit through those culverts.

 

[redman135]

I agree with 4570man about the pipes being undersized.
The MAIN point I want to make is your crossing has NO protection on the bottom side for when the water goes over the top. Water will dig out the botttom side, and the erosian will work it's way upstream.

 

[Streetcar]

You are making a dam in the creek. It will need to be anchored in creek and armored on both upstream and downstream sides

 

[Rockbadchild]

It is hard to estimate without knowing all the data necessary to do the calculation... in order to calculate you need to know the 100 years storm precipitation for your area, the stream basin area, the upstream volume and the flow of that volume... without these it is impossible to calculate... so if you don't know and won't find out then overkill it, perhaps have three pipe and have the road build as demonstrated below so if it's overflow it will flow on each side of the culvert on the road.

other than that, my opinion is most of the concrete work seems over kill.. thrench out 12 inch below the culvert grade and back fill with A gravel, compact, back fill the rest with A gravel and compact every foot... if you want a up stream and down stream concrete bulkhead fine but the rest is over kill.

 

[Spike56]

I have a fry creek that runs across my driveway. After heavy rains the water runs through & will get up to 3-4’ deep and might run 60-70’ wide. I want to hire a dozer to come and clean the creek bed up (push gravel to the banks and straighten the run a bit. After that I would like to install two 36” HDPE culvert pipes. The plan is to trench out a footing on the upstream side 24” deep under the culverts, pour concrete in the trench, pour 12” of concrete on each side of the culverts as well as between them. Use 3/4” minus to fill any voids in the driveway and ‘level’ it out. After that I’ll pour a 6” concrete slab on top with #3 rebar 12”OC. The upstream side would be concrete (to keep the water from getting under the bridge) & footings would be on each end of the slab. This is the only access I have to my house & property and it would need to be able to stand up to occasional heavy traffic. ( concrete trucks, logging trucks, triple axle trailers & such) Will in work? Am I going overboard, do I need more ‘fill’ over the culvert. TIA for your help.I will try and post an example of the bridge I thinking of.
garymartin63965

I would strongly recommend that you contact the National Resources Conservation Service (NRCS) or Local USDA office. I am in process working with them to engineer a similar structure. This will be an expensive endeavor and you will want to get it right. At least here (Texas), there is no charge for this. They can offer a detailed plan for construction and are able to view not only your soil types, but maps that can estimate the water flow amounts and speeds (drainage) you will encounter.
So, some may tell you how-to and I respect their opinions, but one mistake can lead to total destruction. You can compromise the plan they offer of course. But it is definitely a good way to start. My 2 cents.

 

[duffer]

I had a similar problem to yours. Not quite as big, but similar. Ended up doing it 3 times before I got it right.
Totally agree with Spike56 to get your county storm water dept out there to eyeball it, and see what they say.
If the water gets to 4' deep, in 2"-3" rainstorms, then a bridge may indeed, be a better and cheaper (long term) solution.

 

[ArlyA]

If you put in to large of culverts, you wasted $500*... If they are too small, them you buy bigger ones and start over and see $5000* washed away. Go big the 1st time.

* not real numbers.

 

[deezler]

Is a bridge not an option? Pretty easy to engineer and build a 10-12' span that can hold concrete trucks and heavier. The cross sectional area for water flow under such a bridge would be immensely more than your listed culverts.