Help asmo build road/bridge -- want ideas and thoughts

[asmo]

As a couple of you know I bought 10 acres recently and plan on moving out there when we finally build a house. However, the precursor to building the house is improving the road/bridge that is our only access point to the property. There is a 25' deep ravine that separates the entrance of the property from the major acreage where we are building the house. The previous land owner did a super shitty job of dumping some dirt in the ravine and making a crappy little bridge/road. While it technically works - its not what I want permanently. The biggest issue with it is that it actually slopes down 15' in the middle from the entrance to the property to and rises back up 15 feet as you come onto the acreage.

Pictures:
57537575385753957540

and for the more engineering minded - a real topo that I had commissioned (parts removed to protect the guilty):

57541


There is a CMP that connects the two sides of the road to allow for some type of water flow between the two sides (its a dry creek - but technically it could have water in it). The weight of all that dirt has the CMP bowed in and the whole bridge is eroding away.

So I want to fix it. Make it better and make it permanent. Put a real road (asphalt, crushed based, whatever) through this. I am thinking to do this right it will need to be really engineered and have a major construction company do the whole deal. But I really don't know. Big problem is - I don't even know where to start. I have some good ideas on "how" to do it *(box culvert type setup, or major concrete pylons with concrete walls between them, etc), but I don't have the tools/heavy machinery to make it happen.

My ideal is to have the whole driveway/entry level'd off at around 5000' (curb elevation) to the same elevation on the property. Thinking 15' to 20' wide but really only need it wide enough to allow for EMS to get to the site and pass code. Total length is ~250', of which only about 60' is actually over the ravine.

So I am coming to the peanut gallery to solicit ideas, ask for help, and get some thoughts. Any of you here do this kind of work - or know someone that does? Any thoughts on how you would go about it if you were going to do it yourself? Any of you ever done something like this before - or watched someone else do it.

[kwando]

Never done it but I'll help... Subscribed

[Monky]

I'd be interested to see how this ends up... I'm no engineer but I have ideas. All of which involve heavy machinery though just because well... Slavery is illegal


Sent by a free-range electronic weasel, with no sense of personal space.

[DFBrews]

Bigger culvert maybe plural in the ravine to take some weight off of it with road base to fill it the rest of the way in. Get some bigger rock like ft in diameter or so on the sides to keep rain water from eroding it away.

[Great-Kazoo]

What ever you do, make sure NOTHING is done that removes trees, water flow etc. Or prepare to face the wrath of the EPA. If some nosey .gov entity wanders through the area.

[CO Hugh]

What ever you do, make sure NOTHING is done that removes trees, water flow etc. Or prepare to face the wrath of the EPA. If some nosey .gov entity wanders through the area.

Yikes, isn't that the 404 permit?

Dynamite!!!!

[BPTactical]

Yikes, isn't that the 404 permit?

Dynamite!!!!

If it is considered a "permanent" waterway then I belive a 404 would be required, not sure on a temporary/ occasional drainage.
Get rid of the CMP(corrogated metal pipe) if you can, they eventually will rot out. A CBC (concrete box culvert) will last forever and be less likely to accumulate debris. That CMP is way too small for that deep of drainage, I would imagine given the depth of the wash it has the capability of draining a pretty large area. An engineering report would be wise, if not required.
Check into recycled concrete instead of roto millings, last I knew it was about half the price of millings.
You have already gotten a topo of the area, now figure your length x width of your proposed drive and the elevation changes.
Over a 5k' run, that is a whole lot of tonnage to move.
Ain't gonna be cheap.
I will come run a loader, backhoe or blade for you.

[rondog]

Looks 'spensive.....

[68Charger]

OK, you've cropped the topo to "protect the guilty"... But what is REALLY upstream is critical.

Decide what percentage of wash across the road is acceptable... (Or what 'year' flood).
Because unless you're willing to put an 18' culvert down there and bring the level to 4995-5000' ASL, it will eventually cross that road... Been there, done that.

That being said, there are lots of things you can do to mitigate water flow across the road, as rare as it will be...
Make the lowest wide, flat and level... Think 30+ feet wide, dead flat with real heavy boulders on the downhill side.
Concentrated water flow destroys, if you give a small area for the water to flow through, it will cut through just about anything.

Don't worry about what is on the uphill side, that water will be slow, except right near the culvert and across the road.
The downhill side will be eroded FAST in the first major storm if it's not reinforced, flat, level, and WIDE. the wider it is flat, the slower the water.

I lost 4'-5' of road when a major storm hit because an 18" culvert couldn't keep up (not even chose), mitigation is to refill with 3-4' boulders, level and flatten crossing, and plan for when it will be under water.

If you want 100% access, it will get very expensive... I settle for 99+%

[bkincaid]

First, I'd check with the jurisdiction where the property was subdivided. Depending on when that was done, they may have a drainage report on file that you could look at or maybe even get a copy, this would save a bunch of work and cost for you. Also look to see if any of the neighbors have the same situation present. If so, chat with them and see what they have. Is there any evidence/first hand knowledge of high flow events in the area?

Assuming no drainage report available, I'd look into getting an engineer to perform the drainage calcs for the different moisture events (10, 20, 100 year or whatever) so I'd know exactly what I'm up against, flow wise. Then I'd make the needed/wanted treatment decision based on those numbers as compared to my level of comfort regarding access to my home.

A CMP can last many years, especially in dry wash flow events, but, soil and water ph as well as abrasive contents of flow all have a tremendous effect on life expectancy as does proper installation techniques and materials. There are many millions under the roads in this country. I suspect that existing culvert has no where near maximum cover depth, even assuming thinnest culvert material. Here's a link to some CMP specs and such: http://www.conteches.com/products/pipe/corrugated-metal-cmp/hel-cor-pipe.aspx#176792-technical-info , take a gander and see what's possible.

If the flow calc numbers and comfort level work for the existing size culvert, as well as previously stated soil and water ph levels and abrasive level of flow, let it ride. If the CMP ever needs replacing, determine what size HDPE culvert you can insert into the CMP (slip-lining), insert and fill the space between the two with grout or such. Smooth bore HDPE of equivalent size will carry a much greater flow capacity, hence sliplining with a smaller size while retaining same/similar flow capacity. Add material as necessary both upstream and downstream to prevent backpooling conditions and rip-rap downstream to help minimize incision/erosion activities.

If flow calcs show the existing CMP size to be inadequate to handle the flow of the given storm event versus my comfort level, I'd look into a CBC with cut-off walls and wings and engineered channel design.