Detecting buried/missing road culverts

[salmonriverhotrock]

Last year, one of the Lead Workers on another highway section in our area, asked me if I thought I could metal detect and find a culvert for him. I told him I had never done anything like before but thought it possible. We had other work going on but one morning I ran up to his section and met with him at a location he thought should have a culvert. With me was my Pioneer 505 and the Garrett ADS Ground Hog. There was not much time we could spend on this so I grabbed the Garrett with a 10 inch coil and my headphones. Got it ground balanced in the ALL METAL for about 2 inches above the pavement and took to listening to sounds but can not recall how much Gain or Sensitivity I had it set to. This area is also mineralized and full of hot and occasional cold rocks. I finally picked up a sound that I felt more inclined to stick with but was not exactly knocking the door down either. It ran me from the dirt in the ditch across the fog line and across the yellow line and then was gone. 2 or 3 times, I re-detected this and came up with the same location and ended just past the yellow line. We walked to the river bank and searched for the end of the pipe but no visual or could I pick up anything with the machine. What I noticed though was a section of culvert was laying in the river about 30 yards down and it would have been about the size we would have expected to find and the length I would say was close to that portion I could no longer get a sound.

A year later just a few weeks ago, this time we had the time so I took the Pioneer 505 and the Garrett ADS Ground Hog with me. The location we went to was not far from last year but again the Lead Worker thought there should be a culvert in this location. I set up the 505 in ALL METAL and Ground Trac'ed for about 2 inches above the pavement with the Sensitivity (Power) turned all the way up. This was with the standard size BH coil. Again like with the Garrett, I was having to do some listening through a lot of other sounds but found nothing that would have caught my ear. At this point, I decided to do a trick I learned a long time ago to get away from the effects of iron and mineralization and so I raised the coil up and out away from me and reset the Ground Trac. From there I lowered the coil to just the point it was no longer silent but was not sounding like a target either which was at or about 1-1/2 to 2 feet above the ground. I re-searched the area and nothing. I told the Lead Worker that I needed to do this over a culvert we know exists so to figure out what I'm listening for and so found one not far down the road. After resetting the 505 away and above ground like before, I lowered the coil to the where silence was broke about 2 feet above the road and worked my way towards where the culvert would be. Sure enough, there was no missing it. It was not a crisp clear target sound but it was distinct enough in relation to coil swing and the fading out on the ends of the swing to know I was on it and following it. Now I knew for sure what I was listening for.

We went back to the previous spot I found nothing and reworked it and found nothing. From there, I told him I would like to go back to the spot we did last year and so we did. I set up the 505 above ground and worked my way towards the spot we paint marked last year and sure enough, there was no missing it and was right where the Garrett sounded for me detecting in a normal fashion of about 2 inches above ground. I detected out into the shoulder dirt until the sound ended and I got a crackle that I believe to be the end of the pipe. From there, I worked back onto the highway and like last year with the Garrett, the signal ended just past the yellow line and again I got a crackle sound off what I think now is the end of the pipe. The piece laying in the river may be the other section of it.

At this point I reminded him there was still another location we thought a culvert was missing and so we drove to it. He was walking down the road to where he thought it was and as I followed, I set up the 505 and put it over the road about 2 feet. Sure enough, I found a sound and called for him to come back towards me. I followed the sound into the ditch until it ended with a crackle and paint marked it, then returned to the pavement following it across the fog line, the yellow center line, but the sound ended just before the next fog line with a crackle. We walked to the river bank and no pipe and I could not detect anything. To make sure, I reworked it again and had the same results. On the mountain side of the road, he dug down with a shovel in the muddy water and crap until he hit something, then got down on his hands and knees to dig by hand. Sure enough, he said it's a culvert and could feel the ribs. What I began to suspect now was the road in the old days at these locations were single lane and when it was widened a bit, the river ends of the pipe were covered up and paved over.

Here on my own section, we had a gully washer rain the other day and the debris came out of a gully I've always suspected should have a culvert but was possibly buried some years ago. I set up the 505 and found that sound, followed it across the road and to the river side of the highway where I found the exposed end of the pipe in the brush. We went back to the other end and worked it towards the mountain until the sound I was listening for stopped but ended with no crackle. The pipes on this section are different in that on the mountain side of the road, they have wide metal catch flumes where on the other section I helped the Lead Worker with, they have none and so could possibly explain why no crackle sound. We also roughly stepped off a known pipe and flume from the pavement edge not too far away and where my sound ended would be about the right distance for the catch flume.

These metal culverts are anywhere from 2-4 or more feet deep on the other highway section to 3-5 or more feet on ours and can be bigger sizes. As a rule of thumb, a detector coil is most effective as deep as it is round or narrow near ground. Raising the coil up and setting the Ground Trac in air got me away from the close up effects of ground and trash so I could run Max power or Sensitivity. What I gave up though was an ability to detect smaller items and the deeper they were though ALL METAL as a rule of thumb is the deepest seeking mode. So, if some of you are looking for buried caches or large metallic things, you may want to play with this. I have never ran a Two Box for buried caches or treasure but I suspect it is run on the same principles as I applied to my 505 because I have never seen anyone ground balance a Two Box, 2 or so inches off the ground.

Remember all the Manufacturer warnings about finding buried power, phone, gas, oil, and water lines and possibly unexploded War ordinance and at greater depths than you typically detect.

 

[Mike Hillis]

n/t

 

[downeaster]

Great post !!! Thank you !!!

 

[salmonriverhotrock]

I think I may have started something. My Lead Worker on our section of highway along the Little Salmon and the Salmon Rivers decided to begin searching for Culverts and updating our very out dated questionable inventory. We have had some small old partial inventory lists to try and go by Mile Markers but amazingly, I'm finding culverts we did not know about or that are not on the lists at all.

Today the Lead Worker and I checked 15 miles of highway. Some culverts were pretty easy to detect and others I could not at all at the pavement grade of the highway. Those I could not detect, were clearly buried very deep or I had a couple three that drained so steep from the mountain side of the borrow ditch, that at the pavement they were already well over 5-6 or more feet deep and way past 10 or more feet deep on the outlets. One location had a water pipe about 5-6 inches that supplies a small sort of community. I thought maybe they had run it through a culvert but it was very hard to hear and detected it most of the way across the highway before losing it. What I found out though was I had followed a sound straight across the highway towards where a remnant of a pipe the same size had been cut out of the system and was left abandoned in the brush. I know they still get water from the one I was detecting. There was one location that was supposed to have a culvert and I got a sound out in the borrow ditch and followed it onto the road and it stopped before the yellow center line. This was a location the outlet could not have gone too deep to detect. All I can figure is there is a remnant of a culvert there and maybe part of it was torn out and the rest abandoned. We did have one that visually, we found the outlet way below the grade of the highway about 40 feet but where we thought the inlet should be, no sound. This one though could have been abandoned because of a major land slide that covered the highway and so the highway was built over the land slide and this culvert could have been from the old highway.

I did have one other location that it turns out, had a 5-6 inch water pipe under the road. While I was detecting through a location we thought should have a culvert, the other guy was across the highway talking with a land owner. Across from them, I hit a sound and sure enough, it headed me across the highway. I detected right up behind where my Co-Worker was standing and so he moved and I went to almost the fence and then the land owner stopped me to let me know there was a pipe elbow sticking out of the ground right where I was headed for. None of us knew that pipe was there but the remnant of it on the mountain side of the highway was in the brush. Must have been a water source for a home way back when.

As for County Road and Private approaches to the highway, most of them were pretty easy to detect the culverts. There were a few so deep I could not detect them but visually we could see them. What amazes me is how many highway culverts we have that the inlets and or outlets have been buried or the approaches with culverts have one or both ends buried. We do get pulled away from our section a lot to help other sections so we end up neglecting things we need to do here. Maybe with making this new list of the culvert conditions, we can get our New Foreman to realize unlike the old one that was thinking more about retirement in the next two years than his job, we do have things down here to fix.

The 505 has done well. Considering all the empty cans and other metallic trash along the highway, it delivered me a surprising number of culverts we could not see or did not know about. Just maybe, one of these days we will get a chance to backhoe dig some of these that are buried to clean them out. The traffic though is always an issue and was a challenge even though we wore our reflective safety vests and tried to watch each others backs. Very few People ever slow down for road crews and amber flashing lights. It just don't register in their gray matter to think CAUTION!. Maybe if we drove as fast through their offices or homes as they do our work, things would change. I've had people broad day light hit very visible rock falls at highway speeds while we were trying to quickly kick tire busters out of the travel lanes. If it were not so dangerous trying not to get hit by fragments of the rocks they hit, you would be rolling on the ground laughing at them. Well, we have 36 more miles to check on our section. I know this kind of detecting is not like finding coins and such but it is showing me what a detector will do in ALL METAL and with some playing around with the ground balance and height above the ground. Never know, may be some land owners or road workers out there that need to find a culvert and maybe this will help them or encourage them that it is possible to use your old VLF to find them.