I have been working on a dam rehab project for over a year now. The dam was built in 1912. Early last year, I did a topo of the spillway and located some monitoring well locations as well as set photo panels used for Lidar. I did cross sections of the 12’x18-20’ discharge tunnel on the downstream side of the control gates.
This year it has been some staking for the improvements and a grout curtain to help seal the earthen dam. The concern we have is the grout curtain is on the upstream side of the control gates and the engineer has a best guess of the location of the upstream side of the discharge tunnel. We had a discussion about it and he is trying to get the water district to lower the reservoir level below the coffer dam so I can get a location of the tunnel. The water district is not in favor of lowering the water level any lower than what it is at this point for the dam clay liner we are installing.
So, now they are asking about getting divers to remove the trash grate to get inside of the upstream side of the discharge tunnel for the survey. I’ve never surveyed under water. What equipment can be used to accurately locate this tunnel in 3D under water?o.O :-S
SD
That is a pretty large tunnel. We ran a traverse up a 10' diameter circular outflow tunnel to the upstream end (with the intake gates closed, of course) which was at the base of a 225' high intake tower. It had two curves in it, and we took shots every 50 feet (top, bottom, left, right) and also located all of the seeps where water was leaking in.
Sounds like you might want to speak with a specialist with access to inertial/multibeam hydro systems and sub-bottom profilers.
You might be surprised what you can accomplish without divers wedging themselves into some turbid claustrophobic lightless nightmare with a tape and compass.
Bump. I hope you will get better responses if we keep this post alive.
> That is a pretty large tunnel. We ran a traverse up a 10' diameter circular outflow tunnel to the upstream end (with the intake gates closed, of course) which was at the base of a 225' high intake tower. It had two curves in it, and we took shots every 50 feet (top, bottom, left, right) and also located all of the seeps where water was leaking in.
>
Yikes! You are crazy, and I am claustrophobic. That does sound cool though, I probably would have done that in my younger days.
SD
Are you trying to survey the entrance to the tunnel or the bore of the tunnel?
GPS/multibeam would be best to locate the entrance if there aren't obstructions/complex shapes. Did something similar with a mini ROV with camera guiding a plumb line/tape from the surface, we located the plumb by GPS and depth below the water surface.
Are there any original drawings or copies archived somewhere?
We are trying to get a positive location on the bore of the upstream side of the control gates. I have the downstream side and it matches pretty close to the plans of 1912. On the upstream side, we don't know for sure, but could assume something based off the original plan and what I found last year downstream.
Going up there today to talk some more with the irrigation district.
