Worked on a project for the City of Phoenix 6 years ago, locating and dipping over 5500 manholes.
It's difficult to know how many manholes a crew can do in a day without knowing the conditions. You can estimate a certain percentage of the manholes can be GPSed, while the remaining percentage would have to be done with a total station. Time spent on a manhole is dependent on the method used. And that's only for the manholes that you can actually find out in the field.
Deral is right; a crew might do 10 in a day or they might do 50. We had some days where we got 60 manholes located and dipped. We had one day where we got exactly 1 manhole located and dipped. Then again, that manhole was on an Interceptor line on a dike and the manhole rim was 17' below ground, so we had to work with a backhoe operator from the City to find that one.
Deral is also right about those interceptor lines and their depth and flow. No measuring rods there; they would have snapped. We used iron pipes.
Preparation and knowing what the data is to be used for are key. The crews always had maps with the manhole locations and manhole IDs for each day's work. We also had prepared forms that the crew chiefs filled out for each manhole (Quarter Section #, Manhole #, Inverts N,S,E,W, a sketch area for the manhole and an area for any additional remarks). That simplified the notekeeping as well as making the notekeeping consistent from one crew to the next.
Our data went into a GIS database, so a Template was set up prior to beginning fieldwork that would limit what each crew could input. The template was then put into each GPS unit. Again, it kept things consistent from one crew to the next. It also made downloading data much easier when preparing for GIS input.
What's your contingency for manholes that aren't found? How much time to you spend looking for them? I would assume that you will have return visits to the field to measure those manholes once they have been uncovered. Make sure that you account for those possible return visits.
Do any of the manholes require any special permission to get to? We had some manholes at the Airport, so that required getting an escort to work with us. Again, something to think about.
You'll also have some manholes that have to be rechecked.....just because. It could be a negative flow issue, it could be a crew made an incorrect invert measurement. It happens. Try and estimate beforehand how much time might be needed for this.
Again, preparation and knowing what the data is to be used for are key. Good luck!
A slight hijack. I have done lots of MH dipping over the years. Some additional thoughts that may, or may not, help:
Never try to open a cracked lid. Once that piece of lid falls down in the MH, you are stuck with an open hole.
Cleaning the rim before replacing the lid is a must.
Banging on the rim with a 2 or 3 pound hammer might release the frozen mud or asphalt that is locking it tight. See the first tip if you crack it.
The engineer who designed the lid with the hole that does not go all the way through the lid should be shot!
Look in the hardware store for a plumbers pipe slope indicator; essentially a weighted indicator on a protractor with two 90 degree quadrants. It works great on measuring the slope for that invert that you cannot get vertically. The indicator gives you the slope, a minute with your calculator and some trig and you can compute the vertical side of the triangle you measured. No batteries. Simple. It works.
A good flash light helps to see that missing pipe.
Use the same routine for each manhole. I figure out which pipe is the exit pipe, then go clockwise to the next one, measuring all clockwise until the exit pipe, the last one. It helps you to get them all, when there are lots of pipes.
Take a few minutes to be sure of your notes. It is a lot easier than having to go back.
If it is in your shirt pocket, it WILL fall into the manhole. Manhole depth, nastiness and the value of the object in your pocket will increase the odds of it falling.
Don't get complacent with the traffic! After a while, you may tend to forget you are out in the road with tools and an open manhole. That car coming around the corner does not know you will be there!
Bring some sort of anti-bacterial spray and wipes to clean up the rod and hands as the day goes on. Gloves cannot hurt either.
Be safe!
KS
This is entirely dependent on the number of members of your field crew. You didn't state the obvious, how many people are working?