Vern's Travels Thru Time and Other Places 

 

 

Period Surveying Techniques 2

How to do leveling, contours and elevations?

By Lt. Vernon Catron 1st New York Volunteer Engineers, Company A

Several months ago I was asked to write a brief series ofarticle son different aspects of surveying with period techniques by Major Poe. This is the second article in the series.

How do I make sure that my foundation is level? How do I get this fence even in height? The answer is leveling. This also ties into determining elevations and contours.

I will begin with determining elevations. To determine elevation you need a benchmark or other point with known elevation, a transit or builders level, and a rod (preferably in feet & 10ths). You also need a sight book to record in. There are several terms you need to know. BS is backsight, HI is height of instrument, FS is frontsight , IP is intermediate point, BM is benchmark, TP is turning point, and Elev. is elevation.

  BS HI IS FS Elev.  
BM            
BM            

The procedure for determining HI is easy if you remember to add the BS backsight to Elevation (HI = BS + Elevation). If you look at chart 1 below you can see the HI for BM-1 = 161.273 +2.828. The elevation = HI - IS or FS. The IS and FS are looking towards and BS is looking back. You work forwards then backwards. To check your figures (sum) BS, FS. Beginning elevation +BS-FS = ending elevation.

Set up the instrument and backsight to your benchmark reading the rod with the center wire. The rodman must hold the rod vertical and solidly on the ground. Now you have the information to determine your initial HI. Now you can sight your intermediate points if you have them or to your turning point. To determine the elevation at the IS or FS subtract the rod reading from the HI. Once you have shot the Turning point you can move the instrument and set it up again. Now you continue as before. Once you have all figures perform your math check (sum) BS, FS. Beginning elevation +BS-FS = ending elevation.

The IS and FS points give you a contour of the ground. To use this information to level is a short step. If we were building a structure we first set a point on a corner batter board to be our master base line. We then shoot the elevation of the spot with the rod on the ground. Next we raise the rod the required distance, mark the batter board at the base of the rod and remember the reading. Do this on all remaining batter boards marking them when the reading is the same. Now you can set your horizontal string boards for your footing lines.

Chart 1 in meters

STATION BS HI IS FS ELEV  
BM-1 2.868 164.141     161.273  
0+00     2.06   162.081  
0+06     1.17   162.971  
0+20     1.63   162.511  
0+40     1.62   162.521  
0+60     1.41   162.731  
0+80     1.01   163.131  
TP#1 1.977 165.136   0.982 163.159  
1+00     1.73   163.406  
1+20     1.7   163.436  
1+30     1.89   163.246  
1+40     1.67   163.466  
1+60     1.6   163.536  
1+80     1.31   163.826  
1+91     1.93   163.206  
2+00     0.64   164.496  
BM-2       0.54 164.596  
sum 4.845     1.522    
4.845 + 161.273 - 1.522 = 164.596


This web maintained and written by Vernon Catron, I am not responsible for opinions of others. For comments Email me.