US Army Corps of Engineers - cdn.cloud1.cemah.net · US Army Corps of Engineers Detroit District Surveying Basics Surveying – a measure of where you are (x,y) and the elevation

Surveying Basics

US Army Corps of Engineers

Detroit District

Great Lakes Hydraulics and Hydrology Office


Detroit District

Surveying Basics

Surveying – a measure of where you are (x,y) and the elevation (z) of

that point

Horizontal Coordinate (x,y) measured in:

•Latitude/Longitude

• UTM (in meters)

• Michigan Georeference

• State Plane

• and many others


Detroit District

Surveying Basics

Vertical Coordinate (z) usually measured as the number of feet above

some measure of sea level. Sea level is your starting point or zero

point.

• IGLD

• NGVD

• and many others

Our elevation here at Holiday Inn is ~550 ft above sea level

(Lake Ontario is ~240 ft)


Detroit District

Surveying Basics Benchmarks

Benchmark – A place of known position and elevation (x,y,z). For

the stream monitoring we will be doing, we are primarily interested

in the elevation (z) and have little use for the latitude and longitude

(x,y).

Brass monument Chiseled “X” in rock or

concrete (bridge deck)

Nail or lag bolt in tree

Rebar in the ground


Detroit District


We will usually not have a benchmark near our study site, so we

will establish our own and assign an arbitrary elevation to it

(usually 100 ft). It’s a good idea to have more than one BM in

case your BM gets stepped on, tree falls, shoved up by frost

heave, et c. Try to have 3 BMs.

Nail or lag bolt in tree Chiseled “X” in rock or

concrete (bridge deck)

Rebar in the ground (end pins for your x-section can by BMs).


Detroit District


To locate benchmarks near your study area, you can search for them at:

www.ngs.noaa.gov

Or talk to local government agencies:

- Road Commission

- Department of Public Works

If there is infrastructure near by, there is likely a benchmark

http://www.ngs.noaa.gov/


Detroit District

Surveying Tools

• Survey Rod

• Level and Tripod

• Survey Tape

• Misc Equipment


Detroit District

Surveying Basics Survey Rod

Survey Rod – a graduated rod which measures the height

above the ground (a very large yard stick). We will take all

rod measurements to the 1/100 ft.


Detroit District

Surveying Basics Survey Rod

Reading a Survey Rod

Feet in RED Tenths of a foot in BLACK

Source: North Carolina DENR


Detroit District

Surveying Basics Level (Instrument)

Level – (optical) device that projects a level line. Similar to a rifle

scope if you could hold it perfectly level.

Level Line

If you know the elevation of the level (use a

benchmark), then everything intersecting

that line is at the same elevation


Detroit District


• Leveling the level

• Proper care of a level


Detroit District


How to use a level to determine the elevation of a stream-bed.

Elevation = 700 ft

Survey

Rod

Elevation?

10 ft

Elevation = 700 ft – 10 ft = 690 ft

……and repeat

(Foresight)


Detroit District


Survey

Rod

(Foresight)

Foresight – a rod reading taken on any point to determine its

elevation


Detroit District


How to we determine the height of the instrument?

Elevation = ??? ft

Survey

Rod

10 ft

Height of Instrument (HI) =

695 ft + 5 ft = 700 ft

(Foresight)

(Backsight)

5 ft

Benchmark

Elevation = 695 ft


Detroit District

Surveying Basics

Backsight – A rod reading taken on a point of known

elevation. There is only ONE backsight for each setup

of the instrument.


Detroit District

Surveying Basics Survey Tape

• Used for measuring the distance along your survey

• Usually 300 ft tapes are used

Source: SFSU.com

Source: naparcd.com


Detroit District

Surveying Basics Misc Equipment

Rebar (end pins)

Candy-canes

Clamps

Plastic flagging

Bubble level

Tree pruner/machete

http://www.benmeadows.com/seco-surveyors-steel-arrows_36815491/


Detroit District

Surveying Basics Turning Point

X

1

2

Turning Point

(Large Rock)

As your survey progresses

downstream, you may get to a

location where you cannot see

the rod any more. You must

move the level to a new location

to complete the survey. To

preserve the continuity of the

elevations, you must adjust the

height of the instrument with a

TURNING POINT.

Flow


Detroit District

Surveying Basics Turning Point

Turning Point (TP) – A stable point (large rock, stump, et c.)

upon which a foresight is taken to establish an elevation.

The level is then moved and a new backsight is made to

determine the new height of instrument and to continue the

line of levels. You need to create TPs when you can no

longer see the survey rod, such as when going around a

bend in a river or around a building.


Detroit District

Surveying Basics Closing the Survey Loop

Closing the survey loop

• A technique to ensure the quality of your survey data

• Running your survey loop back to the original benchmark (BM) and

checking that the elevation is the same (or very close) to the original

elevation.

• Typically 0.02 ft of error is acceptable.


Detroit District

Surveying Basics Closing the Survey Loop

X

1

2

Turning Point

(Large Rock)

Flow

Benchmark


Detroit District

Surveying Basics Other Types of Survey Instruments

Laser Level • Uses a laser beam to shoot a horizontal line. A sensor on the survey

rod beeps when intersected with the laser

• Allows you to survey with 1 person

• Inexpensive

• Noisy

• Needs batteries


Detroit District


Total Station • Measures travel time of laser to determine distance

• Also measures horizontal and vertical angles to calculate your exact

x,y,z coordinates.

• Expensive


Detroit District


RTK GPS • Uses satellites to triangulate your location

•Uses ground beacons to refine these coordinates

• No need for benchmarks

• Expensive (~$50k)

• Tree cover limits use in forested watersheds


Detroit District

Questions

Contact:

Dr. Jim Selegean, P.E., P.H.

U.S. Army Corps of Engineers, Detroit District

Great Lakes Hydraulics and Hydrology Office

477 Michigan Ave

Detroit, MI 48226

313.226.679

[email protected]

mailto:[email protected]

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US Army Corps of Engineers - cdn.cloud1.cemah.net · US Army Corps of Engineers Detroit District Surveying Basics Surveying – a measure of where you are (x,y) and the elevation