8
Exercise 1
flagperson at position C. Draw the line of sight; record distance if a telescopic alidade is used
or estimate length if an extendable open-sight alidade is used. Repeat the procedure for
each stake at shore line positions until the area is circumscribed.
7. Move the plane table to the other end ofthe base line (B) and repeat all angular and distance
sightings.
8. Construct an outline map as discussed earlier.
9. Accuracy of the positioning of depth soundings is improved when persons making the
soundings (from boats or through ice) determine depths along the transects as the shore line
is being established. The depths are noted against distance sightings by the alidade along the
transects.
10. Deviations in physical features of the shore line from a general circular configuration, such as
inlets, outlets, and bays, should be noted by the flagpersons as the periphery is traversed.
Alternative Methods
1. When the body of water is very small, such as a pond or a section of a stream, measurements
often can be made directly with tape measures. Simply establish a continuous series of
triangles, the lengths of whose sides are known, and the apices of which are located at
various points on the shore line.
2. Small bodies of water also may be mapped by direct measurements made perpendicularly
from a base line extending along the entire length of the water body. The distance from
the base line to the intersection of the parallel transverse lines from points on the shore
line on both sides permits an accurate evaluation of the periphery.
3. A rather crude map can be constructed by using only a surveying compass and a tape
measure. Angular measurements from a base line oriented north-south are made by compass
bearings at points of measured distance around the shore line.
In the construction of the map of a body of water, the map should include the shore line, depth
contours at meter intervals, a scale in metric units, the name of the body of water, the exact
geographical location including section, date of the survey, and names of the surveying crew.
Table 1.1. Exemplary data obtained from field measurements of a plane table-alidade
survey of the shore line of a small lake.
Lake:
Omega
Date:
August 18, 1976
Workers: 1. Blown
Station
lines
S. Scatter
W. Cloud
Distance
(m)
AB (base line)
43.2
AC
58.5
AD
81.5
AE
92.6
AF
109.0
AG
111.5
AH
83.0
AI
80.0
AJ
73.5
AK
70.0
AL
62.0
AM
28.5
Angle between
AB and line
13'
26'
38.5"
59°
73°
88°
106 0
119.5°
132°
140.5"
154°
Location: Sec. 14, TIN, R3W,
Theta County, North Dakota
Reference: 3.5 m below USGS
Bench Mark at 146.3 m
above mean sea level
Base line N57°30'W
Bearing:
Station
Distance
Angle between
lines
(m)
BA and line
- - - - - -
BA (base line)
43.2
BC
19.0
136'
BD
47.5
IW
BE
65.0
lIT
BF
94.5
97.5"
BG
107.0
84°
BH
93.0
64.5°
BI
101.5
50"
Bl
102.0
39S
BK
104.5
30S
BL
99.0
24"
BM
70.0
lOS
Exercise 1
flagperson at position C. Draw the line of sight; record distance if a telescopic alidade is used
or estimate length if an extendable open-sight alidade is used. Repeat the procedure for
each stake at shore line positions until the area is circumscribed.
7. Move the plane table to the other end ofthe base line (B) and repeat all angular and distance
sightings.
8. Construct an outline map as discussed earlier.
9. Accuracy of the positioning of depth soundings is improved when persons making the
soundings (from boats or through ice) determine depths along the transects as the shore line
is being established. The depths are noted against distance sightings by the alidade along the
transects.
10. Deviations in physical features of the shore line from a general circular configuration, such as
inlets, outlets, and bays, should be noted by the flagpersons as the periphery is traversed.
Alternative Methods
1. When the body of water is very small, such as a pond or a section of a stream, measurements
often can be made directly with tape measures. Simply establish a continuous series of
triangles, the lengths of whose sides are known, and the apices of which are located at
various points on the shore line.
2. Small bodies of water also may be mapped by direct measurements made perpendicularly
from a base line extending along the entire length of the water body. The distance from
the base line to the intersection of the parallel transverse lines from points on the shore
line on both sides permits an accurate evaluation of the periphery.
3. A rather crude map can be constructed by using only a surveying compass and a tape
measure. Angular measurements from a base line oriented north-south are made by compass
bearings at points of measured distance around the shore line.
In the construction of the map of a body of water, the map should include the shore line, depth
contours at meter intervals, a scale in metric units, the name of the body of water, the exact
geographical location including section, date of the survey, and names of the surveying crew.
Table 1.1. Exemplary data obtained from field measurements of a plane table-alidade
survey of the shore line of a small lake.
Lake:
Omega
Date:
August 18, 1976
Workers: 1. Blown
Station
lines
S. Scatter
W. Cloud
Distance
(m)
AB (base line)
43.2
AC
58.5
AD
81.5
AE
92.6
AF
109.0
AG
111.5
AH
83.0
AI
80.0
AJ
73.5
AK
70.0
AL
62.0
AM
28.5
Angle between
AB and line
13'
26'
38.5"
59°
73°
88°
106 0
119.5°
132°
140.5"
154°
Location: Sec. 14, TIN, R3W,
Theta County, North Dakota
Reference: 3.5 m below USGS
Bench Mark at 146.3 m
above mean sea level
Base line N57°30'W
Bearing:
Station
Distance
Angle between
lines
(m)
BA and line
- - - - - -
BA (base line)
43.2
BC
19.0
136'
BD
47.5
IW
BE
65.0
lIT
BF
94.5
97.5"
BG
107.0
84°
BH
93.0
64.5°
BI
101.5
50"
Bl
102.0
39S
BK
104.5
30S
BL
99.0
24"
BM
70.0
lOS