1Hydrographic surveying
surveying of water environments; considered the wet equivalent of topographic surveying.
2Hydrographic maps or nautical charts
maps that delineate submerged surfaces and provide data on water depths and underwater features.
3Hydrography
science of water surveying.
4Sounding
measurement of water depth.
5Stream gaging
measurement of stream discharge.
6Discharge
volume of water flowing per unit time.
7Fathom
unit of depth equal to 6 feet.
8Hydrographic chart
map showing water depths and features.
9Subaqueous contour
line connecting points of equal underwater elevation.
10Dredging
removal of underwater material.
11Stream
natural watercourse.
121. Station location
2. Water depth
3. Discharge measurement
Basic Requirements
131. Water Resources and Development
2. Transportation and Infrastructure
3. Navigation and Underwater Investigation
Applications of Hydrographic Surveying
14Tides
periodic changes in water level caused mainly by the gravitational effects of the Moon and Sun.
15Moon
primary celestial body responsible for tides.
16Sun
also contributes to tides through its gravitational attraction.
17Tidal current
horizontal movement of tidal water.
18Flood tide
incoming tide, when water moves toward the shore or into an area.
19Ebb tide
outgoing tide, when water moves away from the shore or out of an area.
20Slack water
period when there is little or no tidal current between incoming and outgoing tidal currents.
21Set
direction of the tidal current.
22Drift
speed of the tidal current.
23High water
maximum water level.
24Low water
minimum water level.
25Tide range
difference between high water and low water.
26Tidal day
period between successive high waters.
27Stand
period of little tidal change.
28Mean sea level
average sea surface level.
29Mean low water
average low-water level.
30Mean lower low water
average of the lower low waters.
31Semidiurnal tide
has two high waters and two low waters each day.
32Diurnal tide
has one high water and one low water each day.
33Mixed tide
has unequal high waters and unequal low waters.
34Tidal waves
long-period movements of tidal water.
35Tidal bores
occur when tidal waves move rapidly through rivers.
361. Navigation
2. Salvaging
3. Fishing
Tidal information is particularly important in:
37Reconnaissance
first basic operation; involves inspecting the survey area before conducting the actual survey.
38Horizontal control
establishes the horizontal positions of survey observations.
39Vertical control
establishes the elevations or vertical references.
40Topographic survey
determines land features.
41Hydrographic survey
measures underwater features.
42Map preparation
produces the final hydrographic map.
43Sounding craft
vessel used for sounding.
44Sounding pole
measures shallow-water depth.
45Lead line
uses a weighted line to measure depth.
46Sounding machine
mechanically measures water depth.
47Fathometer
uses sound waves to measure water depth.
48Signals
provide position and navigation references.
49Tide gauges
measure water levels.
50Chief of party
leads the sounding chart party.
51Instrument man
operates surveying instruments.
52Recorder
records survey measurements.
53Leadsman
handles the sounding lead.
54Coxswain
operates the sounding craft.
55Lookout
watches for hazards.
56Signal man
communicates signals during sounding.
57Fathometer attendant
operates the fathometer.