Hydrographic Survey midterm
Cards (100)
- the study, description, and mapping of oceans, seas, lakes, and rivers especially with reference to their navigational and commercial or other uses.
- the process of measuring the depth of a body of water at a particular point.
- the process of making measurements in streams and rivers for the purpose of predicting the rate of discharge at various water levels or stages.
- unit used for the measurement of water depth and is equivalent to six (6) feet.
- a map or chart used in navigation. It is basically similar to a topographic map except that water depths, navigational markers, and the character of underwater surface are indicated.
- are specific tide levels which are used as surfaces of reference for depth measurements in the sea and as a base for the determination of elevation on land.
- the volume of water flowing past a section of a stream, canal, flume, and other waterways. It is usually expressed in cubic feet per second or cubic meters per second.
- a current or steady flow of water running along the earth's surface.
- the process of scooping or sucking up mud, sand, rocks and other material underwater for the purpose of enlarging, deepening or clearing channels, harbors, rivers, and other bodies of water.
- an imaginary line on the surface of the earth found underwater, all points of which are of the same elevation. They are sometimes known as depth curves or bathymetric contours.
- is characterized by the observations and measurements which are undertaken to determine and subsequently portray the topography above and beneath the water surface, as well as the location of important marine features
- A preliminary step is the careful reconnaissance of the area to be surveyed. This is done in order to select the most suitable manner of executing the survey and in planning all phases of work.
- The second step is the establishment of the framework by which land and water features are held in their true relationship to each other. Horizontal control is usually defined by triangulation systems.
- Prior to the execution of sounding operations, vertical control must first be defined in order that the elevation or stage of the water surface can be correctly referenced. Vertical control data are also needed for the limited topography which will be portrayed on a nautical chart.
- In a hydrographic map or nautical chart, only a relatively narrow fringe of the nearby ground surface is shown since the expected users are not particularly interested in this area except for a few prominent landmarks which could be used for referencing positions.
- the measurement of water depths and establishing their respective locations are the most important operations in a hydrographic survey. Different procedures and techniques have been devised to suit various field conditions, scope of work, purpose and the desired accuracy of the hydrographic survey.
- The final product of a hydrographic survey is the preparation of a hydrographic map or nautical chart. In the case of subsurface surveys for engineering requirements, the end result may be the calculation of, water volume contained in a body of water, amount of dredged material, discharge of a stream, or the fluctuations of level in a body of water.
- The Hydrographic Survey processare?
- Various types are used for hydrographic surveys. These includes rowboats, motor launches, and small vessels. Most fishing vessels are. suitable because they are seaworthy, have reliable motor performance, and can be adapted to the various operations associated with hydrographic surveying.
- A graduated and rounded piece of lumber, about 3 meters long, used for taking soundings. It is suitable for use where the water depth does not exceed 2 meters. At each end is a metal shoe which may be weighted to make the pole sink through the water more quickly.
- or sounding line is usually a length of sash or hemp cord, braided flax, or nylon cord, with a sounding lead attached to one end. They are seldom used for depths greater than 25 fathoms.
- When the depth of water is too great to permit the use of a leadline, a sounding machine is used. It is a simple device in which piano or stranded wire is used and wound on a reel mounted on a stand.
- is a measuring device which is automatically records the sounding taken
- are constructed in various ways but they should be seen and easily distinguished from each other.
- The sextant is a portable and hand-held instrument used for principle that a light ray striking a plane mirror causes the angles of measuring horizontal and vertical angles. It functions by the physical incidence and reflection to be equal.
- THE CAUSE OF THE TIDES
- the half-daily cycle of rhythmic rise and fall of the surface of oceans, seas, lakes, bays, rivers, and other bodies of water connected with them due to the gravitational attraction of the sun and the moon acting upon the rotating earth.
- the horizontal movement of water accompanying tides and which is produced by the combined action of astronomical, hydrological, and meteorological factors.
- the period within which the water surface is rising and moving in toward the shore.
- the period within which the water surface is falling and moving seaward.
- the instant at which the tidal current is changing direction and flows neither in nor out.
- refers to the direction of current flow.
- refers to the speed of current flow.
- refers to the maximum height to which the water surface rises above the standard datum plane during a given period. It is also known as high tide.
- _ or low tide refers to the greatest depression of the water surface below the standard datum plane during a given period.
- the range of the tides is the difference between the high and low tide at a certain location on a given date. It may vary both for different locations and for high and low tides measured on different days at the same location.
- consists of an idealized average period of 24 hours and 50 minutes between the occurrence of two successive high tides of the same type at the same location.
- the _ of the tide is the period around which the greatest peak or depression of the tides is reached and during which any change in height of the tide is scarcely noticeable.
- consists of a large head or front of water genera ted at the surface of the ocean by force winds of hurricanes or typhoons, or by isostatic adjustment of the ocean floor accompanying a submarine earthquake.
- The principal tidal datums