Hydrographic Surveys Overview

Questions and Answers

What is the primary purpose of hydrographic surveying?

To gather data for the construction of bridges exclusively

To measure the speed of currents for recreational purposes

To locate submerged vessels only

To provide data for hydrographic maps and nautical charts for navigation and related projects (correct)

Which of the following terms refers to the process of measuring the depth of water at specific points?

Gaging

Sounding (correct)

Hydrography

Discharge

What are range lines primarily used for in hydrographic surveys?

To construct tidal datum for forecasting

To set reference lines along which soundings are taken (correct)

To measure the temperature of the water

To indicate shaping of the land in a topographical sense

Which statement accurately describes a hydrographic chart?

It includes detailed information about tidal fluctuations and navigation markers Signup and view all the answers

What is the function of a gaging station in hydrology?

To provide data on water flow at specific river cross-sections Signup and view all the answers

What is the primary purpose of a current meter in hydrographic surveys?

To indirectly measure the velocity of flow in water. Signup and view all the answers

In hydrographic surveys, what are tidal datums used for?

As reference surfaces for depth measurements and land elevation. Signup and view all the answers

Which operation is NOT included in the basic operations of a hydrographic survey?

Identification of ecological factors in aquatic life. Signup and view all the answers

What unit is equivalent to six feet and is used for measuring water depth?

Fathom Signup and view all the answers

What does the subaqueous contour represent in hydrographic terms?

An imaginary line of equal elevation underwater. Signup and view all the answers

Study Notes

Hydrographic Surveys Overview

Hydrographic surveying collects data about water bodies and adjacent land.
Essential for creating hydrographic maps and nautical charts to support navigation and development projects.

Purposes of Hydrographic Surveying

Provides critical data for navigation, harbor enhancements, dredging, and yardage.
Essential for flood control, water supply management, hydroelectric power projects, and irrigation.
Determines water volumes, current directions, velocities, and drainage capacities.
Establishes tidal datum for consistent height measurement.
Aids in designing various infrastructures like bridges, dams, and docks.
Locates navigational hazards, including submerged objects and sandbars.

Key Hydrographic Terms

Hydrography: Study and mapping of aquatic environments with a focus on navigation.
Hydrographic Chart: Specialized map indicating water depths, tide fluctuations, and navigation markers.
Sounding: Measurement of water depth at specific points using established tools.
Buoy: Floating marker anchored to denote locations underwater.
Discharge: Volume of water flowing at a specific section of a stream per time unit.
Current Meter: Device that measures the velocity of water flow indirectly.
Fathom: A depth measurement unit equivalent to six feet.

Hydrographic Survey Process

Reconnaissance: Initial survey planning which may involve aerial photos and existing maps.
Horizontal Control: Establishing reference points for land-water relationships, including hydrographic signal positioning.
Vertical Control: Using instruments like sextants to determine vessel positions during surveys.

Importance of Tides

Crucial for marine activities such as ship launches and dredging.
Directly influences navigation, fishing, and aquatic sports.

Causes of Tides

Primarily driven by the moon's gravitational pull, with the sun's influence as a secondary factor.
Tidal phenomena influenced by Earth's rotation and orbit patterns.

Tidal Definitions

Tide: Rhythmic rise and fall of water surfaces caused by gravitational forces.
Flood Tide: Water surface rising towards the shore.
Ebb Tide: Water surface falling and retreating seaward.
High Water/Low Water: Extremes of tidal elevation.

Types of Tides

Semidiurnal Tides: Two high and two low waters each tidal day, common in the Atlantic.
Diurnal Tides: One high and one low water daily, seen in the Philippines and China.
Mixed Tides: Combination of semidiurnal and diurnal observations.

Tidal Datums

Specific tide levels used as references for depth and elevation calculations.
Mean Sea Level (MSL): Average sea height across all tide stages, often used as a primary datum.
Mean Low Water (MLW): Average of low water heights observed long-term.
Mean Lower Low Water (MLLW): Average height of the lower of two daily low waters.