May 18, 2011

Earth's Water Distribution

Where is Earth's water located and in what forms does it exist? 

You can see how water is distributed by viewing these bar charts. The left-side bar shows where the water on Earth exists; about 97 % of all water is in the oceans. The middle bar shows the distribution of that three percent of all Earth's water that is freshwater. The majority, about 69 %, is locked up in glaciers and icecaps, mainly in Greenland and Antarctica. You might be surprised that of the remaining freshwater, almost all of it is below your feet, as ground water. No matter where on Earth you are standing, chances are that, at some depth, the ground below you is saturated with water. Of all the freshwater on Earth, only about 0.3 % is contained in rivers and lakes—yet rivers and lakes are not only the water we are most familiar with, it is also where most of the water we use in our everyday lives exists.


Fresh water is a renewable resource, yet the world's supply of clean, fresh water is steadily decreasing. Water demand already exceeds supply in many parts of the world and as the world population continues to rise, so too does the water demand. Awareness of the global importance of preserving water for ecosystem services has only recently emerged as, during the 20th century, more than half the world’s wetlands have been lost along with their valuable environmental services. Biodiversity-rich freshwater ecosystems are currently declining faster than marine or land ecosystems. The framework for allocating water resources to water users (where such a framework exists) is known as water rights.


For further detail, you can visit Water Distribution.

Sources of Water

  • Surface water

Surface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, evapotranspiration and sub-surface seepage.


  • Under river flow

Throughout the course of the river, the total volume of water transported downstream will often be a combination of the visible free water flow together with a substantial contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain called the hyporheic zone. For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. The hyporheic zone often forms a dynamic interface between surface water and true ground-water receiving water from the ground water when aquifers are fully charged and contributing water to ground-water when ground waters are depleted. This is especially significant in karst areas where pot-holes and underground rivers are common. 

  • Ground water


Ninety-six percent of liquid fresh water can be found underground.Groundwater feeds springs and streams, supports wetlands, helps keep land surfaces stable, and is a critical water resource. About 60% of the water that is taken from the ground is used for farming in arid and semi-arid climates, and between 25% and 40% of the world’s drinking water comes from underground. Hundreds of cities around the world, including half of the very largest, make significant use of groundwater. This water can be especially useful during shortages of surface water.


Groundwater aquifers vary in terms of how much water they hold, their depth, and how quickly they replenish themselves. The variations also depend on specific geological features.
  • Desalination
Desalination is an artificial process by which saline water (generally sea water) is converted to fresh water. The most common desalination processes are distillation and reverse osmosis. Desalination is currently expensive compared to most alternative sources of water, and only a very small fraction of total human use is satisfied by desalination. It is only economically practical for high-valued uses (such as household and industrial uses) in arid areas. The most extensive use is in the Persian Gulf.

  • Frozen water
Several schemes have been proposed to make use of icebergs as a water source, however to date this has only been done for novelty purposes. Glacier runoff is considered to be surface water.



Glaciers store water as snow and ice, releasing varying amounts of water into local streams depending on the season. But many are shrinking as a result of climate change. River basins are a useful “natural unit” for the management of water resources and many of them are shared by more than one country. The largest river basins include the Amazon and Congo Zaire basins. River flows can vary greatly from one season to the next and from one climatic region to another. Because lakes store large amounts of water, they can reduce seasonal differences in how much water flows in rivers and streams.


Sources : WikipediaGreen FactsUSGS

What does an oceanographer do?

An oceanographer studies the ocean




Oceanography covers a wide range of topics, including marine life and ecosystems, ocean circulation, plate tectonics and the geology of the sea floor, and the chemical and physical properties of the ocean.

Just as there are many specialties within the medical field, there are many disciplines within oceanography.


Oceanographers at work
Several thousand marine scientists are busy at work in the United States dealing with a diversity of important issues — from climate change, declining fisheries, and eroding coastlines, to the development of new drugs from marine resources and the invention of new technologies to explore the sea.


Biological oceanographers and marine biologists study plants and animals in the marine environment. They are interested in the numbers of marine organisms and how these organisms develop, relate to one another, adapt to their environment, and interact with it. To accomplish their work, they may use field observations, computer models, or laboratory and field experiments.


Chemical oceanographers and marine chemists study the composition of seawater, its processes and cycles, and the chemical interaction of seawater with the atmosphere and sea floor. Their work may include analysis of seawater components, the effects of pollutants, and the impacts of chemical processes on marine organisms. They may also use chemistry to understand how ocean currents move seawater around the globe and how the ocean affects climate or to identify potentially beneficial ocean resources such as natural products that can be used as medicines.

Geological oceanographers and marine geologists explore the ocean floor and the processes that form its mountains, canyons, and valleys. Through sampling, they look at millions of years of history of sea-floor spreading, plate tectonics, and oceanic circulation and climates. They also examine volcanic processes, mantle circulation, hydrothermal circulation, magma genesis, and crustal formation. The results of their work help us understand the processes that created the ocean basins and the interactions between the ocean and the sea floor.

Physical oceanographers study the physical conditions and physical processes within the ocean such as waves, currents, eddies, gyres and tides; the transport of sand on and off beaches; coastal erosion; and the interactions of the atmosphere and the ocean. They examine deep currents, the ocean-atmosphere relationship that influences weather and climate, the transmission of light and sound through water, and the ocean's interactions with its boundaries at the sea floor and the coast.

All of these fields are intertwined, and thus all oceanographers must have a keen understanding of biology, chemistry, geology, and physics to unravel the mysteries of the world ocean and to understand processes within it.


Source :  http://oceanservice.noaa.gov

May 16, 2011

Civil Engineering Sub-Disciplines (Water)

Civil Engineering Sub-Disciplines (Water)


Introduction to civil engineering in water-engineering   


  • Coastal & Ocean Engineering
Coastal engineering is the study of the processes ongoing at the shoreline and construction within the coastal zone. The field involves aspects of nearshore oceanography, marine geology, and civil engineering, often directed at combating erosion of coasts or providing navigational access. 


Ocean engineers study the oceans to determine the effects of waves, currents, and the salt water environment on ships and other marine vehicles and structures.


  • Hydraulic Engineering
Hydraulic engineering is a branch of civil engineering that studies the flow of fluids, especially water. This branch of engineering studies the water in motion and the interactions between it and the surrounding environment.


Hydraulic engineering is the application of fluid mechanics principles to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water. This area of civil engineering is intimately related to the design of bridges, dams, channels, canals, and levees, and to both sanitary and environmental engineering.


  • Hydrology
Scientific discipline concerned with the waters of the Earth, including their occurrence, distribution, circulation via the hydrologic cycle, and interactions with living things. It also deals with the chemical and physical properties of water in all its phases.



The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface. In terms of the hydrologic cycle, the scope of hydrology may be defined as that portion of the cycle from precipitation to re-evaporation or return to the water of the seas. 


  • Port and Marine Structure
Most marine and offshore construction takes place at substantial distances from shore, and even from other structures, often being out of sight over the horizon.


Thus, construction activities must be essentially self-supporting, able to be manned and operated with a minimum dependency on a shore-based infrastructure.



December 2, 2010

Cremona Method

The Cremona diagram is a graphical method used in statics of trusses to determine the forces in members (graphic statics). The method was created by the Italian mathematician Luigi Cremona.

In the Cremona method, first the external forces and reactions are drawn (to scale) forming a vertical line in the lower right side of the picture. This is the sum of all the force vectors and is equal to zero as there is mechanical equilibrium.

Since the equilibrium holds for the external forces on the entire truss construction, it also holds for the internal forces acting on each joint. For a joint to be at rest the sum of the forces on a joint must also be equal to zero. Starting at joint Aorda, the internal forces can be found by drawing lines in the Cremona diagram representing the forces in the members 1 and 4, going clockwise; VA (going up) load at A (going down), force in member 1 (going down/left), member 4 (going up/right) and closing with VA. As the force in member 1 is towards the joint, the member is under compression, the force in member 4 is away from the joint so the member 4 is under tension. The length of the lines for members 1 and 4 in the diagram, multiplied with the chosen scale factor is the magnitude of the force in members 1 and 4.

Now, in the same way the forces in members 2 and 6 can be found for joint C; force in member 1 (going up/right), force in C going down, force in 2 (going down/left), force in 6 (going up/left) and closing with the force in member 1.

The same steps can be taken for joints D, H and E resulting in the complete Cremona diagram where the internal forces in all members are known.

In a next phase the forces caused by wind must be considered. Wind will cause pressure on the upwind side of a roof (and truss) and suction on the downwind side. This will translate to asymmetrical loads but the Cremona method is the same. Wind force may introduce larger forces in the individual truss members than the static vertical loads.
The Cremona diagram is a graphical method used in statics of trusses to determine the forces in members (graphic statics). The method was created by the Italian mathematician Luigi Cremona.



source : Wikipedia