Tuesday, March 14, 2006

Underground water and cemented lands

Underground, fresh water, is one of nature's best gifts to humanity.
All that man has to do is find a place where this water comes out naturally -- through a spring, or dig a hole undergound, put steel tubes into it, and pump the water up, manually or mechanically.

As human population expands in all countries and continents of the world, more water pumps are constructed as water from rivers and lakes via water utilities become less sufficient for the expanding population especially in urban areas. This continued extraction of underground water decreases the water table below. This process can be mitigated or controlled if rain waters are not hindered to penetrate the soil and rocks below, later on reaching the water table underground.

As civilizations improve and economic activities expand, more and more lands are being cemented or covered by bricks and cobblestones. Examples are roads and highways, parking lots, sidewalks, wide and sprawling malls. Here, rain waters fall on cement and hard surfaces, heading towards the drainage, into creeks and rivers, and ultimately into the seas and oceans. Hence, a big portion of rainfalls do not penetrate the soil and rocks anymore, and underground water that experience heavy withrawal through strong water pumps, are not replenished.

Among the long-term negative impact of this situation are as follows. One is salt water intrusion of water tables in areas near seas and oceans. As more undergound water is pumped out, bigger vacuum is created, which allows salt water to flow in trickles. Salted water is now experienced in a number of cities and communities that rely on underground water for their household needs.

Two, the geological foundation of a city or community becomes less stable. As more vacuum is created underground due to decreasing water table, moderate to strong earthquakes can shake the soil and rock foundation of structures built above them. Not that buildings will collapse -- unless there is intensity 7 or stronger earthquakes, but buildings and other structures will experience mild cracks in its floors and walls even in mild earthquakes. Sometimes, "sinking" structures have been observed.

One solution to these problems is to have more open spaces and non-cemented land in cities and communities where large underground water pumping is practiced. Many people, especially environmentalists will not like this, but more golf courses and their grass-and-trees surfaces are actually helping the underground water replenish the sinking water table. Also, old and cemented but dilapidated parking lots should not be cemented again. Better use crushed stones to prevent the surface from getting muddy during the rainy season, as crushed stones allow spaces for rainwater to seep in below the ground.

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