Wednesday, July 2, 2014

Watershed


WATERSHED
by Antonio C. Antonio
July 17, 2013

There is a perception that Metro Manila is a watershed area.  This mindset could have been the result of regular yearly flooding that is now part of the landscape… or seascape?  Let us understand better what a watershed is…

WHAT IS A WATERSHED?  The term watershed is often used in discussions about water quality or flood prevention, but most people do not really understand what a watershed is.  The definition of a watershed is based on a concept with which everyone is familiar:  “Water runs downhill.”  A watershed is a land area whose runoff drains into any stream, river, lake, and ocean.  Watershed boundary is the divide separating one drainage area from another.  Watersheds may be small as the portion of a yard draining into a mud puddle or as large as the Mississippi River Basin, which drains 1.2 million square miles.  Terms like catchment or drainage basin are also used to refer to watersheds.

WHERE DO WE FIND WATERSHEDS?  All land area is part of a watershed.  Regardless of whether we live in Florida or any other state or country, we all live in a watershed.  You can find the watershed in which you live by browsing a map and looking for the stream closest to you.  If you trace the stream upward to its beginning you will reach the headwaters, whereas if you trace it downward you will eventually reach a larger stream or river, a lake, or the Atlantic Ocean or Gulf of Mexico.

HOW DOES A WATERSHED FUNCTION?  As water flows downhill in small to progressively larger streams and rivers, it moves over land and provides water for urban, agricultural, and environmental needs.  The watershed community is made up of everyone who lives there plus all other animal and plant life.  The community of humans, plants, and animals depends on the watershed and influence it in some way.  Flowing water carries organic debris and dissolved organic matter that provide food and shelter for aquatic life.  At the same time, water may also carry pollutants like motor oil, fertilizers, and pesticides.  Numerous activities in a watershed have the potential to degrade water quality.  There is no pure water in nature, all water is polluted to some extent.  Even in pristine watersheds where water quality is not affected by humans, natural pollutant sources are abundant.  These include sediment from stream bank erosions, bacteria and nutrients from wildlife, and chemicals deposited by rainfall.

WHAT ARE THE FUNCTIONS OF A WATERSHED?  A watershed has five important functions:
           a)    It collects water from rainfall;
           b)    It stores water of various amounts and for different times;
           c)    It releases water as runoff;
           d)    It provides diverse sites for chemical reactions to take place; and,
           e)    It provides habitat for flora and fauna.

The first three functions are physical in nature and are termed hydrologic functions.  The last two are the ecological functions.  Human activities affect all the functions of a watershed.

To support the argument that Metro Manila is actually a coastal area, please allow me to mention that I used to work for a oil and gas exploration management company which conducted several exploration projects in Central Luzon.  The company’s resident geologist, in our casual conversations, used to say: (1) that in the past, Manila Bay, Laguna de Bay and Lingayen Gulf used to be interconnected and people used to travel from Laguna to Pangasinan using wooden boats; (2) that the Zambales mountain range used to be an island separate from Luzon; (3) that Mt. Arayat used to be an island-volcano (similar to Taal Volcano); (4)  that the Central Luzon provinces of Bulacan, Pampanga, Tarlac, Nueva Ecija and the northern part of Metro Manila were all submerged in sea water; and, (5) that the land mass in Central Luzon was created by volcanic eruptions principally by Mt. Pinatubo and Mt. Arayat.  These information are consistent with the fact that most of Metro Manila is coastal and not a watershed.

Just my little thoughts…

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