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…
REFERENCES:
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