Watersheds and “ridge to reef”

A watershed is an area where rainwater drains down through rivers and streams, to groundwater, lakes, bays, wetlands, and/or oceans. Also known as basins, watersheds can be as small as a few hectares or as large as hundreds of square kilometers.

Watersheds are important because they are a source of fresh water that we use for drinking, chores, food production, industry, and recreation!

“Ridge to reef”

When water travels from the tops of mountains to the lakes or the sea, this water can be said to be traveling from “ridge to reef”.

Imagine a basin, palanggana, or large bowl. A drop of water near the edge of the bowl eventually falls to the bottom. The edge is the ridge. At the lowest point of the bowl is a small pool of water where the water drops are collected. This pool is the ocean where reefs can be found.

You have seen water running down your street and into drains or canals. Gravity is pulling water down as it travels toward the lowest points of your neighborhood. This is what has happened for many years from our mountain tops, through our rivers, and into our lakes and oceans!

Forests and watersheds

Now imagine the edge of your bowl full of bumps and grooves. This slows down the amount of water going down. Forests are almost like these bumps and grooves, in that they help control the amount of water that drains down a watershed.

Not only this, forests also stabilize soil and reduce erosion, regulate water flow to mitigate floods and droughts, and purify water! Forests also are home to a wide variety of wildlife, and provide store carbon from the atmosphere which helps control our climate. These are all called ecosystem services.

Forests and watersheds are a powerful natural combination that helps all life.

A shortlist of watershed ecosystem services from ridge to reef:

  1. Forests absorb and hold water, reducing run off and preventing landslides.
  2. Forests filter pollutants from rain and water.
  3. Forests absorb carbon, mitigating the affects of climate change.
  4. Water is slowly released through springs, streams, and rivers.
  5. Rivers deliver water to farmlands, industries, & business.
  6. Water flows to treatment plants and is distributed to you.
  7. Your neighborhood thrives thanks to the availability of food and water.
  8. Where fresh water meets sea water, mangroves, fish, and waterbirds thrive, supporting the local economy and recreation.
  9. Mangroves serve as our natural wall against storm surges and typhoons.
  10. Seagrasses absorb carbon, and are home to dugong and other wildlife.
  11. Healthy coral reefs provide communities with food and livelihood while protecting them from strong waves.

Watersheds in the Philippines

All land is part of a watershed. Even deserts that receive a small amount of rain per year shed water (in smaller amounts).

But there is no better visual example of a watershed from ridge to reef, than the mountains and coastlines of the Philippine islands.

Today, these watersheds provide 126 billion cubic meters (BCM) of water for human use every year! This is the water you use to take a bath, enjoy in drinks, and is used to grow your food. If properly managed and protected, these watersheds could supply 146 billion cubic meters (BCM) of water for human use every year.

Unfortunately 267 watersheds in the Philippines are in need of immediate rehabilitation. Only 146 watersheds are proclaimed watershed forest reserves.

Meanwhile, the DENR River Basin Control Office lists 142 Critical Watersheds, or degrading watersheds that already provide Filipinos with water for food through irrigation, and electricity for our homes through hydropower.

Watershed trivia

  • The largest proclaimed watershed is Lake Lanao Watershed Reservation in Mindanao. It is 180,460 hectares, or three (3) Metro Manilas!
  • Metro Manila residents are estimated to consume 42 liters of water per day. This includes bathing, drinking, toilet flushing, house cleaning, dish washing, and food preparation.
  • 97%–98% of the water used in Metro Manila comes from Angat Dam.
  • Instead of building more dams in forest watersheds, conserving forests in existing watersheds like Angat and La Mesa is not only more cost effective but will ensure continued water supply for Metro Manila and nearby provinces for years to come.
  • Protection & rehabilitation is known as an affordable, practical, and preemptive solution in ensuring sustained water supply. Using native tree species ensures the persistence of local biodiversity to sustain ecological services effectively.

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