Environmental Minute: Fena watershed a natural resource for water
The Fena watershed on Guam collects and funnels water into the Fena reservoir, providing drinking water for U.S. Naval Base Guam and a number of Guam’s southern village residents.
According to the U.S. Environmental Protection Agency, a watershed is a landscape feature where all of the water that is under it or drains off of it is deposited into the same place.
Naval Facilities Engineering Command (NAVFAC) Marianas Natural Resources Specialist Paul Wenninger said the condition of the watershed is very important to the quality and quantity of water it dispenses.
“A forested watershed ‘filters’ the rain and reduces the amount of sediment that runs off, enhancing the quality ‘cleanliness’ of the water,” he said. “A forested watershed also soaks up the rain, holding it for longer periods of time like a sponge and maintains a more constant, even follow into the drainage.”
According to Wenninger, when a well-forested watershed holds more water, it balances periods of low rain by slowly releasing the water, keeping the flow continuous.
“When a watershed lacks trees and, or is impacted by rooting…over grazing by deer, pigs and carabao (ka-rah-BAO), and fire, the soil is exposed and sediment runs off at a greater rate, polluting the reservoir and our reefs,” he said.
Wenninger added that when a watershed is comprised mostly of man-made surfaces such as roads and buildings, the water quality also drops.
“The water that flows out is generally higher in pollutants and of low quality,” he said. “Flooding is more common in areas like this (because) the water does not soak in, just runs off hard surfaces all at once.”
Flooding, according to Wenninger can prove a substantial problem for water reservoirs.
“During extreme rain events, the water filtration system cannot handle the sediment load and has to shut down,” he said. “Also, this sediment load fills in the reservoir, reducing its lifespan and the volume of water it can hold.”
To protect the watershed, there are restrictions placed on cutting trees in the area, silt fencing to filter sediment run-off, grass planting after disturbance and tree planting after construction.