WEBVTT

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^- [Voiceover] The most well-known forms of outflows

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^from our reservoirs are the normal releases from the dams

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^that send water downstream.

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^But there's another form of outflow

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^that claims substantial volumes of water

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^during the summer months.

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^We've written about it before on this blog,

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^but this video is an attempt to capture visually

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^the significance of this invisible outflow.

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^Evaporation and transpiration

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^account for no small amount of water loss,

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^especially in July, August, and September.

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^Now we are familiar with the process of evaporation.

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^In the Savannah River Basin alone,

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^evaporation accounts for billions

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^of gallons of water per day,

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^even in the winter.

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^Evaporation over the three reservoirs

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^can be as much as a staggering 1200 cubic feet

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^of water for every second.

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^Now that's a substantial part of overall outflows.

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^Transpiration, on the other hand,

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^may not be as familiar to us.

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^Simply put, it is water absorbed and evaporated

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^by trees and vegetation.

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^These trees and vegetation absorb water up from the soil,

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^and then release water vapor

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^through small pores, called stoma.

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^To illustrate this,

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^we'll tie a plastic bag around this tree branch,

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^and watch the water collect on the inside of the bag

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^over the course of the day.

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^The amount of water transpired

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^depends on the size and the number of plants and trees.

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^For example, a large oak tree can transpire

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^more than 40,000 gallons of water per year.

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^Okay, so it's been about 24 hours,

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^and here we are back at our sample tree.

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^You can see how fogged up this bag is

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^and how the water droplets

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^have gathered near the bottom.

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^The tree basically sweated out this water

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^that it absorbed up from the soil.

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^Just as we drink water to maintain our bodies,

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^and perspire when it's hot,

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^the vegetation around us

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^transpires water in a comparable biological process.

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^Evaporation and transpiration is something you

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^may not have considered when you think

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^about the outflows to our lakes.

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^But it is a real, contributing factor

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^to the reservoir levels,

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^especially in the summer.

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(upbeat music)