How Much Water is Flowing Down That River?

How Much Water is Flowing Down That River?

By Oscar Flite, Ph.D.

Riverwalk Ampitheater The Savannah River has been at the highest level over the past year than it has been in many years.  But can you visualize how much water is flowing down the river at a time?  Our CEO / Senior Scientist, Dr. Oscar Flite, explains just how much water flows down the river at a time using our own homes and a view from a boat dock. Measurements of how much water is flowing in a river, or river discharge, is quantified in units of cubic feet per second. Well, what is that?  To answer that, we have to think about two things, a volume component (cubic feet) and a time component (seconds). For the volume component, we can visualize a standard floor tile which is often 12 inches on each side, or 1 foot x 1 foot, or one square foot (1ft2).  If you built a box around that floor tile using the same sized floor tiles, you would have four sides of the box that were each 1ft high x 1 ft wide (1ft2), and a lid that was the same as the first floor tile, 1ft2.  The box would then be 1ft long x 1ft wide x 1 ft tall and would have a volume of 1 cubic foot (1ft3).  The amount (volume) of water in streams and rivers is measured relative to the size of that box, a cubic foot. For the time component, we can visualize ourselves sitting on a dock on the river.  The time component of the discharge measurement is how much water passes a stationary location each second – in this case, the dock.  That stationary point is actually an imaginary thin pane of glass that crosses the entire river along the water surface and extends to the bottom from the water surface, straight down to the bottom of the river at each point along the glass pane. The discharge in a river is then equivalent to how many of those 1 cubic foot boxes pass through the glass pane each second, or cubic feet per second (cfs or ft3/s). If we extend the floor tile concept, the ceiling height in most homes is 8 feet high.  If a particular room is 10 feet long x 10 feet wide x 8 feet high, the room is then 800 cubic feet (ft3).  The average square footage of a home in the US in 2010 was just under 2400 ft2.  If the entire house had 8ft ceilings, then the total volume of that 2400 ft2 house would be 19,200 ft3. The daily average flow for the Savannah River at the Augusta USGS gauge since 1956 is approximately 7000 ft3/s. That is equivalent to a home with 875 ft2 of living space and 8ft ceilings floating past the dock each second. The river is currently flowing at 30,000 ft3/s.  That is equivalent to a home with 3,750 ft2 of living space.  Last year’s flood event had a maximum flow of 40,000 ft3/s, or a home equal to 5,000 ft2.  Since Thurmond Dam was constructed, the highest daily average flow was nearly 85,000 ft3/s, which is equivalent to a home with 10,625 ft2 of living space.  Some of the highest measured flows for the river, prior to Thurmond Dam installation, exceeded 100,000 ft3/s, which is equivalent to a 12,500 ft2 home floating down the river every second.  For interest, the daily average flow of the largest river in the world, the Amazon River, is over 6,000,000 ft3/s, or a building with 8 ft high walls and a square footage of 750,000 or 17.2 acres!