Measuring the Potential
Stream levels change through the seasons,
so it is important to measure FLOW at various times of the year.
If this is not possible, attempt to determine various annual
flows by discussing the stream with a neighbor, or finding
geological survey flow data for your stream or a nearby larger
stream. Also keep in mind that fish, birds, plants and
other living things rely on your stream for survival.
Especially during low water seasons, avoid using all the
water for your hydro system.
FLOW is typically expressed as some volume
of water per
second or minute. Common examples are gallons or liters
per second (or minute), and cubic feet or cubic meters per
second (or minute): Each can be easily converted to
another, as follows:
1 cubic foot = 7.481 gallons
1 cubic meter = 35.31 cubic feet
1 cubic meter = 1,000 liters
There are three popular methods for
measuring FLOW: using a Container, Float, or Weir. Each will
be described in detail below. Once again, accuracy is
important to ensure correct system design and optimum power
The Container Fill method works only for
very small systems.
Build a temporary dam that forces all the
water to flow through a single outlet pipe, Using a bucket or
larger container of a known volume, use a stopwatch to time how
long it takes to fill the container. Then, divide the
container size by the number of seconds.
Container = 5 gallon paint bucket
Time to fill = 8 seconds
5 gallons / 8 seconds = 0.625
gallons per second (gps)
To convert into Cubic Feet per Second (cfs):
7.481 gallons per second = 1 cubic
foot per second, so
0.625 gps / 7.481 = 0.0835 cubic
feet per second (cfs).
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