The allowable leakage rate for a principal spillway pipe
installation in a dam shall not exceed 1,000 gallons per inch diameter of pipe
per mile of pipe per day. The applicant shall use one of the following test
methods in determining whether the allowable leakage rate has been exceeded:
(a) The applicant shall use the
following test method procedure for a drop inlet
structure if the starting and
ending elevation of the water is within the vertical drop
structure and above
the top of the barrel:
(1) Calculate the
allowable leakage rate in gallons per minute for the pipe being tested based on
the following formula:
The allowable leakage rate in gallons per minute = 0.000132 * d
* l where:
d = diameter of the tested pipe in inches
l = length of the tested pipe in feet
If the allowable leakage rate in gallons per minute is
determined to be less than one, then it shall be assumed for the purposes of
the test that the allowable leakage rate in gallons per minute is one.
(2) Conduct the test for 15
minutes.
(3) If the allowable
leakage rate is one gallon per minute, the applicant may use the following
table to determine the allowable drop in the elevation of the water in the
riser.
Nominal diameter of riser (inches) Allowable drop (feet)
18 1.13
20 0.83
24 0.64
30 0.41
36 0.28
(4) If the measured drop in the riser exceeds
the corresponding allowable drop in paragraph (a)(1) above, the allowable
leakage rate has been exceeded, which shall not be acceptable. If the measured
drop in the riser is less than or equal to the corresponding allowable drop in
paragraph (a)(1) above, the allowable leakage rate has not been exceeded and
shall be acceptable.
(b) The applicant shall use the following
test method procedure for all other types of installations, including canopy
inlets:
(1) If filling the pipe with water up
to an elevation of 10 feet above the outlet puts water within the vertical
riser below the top of the barrel, the elevation shall be reduced below the
bottom of the vertical riser before the test begins.
(2) The allowable drop in elevation is a
function of the allowable leakage rate, test duration, and the diameter and
slope of the pipe. The allowable drop in the pipe in feet shall be calculated
by use of the following formula:
allowable rate (gallons per minute) * test duration (minutes) *
slope (%) [diameter (inches)]2 * 4.08
(3) The minimum test duration shall be 15
minutes. If the above formula results in an allowable drop of less than 0.1
foot in 15 minutes, the test duration shall be extended so that the allowable
drop is greater than 0.1 feet.
(4)
The water surface elevation drop shall be measured by means of a clear plastic
tube installed in the plug at the downstream end of the principal spillway
pipe. Any other means of measuring the drop in elevation shall be approved by
the chief engineer in advance of the test.
(5) If the measured drop is greater than the
allowable drop as calculated in paragraph (b)(2), the allowable leakage rate
has been exceeded, which shall not be acceptable. If the allowable drop is less
than or equal to the allowable drop as calculated in paragraph (b)(2), the
allowable leakage rate has not been exceeded, which shall be acceptable.
