Current through Register Vol. 43, No. 39, September 26, 2024
(a) Each conduit
through any portion of a dam below the elevation of the permanent pool shall be
constructed to protect the dam from seepage along the conduit by means of
cutoff collars or a drainage diaphragm. Cutoff collars may be used only on
hazard class A dams that are class sizes one and two.
(b) Each drainage diaphragm shall meet all of
the following design criteria:
(1) Be
installed so that the largest face is perpendicular to the conduit;
(2) be sized as follows:
(A) If the conduit is circular, the diaphragm
shall extend a minimum of two feet or three times the outside diameter of the
conduit, whichever is greater, from the outside surface of the conduit
horizontally and vertically upward. The diaphragm shall extend vertically
downward a minimum of two feet from the outside surface of the conduit;
(B) if the conduit is rectangular,
the diaphragm shall extend minimum of two feet or three times the vertical
dimension of the conduit, whichever is greater, from the outside surface of the
conduit horizontally and vertically upward. The diaphragm shall extend
vertically downward a minimum of two feet from the outside surface of the
conduit;
(C) a drainage diaphragm
shall not be required to penetrate unweathered bedrock; and
(D) the diaphragm shall not be required to
extend vertically upward to an elevation higher than the crest of the auxiliary
spillway;
(3) have a
dimension parallel to the conduit that is at least three feet thick;
(4) except as specified in subsection (d), be
located downstream of the centerline of the dam, downstream of the cutoff
trench, and far enough upstream of the toe so that there is a minimum of two
feet of fill, measured perpendicular to the surface of the embankment, over the
top of the diaphragm after settlement of the embankment; and
(5) have an outlet that provides positive
drainage of the diaphragm to the stilling basin or other point below the
downstream toe of the dam. The flow line of the outlet shall be no lower than
one-half foot above the elevation of the outlet of the stilling basin.
(c) Except as specified
in subsection (d), each cutoff collar shall meet all of the following design
criteria:
(1) Be constructed of the same or
similar material as that of the conduit;
(2) be attached to the conduit with a
watertight seal;
(3) be of
sufficient size and number to increase the length of the seepage path by at
least 15 percent;
(4) be spaced at
intervals of at least twice the vertical dimension of the largest collar being
used;
(5) be located along the
conduit in that portion of the dam that will be saturated;
(6) project a minimum of two feet beyond the
outside wall of the conduit; and
(7) be located no closer than two feet from
any conduit joint.
(d)
If cutoff collars or a drainage diaphragm is located in a zoned fill, the
location shall be justified in the design report and established in accordance
with sound engineering principles and commonly accepted engineering practices.
(e) If another drain included in
the design meets the requirements for a diaphragm in subsection (b), that other
drain may be considered to be the diaphragm required by subsection (a).
(f) If the applicant desires to
use any other type of seepage control, the applicant shall demonstrate to the
chief engineer that the proposed type of seepage control protects the dam from
seepage along the conduit and meets the requirements of sound engineering
principles and commonly accepted engineering practices.
