Overland flow, including flow through litter, shallow ground
water flow from undisturbed areas, and flow in ephemeral streams, may be
diverted from disturbed areas by temporary or permanent diversions, if required
or approved by the commission. The following requirements must be met for
diversions and collection drains used to transport water into treatment
facilities and for diversions of overland and shallow ground water flow and
ephemeral streams:
1. Temporary
diversions must be constructed to pass safely the peak runoff from a ten-year,
twenty-four-hour precipitation event, or a larger event as specified by the
commission. A two-year recurrence interval may be used for designing collection
drains used to transport water into treatment facilities if:
a. The diversion will be used for less than
one year; or
b. The commission
determines that the design integrity of the water management plan is maintained
during a ten-year, twenty-four-hour design storm.
2. Permanent diversions must be constructed
to pass safely the peak runoff from a ten-year, twenty-four-hour precipitation
event; however, where necessary to protect fills and property and to avoid
danger to public health and safety, permanent diversions must be constructed to
pass safely the peak runoff from a one-hundred year, twenty-four-hour
precipitation event, or a larger event as specified by the commission.
Permanent diversions must be constructed with gently sloping banks stabilized
by vegetation. Asphalt, concrete, or other similar linings may be used only
when approved by the commission to prevent seepage or to provide stability.
3. Diversions must be designed,
constructed, and maintained to prevent additional contributions of suspended
solids to streamflow and to runoff outside the permit area to the extent
possible using the best technology currently available. Appropriate sediment
control measures for these diversions may include maintenance of appropriate
gradients, channel lining, revegetation, roughness structures, and detention
basins.
4. No diversion shall be
located to increase the potential for landslides. No diversion shall be
constructed on existing landslides, unless approved by the commission.
5. When no longer needed, each
temporary diversion must be removed and the affected land reclaimed. The
operator shall reestablish ephemeral stream channels to a longitudinal profile
and cross section that approximate premining channel characteristics.
6. Diversion design must
incorporate the following:
a. Design channel
lining using standard engineering practices to pass safely the design
velocities.
b. Freeboard must be
no less than three-tenths of a foot [9.14 centimeters]. Design freeboard may be
increased where the area protected is a critical area as determined by the
commission.
c. Protection for
transition of flows and for critical areas such as swales and curves.
d. Install energy dissipators when
necessary at discharge points, where diversions intersect with natural streams
and exit velocity of the diversion ditch flow is greater than that of the
receiving stream.
e. Dispose of
excess excavated material not necessary for diversion channel geometry or
channel regrading according to chapter 69-05.2-18.
f. Handle suitable plant growth material in
compliance with 69-05.2-15.
7. Diversions may not be constructed or
operated to divert water into underground mines or an abandoned surface mine
without commission approval under section
69-05.2-16-18.