Page 80 - 00 Volume 5 The Mine

its timing in relation to the removal of With the extraction of coal from the
coal underground will depend on the
mining methods and recovery factors
applied to different sections of the
coalfield. New land use development
over the coal to be removed cannot be
undertaken as the risk of subsidence
would preclude the maximum
extraction of the underlying coal.
Catchment Management
Prior to mining, the study area as the original into the Waikato River.
Lake Kimihia, performed a necessary function
ponding the stormwater for the whole Kimihia
catchment. With the reduction in area of the lake
and decrease in water holding capacity, the two
perimeter drains constructed around the edge of
the original lake drain the catchment quickly
during times of very heavy rainfall. This results in
the ponding of floodwater on farmland between
Kimihia outlet and the Waikato River. When the
Waikato River is at high flow, the flood gates in
the stopbanks prevent water from the river
flooding the low lying farmland.
Huntly East Mine, subsidence will occur at the
surface. The degree of subsidence and area
affected will depend on the thickness of coal
removed, and what coal is left in the ground as
support. Maximum recovery would cause the
surface to subside below the present water table
and create another shallow lake.
This new ponding area would go some
way to replacing the function originally
performed by the whole of the study area of
holding stormwater run-off prior to discharge
The existing lake and wetlands will continue
to act as a ponding area for flood waters, but the
total area cannot be considered for ponding until
the cessation of underground mining and the
opencast is flooded.
Post Mining Constraints
On completion of the mining at the Huntly
East Mine, it will no longer be necessary to
continue pumping water out of the opencast.
With the impoundment of surface waters and
seepage in the opencast, a new lake will be