Drainage is an important aspect of any quarry, and has to be
considered both during its working life and as part of the
restoration proposals. Water may enter quarries from rainfall
and run-off (known as 'surface water') or by seepage out
of rock faces and through the quarry floor (known as 'ground
water'). Without proper control water can be erosive, forming
gullies and hollows, and can undermine the stability of quarry
faces or other slopes and banks.
It can also lead to flooding of the quarry
floor. In some situations the layout and design of quarry
operations are dictated by the need for drainage control
and this may override other planning considerations.
To avoid localised increased in water pressures within quarry
slopes, control and diversion measures are often necessary
and these may include:
- Diversion of permanent water courses or surface run off
outside the rim of the quarry excavation.
- Diversion of surface run-off on benches using
lined ditches. Wherever possible these should run along
the bench, not across it.
- Allowing for drainage gradients on benches and the quarry
floor. On benches these gradients should dip towards a
lined ditch at the base of the next higher quarry face,
and not towards the edge where the water may cause erosion.
- Sealing major cracks with clay to avoid infiltration
behind a quarry face.
- Using drainage holes to relieve pressure build up. These
are drains that run from behind a quarry face out onto
a bench, and should ideally link up with a lined ditch
running along the length of the bench to avoid ponding.
All drainage measures should be periodically inspected to ensure
free flow. Hence, they should be located where access is safe.
If the after use of a restored quarry includes buildings, it
is essential that the local surface and groundwater flows are
clearly understood so that water levels within the quarry will
not rise to a level where they flood the buildings.
quarry used for water sports.
Many quarries require pumping during their operation and they
are unlikely to remain dry without continued pumping once quarrying
ceases. Any after-use needs to reflect this.
It is important to realise that many structures, including screening
banks and lagoons, that are associated with quarries require
continued drainage. Drainage within screening banks, or other
tips, is particularly important if landslips are to be avoided,
especially if the tip is located on a hillside. This drainage
is often achieved by using layers (or blankets) of granular
material that allow for controlled seepage of water. These
drainage blankets must be kept clear and not blocked with layers
of soil or clay.
Various plants, such as willows, can be helpful in securing
drainage in wet areas and should not be removed without replacement
arrangements being made.
lake in the floor of a former quarry.