Why Use Batgates as a Mine Closure Method?

Why do you want to use a bat gate as an abandoned mine closure method?

• This mine has “significant” bat use by a high priority T&E bat species, or a maternity colony, or as a hibernaculum.

• This mine has other important bat use as a night roost or day roost.

• To preserve potential bat habitat without knowing the level or type of bat use.

• To preserve the natural ventilation system for interconnected workings which have significant or important bat use.

• This is the easiest closure to install due to the remote location and difficult access.

• I want a closure to secure the opening and allow visitors to look inside.

What are the physical constraints and site conditions for installing a bat gate?

The rock at the mine opening must be durable enough to support drilling holes to insert anchor pins in the ribs (sides of the opening) and roof. Durable enough means the rock is not soft, easily breaking off, friable or highly fractured. The rock in the ribs and roof must be competent enough to support pinned anchors for the metal gate. It is helpful if the floor rock is also competent, however, a concrete footer can sometimes be used as a floor anchor reinforcement.

It must be possible to haul the necessary supplies to the site. Delivery methods could include by vehicle, 4-wheel drive, ATV, pack horses, foot traffic or helicopter. Supplies would include all the steel materials to construct the gate (angle iron, round steel bars, manganal steel, etc.), a portable gas-powered welder, welding rods and supplies, a rock drill (gas powered or powered via the welder-generator) and drilling supplies, a portable fan or leaf-blower, fire suppression equipment, and safety equipment for the work crew.

The mine opening must be stable enough to ensure the crew installing the gate can safely work under the brow (roof) of the opening as determined by a qualified mine safety person.

What are the timing constraints for installing a bat gate?

The bat gate should not be installed when bats are actively using the mine or connected mine workings. The physical presence of workers, noise, dust, or welding fumes could disrupt the bats. This would be extremely detrimental to a maternity colony or a hibernaculum. If the mine workings are not being used as a hibernaculum, then the best time for installation is during the winter or cold season for this location.

The bat gate should not be installed during high fire danger since welding or running a gas-powered generator could create sparks and ignite a fire. Drilling in hard rock may create sparks which could ignite a fire.

Are there size limitations for a bat gate?

Small bat gates are not very functional as a flyway for bats, but a small bat gate may help preserve the natural ventilation into interconnected underground mine workings in support of bat use. Small would be less than four (4) feet in diameter if round, or less than four (4) feet in width or height. The minimum size depends on several factors including site conditions, underground workings, and the purpose of this bat gate. Having a very small bat gate would make it difficult for bats to negotiate the opening which would also make them easy prey for a predator hanging around the opening. Installing a small gate may be important if the opening connects to underground workings with bat use and one or more other bat-compatible gates installed.

On the other side of the scale, the rock surrounding the mine opening may not support the weight of a very large gate. Also, the bat gate itself may not be structurally strong enough to support the weight of all that steel and endure vandalism attempts. A very large bat gate would require very many anchor pins to support the structure.

What is this “flyway” thing and why should I care?

The flyway is the space bats need to easily fly through the gate. The minimum space for this flyway is typically four (4) inches high by 24-inches wide. A space that is larger in height or wider is acceptable for bats, however, a larger flyway makes the gate easier to vandalize or easier to crawl through.

What is a cupola? Why not use a cupola instead of a bat gate?

A cupola is a dome shaped or box shaped structure that was initially used for ventilation through the rooftop of buildings. A cupola for bats would be a box shaped grid of steel bars or plates which would provide a flyway for bats. Cupolas would be used as a bat-compatible closure over a mine shaft. The box shape allows bats to circle up into the cupola and then fly out through the flyway. Think of the bat flight path as a corkscrew up into the cupola and then straight (horizontal) out the side. A cupola constructed of angle iron or steel bars can be very heavy and may require a substantial support system of steel beams or a reinforced concrete foundation.

It may be difficult to construct a cupola at a remote location with limited vehicle access. A four (4) foot by four (4) foot cupola would require four (4) times the steel of a four (4) foot by four (4) foot bat gate, and the cupola may weigh nearly four (4) times as much as the gate.

How long does a bat gate last?

The longevity depends on several factors. A bat gate installed in competent rock that is not exposed to rain, snow or ground water will last much longer because the metal will not rust or corrode as easily. A bat gate that is highly visible and easily accessible may not last long due to vandalism such as cutting the anchor pins, cutting the metal bars, or digging around the anchor points. Bat gates located in competent rock without any vandalism have been in place for 15-20 years in some locations.

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