Cave Gating Criteria
Rationale
Poor cave gates can harm wildlife and cave resources. There are many reasons for not gating a cave, and cave gating is not automatically recommended by the Missouri Department of Conservation (MDC). Cave gating is a technical subject that requires knowledge and experience; for example, it cannot be done properly by a general welding contractor without providing specifications, a design and on-site supervision by an experienced cave gater. Knowledge of the cave's ecology, especially bats, is necessary before a gate is considered. MDC assists cave owners in cave gating, but first a decision guide must be followed (below).
Cave Gate Styles
Depending on the needs of the cave, the type of entrance, bats and other wildlife, the design could specify a full gate, half gate or tube gate (particularly for maternal gray bats), cupola or cage gate, enclosure, fence or no gate at all. For example, some bat caves that may need a gate for protection are not feasible to gate for certain physical reasons. Many caves that are feasible to gate do not need to be gated because other modes of protection may work better.
Proper design for a "full" bat gate by ACCA's Roy Powers. From BCI's Bats and Mines.
Who is Qualified?
Currently three MDC personnel are trained in the latest cave gating methods: Bill Elliott, Brian Loges and Ben Groner. In addition, Rick Clawson, MDC's bat biologist, is experienced in bat ecology and gating questions. I have many years of experience in cave ecology, cave management and cave gating. The three of us were trained in June 2001 at a cave-gating seminar co-sponsored by MDC and other agencies. At the seminar 15 students learned how to properly design and construct a special bat gate on McDowell Cave in Lake of the Ozarks State Park.
It is strongly recommended that MDC personnel coordinate with me as MDC's cave biologist. Then we can discuss the gating proposal with Ben Groner, our engineer in Design & Development, who may act as "point man" on cave gate designs. If he is busy, then we should seek a qualified expert in this field.
Two leading experts are Roy Powers, Jr., of Duffield, Va., and Jim Nieland, U.S. Forest Service, Mount St. Helens, Wash. Mr. Powers is an engineer and cave ecologist who has designed, built, or supervised, more than 600 cave gates. Roy is the leading innovator of bat-friendly cave and mine gates, sometimes called "air-flow bat gates," and is president of the American Cave Conservation Association (ACCA). ACCA is a nonprofit organization based in the city of Horse Cave, Ky., with expertise in cave conservation, restoration, gating and education. ACCA's designs were adopted by Bat Conservation International (BCI) and many government agencies, and have become the industry standard, as specified in the publication "Bats and Mines" by BCI (see Recommended Reading below). Mr. Nieland is a cave specialist and an ACCA director who builds cave gates and teaches cave gating.
ACCA and BCI, in cooperation with the U.S. Fish & Wildlife Service, U.S. Forest Service and many agencies, have taught numerous, regional, cave-gating workshops to demonstrate the proper decision-making process, design and construction techniques for ecologically sound cave gates. These gates have resulted in significant protection and increases of colonies of endangered bats, such as grays, Indianas and others. Protection of other irreplaceable cave resources is another benefit of properly built gates. Major clients include U.S. Army Corps of Engineers, Bureau of Land Management, U.S. Forest Service, National Park Service and numerous state and local agencies.
Cave gaters within MDC should also communicate with the caving and conservation communities, who want to know which caves are proposed for gating and why, especially on public land. Three members of the Missouri Caves & Karst Conservancy were trained at the Missouri cave-gating seminar under scholarships granted by MDC's Natural History Division. Those three may be available to lead cave-gating projects or muster volunteers from the cave conservation community. Some people will sometimes oppose cave gates for various reasons, but if a good decision process has been followed for gating the cave, most cavers probably would agree with and support the decision. The following "Cave Gating Decision Guide" can help.
Specifications
Specifications vary for different gate styles (see "Bats and Mines" by BCI). Gates are made of mild steel. Stainless steel is an option for parts of a gate that may be submerged, but stainless is up to 10 times more expensive than mild steel, is more difficult to work with and is unnecessary in most applications.
A good gate is made mostly of _" thick angle iron, stronger than the common 1/4-inch. The sill (bottom of the gate) is of 6 by 6-inch angle, usually set over a mat of expanded metal, which prevents vandals from tunneling under the gate. The gate is pinned to the walls, floor and ceiling with large 1-inch steel pins set deeply into the bedrock by drilling holes with a large hammer-drill. The pins are welded to the gate via large hangers made of 6-by-6-inch angle, providing more strength than welding the pins directly to the gate. The horizontal bars and columns usually are made of 4 x 4-inch angle iron strengthened with T-bar stiffeners welded inside from 1 1/2 x 1 1/2 x 1/4-inch angle; this resists bending from hydraulic jacks. The horizontal bars are spaced at 5 3/4 inches between bars on hangers made from 6 x 6-inch angle. The bars are spaced using custom-made precision steel spacing gauges that can be knocked out after the bars are welded to the hangers. One problem with gates built by novices is that the bars may be irregularly spaced, which can discourage bats and invite humans to crawl through. The drawings below from Roy Powers detail bars and stiffeners.
To finish the gate, a "bat guard" is welded on the front of the bars at each column to prevent bats from tearing their wings on hangers. A removable bar with a hidden latch and boxed-in lock area is now standard and is more resistant to vandals with tools than a hinged door. We normally use padlocks with brass innards to resist rust. Combination locks and chains around the gate should be avoided because they are more vulnerable to bolt cutters and hammers. However, a well protected, heavy-duty combination lock may be useful on a cave that is monitored often; the combination should be changed routinely.
Many gates are not coated, but any coatings that are applied should be brushed on, not sprayed, to avoid volatiles from entering the cave. Cave gates usually are constructed during a season when bats are not vulnerable or when air is flowing out of the entrance, thus removing welding fume from the cave. If airflow is not adequate, an air curtain should be put up to keep fumes out of the cave. Ventilation fans may be needed for worker safety (see Elliott, 1995).
Limited space does not allow a full discussion here of the many construction techniques that have been developed for cave gating. A new cave-gating manual is being developed by BCI, ACCA and the National Speleological Society and may be available in 2002.
What to Avoid
A few rules of thumb can be followed. Natural entrances should not be sealed, but opening a long-sealed cave also can cause problems unless some means of protection is devised. Gates should not be made of re-bar (it is much too weak). Chain link fences are easily violated. Do not construct any raised footings, stone work, or concrete walls on the floor or around a gate because they can hinder air exchange and cause a change in temperature at the bats' favorite roosts. Gates should be tailored for the wildlife inhabiting the cave. A cave gate is not a substitute for good land management, but a last resort.
The finished half gate at Blackwell Cave, Hickory County, Mo. The expanded-metal overhang at the top will discourage all but the most determined vandal. Pictured are Roy Powers, engineer, and Kristen Bobo, welder.
Recommended Reading
Elliott, William R. 1995. Air monitoring during construction of a cave gate. Pp. 55-51 in: Dale L. Pate, ed., Proceedings of the 1993 National Cave Management Symposium Held in Carlsbad, New Mexico October 27-30, 1993. This article describes how an exhaust system was set up over a gating site far into a cave, and how air contaminants were monitored.
Elliott, William R. 1996. The evolution of cave gating: How the philosophy and technology have changed. American Caves, 9(2):9-15. A review of cave gating innovations and the decisions that precede a cave gate.
Elliott, W.R., and Jonathan B. Beard. 2000. Cave restoration. Missouri Conservationist, 61(10):14-16. Discusses the gating of Little Scott Cave and how it prevented vandalism.
Taylor, Daniel A.R., and Merlin D. Tuttle. 1998. Bats and Mines. Resource Publication No. 3, Bat Conservation International, Austin, Texas. 50 pp. This publication is the current standard followed by government agencies and cave conservancies for gating caves and mines. It contains information on bat ecology and 13 pages of engineering drawings for designing and building air-flow bat gates.
Cave Gating Decision Guide
1. Are there poor reasons not to gate the cave? For example,
- Purely aesthetic objections to a gate while the cave's resources are being degraded anyway.
- It may "start a trend" towards too much gating.
- Because a few people consider themselves above the rules and may threaten the gate.
Score no points for any poor reasons not to gate.
2. Are there poor reasons for gating the cave? For example,
- For fear of liability, which probably is nonexistent. Cave owners are protected by law in Missouri.
- For administrative convenience (instead of having a comprehensive conservation program).
- To keep wild animals or competing explorers out.
Score no points for any poor reasons to gate.
3. Are there good reasons not to gate the cave? For example,
- The gate will not comply with current ACCA and BCI standards.
- A vigilant owner or manager lives nearby.
- Other controls can be used-road gates, signs, surveillance.
- Visitors probably will comply with a good permit system.
- Experts are opposed to the gate.
- The cave gaters are inexperienced and overconfident.
- No one will commit to checking and maintaining the gate.
- Technical reasons: The entrance is too small for a proper gate (e.g., half gate for Gray bat maternity colony), or the environment or budget will not allow a good design.
Score one point each against gating if any good reasons against gating hold true.
4. Are there good reasons to gate the cave?
- The cave is hazardous to casual visitors and no other controls (permits and signs) are adequate.
- Endangered species inhabit the cave and can be bolstered by protection.
- The cave is a target for vandals, looters and trespassers. A "better clientele" is needed.
- The cave has high value, is threatened, and it can best be studied and appreciated with a good permit system combined with a gate.
Score one point each for gating if any good reasons hold true.
Final results:
Add up the points for and against gating, and determine which seems more important. Other criteria may have to be considered.
Elliott, 10/31/01
