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The physical impacts of recreational users in caves: methods currently in use for assessing recreational impacts in two New Zealand caves.

Benjamin Bunting, Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand

Abstract

The aesthetic and scientific values of caves are being degraded by the impacts of recreational use. Although these impacts are recognised, little research has been undertaken in impact assessment, mitigation and monitoring. This paper discusses the physical impacts of recreational use on caves and some research methods which are currently being used to assess and monitor impacts in Gardner's Gut Cave, Waitomo and Honeycomb Hill Cave, North Westland, New Zealand.

Introduction

Caves, and the features within them, are of considerable scientific interest and recreational value, both intrinsically and aesthetically. They also have cultural and historical significance, as well as being of educational importance. Human activity in caves is likely to have a detrimental impact on the cave environment. The activities of cavers have had widespread impacts on caves throughout New Zealand, despite the conservation ethics that are stressed by organised caving clubs and the New Zealand Speleological Society.

This study considers the activities of cave visitors including caving clubs, organised recreational groups, and casual cavers. The scope of this study excludes conventional tourist caves as these have been hardened against visitor impacts by management procedures such as the provision of electric lighting, constructed walkways and barriers.

Many disturbances or impacts on a cave system are likely to be irreversible. It is important that impacts are quantified and monitored so that management strategies can be implemented. This is important in order to avoid or minimise disturbance to the cave environment in the future and to check that current management strategies are effective. Possible management strategies may relate to controlling both visitor behaviour and numbers, and identifying limits of acceptable environmental change.

Few detailed scientific studies concentrating explicitly on human impacts in caves and cave management have been undertaken in New Zealand. However, notably research by Wood (1983) on cave carrying capacity at Zweihohlen, Waitomo; and Rautjoki and Millar (1985) on the management of Honeycomb Hill Cave, Karamea; have discussed impacts of human activities on the cave environment.

Objectives

To properly manage the cave resource, it is important to be able to accurately assess human use and impacts on the resource. Impact mitigation and monitoring are also essential if successful cave management is to occur. The objectives of this study are to:

  1. Assess the natural state and conservation status of the cave resource, at Gardner's Gut and Honeycomb Hill Caves, and identify the attributes and values of significance that are vulnerable to human disturbance, including disturbance from recreational use.
  2. Develop a method of assessing the vulnerability of areas of the cave to recreation impacts and prepare a vulnerability map for sections of the cave systems.
  3. Assess impacts of recreation activities that have already occurred on the Gardner's Gut and Honeycomb Hill cave environments.
  4. Identify management methods to avoid, remedy or mitigate adverse human effects in Gardner's Gut and Honeycomb Hill caves.
  5. Develop methods for quantifying recreation impacts and potential impacts on the cave environment.
  6. Assess the effectiveness of photomonitoring as a recreational impact assessment method in Honeycomb Hill Cave.
  7. Set a baseline for future monitoring of recreation impacts.
  8. Consider using the results to contribute to a development of a generic methodology for assessment of individual cave values, their spatial distribution and their vulnerability, including reference to the comparative conservation value of other cave systems.
  9. Provide general recommendations on ways in which management might remedy or mitigate recreational impacts in Gardner's Gut and Honeycomb Hill caves.

Study sites

There are two study sites for this project; a site at Waitomo, and a site in the Oparara Valley near Karamea.

The Waitomo site for this research is the Zweihohlen and Henry Lambert sections of Gardner's Gut Cave, near Waitomo Caves. Gardner's Gut is the longest cave system in the North Island at almost 13 kilometres in length (Worthy 1991). The section of cave to be included in this study lies under the Ruakuri Scenic Reserve. Access to the Cave is uncontrolled and managed by the Department of Conservation. It is one of the most visited sections of cave in New Zealand and has seen heavy use by cavers over the last 35 years (Ash 1985).

Gardner's Gut Cave is presently used heavily by cavers, recreational groups and commercial adventure tourist operators. The increased activity has had a detrimental effect on the Cave. Conservation measures have been carried out in the Cave by the New Zealand Speleological Society since the 1960s however the damage is continuing. There has been no previous study of the physical impacts of visitors to the Cave.

Honeycomb Hill Cave is located in the Oparara Valley to the north of Karamea, North Westland. The Cave was discovered in 1976 by local cavers. Further exploration realised the significance of the unique formations and, more importantly, sub-fossil bone deposits that are up to 20,000 years old. Entrance to the 14 kilometres of passages is controlled with a gate and permit system administered by the Department of Conservation from its Karamea office. The Department of Conservation also has a photomonitoring record of key sites within Honeycomb Hill Cave beginning in 1985.

Since the Cave's discovery cavers have extensively explored much of the Cave and, more recently, part of the Cave has been opened for a commercial tourist operation. Both the cavers and the tourist operation are likely to have a detrimental impact on the fragile cave environment — most of which is irreversible. Honeycomb Hill Cave receives far fewer recreational cavers than Gardner's Gut — records indicating only 850 permitted visitors since 1987.

Despite the contrast in visitor numbers and management between the two caves, similar impacts have occurred in both areas.

Impacts of Recreational Cavers

Literature focusing on the human impact on caves and cave conservation is limited. Considering there is much literature on the scientific and recreational value of the cave resource and the "conservation" ethics and codes accepted by the caving fraternity internationally, it is surprising that there has not been more objective discussion or criticism of caver impacts. Unfortunately these impacts are poorly documented — likely due to the difficulty in quantifying and subsequently documenting impacts.

One of the overall themes in cave conservation literature states that cavers do have an impact and stress the need for research into this area (Gillieson 1996; Wilde & Williams 1988). The lack of research is surprising considering the value and vulnerable nature of the cave resource that is frequently echoed.

In reviewing the literature such as Gillieson (1996), Hardwick and Gunn (1993), Reider (1976), and Spate and Hamilton-Smith (1991), the physical impacts of recreational cavers can be categorised into groups as follows:

Impacts to be investigated

1. Speleothem damage

Damage to speleothems may be intentional or accidental. In both cases the damage is permanent. Damage includes formation breakage, discolouration due to mud transfer onto formations from caver's hands and clothing, as well as graffiti. Vandalism includes the intentional destruction of formations and evidence of mud fights.

2. Sediment transport/deposition

Sediments may be tracked into the cave from outside or between different areas of the cave. Organic material transported into the cave on the boots and clothing of cavers may have an impact on cave biota. Sediments are transported by cavers and also by natural processes. Mud transfer from sediment areas to clean surfaces and to stalactites and stalagmites is an obvious sign of degradation. The clastic deposits on the cave floor are very vulnerable to trampling. Once disturbed, these deposits may be compacted, liquefied, eroded and subsequently transported to other places within the cave. Often beautiful and delicate structures may be destroyed along with their scientific and aesthetic values.

3. Erosion of floor and slopes

Visitors moving through caves can have long lasting impacts on the scientific and aesthetic value of silt deposits and surfaces. This is because the forces of weathering and erosion (which are constantly reworking deposits above ground) often do not exist in caves making it possible for deposits to remain undisturbed for thousands of years. Constant removal of cave floor sediments by the activities of cavers can cause the development of an incision in the cave floor. This incision may proceed to the bedrock, often breaking through interbedded layers of calcite as it becomes exposed to the impacts of human trampling (Wood 1983).

The erosion of unconsolidated cave materials may also have an impact on water quality within the cave streams. Transport and compaction of floor sediments may lead to 'dimpled' pathways, which are common in heavy use areas. Sediment transport from elsewhere in the cave can lead to the development of a pathway on which the surface actually builds up above the original floor level (Spate & Hamilton-Smith 1991).

Visitor movement up and down silt and talus slopes within the cave causes considerable reworking and movement of material downslope. Movement of visitors up and down limestone faces may lead to a polishing effect to the point where it becomes difficult to climb the faces and thus visitors will seek an easier less challenging route thereby expanding the impact (Spate & Hamilton-Smith 1991).

4. Floor impacts

The flowstone floors in areas of the cave are easily damaged or discoloured. Cavers aware of this fact often remove their boots before walking on the flowstone. Once the flowstone is cracked or broken a knick point may develop which retreats as the edge of the flowstone is broken back. This exposes the fragile clastic material beneath to disturbance by visitors.

Research Methods

This study is attempting to gain both qualitative and quantitative information regarding caver impacts — the latter has proved to be the more difficult of the two.

Acquisition of quantitative data in cave research is difficult for two main reasons:

  1. Difficult work environment
    • Darkness and humidity causes difficulty in accurately reading instruments
    • Equipment problems such as instruments fogging and becoming affected by water and mud
    • Access - both to the cave and within the cave
    • Mobility and movement of equipment within the cave can be difficult and may cause damage to both equipment and cave
    • Likelihood of causing further impacts (an issue frequently ignored by researchers)
  2. Many processes within caves operate slowly
    • Limited timeframe for a research project poses difficulties for long-term monitoring data collection

Quantitative data is being collected in three experiments:

Qualitative data that is being collected includes:

Monitoring of a cave environment is the best method to determine the extent of human impact on the area. It provides a means of gauging how visitor activity affects the resource, or how the impacts relate to existing visitor patterns/activity.

Trench-line surveys

Some floor areas in the cave that receive heavy human traffic are several centimetres lower than undisturbed areas. This indicates that visitors have either compacted, or removed, unconsolidated material from the area as they move over it. This is referred to as trenching. The amount of trenching may be measured by stretching a string or level bar between relocatable points across the passage containing the trench. Distances and corresponding depths along the strings can be measured and then repeated at a later date to determine if significant trenching occurs. Changes in sediment compaction and trail width are also being recorded at trenchline sites.

Measurement of sediment tracking at entrance

Organic rich material is being tracked into the caves by cavers. This has an obvious aesthetic impact on the floor surfaces of the cave but there may also be cumulative impacts on other parts of the cave. The extent of areas covered and volume of material may be determined and graphed.

At Gardner's Gut Cave an experiment will be carried out to determine what effect a boot bath at the entrance to the cave may have on sediment tracking. This will be done by firstly assessing the extent of the sediment tracking prior to the introduction of a boot bath and signage at the entrance and then cleaning up the tracked sediment and providing cleaning facilities. Impacts will be assessed after a recorded number of visitors.

Mud tracking onto speleothems is difficult to control. Visitors must be made aware of the potential impact of touching these formations. Photomonitoring will assess how much of the formation is affected and impact mapping will determine the severity of the damage to the formation.

Vulnerability and impact mapping

Vulnerability mapping involves dividing the cave into manageable sections and then mapping the sections according to their vulnerability to visitor impact. I propose to develop a scale to rate vulnerability of cave areas to visitor impact. The vulnerability of each section/type of formation will be rated on a scale from 1 (high vulnerability) to 5 (low vulnerability) dependent on the risk of damage and the type of formations at risk. For example areas within the immediate reach of visitors on the trail are more vulnerable to damage than those out of reach. Other particularly vulnerable areas are fragile formations such as straws, helictites and crystal pools.

Impact mapping will be used to assess the impacts of human activities that have already occurred. Areas of the Cave will be divided into sections and both floor and/or ceiling impacts in each of the grids are ranked relative to the severity of the impacts. This study plans to utilise a system adapted from Bodenhamer (1995). An impact mapping system can then be repeated at a later date and data is compared to note the extent of change.

Vulnerability and impact mapping will give a good indication of the range of impacts occurring or likely to occur in each area of the cave and is a useful management tool when combined with photomonitoring. The maps are also important for management as they provide an inventory of cave resources. Obviously a good basemap of the cave is needed before any vulnerability/impact mapping can take place. This meant a total re-survey of the Waitomo study site.

Photomonitoring

Cave photomonitoring is a term to describe precise photographs of selected points within the cave taken on a regular basis. The photographs can be used for inventory, as a record of change, and as a basis of information for management decisions. Regular photomonitoring of key sites (fixed photo points) within the cave will become an invaluable management tool for the future. A good photomonitoring record will establish a baseline database which can be added to over time as the sites are re-photographed on a regular basis and photos compared to identify any changes. The key to a successful photomonitoring system is that it must be effective, efficient and simple to use and must be used regularly.

The Department of Conservation has a photomonitoring record of key sites within Honeycomb Hill Cave. This record began in 1985. As part of this project the photosites within Honeycomb Hill Cave will be re-photographed and compared to the 1985 photos. The comparison will be useful in determining the appropriateness of photomonitoring as a management tool in cave management.

Some photomonitoring of Gardner's Gut Cave was carried out in the mid 1980s and the sites will be photographed again to compare changes. In the past photomonitoring has been a very slow process as information at each photopoint must be accurately recorded. At each photopoint many measurements are taken, including grid references, compass bearings, elevations, camera, flash and film details, tripod height, distances from subject, distances and orientation of flashes from subject. This all makes the process very time consuming and poses many difficulties in accurately repeating the survey at a later date.

As part of this study, photomonitoring is being carried out in the Zweihohlen and Henry Lambert levels of Gardner's Gut Cave in order to establish accurate baseline data.

The photomonitoring method being used does not require fixed photopoints within the cave that can be relocated at a later date. Initial baseline photos are taken in the cave and the location (on the cave map or detailed sketch map), tripod height, camera, lens, film and flash details are recorded. When repeating the photomonitoring it is possible with previous photo data on hand to accurately replicate past photos using a centre frame system on a tripod mounted camera.

Camera flash systems are the most crucial factor in replicating past photo surveys as the slightest shift in flash orientation can dramatically alter photo detail, texture, tone and colour. I propose using a camera with a single fixed flash unit at a measured distance from the lens and a second flash located on a bar fastened to the tripod at a fixed distance from the camera lens with flash orientation directed towards centre frame.

To improve consistency in film processing a close-up shot of a colour scale will be taken on the first shot on every roll of film. A colour scale will also be included in every photo of the survey. All data for each photo will be included on a standardised data sheet with a sketch-map, as this will aid surveys in the future.

The repeat of the photomonitoring at Honeycomb Hill was undertaken in April 1997. Outlined below are some of the problems that were experienced:

Conclusion

Caves have unique scientific, recreational, and scenic values. These values are endangered by increasing use and misuse of the caves by cave visitors. Once these values are diminished they cannot be recovered. Therefore, it is crucial that research be carried out to quantify and monitor impacts, and to suggest appropriate mitigating strategies.

This study is due for completion in February 1998 and it is hoped that the results and further discussion will be presented at the next ACKMA conference.

Acknowledgements

I would like to thank my supervisors Dr. Megan Balks and Dr. Peter Urich for their constructive comments. Acknowledgement and appreciation must also go to Dave Smith, John Ash, Robert Brodnax and Craig Miller for their generous advice and assistance. I am grateful to the Department of Conservation and Waikato Branch of Forest and Bird Society for financial support.

References

Ash, J 1985, Adventure caving at Waitomo, Proceedings Sixth Australasian Conference on Cave Tourism and Management, Waitomo: 38-48.

Bodenhamer, H 1995, Monitoring Human Caused Changes With Visitor Impact Mapping, Proceedings 1995 National Cave Management Symposium, Indiana: 28-37

Gamble, F M 1981, Disturbance of underground wilderness in karst caves, International Journal of Environmental Studies. 18: 33-39.

Gillieson, D S 1996, Caves: Processes, Development, Management, Blackwell, Oxford.

Hardwick, P & Gunn, J 1993, The impact of agriculture on limestone caves, in Karst Terrains, Environmental Changes, Human Impact, ed. P W Williams, Catena Supplement 25: 235-249.

N.Z.F.S 1986, Honeycomb Hill Cave photomonitoring site, New Zealand Forest Service, Nelson.

Rautjoki, H A & Millar, I R 1985, Management of Honeycomb Hill Cave - An example of integrating conservation and development, Proceedings Sixth Australasian Conference on Cave Tourism and Management, Waitomo, pp. 83-95.

Reider, L G 1976, Some user impacts on cave environments and the concept of cave carrying capacity as a central management principle, in Proceedings of the 11th Biennial Conference of the Australian Speleological Federation, eds A P Spate, J Brush & M Coggan, Canberra, pp. 21-25.

Spate, A & Hamilton-Smith, E 1991, Cavers impacts - some theoretical and applied considerations, Proceedings Ninth AKCMA Conference: 20-30.

Wilde, K A & Williams, P W 1988, Environmental monitoring of karst and caves, Symposium on Environmental Monitoring. Otago University.

Wood, M R 1983, Cave Wilderness, the Reconciliation of Conservation and Use, unpublished dissertation, Lincoln College, Canterbury, New Zealand.

Worthy, T 1991, Honeycomb Hill Cave, New Zealand Speleological Bulletin 8 (157): 483-499.