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Overview of trail survey and risk management: hazards and physical assessment

Risk factors for trails: inventory of trail data were gathered to produce an environmental and recreation risk management plan for trails on the Hawaiian Islands.
See Reported Incidents on Trails in Hawaii during year 2000, below.
Also see "The Design and Placement of Warning Signs on Improved Public Lands"

From Hawaii Trail Analysis Survey & Risk Management Data Profile: download complete document (95 pages, illustrations, tables; pdf format 4.0 mb)

By University of Hawaii at Manoa, Practicum 751, March, 2001

Map of HawaiiThe purpose of this project is to provide information to enable the Department of Land and Natural Resources to shape a risk management program for the management of public lands. An additional purpose is to provide information to the Department of Health on the characteristics of Hawaii residents who hike to be used for future long-range planning efforts.

Photo: waterfall

Rockfall is a concern on the Manoa Falls Trail

Due to the realization for the need to inventory and assess the risks inherent on DLNR properties and provide mitigative efforts to reduce these risks, DLNR initiated a program that would pursue the identification, assessment and reduction of risk from natural hazards. Such a program would assist in increasing public safety, while forestalling the need for regulation, reducing the exposure to future liability claims, reducing uncertainties, and increasing effective use of limited funds.

Specifically, this report presents information on the characteristics of the users on Category I lands, collected from a sample of State Parks and Division of Forestry and Wildlife, Na Ala Hele trails on the four major islands. This project also provides an inventory of the physical conditions of the state recreational features where users were surveyed.


The purpose of the trail and park user census was to gather baseline usage data on trails managed by Na Ala Hele and State Parks for general public use. The initial understanding was the need to collect data on park and trail usage, activity levels, and basic demographic information of local residents and visitors using the DLNR features such as hiking trails and state parks.

Based on discussions with DLNR, additional information on users' perception of risk, the users' degree of experience, the users' knowledge of local conditions, the users' source of information, and the users' behavior on a trail was requested for collection. The purpose of this additional information was to gain insight on what ways trail and park users, particularly visitors, may be unprepared for hiking in Hawaii and on what aspects of user behavior can be changed to increase public safety.


An inventory of the physical conditions of these select recreational features provides the study with baselines of both the identification of the potential trail hazards as well as the evaluation of trail user preparedness. All observations, judgments, and recommendations contained in this report are for exploratory purposes only and should not substitute for the seasoned opinion and experience DLNR staff and expert consultants. Moreover, potential hazards are identified without assessment of the degree of harm or consideration of available resources for mitigation.


photo: trail along ridge
Waihee Ridge Trail, Maui, climbs 1,500 feet in 2.5 miles

Natural hazards are all around us and may occur at any time. The volatile climate of the tropics and varied geography of Hawaii increase the uncertainty and intensity of these hazards. Large-scale hazards such as hurricanes, tsunamis, volcanic eruptions, and earthquakes can be catastrophic events, but the more localized hazards can be equally harmful. As hurricanes, for instance, are broad-region, well-monitored events, a flash flood occurs without warning and is very specific to the affected area.

The ignorance of hazard and the affiliated lack of preparedness of people exposing themselves to a flash flood, or any other localized hazard, is where the true hazard lies. These events have happened for millennia and will continue to take place despite management efforts to contain them. What can change is how aware and prepared people are to these hazards so that the severity of the consequences may be reduced. As part of this study, several localized hazards were identified and evaluated. These hazards include landslides, flash floods, hazardous trees, hazards associated with climate and topography, and trail surface. There are other hazards, such as infections or animal attacks for instance, that have a more limited effect on users, but may be addressed in a comprehensive study in the future.


Landslide event probability begins with the height and steepness of the slope, whether it is a ridge or valley trail. The greater the shear of a cliff, the narrower the zone of impact would be. However, in narrow valleys such as Sacred Falls, a high vertical drop still renders the entire valley exposed because of the ricochet effect. Lesser grades usually cause more lateral movement, so a trail that is a short distance from the cliff base would still be at risk of rockfall. Soil type also has an effect on landslide possibility, with regards to their response to moisture content and adhesion qualities. Naturally, composite substrates of rock and soil or a predominance of solid rock has considerably more damage and injury potential than a slide containing only soils, so the level of heterogeneity also has an effect on the consequence of a landslide incident (Bauer, 2000).


Photo: trail under big trees
Fast-growing trees in a wet climate create potential for tree hazards

The giant trees that may be seen over a given trail also pose a potential hazard. When trees reach their mature size, they tend to deteriorate and eventually lose their limbs, and in some cases, fall down altogether. Many of the trees used for reforestation of the higher watershed regions of the Hawaiian Islands are non-native, quick-growing varieties. Eucalyptus and albizia are two introduced species that were extensively planted.

In an attempt to approximate the risk of hazard trees observed in the area, several criteria were developed for the purposes of this project. First, a hazard tree was identified by its aspect to the target, that is, is it leaning toward or over the trail. Unless there was a spur trail leading up to a potentially hazardous tree beyond the falling reach of the main trail, the hazard tree was not documented. The specie of the tree was noted, as the constitution of some tree varieties are more apt to breakage than others. Then factors such as the girth of the bough or limb was considered and rated, as well as the nature of the break, the degree of tree rot, and the health in general of the tree in a Hazard Tree (HT) factor from 1 to 5.


photo: trail through mud and roots
Roots and mud are typical conditions along the Waikamoi Trail nature trail

Flash flooding is a hazard related to characteristics specific to a certain area. The presence of perennial streams indicates a high annual rainfall with consistent distribution in the specific region. Any sudden aberration from this normal precipitation and a narrow stream course may soon bear several times its usual volume, creating a quick-moving, potentially fatal hazard if people are present. Most flash floods cause the most harm downstream where it may not even be raining at the time of the flood, catching hikers off-guard. Although hikers may be directly exposed to a flash flood for a very short time, if the trail requires passing back over a recently swollen river, the hikers may be prevented from completing the course. This may prompt a desperate user to attempt to cross a rushing stream and risk being swept downstream and drowning. For the purposes of this study, if a stream course is present on the trail, whether it be flowing or not it is considered a potential flash flood zone.


Wandering off a trail may happen either intentionally or unintentionally. Hikers may seek an improved vista for sightseeing or for a photographic opportunity. Some trails like the Nakoa Loop in Kahana Valley, only cover a small area and do not explore the back of the valley, which prompts some more adventurous hikers to venture off on spur trails blazed by hunters, who are more familiar with the valley and seldom use a particular marked trail. Additional visitors using trails means that there are more people unfamiliar with that feature and with the local conditions.

A hiker may not know that he or she has left the trail due to poor markings or the presence of spur trails with comparable tread-ware to the main trail, or the user may simply not be paying attention. Hunters and hikers alike use colored ribbons to find their way back to familiar territory, but often leave the ribbons behind, which may be mistaken by the next trail user as the official trail.


This is a broad category of hazards that includes the effect of elevation gain on users, exposure to solar radiation, and the risk of fire. Some of the trails in the Na Ala Hele system, such as the Ainapo Trail on the Big Island, wind up to the very summit of 13,679 ft. Mauna Loa, exposing the hiker to freezing temperatures and effects related to altitude. None of these extreme conditions were surveyed as part of this study.

Exposure to solar radiation is related to the amount of tree cover over a trail. If the trail is particularly long, attempted in the middle of a cloudless day and features little forest canopy, then the user runs an increased risk of heat stroke and dehydration. This is amplified if the trail has variable elevation. The risk of fire is related to climate, as only drought-tolerant species can survive, which are usually quite flammable. At Diamond Head State Park, for example, if a lit cigarette ignites the dry understory at the bottom of the trail, those who have completed most of the trek may be stranded or directly harmed by the blaze.

Reported Incidents on Trails in Hawaii during year 2000
Date - Location - Incident

1/18/2000 - Kahana Valley

Oahu Helicopter rescue of 2 20 year old males and 14 year old girl from Kahana Valley after dark after being stranded on the ridge when darkness fell

1/19/2000 - Wahiawa, Oahu

Fire personnel respond to 911 call to rescue 33 year old female hiker off Puamoho trail

2/20/2000 - Manoa Falls, Oahu

Fire personnel rappel to rescue of 23 year old who wandered off Manoa Falls trail and was trapped on cliff after other hikers call 911 on cell phone

3/17/2000 - Kipahulu, Maui

Firefighters, police and ambulance assist in rescue of 22 year old Canadian woman who fell off ledge while hiking in Cosmic Gardens area; injuries include head, thigh and elbow

3/25/2000 - Pali, Oahu

Fire crews hike to 22 year old man, rappelling without proper equipment and rescue him from cliffs near Pali lookout; slight injuries (no hospital treatment)

3/29/2000 - Kahana Valley

Helicopter rescue of California couple (ages 40 & 62) left the trail in Kahana and were lost for 4 days; rescue efforts began when resident noticed rental car had not moved; couple had left map and water in car

3/29/2000 - Alakai, Kauai

Helicopter rescue of young couple (21 yr Honolulu female; 22 yr Az male) lost in Alakai Wilderness for 3 days; in good condition - had rationed food and moved to high ground; rescue efforts began when family who knew of their plans saw they did not return

4/24/2000 - Mokuleia, Oahu

Helicopters and fire personnel searched on foot and found 50 year old Iowa male at base of 400 foot waterfall after hiking up Kealia trail; rescue efforts began when missed rendezvous with son; severe trauma indicated fall caused death

6/27/2000 - Wailua Falls, Kauai

Helicopter and fires personnel rescue two 22 year old California men seriously injured jumping off Wailua Falls (200 ft)

6/28/2000 - Wailua Falls, Kauai

Helicopter and fire personnel rescue 22 year old California man who slipped and fell over Wailua Falls; man swam to side; man was unaware of incident day before

7/3/2000 - Aiea Loop Trail

Helicopter and firefighters search for 2 women and 1 male who failed to return from early evening hike at Aiea Loop, trio left trail to go see a waterfall and got lost; reported missing 9:30 pm; hikers escorted out at 2:00 am; no injuries

7/4/2000 - Manoa Valley

Helicopter rescue of 24 year old male resident who fell from rope ladder along Waiakeakua Stream in Manoa Valley in response to 10 year old nephew 911 cell phone call; suffered head & leg injury and shock

8/29/2000 - Wailuku, Maui

Fire personnel and divers search for 15 year old male visitor last seen at top of falls, found drowned at base of waterfall near Kailua Stream

9/22/2000 - Kahana Valley

Thirty searchers, in 4 teams, and helicopter search for 35 year old visitor hiking on Puu Manamana trail; man fell 200 feet and cut knee and was alone for 43 hours; rescue efforts began when police noticed rental car parked alongside of road

10/2/2000 - Volcano, Hawaii

43 year old Colorado man discovered dead a mile beyond end of Chain of Craters road; cause of death unknown

11/6/2000 Volcano, Hawaii

Two hikers (41 year Volcano female, 42 year DC male) found dead of burns near lava flow; actual cause of death unknown

11/27/2000 - Olomana Cliff Trail

Fire rescue helicopter and rappellers from helicopter down cliff rescue 22 year old Marine injured after fall from sheer cliff at Olomana; rescue efforts began when other hikers heard shouts for help and called 911; appeared to have suffered head, shoulder and leg injuries

From Hawaii Trail Analysis Survey & Risk Management Data Profile: download complete document (95 pages, illustrations, tables; pdf format 4.0 mb)

Also see "The Design and Placement of Warning Signs on Improved Public Lands"

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