GIBRALTAR FALLS TRAIL
Explore the wild beauty
Brief
Introduction
Gibraltar Falls, located approximately 50km southwest of Canberra on the traditional lands of the Ngunnawal people, is a popular destination for visitors. They’re drawn to the area for activities like birdwatching, nature observation, picnicking, walking, fishing, swimming, and camping in the nearby Woods Reserve. Currently, access to the falls is closed for safety upgrades.
Project Aim
This project aims to design a new walking trail that connects Gibraltar Falls to Woods Reserve and extends further to Snake Rock Boulder, enhancing the recreational value of the area. The trail will follow the western bank of Gibraltar Creek, offering captivating scenery and access to a series of waterholes.
Design Considerations
Accessibility: While prioritizing accessibility, the rugged terrain necessitates some steep climbs, leading to an anticipated Class 3 standard according to Australian Walking Trail Standards.
Length and Duration: The trail is estimated to be approximately 3km long, with an estimated walking time of 1-2 hours each way.
Key Features:
Close proximity to Gibraltar Creek for scenic views and waterhole access.
Integration with existing infrastructure at the falls viewing platform and Woods Reserve.
Project Details
Location: Gibraltar Falls, Corin Road ACT (approximately 50km southwest of Canberra)
Land Manager: ACT Parks & Conservation Service
Trail Standard: Class 3 Australian Walking Trail Standard
Length: 3km (approximate)
Terrain ANALYSIS
A high-resolution (1m) LiDAR ground model was used to conduct a terrain analysis of the project area, utilizing Geographic Information System (GIS) software. The analysis aimed to identify optimal areas for the trail by examining elevation and slope gradients.
The trail begins at an elevation of 980m near the Gibraltar Falls car park and descends 200m to the endpoint at 780m near the Snake Rock Boulder trail junction. This elevation change is expected to provide a moderately challenging hike, suitable for those with a moderate level of fitness.
Analysis of the terrain's side slope highlights areas suitable for trail construction. Side slopes below 10% (shown in white) generally drain poorly and are therefore too flat for sustainable trail building. Conversely, side slopes above 100% are typically very rocky and excessively steep for construction. The majority of the terrain near Gibraltar Creek falls within the 10-60% range (shown in green to red), indicating suitability for trail placement.
LiDAR DEM Source: ACT LIDAR AND MULTISPECTRAL IMAGERY ACQUISITION 2020
Resolution: 1m
Highest point: 980m (near Gibraltar Falls car park)
Lowest point: 780m (near Snake Rock Boulder trail junction)
Elevation Difference: 200m
FLOOD ANALYSIS
This flood analysis identifies potential flood zones along Gibraltar Creek to inform sustainable trail design and placement. It utilizes a LiDAR ground model, historical rainfall data, and runoff estimations to simulate water flow.
The entire catchment for Gibraltar Creek within the project area extends back towards Corin Dam, covering 19 556 750 m² (1 956 hectares). It has 8 major tributaries along its length.
Without flow data available for Gibraltar Creek, rainfall records from the closest weather station, Corin Dam at Boat Ramp, were used. Since 1984, the highest rainfall recorded was 190mm on 20/01/1995. On this day, the highest rain intensity was measured as 18mm/hr, which was taken as the most extreme case for flood simulation. Based on historical data from the Australian Water Outlook an average runoff coefficient of 0.25 was used in the simulation. This equates to an estimated flow rate of 25 m³/s.
Simulation results show flood levels reaching 1.4m to 2m deep and spreading 14m to 72m wide along Gibraltar Creek. Flatter areas where tributaries join Gibraltar Creek, including near Woods Reserve, are shown to be inundated in these conditions and should be avoided where possible.
Data:
LiDAR DEM: 1m resolution
Catchment Area: 19 556 750 m²
Rain Station: Corin Dam at Boat Ramp 570947 (Australian Government, Bureau of Meteorology)
Max Probable Rain Intensity: 18mm/hr
Runoff Coefficient: 0.25
Estimated Flow Rate: 25 m³/s
Manning’s N value: 0.05 (estimated roughness for creek channel)
Results:
Water Depth: 1.4 - 2m
Flood Width: 14 - 72m
Note: This analysis serves as a preliminary guide for sustainable trail placement. It's based on estimated rainfall and runoff data, which may not account for long-term cycles or climate change. Further research and risk assessment is needed for infrastructure design where safety is critical.
FLOOD ZONE GIS FILE
Ground Truthing
Following a thorough investigation of the site's terrain and water patterns, the next stage of the Gibraltar Falls Walking Trail design involved a detailed on-site validation of the proposed trail path by Advanced Trail Design. This process aimed to enhance our understanding of the location, refine the trail alignment to highlight areas of high visual appeal along Gibraltar Creek, and improve the accuracy of infrastructure requirements.
Objectives:
Follow the GPS trail path plotted in the desktop design.
Confirm that the trail alignment conforms with AS2156.1 Class 3 walking trail standards and make adjustments as necessary.
Identify areas of high value along Gibraltar Creek, such as waterholes and or spectacular views, to incorporate into the trail path.
Confirm locations and approximate quantities for stair placement based on AS2156.2 Trail Infrastructure standards.
Confirm placement and approximate quantities for safety barriers/handrails as per AS2156.2 Trail Infrastructure standards.
Identify suitable treatments for watercourse crossings.
The assessment was carried out over two days with staff from Advanced Trail Design, ACT Parks and Conservation Service, and Path-Co Ecologists.
Gibraltar Falls to Woods Reserve
This section of the trail presented challenging terrain. From Woods Reserve, the trail can remain close to the creek; however, as it approaches Gibraltar Falls, the terrain becomes steep with large boulders. To navigate this, the trail rises higher, utilizing steps to access more manageable terrain while offering sweeping views of the creek and surrounding landscape. Handrails will be necessary in several areas due to high exposure risks.
During the ground truthing, Sam Patmore from Path-Co Ecologists conducted an ecological assessment of the trail corridor. One section near the creek required rerouting compared to the plotted path, as the steep terrain and large boulders would have caused significant ground disturbance during construction. The alignment was adjusted to avoid this area. Additionally, observation stations were set up to monitor for the endangered Smokey Mouse.
Woods Reserve to Snake Rock
This alignment proved to work well. The side slope provides good drainage, while the creek remains visible for most of the trail. The design incorporates several picturesque features, including waterholes, cascades, and a large rock shelf ending in a waterfall.
The trail corridor was flagged using surveyors tape. See below for colour coding details.
Overview:
Dates: 14th & 15th November 2024.
Present:
Jack Rahilly, Advanced Trail Design
Mim Jambrecina, ACT Parkes and Conservation
Sam Patmore, Path-Co Ecologists
Chris Hall, Path-Co Ecologists
Gibraltar Falls to Woods Reserve
Gibraltar Falls.
Views north from top of trail.
Views north from bellow Gibraltar Falls.
View south to falls bottom.
Traversing the southeast slope.
View from northeast face.
Approaching the creek before Woods Reserve.
Stepping stones to existing trail.
Woods Reserve to Snake Rock
Creek from south bank.
Camera traop for smoky mouse.
Current crossing woods reserve to south bank (rebuild required).
Creek from south bank.
A rocky section to negotiate.
Waterhole.
Waterhole.
The rock gateway.
Cascades.
Cascades.
Waterfalls at end of trail.
Fall line section of trail to be re-routed.
Refer to the design map bellow for image locations.
DESIGN
The proposed trail alignment fulfills the recreational requirements of the area. It achieves this while fitting within the boundaries posed by the natural terrain and water patterns. The trail hugs Gibraltar Creek, showcasing the picturesque settings, wildlife, and waterholes. It also avoids flood zones and flat areas, taking advantage of the terrain's slopes for effective drainage and long-term sustainability.
The total length from Gibraltar Falls to the Snake Rock Boulder parking area is 3070m. Starting at a 980m elevation and ending at 780m, the trail has an elevation difference of 200m and an average gradient of 6%. This would take approximately 45 minutes to 2 hours to complete each way, requiring a moderate fitness level.
To adhere to Class 3 walking trail standards, short, steep sections are limited to a 12% maximum gradient. Flights of stairs will be strategically placed to negotiate steeper obstacles. The trail will be built 1m wide, potentially narrowing to 0.6m over time due to vegetation regrowth and natural wear.
Gibraltar Falls to Woods Reserve (1200m)
This section begins at the falls viewing platform and follows the north side of the creek. It traverses the initial steep terrain using a series of switchbacks and steps before joining the creek bank and continuing to the reserve.
Woods Reserve to Snake Rock Boulder (1870m)
This section is located on the south side of the creek, taking advantage of the preferable terrain with good side slopes for drainage. The north side has larger water tributaries and flat areas that could become boggy, making the south side a more suitable choice.
Creek crossings will be needed at the Woods Reserve and Snake Rock Boulder ends. Consistent with Class 3 standards, these crossings could be constructed using local stone to create stepping stones. Alternatively, to allow all-weather access and create a unique feature, bridges could be installed.
Trail Specifications:
Rating: Class 3
Length: 3070m
Width: 1m
Average Gradient: 6%
Maximum Gradient: 12% (40% at steps)
Estimated Duration: 45 minutes - 2 hours each way
— Existing Trail
— Proposed Trail
— Stairs
— Creek Crossing
— Watercourse Crossing
— Barrier
GPS TRACE
STEPS
To navigate steeper sections of the terrain and prevent shortcutting on switchbacks, steps have been strategically placed along the trail.
A comfortable walking experience is achieved by using a rise of 180mm and a run of 450mm for each step, this also complies with Australian design standards. These dimensions can be adjusted to suit different locations, but consistency must be maintained within each flight of stairs.
In line with Australian Standard AS 2156.2 for Class 3 walking trails, no more than 36 steps are placed between rest points (risers).
Quantity:
Total flights: 17
Total diagonal length: 170m
Total steps: 380
BARRIERS
Australian design standards for walking trail infrastructure (AS 2156.2) require barriers in certain circumstances to mitigate the risk of falls. The type and placement of barriers depend on the effective fall height and trail classification.
For Class 3 trails, barriers are required where the effective fall height exceeds 1 meter.
Up to 1.5m: Type D barrier
1.5m and over: Type C barrier
The proposed route traverses rugged terrain with steep side slopes, necessitating barriers in some sections. The estimated quantity is:
Type C: 136m
Note: These quantities are estimates based on desktop plotting and the available ground model. A risk assessment should be conducted during the construction phase to determine the final placement and type of barriers required. Relevant Australian standards must be reviewed, and land managers consulted, before any safety barrier design and installation.
Watercourse CrossingS
The proposed trail crosses Gibraltar Creek and its tributaries. To ensure user safety and long-term sustainability, appropriate crossings will need to be installed.
Trail Approach: The trail must descend into any watercourse from both sides to prevent water from flowing down the trail and causing erosion.
Smaller Watercourses: Smaller watercourses must be armored with flagstone paving to create a durable, erosion-resistant surface, even when wet.
Gibraltar Creek Crossings: Stepping stones should be installed using local stone at Gibraltar Creek crossings. This allows users to cross safely while minimising disruption to the creek's natural flow and aesthetics. The stepping stones should be approximately 500mm wide and spaced 500mm apart.
Example of Flagstone paving on site.
Example of creek stepping stones on site.
Trail Guidelines
In lieu of a standard for walking trail construction, it is advisable to adhere to the five sustainable trail construction principles outlined by the International Mountain Biking Association (IMBA). First published in 1993 these are considered the world-class standard for constructing natural surface trails, not just for mountain biking but for all trail use. The primary aim of these guidelines is to manage water flow on trails, thereby reducing erosion, maintaining trail quality, lowering maintenance costs, and protecting the surrounding environment.
The trail corridors, provided in GIS format and flagged on site, have been designed following these IMBA guidelines:
The Half Rule.
The 10% Average Gradient Rule.
Maximum Gradient Rule.
Construction Phase Implementation:
The following steps should be implemented during the construction phase to further enhance sustainability:
4. Grade Reversals.
5. Outslope.
Australian Standards Walking Track - Class 3 Guidelines
Full details refer to: AS2156.1-2001, Walking Tracks - Part 1: Classification and signage
Trail Corridor
Dimension required for safe passage and visibility.
Trail Tread: 1m
Trail Corridor: 1.5 - 2m
Trail Ceiling: 2.4m
Trail Bench
Full benching is the preferred method for achieving durability and consistency in the tread surface of the trail. In cases where partial benching is unavoidable, such as around tree roots or impenetrable rock, a retaining wall made from local rock should be used to reinforce the downside and prevent erosion.
Trail Flagging
During the ground truthing stage the trail corridor was flagged using surveyors tape. In combination with the supplied GPS trace this can be used to guide future surveying and construction.
Colour coded tape has been used to indicate where different infrastructure is expected, however as noted above this may be altered during the construction phase.
Pink: General trail corridor.
Pink + Orange/Yellow: Steps required.
Pink + Blue: Water Crossing.
Using in the Field
The flagged corridor and GPS traces are supplied to guide the trail building process, ensuring that the trails are built at the appropriate gradient for their designated difficulty level and stay within the approved corridor.
Modifications may be made during the trail building process to avoid obstacles or reduce construction impacts, provided you stay within 7 meters of the trace.
References
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