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Six Rivers Charter School pirate's cove corner

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Pirate's Cove Corner before project.
Pirate's Cove Corner after garden renovation.


This project was created to preserve the outdoor learning area at Six Rivers Charter School in Arcata, California. A retaining wall, extra bench, improved footing, and pirate-themed design were added to the square to allow improved educational usage. The project was designed to both maintain the existing garden space as well as further its availability as an outdoor learning environment.


Representatives from Six Rivers Charter School wished to improve the existing garden area on campus, which had been becoming rundown. This need was met by a group from the Fall 2018 Intro to Design engineering class at Humboldt State University, under instructor Lonny Grafman. The team took the open-ended task and narrowed its focus to improving the educational use of the existing space used for teaching, with the endgoal being to allow any class to utilize the space for outdoor lectures and learning.

Problem statement and criteria[edit]

The garden area at Six Rivers Charter School needed to be generally improved, and the group needed to decide how to best help achieve that goal. The final decision was centered around preventing a landslide into the garden area, and took into account the following criteria. Each criteria was assigned a weight in respect to a fixed set of constraints.

Criteria Constraint Weight
Educational Value Must have an educational aspect 8
Maintainability Must require two days of maintenance a week or less 8
Time Must take ten weeks or less to complete 7
Longevity Must remain functional for at least a year 6
Sustainability Must include at least three sustainable methods 6
Cost Must be less than or equal to $325 in expenses 5

Description of final project[edit]

The final design involved replacing a retaining wall, leveling the ground, adding pea gravel and an additional bench, and applying a pirate theme to the retaining wall area. The retaining wall replaced a pre-existing rotted wooden retaining wall, and consists of 26 ft of gabion cages on the hill behind the pre-existing student bench used for outdoor classes. The ground in the square was leveled and covered in pea gravel to allow classes to be held outside after rain. An additional bench length was added next to the existing bench to allow a full class to sit for outdoor lectures, enabling more than just agricultural classes to utilize the space. Finally, manilla rope was draped across the gabion cages, and a 3 ft ship wheel was added as a center piece to incorporate the school's pirate theme into the square.

Final Designs
The final project overall.  
Additional redwood bench.  
Leveled ground with pea gravel.  
Gabion cage retaining wall displaying nautical elements.  

Prototyping - Early Designs[edit]

Due to the long-term use and public knowledge of gabion cages, benches, and leveling, the group used design ideas in lieu of prototyping to decide upon a final design. The first ideas included a variety of specific ideas that could improve different aspects of the garden area in general. Correspondence with the charter school representatives led to a narrowed focus pertaining to the retaining wall. After consulting an architect at Humboldt State University, the final design shifted from a wooden to gabion retaining wall, but retained the nautical-themed characteristics.

Early Designs
Redesign stylized to resemble the side of a pirate ship, centerpiece removed.  
Retaining wall cross-section with plank/stanchion format.  
Gabion wall design with nautical elements  
Top-side view of the autocad design.  


Item Quantity Project Cost /yard Retail Cost /yard Project Cost Retail Cost
Gabion Cages

1 (8ft x 3ft x 4ft)

3 (6ft x 3ft x 4ft)

18.5 n/a $35.00 Donated $650.00
Gabion Cage Rocks 8.0 n/a $35.00 Donated $277.76
Pea Gravel 3.5 n/a $50.00 Donated $175.00
1 in Manila Rope 10 $1.77 $1.77 $19.20 $19.20
3 ft Nautical Wheel 1; 3 ft diameter n/a n/a $49.69 $49.69
Lumber 24 yd n/a $9.99 Donated $239.76
Paint Sealant 1 can n/a $24.99 Donated $24.99
Plotting Supplies Cordage and Stakes n/a n/a $11.00 $11.00
Total Cost $79.89 $1447.40

How to build[edit]

Gabion Cages

The cages were assembled using Hilfiker's manual for Gabion wall building, which can be found here:

Installing and Filling Gabion Cages
Debris Step 1 : Remove any debris from the site.
Marked hillside Step 2 : Mark out a straight guideline.
Leveling Process Step 3: Start leveling the ground and straightening the hillside wall.
Tamped ground Step 4: Tamp the ground and ensure it is level.
Installed cages Step 5: Install the cages at a slight angle into the hillside to account for both the pressure from adding rocks and from the hillside.
A ramp for loading rocks Step 6: Fill the cages with rocks using whichever method works best for the given situation. Pictured is a wooden ramp technique.
Nautical elements Step 7: Add manila rope and a ship wheel to complete the pirate theme!
Creating the Flooring
A cleared ground Step 1: Start evening the ground starting with the boundaries.
Larger rock cover Step 2: Level the ground and add larger rocks. The final design aesthetic for this project included leaving a border of wider rocks around the defining edges of the area, creating a rocky beach appearance that added to the pirate theme.
Pea gravel cover Step 3: Add pea gravel to compensate for mud due to rain and add aesthetic.


The maintenance for this project is relatively low. Gabion walls are composed of galvanized steel and last for 25 years. In drier climates the bench and flooring would last longer but with the heavy rainfall in Arcata the bench will most likely need to be replaced after 15 years, and the pea gravel may need to be supplemented every 5 years.

Maintenance Schedule[edit]

  • Weeding
  • Light inspection of gabion cages for wear and breakage
  • In depth inspection of gabion cages
  • Minor re-leveling of square ground
  • Inspect manila rope
Every 5 years
  • Re-leveling of square ground
  • Replace gravel
  • Inspect and possibly replace manila rope
Every 25 years
  • Replace gabion cages


Maintaining the Ground
Pea gravel before and after leveling. Step 1: Use shovels and rakes to shift gravel back to being level. If necessary, pile gravel aside to level underlying dirt, then replace and level gravel.
Inspecting the Cages
Inspecting the gabion. Step 1: Inspect the condition of the metal of the cages, particularly the corners.
Checking the angle of the gabion with a level. Step 2: Inspect the angle of the gabion cages. Are they still angled back towards the hillside slightly, did they level out, or are they leaning towards the square?


Basic troubleshooting guidance

Problem Suggestion
Rope fell down If a corner fell down, find where rope was attached and re-tie. The current roped is tied with a slip knot. If one of the center loops fell down, use the spare hog rings left in the shed to reattach the rope in desired position.
Metal attachments overly rusted or missing Remember to use leftover replacement pieces.
Wheel needs to be replaced or taken down Use bolt cutters to remove the two locks on the current wheel.
Troubleshooting References
The current slip tie knot.  
The box of spare hog rings.  

Suggestions for future changes[edit]

Recommended changes for the future would be the addition of more plant life in the areas bordering the wall and benches. Additionally portable seating could be added to accommodate larger class sizes for lectures in this area. Lastly, it would be beneficial to replace all of the remaining eucalyptus retaining walls with gabion cages, as eucalyptus is sure to fail in the future in the climate of this region.