Dry Forest Enviroblanket
CASE STUDY
Dry Forest Enviroblanket® Stormwater Detention Basin
Curletts Road, Christchurch
Backstory:
Land erosion, sedimentation, and poor drainage, resulting from the impacts of the 2011 Christchurch earthquake sequence produced flooding and damage to properties adjacent to the Heathcote River.
To mitigate this inundation, the Christchurch City Council Waterways and Catchment Management Team commissioned the Curletts Road Stormwater Detention Basin to provide upstream flood prevention and peak flow attenuation.
Prior to creating the detention basin, the area was pasture with the Curletts Stream running through it. In order to detain and filter water, a sizeable ~8 hectare excavation needed to be formed and landscaped accordingly.
"The first commercial large scale Enviroblanket®, – effectively an on-site nursery; could it be done?"
The Challenge:
The first commercial large scale Enviroblanket®, effectively an on-site nursery; could it be done?
Native direct seeded Enviroblanket® technology, developed by Red Tree Environmental Solutions (Red Tree), is essentially disruptive in that it bypasses the nursery system, interacting directly with disturbed substrates in a responsive time frame. Letting nature lead and assisting with biomimicry and self-design principles, Red Tree aims to replicate the life-giving function of the forest floor.
An undisturbed soil profile provides established networks of root systems, microorganisms, and mycorrhizal creating nutrient pathways, aeration, and drainage. Once the natural soil structure is disturbed and modified, there is a significant loss of soil ecology. This disturbance and compaction of engineered soils produced a major challenge to seed germination and healthy plant growth on this site.
Exposed to the elements, this large and open area is continually subjected to environmental extremes such as high wind velocity, sun exposure in the summer, and sinking cold during the winter with the attrition of browsing pest animals such as rabbits and hares.
The Solution:
Adjacent to a traditionally planted area, a one hectare dry forest Enviroblanket® was applied in August 2019 around the perimeter of the wetland basin. Nature provides direct feedback as to which species are best suited to variance within specific microclimates; species best suited to environmental conditions display higher germination rates with success being reflected in strong growth and plant resilience. Biomimicry and self-design capacity that the Enviroblanket® provides, gives nature the best opportunity to select species best suited to adapt and thrive in local environments.
During site preparation, mechanical ripping was undertaken to address compaction, improve poor soil structure and drainage. Biological additives were applied to the Enviroblanket® post-application to assist biogeochemistry health. Microorganisms and fungal networks rebuild microbial activity in the soil which in turn creates a symbiotic relationship between plant communities, builds resilience, and improves growth.
As this site is widely exposed to the elements, Red Tree utilised a fast-growing native nurse crop to provide protection and cover during the first year of establishment for the slower growing natives to emerge through.
Mitigation of pest browsing effects was undertaken in conjunction with Excell Biosecurity, implementing pest reduction controls and perimeter fencing in the most challenged areas.
Outcomes:
Initial germination: September and October of 2019.
November 2020: Plant establishment range in height from 5cm to 50cm and secondary germination observed among wind dispersed pioneer species.
Late 2021: Plants range in height from 30cm to 1.8m; a stark contrast to traditionally planted natives exhibiting signs of dehydration and transplant shock.
Canopy cover in standard revegetation, growing in optimal conditions at 1.5 m spacings, will take approximately three years.
The Enviroblanket® has demonstrated at Curletts Road that this outcome can be achieved within 20 months post-installation, facilitating rapid growth and establishment.
Directly applying eco-sourced native seeds into an environment conducive to their success ignites healthy competition and builds resilience.
Plants naturally grow more successfully and with greater resistance to pests and diseases in supportive and biodiverse communities.
The observed increased density brought about by direct seeding supports plants to outcompete weeds therefore reducing inputs and maintenance costs.
Cut Slope Land Stabilisation
CASE STUDY
Cut Slope Land Stabilisation, Lyttelton Port Company
Lyttelton, Christchurch
Backstory:
As part of the 10 hectare land reclamation occurring at the Lyttelton Port Company (LPC), the haul road to their existing quarry was to be upgraded to improve access for heavy vehicles.
Vertical cuts had to be made into the steep cliff to lower the gradients of the haul road. Excavation of the cuts revealed pockets of erodible loess clay among the rock. Red Tree was contacted by Fulton Hogan, the civil contractor undertaking the excavations, to remediate the potential for further erosion.
"Being directly above the port operations and below the new road construction, this site was extremely high profile."
The Challenge:
Loess is comprised of platelets which carry a negative charge facilitating ion exchange once saturated and is therefore extremely partial to erosion. During precipitation onto the Sumner Road catchment, high velocity sheet flow was running down slopes above the vertical cuts and eroding the loess faces.
Sumner Road above LPC was still under construction after being closed following the Christchurch earthquake sequence. Being directly above the port operations and below the new road construction, this site was extremely high profile.
Coordination and communication between these two large civil construction projects was a challenge that required high levels of compliance and health and safety. Once windows of ingress were coordinated, gaining access to the steep slopes above the vertical cuts was also a challenge. Rope access teams were required to move across the slopes and work on the eroding cut faces.
The Solution:
A series of Enviroberm®’s and an Enviroblanket®, delivered via Canterbury Woodchip’s industrial high tech pneumatic applicator, was considered as an effective solution for the vertical cut faces and steep gradients above.
Trapezoidal Enviroberm®’s with dimensions 300mm high and 600mm wide were installed perpendicular to the gradient on the steep slopes above the eroding loess cut face. Enviroberm®’s bisected the slopes; constructed at intervals to interrupt sheet flow and facilitate infiltration. Rilling etched into the landscape from previous water flow indicated how best to work with the hydrology of the slope.
To remediate continued loess erosion, Red Tree Rope Access Teams securely pinned a dense three-dimensional reinforcement mat onto a portion of the vertical cut and managed the pneumatically applied Enviroblanket® onto the interface. Specific species of clover and drought tolerant grasses were selected and seeded over the Enviroblanket® to stabilise and vegetate the cut face.
Outcomes:
The Enviroberm® successfully acted as a slope interruption device, slowing the velocity of sheet flow and facilitating infiltration.
The loess cut is no longer eroding from the slopes above and the vertical face is heavily vegetated from the Enviroblanket® installation.
A high level of safety compliance was achieved with seamless communication occurring between the multiple contractors on site, allowing the completion of the project on time and to budget.
Legacy Planting - Tai Tapu Heritage Project
CASE STUDY
Legacy Planting - Tai Tapu Heritage Project
Tai Tapu, Christchurch
Backstory:
With a vision to the future, public and private visions can become intertwined in the repurposing of landscapes. In this case, our clients engaged in a heritage subdivision project, situated in rolling country below a public reserve, with high aesthetic requirements.
As a natural watershed, beneficial collaboration with the Christchurch City Council was part of the landscaping process. A series of water channels and holding basins were created to safeguard against downstream inundation and sedimentation. In 2019, Red Tree were called upon to design and plant the riparian margins.
The Challenge:
The landscape design and planting required functionality and high amenity value.
As the project backs onto native bush, this site is a hotspot for goats, deer, rabbits, and hares. The pests meandering down the valley and browsing the plantings has been a significant challenge in this project, with some of the bigger tree species becoming victimised by young stags shedding their velvet.
The Solution:
Moved by the sculptural ribbon like topography, Red Tree’s in-house Landscape Designer allowed the plantings to accentuate the contour of the land and water course, creating corridors of visual passage across the plantings. Kowhai, ribbonwoods, lancewoods, mountain flax, pittosporum, carex virgata, and silver tussocks were all part of the plant palette.
In consultation during the conceptual design phase, Red Tree’s horticultural team anticipated the presence of pest plants and recommended ideal plant spacing and full mulch coverage at ~75 mm depth. For ease of mind, our clients engaged with our three year maintenance and monitoring package, which allows Red Tree to guarantee 95% establishment success and protection of their investment.
Plant losses due to pest browsing were detected early in the maintenance phase. Pest management was then undertaken and the unharmed plants were caged, with replacement plants being installed the following planting season.