Street Trees – Finding their Place

STREET TREES – FINDING THEIR PLACE IN THE URBAN ENVIRONMENT

Available in ANNUAL CONFERENCE PROCEEDINGS

Jason Reepsdorff Bundaberg Regional Council

Bundaberg Regional Council (BRC) in partnership with AECOM recently undertook a review of BRC’s street tree standard drawings for planting trees in road reserves. The review sought to harmonise internal and external stakeholder needs while updating the standard drawings to reflect current industry best practice. The process was driven by competing interests and confusion when applying the previous standard drawings. To address concerns from internal asset owners and external developers AECOM were engaged to provide an independent external peer review and to facilitate collaborative workshops with key stakeholders within Council. The process commenced in May 2020 and was finalised in January 2021. During this period a moratorium was placed on street trees being planted in road reserves.

The review was multi-disciplinary and involved the following disciplines: • Landscape Architect • Civil Engineer • Environmental Scientist • Arborist

And the following stakeholders from Council: • Engineering Services • Parks, Sport and Natural Areas • Development Assessment • Strategic Planning • Civil Works • Water Services • Major Projects

The collaborative process highlighted the competing interests for all stakeholders in the road reserve space and sparked strong debate with a lot of passionate views on trees. In principle all parties supported quality trees in our urban neighbourhoods however how BRC went about this has proven challenging. We are now in the implementation stage of the new drawings and we will review them again after 12 months to measure their performance.

There were two main sticking points during the review, these being: • Optimal size of the planting area and soil volumes for a tree; and • Finding space to install trees.

The Queensland State Government developed the ‘Model Code for Neighbourhood Design’ to help local government address aspects of the liveable communities state interest of the State Planning Policy 2017. The model code sets a benchmark of at least one street tree to be provided per 15m on each side of all streets. IPWEA with the help of the industry developed the ‘Street Design Manual – Walkable Neighbourhoods’ to complement the objectives of the model code. The document talks about road reserve widths, truncations and road width treatments to help create spaces for significant trees to be planted or retained.

The document is a great tool, however there are further issues that are encountered in brownfield sites where BRC are undertaking street tree planting as part of the ‘One Million Trees Bundaberg Region’ project.

This paper looks at the journey BRC undertook to develop the new suite of standard street tree standard drawings. In particular, engineering aspects of planting trees in the road reserve, the judgements and risk analyses that were undertaken to arrive at a decision matrix to guide street tree planting.

Introduction

Street trees vary in size, colour and function, and in the urban environment they vary in health and appearance. How important are they?

Quality street trees perform a critical role transforming the urban jungle of hard surfaces into a sense of place connecting to nature. The benefits of street trees are numerous and include: • Improved streetscape amenity • Aesthetics • Liveability • Improved biodiversity

Figure 1 – Woongarra Street Figs, Bundaberg

• Reduction of urban heat • Encourages active transport • Sense of place.

In addition to providing the listed benefits, some places are known for their distinct boulevards e.g. Jacarandas in Brisbane and Sydney, Figs in Bundaberg – Refer Figure 1.

‘Soft’ assets like street trees play a critical role in the urban environment and are as every bit important as ‘hard’ assets. Street trees form an integral part of the hard footpath asset.

Balancing the needs of delivering a streetscape that benefits the community and the environment, while also providing essential services in terms of civil, drainage, water, wastewater and other infrastructure is a challenging one.

It is important that quality is emphasised when referring to street trees. It was this focus on quality that prompted Bundaberg Regional Council (BRC) to undertake a review of its street tree planting standard drawings.

Standard Drawing Review

BRC’s Engineering Services department is the custodian of BRC’s standard drawings and oversaw an external review of BRC’s standard street tree planting drawings. The review was completed by AECOM who undertook a multi-disciplinary and collaborative approach with a team that consisted of Landscape Architects, Civil Engineers, Environmental Scientists, Arborists and BRC Stakeholders.

The need for a review was driven by feedback from developers that the previous standard drawings were contradictory, not practical and didn’t represent best practice. It was a conscious decision to engage an external consultant to undertake the review to ensure independence that could be defended to developers if queries arose. Synergy was also required between Council’s Infrastructure branch, who are the owners of the road reserve asset, and the Parks branch, who plant and maintain significant amounts of trees in these reserves. BRC’s vision of planting one million thriving trees in the Bundaberg Region by 2024 also highlighted the importance of ensuring the standard drawings were practical and had ownership by all stakeholders.

The review included two workshops with key Council stakeholders to achieve a thorough understanding of Council’s concerns. In conjunction with AECOM’s work BRC undertook a Safety in Design Risk Assessment and developed a Street Tree Treatment Selection matrix. Whilst the review was being undertaken a moratorium was placed on new trees being constructed in road reserves as part of Council works.

The review process commenced in May 2020 and was completed in January 2021 with the adoption of seven new standard drawings and accompanying technical note. There were two main points of debate during the standard review, these being: • Optimal size of the planting area; and • Finding space to install trees.

Planting Area

Each discipline had their own ideas on minimum planting area requirements and what volume of soil was required to give street trees the best chance to establish and flourish. It is important to BRC that planted trees develop into quality trees that improve the streetscape. BRC didn’t want to see trees struggling and looking in poor condition providing no benefit to the community.

Council’s preference is for up to 25L pot size trees to be

Figure 2 – BRC Standard Drawing R4501

installed. This direction is based on younger trees having a better chance to adapt to the surrounding in-situ soils when their roots reached that level of maturity. For BRC’s approved tree list, climatic conditions and soil condition requirements, a minimum depth of 600mm and volume of 1m3 of planting hole was adopted. The planting surface areas adopted are a minimum of 3m2 for road shoulder plantings and 2m2 for back of kerb plantings. Refer to Figure 2 for example BRC standard drawing showing planting requirements.

Guiding Policy and Documents

The Queensland State Government Planning Regulation 2017 is the head of power for planting requirements. It sets a benchmark of at least one street to be provided per 15m on each side of streets in new developments. The Queensland State Government developed the Model Code for Neighbourhood Design to help local government address this and other aspects of the liveable communities state interest of the State Planning Policy 2017. It achieves this by setting a set of standards that can be used by local government to support healthy and active communities and promotes the creation of walkable neighbourhoods.

IPWEAQ with the help of industry developed the Street Design Manual – Walkable Neighbourhoods to complement the objectives of the Model Code. The document provides guidance on how to create spaces in the urban environment where significant trees can be planted or retained. Examples of these include varying road reserve widths, providing larger corner lot truncations and road width treatments.

This document is a great tool, however brownfield sites present additional challenges when trying to incorporate street trees. Particularly when trying to retrofit a tree every 15m to align with the Planning Regulation 2017 that guides new developments.

Engineering Guidelines and Standards

From a civil engineering perspective there are numerous standards and guidelines that need to be considered when designing components of the road reserve. A number of these standards and guidelines impact the availability of locations for street trees to be planted. Examples of standards and requirements that should be desirably met include: • AS2890: the carparking standard provides guidance on sight distance requirements for driveways • AS1158: provides guidance on street lighting • Austroads Guide to Road

Design Part 4 : Guidance on

Figure 3 – Street Tree Assessment, Recent Development

Figure 4 – Street Tree Assessment, Historic Development

obstructions near intersections, bus stops, pedestrian refuges and crossings. • Austroads Guide to Road

Design Parts 4A and 4B: provide guidance on sight distance requirements at intersections and roundabouts. • Austroads Guide to Road

Design Part 6: provides guidance on roadside hazards • DTMR supplement to Austroads

Guide to Road Design Part 6: provides guidance on clear zone requirements • DTMR Road Landscape

Manual: provides guidance on clear zone and sight distance requirements • BRC Planning Scheme:

nominates expected standards to be followed and provides additional planting requirements • Ergon Energy Trees and

Powerlines: provides guidance on planting trees near powerlines and power poles

Case Studies

Existing urban areas in the Bundaberg Region were assessed against the previously mentioned engineering guidelines and standards to identify opportunities for street tree planting. These were a recent development at Bargara and an older area in West Bundaberg developed in the early to mid 1900’s. The following tests were applied to the Bargara development, refer Figure 3: • Clearance to Street Lights nominated in BRC Planning

Scheme (7.5m), (Magenta circle) • Intersection/Pedestrian Bus

Stop obstruction exclusion nominated in Austroads Guide to Road Design Part 4 and

BRC Planning Scheme (Green polygons) • Intersection Sight Distance

Requirements nominated in Austroads Guide to Road

Design Part 4A (Blue polygons) • Driveway Sight Distance nominated in AS2890.1 (Orange polygons) • Standard Service Corridors (Red polygons)

The assessment shows that available areas for street tree planting were very limited and nowhere near the desired street tree every 15m. Available areas are shown with a green dot, of which there are 6 in the area assessed. On the ground there are 21 trees planted in the area of assessment.

The following tests were applied to the West Bundaberg site, Refer Figure 4: • Clearance to Street Lights nominated in BRC Planning

Scheme (7.5m), (Magenta circle) • Clear Zones (wide road reserves with wide grass verges before kerb and channel), (Yellow polygons) • Intersection/Pedestrian Bus

Stop obstruction exclusion nominated in Austroads Guide to Road Design Part 4 and

BRC Planning Scheme (Green polygons) • Intersection Sight Distance

Requirements nominated in Austroads Guide to Road

Design Part 4A (Blue polygons) • Driveway Sight Distance nominated in AS2890.1 (Orange polygons) • Standard Service Corridors (Red polygons)

This assessment showed that in the older areas of Bundaberg

Figure 5 – Street Tree Treatment Selection Matrix

Figure 6 – Street Tree Assessment using Matrix, Recent Development

that had wide road reserves (30m) there was ample opportunity for street trees to be planted in the road shoulder and behind kerb.

Finding Room for Street Trees

The results at the example development at Bargara highlighted the need to reassess what guidelines and standards could be relaxed to accommodate street trees. There were already developments with street trees that didn’t have identified issues and higher density developments in SEQ also seem to function without concern.

It was agreed that an outcome that was fit for purpose was needed that applied engineering judgment to assess the risks of relaxing standards to accommodate trees.

Risk Assessment

Crash data was analysed for well landscaped residential areas in Bundaberg over the preceding 20 year period to see if trees were a contributing factor. The crash data showed that no accidents at intersections and driveways were attributed to the presence of trees. This scenario was run through BRC’s safety in design risk assessment tool to outline control measures to mitigate the risk of street trees causing vehicle conflicts. It was decided to relax standards on low speed, low traffic roads, i.e. road classifications lower than trunk collector. The assessment showed that the risk after mitigation was at a tolerable level. For higher classification roads it was decided that traffic volumes and speeds made a relaxation of standards intolerable, however typically these roads have wider road reserves that can accommodate street trees.

It was also documented that the assessment is to be reviewed after five years. This length of period was chosen to assess the

Figure 7 – Passively Irrigated Street Trees, Sinclair Street

judgement that whilst newly established trees were growing to mature height the potential to restrict sight lines is greater. This is due to foliage being at driver eye height when planted, while after five years the tree trunk should be the only restriction. If this was an issue Council’s customer request system will have documented any complaints and crash data could again be reviewed.

Matrix for Street Tree Treatment Selection

As part of the standard drawing review BRC wanted passive irrigation options to be added and that this type of installation was to be the preferred outcome. A matrix was developed to guide the selection of street tree treatments that incorporated the outcomes of the risk assessment and highlighted the priority for passive irrigation installations. Another important feature of the matrix is that it isn’t a hard no if criteria couldn’t be met for planting, if this occurred approval is required. This allows further engineering judgement to be applied in some situations.

The matrix covers road shoulder plantings and back of kerb plantings for low speed, low volume or high speed, high volume roads, refer Figure 5.

Case Study Reassessment

The developed street tree selection matrix was used to reassess the development at Bargara. Using the adopted criteria there is a greater opportunity for trees to be planted. This is due to sight distance criteria for intersections and driveways being relaxed as Malo Drive and Lavella Street are not trunk collector streets.

At a desktop assessment, 19 of the 21 street trees that were planted as part of the development comply with the matrix. In fact there is an opportunity for more trees to be planted, refer Figure 6.

Trial Site

After adoption of the new standard drawing suite BRC has embarked on a number of trial planting sites. One of these is a section of Sinclair Street where 31 trees have been planted. These trees are passively irrigated behind kerb plantings, refer figure 7.

A local CQU student is undertaking a thesis project on The Comparison Between the Effectiveness of Active and Passive Irrigation for Establishing Street Trees using Sinclair Street to undertake testing. The thesis includes: • Establishing a water balance model to study scenarios representing the standard passive irrigation plantings. • Taking empirical measurements of soils moisture percentage using a soil temperature and moisture recorder. • Providing recommendations on improving the effectiveness of active and passive irrigation methods.

Further Refinement

It is acknowledged that the drawings will need fine tuning with the addition of more drawings possible. It is hoped the drawings are a step in the right direction and have started the process of all stakeholders engaging in working towards success. BRC will continue to look to improve the drawings based on user feedback.

Acknowledgements

Adam Johnston, Manager Design, Bundaberg Regional Council

Wiebke Witte, Principal Landscape Architect, AECOM

References

• IPWEAQ. 2020. Street

Design Manual: Walkable

Neighbourhoods. • Witte, Wiebke (AECOM) (2021)

Bundaberg Regional Council –

Street Tree Detail Review.

Jason has over 26 years experience in civil design and documentation of subdivisions, retirement villages, unit developments and infrastructure in the Agnes Water, Bundaberg, Bargara, Caloundra, Hervey Bay and Townsville areas including earthworks, roadworks, stormwater drainage, sediment & erosion control, sewerage and water reticulation, estimates and scheduling. He is a skilled 12d, AutoCAD, XPSWMM, XPRatHGL, XPRafts, and HECRAS operator.