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Water Streets: Transport Infrastructure That Makes Space For Water
The role of water in shaping the places we live cannot be overstated. Let's assess the potential for the public streetscape to contribute to stormwater management.
Water
This article was written by Ed Clayton and Stu Farrant, based on a presentation delivered at the Transportation Group Conference in Nelson. The water street renders are by Tom Greer.
The role of water in shaping the places we live cannot be overstated. As a dynamic and geologically young landmass the influence of water over millennia is clear to see across Aotearoa New Zealand. As tectonic uplift raised our central ranges, the power of water eroded them down to create a landscape intersected by waterways which have deposited vast amounts of sediments to create coastal plains, estuaries and a variable landscape of freshwater wetlands, lowland forests, and waterways at all scales.
It is this landscape that informed and guided initial development and movements, with early Māori explorers quickly recognising the importance of living alongside these natural features. As sources of food and materials (mahinga kai), providing natural barriers to invaders and useful pathways between coastal settlements and inland hunting grounds, water provided a wealth of resources and benefits.
The European colonisation throughout the 1800’s brought a similar linkage with water, albeit on the different scale. Initially seeking safe anchorage and protected harbours, many coastal estuaries were favoured for early colonial settlement. This often brought conflict with the resident Māori inhabitants who had long established Pā, kāinga and mara in these same locales.
Where streams and wetlands were not filled in or drained, they were used as open drains to convey human and commercial waste away from the growing towns and cities. The original Māori pathways (which often followed waterways) were gradually expanded as they progressed from walking paths to bridle tracks, bullock cart tracks and eventually roads to support the rapid ‘development’ of inland areas.
As communities grew – and our connection with the natural environment which initially drew us to specific locations dwindled – our urban infrastructure continued to be built across these once vibrant networks of waterways, with streams piped, lowlands developed on and roads slicing across landscapes with limited consideration of flowpaths and flooding.
This defines the position we now find ourselves in today with many of our urban centres built either on or adjacent to floodplains and our roading network either sitting above or transecting the natural flow of water. Layered on top of this is the spectre of a changing climate with increasing intensity of rainfall falling on increasingly impervious landcover.
But these same communities still exist within the bounds of a hydrological catchment and in many instances maintain linkages with freshwater ecosystems through upstream/downstream remnant waterways and the unique indigenous biodiversity that these support. These catchments and the waterways which once flourished in the landscape still have the potential to provide a sense of place for communities and have a clear role in how we strive to co-exist alongside nature.
Regardless of whether streams are currently within pipes or flow openly, where they flow through urban and developed areas they are subject to a range of acute and chronic impacts as a direct result of urbanisation. Modified flow characteristics, discharge of urban contaminants and changes in the physical characteristics of the water combine to adversely impact on the health of these streams and the ability of them to support functioning ecosystems. Further, instability and persistent discharge of flashy flow in even small to moderate rainfall events cause ongoing undermining of public and private infrastructure resulting in often expensive (and impactful) to fix.
This results in “Urban Stream Syndrome”, where paved areas create faster runoff, leading to streams that have higher flood peaks and more erosive power, transport more pollutants and sediment and have fewer species and less complex ecosystems. In turn, we have experienced a declining connection between communities and the waterways which define the catchments in which they live, work or travel through. Where streams have historically been piped, the urban stream syndrome is further compounded by the lack of any visual connection with waterways and in many instances a lack of awareness of the presence of waterways and the role they once played in defining the landscape and the ecosystem services that attracted people to the catchment all those years ago.
But when it rains these long-neglected streams rear their heads and make their presence felt at the surface of our urban centres. Due to limited capacity of underground piped networks, development within overland flow paths and infilling of flood plains, these waterways re-engage the water landscape and again flow across our now highly modified landscape. Where once the presence of riparian/flood plain forests and deep, rich soils slowed down and adsorbed rainfall, the now increasingly impervious landcover results in increased volumes and flowrates of floodwaters. These are increasingly concentrated through restricted overland flow paths which are often aligned or intersected by road corridors.
Mitigating the effects of road runoff has long dealt with altering the energy characteristics of stormwater in order to reduce the energy available for transporting pollutants or eroding stream channels. This results in such features as vegetated swales, rain gardens and constructed wetlands designed to filter and detain runoff, additionally allowing adsorption of contaminants and removal of sediments.
The effectiveness of these devices varies with different reported factors of load or concentration reduction dependent on catchment, location, device and climate circumstances. However effective they may be, these industry-accepted solutions do nothing to change the underlying cause of road-derived pollution or water volumes – the transport activity and infrastructure materials themselves. (For more information on water pollution, see my other articles on GA, here, here and here).
The concept of “making space for water” is increasingly being promoted across Aotearoa and internationally and specifically by Auckland Council’s Healthy Waters department following the damaging floods of early 2023. The concept recognises that flooding is both natural and expected to increase with future climate change and that there is therefore a need to ensure that communities are safe from potential harm and to minimise financial costs from damage to property and infrastructure. In part, it aims to increase resilience to flooding by creating blue and green networks through cities so that stormwater can safely move through the city, and to manage overland flow paths.
This often encompasses existing open stream corridors and adjacent green spaces (such as sports fields) and from an engineering sense there is a tendency to look at achieving this through further modifying remnant streams to increase the available cross sections and manage the channels as flood conveyance ‘drains’. This approach further degrades the ecological integrity of remnant streams and waterways and is counter to aspirations to enhance urban ecology and re-connect communities with natural freshwater environments.
Conspicuously absent from discussion has been the potential to appropriate the public streetscape to contribute to stormwater management. Mode share of transport is still dominated by private vehicle use, prioritizing individual transport needs rather than the best use of public space. With the knowledge that our streets have followed and built over streams in the past, here we explore how we could reimagine our streets to make space for water. Making space for water requires us to examine the value that we place on stormwater. Rather than a nuisance, to be piped and conveyed “away” as fast as possible, what if our urban spaces could claim stormwater as a resource and amenity?
One of the common challenges with the management of stormwater for ecological or socio-cultural values is the misalignment with requirements legislated under the land transport act. This act is quite rightly intended to manage the safe and resilience of land transport infrastructure and its users but unintentionally is often an impediment to configuring and operating road corridors to support multiple benefits.
This typically results in road corridors (and associated stormwater infrastructure) being designed, implemented and operated by separate arms of councils and except for regulated requirements for water quality (where mandated) and passage of existing overland flow paths they are not designed holistically with the wider catchment in mind.
The concept of ‘roads as a catchment’ reflects the fact that typically roads are characterised by extensive areas of impervious landcover within were what once natural stream catchments. This contributes to an increased volume of stormwater, particularly during small to moderate rainfall events which is often referred to as an “urban excess”.
Given the need to capture and treat this stormwater to mitigate water quality impacts and the importance of retaining a portion of this increased volume, there are clear opportunities to divert treated stormwater to nearby and adjacent demands for non-potable water. This can include large scale irrigation demands (such as sport fields, plant nurseries, community orchards or high amenity landscapes) or appropriate commercial users (such as water tanker refill, washdown or process water for suitable manufacturing activities).
Following damaging urban flooding in Copenhagen in 2011, the municipality, stormwater managers and urban planners looked at the levers and barriers to providing more space for water within a highly constrained urban environment. This identified that existing road corridors were ideally located to collect, attenuate and convey stormwater but that these are largely managed solely for the transport function for which they were originally designed.
To rectify this, changes were made to the national legislation to enable these road corridors to be managed for stormwater (as well as transport) and therefore enabling stormwater planners to consider projects to lower the surface levels and where appropriate intentionally increase the depth and extent of inundation within road corridors. This is seen in the “cloudburst” retention boulevard profile, but is also supported by redesigning the smaller adjacent streets to slow the movement of water before it reaches these flow paths.
This approach has also been manifested in Gothenburg, Sweden, where the fact that it rains on average every three days has been claimed by city officials to create a “Regnlekplatsen (Rain Playground)”. Playgrounds are designed to retain rainwater as puddles for jumping in, with sheltered benches and tables. The winning design for a new school features a schoolyard that changes when it rains, with waterfalls, a canal and a marshland with real mud.
Taking this approach to a streetscape could look something like what has been proposed as a
“stormwater greenway” in North America. The centre of the street features a daylighted channel, trees are planted to intercept rainfall and raingardens provide biofiltration functions. The reduction of car traffic reduces pollutant generation and bike paths are installed with permeable surfaces to promote infiltration. Pedestrian areas are elevated so that surface flooding affects these spaces last, this can be achieved with a cross section utilising an inverted crown so that all surface water flows towards the centre of the street (and hence the daylighted channel).
In some instances, there is a tendency to jump to the large and audacious end point with aspirations for things like stream daylighting like happened for Cheonggyecheon in Seoul. As community awareness of these piped awa becomes more widespread, and increasing mana whenua calls for uplifting the Mauri of the awa, the temptation to visualise what could be is strong.
These daylighting projects create beautiful streets, but often require large scale engineering works that can make these aspirational ideas easy fodder for disparaging engineers who can use the inherent challenges as a reason to do nothing instead. (Full disclosure, I love these aesthetics and want daylighted streams with green light rail everywhere!)
Creating Water Streets doesn’t have to be an immediate, all-encompassing project. It is important to understand the challenges with the very real constraints such as highly degraded water quality, clashes with a myriad of underground services and ‘forced’ invert levels due to historic piping.
There is a strong need to first establish a clear vision of what is wanted in the long term and then clearly communicate the longer-term trajectory to achieve this.
Before we achieve full stream daylighting as envisaged above, we may need more integrated solutions where baseflows are diverted to smaller scale surface recreated waterways integrated with the public realm. Existing pipes remain in the ground to pass the more contaminated ‘first flush’ and infrequent large scale flood flows are accommodated within the wider road corridor with event triggered restrictions on the use of some or all carriageway during large scale storms, priority being given to passage of public transport, emergency vehicles and pedestrians/active transport.
The greater the intensity of rainfall and severity of the flood, the more of the cross section can be used to convey water. Signalised pedestrian crossings can recognise when it rains and increase the frequency at which pedestrian priorities are called, reducing the time that people wait in the rain. Cycle lanes with permeable paving can provide an infiltration buffer and would be built wide enough to accommodate emergency vehicles.
Such an approach would also achieve objectives of the Aotearoa Urban Street Planning and Design Guide. This actively encourages street designs that work towards living environments that provide the unique context and value of their location.
Our approach of streets that make space for water directly aligns with the document’s recognition that streets are public space and multidimensional, and that we need to realise that streets are ecosystems. One lever that could be applied to facilitate these adaptations would be for local authorities to recognize and plan for water streets in district plans.
These changes will necessitate a change in mindset – where communities collectively recognise that private vehicle travel will be less convenient during extreme rainfall, but that this contributes to reduced adverse impacts on private and public property and enables cities to be more resilient and able to return to ‘normal’ sooner. In turn, recognition of the increased resilience is reflected in reduced insurance premiums.
Put together, these approaches provide further intangible benefits. Increasing urban blue-and-green-space is known to improve people’s wellbeing, even if it is only experienced through passive observation.
Provision of street trees and native vegetation in nature-based stormwater devices such as raingardens, swales and floodable pocket wetland parks can encourage wildlife back into urban areas, allowing streets to function as ecological corridors. Increased pervious surfaces allows more water to seep back into groundwater, recharging local aquifers and providing more consistent stream baseflows and better aquatic habitats.
To summarise, integral to this approach will be the improvement of our connections with urban freshwater, visually, socially and culturally. Such an approach presents multiple benefits but will be challenging, requiring a shift in the way we place value in stormwater from nuisance to resource.
If we wanted to extend the management of stormwater further than just the streetscape we could then look to implement catchment-scale Ecological Build Zones, where we reward green infrastructure and stormwater management on private property with bonus development rights.
As I was finishing this article, RNZ published a story of a 44-day-long leak on Kent and Cambridge Terraces, where the Waitangi Stream is buried. Coincidence? Probably; the Waitangi is around 4m deep underground and there are a lot of potable water pipes here too.
Even so: could this be an opportunity to not just build back as it is, but for something better? Tom Greer’s render above is placed within the 40m wide corridor of Kent and Cambridge Terraces, so what are we waiting for?!
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