Sam Trowsdale

SUDS, LID, BMPs, WSUD and more - The evolution and application of terminology surrounding urban drainage

The management of urban stormwater has become increasingly complex over recent decades. Consequently, terminology describing the principles and practices of urban drainage has become increasingly diverse, increasing the potential for confusion and miscommunication. This paper documents the history, scope, application and underlying principles of terms used in urban drainage and provides recommendations for clear communication of these principles. Terminology evolves locally and thus has an important role in establishing awareness and credibility of new approaches and contains nuanced understandings of the principles that are applied locally to address specific problems. Despite the understandable desire to have a ‘uniform set of terminology’, such a concept is flawed, ignoring the fact that terms reflect locally shared understanding. The local development of terminology thus has an important role in advancing the profession, but authors should facilitate communication between disciplines and between regions of the world, by being explicit and accurate in their application.

Emerging threats in urban ecosystems: a horizon scanning exercise

As urbanization intensifies, urban ecosystems are increasingly under pressure from a range of threats. Horizon scanning has the potential to act as an early warning system, thereby initiating prompt discussion and decision making about threat mitigation. We undertook a systematic horizon scanning exercise, using a modified Delphi technique and experts from wide-ranging disciplines, to identify emerging threats in urban ecosystems. The 10 identified threats were generally associated with rapid advances in technology (eg solar panels, light-emitting diode lights, self-healing concrete) or with societal demands on urban nature (eg green prescriptions). Although many of the issues identified are also technological opportunities with recognized environmental benefits, we have highlighted emerging risks so that research and mitigation strategies can be initiated promptly. Given the accelerated rate of technological advancement and the increasing demands of urbanized populations, horizon scanning should be condu...

Mandatory urban rainwater harvesting: learning from experience

Rainwater harvesting is effectively mandated in several urban areas of New Zealand. To understand the costs and benefits of rainwater harvesting from an end-user perspective, semistructured interviews were conducted with 14 homeowners in northern Auckland affected by these regulations. Residents report differences in four aspects of urban rainwater infrastructure - security of supply, water quality, the learning process and financial costs - that could represent key values for public acceptance. When responses are examined from the perspective of experience that has built empirical knowledge, participants explained how their satisfaction with rainwater harvesting increased over time. We hypothesise that for those lacking experience, urban rainwater consumption is a function of empirical knowledge and has initially rising marginal utility. Regulation that recognises the costs of social learning is likely to be a more effective pathway towards maximising the social benefits associated with integrated urban water management.

Dominant perspectives and the shape of urban stormwater futures

Cognitive mapping is used to elicit perspectives on stormwater problems and solutions in West Auckland, New Zealand. In-depth interviews with key stakeholders reveal three dominant perspectives that underlie contemporary approaches to stormwater management: conventional fixes, low impact solutions and community development. Analysis confirms that these perspectives are diverse and partially conflicting. Traditional engineering approaches to managing urban stormwater generate feedback loops that necessitate continued construction of infrastructure to the detriment of environmental systems. Low impact solutions are environmentally sensitive, but they do not break this feedback loop. Community development could reduce the need for more urban stormwater infrastructure in the long-term but it does not address current adverse impacts of urban growth. Analysis suggests that none of the perspectives in themselves will lead to sustainable outcomes. Rather, the transition to a water-sensitive future requires understanding of and engagement with these diverse perspectives in efforts to establish more integrated social-ecological outcomes.

Understanding barrier interactions to support the implementation of sustainable urban water management

The prevalence of barriers to the implementation of alternative and more integrated approaches to urban water management has been observed by many researchers and managers. This study analyses the interconnected nature of these barriers using a combination of interpretive structural modelling and systems thinking methods. Based on empirical data from an urban case study catchment this study shows that barriers not only reinforce each other, but also create persistent self-reinforcing effects within a barrier interaction network. Evidence of feedback structures was primarily found in the institutional and logistical management areas. These systemic feedback structures create resistance to the implementation of alternative urban water management strategies resulting in the status quo. Knowledge of barrier interactions provides a rational basis for targeted and prioritized management interventions.

The role of landscape setting in minimizing hydrogeomorphic impacts of flow regulation

Abstract The Tongariro Power Development Scheme (TPDS) is used to regulate flow in the headwaters of the largest catchment on the North Island of New Zealand (the Waikato). Two small dams, the Rangipo Dam and the Poutu Intake Dam, were constructed in 1973 and 1983. The flow regime of the river is managed to divert freshes into the power scheme, but allows flows larger than 100 m 3 s −1 to be released, to rework and transport sediment through the catchment. Analysis of aerial photos and maps spanning 1928 to 2007, alongside field measurements, show that there have been few hydrogeomorphic adjustments since dam construction. This includes limited changes to channel geometry, channel planform and bed material organization immediately downstream of the dams. In addition, offsite effects are minimal, both 500 m downstream of each dam, and in the more sensitive, less confined reaches in the lower catchment (11 km downstream of the Poutu Intake dam). The limited changes can be attributed to the locations of the dams within reaches characterised by bedrock gorges and confined within terraces. These locations act to flush sediments and impose margins that allow minimal adjustment of the channel. Bed material within this reach is characterised by the presence of a boulder lag. This is sourced from long-term incision into lahar deposits, and acts to limit the rate of incision, creating a steep and stable base upon which active fractions are transported. Just as importantly, significant storage in the low-relief volcanic plateau located in the upper catchment acts to disconnect and store the high sediment yields generated by active volcanic cones in the western sub-catchment upstream of the dams. This limits the rate of sediment supply to regulated reaches. Findings from this study show that analysis of reach-scale controls is essential in framing dam site locations in relation to the distribution of reaches and landscape units across the catchment. In this instance, tributary inputs downstream of the dams do not replenish the sediment and flow removed at the dam locations, as has been observed in other regulated systems. Rather, the river itself is resilient to change and flow variability is well managed allowing geomorphically effective floods to occur. Landscape setting is a key consideration in determining the hydrogeomorphic impact of flow regulation.

Writing and photographing ‘little water’

Abstract The ‘average water user’ concept which informs much research into household water use neglects the beliefs, knowledges and rationalities that underpin peoples water use and limits management strategies. Photo diaries and participant-led reflexive diaries supported with interviews are used as complementary research methods to critically analyse what Allon describes as ‘little water’ in residential households. The article also considers the use of ethnographic methods to explore everyday practices. Of primary importance are multiple realities that are revealed through this methodological approach about the constitutive effects of water practices in everyday life. The initial findings demonstrate that there are multiple water cultures existing within urban Auckland, contesting mainstream conceptualisations of water user and water cultures. The approach and findings demonstrates potential to transform the ways we know and manage water, and provides a richer, more complex picture of everyday water cultures.

Integrated urban water management in commercial buildings.

Monitoring results are presented as an annual water balance from the pioneering Landcare Research green building containing commercial laboratory and office space. The building makes use of harvested roof runoff to flush toilets and urinals and irrigate glasshouse experiments, reducing the demand for city-supplied water and stormwater runoff. Stormwater treatment devices also manage the runoff from the carpark, helping curb stream degradation. Composting toilets and low-flow tap fittings further reduce the water demand. Despite research activities requiring the use of large volumes of water, the demand for city-supplied water is less than has been measured in many other green buildings. In line with the principles of sustainability, the composting toilets produce a useable product from wastes and internalise the wastewater treatment process.