Poor use of a swaleIn a great many catchments within New Zealand the issues of concern to the roading or stormwater practitioner will remain volume, velocity and sediment. Nevertheless, in many there will be increased risk of other contaminants or greater sensitivity.  An extensive range of resources is available to practitioners to assess these risks and respond appropriately.

A Stormwater Risk Assessment Guide for Road Engineers has been designed as a practical guide for road asset managers and roading practitioners to assess the potential for environmental effects from stormwater from roads.

Rain-garden Maintenance Guidelines have been developed to provide an introduction to rain-garden maintenance, with a suggested maintenance schedule and short troubleshooting section.  Rain-gardens are now well-established components in the tool-kit of low impact urban design treatment devices for stormwater and runoff, both for the attenuation of flows and the filtration of sediments and metal contaminants.  In common with any other device, the quality of performance of a rain-garden will depend on both its quality of design and on the quality of its maintenance.

Case studies from Wellington Quays provide useful lessons.

Guidelines on Management of Road Run-off have also been developed and published by the Stormwater Group. 

The NZTA Stormwater Treatment Standard for State Highway Infrastructure  and NZTA Draft Erosion and Sediment Control Standard for State Highway Infrastructure and Field Guide for Contractors contain detailed resource material.

The On-site Stormwater Management Guidelines, published jointly by the Ministry for the Environment and the New Zealand Water Environment Research Foundation in October 2004, although seriously out of date for research and organisational changes during the past decade, remain a solid, practical guide to the issue. The Guideline is set out in six sections with appendices.  Section 1 contains the aim, scope and limitations of the guideline.  Section 2 contains a set of rapid reference sheets that set out the benefits and trends in on-site stormwater devices.  Section 3 provides guidance on selecting the appropriate on-site device.  Section 4 provides detailed descriptions and designs.  Section 5 provides a description and maintenance requirements for a range of devices.  Section 6 sets out some examples of on-site stormwater devices.  The appendices include comments on various guidelines, references, hydrologic/hydraulic analysis and maintenance and operation of devices. 

The former Auckland Regional Council Technical Publications, designed for Auckland application, can be adapted for use elsewhere, especially the design guideline manual stormwater treatment devices index (TP10), the erosion and sediment control guidelines (TP90) and the low impact design manual (TP124).

Further resources are available through the extensive range of relevant research that has been undertaken within New Zealand over the past two decades.  See our Stormwater Research and NZTA Stormwater Research pages. An extensive resource list is included within our Stormwater Issues section.

There are numerous case studies on proprietory treatment devices available, too.  Links to some of these and a discussion of the recent research evaluation of the performance of such devices in the field compared with their design specifications are availble on the Devices and case studies page.

Stormwater Risk Assessment Guide

The Stormwater Risk Assessment Guide for Road Engineers has been designed as a practical guide for road asset managers and roading practitioners to assist decision-making as a tool to assess the potential for environmental effects from stormwater run-off from roads.  The Guide addresses the pathway for the stormwater flows, including the presence of treatment devices, the character and sensitivity of the receiving environment, and the source risks (road characteristics, traffic flow and congestion) to allow a network or site-specific risk assessment.

Local and international research has shown that the relationship between road run-off and potential environmental effect is complex and site-specific.  The Guide describes the interaction of the three sets of variables that determine potential effects and uses these to assess risks.  A flowchart provides a graphic summary of the process, while the more detailed assessment matrix allows for all aspects of the interaction of the variables at a site to be included in the risk assessment.  The assessment tool is supported by a separate guide explaining the key variables and the application of the assessment flowchart.