Ecosensitive stormwater system design for sub-division

Abstract

Stormwater management is a contentious aspect of development in the 21st century. Although hydrological neutrality before and after a development is sought, it is acknowledged that any alterations to land form result in a change in the hydrological regime. Thus the goal of agencies whose responsibility it is to manage stormwater effectively is to minimise the adverse impacts of new developments on the environment. To achieve this more reasonable objective, these agencies have developed objectives and policies backed up by design criteria and requirements that developers are required to meet as part of their development proposals.

The Waitakere City Council (WCC), and the Auckland Regional Council (ARC) have worked closely together to develop a number of stormwater management manuals and design standards consistent with the Resource Management Act (1991). This paper reports the outcome of an investigation into the sustainable engineering design options satisfying the above guidelines for stormwater management for a residential sub-division in Henderson, Waitakere City using a Triple Bottom Line (TBL) assessment and a Cost Benefit Analysis (CBA).

Following the evaluation of various stormwater management devices such as shared common areas to minimise impermeable surfaces, restricted earthworks onsite, stormwater reuse and attenuation tanks, rain gardens, flow dispersion devices and swales, a detailed design was produced for two types of device: Those constructed as part of the initial development of the site and those constructed by the individual plot owners. This highlights the value of apportioning the responsibilities to relevant personnel at sub-division level as well as at individual property development level.

It is shown that it is both feasible and practical to design and construct an eco-sensitive, sustainable, low impact stormwater management system that meets the needs of the client and the requirements of the regulatory authorities.