StormFlood Engineering

Stormwater Management Plan: What is it, and why might you need one.

Top Blogs

Catch basin square drainage grate over storm water drain surrounded by green grass.

When contemplating any significant development project, the need for a stormwater management plan (SMP) cannot be overstated. An SMP is a strategy document typically provided to council for assessment, that outlines how stormwater runoff will be managed. The SMP outlines the proposed approach to mitigate the risk of external stormwater quantity impacts and improve the stormwater runoff quality from your site. There are also legal requirements to provide an SMP in many local government authority areas, particularly for construction projects that will disturb existing landforms.

The fundamental goal of an SMP is to minimize the impact of stormwater runoff on the surrounding environment (e.g. create a ‘non-worsening’ affect). This is achieved by implementing measures to control the volume, rate, and pollutant load of runoff from the project site. An SMP may include strategies such as bioretention basins, swales, rain gardens, bioswales, permeable pavements, stormwater ponds, first flush devices and green roofs. By effectively managing stormwater, we can prevent erosion, protect water quality, maintain natural hydrological processes, and reduce the risk of overloading stormwater infrastructure and ultimately reduce downstream flooding issues.


What does ‘non-worsening’ mean?

Within the Queensland Urban Drainage Manual (QUDM), ‘non-worsening’ refers to the condition where a proposed development does not increase the flood risk or adversely impact the existing stormwater runoff and flooding characteristics beyond the development site. This means that the proposed development should not exacerbate existing flood levels, velocities, or flood hazard, either on-site or on any other properties.

This is achieved by ensuring that post-development peak runoff rates, volumes, and velocities do not exceed the pre-development conditions for a range of storm events. In other words, the stormwater drainage system for the new development must be designed in such a way that it does not increase the risk (ie. Maintain) of increased stormwater, flooding or create new flood risks.

By adhering to the ‘non-worsening’ requirement, developers and engineers can design new developments that do not negatively impact surrounding properties or the broader catchment. This principle is a significant part of sustainable and responsible urban development, ensuring that growth does not come at the expense of increased load on stormwater infrastructure or an increase to flood risk external to the site.


Engaging a flood engineer, such as Stormflood, in the process of preparing an stormwater management plan brings numerous advantages. Stormflood can:

  • Provide expert analysis of the development site, assessing the flood risk and identifying potential issues.
  • Develop cost effective strategies for stormwater management tailored to the unique characteristics of the site and the local climate.
  • Ensure compliance with local and state planning regulations related to stormwater management and flood control.
  • Design stormwater infrastructure that is integrated with the overall development plan, enhancing the functionality and aesthetics of the project.

A stormwater management plan is a vital part of any development project, helping to mitigate flood risks and protect the environment. Engaging a flood engineer in the process can ensure a comprehensive and effective plan, leading to a successful, sustainable development. As we face the challenges of a changing climate, responsible management of stormwater is more important than ever, safeguarding our communities and the natural world for future generations.

Have a development that might need some stormwater management? Get in touch with Stormflood today.

Leave a Comment

Your email address will not be published. Required fields are marked *