On-site stormwater detention

Impacts of development on stormwater

Development of land often leads to an increase in the area covered by hard impervious surfaces, such as roofing and paving.

The increase in impervious surfaces significantly increases the volume of stormwater runoff, impacts downstream drains and other assets and can negatively impact the local environment. 

Benefits of on-site stormwater detention

On-site detention manages stormwater at the location of the source. Stormwater detention is designed to temporarily retain water and then slowly release it over time. This process limits the maximum flow rate of water into the drainage system and minimises potential damage to infrastructure and impacts on the environment.

The Shire has adopted the use of on-site stormwater detention systems to prevent local flooding and to decrease peak flow rates into drains and waterways.

Types of detention systems

There are different types of on-site stormwater detention systems, however most will have the following components:

• Discharge control pit – this is located at the lowest point on the detention system. All flows leave the site through this pit. The pit contains an orifice at the bottom of a baffle wall located centrally within this pit. Refer to the Shire's standard drawings MP244-1 & 2 for details of this pit. The orifice is sized to limit the discharge of water from the site to the maximum permissible site discharge rate. Some designs may have an orifice opening with a rainwater tank being used as the detention and the remainder of the water to be used for re-use within the development. Refer to the Shire's MP245 drawings for details of a rainwater tank for dual purpose detention/storage.
• Storage – this can be located underground by the use of pipes or tanks, or above ground through rainwater tanks. The storage fills up due to the orifice restricting the flow and then empties through the pit once the rain eases. At least 50% of the total detention storage for the site is to be located underground.
• Collection network – consists of gutters, channels, pipes, and hard surface areas which are all collected and discharged to a pit.

Developers may be required to construct new public infrastructure assets. These assets must be constructed to Mornington Peninsula Shire standards prior to the Shire approving the release of the development works or agreeing to assume future maintenance responsibility for the infrastructure.

The Shire has Specifications, Standards and Guidelines to assist developers in the preparation of plans for subdivision and private development works.  The Planning Permit will advise of specific conditions.

Download and use this Checklist for Development Engineering Plan Approval(PDF, 233KB) to assist with the preparation and submission of Development Engineering construction plans.

Find out more about Construction Management Plans.