The Council has completed a series of technical reports to support the development of an ICMP for the Mangaheka Stream and its catchment (see map below).
An ICMP outlines how the Council's services, such as pipes for water supply, wastewater and stormwater, will be managed. These investigations will build on work undertaken by others in recent years, and assist the Council in the management of stormwater generated by urban growth in the area.
To give us your feedback and to review the draft ICMP click here. Consultation will be open from Friday 16 February until Friday 9 March or you can attend our information Open Day on Tuesday 27 February 2018, 4.30 to 6pm at the Western Community Centre (46 Hyde Avenue, Nawton) between 4.30 and 6pm.
If you require additional information, or wish to provide feedback, you can email firstname.lastname@example.org or phone 07 838 6903.
What is an ICMP?
The purpose of an ICMP is to outline how the Council manages water supplies, wastewater and stormwater in a catchment. It recommends improvements in areas that have already been built, and plans infrastructure for areas where future developments will be built.
Stormwater is the focus of an ICMP, although wastewater and water supplies are also managed through ICMPs.
ICMPs give guidance on issues including:
- Pipes and infrastructure.
- Requirements on new development or subdivisions to manage water supplies, wastewater and stormwater.
- Managing streams and waterways, including identifying problems like stream erosion and coming up with projects to help fix these problems.
- Identifying flooding issues and options to reduce flooding.
- Restorations and environmental projects.
Why do we have to treat and manage stormwater?
Storm water is often thought of as clean, but when it meets other surfaces it can collect contaminants such as sediment, phosphorus, copper and zinc. These contaminants flow into waterways (such as streams and lakes) and can create poor water quality environments for our native fish, wild life and plant life.
When rain falls on hard surfaces such as paths, roads and roofs, it can't sink into the ground. Instead it flows quickly downstream into gutters, pipes and streams. In some cases, where there is too much stormwater, this can cause flooding. Fast flowing water can also cause erosion and scour.
What important stormwater features are in the catchment?
The Mangaheka stream is the major stormwater network feature in the catchment. Historic drainage has resulted in poor ecological habitat, which is home to many at-risk native fish species (including black mudfish, short and longfin eel and banded kokopu). Ecological restoration work is being carried out by Project Watershed and the Tangirau Restoration Group in the downstream reaches of the catchment.
How do we treat stormwater?
There are many ways to treat stormwater to remove contaminants and reduce its speed before it gets into our waterways. These include encouraging more public and private green spaces, and building stormwater treatment devices such as wetlands and raingardens. Treatment can also include collecting rainfall and slowly releasing it or even re-using it so pipes and streams do not become overwhelmed with stormwater.
What is a treatment system (train)?
Sometimes it will take several devices to remove certain contaminants and manage the volume of water. A treatment train is made up of many individual treatment devices. Water flows from one device into the next, with the goal of removing a higher percentage of contamination than a single device could achieve. A treatment train can be on private or public property.
Who maintains treatment devices?
Treatment devices located on private property such as rain tanks and rain gardens, are required to be maintained by the property owner. Treatment devices which have been assigned to the Council such as wetlands, will be maintained by the Council after a contractor or developer maintenance period.
What are the key outcomes in this catchment?
1. Centralised stormwater management devices for stormwater attenuation and treatment, designed and maintained to comply with the Council's Infrastructure Technical Specifications.
2. Flood attenuation is required to generally 70% of the pre-development rate, (additional flood detention may be required on-lot depending on the design of the downstream device).
3. Water quality and contaminant removal needs to be managed by a combination of centralised and on-lot devices (treatment train approach).
4. Mandatory on-lot rainwater re-use tanks, plumbed for use in the toilet, laundry and landscaping.
5. Secondary overland flow paths need to be considered during the design of developments.
6. Preparation and implementation of Pollution Control Plans for managing contaminants from high risk activities.
We are also proposing a programme of works to jointly manage the effects of downstream erosion in the catchment.
If you require more information or would like to provide feedback, email email@example.com or phone 07 838 6903.
You are also welcome to attend the public open day which will be held on Tuesday 27 February, 4.30 to 6.pm at the Western Community Centre, 46 Hyde Avenue, Nawton.