Coffs Creek, Coffs Harbour, is a popular recreation area for locals and tourists and a highly urbanised waterway. The use of the waterway and the impacts of urbanisation present multiple challenges to the creek’s management, especially regarding public health and safety, ecological impact, and stormwater pollution pressures. Coffs Creek has a history of increased sedimentation, pollutant loads and flooding, resulting in challenging stormwater management and operation considerations.

To improve the health of Coffs Creek and the management of the local stormwater assets, Coffs Harbour City Council engaged Water Technology to develop an Operational Stormwater Management Plan (SMP) for Coffs Creek, Coffs Harbour. This study developed solutions to remedy current waterway issues whilst reducing ongoing maintenance requirements. The SMP was specific to Coffs Creek but presented in a transferable manner to other catchments within the Local Government Area.

Scope:

Stormwater Management Plan

Location:

Coffs Harbour

Client:

Coffs Harbour City Council

As part of this project, Water Technology performed an onsite inspection of all stormwater outlets feeding to Coffs Creek, completed a literature review on past studies and a gap analysis on Council’s stormwater data. Following the review stages, Water Technology created a systematic, pragmatic and succinct operational maintenance manual to guide Council on best practices in managing waterway pollution, municipal infrastructure and estuarine health. A variety of potential in-network stormwater quality improvement devices (SQID) were suggested for implementation, with supporting computational analyses to illustrate their net benefits, and sequential procedural protocols were provided to aid in identifying common waterway problems and their remedies.

Water Technology identified that there was a history of insufficient maintenance of the gross pollutants traps (GPTs), pollutant nets, bioretention basins and stormwater pits contributing to Coffs Creek. It was clear that by addressing the gross pollutant build-up, and its sources, that the existing problems of constriction and localised flooding would be partially or fully resolved. Long-term sediment build-up and limited maintenance also contributed to progressive mangrove forest intrusion into Council stormwater assets which subsequently limited maintenance capabilities due to environmental constraints. Water Technology guided Coffs Harbour City Council through the process of obtaining permits and collating the supporting documentation required to operate in these environmentally significant areas.

In reviewing the Council’s ongoing Water Quality monitoring programs, Water Technology found that the industrial and commercial areas contributing runoff to the mangrove areas were the primary source of debris and litter. This was further supported onsite with their nearby stormwater channels heavily inundated with rubbish, debris and algal blooms. The cause of these issues was observed to be poor waste management rather than fluvial processes. Consequently, Water Technology recommended enforcement actions for these areas, preliminary SQID placements and potential educational schemes on good litter management practice. Water Technology’s thorough gap analysis of Council’s Stormwater Network Digital Database in comparison to site inspection photographic logs also provided clarity between onsite data and Council’s digital database information.

Water Technology completed stormwater quality modelling for each outlet feeding to Coffs Creek to identify potential devices needed to improve waterway health. It was found that additional GPT’s would reduce pollutants entering Coffs Creek. However, their placement was shifted to in-network arrangements rather than at the network’s outlet. These solutions would be less of administrative overhead than the current GPT’s which are positioned in environmentally and physically constrained sites. To ensure existing GPT performance was ameliorated, Water Technology included comprehensive Audit and Maintenance procedural lists within the SWMP report, outlining important cleaning parameters for each pollutant trapping system and the contributing upstream area. Overall, a thorough and comprehensive document was provided to Council to aid in restoring waterway health to Coffs Creek, which contained pragmatic stormwater maintenance solutions and sequential approval pathways to implement these solutions.

Key Services Provided

  • Site inspection
  • Gap Analysis
  • Literature Review
  • MUSIC Stormwater Quality Modelling
  • Water Quality Auditing and SQID recommendations
  • Legislative and State Planning Policy Guidance
  • Audit and Procedural Protocols for Waterway Assessments
  • Stormwater Maintenance Checklist and Flowcharts
  • Community Education Leaflets.

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