Prioritising to Deliver Safe Waterways and Harbours, Catchpit by Catchpit

Auckland Transport (AT) is responsible for the management of 7,500 km of roads and associated infrastructure throughout Auckland, including over 92,000 road catchpits. Stormwater runoff contaminants and gross pollutants are being discharged from their road corridors into Auckland’s waterways and harbours.

GHD Limited is assisting AT to develop and implement a programme for improving the water quality from road catchpits. The objective of AT’s City-wide catchpit prioritisation and intervention programme is to reduce the impact of road runoff discharges in an innovative, sustainable, integrated and cost effective manner. Through the targeted installation of stormwater treatment devices in road catchpits in priority areas, this programme will provide improved operations and reduce pollutant loads entering our waterways.

AT has allocated funding over the next ten years in the 2018-2028 LTP, with a total investment of capex $9 M for stormwater treatment and improved cleaning programmes. A systematic and collaborative approach is required to determine how to utilise this funding to provide best value for money, the desired environmental outcomes and manage risks.

The guideline for prioritising treatment areas were to assess where high levels of contaminants and litter are generated, and the associated impacts across a range of criteria such as public health, water quality, flood prevention and preventative maintenance.

Based on these guidelines, GHD identified a number of priority areas to be targeted for treatment. These include:

• AT PT Facilities - Park and ride, bus stations and rail stations where high litter and contaminant generation is evident.
• Amenity Areas - Road corridor drainage systems that discharge directly to beaches, waterways, or other high-use receiving environments eg. marinas.
• Critical Soakpits - Catchpits discharging to critical soakpits at risk of blockage.
• High Sedimentation in Runoff - Catchpits that receive high levels of sediment and litter from upstream overland flows (from parks, highly vegetative areas) and which may impact on downstream infrastructure (pipes and treatment devices such as stormwater ponds).
• Flooding due to Blocked Catchpits - Catchpits where blockage will lead to significant flooding which impacts on the integrity of the road pavement, affect private properties and road users, create safety issues and require multiple maintenance call outs.
• Town Centres - Town centres with high gross pollutant loads in catchpits.
• Sensitive Receiving Environments - Sub-catchments with sensitive receiving environments eg streams with high ecological value.
• High Use Arterial Roads - High-use roads in sub-catchments with sensitive and high-use receiving environments.
• Areas covered by Auckland Council’s Safeswim programme - Areas that are continually assessed as contaminated and unsafe to swim.

Priority catchments are identified using mapping tools which analyse a range of geospatial data, including asset data, traffic volumes, land use, recreational areas, hydrology, and flood hazards.

Based on the maps and workshops with AT and Auckland Council stakeholders, a prioritisation tool has been developed for the Auckland region. This will be the road map for implementing a robust treatment programme over the next ten years.