The holy grail for councils dealing with urban waterways is how to balance the need for urban water channels that meet community expectations (who prefer natural and vegetated channels), are easily maintained, cope in extremes, and deliver the best outcome over from a life cycle perspective.
Alluvium and the Mackay Regional Council have been exploring the lifecycle costs and resilience of a range of urban waterway drainage channel designs (traditional channel design and more natural channel designs.
The needs of the Council, which we captured through a series of interviews and workshops, included:
Traditional channel design
- designs must have adequate channel capacity in flood events
- designs must have a low lifecycle cost
- the channels must be easy to maintain
- the Council must acquire more expertise in the areas of design and maintaining
- the designs must be resilient in the face of cyclones and droughts.
Our results showed that:
- the capital cost is similar for all types of water drainage channel designs
- the overall lifecycle cost for operation and maintenance in normal circumstances cost is similar for all types of water drainage channels (i.e., traditional designs were only 5% cheaper than the naturalised water drainage channel, and 10% cheaper than the vegetated channel)
- However, when the impacts of extreme events (particularly cyclones) are included, the lifecycle costs of a traditional water drainage channel can be between 30% (compared to naturalised waterway) and 50% (vegetated waterway) cheaper.
How much value does the community place on natural/vegetated channels over other attributes? The next challenge will be to consider these lifecycle costs in the context of the significant additional community and environmental outcomes these systems can provide compared with the traditional drainage approaches.
Natural channel design