Chapter 13 of the
'Australian Runoff Quality' manual by Engineers Australia focuses on urban water corridors.
The chapter opens with a comprehensive outline of the factors that influence the ecological health and condition of urban waterways - including biological, ecological, hydrology, hydraulics and geomorphology factors. A well referenced synopsis of a decade of research into the impacts of urbanisation on waterway health follows. It covers:
- Hydrological impacts (such as increases in the rate and volume of runoff; and increases in the frequency of high volume flows);
- Changes in land use (reduction and loss of riparian zones, and loss of continuity between up-stream and down-stream communities);
- Water quality issues (increased rates of sedimentation, erosion and channelisation; contaminated sediments); and
- Biological impacts (loss of instream habitat; pests and weed species, etc).
This chapter proposes a categorisation system for urban water drainage waterway types. Seven broad categories are defined and described in terms of their rehabilitation potential and other characteristics. They range from built, regular cross section shapes that maximise conveyance to semi-natural, irregular channel forms and shapes.
The authors concur with industry guidance - the ANZECC guidelines and Australian Stream Restoration Manual - and suggest that for highly modified systems, such as urban waterways, it may not be possible to restore systems to their 'pre-developed' or natural state.
They contend that remediation strategies (improving waterway ecosystem condition, rather than re-establishing pre-urbanisation conditions) is typically the most appropriate urban waterway management response. They note this requires balancing of a range of 'competing performance objectives' across:
- Flood conveyance,
- Amenity and landscape values,
- Aquatic ecosystems,
- Protection of downstream ecosystems, and
- Safety.
A 'decision support framework' for selecting remediation options for urban waterways is provided that integrates the above set of objectives with drainage channel types.
The final portion of the paper overviews the many practical considerations that need to be made by those who are developing a prioritised works programs and strategies for urban waterways and is a useful discussion on waterway management for Local Government.