An Australian form of Open Marsh Water Management (runnelling): long term monitoring, ancillary and extended research

The paper outlines the evolution of an Australian form of Open Marsh Water Management (OMWM) called runnelling which was implemented in relatively pristine saltmarshes. Runnelling involves shallow channels and was distinguished from OMWM which involves ditching. Both methods aim to conserve tidal hydrology. The core research covers 28 years of research on the original experimental site (Coomera Island, Queensland), in routine monitoring and impact assessments that were made periodically. It also introduces and incorporates information from associated research. This includes effects of runnelling on non-target aspects—snails and crabs. Emerging issues during the course of the longer-term research included the risk of mobilising acid sulfates and of mangrove encroachment into the saltmarsh. As well, use of the data was extended to retrofit it to address broader questions about saltmarsh processes and how to identify them. That identified progressive changes at the Coomera site, and so a further query was whether the system showed signs of approaching a tipping point. In summary, there were some identifiable effects of runnelling in all parts of the research. These were mostly related to the increased wetness near runnels, as flooding by tides would occur at tides up to 0.30 m lower than the pre-runnelling situation. The increased wetness was related to plants, snails and crabs. From a mosquito management perspective the method was successful. From an environmental perspective the environmental changes were only very close to runnels (within 10 m). The overall changes at the experimental site were consistent with other changes in eastern Australia, especially of mangrove encroachment into saltmarshes. Once the runnelling method appeared to manage mosquitoes without damaging wetland values it was adopted widely throughout south east Queensland, encouraged by the positive attitude of permitting agencies, but longer-term evaluation was hindered by lack of relevant records.