Upland Swamp Rehabilitation Workshop
In early December 2007 a two-day workshop was held on ‘Upland Swamp Rehabilitation and Management’.
Attendees at the ‘train-the-trainer’ style workshop included key Council and NPWS staff and representatives from local bush regeneration contractors.
The workshop was held as part of Council’s Upland Swamp Rehabilitation Project, which has received $87, 000 of federal funding from the Natural Heritage Trust, through the HNCMA’s Wetland Management Program.
The project will comprise trials of soft engineering techniques, targeted weeding and regeneration works within and above degraded upland swamps primarily in the Jamison Creek and Yosemite Creek sub-catchments.
An Environmental Trust Grant (NSW Govt.) is in the process of being assessed which will secure further funding to extend these works into a further six priority sub-catchments.
Key Outcomes of the workshop were: Soft engineering (coir logs, straw bales etc) are often preferable to hard engineering solutions as they are cost effective and can be left in situ to become part of the swamp system. Soft engineering is particularly effective for spreading and slowing concentrated flows into a more natural pattern allowing absorption. Soft engineering techniques are able to be adapted on a site by site basis.
WHAT ARE THE PROBLEMS?
Many upland swamps in the urban interfaces of the Blue Mountains continue to be degraded by the impacts of our towns, roads and lifestyles. Stormwater is one of the leading culprits, with increased, concentrated and polluted flows leading to channelisation, piping, headcuts, gully erosion and weed invasion in our swamps. These changes to the natural hydrological cycle are very detrimental to swamp communities and if unchecked may lead to the loss of the swamp altogether. For example, where swamps are dissected by eroded channels and gullies water that would normally be spread out and held within the peaty soils are drained into that centralized point changing the hydrology of the swamp-causing draining and drying – especially in the peripheral areas. Once the organic swamp substrate dries out, it may become hydrophobic (water repelling) – at this point the recovery of the swamp community is highly unlikely. These problems are further exacerbated by changed fire regimes-either too frequent or too infrequent and/or at inappropriate intervals between events. This leads to changes such as the proliferation of obligate seeders, altering the floristic assemblages within many urban swamps. Over extraction of groundwater is a potential threat as recharge areas and times are very poorly understood and there appears to be a reticence on the part of managers to apply the precautionary principle. Climate change will intensify the consequences of these threats.
This project is the first step in achieving a holistic approach to the management of upland swamp systems by addressing the immediate problems of inappropriate stormwater delivery.
WORKSHOP DAY 1:
BACKGROUND TO SWAMPS AND ISSUES
The workshop was held in two distinct parts. Attendees initially listened to presentations from a variety of speakers. Eric Mahony (BMCC) and Paul Richardson (formerly BMCC) gave a brief history of the nature of problems in Blue Mountains swamps and past approaches to these issues.
Geoffrey Hope is the Professor of Natural History in the Department of Archaeology and Natural History at the Australian National University (Canberra). Geoffrey spoke on the history of upland sandstone wetlands, which he has researched using pollen analysis and other fossils such as charcoal. To Geoffrey, “peatlands are archives” of materials that allow an understanding of vegetative cover over time, fire history and long-term ecological processes.
Geoffrey said that Blue Mountains swamps are mainly alluvial, with some peat interspersed in the substrate. In general, upland sandstone bogs commence 16-12000 years ago, while some are 5-3000 years old. Some bogs appear to have a history of natural failure but in general they have been fairly stable communities for around 10000 years. Fire has always featured in the history of bogs, but has become far more significant post-European settlement. Geoffrey suggested that peat will usually not burn (providing it is moist at the time of fire), but the removal of the shading effect provided by shrubs can change the nature of the swamp post-fire.
Allan Fox has worked for the NSW NPWS in a range of capacities including wildlife management, education/interpretation and management plan development. Allan outlined the geology of the Blue Mountains and the physical basis for the formation of hanging swamps.
Roger Good re-emphasized the need to adapt the approach according to the desired outcomes (e.g. just weed control or the re-establishment of a functional wetland), the degree of degradation and the size and gradient of the catchment. Some of the main points conveyed by Roger included the need for clarification of the problem to be addressed and the techniques to be used, the importance of an assessment of detrimental effects likely to be caused by the rehabilitation work itself, the need for adaptive management and adherence to the precautionary principle, and the importance of conducting ongoing monitoring and maintenance for years following the initial works to ensure that natural processes are being restored and the vegetation community is self-sustaining.
Day 1 of the workshop concluded with a field inspection of various types of degradation in or near the swamps around Wentworth Falls Lake.
WORKSHOP DAY 2:
IMPLEMENTATION OF TECHNIQUES
Day 2 of the workshop involved all participants in hands-on work to illustrate soft engineering methods for the treatment of channelisation in or above swamps. A site at Wentworth Falls Lake was chosen for the demonstration, with participants building walls of coir logs and/or wrapped straw bales to slow flow and send water sub-surface to re-wet the swamp. If more time had been available a “chain of ponds” would have been constructed as water itself these are excellent energy dissipaters.
Geoffrey Hope demonstrated coring in the peat near the western end of the swamp. Distinct layers of charcoal could be observed dating back thousands of years indicating fire events, and sediment inputs were clear after some of these fire events indicating post fire erosion. Not surprisingly the newest layers were extremely sandy indicating the beginning of European settlement.
Source: Bushcare Blue Mountains BMCC 2007