ACT State of the Environment 2007

Indicator: Riparian condition

Summary

As with the previous reporting period, reporting on this indicator is limited by the paucity of data and the lack of scientific monitoring. Given the lack of data, it is difficult to demonstrate an overall state of riparian condition in the ACT therefore linkages are made with other indicators and, at the end of the reporting period, a snapshot of information was gathered for this report (Table 1).

It was not possible to measure the impact of the drought on riparian zones in the ACT; however, importantly for this reporting period, the 2003 bushfire heavily affected some significant riparian zones. In the conservation areas affected by the fire, analysis of satellite data demonstrated a rapid and positive vegetation response, including within the riparian zones, in the first year after the fire.

For the fire-affected areas outside the conservation reserves, satellite and water quality results indicate that vegetation growth was poor. Water quality results suggest this problem remained throughout the reporting period (Worthy et al. in prep).

For all catchments not affected by the 2003 bushfire, there is not sufficient qualitative data to estimate the condition of the riparian zones.

While riparian zones are well regarded for their range of roles and functions relating to biodiversity and stream water quality, the fact is that little is known in the ACT about the state of the riparian zones during the reporting period. Progress in this area will improve with the 2007 release of Action Plan 29 Ribbons of life: Aquatic Species and Riparian Zone Conservation Strategy.

What the results tell us about the ACT

Since, the previous report, a very general survey (Table 1) suggests the condition of riparian zones within the ACT has improved (Starr 2007), except in some areas where the 2003 bushfire occurred. Post-firestorm events eroding soils from the hill slopes and stream banks in intense land use areas has, in some cases, adversely altered the riparian zone. However, this soil erosion was limited in conservation areas (Worthy et al. in prep).

Riparian condition

The interface between the land and the water that flows across the surface of the land is a key component of a well functioning catchment. The riparian zone plays a significant role in limiting movement of solid and solute loads into adjacent streams thereby safeguarding water quality from disturbances that result in sediment movement. It also significantly influences overall catchment ecology.

Following the 2003 bushfire in the catchments to the west of Canberra, the riparian condition between sites varied (see Table 1). The main factors limiting recovery during this reporting period have been land use and reduced water availability due to the drought.

The riparian zones in the conservation areas of Namadgi National Park have seen a rapid rate of revegetation since the fire and sediment is therefore trapped and protecting the waterways. However, some deposition of material in streams has occurred after intense rainfall has caused hill slope and channel erosion.

Land use and the 2003 bushfire have weakened the ability of the riparian zone to protect the waterway in the former pine plantations (Lindenmayer et al. 2004; White et al. 2006; Worthy et al. in prep). The extensive road networks, use of heavy machinery, hazard reduction burns and other salvage-related activities have affected the ability of native vegetation to establish and provide an effective riparian zone. Opportunistic weeds have prospered under these conditions. While management actions with a long-term view are underway to relieve some of the problems, the history of land use and salvage operations will have a lasting effect on the ability of these areas to respond.

Comparison of the riparian areas and catchments that have been subject to intensive land use to those of conservation or less intense land uses shows a clear distinction in response rates to disturbance. While no empirical data were available on the issue, the snapshot assessment (Starr 2007) indicates conservation areas are on track to recovery while riparian zones in areas of heavy land use are far from the initial vegetative response stages.

Elsewhere in the ACT the state of riparian zones has remained, for the most part, stable.

Riparian management strategy

In response to the importance of the riparian zone for conservation and water quality, the ACT Government launched Action Plan 29 Ribbons of life: Aquatic Species and Riparian Zone Conservation Strategy in 2007. The plan sets out a number of goals to gaining a greater understanding, better protecting and managing riparian ecosystems and their flora and fauna in the ACT.

Specifically, the plan aims to identify vegetation communities and describe riparian fauna, including vulnerable and threatened species and communities. This knowledge will aid conservation goals, objectives and actions for the riparian zone, and provide a basis upon which to plan and make land management decisions about threatened communities and species.

At the time of writing, a Riparian Zone Officer had been appointed within the ACT Government to help implement the strategy. The Officer will, among other things, prepare and undertake a monitoring program for riparian ecological communities and component flora and fauna across the ACT. Progress on implementing the strategy will be reported in the next state of the environment report.

Community involvement

During the reporting period the community contributed a massive effort toward improving riparian environments.

For example, the ACT Government funded a riparian project called ACT River Rescue that focused on recovering riparian habitat along priority streams in the ACT to address biodiversity and water quality problems. Works included fencing, erosion control, and provision of alternative stock water, weed and willow control, and revegetation. Between June 2005 and June 2007, works were conducted at 62 riparian sites spanning some 350 hectares of land; 46 kilometres of river restoration works were carried out along riparian zones.

Table 1: Assessment of riparian condition in the ACT, 2000, 2003 and 2007    
Site 2000 condition* 2003 condition* 2007 condition*
Black Jack's Creek (Murrumbidgee River) 'Lanyon' Increase in vegetation (Typha spp.) since 1944 Not impacted by fire. Vegetation improved since 2000. Condition good Major storm event flooding in early 2007 had no significant impact on the channel. Channel and banks well vegetated. Condition good.
Blue Gum Creek (Paddys River) 'Booroomba' Substantial natural regeneration within the channel, which is still adjusting to major erosion of January 1995 Catchment and creek impacted by fire. Danger of further destabilisation if ingress of large woody debris occurs. Condition poor Extensive regeneration of trees and shrubs is occurring in areas of recent rainfall leading to major erosion of unstable ground and stream banks. Condition good.
Bulgar Creek (Murrumbidgee River) Bed and bank vegetation has increased Impacted by fire. Riparian vegetation principally groundcover and shrubs. Increase in erosion unlikely unless there is an extreme rainfall event in the short term. Condition moderate Riparian vegetation burnt during the 2003 fires is recovering. Condition good.
Castle Hill Gully (Murrumbidgee River) 'Castle Hill' Vegetation colonisation on gully floor in middle–upper reaches Not severely impacted by fire. Despite appearance (high, bare and vertical walls) system is stable. Condition moderate No significant change since 2003. Condition moderate.
Condor Creek (Lower Cotter River) Not assessed for this report Not assessed for this report Heavy erosion of stream banks and surrounding areas. Native vegetation regrowth limited. Condition poor.
Congwarra Creek (Paddys River) 'Congwarra' Channel yet to reach full width; no vegetation on bed Catchment burnt. Ingress of large woody debris unlikely. Sediment ingress possible. Channel still to reach lateral extent. Condition poor Creek eroding with a number of gully headcuts evident. Creek is undercutting Paddys River Road. Condition poor.
Cotter River (Namadgi National Park) Not assessed for this report Not assessed for this report Vigorous regrowth of native riparian vegetation. Rare but occasional stream bank collapse. Condition good.
Doughboy Creek (Woolshed Creek) Increase in grasses, sedges and rushes since 1944 Not impacted by fire. Channel is still adjusting (incising) to reduced sediment supply from catchment. Condition moderate Channel continues to incise as a response to reduced sediment supply regime. This process will continue. Condition moderate.
Dunns Creek/Monks Gully (Tuggeranong Creek) 'Melrose Valley' Channel well vegetated with Typha spp. Not impacted by fire. Little advance in major headcut since 2000. Condition moderate. Channel vegetation remains intact. There has been little advance of the major gully headcut. Condition moderate.
Freshford Creek (Murrumbidgee River) 'Freshford' Increase in bed vegetation Impacted by fire. Bed vegetation is intact. Erosion is still active. Condition poor Active erosion is still evident although bed vegetation remains largely intact. Condition poor.
Freshford Gully (Freshford Creek) 'Freshford' Not assessed for this report Not assessed for this report Active erosion in the channel is evident. Condition poor.
Geals Creek (Paddys River) Some natural regeneration, mainly native species Impacted by fire. Mainly shrub species damaged. No evident erosion before fire but increase in risk due to fire. Condition moderate Despite loss of shrubs during the 2003 bushfire, there has been no erosion. Condition good.
Gibraltar Creek (Paddys River) 'Gibraltar Creek' and 'Gibraltar View' Significant natural regeneration of native species and blackberry on 'Gibraltar Creek' less so on 'Gibraltar View' Impacted by fire. Pines in catchment destroyed by fire. Increased sediment loads from pine area evident before the fire and it is highly probable that a further increase in sediment yield from the pine area will occur further destabilising the creek, particularly on 'Gibraltar Creek'. Condition poor Riparian vegetation burnt in 2003 bushfire has had limited recovery. High sediment loads from areas of pine plantation in the catchment continues. Sediment yields are expected to increase with replanting of pines in steep, highly erodible parts of the catchment. These areas are, at present, covered with dense native regrowth. Lower reaches of the creek are stable. Condition poor.
Gudgenby Creek (Naas River) No vegetation in the bed of the lower reach Catchment impacted by fire. Ingress of large woody debris and increase in sediment loads possible. Potential erosion is likely to be limited by the soil type (heavy, erosion resistant clay). Condition moderate No evidence of the ingress of sediment or woody debris following the 2003 bushfire. Channel unchanged. Condition moderate.
Gudgenby River upstream of Naas confluence (Murrumbidgee River) A substantial decline in willow numbers, though seedling willows now present Impacted by fire. Debris already present in stream. Elevated sediment loads are possible. Condition poor Despite high rainfall events in the catchment that mobilised a mass of sediment, this has not reached the creek and is unlikely to do so due to anchoring by vegetation. Condition good.
Gudgenby River downstream of Naas confluence (Murrumbidgee River) A substantial increase in native riparian vegetation, though seedling willows now present Severely impacted by fire. A major increase in load is occurring due to impact of storm event on the east slopes of Mount Tennent. Condition poor Large quantities of sediment mobilised by storm events have either not reached the river or have been washed into the Murrumbidgee River. Channel similar to pre-fire condition. Condition moderate.
Guises Creek (Murrumbidgee River) Increase in tree and shrub numbers since 1944 Not impacted by fire. Not eroding. Vegetation increasing. Condition good Stream remains stable. Vegetation good. Condition good.
Honeysuckle/Booroomba Creek (Gudgenby River) 'Ballineen' Marked increase in willow numbers Impacted by fire. Ingress of large woody debris unlikely. Sediment loads have increased. Condition moderate Reduction in sediment loads since 2003. Condition good.
Jerrabomberra Creek ACT reach only (Lake Burley Griffin) Increase in bed sedges and rushes but no shrub regeneration Not impacted by fire. Vegetation stable. Condition good Vegetation colonisation of channel continues. Chains-of-ponds are reforming in lower reaches. Condition good.
Larry's Creek (Paddys River) near Tidbinbilla Tracking Station and confluence with Paddys River General increase in exotics and native species since 1944; seedling willows present in creek near tracking station Impacted by fire. Sediment loads likely to increase and erosion as noted in Starr (2000) is likely to continue. Condition poor No major erosion since 2003, but likely under high flow conditions. Condition poor.
Naas River (Gudgenby River) 'Caloola' Channel heavily colonised by natives. Number of large eucalypt snags in channel. Some coppiced willows in channel Catchment burnt. Ingress of woody debris highly likely. Condition poor No evidence of increased sediment loads or ingress of woody debris following fire. Vegetation management carried out. Condition moderate.
Naas River (Gudgenby River) 'Glencoe' Reeds, sedges and tussocks colonised channel and surrounds. Large, senescent willows are at abandoned channel edge. Willow seedlings, possibly sourced from those in 'Caloola' are present on bar deposits. Eroded bank is bare Catchment burnt. Ingress of woody debris likely and subsequent erosion highly likely due to condition of banks (bare unconsolidated sediment). Condition poor No change in channel form since 2003. Erosion of banks comprising unconsolidated sediment will occur as channel responds to high flows; active channel width still to be established by flow events. Condition poor.
Naas River (Gudgenby River) 'Glencoe' to 'Naas valley' Reeds, sedges and tussocks. No colonisation by shrub species. Willow numbers have declined Catchment burnt. Ingress of woody debris possible. Risk of subsequent erosion is low due to the width of the channel. Condition good Full channel width (to high banks of consolidated sediment) has been reached. No evidence of active bank erosion, further significant erosion not likely. Condition good.
Naas River (Gudgenby River) 'Naas valley' to Gudgenby River confluence Grasses. Willow numbers have declined. Seeding willows are present in a depositional area near the Gudgenby River confluence Catchment burnt. Ingress of woody debris possible. Risk of subsequent erosion is low due to the width of the channel. Condition good No change in past four years. Seeding willows still present; source of parent trees unknown. Condition good.
Orroral River (Gudgenby River) Marked loss in channel definition in some sections and an increase in sinuosity in others; both presumably because of increased ground vegetation Fire impacted. Unlikely to cause problems as vegetation is of wet tussock type. Condition good No evidence of increase of erosion within wet tussock areas. Condition good.
Paddys River (Cotter River) 'Booroomba' Grasses, grassy swamp adjacent Catchment burnt. Ingress of woody debris and sediment is unlikely due to presence of large depositional area upstream. Channel still adjusting from initial incision. Condition poor The channel, as most likely excavated through the grassy swamp in the 19th century, continues to adjust by widening. Little vegetation despite fencing. Condition poor.
Paddys River (Cotter River) 'Booroomba' Wet tussocks, some teatree colonisation at downstream end of the reach since 1944 Catchment burnt. Ingress of woody debris and sediment is unlikely due to presence of large depositional area upstream. Bank erosion is likely to continue as a result of sediment sourced from upstream (Site 24). Condition not stated Minor bank erosion continues. Condition poor.
Paddys River (Cotter River) 'Booroomba' to 'Miowera' Extensive natural regeneration in the channel and on the banks since 1944. Mainly native species Stream burnt. Risk of accelerated erosion due to loss of bank protection. Condition poor Vegetation recovery has limited erosion potential. Condition good.
Paddys River (Cotter River) 'Miowera' Native shrubs. Active erosion noted in Starr (2000) Increased risk of erosion due to possible increase in sediment load. Condition poor No increase in sediment loads. No recent erosion at site of meander migration identified in previous reports. Condition good.
Paddys River (Cotter River) 'Oakey Creek' to 'Riverlea' Dominated by willows planted between 1944 and 1968 and offspring seedling willows Major depositional area with history of substantial erosion. Erosion likely to increase. Condition poor No active erosion since 2003, but most likely to occur when upstream sediment is mobilised and deposited. Condition poor.
Pierces Creek (Lower Cotter River) Not assessed for this report Not assessed for this report Heavy erosion of stream banks and surrounding areas. Native vegetation regrowth limited due to land management. Condition poor.
Reedy Creek (Molonglo River) northern ACT Grasses and trees. Alpine Bottlebrush (Callistemon sieberi) has colonised the channel in the upper reaches Not fire impacted. Creek has incised to bedrock, with channel width yet to be established in some reaches. Extensive management. Condition good Extensive natural regeneration along with tree planting and fencing. Channel yet to reach full width in some sections. Increase in sediment loads highly unlikely due to extensive sediment entrapment works in large part of catchment (Majura Field Firing Range). Condition good.
Spring Station Creek (Murrumbidgee River) Tharwa The channel floor upstream and downstream of the headcuts is (and was) well vegetated with various grasses and reeds including Common Reed (Phragmites australis) Catchment burnt. Increase in sediment loads since fire. One major headcut controlled since Starr (2000). Second headcut can be treated after it advances to a suitable site. Condition moderate Further mobilisation of sediment since 2003 due to storm events. Most sediment remains in store in tributary channels of Spring Station Creek. Gully headcut to be treated has not advanced to a site where suitable works can be carried out. Condition moderate.
Tanners Flat Creek (Murrumbidgee River) 'Oakey Creek' Colonisation by channel rushes, sedges and shrub species since 1944 Catchment burnt. Ingress of woody debris or elevation of sediment load unlikely. Condition good Channel remains well vegetated. Condition good.
Tarpaulin Creek (Murrumbidgee River) Uriarra Station Marked increase in bed and bank vegetation since 1944 Catchment burnt. Erosion due to woody debris or increase in sediment load is unlikely as the form of the creek indicates antiquity (well before European settlement). Condition good No evident active erosion or significant soil loss anticipated due to width of channel and longitudinal gradient. Condition good.
Tidbinbilla River (Paddys River) 'Tidbinbilla' Natural regeneration since 1944 from 'Tidbinbilla' to Paddys River confluence. River channel now dominated by blackberry Catchment and river vegetation both burnt. Ingress of woody debris and increase in sediment loads likely. Sections eroded in January 1995 remain prone to further bank loss. Condition poor Vegetation burnt in 2003 has recovered. Some sections where erosion was initiated in January 1995 remain prone to further bank loss. No evidence, so far, of ingress of sediment mobilised in the catchment following 2003 bushfire. Condition poor.
Tuggeranong Creek (Murrumbidgee River) lower reaches No natural increase since 1944 Catchment not burnt. Some revegetation, planting and natural regeneration. Condition good Revegetation, planting and natural regeneration continues. Condition good.
Woolshed Creek (Molonglo River) Major improvement since 1944 with marked increase in tree numbers along upper reaches and groundcover in the lower reaches. Some instream colonisation by willows Catchment not burnt. Vegetation continues to improve. Condition good Vegetation similar to 2003. Condition good.

Note: *Condition is subjectively rated as poor, moderate of good depending on vegetation condition and stability, bank erosion risk, sediment loads and catchment land uses.
Source: Starr B 2007, Visual assessment of ACT state of the environment Riparian Condition sites, Report to the Office of the Commissioner for Sustainability and Environment

Data sources and references

Consultant, Barry Starr, carried out visual assessment of sites in 2000, 2003 and 2007; the information gathered was supplemented with ACT Government reports and staff observations during the reporting period.

Lindenmayer D, Foster DR, Franklin JF, Hunter ML, Noss RF, Schmiegelow FA & Perry D 2004, Salvage harvesting policies after natural disturbance, Science, vol. 303, 5662:1303 Academic Research Library, available at <http://www.wle.umaine.edu/MaineLeap/Lindenmayer%20salvage.pdf>

Starr B 2007, Visual assessment of ACT state of the environment riparian condition sites, Report to the Office of the Commissioner for Sustainability and Environment

White I, Wade A, Worthy M, Mueller N, Daniell TM & Wasson R 2006, The vulnerability of water supply catchments to bushfires: impacts of the January 2003 wildfires on the Australian Capital Territory online, Australian Journal of Water Resources, vol. 10, no. 2:179-194, available at <http://search.informit.com.au/documentSummary;dn=203285123640127;res=IELENG>

M.Worthy, R.J. Wasson, N. Mueller, I. White, A.Wade (in prep) , Geomorphic and Water Quality responses to erosive rainfall following fire in the Cotter Catchment, Australia

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