6.4 Back Creek Management Unit 6.4.1 Site 9 Issue: Gully bank erosion Location: E 0692355 N 5994985 Waterway: Bunyan Gully Management Unit: Cooma Back Creek

Bank erosion along gully Debris build-up within gully Condition Assessment:

This Bunyan tributary gully is steep in nature and susceptible to further erosion. Active incision and headward extension is apparent. This site has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 2 12 Risk Rating: Low Management Option: Undertake grade control via the construction of a rock chute. Stabilise the remainder of the site with minor battering coupled with revegetation.

98

6.4.2 Site 10 Issue: Sediment transport Location: E 0693252 N 5994199 Waterway: Bunyan gully (deposition) Management Unit: Cooma Back Creek

Sediment deposition along lower reach of gully Sediment deposition Condition Assessment:

This site is located at the intersection of the gully documented in Site 8 and Bunyan Creek. Coarse sediments are being deposited at the bottom of gully, with expected high connectivity of fine material to connecting creek. Suggested that aim of stabilisation works should be to encourage deposition of sediments across floodplain. This site has been assessed as having a low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 3 18 Risk Rating: Moderate Management Option: Undertake sediment extraction to increase channel capacity. Follow up with fencing and revegetation of the riparian zone to encourage channel definition.

99

6.4.3 Site 11 Issue: Bank and gully erosion Location: E 0689950 N 5986127 Waterway: Cooma Back Creek Management Unit: Cooma Back Creek

Cooma Back Creek immediately upstream of Snowy Cooma Back Creek immediately upstream of Snowy Mountains Hwy Mountains Hwy

Gully erosion along Cooma Back Creek Bligh St Facing down the gully to the waterway crossing

Gully erosion along Bligh St viewed from opposing bank Upper section of the localised gully erosion Condition Assessment: Localised bank erosion is present along Cooma Back Creek upstream of Cooma. This site has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages. Additionally, gully erosion is present along Bligh Street connecting directly to creek. It has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

100

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 4 24 Risk Rating: Moderate Management Option: Install rock beaching to stabilise eroding banks. Construct rock chutes to stabilise gully erosion. Undertake works to improve road drainage.

101

6.4.4 Site 12 Issue: Bank erosion Location: E 0690396 N 5988308 Waterway: Cooma Back Creek Management Unit: Cooma Back Creek

Cooma Back Creek facing upstream Back erosion along Cooma Back Creek Condition Assessment:

Banks along this section of Cooma Back Creek are 3m high with localised bank erosion present. This creek has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 3 12 Risk Rating: Low Management Option: Localised rock beaching to manage bank erosion. Fencing and revegetation of site recommended in consultation with landholder.

102

6.4.5 Site 13 Issue: Bank erosion Location: E 691279 N 5983884 Waterway: Cooma Back Creek Management Unit: Cooma Back Creek

Erosion of outside bend Willow blockage on neck cutoff Condition Assessment:

This site is located on an outside bend of Back adjacent to Myalla Road. The majority of flow now passes through a neck cutoff held by a willow blockage. The outside bend flows in higher flow events and has some active bank erosion present. This could be stabilised by removing the willow blockage and installing native large woody debris, localised toe rock beaching coupled with fencing and revegetation would be installed on the outside bend.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 3 18 Risk Rating: Moderate Management Option: Remove in-stream willow blockage. Complete rock beaching at toe of bank to manage bank erosion. Fencing and revegetation of site in consultation with landholder.

103

6.4.6 Site 14 Issue: Bank erosion Location: E 691283 N 5983890 Waterway: Cooma Back Creek Management Unit: Cooma Back Creek

Eroding outside bend Side gully entry point Condition Assessment:

This is an eroding bank approximately 3m in height. The bank could be stabilised with toe rock beaching. An additional side gully enters the site and may require stabilisation with a rock chute.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 3 18 Risk Rating: Moderate Management Option: Rock beaching of eroding bank. Fencing and revegetation of site in consultation with landholder.

104

6.4.7 Site 15 Issue: Bed and bank erosion Location: E 0691685 N 5985643 Waterway: Cooma Creek Management Unit: Cooma Back Creek

Localised bank erosion along Cooma Creek Condition Assessment:

This site along Cooma Creek upstream of Cooma has undergone localised bank erosion. It has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 3 12 Risk Rating: Low Management Option: No structural works recommended. Fencing and revegetation of site recommended in consultation with the landholder.

105

6.4.8 Site 16 Issue: Urban water quality Location: E 0691406 N 5987949 Waterway: Cooma Back Creek Management Unit: Cooma Back Creek

Cooma Creek Condition Assessment:

The banks along this section of Cooma Back Creek are relatively stable due to their shallow sloped nature. It has been assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 2 8 Risk Rating: Low Management Option: Efficacy of gross pollutant traps to be investigated to mitigate impact of urban drainage on waterway. Revegetation with appropriate native species should be considered.

106

6.4.9 Site 17 Issue: Bank erosion Location: E 0693753 N 5994443 Waterway: Cooma Creek Management Unit: Cooma Back Creek

Cooma Creek upstream of Hwy Cooma Creek downstream of Monaro Hwy Condition Assessment:

The banks along Cooma Creek at this site are stable and highly vegetated. Assessed as having low connectivity for fine sediments due to long travel distance to Murrumbidgee water extraction point with opportunities for storage along channel margins and across floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 2 8 Risk Rating: Low Management Option: No structural works recommended. Fencing and revegetation of site recommended in consultation with the landholder.

107

6.4.10 Site 18 Issue: Bank erosion Location: E 0696967 N 6001721 Waterway: Lower Cooma Creek Management Unit: Cooma Back Creek

A view of lower Cooma Creek (foreground) and Facing upstream of Cooma Creek (background) Condition Assessment:

This site is located just upstream of the Numeralla and Lower Cooma Creek . The bottom reach of this creek has eroding banks and is likely to be a significant source of fine sediments to the . This site has been assessed as having high connectivity for fine sediments due to direct input of fine sediments from channel banks into stream flow.

Risk Assessment: Likelihood Consequence Trajectory Risk 4 4 3 48 Risk Rating: Very high Management Option: Rock beaching of eroding Creek banks. Fencing and revegetation in consultation with landholder.

108

6.5 Management Unit 6.5.1 Site 19 Issue: Bed and bank erosion Location: E 0688131 N 6066089 Waterway: Gudgenby River Management Unit: Gudgenby River

Debris build-up against bridge Overlooking river valley

Bank erosion visible along right-hand bank Bank erosion visible along left-hand bank Condition Assessment:

There has been recent channel widening and stripping of fine sediments from the channel banks and floodplain. This is likely to be a significant source of fine grained sediment (silt/clay and sand) to the channel. The banks at this location are up to 3m in height. This site is assessed as having a high connectivity for fine sediments; there is a high probability of eroded fine sediments being transported directly to the Murrumbidgee.

Risk Assessment: Likelihood Consequence Trajectory Risk 4 4 3 48 Risk Rating: Very High Management Option: Relocation of debris built up against bridge. Stabilisation of river banks with rock beaching. Fencing and revegetation of the site in consultation with the landholder.

109

6.5.2 Site 20 Issue: Bed and Bank erosion Location: E 685098 N 6068353 Waterway: Spring Station Creek Management Unit: Gudgenby River

Bank erosion at the confluence Overview of deepening up the gully line Condition Assessment:

This site consists of active bank erosion on Spring Station Creek at a location where a secondary gully enters the creek. The creek was previously unchannelised, however following flooding in 2012, the gully has now channelized and is actively deepening and delivering sediment downstream. To stabilise the confluence of the gully and Spring Station Creek, bank stabilisation is required to prevent further erosion. To manage deepening in the gully survey should be undertaken, and then strategic grade control constructed to manage deepening.

Risk Assessment: Likelihood Consequence Trajectory Risk 4 4 4 64 Risk Rating: Extreme Management Option: Construct rock beaching to stabilise bank at confluence of gully and Sheep Station Creek., Construct rock chutes in gully to control bed deepening. Fencing and revegetation of the site in consultation with the landholder.

110

6.5.3 Site 21 Issue: Bed and bank erosion Location: E 0687289 N 6060864 Waterway: Gudgenby River Management Unit: Gudgenby River

Facing upstream showing bank erosion Bank erosion along river

Gudgenby River, facing upstream Gudgenby River, facing downstream Condition Assessment:

Erosion of banks contributing fine sediments, sand deposited on benches. This site has been assessed as having high connectivity for fine sediments, fine grained sediments eroded from bank input directly into channel flow.

Risk Assessment: Likelihood Consequence Trajectory Risk 4 4 3-4 48-64 Risk Rating: Very High to Extreme Management Option: installation of rock beaching to stabilise bank of the Gudgenby River. Fencing and revegetation of the site in consultation with the landholder.

111

6.5.4 Site 22 Issue: Mobile sediment and bank erosion Location: E 0684018 N 6057252 Waterway: Half Moon Creek Management Unit: Gudgenby River

View across Half Moon Creek Condition Assessment:

This site exhibits a stable channel configuration. It has been assessed as having low connectivity for fine sediments, part of a broader area of sediment deposition.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 3 3 18 Risk Rating: Moderate Management Option: No structural works recommended. Fencing and revegetation of site recommended in consultation with the landholder.

112

6.5.5 Site 23 Issue: Bank erosion and coarse mobile sediment Location: E 0685209 N 6059222 Waterway: Honeysuckle Creek Management Unit: Gudgenby River

Active erosion along some banks View upstream from Apollo Rd bridge Condition Assessment:

Erosion of fine sediments from channel banks has occurred at this location along Honeysuckle Creek. It has been assessed as having high connectivity for fine sediments. Fine grained sediments eroded from banks are input directly into channel flow.

Risk Assessment: Likelihood Consequence Trajectory Risk 4 5 3 60 Risk Rating: Very High Management Option: Install rock beaching to mitigate bank erosion. Fencing and revegetation of site in consultation with landholder.

113

6.6 Management Unit 6.6.1 Site 24 Issue: Gully erosion Location: E 0712792 N 5987692 Waterway: Kybeyan gully tributary Management Unit: Kybeyan River

Gully erosion Gully erosion Condition Assessment:

The gully has partially stabilised as noted by the establishment of vegetation on lower banks and the entrenched channel. There is potential for high connectivity of sediment transfers to the Kybeyan and Numeralla River. This gully is assessed as having a low connectivity for fine sediments as there is a long transport distance to Murrumbidgee with opportunities for storage along channel margins and across intermediate floodplain storages.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 2-3 8-12 Risk Rating: Low Management Option: Complete localised battering and large woody debris alignment to improve bank stability. Fencing and revegetation of site in consultation with landholder.

114

6.6.2 Site 25 Issue: Sediment transport Location: E 0712324 N 5989029 Waterway: Kybeyan River Management Unit: Kybeyan River

Facing downstream from the river crossing Condition Assessment:

Stable bed and banks downstream of road crossing. Assessed as having low connectivity for fine sediments, stable vegetated channel will trap sediments and reduce connectivity.

Risk Assessment: Likelihood Consequence Trajectory Risk 2 2 1 4 Risk Rating: Low Management Option: No structural works recommended. Fencing and revegetation of site recommended in consultation with the landholder.

115