Mulloon Creek
About the catchment
Location | Traditional Owners | Climate | Landform | Hydrology | Geology | Soils | Vegetation | Land Use
Location
Mulloon Creek is located in the NSW Southern Tablelands about 50km east of Canberra. The nearest towns are Bungendore (16km to the west) and Braidwood (35km to the east).
Mulloon catchment covers about 23,000 Hectares. It takes in the sub-catchments of Rattal Creek, Sandhills Creek and Shiel Creek.
Mulloon Creek is a tributary of Reedy Creek, which itself is a tributary of the Shoalhaven River. The Shoalhaven flows to the Pacific Ocean near Nowra on the NSW South Coast. It is part of Greater Sydney’s drinking water supply.
Traditional Owners
Being on the spine of the Great Dividing Range, it is likely that Mulloon played host to a number of Indigenous nations. Mulloon is nearby to the traditional lands of four nations - Ngunnawal Ngambri, Yuin, Ngarigo, and Gundungurra.
Climate
Generally, Mulloon’s climate is cool temperate. Summer maximum temperatures can reach 38 degrees C. Winter minimum temperatures can be as low as -10 degrees C. The annual average temperature is about 20 degrees C.
Average annual rainfall is around 650mm.
The Mulloon Institute has been closely monitoring the weather in the catchment for the past four years. This monitoring paints a dramatically different picture of the climate than the annual averages would make you think.
Average annual rainfall for the past four years has been over 1,100mm. 2021 recorded 1,261mm which is higher than for any of the past 120 years of rainfall recorded at nearby weather stations.
2023 recorded 900mm, yet the six months between May and November were close to the driest on record. This period was also the hottest on record, which echoed the global picture - 2023 being the hottest year on record for the entire planet.
Landform
Mulloon catchment sits immediately east of the Great Dividing Range. It is part of the Lachlan fold Belt - a south to north tending series of mountain ranges and valleys extending west from the Pacific Ocean to the plains of the Murray-Darling Basin, and north from Victoria to southern Queensland.
The catchment is about 40km long and around 6km at its widest. The elevation ranges between 700m and 1,200m. The headwaters of the catchment are steep and heavily timbered. The valley floor is interspersed with a series of floodplain pockets that become larger further downstream as the slopes become gentler and the flow of the creek is able to slow and spread out more.
Lower Mulloon is characterised by a large floodplain pocket 10km long and around 1km wide. This, and the other smaller floodplain pockets of the catchment, is understood to a be former chain-of-ponds system that has become deeply incised since European settlement.
Hydrology
Formerly, the intact floodplain pockets of Mulloon Creek would have allowed pulses of water to spread out, de-energizing and filtering such events. Today, the incised nature of the Mulloon Creek means that pulses remain confined to a single channel, creating high energy flows that cause further erosion and poor water quality.
The Mulloon Rehydration Initiative (MRI) is aiming to rebuild the valley floor of the Mulloon catchment so that once again flow pulses can spread out, de-energise and be filtered by the re-estabishing vegetation.
Geology
The geology generally defines the shape of the catchment, and the course of Mulloon Creek and its tributaries. Generally, the creek itself flows along the boundaries between differing geological units which comprise a combination of granite and sedimentary rock.
The age of the underlying geology ranges from Devonian granites (355-420 MYBP) through to deep marine Silurian and Ordovician shales and sandstones (420 - 485 MYBP) laid down well before the Lachlan fold belt was formed about 120 MYBP.
The catchment also contains much younger sedimentary geology. There are small pockets of remnant Tertiary age (65 MYBP) stream terrace sediments above the floodplain at lower Mulloon.
There are also substantial alluvial sediments, mostly laid down within the last 12,000 years, that comprise the floodplain pockets and alluvial fans of the catchment.
There is also the odd outcrop limestone in the catchment.
Soils
The soils of the catchment are generally a reflection of their underlying geology. If associated with the shales and sandstones, they are shallow, infertile and erodible. The granite soils are deeper, but because of the type of granite, the soils tend to be poorly draining, prone to water logging, and erodible.
There are substantial areas of alluvial soils in the valley floors and alluvial fans, which have moderate fertility, but are also susceptible to erosion.
An interesting feature of the catchment is the extent of aeolian (wind blown) soils. Sandhills Creek catchment gets its name because of the extensive aeolian sands in the catchment. It is thought that these sands were blown up out of the Weereewa (Lake George) basin during the last ice age 12,000 - 40,000 YBP.
Vegetation
About half of 23,000 hectare Mulloon catchment is covered in native woodland and forest. Much of this is in the upstream part of the catchment, and most is in National Park or State Conservation Area. The remainder of the catchment has either been cleared for agriculture or is naturally grassland.
The ridges and the upper hill slopes of Mulloon are generally classified as Southern Tablelands Dry Sclerophyll forest comprising Red Stringy Bark, Brittle Gum, and Scribbly Gum.
In the National Park and Conservation Area there is also Southeast Dry Sclerophyll Forest co-dominated by Sivertop Ash and Narrow Leaf Peppermint.
The mid-slopes are generally classified as Tablelands Grassy Woodlands, comprising Snow Gum, Black Sally, Candle Bark and Ribbon Gum.
In the upstream part of the catchment, and in the immediate vicinity of Mulloon Creek, the vegetation is mapped as Tablelands Swamp Flats Forest, comprising Ribbon Gum and Snow Gum overlying grassy, damp flats.
The floodplain pockets generally comprise wet and dry grassland complexes dominated by Poa Tussock, Weeping Rice Grass, Wallaby Grass and a range of sedges, herbs and forbs. In many cases these areas also comprise introduced pasture grasses. Invasive species such as Serrated Tussock, Chilean Needle Grass, Cane Needle Grass, and African Love Grass can also be present in these grasslands.
The riparian areas comprise reeds such as Cumbungi and Phragmites, and rushes such as Schoenoplectus and Eleocharis. Such areas can also be dominated by Crack Willow and Blackberry.
Instream vegetation generally comprises Milfoil, and Entire Marshwort.
Land Use
Historic
Post settlement historic land use has been dominated by grazing, as is the case today. However, other activities included gold, copper, lead and zinc mining. These minerals were also smelted in the catchment. This activity was responsible for much of the early land clearing as timber was required for the smelting process.
Eucalyptus distilling was also a major activity in the catchment in the 19th and early 20th Century. This product was and continues to an important disinfectant.
The forests of the upper catchment have also been an important source of saw logs and other timber products for much of the past 200 years.
Current
Current land use is predominantly sheep and cattle grazing. However, more recently land use is diversifying into other commodities such as pastured egg production, goat herding, and compost making. Ecotourism is also gradually expanding as people from the city seek peaceful retreats in the country.
Importantly, Mulloon occupies part of Sydney’s drinking water catchment. Therefore, a key commodity for the catchment is its water.
As we move into a future that places greater value on ecosystem services, then water quality, carbon credits, and even biodiversity conservation incentives will become an increasingly important component of the economic output of the catchment.