Deep Creek (drought refuge reach)
Deep Creek refuge reach location, surface geology and depth to watertable mapping along with locations of indicative cross sections, pools in the upper se
Deep
Creek refuge reach location surface geology and depth to watertable mapping along with locations of indicative cross sections pools in the upper seection of the reach and radon ection of the reach and radon
field assessment sites are shown below (Figure 1 & 2). Figure 3 illustrates the local hydrogeology (including physical processes), topography and key floral species of a representative river pool (Doggetts Bridge). The location of this reach in the broader landscape is shown in Figure 5. Figure 4 gives some indication of the variation in geology and associated geomorphology along the refuge reach.
LOCAL ECOHYDROGEOLOGY DEEP CREEK (DOGGETTS BRIDGE
(
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Figure 3
Ecosystem Type: River system with numerous permanent pools. Ecosystem Type:
River system with numerous permanent pools
Land use: Deep Creek Catchment is significantly altered due to land use change. Major land use is dryland grazing of cattle and sheep. Clearing and introdu
uction of exotic woody species such as willows have impacted geomorphologic and physical processes in the catchment.
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Values: Deep Creek supports numerous threatened and vulnerable species listed under the Envirnonmental Protection and Biodiversity Conservation Act including a population of Yarra P
Pygmy Perch –
P h the most northerly population in Victoria, and last recorded in the Melbourne Water region. A high percentage of other native fish species h
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Geology/geomorphology: The flow path of Deep Creek is controlled by geological structures. The catchment is dominated by basalts of the Newer Volcanics that forced the creek to realign when they flowed over the pre‐existing landscape. Basement rock (shales and sandstones etc) underlying outcrops (at the surface) and faulting havve had significant impacts on the sinuosity and stream form. Chain of Ponds geomorphology occurs across the alluvium beds north of Lancefield as the creek runs east from the headwaaters, where a shallow, often indistin t hannel links relati el deep pools So th ards northeast of Lan efield the basalt pin hes o t e posin the nderl in bedro k in the hannel in
indistinct channel links relatively deep pools. Southwards northeast of Lancefield; the basalt pinches out exposing the underlying bedrock in the channel in
n pla es b t still s pportin
n places but still supporting marshy backwaters in the alluvial floodplain. Further south a more incised stream form dominates; the floodplain narrows within low‐sediment yielding geeologies, and channel confinement against topographic/basement highs and faulting has forced incision of the creek through the basalt into the fractured rocks of the underlyingg basement.
Hydrology/Hydrogeology: Deep Creek is a seasonal creek; typically flowing near‐permanently for most of the year. Discharge mainly occurs in response to
o rainfall events and can dry out completely during medium term drought Release of bank storage following flood events contributes to baseflow with localised groundwater cells with
out completely during medium term drought. Release of bank storage following flood events contributes to baseflow
with localised groundwater cells with
hin the fractured rock aquifers
hin the fractured rock aquifers feeding permanent pools.
Groundwater flows from areas of higher elevations towards lower topographic areas in the catchment such as drainage lines. The groundwater elevation is above and below the level of the creek bed at different locations along the reach which leads to associated spatial variability in groundwater discharge. This is supported by radon analyysis results (map on right). Permanent pools are maintained by groundwater discharge where the river bed level intersects the watertable or by a localised flow path within a geological structure (fault or joint). The shallow channel bed in the Chain of Ponds river style (map on right) is thought to lie at or above groundwater elevation; groundwater discharge may cause waterlogging but not permanent baseflow during low flow periods in this area. In more incised reaches down
nstream, groundwater is likely to contribute to baseflow for much of the year. However, prolonged dry periods have reduced groundwater levels previously, in turn reducing groundwater contributions to pools. This may be visually evident by the cessation of spring discharge, or alternatively by the rreappearance of springs post the wet periods of 2011.
Ecosystem Services: Groundwater discharge to the creek provides baseflow and maintains permanent pools that provide refuge for aquatic flora and fauna including Yarra Pygmy Perch during low flow and drought periods Groundwater fed springs (including contact and fault springs) create unique
fauna, including Yarra Pygmy Perch, during low flow and drought periods. Groundwater‐fed springs (including contact and fault springs) create unique habitats, on which some species are likely to be reliant. LOCATION GEOLOGY AND DEPTH TO WATERTABLE
LOCATION, GEOLOGY AND DEPTH TO WATERTABLE
Figure 1
Threats: The catchment is under pressure from development, and increased extraction (from groundwater and surface water), which could impact water quality (due to stormwater runoff to the creek) and induce groundwater level declines, respectively. Stream morphology of Deep Creek and groundwater discharge maintain the ecological values of the system Changes in groundwater elevation could reduce groundwater inflows to the pools groundwater discharge maintain the ecological values of the system. Changes in groundwater elevation could reduce groundwater
inflows to the pools
and/or see them dry up completely. Water quality of the refuge pools is critical in low flow and drought periods therefore reduced groundwater quality due to land use and/or recharge changes could also influence habitat quality and species survival in the pools. Lack of riparian vegetation is a major problem (provides shade, bank stability and filtration of surface water runoff) and existing stands could be at risk from falling watertables where they depend on subsurface presence of groundwater. Stock access prevents establishment of healthy riparian vegetation and is a major threat to bank stability and water quality, particularly to refuge pools during dry periods.
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Figure 2
Sensitivity: The refuge pools are highly sensitive to changes in the hydrological regime and hence changes in groundwater elevations, which could lead to reduced inflows during low flow periods. Fewer, shallower refuge pools, with lower resistance to drying and changes in water quality may result in loss of individuals and/or species as refuge habitat declines.
Groundwater extraction from nearby bores (e.g. within 1km) will have significantly more potential to impact the pools than extraction from more regional locations (e.g. at >1km distance), due to the localised groundwater flow systems that support them.
Monitoring: Knowledge gaps exist around the groundwater flux to streams in high flow and low flow periods. There is a need to understand and
quantify groundwater contribution to the refuge pools and to stream quality throughout the year through: detailed analyses of baseflow chemical properties (under assessment from DSE) to determine baseflow contribution; assessment of remnant permanent pool dynamics by monitoring localised groundwater levels and pool levels to develop a water budget illustrating groundwater contribution; and coordination of groundwater and ecological monitoring to identify links between groundwater contributions and ecosystem health/quality.
Key information sources:
GHD, 2010. Report forRomsey
GHD
2010 Report forRomsey
Groundwater Investigation Groundwater Assessment Report for Ministerial Guidelines.
CHANGING LANDSCAPES AND GEOMOR
CHANGING LANDSCAPES AND GEOMOR
RPHOLOGY
E
F
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B
E th T h 2006
Earth Tech, 2006. Environmental Flow Determination for the Maribyrnong. Issues
Paper.
Ryan, 2011. Flood assessment
Post flood assessment of Yarra
pygmy perch and other fish in Deep Creek near Lancefield (
(2010)
)
Figure 4
Figure 5
Water Technology, 2008. Site Specific Geomorphic Investigation ‐ Deep Creek Upper Management Unit.