AECOM does not warrant the accuracy or completeness of information displayed in this map and any person using it does so at their own risk. AECOM shall bear no responsibility or liability for any errors, faults, defects, or omissions in the information.
DRY
CREEK
220
rt
No
24
0
H
rn
23
0
he
wy
FFoorrbbeess
300
280
Wa
Watteerrffoorrdd
P
Paarrkk
370
380
Powlett S
t
310
St
K
Kiillm
moorree
0
27
ney
Syd
Dry Creek
Option
SUNDAY
CREEK
25
0
S
Suunnddaa yy
C
Crree eekk
K
Kiillm
moorree
E
Eaa sstt
Hume Fwy
DRY
CREEK
26
0
KILMORE
CREEK
Quinns Road
Option
290
340
C
Clloonnbbiinnaa nnee
350
Western
Option
420
0
36
BROADHURST
CREEK
0
32
500
480
510
330
n Hwy
520
Norther
0
40
0
41
Wa
Wannddoonngg
490
B
Byyllaa nnddss
H
Heeaa tthhcc oottee
JJuunnccttiioonn
460
0
47
440
39
0
430
450
H
Hiiddddee nn
Va
Va lllleeyy
High St
DRY
CREEK
PROJECT ID
60242832
CREATED BY
TCH
LAST MODIFIED TCH 30 JAN 2014
LEGEND
www.aecom.com
Proposed Bypass Alignment
N
Index Contour
DATUM GDA 1994, PROJECTION MGA ZONE 55
0
0.5
1:80,000
1
Wa
Wallllaann
Kilometres
2
when printed at A4
Contour
Data sources:
Base Data: (c) 2013 DSE
Map Document: (P:\60304304\4. Tech work area\4.99 GIS\02_Maps\M012_WaterTable.mxd)
Watertable Depth Below Surface (m)
FIGURE 16
WATERTABLE DEPTH
<5
5-10
VicRoads
10-20
Kilmore-Wallan Bypass
20-50
>50
Figure
16
A4 size
AECOM does not warrant the accuracy or completeness of information displayed in this map and any person using it does so at their own risk. AECOM shall bear no responsibility or liability for any errors, faults, defects, or omissions in the information.
DRY
CREEK
220
rt
No
24
0
H
rn
23
0
he
wy
FFoorrbbeess
300
280
Wa
Watteerrffoorrdd
P
Paarrkk
370
380
Powlett S
t
310
St
K
Kiillm
moorree
0
27
ney
Syd
Dry Creek
Option
SUNDAY
CREEK
25
0
S
Suunnddaa yy
C
Crree eekk
K
Kiillm
moorree
E
Eaa sstt
Hume Fwy
DRY
CREEK
26
0
KILMORE
CREEK
Quinns Road
Option
290
340
C
Clloonnbbiinnaa nnee
350
Western
Option
420
0
36
BROADHURST
CREEK
0
32
500
480
510
330
n Hwy
520
Norther
0
40
0
41
Wa
Wannddoonngg
490
B
Byyllaa nnddss
H
Heeaa tthhcc oottee
JJuunnccttiioonn
460
0
47
440
39
0
430
450
H
Hiiddddee nn
Va
Va lllleeyy
High St
DRY
CREEK
PROJECT ID
60242832
CREATED BY
TCH
LAST MODIFIED TCH 30 JAN 2014
LEGEND
www.aecom.com
Proposed Bypass Alignment
N
Index Contour
DATUM GDA 1994, PROJECTION MGA ZONE 55
0
0.5
1:80,000
1
Wa
Wallllaann
Kilometres
2
when printed at A4
Contour
Data sources:
Base Data: (c) 2013 DSE
Alignment: (c) VicRoads
Map Document: (P:\60304304\4. Tech work area\4.99 GIS\02_Maps\M011_WaterSalinity.mxd)
Watertable Aquifer Groundwater
Salinity (mg/L TDS)
<500
7,000-13,000
500-1,000
13,000-35,000
1,000-3,500
>35,000
3,500-7,000
FIGURE 17
GROUNDWATER SALINITY
VicRoads
Figure
Kilmore-Wallan Bypass
17
A4 size
AECOM
8.2
Kilmore Wallan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
36
Hydrogeology
Groundwater is also described in the Kilmore-Wallan Bypass Geotechnical Study (VicRoads, 2013), including the
following key points:
-
A review of bore information available from DSE indicated a static groundwater level table between 3.6m
and 48m below ground level in the vicinity of the study area.
-
There is potential for groundwater to be intercepted in areas of deep cut, as well as the possibility of
encountering perched water tables along the alignments.
-
The Newer Volcanics aquifer is a fractured rock aquifer, primarily recharged through areas of basalt rock
outcrop. Hydraulic conductivity of the aquifer is likely to be highly variable and dependent on the degree of
interconnection and fracture patterns.
-
The presence of springs, while not observed, is possible. Although localised, these features may have a
high recharge capacity due to the steep surrounding hills.
-
Salinity recorded in the identified registered bores identified ranges between 510 S/cm and 6700 S/cm.
8.3
Information sources
Databases from a range of sources were available to inform an investigation of groundwater, although each
database is largely informed by common data that may exist for known bores. The following databases were
reviewed:
-
Victorian Water Resources Data Warehouse (DSE) – an interactive map-based tool that enables specific
sites to be identified and their related data extracted
-
National Groundwater Information System (NGIS) – facilitated by the Bureau of Meteorology, this database
is currently only available on request but scheduled to be released as a web portal in 2014
-
Information received from VicRoads comprising consolidated reports and databases from a range of
sources.
Mapping of water table depths across Victoria (available within the information supplied) provides an overview of
approximate depth to groundwater within the study area. This aligns with the previous findings from individual
bores, indicating a depth to the water table that ranges from less than 5m to between 20m – 50m.
Regional mapping also suggests that the salinity of groundwater within the study area is most likely to range from
between 500 - 1,000 mg/L across approximately half of the area, with the remainder up to 1,000 – 3,500 mg/L.
Groundwater salinity may be below 500mg/L in some limited areas. A plan indicating the location of the bores is
provided in Appendix C.
8.4
Potential Impacts
The following is broad outline of the potential groundwater bearing units / conditions that may be encountered in
the larger cuttings along the possible road alignments. This summary is based on a limited review and should be
considered as indicative only. Additional desktop review, database interrogation and eventually site investigation
is strongly recommended in order to validate (or adjust) the information presented.
It should be noted that the general literature does not typically provide commentary on perched water table
conditions as this is a localised, site specific issue which cannot be discounted until proven to be absent from a
site and field testing would be required to provide certainty relating to the presence or absence of groundwater.
The Variation to State Environment Protection Policy (Waters of Victoria) indicates that salinity levels for water
discharged to waterways in the Broken catchment should be below 500 S/cm. Intercepted groundwater with
salinity levels in excess of 500 S/cm will require treatment prior to being discharged to a waterway.
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8.4.1
Kilmore Wallan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
37
Impact of groundwater on road
Where the proposed option intersects local groundwater, it is likely to infiltrate through the ground and enter the
road drainage network. While the roadside swales can be designed to cater for the additional flows, the existing
high salinity of the groundwater may mean that it cannot be discharged to local waterways.
Where the road alignment is higher than the top of the aquifer, soak away pits can be designed to capture base
flows in the swales and allow the groundwater to re-enter the aquifer.
If the road surface is below the local groundwater level swales may need to be used to convey flow to a location
where the groundwater is lower so that soak away pits can be effective. This will often be achievable as part of
the normal road drainage design. Groundwater may also enter excavated areas during construction. Where this
occurs, sumps may be required to capture groundwater to keep the working area dry.
8.4.2
Impact of road on local groundwater
Proposed excavations have the potential to lower existing groundwater levels as water infiltrates into the cuttings.
In extreme cases, this can result in local land subsidence, however the most likely impact may be to reduce bore
extraction rates in close proximity to the alignment.
The bypass options have been reviewed for their relative likelihood of encountering groundwater, based on the
indicative geology and depth to the water table in areas where the alignments require deep cutting. The options
are discussed further below and the geology and implications for each section of cut summarised in Table 15.
The impact of excavation on nearby bores is difficult to determine due to limited existing information and the
variable nature of the local geology. Further field investigations would need to be undertaken as the project
progresses to determine whether the proposed works may impact existing bore yields.
8.4.3
Quinns Road option
Potential interaction with groundwater would be most likely in areas of significant excavation. The likelihood of
impacts associated with groundwater along the Quinns Road alignment should consider the following:
-
Near South O’Grady’s Road the alignment is cut into the slope for a distance of approximately 700m up to a
maximum depth of approximately 12m. The indicative water table depth in this area is mostly 20m – 50m
but may be shallower. There is some potential to encounter groundwater at the base of the cutting.
-
A section of cut following Mathiesons Road is less likely to encounter groundwater given the surrounding
terrain and the indicative depth to the water table in excess of 10m.
-
Approximately 600m of deep cut with a maximum excavation depth of 25m following the Epping-Kilmore /
Quinns Road roundabout has the potential to encounter groundwater, which may be recharged by the hills
to the east.
8.4.4
Western option
The Western option follows same geometry as the Quinns Road alignment as far as the Northern Highway and
therefore shares the conditions described above in the first three points. Beyond the intersection with the
Northern Highway the following is noted:
-
Near South O’Grady’s Road the alignment is cut into the slope for a distance of approximately 700m up to a
maximum depth of approximately 12m. The indicative water table depth in this area is mostly 20m – 50m
but may be shallower. There is some potential to encounter groundwater at the base of the cutting.
-
A section of cut following Mathiesons Road is less likely to encounter groundwater given the surrounding
terrain and the indicative depth to the water table in excess of 10m.
-
Between Mill Road and Fitzgerald Road the road rises gently through a section excavated at a depth of
generally less than 5m. The water table in the vicinity of Mill Road is indicated as less than 5m, increasing
to 10m – 20m at Fitzgerald Road. There is therefore some potential to encounter groundwater but given the
relatively shallow depth of cut this is likely to be limited to localised, rather than regional, groundwater
interaction.
-
The option includes an excavation depth up to approximately 15m as the road descends towards the
Kilmore Creek Bridge. The depth of cut presents some risk of encountering water-bearing horizons within
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Kilmore Wallan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
38
the underlying geology. Indicative groundwater salinity in the vicinity is indicated as between 1,000 to 3,500
mg/L, which could represent a potential impact on water quality in Kilmore Creek if groundwater was
encountered and permitted to drain to the waterway.
8.4.5
Dry Creek option
The topography of the Dry Creek option is subject to far greater variation and change in elevation than the other
options. The indicative water table depth along much of the length is often less than 5m, increasing to 10m – 20
m on steeper, upslope areas. However, the local geology suggests a lower likelihood of intersecting significant
regional groundwater. Groundwater is most likely to be encountered at the base of the deeper sections of cut.
The regional salinity of groundwater is indicated as between 500 – 1,000 mg/L for most of the alignment, but
rises to 1,000 – 3,500 mg/L (and potentially even higher) in some sections. As the option follows Dry Creek for
much of its length, drainage of saline groundwater to the waterway could potentially impact water quality.
However, it should be noted that this prediction of water quality is based on regional mapping and actual water
quality is likely to be site specific and depend on the particular groundwater lens that may be intersected.
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Kilmore Wallan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
Alignment
Cutting ID
Quinns Road*
Quinns Road*
Quinns Road*
1
2
3
(Approx.)1 Cut max. depth
Potential Subsurface Geological Profile2
(Approx.) 2
To
102150
10
Kilm ore Siltstone / Sands tone
103070
8
Kilm ore Siltstone / Sands tone
103600
7
Kilm ore Siltstone / Sands tone
Quinns Road*
4
104550
105500
7
Quinns Road
5
107900
109100
23
Quinns Road
6
110300
110400
3
Quinns Road
7
111300
111400
5
Western*
Western*
Western*
Western*
8
9
10
11
501200
502650
503050
504300
501900
502850
503400
505300
10
8
7
7
Wes tern
12
507100
507600
4
Wes tern
13
508100
508300
3
Wes tern
14
508650
509750
7
Wes tern
15
515900
516500
12
Wes tern
16
517000
517200
5
Dry Creek
17
301900
302450
15
Dry Creek
Dry Creek
Dry Creek
18
19
20
304250
307800
308350
304400
308200
308950
4
25
25
Dry Creek
21
310300
311800
20
Dry Creek
22
312400
312800
4
Notes :
Table 13
Cut Chainage
From
101400
102870
103300
39
Potential Groundwater Implications 4
Silurian Aged s edim entary unit - groundwater table may be intercepted towards bas e of cutting (if at all). If
pres ent, water inflow will be dis continuity controlled (joints, s hears and faults)
In places , Newer Volcanics have been known to be a low volum e aquifer (typically good water quality) however,
Newer Volcanics overlying Kilm ore Silts tone /
water quality and whether horizon is water bearing is s ite s pecific. Although a s hallow cut, being on the edge of a
Sandstone (if the cut extends through volcanics ,
valley there is potential that the cutting could penetrate through the volcanics capping and into the underlying
depending on location, m ay encounter water
Silurian (see above for s um m ary). Given location, there is a pos s ibility that a paleochannel m ay be present and if
bearing alluvials between volcanics and silts tone)
intercepted this could be a source of higher inflows.
Silurian Aged s edim entary unit - groundwater m ay be intercepted in cutting and pos s ibly greater flows than above
Kilm ore Siltstone / Sands tone
may occur (as cutting is pos itioned in foothills of larger Silurian Rock ridge). If pres ent, water inflow will be
dis continuity controlled (joints , s hears and faults )
Kilm ore Siltstone / Sands tone
Lower likelihood of groundwater iss ues at this location (com pared to above)
Kilm ore Siltstone / Sands tone capped by either
Lower likelihood of groundwater iss ues at this location (com pared to above). Note: com pared to Newer
Pintadeen Basalt or Newer Volcanics
Volcanics the Pintadeen Bas alt is less known as a potential aquifer
Sam e as cutting no.1
Sam e as cutting no.2
Sam e as cutting no.3
Sam e as cutting no.4
Poss ible that s om e groundwater m ay be intercepted in Newer Volcancis (s ee above), but given elevation and
Newer Volcanics capped plateau
shallowness of cutting lower likelihood of regional groundwater is sue (localis ed m aybe)
Poss ible that s om e groundwater m ay be intercepted in Newer Volcancis (s ee above), but given elevation and
Newer Volcanics capped plateau
shallowness of cutting lower likelihood of regional groundwater is sue (localis ed m aybe)
Kilm ore Sils tone / Sands tone
Lower likelihood of groundwater iss ues at this locaiton
Newer Volcanics capped plateau - cut s ufficiently In places , Newer Volcanics have been known to be a low volum e aquifer (typically good water quality) however
deep that it is pos s ible that it m ay extend through
whether the horizon is water bearing and what the water quality is , is s ite s pecific. Although relatively s hallow
volcanics and into underlying Kilm ore Silts tone /
there is potential that the cutting could penetrate through the volcanics capping and into the underlying Silurian
Sandstone (pos s ibly m ay intercept water bearing (see above for s um m ary). Given location, there is a pos s ibility that a paleochannel m ay be pres ent and if
alluvial paleochannel depending on location)
intercepted this could be a source of higher inflows.
Poss ible that s om e groundwater m ay be intercepted in Newer Volcancis (s ee above), but given elevation and
Newer Volcanics
shallowness of cutting lower likelihood of regional groundwater is sue (localis ed m aybe)
Silurian Aged s edim entary unit - groundwater table may be intercepted towards bas e of cutting (if at all). If
Kilm ore Siltstone / Sands tone
pres ent, water inflow will be dis continuity controlled (joints, s hears and faults)
Kilm ore Siltstone / Sands tone
Lower likelihood of groundwater iss ues at this location
Silurian Aged s edim entary unit - groundwater table may be intercepted towards bas e of cutting (if at all). If
Kilm ore Siltstone / Sands tone
pres ent, water inflow will be dis continuity controlled (joints, s hears and faults)
Kilm ore Siltstone / Sands tone
Underlying Silurian Kilm ore Silts tone / Sands tone m ay discharge groundwater (if present likely to be intercepted
Pintadeen Basalt pos s ibly overlying Kilm ore
towards bas e of cutting). If pres ent, water inflow likely to be dis continuity controlled (joints , s hears and faults ).
Silts tone / Sands tone
Pintadeen Bas alt (if present) near s urface les s likely to be water bearing.
Pintadeen Basalt pos s ibly overlying Kilm ore
Lower likelihood of groundwater iss ues at this location.
Silts tone / Sands tone
*com m on alignm ent
1 Approxim ate Cutting locations bas ed on alignm ents and long s ections provided by VicRoads
2 Approxim ate Cutting Depths based on alignment long s ections provided by VicRoads
3 Pos s ible Subs urface geological profile is a broad es tim ation bas ed on the 2011 Geological Survey of Victoria 1:250 000 Seam les s Geology m ap and actual s ite conditions m ay vary appreciably. Site s pecfic inves tigation
required to validate (or adjus t) broad des ktop s um m ary
4 All cuttings m ay have perched groundwater tables . Perched groundwater tables are a localised s ite s pecific feature and need to be identified as part of the s ite inves tigation phas e. If pres ent, perched water tables have the
potential to im pact cons truction and batter s tability
Potential groundwater interaction
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Kilmore-Wallan Bypass Hydrological and Hydraulic Study
9.0
Assessment of Creek Crossings
9.1
General Principles
40
The waterways impacted by each of the three options are ephemeral and generally only flow after a storm event.
At the time of the site inspections, Dry Creek had some permanent water, however this was confined to the low
flow section of the waterway. All of the waterways are well defined with the primary channel incised and the
overbanks acting as part of the floodway.
The existing design is generally favouring bridge structures instead of culverts. This will significantly reduce the
impact on waterway health by maintaining continuous waterway habitat and preventing disruption to fauna
movement.
Avoiding culverts also reduces the impact on flow conditions in the waterway and avoids higher velocities and
eddying as the waterway area reduces at the culverts. This helps avoid bank erosion and scour around the
hydraulic structures.
In all cases apart from the rail crossing on Dry Creek, the bridge piers are located outside of the defined
waterway. This will assist in minimising the impact to waterway health during construction and operation of the
bypass.
9.2
Dry Creek
The location of the following waterway structures is indicated in Figure 6
9.2.1
Northern Bridge – Location 3
The proposed structure at the northern end of the Dry Creek option is complicated by the requirement to span
over an existing rail and local road as well as Dry Creek. The geometry also means that is it not possible to span
all three with a single span bridge and as a result it will be necessary to locate some piers within the waterway
area. A preliminary bridge layout design indicates that two or three pier sets consisting of two 1200mm maximum
diameter piers would need to be located within the existing waterway area.
An inspection of Dry Creek indicates that the waterway alignment has been previously modified to pass under the
existing rail structure. Further modification of the defined waterway would improve the hydraulic conveyance of
the major storm event and minimise any increase in water surface levels.
9.2.2
Central bridge Structures – Location 2
Two bridge structures are proposed to cross Dry Creek at the centre of the Dry Creek option. There would be high
fill embankments at this location of the option and the proposed structures would be able to be clear of the defined
waterway.
9.2.3
Southern Bridge – Location 1a & b
The proposed bridges, in lieu of a bridge and culvert arrangement, at the southern end of the Dry Creek option
would ensure that there are no hydraulic structures in the waterway and the abutments would be clear of the
defined channel. This would result in minimal increases in water levels and ensure that existing flow
characteristics in the waterway are maintained.
9.2.4
Impact on water surface levels
The proposed bridge structures are likely to have some impact on water surface levels within Dry Creek however
the hydraulic modelling indicates that the increase is contained within the existing waterway banks and due to the
energy grade, the increase does not extend far upstream of each structure. The structures have been designed to
ensure that any increase in water surface levels meets the CMA’s design criteria and at most locations, the
bridges included as part of the preliminary design exceed the minimum requirements listed in this report.
9.2.5
Loss of floodplain storage
As the Dry Creek option tends to follow the alignment of the creek, there are more locations where there may be a
loss of floodplain storage due to the fill batters encroaching into the 100 year flood extent. However the reduction
in floodplain storage as a proportion of the total flood volume will still be minor. It is likely that the bridge
abutments at the southernmost crossing of Dry Creek will encroach into the floodplain to a small extent.
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9.3
Kilmore W allan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
41
Kilmore Creek
Two crossing are proposed over Kilmore Creek as part of the Western option. The southern crossing, located
towards the top of the catchment would consist of a number of piped culverts. At this location, the waterway is not
well defined and some local reshaping may be required to direct water towards the proposed culverts. While the
culverts would disrupt the waterway at this location, the area is currently farmed and there is no obvious remnant
vegetation.
The northern crossing would consist of a bridge over the defined waterway. Although many sections of Kilmore
Creek have been modified, the proposed structure would have a minimal impact on the existing waterway.
9.3.1
Impact on water surface levels
The proposed culvert and bridge structures on Kilmore Creek will result in a combined afflux of approximately
200mm, however at both locations the increase will be contained within the existing waterway.
9.3.2
Loss of floodplain storage
The Kilmore Creek options will result in placing fill within the floodplain at two locations, however loss of floodplain
storage is only likely to occur at the upstream crossing where the structure will not span the existing flood extent.
This is largely due to the waterway not being well defined at this location and the loss of storage will partially be
offset by excavation of the waterway
9.4
Broadhurst Creek
It is proposed to construct a new bridge over Broadhurst Creek for the Western and Quinns Road options and
maintain the existing culvert to provide local emergency access. This would result in minimal impact to the
waterway during construction and operation as there would be no new structures in the waterway during the 100
year ARI event.
9.4.1
Impact on water surface levels
Broadhurst Creek is highly incised and located at the base of a steep gully. As a result, the proposed bridge
structure will have no impact on water surface levels as the abutments will be clear of the existing flood extent.
9.4.2
Loss of floodplain storage
The crossing of Broadhurst Creek will not impact the main waterway as the structure will span the 100 year flood
extent, however there may be some loss of storage from the contributing catchments. This is unlikely to have a
measurable impact on downstream flood levels.
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10.0
Environmental Management Practice
10.1
Waterway Crossings
42
Incorporating environmental management practices into the design and construction methodology can assist in
mitigating many impacts of the proposed road alignments.
Constructing within the defined waterways can result in degradation of the waterways bed and banks and may
also result in loss of vegetation, leading to long term bank instability and increased erosion. Minimising works
within the waterway would assist in reducing the impact to waterway health. The use of bridge structures in lieu
of culvert structures would make this more achievable, however temporary haul roads and access tracks may still
require in stream works. Disturbance of land required for construction may also result in a temporary increase in
sediment loads reaching the waterway. This would be more difficult to manage on the Dry Creek option due to the
proximity to the waterway and steep terrain. Sedimentation basins would assist in removing sediment from
stormwater runoff prior to discharging to local waterways. Where areas near waterways are disturbed, they should
be reinstated and revegetated as soon as practical to minimise erosion and sediment transport.
During operation, stormwater runoff from the alignment would discharge to the waterways in larger volumes and
more frequently. This has the potential to erode the existing waterway at the discharge point. The impact can be
minimised by using WSUD to disconnect the impervious surface of the road from the waterways. Proposed
swales would be effective in achieving this as they would provide an opportunity for infiltration which will assist in
reducing runoff during small frequent rainfall events. Providing an ephemeral pool for water to discharge to within
the waterway is also an effective way of dissipating energy and reducing erosion where stormwater enters the
creeks.
There is also the potential for the alignment to intersect groundwater aquifers, which may result in saline water
discharging to the local waterways. The SEPP for waterways in Victoria, set limits for saline water that can be
discharged to water courses for various catchments in Victoria. Where intersected groundwater is too saline to
discharge to the creeks, soak away pits can be installed in the base of the swales to allow low base flows to soak
back into the ground or an aquifer.
10.2
Along the Alignment Options
Accumulation of sediment during construction has the potential to result in significant environmental impact,
however the use of sediment basins and silt fences along with re-establishing disturbed areas quickly would assist
in minimising any impact. The Dry Creek option is likely to be the most difficult to manage as approximate 50% of
the route length is in close proximity to the waterway and the steep terrain will make management of runoff during
construction difficult to control.
During operation, WSUD will assist in removing pollutants from stormwater runoff. Providing WSUD along the
corridor also helps manage stormwater at the outlet to waterways by reducing velocities and reducing peak flows.
Consideration should be given to potential impacts on surrounding groundwater whenever deep excavation
occurs and the potential to reduce the effectiveness of existing bores should be investigated.
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11.0
Kilmore W allan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
43
Options Risk Assessment
A risk and impact assessment was conducted on the three shortlisted bypass options. A risk assessment
workshop was undertaken with representation from the specialist consultants and VicRoads. This risk assessment
identifies and describes hydrology cause and effect pathways associated with the construction and operation of
the Project. In some cases risks and impacts are common to two or all three options, and in other cases the risks
and impacts are specific to one alignment option only. The risk assessment is provided separately within the EES
documentation.
VicRoads has a standard set of environmental protection measures which are typically incorporated into their
construction contracts for road works and bridge works VicRoads, August 2012, Contract Shell Standard Section,
Section 177 Environment Management (Major) hereafter referred to as the 'VicRoads standard environmental
protection measures'. These measures have been used as the starting point for the risk assessment. As a result
of the initial risk assessment, and for construction and operational risks, additional project specific controls have
been proposed to reduce risks in some cases.
These are outlined in the 'additional controls' column of the risk assessment; and are described in more detail in
section 11 of this report. Both VicRoads standard environmental protection measures and the additional project
specific controls have been included in the Environmental Management Framework for the Project. Key
observations from the risk assessment in relation to this report are:
-
Risks relating to increased water surface levels, stormwater quality resulting during the construction &
operation phase and groundwater management can largely be addressed during the design phase.
-
Implementation of some control measures may be more difficult on some sites than others due to
topography and limited space.
-
Groundwater infiltration into the deeply excavated areas may occur but can be managed with soak away
pits.
-
The design can met the stormwater quality requirements required under SEPP.
11.1
Table 14
Comparison of designs
Comparison of designs
Dry Creek
Moderately Poor
The proposed alignment closely follows Dry Creek and includes 5
crossings. As a result, the overall increase in water surface levels is likely
to be highest for this option, however the increases are isolated to the
structures and do not accumulate upstream. The steep terrain is also likely
to make managing stormwater runoff during construction more difficult
than may be encountered in the other options. Long sections of deep
excavation may result in encountering groundwater more often and in
greater volumes, while the shorter length will result in less pollutants being
generated over time.
Quinns Road
Negligible
The hydraulic structures required as part of the Quinns Road option are
likely to have minimal impact on waterway health and will not result in any
increase in flood levels. There is some potential to encounter
groundwater; however the shorter lengths of excavation means that it is
less likely compared to the Dry Creek Option. The total pollutant load
generated by the Quinns Road Option is only slightly higher than for the
Dry Creek Option.
Western
Negligible
The longer length of the Western option will result in higher stormwater
pollutant loads than for the other options; however the flatter terrain may
make treatment measures more effective and easier to implement. The
excavation extent and depth is not as significant as the other options
which may indicate that encountering groundwater is less likely. The two
crossings of Kilmore Creek can be managed to ensure there is no
significant increase in flood levels.
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AECOM
11.2
Kilmore W allan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
44
Risk Measures
The following criteria and measures have been developed to assess each of the options discussed in this report.
1)
The length and number of proposed waterway crossings are minimised to reduce the impact on Dry and
Kilmore Creeks. Measure: number of waterway crossings.
2)
Minimise the increase in water surface elevation as a result of the proposed crossings. Measure: the total
increase in water surface elevation is minimised.
3)
Avoid potential impact to local groundwater. Measure: option with the least deep excavation.
4)
Minimise pollutants discharged to waterways. Measure: total suspended solids load.
Table 15
Summary of option comparisons – surface water
Impact
Quinns Road
Dry Creek
Western
Number of proposed
hydraulic structures
One Bridge, minimal
impact
Five Bridges, Rail
overpass will have some
impact on waterway
health
Two Bridges
Cumulative increase in
water surface levels
0m
Approximately 1.1 m
Approximately 0.2 m
Total suspended solids
load
29,740 kg/year
27,020 kg/year
38,480 kg/year
Overall Performance
Negligible
Moderately Poor
Negligible
Table 16
Summary of option comparisons – groundwater
Impact
Quinns Road
Dry Creek
Western
Length of deep
excavation
Some sections of
excavation up to 25m
deep
Long sections of deep
excavation up to 25m
Some sections exceeding
10 m
Overall Performance
Negligible
Moderately Poor
Negligible
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AECOM
12.0
Kilmore W allan Bypass
Kilmore-Wallan Bypass Hydrological and Hydraulic Study
45
Glossary
12D – Is a terrain and surveying program which for purposes of this study, was used to define the HEC-RAS
cross sections.
Average Recurrence Interval (ARI) – A statistical estimate of the average period in years between the
occurrence of a flood of a given size or larger (e.g. floods as big or larger than the 100 year ARI flood event will
occur on average once every 100 years). The ARI of a flood event gives no indication of when a flood of that size
will occur next.
Bransby Williams Equation – Is an equation prescribed by AR&R (2001) to calculate the time of concentration
defined as:
58
=
.
.
Fraction Impervious (FI) – This value represents the fraction of area in a sub catchment where water cannot
infiltrate the ground surface.
HEC-RAS – Is a hydraulic analysis program developed by the United States Department of Defense, used in the
modelling the hydraulic effects of one-dimensional flow through a series of defined cross sections.
HY-8 – Is a hydraulic analysis program developed by the United States Department of Transportation, used in the
modelling the effects of hydraulic controls such as culverts.
Intensity Frequency Duration (IFD) Factor – Are statistically determined rainfall characteristics relating to the
intensity frequency and duration of rainfall events.
Modified Friends Equation – Is an equation prescribed by AR&R (2001) to calculate the time of concentration
defined as:
=
.
8.5
.
.
.
RORB – A general runoff and stream flow routing program used to calculate flood hydrographs from rainfall and
other channel inputs.
Time of Concentration (tc) – The time taken for water in the furthest most reach of a catchment or sub
catchment to reach the outlet.
G – regional skewness parameter documented in Australian Rainfall and Runoff Volume 2
F2 – Factor for 2 year rainfall intensities documented in distribution maps in Australian Rainfall and Runoff Volume
2
F50 – Factor for 50 year rainfall intensities documented in distribution maps in Australian Rainfall and Runoff
Volume 2
22-May-2014
Prepared for – VicRoads – ABN: 61760960480