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HYDROLOGICAL MODELLING FOR TENTERFIELD CREEK DAM UPGRADE DESIGN
NSW Public Works September 2013
REPORT TITLE: Hydrological Modelling for Tenterfield Creek Dam Upgrade Design
CLIENT: NSW Public Works
REPORT NUMBER: 0974-01-C
Revision
Number Report Date Description
Report
Author Reviewer
Draft 27 August 2013 Original issue WW/TB SM
0 23 Sept 2013 Final WW SM
For and on behalf of
WRM Water & Environment Pty Ltd
Dr Sharmil Markar
Managing Director, RPEQ
NOTE: This report has been prepared on the assumption that all information, data and reports provided to us by our
client, on behalf of our client, or by third parties (e.g. government agencies) is complete and accurate and on the basis
that such other assumptions we have identified (whether or not those assumptions have been identified in this
advice) are correct. You must inform us if any of the assumptions are not complete or accurate. We retain ownership
of all copyright in this report. Except where you obtain our prior written consent, this report may only be used by our
client for the purpose for which it has been provided by us.
0974-01-C 23 September 2013
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TABLE OF CONTENTS Page
1 INTRODUCTION 1
1.1 OVERVIEW 1 1.2 SCOPE OF WORK 1
2 DATA AVAILABILITY 4
2.1 OVERVIEW 4 2.2 JANUARY 2011 EVENT 6 2.3 FEBRUARY 2001 EVENT 7 2.4 STAGE-STORAGE CURVE FOR TENTERFIELD CREEK DAM 11 2.5 RATING CURVES 11
3 RORB MODEL CONFIGURATION 13
3.1 MODEL CONFIGURATION 13 3.2 MODEL CALIBRATION 13 3.3 MODEL VERIFICATION 15
4 PROBABLE MAXIMUM PRECIPITATION 17
4.1 OVERVIEW 17 4.2 PMP ESTIMATES 17
5 PROBABLE MAXIMUM FLOOD ESTIMATION 18
6 REFERENCES 19
APPENDIX A 20
PMF HYDROGRAPHS – 1 HOUR STORM DURATION 20
APPENDIX B 22
PMF HYDROGRAPHS – 2 HOUR STORM DURATION 22
APPENDIX C 24
PMF HYDROGRAPHS – 3 HOUR STORM DURATION 24
APPENDIX D 26
PMF HYDROGRAPHS – 6 HOUR STORM DURATION 26
APPENDIX E 28
PMF HYDROGRAPHS – 12 HOUR STORM DURATION 28
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APPENDIX F 30
PMF HYDROGRAPHS – 24 HOUR STORM DURATION 30
APPENDIX G 32
PMF HYDROGRAPHS – 48 HOUR STORM DURATION 32
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LIST OF TABLES
Page
Table 2.1 Data Availability 4
Table 2.2 Daily Rainfall Totals in the Tenterfield Vicinity (January 2011) 7
Table 2.3 Daily Rainfall Totals (to 9am) in the Tenterfield Vicinity, January and February 2001 11
Table 3.1 Hydrograph Reporting Locations 13
Table 4.1 PMP Estimates for Various Storm Durations 17
Table 5.1 Critical Storm Duration for PMF Discharges at Various Locations 18
LIST OF FIGURES
Page
Figure 1.1 Tenterfield Creek Catchment Locality Map 2
Figure 1.2 Major Creeks in the Tenterfield Creek Catchment Study Area 3
Figure 2.1 Gauging Station Locations 5
Figure 2.2 Rainfall at Tenterfield Creek and Mt McKenzie Gauges (9 Jan 2011 to 13 Jan
2011) 6
Figure 2.3 Discharge Data (9 Jan 2011 to 13 Jan 2011) – showing inconsistency with rainfall 8
Figure 2.4 Water Level Data (9 Jan 2011 to 13 Jan 2011) – showing inconsistency with
rainfall 8
Figure 2.5 Shifted Discharge Data by 11 hours 9
Figure 2.6 Shifted Water Level Data by 11 hours 9
Figure 2.7 Tenterfield Creek Dam Outflows and Black Swamp Rainfall (31 January to 4
February 2001) 10
Figure 2.8 Water Levels Recorded at Tenterfield Creek Dam and Douglas Street Gauging
Stations (31 January to 4 February 2001) 10
Figure 2.9 Stage-Storage Curve for Tenterfield Creek Dam 11
Figure 2.10 Rating Curve for Tenterfield Creek Dam Outflow (Spillway) 12
Figure 2.11 Rating Curve for Currys Gap Gauging Station 12
Figure 3.1 RORB Model Configuration 14
Figure 3.2 Calibration Plots at Dam Outflow and Currys Gap Gauging Stations for January
2011 Event 15
Figure 3.3 Verification Plots at Douglas Street Gauging Station for February 2001 Event 16
Figure 3.4 Verification Plots at Tenterfield Creek Dam for February 2001 Event 16
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1 INTRODUCTION
1.1 OVERVIEW
The township of Tenterfield is located in northern New South Wales (NSW) about 150 km
west of Ballina, close to the NSW-Queensland border (Figure 1.1). It is a major inland
town serviced by three major highways i.e. the New England, Mt Lindsay and Bruxner
Highways.
Tenterfield Creek Dam is located about 2 km upstream of Tenterfield town, on
Tenterfield Creek. The Dam was constructed in 1931 and augmented by 1.8m in 1974
as a water supply dam for the town. The dam commands a catchment area of about 38
km2 and has a capacity of 1,150 megalitres. Tenterfield Creek flows across the NSW-
Queensland border into the Severn River.
Figure 1.2 shows the major tributaries of Tenterfield Creek upstream of the Dam namely
Green Swamp and Hawkins Creeks. The major tributaries downstream of the Dam in the
study area include Groombridges, Currys Gap, Pitkins Swamp, Bryans Gap, Ghost Gully
and Washbrook Creeks.
NSW Public Works (NSWPW) is currently undertaking design studies to upgrade the
Tenterfield Creek Dam. To assist with these studies, NSWPW requested WRM Water and
Environment Pty Ltd (WRM) to estimate the Probable Maximum Flood (PMF) inflows into
the Dam and also the residual PMF discharges into Tenterfield Creek at several locations
downstream of the Dam. This report has been prepared in response to this request.
1.2 SCOPE OF WORK
The scope of work for this study was as follows:
Collect, collate and review available historical rainfall, streamflow, dam storage
level and storage-stage-surface area relationship data,
Develop a RORB model of Tenterfield Creek catchment study area,
Calibrate and validate the RORB model,
Estimate Probable Maximum Precipitation (PMP) on the Tenterfield Creek
Catchment, and
Estimate PMF discharge hydrographs at specified locations along Tenterfield
Creek using the calibrated RORB model.
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Figure 1.1 Tenterfield Creek Catchment Locality Map
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Figure 1.2 Major Creeks in the Tenterfield Creek Catchment Study Area
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2 DATA AVAILABILITY
2.1 OVERVIEW
The most recent flood event in the Tenterfield Creek catchment occurred in January
2011. Prior to that the last reported flood event of any significance occurred in February
2001. Rainfall, water level and discharge data collected for the February 2001 and the
January 2011 flood events were supplied by DHI Water and Environment (DHI). Table
2.1 summarises the available data from DHI for each event and Figure 2.1 shows the
locations of the relevant gauging stations. Further information on the available data is
provided in the following sections.
Table 2.1 Data Availability
Gauge
February 2001 Event
January 2011 Event
Rainfall Water
Level Discharge
Rainfall
Water
Level Discharge
Black Swamp Rain Gauge X
Tenterfield Creek Rain
Gauge X
Mt Mackenzie Rain Gauge
X
Douglas St Stream Gauge
X
X
Currys Gap Stream Gauge
X X
Tenterfield Dam
X X
X X
Daily rainfalls recorded by the Bureau of Meteorology (BoM) at a number of their rainfall
gauging stations in the vicinity of Tenterfield were also available for both February 2001
and January 2011 events. They include Tenterfield (Federation Park) and Tenterfield
(Springside).
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Figure 2.1 Gauging Station Locations
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2.2 JANUARY 2011 EVENT
The rainfall and water level data available for the 2011 event is inconsistent and
appears to contain some errors. These apparent inconsistencies and errors are
discussed below.
Figure 2.2 shows the recorded 15-minute rainfall totals at the Tenterfield Creek and Mt
McKenzie rain gauges for the January 2011 event. Daily rainfall totals are available for a
number of Bureau of Meteorology rainfall stations in the Tenterfield vicinity. Table 2.2
provides a comparison of the accumulated totals at the sub-daily rainfall stations with
the BoM daily rainfall station totals. It appears that the sub-daily rainfall stations are
missing data on 10 and part of 11 (including possibly 12) January 2011, which is also
consistent with BoM radar images showing storm cells moving over Tenterfield at the
times when data appears to be missing. The daily totals at the Mt McKenzie sub-daily
rainfall station for the 12 and 13 January 2011 appear comparable with the BoM daily
station totals.
Figure 2.2 Rainfall at Tenterfield Creek and Mt McKenzie Gauges (9 Jan 2011 to 13 Jan
2011)
0
1
2
3
4
5
6
7
8
9
10
11
09
/0
1/1
1 0
0:0
0
09
/0
1/1
1 0
6:0
0
09
/0
1/1
1 1
2:0
0
09
/0
1/1
1 1
8:0
0
10
/0
1/1
1 0
0:0
0
10
/0
1/1
1 0
6:0
0
10
/0
1/1
1 1
2:0
0
10
/0
1/1
1 1
8:0
0
11
/0
1/1
1 0
0:0
0
11
/0
1/1
1 0
6:0
0
11
/0
1/1
1 1
2:0
0
11
/0
1/1
1 1
8:0
0
12
/0
1/1
1 0
0:0
0
12
/0
1/1
1 0
6:0
0
12
/0
1/1
1 1
2:0
0
12
/0
1/1
1 1
8:0
0
13
/0
1/1
1 0
0:0
0
Ra
infa
ll (
mm
/1
5 m
ins)
Tenterfield Creek Rainfall
0
1
2
3
4
5
6
7
8
9
10
11
09
/01
/11
00
:00
09
/01
/11
06
:00
09
/01
/11
12
:00
09
/01
/11
18
:00
10
/01
/11
00
:00
10
/01
/11
06
:00
10
/01
/11
12
:00
10
/01
/11
18
:00
11
/01
/11
00
:00
11
/01
/11
06
:00
11
/01
/11
12
:00
11
/01
/11
18
:00
12
/01
/11
00
:00
12
/01
/11
06
:00
12
/01
/11
12
:00
12
/01
/11
18
:00
13
/01
/11
00
:00
Rai
nfal
l (m
m/1
5 m
ins)
Mt McKenzie Rainfall
Missing rainfall data
Missing rainfall data
0974-01-C 23 September 2013
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Table 2.2 Daily Rainfall Totals in the Tenterfield Vicinity (January 2011)
Station Name Station
No.
24-hour Rainfall Total (to 9am)
10th 11th 12th
13th
4-Day
Total
Tenterfield Creek Rain
Gauge - 0.0 a 76.0 a 49.5 a 2.0 127.5
Mt McKenzie Rain Gauge - 0.0 a 75.5 a 86.0 1.5 163.0
Black Swamp 56202 62.2 122.4 78.6 15.6 278.8
Tenterfield (Federation Park) 56032 18.0 144.0 88.6 4.0 254.6
Tenterfield (Springside) 56046 - - 234.0 b 0.0 234.0
a Missing or incomplete data b 3-day total
Figure 2.3 and Figure 2.4 show the available discharge and water level data,
respectively, for the January 2011 event. Figure 2.3 and Figure 2.4 also show the 15-
minute rainfall totals at the Mt McKenzie rainfall gauge. There appears to be an
inconsistency between the timing of the rainfall and what should be the subsequent
response in water level and discharge.
As mentioned above, there appears to be a period of missing data prior to about midday
on 10 January 2011. However the recorded sub-daily rainfall station data on 12 January
2011 (especially at Mt McKenzie) appears consistent with the daily rainfall stations and
BoM radar images of storm cells in the Tenterfield vicinity. All rainfall stations in the
Tenterfield vicinity recorded a significant amount of rainfall in the 24 hours to 9am on
the 12 January 2011. However, the water level and discharge data available do not
appear to produce a response to this rainfall. This indicates that it is likely the time
stamps of the water level and discharge data have been recorded incorrectly.
The discharge and water level time series were shifted 11 hours later to provide an
expected match to the recorded sub-daily rainfall data, as shown in Figure 2.5 and
Figure 2.6. This time shift of 11 hours is consistent with the time shift adjustment made
by DHI in their Tenterfield Creek Flood Study (DHI, 2013). This shifted data set was used
in the RORB model calibration.
2.3 FEBRUARY 2001 EVENT
Rainfall data at 6-minute intervals for the February 2001 event was available for the
Black Swamp Rainfall Station (Figure 2.7). This pluviograph data was compared against
the BoM daily rainfall stations available in the vicinity of Tenterfield (see Figure 2.1 for
their locations). Table 2.3 shows that the daily rainfall totals at Black Swamp and
Boonoo Boonoo (Currawong) are generally higher than at Black Swamp (Athlyne) and
Tenterfield (Federation Park).
Figure 2.7 also show the Dam outflows provided by DHI based on their spillway rating
curve (DHI, 2013).
Figure 2.8 shows the water levels recorded at Tenterfield Creek Dam and Douglas Street
Gauging Stations. The water levels at Douglas Street Gauging Station could not be
converted to reliable discharges due to the inaccurate and unreliable rating curve
available (DHI, 2006 and DHI, 2013).
0974-01-C 23 September 2013
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Figure 2.3 Discharge Data (9 Jan 2011 to 13 Jan 2011) – showing inconsistency with
rainfall
Figure 2.4 Water Level Data (9 Jan 2011 to 13 Jan 2011) – showing inconsistency with
rainfall
0
2
4
6
8
10
12
14
0
1
2
3
4
5
6
09
/0
1/1
1 0
0:0
0
09
/0
1/1
1 0
6:0
0
09
/0
1/1
1 1
2:0
0
09
/0
1/1
1 1
8:0
0
10
/0
1/1
1 0
0:0
0
10
/0
1/1
1 0
6:0
0
10
/0
1/1
1 1
2:0
0
10
/0
1/1
1 1
8:0
0
11
/0
1/1
1 0
0:0
0
11
/0
1/1
1 0
6:0
0
11
/0
1/1
1 1
2:0
0
11
/0
1/1
1 1
8:0
0
12
/0
1/1
1 0
0:0
0
12
/0
1/1
1 0
6:0
0
12
/0
1/1
1 1
2:0
0
12
/0
1/1
1 1
8:0
0
13
/0
1/1
1 0
0:0
0
Ra
infa
ll (
mm
/1
5 m
ins)
Wa
ter
Le
ve
l (m
)
Mt McKenzie Rainfall
Tenterfield Dam WL
Currys Gap WL
Douglas St WL
Inconsistency –
hydrographs rise
prior to rainfall
Inconsistency –
hydrographs rise
prior to rainfall
0974-01-C 23 September 2013
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Figure 2.5 Shifted Discharge Data by 11 hours
Figure 2.6 Shifted Water Level Data by 11 hours
0
2
4
6
8
10
12
14
0
1
2
3
4
5
6
09
/0
1/1
1 0
0:0
0
09
/0
1/1
1 0
6:0
0
09
/0
1/1
1 1
2:0
0
09
/0
1/1
1 1
8:0
0
10
/0
1/1
1 0
0:0
0
10
/0
1/1
1 0
6:0
0
10
/0
1/1
1 1
2:0
0
10
/0
1/1
1 1
8:0
0
11
/0
1/1
1 0
0:0
0
11
/0
1/1
1 0
6:0
0
11
/0
1/1
1 1
2:0
0
11
/0
1/1
1 1
8:0
0
12
/0
1/1
1 0
0:0
0
12
/0
1/1
1 0
6:0
0
12
/0
1/1
1 1
2:0
0
12
/0
1/1
1 1
8:0
0
13
/0
1/1
1 0
0:0
0
Ra
infa
ll (
mm
/1
5 m
ins)
Wa
ter
Le
ve
l (m
)
Mt McKenzie Rainfall
Shifted - Tenterfield Dam WL
Shifted - Currys Gap WL
Shifted - Douglas St WL
0974-01-C 23 September 2013
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Figure 2.7 Tenterfield Creek Dam Outflows and Black Swamp Rainfall (31 January to 4
February 2001)
Figure 2.8 Water Levels Recorded at Tenterfield Creek Dam and Douglas Street Gauging
Stations (31 January to 4 February 2001)
0
0.5
1
1.5
2
2.5
3
3.5
0
4
8
12
16
20
24
28
31
/0
1/0
1 0
0:0
0
31
/0
1/0
1 0
6:0
0
31
/0
1/0
1 1
2:0
0
31
/0
1/0
1 1
8:0
0
01
/0
2/0
1 0
0:0
0
01
/0
2/0
1 0
6:0
0
01
/0
2/0
1 1
2:0
0
01
/0
2/0
1 1
8:0
0
02
/0
2/0
1 0
0:0
0
02
/0
2/0
1 0
6:0
0
02
/0
2/0
1 1
2:0
0
02
/0
2/0
1 1
8:0
0
03
/0
2/0
1 0
0:0
0
03
/0
2/0
1 0
6:0
0
03
/0
2/0
1 1
2:0
0
03
/0
2/0
1 1
8:0
0
04
/0
2/0
1 0
0:0
0
Ra
infa
ll (
mm
/6
min
s)
Dis
ch
arg
e (
m3/s)
056202 Black Swamp Rainfall
Tenterfield Dam Outflow
875
875.5
876
876.5
877
877.5
878
878.5
879
879.5
880
839.5
840.0
840.5
841.0
841.5
842.0
842.5
843.0
843.5
844.0
844.5
31
/0
1/0
1 0
0:0
0
31
/0
1/0
1 0
6:0
0
31
/0
1/0
1 1
2:0
0
31
/0
1/0
1 1
8:0
0
01
/0
2/0
1 0
0:0
0
01
/0
2/0
1 0
6:0
0
01
/0
2/0
1 1
2:0
0
01
/0
2/0
1 1
8:0
0
02
/0
2/0
1 0
0:0
0
02
/0
2/0
1 0
6:0
0
02
/0
2/0
1 1
2:0
0
02
/0
2/0
1 1
8:0
0
03
/0
2/0
1 0
0:0
0
03
/0
2/0
1 0
6:0
0
03
/0
2/0
1 1
2:0
0
03
/0
2/0
1 1
8:0
0
04
/0
2/0
1 0
0:0
0
Ten
terf
ield
Da
m W
ate
r L
eve
l (m
AH
D)
Do
ugla
s S
t W
ate
r Le
ve
l (m
AH
D)
Douglas St WL
Tenterfield Dam WL
0974-01-C 23 September 2013
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Table 2.3 Daily Rainfall Totals (to 9am) in the Tenterfield Vicinity, January and February
2001
Station Name Station No.
24-hour Rainfall Total (to 9am)
31-Jan 1-Feb 2-Feb 3-Feb 4-Feb 5-Day
Total
Tenterfield (Federation Park) 56032 22.4 85.6 71.6 37.2 15.5 232.3
Black Swamp (Athlyne) 56203 - 67 95 61 6.2 229.2*
Boonoo Boonoo (Currawong) 56141 85 19 120 104 15 343
Black Swamp 56202 40.8 89.9 112.4 96.1 36.6 375.8
*4-day total
2.4 STAGE-STORAGE CURVE FOR TENTERFIELD CREEK DAM
Figure 2.9 shows the stage-storage curve for the Tenterfield Creek Dam derived using
the surface area versus elevation information obtained from NSWPW and Hydro
Tasmania (2000). The adopted curve was adjusted to fit the full supply capacity of 1,
150 megalitres at 878.43m AHD.
Figure 2.9 Stage-Storage Curve for Tenterfield Creek Dam
2.5 RATING CURVES
The rating curves derived for the Tenterfield Dam outflow (spillway) and the Currys Gap
Gauging Station by DHI (2013) were adopted in this study. Figure 2.10 and Figure 2.11
show the rating curves adopted in the study for the Dam and Currys Gap Gauging
Stations respectively.
868
870
872
874
876
878
880
882
0 500 1,000 1,500 2,000 2,500
Ele
vati
on
(m
AH
D)
Storage (megalitres)
Full Supply Capacity at 878.43mAHD
0974-01-C 23 September 2013
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The rating curve for the Douglas Street Gauging Station is considered inaccurate and
unreliable for the discharges to be estimated from the water level measurements (DHI,
2006 and DHI, 2013). This is discussed in Section 3.3.
Figure 2.10 Rating Curve for Tenterfield Creek Dam Outflow (Spillway)
Figure 2.11 Rating Curve for Currys Gap Gauging Station
878.00
878.50
879.00
879.50
880.00
880.50
881.00
0 200 400 600 800 1000 1200
Ele
vation (
mA
HD
)
Discharge (m3/s)
Dam Crest = 878.43 mAHD
0974-01-C 23 September 2013
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3 RORB MODEL CONFIGURATION
3.1 MODEL CONFIGURATION
A RORB model of the Tenterfield Creek catchment of the study area was set up with 20
sub-catchments, A to T as shown in Figure 3.1. Sub-catchments A to I drain into the Dam.
The total catchment area modelled is 124 km2, of which 38 km2 drains into Tenterfield
Creek Dam.
In addition to the Dam inflows and the catchment outflows, the NSWPW design studies
also require local (residual) inflow hydrographs downstream of the Dam at locations INF1
to INF4 as defined in Table 3.1 and shown in Figure 3.1. The RORB model was
configured to provide these residual downstream inflows.
Table 3.1 Hydrograph Reporting Locations
Reporting
Location
Description Contributing RORB
Sub-catchments
Dam Inflow Combined Inflows into Tenterfield Dam A to I
INF1 Combined Inflows - Groombridges (INF1a)
and Currys Gap Creeks (INF1b)
J, K, L, M and N
INF2 Combined Inflows – local inflows into
Tenterfield town (INF2a) and Un-named
Tributary (INF2b)
O and P
INF3 Combined Inflows – Ghost Gully (INF3a)
and Pitkins Swamp and Bryans Gap Creeks
(INF3b)
Q, R and S
INF4 Washbrook Creek T
Outflow Downstream Boundary of Model A to T
3.2 MODEL CALIBRATION
The RORB model was calibrated against the January 2011 rainfall event using the
available data (described in Section 2.2). The calibration was attempted with sub-daily
rainfall data for both Tenterfield Creek and Mt McKenzie Rainfall Stations. The best
results for the calibration were obtained using the sub-daily rainfall at the Mount
McKenzie Rainfall Station. This is consistent with the observation that the Tenterfield
Creek rainfall data on 12 January 2011 may be incomplete as discussed in Section 2.2.
For reasons provided in Section 2.5, the calibration was undertaken against the
recorded discharge hydrograph at Currys Gap Gauging Station and the outflow
hydrograph at the Dam provided in DHI (2013).
Figure 3.2 shows the calibration results using the RORB model routing parameters, kc =
16 and m = 0.8. The initial and proportional loss model was used with an initial loss of
30 mm. The initial water level at the Dam was set at full supply capacity at the start of
the simulation. The calibration is considered acceptable given the uncertainties in the
available data.
0974-01-C 23 September 2013
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Figure 3.1 RORB Model Configuration
0974-01-C 23 September 2013
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Figure 3.2 Calibration Plots at Dam Outflow and Currys Gap Gauging Stations for January
2011 Event
3.3 MODEL VERIFICATION
The RORB model was verified using the calibrated routing parameters, kc = 16 and m =
0.8, against the February 2001 rainfall event, and using the recorded rainfall at Black
Swamp Creek. The initial and proportional loss model was used with an initial loss of 10
mm. The initial water level at the Tenterfield Creek Dam was based on the recorded
water level of 877.35 mAHD (at 0:00 hours, 31 January 2001) which is equivalent to
330 megalitres below full supply capacity.
0
50
100
150
200
250
11
/01
/11
06
:00
11
/01
/11
09
:00
11
/01
/11
12
:00
11
/01
/11
15
:00
11
/01
/11
18
:00
11
/01
/11
21
:00
12
/01
/11
00
:00
12
/01
/11
03
:00
12
/01
/11
06
:00
Dis
char
ge (
m3 /
s)
Dam Outflow (Predicted)
Dam Outflow (Recorded)
0
50
100
150
200
250
11
/01
/11
06
:00
11
/01
/11
09
:00
11
/01
/11
12
:00
11
/01
/11
15
:00
11
/01
/11
18
:00
11
/01
/11
21
:00
12
/01
/11
00
:00
12
/01
/11
03
:00
12
/01
/11
06
:00
Dis
char
ge m
3 /s)
Currys Gap (Predicted)
Currys Gap (Recorded)
0974-01-C 23 September 2013
16
Although recorded water levels at the Douglas Street Gauging Station were available for
this event, the rating curve for this site is considered inaccurate and unreliable (DHI,
2006 and DHI, 2013). Therefore, the available data could only be used as a check to
ensure the timing and shape of the predicted and recorded hydrographs are in
agreement. As shown in Figure 3.3, the model predicted the timing and shape of the
discharge hydrograph at Douglas Street to be reasonably consistent with the recorded
water level hydrograph.
The model prediction of Tenterfield Creek Dam outflows were also compared with the
recorded Dam outflows (Figure 3.4). The peak outflow is well predicted but the timing of
the rising limb is not so well matched.
It should be noted that the 2001 event is only a small flood with a peak outflow of about
26 m3/s. Given the uncertainties in the rainfall, water level and discharge data available,
the validation shown is considered reasonable for the purpose of the study.
Figure 3.3 Verification Plots at Douglas Street Gauging Station for February 2001 Event
Figure 3.4 Verification Plots at Tenterfield Creek Dam for February 2001 Event
-10
-5
0
5
10
15
20
25
839.8840.0840.2840.4840.6840.8841.0841.2841.4841.6841.8842.0
31
/01
/20
01
0:0
0
31
/01
/20
01
6:0
0
31
/01
/20
01
12
:00
31
/01
/20
01
18
:00
1/0
2/2
00
1 0
:00
1/0
2/2
00
1 6
:00
1/0
2/2
00
1 1
2:0
0
1/0
2/2
00
1 1
8:0
0
2/0
2/2
00
1 0
:00
2/0
2/2
00
1 6
:00
2/0
2/2
00
1 1
2:0
0
Dis
char
ge (
m3 /
s)
Wat
er
Leve
l (m
AH
D)
Water Level (Recorded)
Discharge (Predicted)
0
10
20
30
40
50
60
70
80
31
/01
/01
00
:00
31
/01
/01
06
:00
31
/01
/01
12
:00
31
/01
/01
18
:00
01
/02
/01
00
:00
01
/02
/01
06
:00
01
/02
/01
12
:00
01
/02
/01
18
:00
02
/02
/01
00
:00
02
/02
/01
06
:00
02
/02
/01
12
:00
Dis
char
ge (
m3 /
s)
Dam Outflow (Predicted)Dam Outflow (Recorded)
0974-01-C 23 September 2013
17
4 PROBABLE MAXIMUM PRECIPITATION
4.1 OVERVIEW
For the estimation of Probable Maximum Precipitation (PMP), the catchment of the
Tenterfield Creek Dam is located in the Generalised Tropical Storm Method (GTSMR)
Coastal Zone as defined in ARR (1998).
For storm durations of 6 hours or less, the spatial and temporal patterns were derived
using the Generalised Short Duration Method (GSDM) (BoM, 2003a).
For storm durations of 24 hours or more, the spatial and temporal patterns were derived
using the Generalised Tropical Storm Method- Revised (GTSMR) Method (BoM, 2003b).
Both GSDM and GTSMR methods were tested for the 12 hour storm duration. The
GTSMR resulted in a slightly higher peak discharge at all reporting locations and was
therefore adopted for this duration.
4.2 PMP ESTIMATES
The PMP estimates for the Tenterfield Creek catchment study area for storm durations
ranging from 0.75 to 72 hours are presented in Table 4.1.
Table 4.1 PMP Estimates for Various Storm Durations
Duration
(hours)
PMP
(mm)
0.75 240
1
1.5
290
330
2
2.5
370
400
3 430
5
6
12
24
36
48
72
510
550
660
870
1,060
1,240
1,550
0974-01-C 23 September 2013
18
5 PROBABLE MAXIMUM FLOOD ESTIMATION
The Probable Maximum Flood (PMF) discharges along Tenterfield Creek and its
tributaries were estimated using the RORB model that was calibrated and verified
against the January 2011 and February 2001 flood events respectively. The calibrated
RORB routing parameters (kc =16 and m=0.8) were used for the PMF discharge
estimation.
A zero initial loss and a continuing loss rate of 2.5 mm per hour were assumed for the
PMF estimation. Sensitivity analysis was also carried out using a continuing loss rate of 1
mm per hour but the results were not sensitive to the adopted continuing loss rate (less
than 1 per cent difference in the peak discharges for storm durations of less than 12
hours, and less than 3 per cent difference for storm durations equal or greater than 12
hours).
Depending on the location of interest along Tenterfield Creek, the critical storm
durations for the PMF discharges vary between 1 and 5 hours as shown in Table 5.1.
For example the peak inflow of 1,199 m3/s into Tenterfield Creek Dam is for a 2 hour
critical duration storm, whereas the peak catchment outflow of 2,823 m3/s to the
modelled catchment outlet is for a critical storm duration of 5 hours. The critical storm
durations for residual inflows downstream of the Dam vary between 1 and 2.5 hours.
Appendices A to G show the predicted design discharge hydrographs for selected storm
durations at the different locations defined in Section 3.1, for the PMF event.
Table 5.1 Critical Storm Duration for PMF Discharges at Various Locations
Location Peak PMF
(m3/s)
Critical Duration
(hours)
Dam Inflow 1,199 2.0
INF 1 1,100 2.5
INF 2 999 1.0
INF 3 867 2.0
INF 4 253 1.5
Outflow 2,823 5.0
0974-01-C 23 September 2013
19
6 REFERENCES
ARR (1998)
Australian Rainfall and Runoff, A Guide to Flood Estimation,
Volume 1, the Institution of Engineers Australia, 1998.
BoM (2003a)
BoM (2003b)
The Estimation of Probable Maximum Precipitation in Australia:
Generalised Short-Duration Method, Prepared by the
Hydrometeorological Advisory Service, Australian Government
Bureau of Meteorology, June 2003.
Guidebook to the Estimation of Probable Maximum Precipitation:
Generalised Tropical Storm Method, Prepared by the
Hydrometeorological Advisory Service, Australian Government
Bureau of Meteorology, November 2003.
DHI (2013) Tenterfield Flood Study, prepared by DHI for Tenterfield Shire
Council, May 2013.
DHI (2006) Tenterfield Flood Study – draft Final Report, prepared by DHI for
Tenterfield Shire Council, January 2006.
Hydro Tasmania
(2000)
Tenterfield Flood Forecasting & Warning System, Report No. NSW-
0006-CR-1 prepared by Hydro Tasmania, Hydro Electric
Corporation for Tenterfield Shire Council, June 2000.
0974-01-C 23 September 2013
20
APPENDIX A
PMF HYDROGRAPHS – 1 HOUR STORM DURATION
0974-01-C 23 September 2013
21
PMF Design Hydrographs at Various Locations –1 hour storm duration
Calculated hydrograph, Inf lows Dam
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hr)
Calculated05
1015202530
Rainf
all (m
m) Gross rainfall
Rainfall excess
0974-01-C 23 September 2013
22
APPENDIX B
PMF HYDROGRAPHS – 2 HOUR STORM DURATION
0974-01-C 23 September 2013
23
PMF Design Hydrographs at Various Locations –2 hour storm duration
Calculated hydrograph, Inflows Dam
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Groombridges Outflow INF1a
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Currys Gap Outflow INF1b
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, INF1
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Local Inflow INF2a
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400D
isch
arge
(m³/s
)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Unnamed Trib INF2b
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, INF2
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Pitkins Swamp INF3b
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, Ghost Gully Ck INF3a
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, INF3
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, INF4
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
Calculated hydrograph, END System
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Dis
char
ge (m
³/s)
0 2 4 6 8 10 12 14
Time (hr)
Cal cul ated05
1015202530
Rai
nfal
l (m
m) Gross rai nfal l
Rai nfal l excess
0974-01-C 23 September 2013
24
APPENDIX C
PMF HYDROGRAPHS – 3 HOUR STORM DURATION
0974-01-C 23 September 2013
25
PMF Design Hydrographs at Various Locations – 3 hour storm duration
Calculated hydrograph, Inf lows Dam
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 2 4 6 8 10 12 14 16 18 20 22
Time (hr)
Calculated05
101520253035
Rainf
all (m
m) Gross rainfall
Rainfall excess
0974-01-C 23 September 2013
26
APPENDIX D
PMF HYDROGRAPHS – 6 HOUR STORM DURATION
0974-01-C 23 September 2013
27
PMF Design Hydrographs at Various Locations –6 hour storm duration
Calculated hydrograph, Inf lows Dam
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
500
1000
1500
2000
2500
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated05
1015202530354045
Rainf
all (m
m) Gross rainfall
Rainfall excess
0974-01-C 23 September 2013
28
APPENDIX E
PMF HYDROGRAPHS – 12 HOUR STORM DURATION
0974-01-C 23 September 2013
29
PMF Design Hydrographs at Various Locations – 12 hour storm duration
Calculated hydrograph, Inf lows Dam
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30
Time (hr)
Calculated0
10203040506070
Rainf
all (m
m) Gross rainfall
Rainfall excess
0974-01-C 23 September 2013
30
APPENDIX F
PMF HYDROGRAPHS – 24 HOUR STORM DURATION
0974-01-C 23 September 2013
31
PMF Design Hydrographs at Various Locations –24 hour storm duration
Calculated hydrograph, Inf lows Dam
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
200
400
600
800
1000
1200
1400
1600
1800
Disc
harg
e (m
³/s)
0 5 10 15 20 25 30 35 40 45
Time (hr)
Calculated0
20406080
100120140160180200
Rainf
all (m
m) Gross rainfall
Rainfall excess
0974-01-C 23 September 2013
32
APPENDIX G
PMF HYDROGRAPHS – 48 HOUR STORM DURATION
0974-01-C 23 September 2013
33
PMF Design Hydrographs at Various Locations – 48 hour storm duration
Calculated hydrograph, Inf lows Dam
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF1
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF2
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF3
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, INF4
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess
Calculated hydrograph, END System
0
200
400
600
800
1000
1200
1400
1600
Disc
harg
e (m
³/s)
0 10 20 30 40 50 60
Time (hr)
Calculated0
50100150200250
Rainf
all (m
m) Gross rainfall
Rainfall excess