Shoalhaven City Council
Broughton Creek Flood Study Final Draft Report April 2007
Prepared by
SMEC Australia Pty Ltd
Project Number: 31455
SHOALHAVEN CITY COUNCIL
BROUGHTON CREEK FLOOD STUDY
- FINAL DRAFT REPORT -
April 2007
Prepared by:
SMEC Australia Pty Ltd ABN 47 065 475 149
Project Number: 31455
DOCUMENT RELEASE INFORMATION
Client Shoalhaven City Council
Project Name Broughton Creek and Kangaroo Valley Flood Studies
Document Number 3001049
Document Title Broughton Creek Flood Study – Final Draft Report
Revision Status April 2007
Document prepared by:
SMEC AUSTRALIA PTY LTD ACN 065 475 149 Level 6, 76 Berry Street, North Sydney 2060 Telephone (02) 9925 5555 Facsimile (02) 9925 5566
Prepared by: Reviewed by:
Chris Koutsellis Jerzy Zastawny Amir Deen Water Resources Manager, Water Services
© COPYRIGHT OF SMEC AUSTRALIA 2007 Any use of this material except in accordance with a written agreement with SMEC Australia is prohibited.
TABLE OF CONTENTS
1 FOREWORD ...... 5
2 EXECUTIVE SUMMARY ...... 6
3 INTRODUCTION...... 7
4 BACKGROUND ...... 8
4.1 General...... 8
4.2 The Flood Problem...... 8
5 DATA COLLECTION ...... 9
5.1 Reports ...... 9 5.1.1 General ...... 9 5.1.2 Broughton Creek ...... 10
5.2 Rainfall and Streamflow Data...... 11 5.2.1 Rainfall Stations ...... 11 5.2.2 Streamflow Data...... 12 5.2.3 Zoning and Contours ...... 12 5.2.4 Survey...... 12 5.2.5 Bridge and Culvert Drawings...... 12 5.2.6 Flood information – Newspapers, Plans and Questionnaires ...... 12 5.2.7 Aerial Photographs ...... 12
5.3 Community Consultation ...... 12 5.3.1 General Information ...... 13 5.3.2 Flood History...... 13
5.4 Data Collection Summary ...... 15
6 HYDROLOGY ...... 16
6.1 General...... 16
6.2 Model Selection...... 16
6.3 Broughton Creek Hydrologic Model ...... 16 6.3.1 Design Floods...... 18
6.4 Hydrology Summary...... 20
7 HYDRAULICS...... 21
7.1 Model Selection...... 21 7.1.1 Broughton Creek Hydraulic Model ...... 21
7.2 Model Setup ...... 21 7.2.1 General ...... 21 7.2.2 Cross Sections ...... 22 7.2.3 Boundary Conditions...... 22
7.3 Model Calibration & Verification...... 23 7.3.1 General ...... 23
7.3.2 Results ...... 24 7.3.3 Historical Events ...... 24
7.4 Design Events...... 25 7.4.1 Sensitivity Analysis...... 27
7.5 Severity of the June/July 2005 Event...... 28 7.5.1 Introduction ...... 28 7.5.2 Methodology ...... 28 7.5.3 Summary ...... 32
7.6 Local Drainage ...... 32
7.7 Flood Behaviour ...... 35
7.8 Summary and Conclusions...... 39
8 HYDRAULIC CATEGORISATION & PROVISIONAL HAZARD MAPPING...... 40
9 FINDINGS ...... 41
10 REFERENCES...... 42
11 APPENDICES ...... 43
Figures Figure 1 – Study Area: Broughton Creek – Berry Town Map Figure 2 – RAFTS-XP Sub-Catchment Layout – Broughton Creek Figures 3a-d – Isohyetal Maps Broughton Creek 1974, 1988, 2002, 2005 Figures 4a-b – Mike 11 Model Layout Cross Sections - Broughton Creek Figures 5a-b – Flood Extent Map 2005 Figures 6a-b – Flood Extent Map PMF Figures 7a-b – Flood Extent Map 1% AEP event Figures 8a-b – Flood Extent Map 5% AEP event Figures 9-12 – Flow & Velocity Peaks 2005, PMF, 1%, 5% AEP events Figures 13-15 – Flood Contour Plans PMF, 1%, 5% AEP events Figures 16-18 – Flood Hazard Maps PMF, 1%, 5% AEP events Figures30-33 –Historical Flood RAFTS Results Broughton Creek 1974, 1988, 2002, 2005
Charts Chart 6.1 – Albert Street Drainage Catchment Map Chart 6.2 – DRAINS Plan Layout Albert Street Drainage Chart 6.3 – Albert Street Drainage 100% AEP Flood Profile
1 FOREWORD
The township of Berry has experienced flooding in the past resulting in damage to private property, goods and roads. In response to these flood hazards and a desire to prepare a long-term management plan for the town, Shoalhaven City Council (SCC) are preparing a Floodplain Risk Management Plan to manage the existing and future flood risk to the town. This plan will be developed in accordance with the NSW Flood Prone Land Policy and the principles and guidelines in the Floodplain Development Manual 2005 (The Manual).
The process of developing a Floodplain Risk Management Plan is illustrated in Schematic 1 below.
Schematic 1: Process of Developing Floodplain Risk Management Plan
Floodplain Risk Management Committee Established by the local council, must include community groups and state agency specialists.
Data Collection Flood Study Floodplain Risk Floodplain Risk Compilation of Defines the nature Management Study Management Plan existing data and and extent of the Determines options Preferred options collection of flood problem in in consideration of publicly exhibited and additional data. technical rather than social, ecological and subject to revision in Usually undertaken map form. Usually economic factors light of responses. by consultants undertaken by related to flood risk. Formally approved by appointed by the consultants appointed Usually undertaken the council after council by the council. by consultants public exhibition and appointed by the any necessary council. revisions due to public comments.
Implementation of Plan Flood, response and modification measures (including mitigation works, planning controls, flood warnings, flood readiness and response plans, environmental rehabilitation, ongoing data collection and monitoring) by the council.
3001049 5 Broughton Creek Flood Study – Final Draft Report, April 2007
2 EXECUTIVE SUMMARY
A flood study of the Broughton Creek was undertaken to determine flood behaviour in the catchment. The study produced information on flood levels, velocities and flows for full range of design events including the 0.5%, 1%, 2%, 5%, 10% and 20% AEP and Probable Maximum Flood (PMF).
The Broughton Creek catchment has a catchment of approximately 104 km2. Agriculture industries dominate the major land usage. The study area which included Berry Township was shown in Figure1.
The flood study was carried out using two computer models. The RAFTS hydrological model was used to convert rainfall to runoff and Mike-11 hydraulic model used to calculate water levels, velocities and flows in the study area.
The data collection included review available data, historic rainfall data and flood information collection and revision, and site reconnaissance. Additionally topographical survey was carried out to augment Aerial Laser Scanning (ALS) data used to obtain ground levels and channel cross sections required to establish hydraulic models.
Design rainfall intensities were estimated in accordance with Australian Rainfall and Runoff (AR&R) 1998. Design flows calculated using RAFTS model were input into Mike-11 hydraulic model. The PMF was estimated using methods by the Bureau of Meteorology.
Maps were developed showing the provisional flood extents and flood hazard maps for the PMF, 1%AEP and 5%AEP design events. The report also contains further assessment of flood behaviour including time of rise, duration of flooding, depths, in addition to maximum water levels, discharges and velocities.
3001049 6 Broughton Creek Flood Study – Final Draft Report, April 2007
3 INTRODUCTION
As a part of Shoalhaven City Council’s (SCC) Floodplain Risk Management Programme, SMEC was engaged by the Council to undertake a flood study including hydrology and hydraulic investigation of the floodplains and waterways in and around the town of Berry in the Broughton Creek Catchment. The purposes of the flood study were to identify the technical flooding issues that affect the catchment area and develop detailed hydrologic and hydraulic models of the catchments that were used to establish flood behaviour under existing conditions and will later be used to assess floodplain risk management option, as part of the subsequent Floodplain Risk Management Study.
After formation of a Floodplain Management Committee the next steps in developing a Floodplain Risk Management Plan are data collection and a flood study, to determine the flood behaviour under existing conditions for historical and design floods. Findings from the flood study will be used in the subsequent Floodplain Risk Management Study and Plan that addresses the existing, future and continuing flood risks.
The study area for the Broughton Creek Flood Study is shown in Figure 1. Broughton Creek and its tributaries rise in the ranges to the north and west of the town of Berry, flowing through farming areas and forest to the Shoalhaven River downstream of Nowra. Broughton Mill Creek, Connollys Creek, Bundewallah Creek and the unnamed watercourse locally known as Town Creek are the main source of flooding in Berry. Downstream of Berry the creek near Hitchcocks Lane causes additional flooding problems for the rural/residential areas and access between Berry and Nowra.
Tasks that form part of the Flood Study include: • Data collection and review; • Hydrologic model establishment and calibration; • Hydraulic model establishment and calibration; • Simulation of design events; • Sensitivity runs of key model parameters; • Reporting of flood behaviour; and • Assessment of preliminary flood hydraulic and hazard categories.
3001049 7 Broughton Creek Flood Study – Final Draft Report, April 2007
4 BACKGROUND
4.1 General
Broughton Creek is a tributary of the Shoalhaven River draining the hills of Cambewarra Range and the Shoalhaven floodplain on the northern side of the river. The catchment area is approximately 104 km2 (refer to Figure 2 for sub-catchment layout). Agriculture industries dominate the major land usage type with extensive areas utilised for dairy and beef cattle grazing in private pasture production. The area downstream of the town of Berry is flat and swampy and is generally below the level of the Broughton Creek levees. This floodplain has an elevation generally between 1m and 2m AHD. Tidal influence extends approximately 12 km upstream of the Broughton Creek and Shoalhaven River confluence to the vicinity of the Coolangatta Road Bridge.
4.2 The Flood Problem
Broughton Mill Creek, Connollys Creek, Bundewallah Creek and the unnamed watercourse locally known as Town Creek are the main sources of flooding in Berry. An unnamed watercourse near Hitchcocks Lane can cause flooding problem for the adjoining rural/residential areas.
Floods inundate substantial areas of rural land surrounding Berry and within the township itself including inundation of grounds and roads. During major floods the Princes Highway at Berry could be closed for more than 24 hours, access to David Berry hospital may be cut off and the rail line can be affected as well.
There is concern that potential future development may occur on land subject to flooding and may impact on flow behaviour such that flood effects could be exacerbated and/or transferred to a different locality.
3001049 8 Broughton Creek Flood Study – Final Draft Report, April 2007
5 DATA COLLECTION
5.1 Reports
5.1.1 General i Lower Shoalhaven River Flood Study (Report No. PWD 87049), April 1990, Webb McKeown and Associates
This study was a technical investigation of the entire Shoalhaven River catchment. The WBNM hydrologic and the Cell hydraulic computer models were established and calibrated. The calibration events for the hydrologic model used the following floods: August 1974, June 1975, October 1976, March 1978 and April 1988. The study determined design information for 5%, 2% and 1% AEP and extreme flood events.
This report presents flood related information that was used for this flood study. Information included rainfall and isohyetal maps for past storms and water levels in the Lower Shoalhaven River for the downstream boundary for the Broughton Creek hydraulic model. ii Lower Shoalhaven River Floodplain Risk Management Study, Draft Report, February 2002, Webb McKeown and Associates
This study followed the Lower Shoalhaven River Flood Study as part of the preparation of a Floodplain Risk Management Plan for the Lower Shoalhaven River. The existing WBNM and the Cell models were used. Additionally 0.2%, 0.5% and 10% AEP design floods were modelled. iii Lower Shoalhaven River Flood History at Nowra Bridge 1860 – 1980, 1981, Public Works Department
This document contained information on significant historical flood levels at Nowra Bridge. iv Shoalhaven City Local Flood Plan, Draft (October 2003), SES
This document covered the Shoalhaven City Council area for all levels of flooding, including the township of Berry. It covers preparedness measures, response operations and recovery measures. The document includes some flood information for Berry Township. Some relevant notes from the flood plan were: • the Princes Highway at Berry can be closed during floods for more than 24 hours, • access to David Berry hospital can be lost and the rail line can be subject to closure. v Flood Policy, Interim – Caravan Parks on Flood Prone Land (July 1988), SCC
This policy contains a discussion of the hazards and risks associated with caravan parks located on floodplains in the SCC region. No specific design flood levels are provided.
3001049 9 Broughton Creek Flood Study – Final Draft Report, April 2007 vi Interim Flood Policy, General Conditions for the Whole City and Specific Areas (September 1987), SCC
This policy applies to all land within the City of Shoalhaven. It specifies a design ‘standard’ flood of the 1:100 year ARI event. This policy has limited application for the preparation of the current Flood Study.
5.1.2 Broughton Creek i Study for Proposed Development, Queen Street Berry (February 2004), Storm Consulting Pty Ltd
This Study was carried out to determine the potential impact of development on flood behaviour at a proposed development in Berry. Using an XP-RAFTS model, the 100 year ARI peak flow rate was calculated to be 18.1m3/s, and the PMF 1 hour peak flow rate was 54m3/s. Flood levels were calculated for pre and post-developed conditions using a HEC-RAS model. ii Development Control Plan No 49, Berry Town Centre, Amendment No 4 (December 2003), SCC
This is an amendment to Development Control Plan (DCP) No 49 for No 80 Albert Street in Berry. One of the objectives stated in the DCP is to ‘control storm water quality and quantity and reduce impacts on adjoining properties and existing public systems’. The document states that on-site detention is required where roof or paved areas of new developments exceed 30m2. iii Broughton Creek Hotspot Remediation Management Plan (November 2002), SCC
This report was developed as a result of a study carried out in 1999 by the Department of Land and Water Conservation (DLWC). It addresses the Acid Sulphate Soils (ASS) issue in the Broughton Creek catchment. As part of the investigation, drainage and flood control needs were assessed. Comments from the Plan include: • Average annual rainfall at Berry of 1400mm, • Floods occur at least twice a year, • Floodwaters can take a few days to recede and can reach depths of 1.5 metres.
This document notes the soils on the Broughton Creek floodplain generally comprise of thick estuarine and lagoonal sediments under a thin veneer of alluvium.
3001049 10 Broughton Creek Flood Study – Final Draft Report, April 2007 iv Broughton Creek Catchment Management Plan (November 1999), The Shoalhaven Catchment Management Committee
Appendix 1 of this report contains information on the stormwater pollutant load for unnamed creek (locally known as Town Creek) through Berry. Included in the data are catchment areas for the lower catchment (25Ha), Berry township (65Ha), and upper catchment (60Ha), average rainfall (1.5m/year), and estimates of percentage runoff which were derived from Water Quality Assessment Guidelines for New Urban Developments in the Illawarra (1997). v Acid Sulphate Soil, Priority Management Areas on the Shoalhaven Floodplain, Broughton Creek (1999), DLWC
Broughton Creek has been mapped as a priority area for the management of acid sulphate soils. Although this may be relevant when considering mitigation measures as part of a Floodplain Risk Management Study, it was not relevant for this flood study. vi Broughton Creek Irrigation Project (February 1971), Water Conservation & Irrigation Commission
Design rainfall intensities are provided for different durations of the 1year, 10 year and 20 year ARI events which were determined using methods given in early versions of Australian Rainfall and Runoff (AR&R). The report provides design hydrographs and recorded rainfall depths on Broughton Mill Creek for the different durations. The critical design storm was found to be 180 minutes. The relevance of this document to the current study was limited as it was written prior to the major floods during the 1970’s and 1980’s. vii Plan of Flood Extents 1974 Event – Berry Township, SCC
This plan shows the extent of flooding that occurred during March 1974. Inundation was mapped the day after the flood using debris marks. This data was used for calibration.
5.2 Rainfall and Streamflow Data
5.2.1 Rainfall Stations
There is a good coverage of daily read rainfall stations in the vicinity of Broughton Creek catchment which are adequate to provide information on the distribution of rainfall during historical storm events. The majority of stations are daily read gauges operated by the Bureau of Meteorology (BOM), however some stations are operated by the Sydney Catchment Authority (SCA).
There are no recognised pluviograph stations within the Broughton Creek catchment. Hourly rainfall readings were available, however, for the June/July 2005 rainfall event at the Department of Agriculture building in Berry and at 78 Woodhill Mountain Road.
3001049 11 Broughton Creek Flood Study – Final Draft Report, April 2007
5.2.2 Streamflow Data
There are no stream gauging stations within the Broughton Creek catchment.
5.2.3 Zoning and Contours
SCC provided geographical information in ESRI shape file format including roads, 10m contours, land use zones, waterways, properties, vegetation, acid sulphate soils and threatened species.
Airbourne Laser Scanning (ALS) was provided for Broughton Creek catchment from SCC. This data was used to establish Digital Terrain Model (DTM). The DTM was used to extract cross sections for hydraulic modelling and as well as for mapping purposes.
5.2.4 Survey
Survey has been undertaken to obtain flood marks and details of drainage structures. This information was used for hydraulic modelling. Selected cross sections of the floodplains have also been surveyed to verify topographic information obtained from ALS. In the north west of the Broughton Creek study area, 22 additional cross sections were surveyed, as they were not within the extent of the ALS. Data was supplied in Integrated Survey Grid (ISG) coordinates and to Australia Height Datum (AHD).
5.2.5 Bridge and Culvert Drawings
Drawings for five bridges and one culvert under the railway line at Berry were obtained from Rail Infrastructure Corporation (RIC). Other drainage structures including four (4) culverts under the railway have also been surveyed.
5.2.6 Flood information – Newspapers, Plans and Questionnaires
SCC forwarded local newspaper articles and photographs of past floods. This information has general flood and meteorological information. There are few references to peak flood heights, velocities and discharges.
SCC provided a flood inundation map of Berry for the 1974 event. This event was used as a calibration event.
5.2.7 Aerial Photographs
Council have provided aerial photographs in electronic format.
5.3 Community Consultation
A comprehensive community consultation process was undertaken to obtain flood information for past events. This involved sending a questionnaire, conducting three public meetings and communications with relevant community groups. The questions were concerned with the history of flooding on a property, the extent of flooding, and the evidence available for these flood events. In
3001049 12 Broughton Creek Flood Study – Final Draft Report, April 2007
Broughton Creek, 650 surveys were sent to residents and 72 completed surveys were returned. A full collation of the responses from the surveys is given in Table 5.1. Key findings are presented below according to headings used in the survey questionnaire.
5.3.1 General Information
The 72 survey respondents were residents, landowners or commercial land users who have been living in the area for a varying number of years. Eleven farm owners responded showing a high awareness of flooding in the area; only two of them had not had their land flooded in the past. Thirty- five percent of the respondents have resided in the area for over 20 years and therefore the results should give a reasonably good indication of local flooding patterns.
5.3.2 Flood History
Flooding of property Forty percent of the respondents have encountered flooding to their property with flood marks visible at 7 properties. Three of the residents have encountered flooding at their garage or shed, and two residents have had water encroaching to their home. Depth of water observed during a flood ranges from 0.1m to 4m above ground.
Three of the respondents recalled all four of the flood events specified in the questionnaire (1984, 1978, 1975 and 1971), ten of the residents recalled flooding occurring in the past three years. Thirty percent of the respondents have photographs of flooding in the Berry area.
Flood Duration According to the survey responses, flood duration can vary from less than an hour to several days.
Flood Source and Destination During a flood, respondents had witnessed water flowing mostly to and from the Town Creek. Other sources identified include Broughton Creek, Bundewallah Creek and Connollys Creek. Overflowing stormwater drains and discharge from neighbouring properties were also considered as a reason of flooding.
Flood Behaviour A range of flood behaviour was observed in Berry from fast flowing water to static ponding.
Other Comments Responses indicate minimal disruption to activities during floods. However, disruptions include sewage overflow through manholes leading to problems with the resident’s plumbing system and flooding of a road causeway which blocks the access to the resident’s house (2-4 times a year). One respondent commented that on March 2002, a flood broke the banks of Connollys Creek which inundated their property and cause damages to the farm.
Concern was expressed by a number of the respondents regarding future development in the area and the adverse effects that is likely to have on flooding. Maintenance of channels and stormwater drains is also a concern among residents; as build up of debris and invasive weeds might increase flood levels.
It is considered by a number of residents that the stormwater drainage system has inadequate
3001049 13 Broughton Creek Flood Study – Final Draft Report, April 2007 capacity and needs to be addressed.
The main concern expressed by the farm owners were the effects that future development might have on flood conveyance. Farm owners also commented on the need for maintenance of gutters, drains, open channels and the creek itself, particularly of vegetation.
Table 5.1: Collated Survey Results – Broughton Creek General Information Surveys sent: 650 Responses received: 72 Response rate: 11%
Flood History What is the type of property? 80% Residential; 6% Commercial; 14% Farmland How long at that address? Avg: 17 yrs How long in the Berry area? Avg: 23 yrs Has your property been Yes: 40% (29) affected by flooding? No: 60% (43) Year of flood? (no. of 2004: (1) 1988: (4) responses) 2003: (3) 1986: (2) 2002: (10) 1984: (5) 2001: (1) 1978: (3) 1998: (3) 1975: (3) 1991: (3) 1971: (4) What parts of your property Grounds: 28% (19) were flooded? Garage/Shed: 6% (4) Building: 3% (2) How long did the flooding Minimum duration: <1hr last? Maximum duration: 5 days Where was the water flowing Local Creek: (23) to and from? (no. of Overflowing stormwater drains: (12) responses) Inadequate drainage: (7) Overflow from neighbouring properties: (11) Broughton Creek: (9) Connellys Creek: (1) Bundewallah Creek: (3) Are there any flood marks on Yes: 8 or near your property? 1972 (1) 2001 (1) 1975 (1) 2002 (2) 1984 (2) 2003 (1) What was the worst depth of Average: 1.3m flood? Minimum: 0.1m Maximum: 4.0m What was the worst velocity Stationary: (4) of flood? (no of responses) Walking pace: (5) Running pace: (20) Do you have any photographs Yes: 31% (22% with copies) or records of these floods? No: 69%
3001049 14 Broughton Creek Flood Study – Final Draft Report, April 2007
Comments Proposed development may increase flooding in the area; Flooding occurs quickly (ie 1m within 1hour) around the bowling club and the floodplain behind; The area behind 24 Princes St. is flood prone; The area between Bundewallah Ck and North St is flood prone. Water is liable to flow south through properties (mostly rural land) onto North Street; Water backs up behind the culvert under Prince Alfred St and encroaches into the garage of the property upstream; The culvert under Woodhill Mountain Road is under capacity Ideas and Suggestions Increase capacity of stormwater drainage; Upkeep of riparian vegetation; Maintenance of stormwater drainage to clear potential blockages (ie overgrown vegetation and general debris); Maintenance of local creek and open channels to clear potential blockages(ie overgrown vegetation and general debris); Divert creek to prevent large volumes of water running through town; Replace some channels with concrete lines channels to increase conveyance; Educate new residents on dangers of flooding and mitigation measures; Encourage dams on rural properties to harness excess water; An open channel is needed on the north side of North St to collect overland flows. .
5.4 Data Collection Summary
Data collection was carried out in purpose to support flooding investigation for Broughton Creek catchment area.
Reports, investigations, calculation files, rainfall data and flood information relevant for the preparation of a flood study were collected and reviewed. Topographical survey was carried out to augment Aerial Laser Scanning (ALS) data used to obtain ground levels and channel cross sections required to establish hydraulic models.
Blockage of culvert/pipes and water levels for historic flood events information were obtained during community consultation process.
Details of collected information were presented in Appendices.
3001049 15 Broughton Creek Flood Study – Final Draft Report, April 2007
6 HYDROLOGY
6.1 General
Design discharges were required at various locations throughout the Broughton Creek catchment as an input into hydraulic models which were used to investigate flood behaviour. The adopted approach was to establish rainfall runoff models of the catchment as the primary tool to estimate discharges.
There was no stream flow gauging station within the Broughton Creek catchment and hence it was not possible to calibrate and verify the hydrologic model for this catchment. The adopted approach was to select model parameters based on previous experience with similar catchments.
6.2 Model Selection
The RAFTS-XP model was selected for the hydrological modelling. It was considered suitable for the study as it: • models sub-catchment varied storms which are typical for the study area; • simulates storage within sub-catchments; and • has been used extensively for similar catchments.
6.3 Broughton Creek Hydrologic Model
The Broughton Creek catchment was divided into 28 sub-catchments, as shown in Figure 2, with boundaries derived using 1:25 000 topographic maps. Details of the sub-catchment areas, slopes and impervious portions are described below.
The Broughton Creek catchment includes large floodplain areas that are used for agriculture. No stream flow gauging station was available in the Broughton Creek catchment for calibration of the hydrologic model. Therefore the adopted parameters were based on experience gained in other similar catchments.
Given that Broughton Creek is similar to catchments from which the hydrologic equations were derived1, the default storage parameters in RAFTS were adopted. A “Bx” multiplier of 1 was used, while PERN was set to 0.05. The adopted model parameters and catchment information are given in Table 6.1.
Whilst there was no stream flow gauging data to directly calibrate the hydrologic model, there were recorded flood levels for the events of 1974, 1988, 2002 and 2005. The recorded flood levels were used to calibrate the hydraulic model, and hydrographs were computed for these events as inputs to the hydraulic model. The results of the hydraulic model were then used to verify the hydrographs computed using the hydrologic model. For instance, if the hydraulic model over or under estimates discharges to an extent that can not be explained by expected variations in the channel roughness
1 Rural catchments in NSW with flat terrain or rolling hills
3001049 16 Broughton Creek Flood Study – Final Draft Report, April 2007 parameters, then this suggests an error in the hydrologic model leading to adjustment of the parameters. The results for the modelled historical events are shown in Table 6.2.
Rainfall readings for the 2005 event were sourced from six different locations, most of which were in or near the town. One rainfall gauge reading was located north of the town below the escarpment on Broughton Vale Road, while another was located to the east of the town on the Princes Highway near Tindells Lane. The rainfall isohyetal maps for the 1974, 1988, 2002 and 2005 storm events are shown in Figures 3a-d.
Impervious Areas
RAFTS-XP adjusts the storage delay coefficient according to the percentage of impervious area in a catchment. The impervious areas were estimated from aerial photographs. The adopted values are shown in Table 6.1.
Slopes
The slopes within the sub-catchments ranged from flat to steep (0.3% to 16.8%). The slope affects the response time for runoff, with steeper slopes producing quicker responses to the watercourse. To represent the effect of these slopes, RAFTS-XP uses a subcatchment average weighted slope derived from the maximum change in elevation over the longest flow path (RAFTS-XP user manual). Topographic maps, with a 10 metre contour interval, were used to determine the subcatchment weighted slopes. The slope for each sub catchment is given in Table 6.1.
Channel Routing
RAFTS-XP software enables the routing of hydrographs between each sub-catchment by using either: • a Muskingum-Cunge routine that uses channel length, slope and cross section; or • a simple translation by a fixed time period – hydrograph lagging.
For early stage of the project no cross section data was available and therefore hydrograph lagging method was adopted. The adopted lag time is also presented in Table 6.1.
Rainfall Losses
The simple initial loss/continuing loss model was adopted for the Broughton Creek catchment.
AR&R recommends a value between 10 and 35mm for initial loss and 1.0-2.5mm/hr for continuing loss in design storms. Since there was no gauging station in the Broughton Creek catchment to calibrate the hydrologic model, standard losses within this range were adopted. For all the historic events, the initial loss used was 25mm and the continuing loss was 2.5mm/hr. The design events were run with the same losses, apart from the PMP, which had no initial loss and 1mm/hr continuing loss. The PMF adopted less initial loss and continuing loss in order to provide a better estimate of the Probable Maximum Flood.
3001049 17 Broughton Creek Flood Study – Final Draft Report, April 2007 Catchment Storage
RAFTS-XP models catchment storage using a non-linear storage equation with “B” the linear parameter and “n” the exponent. K(q)=Bq(n)
Where K(q) is the sub-area delay time (hours)as a function of q q is discharge (m3/s) B is the storage delay time coefficient n is the storage non-linear exponent
For each sub-catchment, the software determines a representative catchment storage parameter “B” based on area, slope and impervious percentage. The exponent “n” is specified by the user with a default value of –0.285 recommended for rural catchments. This default value was adopted throughout the catchment.
RAFTS estimates a default value for the coefficient B using the following equation:
B=0.285 A0.52(1+U)-1.97Sc-0.5
Where B is the mean value of coefficient B for the subcatchment A is subcatchment area (km2) U is the fraction of the catchment that is urbanised. Sc is the main drainage slope of the subcatchments as a percentage.
The value of “B” can be modified individually for each catchment at the users discretion or modified globally by a multiplying parameter (“Bx”). To achieve calibration of the hydraulic model for the Broughton Creek, a global storage parameter “Bx” of 1.0 was adopted. The resultant “B” values and other catchment data for each sub-catchment are given in Table 6.1.
6.3.1 Design Floods
The hydrological model was used to estimate the 0.5%, 1%, 2%, 5%, 10% and 20% AEP flood discharges, by applying design rainfall intensities and temporal patterns computed using the procedures outlined in Australian Rainfall and Runoff (AR&R). The Probable Maximum Precipitation (PMP) design event was estimated using the method outline by the Bureau of Meteorology “Estimation of Probable Maximum Precipitation in Australia; GSDM (2003)” for durations less than or equal to 6 hours, and GSAM (2006) for durations greater then 6 hours.
The hydrologic model was run for a range of storm durations in order to determine the critical duration (ie. the storm which produces the highest flood discharge). The critical duration for the Broughton Creek catchment was found to be 9 hours for the ARR storms, while the critical duration for the PMP was 2 hours. Note that these maximum design discharges are for the catchment outlet, so the individual hydrographs may not necessarily be equivalent to the maximum design discharges for every other point in the catchment.
3001049 18 Broughton Creek Flood Study – Final Draft Report, April 2007
Table 6.1 - Summary of RAFTS-XP Sub-catchment Characteristics Area Slope Impervious Downstream Link Label (Ha) (%) (%) B’ Lag (min) BC_AL1 186.4 13.40 0 0.32 12 BC_AL2 112.0 2.34 0 0.59 11 BC_AL3 217.5 0.30 0 2.33 0 BC_ALTrib1 197.8 11.73 0 0.35 0 BC_BC1 263.6 2.65 0 0.87 22 BC_BC2 620.1 1.68 0 1.70 8 BC_BC3 878.8 14.59 0 0.69 10 BC_BC4 438.1 9.15 0 0.61 10 BC_BC5 564.2 14.09 0 0.56 36 BC_BC6 1073.7 0.32 0 5.18 11 BC_BC7 231.4 2.42 0 0.85 6 BC_BC8 194.1 5.09 0 0.53 7 BC_BC9 195.7 2.54 0 0.76 0 BC_BCTrib1 455.3 1.75 0 1.42 0 BC_BM1 137.1 0.93 0 1.04 25 BC_BM2 793.7 16.40 0 0.62 19 BC_BM3 857.0 11.84 0 0.76 18 BC_BM4 464.2 3.56 0 1.01 13 BC_BM5 78.7 0.90 0 0.80 8 BC_BW1 680.5 16.77 0 0.57 20 BC_BW2 745.1 12.12 0 0.70 15 BC_BW3 88.9 1.00 0 0.80 0 BC_CN1 594.7 8.39 0 0.75 0 BC_CP1 64.4 5.20 0 0.30 10 BC_CP2 93.0 2.22 40 0.16 8 BC_CP3 36.1 0.41 0 0.79 0 BC_HL1 71.5 13.34 0 0.20 11 BC_HL2 147.1 3.10 10 0.39 10 Dummy 0.01 0.10 0 0.02 0
Table 6.2 – Results for Modelled Historical Events Event Peak Volume Flow (m3/s) (ML) 1974 592 40920 1988 465 28150 2002 369 16680 2005 1898 32410
The computed hydrographs for Broughton Creek at Berry are presented in Figures 30-33 for each of the historical floods that were used in calibrating the hydraulic model.
3001049 19 Broughton Creek Flood Study – Final Draft Report, April 2007 6.4 Hydrology Summary
The RAFTS hydrological model was established for the Broughton Creek catchment. The Broughton Creek catchment was divided into 28 sub-catchments, as shown in Figure 2, with boundaries derived using 1:25 000 topographic maps. Details of the sub-catchment areas, slopes and impervious portions are shown in Table 6.1. No stream flow gauging station was available in the Broughton Creek catchment for calibration of the hydrologic model. Therefore the adopted parameters were based on experience gained in other similar catchments. The hydrological model was used to estimate the 0.5%, 1%, 2%, 5%, 10% and 20% AEP flood discharges, by applying design rainfall intensities and temporal patterns computed using the procedures outlined in Australian Rainfall and Runoff (AR&R). The Probable Maximum Precipitation (PMP) design event was estimated using the method outline by the Bureau of Meteorology “Estimation of Probable Maximum Precipitation in Australia; GSDM (2003)”. Whilst there was no stream flow gauging data to directly calibrate the hydrologic model, there were recorded flood levels for the events of 1974, 1988, 2002 and 2005. The recorded flood levels were used to calibrate the hydraulic model, and hydrographs were computed for these events as inputs to the hydraulic model. The results of the hydraulic model were then used to verify the hydrographs computed using the hydrologic model.
.
3001049 20 Broughton Creek Flood Study – Final Draft Report, April 2007 7 HYDRAULICS
7.1 Model Selection
A hydraulic model has been set-up for the Broughton Creek catchment. The MIKE 11 flood modelling software was chosen on the basis that: • the model can connect the main stream and floodplains to simulate quasi 2-dimensional flow, storages and structures; • structures such as bridges and culverts can be modelled relatively simply; • survey requirements are less than for a fully 2-dimensional model; • the graphical interface enables the location of cross-sections and branches to be seen; and • future development scenarios, such as changes to the floodplain, can easily be inserted into the model structure without extensive reconstruction of the overall model.
MIKE 11 can model in-channel conveyance and storage, as well as weir flow over structures such as culverts and bridges. It can be readily adjusted to model flood mitigation works that might be considered in the future Floodplain Risk Management Study.
7.1.1 Broughton Creek Hydraulic Model
MIKE 11 was considered to be the most appropriate model to simulate flow through Berry township, which involves several separate creeks, each of which may have several separate overland flow paths. There are numerous road crossings with possible inter-linkages between the different waterways. MIKE 11 is suitable for simulating this quasi two dimensional behaviour and is suitable for assessing the hydraulics of road and railway crossings.
An independent model has also been established for Town Creek using HEC-RAS. This model was originally completed to answer some specific questions, as it can be established much quicker than MIKE 11. HEC-RAS is more capable of simulating a wide variety of configurations for bridges, and was used to check the headlosses computed by MIKE 11. This is of particular benefit in the town of Berry, where a number of structures exist. Both models output water levels, velocities and discharges. Backwater models such as HEC-RAS v.3.0 however can only model steady state conditions and are only suitable to estimate the peak of the flood event. A MIKE 11 model can simulate dynamic unsteady flow conditions and can model the entire flow pattern.
7.2 Model Setup
7.2.1 General
There are six main channels modelled in the Broughton Creek catchment. These are Broughton Creek, Broughton Mill Creek, Bundewallah Creek, Town (Chapel) Creek, Hitchcocks Lane Creek and Andersons Lane Creek. Five additional tributaries have been modelled to accurately define the flood extents within the study area. These are Broughton Tributary, Bundewallah Tributary 1, Bundewallah Tributary 2, Hitchcocks Lane Tributary and Andersons Lane Tributary. In total, there are 130 cross sections modelled within the Broughton Creek catchment. The MIKE 11 model cross sections are shown in Figures 4a-b.
3001049 21 Broughton Creek Flood Study – Final Draft Report, April 2007
The model was more detailed at Town Creek, due to the extra details required for structures, road crossings, obstructions and roughness variations. This was also the most relevant location for detailed information required for future development decisions. Blockage of drainage structures was studied through this area, as this was identified as a relevant issue. Downstream of the railway in the floodplain area, a more coarse layout was adopted due to the smaller variations expected in water level. The tailwater level was also impacted by tidal effects, since the floodplain is only between RL 1m and 2m AHD. Both bridge and culvert structures were modelled for the railway crossings for a number of flow paths. The study area was extended north-west of the town of Berry, to extend further up Kangaroo Valley Rd. These cross sections were surveyed and included in the hydraulic model.
7.2.2 Cross Sections
The modelled cross sections were extracted from following data: • ALS of the Broughton Creek Catchments; • Ground survey of the upper reaches of the north-western part of the catchment; and • Ground survey at structures.
The extent of the ALS data and the surveyed cross sections are shown in Figures 4a-b.
Roughness coefficients were determined on-site, through photographs, topographic maps and aerial photos. The procedure used for estimating channel and floodplain roughness coefficients was adopted from Arcement and Schneider (United States Geological Survey Water-Supply Paper 2339, http://www.fhwa.dot.gov/bridge/wsp2339.pdf). This method involved adopting a base roughness value based on soil type, and then applying adjustment factors based on factors such as vegetation, obstructions, irregularity and channel meander. These estimates were used as roughness coefficients in locations where there were no available floodmarks for calibration. For areas where floodmarks were available, these estimates were used as a starting value, which could then be subsequently adjusted in order to provide a better calibration. A summary of the roughness coefficients adopted is shown in Appendix F.
7.2.3 Boundary Conditions
Inflow to the model requires hydrographs generated by the hydrologic model. These hydrographs were created at nodes located at the downstream end of each subcatchment.
The selection of downstream boundary conditions was an important consideration and has been sensitivity tested for the 1%AEP event. Historical events had their tailwater levels set to the previous ‘Cells’ model, reported in the “Lower Shoalhaven River Floodplain Risk Management Study” (2002) by Webb McKeown and Associates.
The Cells model associated with the above report extended up to the downstream extent of the flood study area for the PMF, 0.2%, 1%, 2% and 5% AEP events. This accounted for the combined effects of flooding in the Shoalhaven River and ocean tide levels. The flood levels for these events (apart from the 0.2% AEP event) were used as tailwater conditions for the Broughton Creek flood model. For the other design events (i.e.0.5%, 10% and 20% AEP events), the tailwater levels were interpolated from the Cells model. The tailwater levels adopted are shown in Table 7.1.
3001049 22 Broughton Creek Flood Study – Final Draft Report, April 2007 Table 7.1 – Tailwater Levels adopted for Broughton Creek flood study AEP Tailwater Level (m AHD) 20% 3.3* 10% 3.6* 5% 3.9 2% 4.5 1% 5.0 0.5% 5.3* PMF 7.0 *Tailwater levels interpolated from Cells model data and Table 3 of Webb, McKeown & Associates (2002)
At the upper end of the hydraulic model’s branches, the total flow hydrographs were used as point sources, while the local hydrographs of sub-catchments further downstream were distributed between cross sections. The distributed inflows better simulate the real life situation as flows enter channels continuously down a creek system.
7.3 Model Calibration & Verification
7.3.1 General
The MIKE 11 model was calibrated to four (4) historical events in 1974, 1988, 2002 and 2005. Only two floodmarks were used for the 1974 event, four for the 1988 event, ten for the 2002 event, and 24 floodmarks for the recent event in June/July 2005. For the first three events, the floodmarks were sourced primarily from photographs showing water levels at identifiable locations. The floodmarks for the 2005 event were surveyed within the two weeks following the rainfall event. Information was also gleaned from discussions with local residents and landowners, community surveys, discussions with Council representatives, and data from both the BOM and SCA. General flood information sourced from these references included: • Debris accumulation against bridge piers, decks, fences, doors and chairs • Water lines on concrete surfaces • Flood photos showing water levels referenced to a known structure.
This information was used to verify the overall results for all calibration events. Given that the floodmarks for the 2005 event were more numerous and accurate than the previous events, priority was given to these floodmarks during the calibration process. The majority of floodmarks were located in the town, with some at North Street, near the sports field, and one further north alongside Broughton Mill Creek on Woodhill Mountain Road. The locations of the floodmarks are shown in Figure 4b.
The MIKE 11 model was initially run assuming no blockage to the structures, and using the roughness coefficients and boundary conditions specified in Section 7.2.1. Under these conditions, the modelled results were often lower than the recorded floodmarks through the town of Berry, where there are a large number of smaller pipes and culverts that cross roads and driveways. Given the vegetative nature of the overbanks adjacent to Town (Capel) Creek and the relatively small diameter of the pipes and culverts in this location, 50% blockage was considered to be a reasonable estimate of the restriction to flow in a flood event. This blockage was applied to all pipes and culverts along Town Creek. There was no variation in roughness coefficient between the events.
3001049 23 Broughton Creek Flood Study – Final Draft Report, April 2007 7.3.2 Results
The final calibrated levels and a more detailed discussion on the calibration and verification process is presented in Appendix F. The flood profiles of these calibrated events are plotted alongside the floodmarks in Appendix E1.
On average, the model replicates observed historical flood behaviour to 0.23m. For the 2005 event, the average difference is 0.15m.
These calibrated results were considered to be sufficiently accurate for the purposes of modelling design rainfall events.
7.3.3 Historical Events i June/July 2005 Event
Compared to the three other historical events the 2005 event provided a larger number of floodmarks, offered a better representation of rainfall and was the largest event recorded. For these reasons more weight was given to these floodmarks during the calibration process.
Twenty four floodmarks were recorded for the 2005 event, with the majority located within the town, although there were also four readings recorded for Broughton Mill Creek. Seven levels were recorded upstream of Queen Street, five upstream of Victoria Street, three upstream of Prince Alfred Street, two each upstream of Princess Street and at the sports field on North Street, and one recorded on the Princes Highway opposite Apex Park. Refer to Figure 4b for the locations of the floodmarks.
Water level profiles for selected historic floods are given in Appendix E1. The simulated profiles match closely at the majority of locations and with the exception of four floodmarks. These levels are all within 0.17m of recorded levels.
Initially in the unblocked case floodmarks were consistently higher than the modelled water levels throughout Town Creek. A constant pipe blockage of 50% was applied throughout the Town and this gave a closer match.
Modelling gave slightly higher levels immediately upstream of the railway and this could indicate that flows in Broughton Mill Creek are slightly overestimated. ii February 2002 Event
A total of ten floodmarks were available for the 2002 event throughout the town of Berry. Five levels were recorded upstream of Queen St. - three on the Princes Highway near the smash repairers opposite Apex Park and one each at Prince Alfred St and the corner of Princess and Albany Streets.
Water level profiles are given in Appendix E1. The simulated profiles match closely at the downstream end of Town Creek, while they are slightly high upstream of Queen St.
Upstream of Queen St, the simulated peak water levels were between 0.19m and 0.75m higher than the observed levels, assuming 50% blockage in the pipes underneath Queen St. For the 2005 event
3001049 24 Broughton Creek Flood Study – Final Draft Report, April 2007 the water levels match observed levels quite closely, which would suggest that the pipes may have been more blocked in the 2005 event than for the 2002 event.
For the remaining locations further downstream, all modelled levels demonstrated a close fit within 0.18m of observed levels. iii April 1988 Event
There were four water levels recorded for this event. Three of them are along Town Creek just upstream of the culvert crossing under Prince Alfred Street. The other floodmark is on the south east corner of Princess and Albany Streets.
Observed levels are shown on the water level profile in Appendix E1. The modelled water levels are all lower than the recorded floodmarks. This could be due to tailwater effects at Town Creek that were not evident in the model, like the overflow from Broughton Mill Creek modelled in the 2005 event. iv August 1974 Event
Only two flood levels were recorded for the 1974 event. Both are located on the Princes Highway near the smash repairers opposite Apex Park. The locations of the floodmarks are shown on Figure 4b. The water level profile along Albert Street Bypass showing the observed floodmarks is found in Appendix E1. The modelled water surface is lower than both floodmarks by up to 700mm. At the same location there is a close fit with recorded data for both the 2002 and 2005 events. This difference could have been caused by either some previous obstruction to flow at that location or the rainfall could have been locally underestimated for the Broughton Mill Creek and/or Bundewallah Creek catchments.
Other factors
Calibration of historic events can be affected by numerous factors. Some of these may include hydrologic factors such as variations in rainfall; or the conditions that are present prior to and during flooding; or localised factors which can affect storage or losses at the time of flooding. Also hydraulic factors such as roughness, blockages, bridge losses, and tailwater conditions, channel shape and erosion also add to the sensitivity of results. Since no gauging station was available within the catchment the sensitivity of the calibration could not be accurately pinned down. Therefore at sites such as at bridges a combination of factors together produce satisfactory results. These results are shown to be satisfactory in the calibrated profiles in Appendix E. The analyses uses a combination of hydrologic factors listed in Table 6.1, and other factors such as 50% blockage of culverts, bridge factors, tailwater conditions, and calibrated roughness values. Topography at the time of survey is assumed to be representative of the ground conditions for planning purposes. The sensitivity of some of these factors is presented in Section 7.4.1 and Appendix G.
7.4 Design Events
The calibrated hydraulic model was run with the same geometric set-up for design conditions. Full results for design events simulated are provided in Appendix C with a summary of the water levels at selected locations given in Table 7.2. Maps showing the flood extents, discharges and velocities, and
3001049 25 Broughton Creek Flood Study – Final Draft Report, April 2007 contours are presented in Figures 5 to 15. These maps are indicative only. Table 7.2 shows consistent results over a broad range of flood sizes. Table 7.2 – Summarised Flood Levels for Design Events
Peak Water Levels (m AHD) 0.5 % 1 % 2 % 5 % 10 % 20 % Branch Chainage PMF AEP AEP AEP AEP AEP AEP ANDERSONS_LANE_CK 500 10.14 9.84 9.80 9.75 9.71 9.67 9.63 ANDERSONS_LANE_CK 900 7.76 7.49 7.45 7.42 7.39 7.34 7.31 ANDERSONS_LANE_TRIB 1406 ------BROUGHTON_CREEK 800 8.77 7.90 7.73 7.58 7.44 7.26 7.09 BROUGHTON_CREEK 2800 7.56 5.75 5.45 5.02 4.56 4.25 3.95 BROUGHTON_CREEK 4519 7.16 5.42 5.12 4.64 4.09 3.80 3.52 BROUGHTON_CREEK 5515 7.02 5.31 5.01 4.51 3.91 3.61 3.31 BROUGHTONMILLCK 3200 13.14 11.59 11.42 11.26 11.09 10.88 10.75 BUNDEWALLAHCREEK 3000 31.61 31.09 31.04 30.98 30.84 30.53 30.26 HITCHCOCKS_LANE_CK 1630 7.14 5.34 5.21 4.88 4.44 4.22 4.07 HITCHCOCKS_LANE_TRIB 1400 15.47 15.08 15.04 15.00 14.96 14.91 14.87 TOWN_CREEK 1509 24.34 24.08 24.05 24.03 24.00 23.94 23.89 TOWN_CREEK 2107 18.53 18.11 18.06 18.02 17.97 17.91 17.85 TOWN_CREEK 2295 16 15.69 15.65 15.60 15.51 15.41 15.33 TOWN_CREEK 2464 14.1 13.86 13.82 13.79 13.74 13.69 13.64 TOWN_CREEK 2534 13.69 13.38 13.35 13.32 13.29 13.25 13.22 TOWN_CREEK 2744 11.57 11.23 11.19 11.15 11.11 11.05 10.99 TOWN_CREEK 2948 9.98 9.61 9.56 9.51 9.45 9.39 9.35 TOWN_CREEK 3074 8.47 7.66 7.58 7.52 7.45 739 7.35 TOWN_CREEK 3382 8.25 7.00 6.75 6.27 5.91 5.54 5.25
3001049 26 Broughton Creek Flood Study – Final Draft Report, April 2007 7.4.1 Sensitivity Analysis
Since channel roughness parameters and blockage rates can vary from one event to another, sensitivity runs were carried out to gain an appreciation of the potential effect of these parameter factors on flood levels. The sensitivity of the hydraulic model was tested for roughness coefficients, blockage of structures, losses through bridges and the tailwater levels. The 1%AEP design flood event was used to determine the impact of these factors on the modelled water levels. The methodology and results are summarised below and described in more detail in Appendix G.
For the sensitivity analysis of roughness coefficients the resistance values were varied by 20%. Roughness coefficients had most impact in Broughton Mill Creek, Broughton Creek and Bundewallah Creek, where water velocities are higher and structures are less of a constraint.
The Broughton Creek hydraulic model was run with a range of blockage factors for the structures within the catchment. Runs were done for the cases where structures were unblocked, 25% blocked, 50% blocked, 75% blocked and fully blocked. A flood profile (shown in Chart 6.1) was produced to demonstrate the impact of 50% and 100% blockage on structures through Town Creek in the PMF and 1% AEP events. Sensitivity to blockage is most evident near Hitchcocks Lane and Andersons Lane, where large culverts control the flow underneath a high level road. Blockage also impacts Town Creek, although overtopping occurs more frequently due to the shallow crossings.
Bridge losses were also run by varying the bridge resistance value. Results demonstrate that the changes in pipe blockage have a greater impact on flood levels than the bridge resistance.
The tailwater level was also varied. A base tailwater value of RL3.9 was used at the most downstream point on Broughton Creek (Ch 5688.755), which corresponds to the tailwater level for the 1974 event. The tailwater for the 1%AEP was also varied by increasing and decreasing the design value by 1m, to determine the impact on water levels further upstream. The 1m difference is based on rounding the 1974 tailwater level. Flood levels along Broughton Creek and in locations downstream of the railway were most affected.
The sensitivity of hydrological parameters was also tested. The storage parameter Bx was varied from 0.6 to 1.5, while the impact of infiltration was also changed from 10mm to 35mm for initial losses and 1.0mm/hr to 2.5mm/hr for continuing losses. These are based on figures in ARR. The storage factor had a much larger impact on peak discharges.
The profile for blockage of structures at Town Creek is shown in Chart 6.3, while the full results for these sensitivity analyses can be found in Appendix G.
3001049 27 Broughton Creek Flood Study – Final Draft Report, April 2007
7.5 Severity of the June/July 2005 Event
7.5.1 Introduction
The rainfall event that occurred from 30th June to the 1st July 2005 was a significant event that caused damage to parts of Berry and its surrounds. The flood levels recorded for this event were higher than any of the previous events that had been modelled as part of the calibration process (1974, 1988 and 2002). The severity of this event has been determined by using the available rainfall and flood level data for calibration, and then comparing both the hydrology (rainfall) and hydraulics (flows and water levels) with design events. This section has previously been written in a separate report (Report on the Severity of the 2005 Flood Event, November 2005) to Shoalhaven City Council, and has been reproduced with minor adjustments here.
7.5.2 Methodology
Rainfall gauge data was used from six different sources, to determine the size and the distribution of the rainfall. Four of these gauges were located in or near the town, while one was located to the east of Berry on the Princes Highway, near Tindells Lane, and another to the north on Broughton Vale Road, near the escarpment. The temporal patterns indicated that the largest amount of rainfall occurred within a 5hour period. However the raw data from the rain gauges ranged from a duration of 5hours (at Broughton Vale Rd and at Woodhill Mountain Rd) to 48hours (at Wharf Rd). Therefore the 5 hour raw data at each gauge was isolated and the average intensity calculated based on this 5hour period. The locations of these gauges are shown in Figure 3d, while the raw data and average intensities for the 5 hour period are summarised in Table 7.3.
Table 7.3 – Recorded Rainfall from the June/July 2005 Event
Reported Rainfall at Berry 5hr period isolated Ave. Time Rainfall Precip Rainfall in 5hr Ave. Precip Source Location (hrs) (mm) (mm/hr) peak (mm) (mm/hr) T. Isaacs Broughton Vale Rd 5 355.6 71.1 355.6 71.1 P. Whitton Princes Hwy (near Tindalls Lane) 7 230 32.9 200.2 40.0 WIN TV Bowling Club 24 300 12.5 179.6 35.9 Dept of Agriculture Schofields Lane 12 172.5 14.4 112 22.4 R. Gainford Woodhill Mountain Rd 5 141 28.2 141 28.2 STP Wharf Rd 48 213.5 4.4 124.2 24.8
When these 5hour rainfall gauge readings are compared to the Intensity Frequency Distribution (IFD) data for Berry (AR&R,2001) in Table 7.4, the Annual Exceedance Probability (AEP) ranges from a 10%AEP to over a 0.2%AEP event. The colour for the average precipitation in Table 7.3 matches the colour shown in Table 7.4. It is clear that the large rainfall reading on Broughton Vale Road near the escarpment is influenced by orographic effects, so this may not represent the same IFD pattern as the town of Berry. This reading has a significant influence on the rainfall pattern at Broughton Mill Creek, given its very high rainfall intensity.
3001049 28 Broughton Creek Flood Study – Final Draft Report, April 2007 Table 7.4 – IFD Data for Berry
IFD DATA - BERRY POINT1 Annual Exceedance Probability (%) Duration (hours) 100 50 20 10 5 2 1 0.2 2 24.11 31.73 43.28 50.39 59.47 71.66 81.16 104.41 3 18.64 24.58 33.72 39.37 46.58 56.28 63.85 82.45 4 15.51 20.49 28.22 33.02 39.13 47.38 53.82 69.68 5 13.46 17.79 24.58 28.81 34.19 41.45 47.14 61.15 6 11.98 15.86 21.96 25.77 30.62 37.17 42.3 54.97 8 9.98 13.23 18.39 21.63 25.74 31.31 35.68 46.49 10 8.66 11.49 16.04 18.89 22.51 27.42 31.27 40.83 12 7.72 10.25 14.33 16.91 20.17 24.6 28.08 36.72 14 7.02 9.33 13.07 15.43 18.43 22.49 25.69 33.63 16 6.47 8.6 12.07 14.26 17.03 20.81 23.78 31.16 18 6.02 8 11.24 13.29 15.89 19.43 22.21 29.13 20 5.64 7.5 10.55 12.48 14.93 18.26 20.88 27.42 22 5.31 7.07 9.96 11.79 14.1 17.26 19.75 25.94 24 5.03 6.7 9.44 11.18 13.39 16.39 18.76 24.66
When the rainfall event is routed through the RAFTS-XP rainfall-runoff model, the 2005 flows can also be compared to design flows at particular locations. The isohyetal map constructed from the rainfall gauge data is shown in Figure 3d.
In the two largest subcatchments, Broughton Mill Creek and Broughton Creek, the peak flows for the 2005 event correspond to at least a 2% AEP event. For the third largest subcatchment at Bundewallah Creek, the peak flow is at least a 2% AEP event. Over the entire catchment, the total peak flow at the downstream end of the study area is 1900m3/s, which is between a 1% and 2% AEP event.
3001049 29 Broughton Creek Flood Study – Final Draft Report, April 2007 Table 7.5 – Peak Total Flow Rates (m3/s) for Different Events Event - AEP (%) 2005 Location 0.5 1 2 5 10 20 Event BC_AL1 55 49 42 36 30 25 24 BC_AL2 136 120 104 89 73 61 63 BC_AL3 217 190 163 138 112 93 109 BC_ALTrib1 57 50 44 37 31 26 28 BC_BC1 81 70 60 50 40 32 45 BC_BC2 234 203 172 142 113 91 163 BC_BC3 511 445 382 321 259 212 358 BC_BC4 650 567 487 408 331 271 447 BC_BC5 828 721 619 520 420 344 600 BC_BC6 934 808 689 571 458 372 691 BC_BC7 1051 912 780 647 520 423 756 BC_BC8 1077 935 800 663 535 435 771 BC_BC9 2317 2020 1736 1451 1178 971 1898 BC_BCTrib1 90 78 66 55 44 35 41 BC_BM1 36 31 26 21 17 14 39 BC_BM2 276 240 206 173 141 116 344 BC_BM3 541 471 406 344 279 229 652 BC_BM4 1197 1042 896 757 615 508 1150 BC_BM5 2141 1866 1604 1342 1091 899 1794 BC_BW1 191 167 144 125 102 86 117 BC_BW2a 255 223 193 166 136 114 - BC_BW2b 234 205 177 153 126 105 - BC_BW2c 355 310 267 227 185 154 270 BC_BW3 534 466 402 341 278 229 410 BC_CN1 512 447 386 327 267 221 400 BC_CP1 18 16 14 12 10 8 9 BC_CP2 45 39 34 29 24 20 23 BC_CP3 50 44 38 33 27 22 26 BC_HL1a 17 15 13 11 9 8 - BC_HL1b 6 5 5 4 3 3 - BC_HL2a 33 29 25 21 17 14 - BC_HL2b 57 50 43 37 30 25 35 Total @ 2317 2020 1736 1451 1178 971 1898 Outlet
The 2005 event was run using the MIKE 11 hydraulic model with the flows as hydrologic inflows and the model set-up calibrated using four historical events. The design flows (shown in Table 7.5) were also run using MIKE 11 and these are compared to the 1%AEP event through the profiles shown in Appendix E2. The flood extent map is shown in Figures 5a and 5b, while Figure 11 show peak flows and velocities during the 1%AEP event.
In Broughton Mill Creek, the flood levels modelled upstream of the railway appear to be greater than the 0.5% AEP event. This reflects the large rainfall recorded in this subcatchment. Just upstream of the railway, part of the flow from Broughton Mill Creek spill into Town Creek and impact the water
3001049 30 Broughton Creek Flood Study – Final Draft Report, April 2007 levels at Prince Alfred St. The peak 2005 flow in Town Creek was only 23 m3/s and the water levels just upstream of railway reflect 1% AEP event. Further upstream at Albany St the water levels suggest a 10%AEP event. Approximately, 250m3/s contributed from Broughton Mill Creek between Prince Alfred Street and the railway. The railway acts as an obstruction to the flow and weir flow over the railway line engages at RL6.0 to a peak water level of RL7.0.
3001049 31 Broughton Creek Flood Study – Final Draft Report, April 2007 Water levels in Broughton Creek indicate a 2% to 5% AEP event. In other subcatchments, there were no gauge readings available, so the 2005 event will not be compared to design events in those areas.
7.5.3 Summary
The rainfall event of June/July 2005 was a significant rainfall event, particularly in the Broughton Mill Creek catchment. Given the variable spatial pattern of the rainfall it is difficult to determine a definitive recurrence interval for the entire event, particularly since it is highly influenced by a large rainfall reading further up the catchment. The modelled flows on Broughton Mill Creek upstream of the railway show that the event is of the order of a 0.5% AEP event. Through the town, the data points to a 10% AEP event. In Broughton Creek flows are in the order of a 2% to 5% AEP event.
7.6 Local Drainage
Local drainage near the corner of Albert Street and North Street was also assessed, using the DRAINS urban stormwater model. A catchment map was produced using the ground DTM of the ALS. The pipe network itself was surveyed on-site. The pipe layout and catchment map is shown in Charts 6.2 and 6.3.
Chart 6.1 – Albert Street Drainage Catchment Map
3001049 32 Broughton Creek Flood Study – Final Draft Report, April 2007
Chart 6.2 – DRAINS Plan Layout Design storms were run for the 1%, 20%, 50% and 100% AEP events, based on IFD data for the catchment (AR&R – Volume 2, 1987). A summary of the subcatchment characteristics, and pit and pipe details are shown in Appendix D.
Pits were given larger inlet capacities than what is located on-site and a blocking factor of 0.2 was applied for on-grade pits and 0.5 for sag pits. This investigation was done primarily to determine the pipe capacity. A default pipe roughness of 0.3mm was adopted throughout. The last pipe length was assumed to be free-draining, although it is likely that there will be tailwater effects for the larger events.
The 100% AEP flood profile is shown in Chart 6.4, while the rest of the results are shown in Appendix D. The current pipe drainage in the vicinity of Albert Street is only able to contain a 100% AEP event within the system. For all events greater than this, overland flow will result.
Areas of particular significance include: • The catchments falling towards North St. The pit inlet and pipe capacities appear to be undersized particularly if this were to be urbanised; • The twin pipes between Pits ALB-01/2 and ALB-01/3 have lower capacity than the upstream pipe. These should be increased in size if possible;
3001049 33 Broughton Creek Flood Study – Final Draft Report, April 2007
Chart 6.3 – Albert Street Drainage 100% AEP Flood Profile
3001049 34 Broughton Creek Flood Study – Final Draft Report, April 2007 7.7 Flood Behaviour
In the very broad temps we can see the following pattern during most flood events. The major flood flows arise in the high ground to the north of the town with flood flows rising in Broughton Mill Creek and Bundewallah Creek. The flows in the creeks are contained within the natural embankments except for a gap in this embankment to the north of the Cricket Oval. This overflow travels parallel to the Princess Highway before entering Town Creek through the town and than flows as a part of Town Creek. The following analyses have been based on the conservative assumption that the Shoalhaven River have peaked and maintains its peak for the duration of the much shorter flood event on Broughton Creek. A more accurate analysis would require joint probability analysis of flood flow in Broughton Creek and the Shoalhaven River, but that is to be beyond the scope of the study at this stage. Flooding at the downstream end of the study area is initially affected by the tailwater conditions from the Shoalhaven River submerging several creeks. In the 1%AEP these include:
• Broughton Creek; • Broughton Mill Creek; • Town Creek; • Hitchcocks Lane Creek; • Hitchcocks Lane Tributary; • Andersons Lane Creek; and • Andersons Lane Tributary;
The creeks flows need to overcome the tailwater level before it can drain away as a hydraulic grade line (HGL). The tailwater levels used at the downstream end of the model were shown in Table 7.6 for each of the design events and are reproduced below. Table 7.6 – Tailwater Levels adopted for Broughton Creek flood study AEP Tailwater Level (m AHD) 20% 3.3 10% 3.6 5% 3.9 2% 4.5 1% 5.0 0.5% 5.3 PMF 7.0
Most of these areas have a provisional flood hazard rating of “high hazard” as the flow depths are greater than 1m in depth. In addition high velocities also add to the hazard rating. Only in areas where there are small depths and small velocities are there low provisional hazard classifications. These are highlighted on Figures 16-18 which show the flood hazard maps for the PMF, 1%AEP and 5%AEP events. These maps are indicative only.
3001049 35 Broughton Creek Flood Study – Final Draft Report, April 2007 However there is more to flood behaviour than simply peak depths and velocities. Firstly, the time that the water levels rise also affect the hazard rating. In the 1% AEP event the 9hour storm produced the peak flowrate at the outlet of the model and this duration was used to assess the time of rise. From the time the water level begins to rise it takes about 1 hours 40 minutes before the tailwater level fills the nearby land as a backwater and takes a further 4hours 50 minutes before it reaches its peak discharge due to runoff from the catchment. At the junction of Town Creek and Albert Street it takes 2hours 30minutes for the 1% AEP depth to reach 1m and a further 3 hours for floodwaters to reach the peak value of 1.4m in depth.
However shorter duration storms can still produce a more critical time of rise for the 1% AEP event. To be able to assess a quicker time of rise of floodwaters the hydraulic model was also run using a short duration storm. The 1.5hr minute storm was chosen for this purpose as it is of relatively short duration and also produces a relatively high discharge. Table 7.7 shows a summary of the time it takes for the water level to reach 1m in depth at a number of locations as result of the 1%AEP 1.5hour event.
Table 7.7 – Time of Rise 1%AEP -1.5hour Duration Event
Time of Rise Max Depth Branch Chainage to 1m depth Decsription (Time to max) (hours) Town Creek 1992 - 0.7m (1.2hrs) George St Town Creek 2075 0.5 1.5m (1.1hrs) Town Creek 2140 <0.1 2.7m (1.1hrs) Queen St Town Creek 2629 0.1 2.8m (1.2hrs) Albany St Town Creek 2993 0.3 3.0m (1.3hrs) Victoria St Town Creek 3259 0.4 2.5m (1.7hrs) Prince Alfred St Albert St & Albert Bypass 918 1.3 1.2m (1.5hrs) Princess Hwy BroughtonMill Ck 2500 0.5 3.5m (1.2hrs) BundewallahCreek 3500 0.5 2.5m (1.1hrs) Overflow of BundewallahCreek 5680 0.5 2.6m (0.5hrs) Bundewallah to Alber St Andersons_Lane_Ck 500 - 0.8m (0.8hrs) Andersons_Lane_Ck 1400 0.6 2.3m (1.5hrs) Town Creek 3382 1.2 2.5m (1.7hrs) U/S Railway BroughtonMill Ck 4860 0.6 4.4m (1.6hrs) U/S Railway Broughton Creek 1600 0.3 5.2m (1.9hrs) U/S Railway Hitchcocks Lane trib 1890 0.5 2.4m (1.5hrs) Junction Town / BroughtonCreek 3531 0.1 5.7m (2.0hrs) BroughtonMillCk / Broughton Creek
Through the town of Berry there is a minimal amount of time before the water levels rise to hazardous levels with the depth rising to 1m in about half an hour. Also at Broughton Creek, Broughton Mill Creek the water levels also rise in about half an hour.
3001049 36 Broughton Creek Flood Study – Final Draft Report, April 2007 At structures such as road and railway crossings overtopping of the road/railway occurs. The duration of flooding over a number of structures in the study area is shown in Table 7.8 along with the flow over the structure, and peak depths and velocities at those sites. These indicate that excluding Edward St @ Chainage 2401 there is a high hazard at the majority of roads along Town Creek. There are high velocities and a relatively high depth of flow which occurs for a prolonged period of time. The duration that the roads at Town Creek would be out of service would affect the public’s access across roads and may cause a hazardous evacuation route.
Along the Princess Highway the duration of flooding is significant with a relatively large depth of flow at Andersons Lane Trib and high velocity at Andersons Lane Creek Ch 500.
The railway would also be out of service in the1%AEP event with the longest duration of overflows being 10.1 hours at Andersons Creek crossing.
Table 7.8: 1%AEP Overtopping of Bridges and Culverts
Flow Duration Depth of Overflow over of flow flow over Chain- Threshold Velocity Description road/r over road/ road/ Branch age Elevation (m/s) ailway railway railway (m) (mAHD) (m3/s) (hours) (m) Queen St 17.54 8.0 6.8 0.52 1.5 Town Creek 2140 Edward 14.57 16.1 5.7 0.48 1.2 Town Creek 2357 Bypass Edward St 14.50 0.0 0.0 0.00 0.0 Town Creek 2401 Princess Dr1 13.14 21.6 9.3 0.46 1.4 Town Creek 2498 Princess St 12.90 22.5 9.1 0.45 1.8 Town Creek 2534 Princess Dr2 12.27 22.5 7.9 0.76 1.7 Town Creek 2586 Albany St 12.34 21.0 6.1 0.47 2.4 Town Creek 2629 Princess St2 9.75 26.3 11.6 0.70 2.0 Town Creek 2823 Victoria St 9.00 25.1 7.5 0.49 1.5 Town Creek 2993 Prince 5.44 27.1 8.8 1.32 1.7 Town Creek 3259 Alfred St Broughton Railway 6.28 - 0.6 0.09 - 1600 Creek Railway 5.89 - 1.8 0.48 - Beachrail 0 Broughton Railway 6.00 - 5.8 1.02 - 4860 Mill Creek Railway 7.00 - 0.0 0.00 - Town Creek 3382 Railway 6.44 - 0.8 0.31 - TownRailPipe 0 Hitchcocks Railway 5.10 20.0 4.5 0.11 0.8 1740 Lane Andersons Railway 5.00 - 10.1 0.41 - 1400 Lane Creek Princess Hitchcocks 10.15 3.9 0.9 0.14 0.7 1890 Hwy Lane Trib Princess Hitchcocks 6.80 0.0 0.0 0.00 0.0 1200 Hwy Creek Princess Andersons 12.20 - 3.8 1.18 - 1190 Hwy Lane Trib
3001049 37 Broughton Creek Flood Study – Final Draft Report, April 2007 Princess Andersons 9.25 18.2 4.9 0.36 1.2 500 Hwy Lane Creek Princess Andersons 9.25 0.4 0.4 0.04 0.7 674 Hwy Lane Creek
In summary peak water levels, peak velocities, direction of flow, duration of flooding, and the time of rise were used to assess flood behaviour. Several crossings such as Queen St, Edward St, Princess St, Albany St, Victoria St, Prince Alfred St, the railway line through the town and many of the crossings along the Princess Highway are considered to be of a high hazard classification.
The PMF event was also used to assess evacuation routes. In the PMF event the only areas not inundated with floodwaters are:
• between Broughton Creek and the floodplain of Broughton Mill Creek, upstream of the railway; • between Town Creek and Hitchcocks Lane Tributary; • between Hitchcocks Lane Tributary and Hitchcocks Lane Creek; • between Hitchcocks Lane Creek and Andersons Lane Tributary; • between Andersons Lane tributary and Andersons Lane Creek; and • at Kangaroo Valley Road, between Town Creek and Bundewallah Creek.
The flood extent for the PMF indicates that the majority of the railway line gets inundated within the study area. This includes all land between Broughton Creek in the north to Andersons Lane Creek in the south.
At the Albert Street-Town Creek junction the PMF reaches 1m in depth in 25 minutes and reaches its peak value of 1.9m in about 1hour. This leaves little time available for the public to evacuate. The peak discharge at this location is 50 m3/s.
At the Victoria Street -Town Creek junction the PMF reaches 1m in depth in 10 minutes and reaches its peak value of 3.3m in about 1hour 20minutes. This also leaves little time available for the public to evacuate. The peak discharge at this location is 77 m3/s.
At the east end of North Street a large quantity of water overtops the banks of Bundewallah Creek crossing North Street to Albert Street before entering Broughton Mill Creek. In the 1%AEP event the flow to Broughton Mill Creek is 320m3/s while for the PMF the flow is 1023 m3/s. The water level in the PMF reaches 1m depth at Albert Street in 45 minutes and reaches the peak of 2.5m in a further 45minutes.
The minor drainage system that includes the pit and pipe network should normally be able to convey at least the 20% AEP design event. The DRAINS model was used to assess the underground drainage system at Berry. It was concluded that the minor system that is currently in-place underperforms for all events larger than the 100%AEP. Also, upgrading the pit and pipe network would have little influence on the 1%AEP and PMF floodwaters and their respective flood hazard categories. However upgrading the pit and pipe network would reduce the risk of inundation in more frequent smaller events.
3001049 38 Broughton Creek Flood Study – Final Draft Report, April 2007 7.8 Summary and Conclusions
The results for the calibration and design events in the hydraulic model include: • Calibration reproduced past flood behaviour to between 0.1 and 0.2m on average. For the 2005 event, the average difference is of the order 0.08m to 0.15m. • Sensitivity analysis indicates that 1% AEP water levels could vary up to about 0.2m with a 20% change to the roughness coefficients; 0.2m within 25% to 75% blockage; 0.2m for variations in bridge loss factors; and by up to 1m at the downstream end of the model due to varying tailwaters • The accuracy of water level estimates in the hydraulic model are considered satisfactory given the results from calibration and sensitivity testing of model parameters • With blockage to structures included, satisfactory representation of observed data was achieved. • The distribution of rainfall may have had a significant impact on the calibration, especially near the confluence of Broughton Mill Creek, Bundewallah Creek and Town Creek. The rainfall pattern appears to be spatially variable, even within the catchment itself. This will have an impact on the relative size of flows for each creek or tributary. Since local gauged data was available for the 2005 event, it is likely that the rainfall distribution is better represented for this event than any of the previous historical events. • The time of rise and duration of flooding were also assessed. At many road crossings and at the railway crossings the duration of flooding adds to the provisional hazard categories based on peak water levels and velocities. • A number of areas can be spotted outside the PMF’s flood extent map for possible evacuation. However many crossings have been identified which have a potential hazard rating, even in the 1%AEP. Also the railway may be out of service by about 10 hours in the 1% AEP design event.
3001049 39 Broughton Creek Flood Study – Final Draft Report, April 2007 8 HYDRAULIC CATEGORISATION & PROVISIONAL HAZARD MAPPING
To achieve effective and responsible floodplain risk management it is necessary to divide the floodplain into areas that reflect, first, the impact of development activity on flood behaviour and second, the impact of flooding on development and people. Division of flood prone land on these two bases is referred to as ‘hydraulic categories’ and ‘hazard categories’.
The NSW Floodplain Development Manual recognises three hydraulic categories of flood prone land – floodway, flood storage and flood fringe – and two hazard categories – low hazard and high hazard. Division of the floodplain on the basis of these two effects produces the following six categories of flood prone land:
• Low Hazard Flood Fringe • Low Hazard Flood Storage • Low Hazard Floodway • High Hazard Flood Fringe • High Hazard Flood Storage • High Hazard Floodway
These categories form the basis for land management and development control.
Council has indicated that the hydraulic categorisation and assessment of the provisional flood hazards needs to be undertaken for the following three events: • 5% AEP – for use in planning in industrial areas • 1% AEP – for use in planning in residential areas • PMF – for emergency planning
The definition of hydraulic categories and assessment of provisional flood hazards was done in accordance with the NSW Floodplain Development Manual 2005. The maps are shown in Figures 16-18.
The floodplain area downstream of the railway is a combination of high hazard floodway and high hazard flood storage.
Provisional high hazard floodways are also evident throughout the study area. Low hazard categories are only categorised at locations where the flow is believed to have a low depth and low velocities. Storages are situated at areas where there’s no main floodway and where storage affects the flood behaviour mainly with its effects on reducing the flood peak and attenuating the hydrograph.
A number of waterways upstream of the railway also have the hydraulic category of floodway, many with a high hazard category. In the town of Berry itself the waterways are considered to be high hazard floodways, mainly from Town Creek and overflows from Bundewallah Creek, but also from local flows that the drainage system (pit and pipe network) could not convey.
Further analysis and interpretation of these categories and hazards will be undertaken in the Floodplain Risk Management Study.
3001049 40 Broughton Creek Flood Study – Final Draft Report, April 2007 9 FINDINGS
The figures in this section show GIS maps, contour plans, flow distributions and velocities, and hazard maps. Results shown in tables and flood profiles are in the Appendices.
FIGURES
Figure 1 – Study Area: Broughton Creek – Berry Town Map Figure 2 – RAFTS-XP Sub-Catchment Layout – Broughton Creek Figures 3a-d – Isohyetal Maps Broughton Creek 1974, 1988, 2002, 2005 Figures 4a-b – Mike 11 Model Layout Cross Sections - Broughton Creek Figures 5a-b – Flood Extent Map 2005 Figures 6a-b – Flood Extent Map PMF Figures 7a-b – Flood Extent Map 1% AEP event Figures 8a-b – Flood Extent Map 5% AEP event Figures 9-12 – Flow & Velocity Peaks 2005, PMF, 1%, 5% AEP events Figures 13-15 – Flood Contour Plans PMF, 1%, 5% AEP events Figures 16-18 – Flood Hazard Maps PMF, 1%, 5% AEP events Figures30-33 –Historical Flood RAFTS Results Broughton Creek 1974, 1988, 2002, 2005
3001049 41 Broughton Creek Flood Study – Final Draft Report, April 2007 10 REFERENCES
BoM 2003, “The estimation of Probable Maximum Precipitation in Australia: Generalised Short- Duration Method”.
HEC-RAS River Analysis System – User’s Manual, US Army Corps of Engineers – Hydrologic Engineering Center, Version 3.1, November 2002
J Meighen, L.J.Minty, Hydrology Report Series, Bureau of Meteorology Australia, December 1998, Temporal Distributions of Large and Extreme Design Rainfall Bursts Over Southeast Australia
MIKE 11 – A modelling Guide for Rivers and Channels – Users Guide, DHI Software, Edition September 2001.
NSW Government 2005, Floodplain Development Manual: the management of flood liable land
The Institution of Engineers, Australia, 2001, Australian Rainfall and Runoff – A Guide to Flood Estimation (ARR2001)
Walsh et al, Oct 1991, Initial Losses for Design Flood Estimation in New South Wales, Conference Paper
XP-RAFTS2000, 2001, User Manual, Version 5
G.J. Arcement, Jr. and V.R. Schneider, United States Geological Survey Water-supply Paper 2339, Guide for Selecting Manning’s Roughness Coefficients for Natural Channels and Flood Plains.
3001049 42 Broughton Creek Flood Study – Final Draft Report, April 2007 11 APPENDICES
A. Historical Rainfall Data
B. Flood Heights for Historical Events
C. Flood Heights and Velocities for Design Events
D. DRAINS Model for Albert Street Stormwater Drainage
E. Flood Level Profiles
1. Historical Events 2. Design Events
F. Calibration Data
G. Sensitivity Analysis
3001049 43 Broughton Creek Flood Study – Final Draft Report, April 2007
Appendix A: Historical Rainfall Data
For historical rainfall hydrographs at the downstream end of the catchment, refer to Figures 30-33.
3001049 A-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix B: Flood Heights for Historical Events
Water Level Branch Chainage 2005 2002 1988 1974 ANDERSONS_LANE_CK 0 14.68 14.54 14.57 14.56 ANDERSONS_LANE_CK 200 12.06 11.80 11.86 11.85 ANDERSONS_LANE_CK 500 9.63 9.51 9.54 9.53 ANDERSONS_LANE_CK 674 8.39 7.73 7.90 7.85 ANDERSONS_LANE_CK 700 7.83 7.50 7.59 7.56 ANDERSONS_LANE_CK 900 7.30 7.10 7.15 7.13 ANDERSONS_LANE_CK 1065 6.29 6.15 6.19 6.18 ANDERSONS_LANE_CK 1194 6.17 6.01 6.05 6.04 ANDERSONS_LANE_CK 1215 5.12 5.51 5.55 5.54 ANDERSONS_LANE_CK 1400 5.12 5.08 5.11 5.11 ANDERSONS_LANE_CK 1540.68 3.98 3.97 3.82 3.99 ANDERSONS_LANE_CK 1550 3.98 3.92 3.72 3.94 ANDERSONS_LANE_CK 2054.69 3.98 3.90 3.11 3.91 ANDERSONS_LANE_CK 2064 3.98 3.90 3.11 3.91 ANDERSONS_LANE_CK 2554 3.98 3.90 3.11 3.91 ANDERSONS_LANE_CK 3084.28 3.98 3.90 3.11 3.91
Water Level Branch Chainage 2005 2002 1988 1974 ANDERSONS_LANE_TRIB 0.00 50.24 50.18 50.19 50.19 ANDERSONS_LANE_TRIB 200.00 28.63 28.53 28.56 28.55 ANDERSONS_LANE_TRIB 360.00 23.70 23.55 23.59 23.59 ANDERSONS_LANE_TRIB 570.00 20.05 19.84 19.89 19.88 ANDERSONS_LANE_TRIB 912.00 16.16 15.96 16.01 16.00 ANDERSONS_LANE_TRIB 1077.00 12.07 11.65 11.73 11.73 ANDERSONS_LANE_TRIB 1190.00 10.92 9.76 10.02 10.00 ANDERSONS_LANE_TRIB 1221.00 9.55 9.11 9.22 9.21 ANDERSONS_LANE_TRIB 1406.00 8.15 8.05 8.08 8.07 ANDERSONS_LANE_TRIB 1700.00 4.08 4.02 3.87 4.06 ANDERSONS_LANE_TRIB 1800.00 3.98 3.97 3.82 3.99 ANDERSONS_LANE_TRIB 1816.85 3.98 3.97 3.82 3.99
3001049 B-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Water Level Branch Chainage 2005 2002 1988 1974 BROUGHTON_CREEK 0.00 8.96 7.05 7.03 7.70 BROUGHTON_CREEK 430.00 8.76 6.99 6.98 7.60 BROUGHTON_CREEK 800.00 7.56 6.05 6.04 6.57 BROUGHTON_CREEK 1320.00 6.05 4.62 4.60 5.04 BROUGHTON_CREEK 1598.59 5.95 4.28 4.13 4.63 BROUGHTON_CREEK 1600.00 5.95 4.28 4.13 4.63 BROUGHTON_CREEK 1830.00 5.62 4.09 3.50 4.27 BROUGHTON_CREEK 1961.00 5.05 4.04 3.48 4.19 BROUGHTON_CREEK 2800.00 4.82 4.01 3.33 4.13 BROUGHTON_CREEK 3050.00 4.75 4.00 3.32 4.13 BROUGHTON_CREEK 3530.89 4.65 3.99 3.30 4.11 BROUGHTON_CREEK 3615.00 4.60 3.99 3.29 4.10 BROUGHTON_CREEK 4519.00 4.20 3.96 3.19 4.05 BROUGHTON_CREEK 4950.00 3.98 3.90 3.11 3.91 BROUGHTON_CREEK 4999.67 3.98 3.90 3.11 3.91 BROUGHTON_CREEK 5073.00 3.97 3.90 3.11 3.91 BROUGHTON_CREEK 5515.00 3.92 3.90 3.10 3.90 BROUGHTON_CREEK 5688.75 3.90 3.90 3.09 3.90
Water Level Branch Chainage 2005 2002 1988 1974 BROUGHTONMILLCK 0.00 30.11 30.11 30.11 30.11 BROUGHTONMILLCK 1700.00 16.73 14.29 14.70 14.83 BROUGHTONMILLCK 1950.00 15.53 13.76 14.02 14.10 BROUGHTONMILLCK 2100.00 15.00 13.44 13.68 13.75 BROUGHTONMILLCK 2500.00 13.60 11.66 12.06 12.18 BROUGHTONMILLCK 2700.00 12.82 10.64 11.18 11.37 BROUGHTONMILLCK 2900.00 12.08 10.24 10.74 10.92 BROUGHTONMILLCK 3200.00 11.72 9.77 10.16 10.32 BROUGHTONMILLCK 3400.00 11.34 9.44 9.75 9.89 BROUGHTONMILLCK 3567.14 11.02 8.94 9.27 9.41 BROUGHTONMILLCK 3700.00 10.66 8.64 8.94 9.07 BROUGHTONMILLCK 3800.00 10.37 8.44 8.70 8.82 BROUGHTONMILLCK 3900.00 10.00 8.05 8.29 8.41 BROUGHTONMILLCK 3923.76 9.63 7.96 8.19 8.31 BROUGHTONMILLCK 4000.00 9.16 7.36 7.69 7.85 BROUGHTONMILLCK 4100.00 8.57 6.80 7.20 7.38 BROUGHTONMILLCK 4300.00 8.08 6.51 6.78 6.99 BROUGHTONMILLCK 4400.00 7.89 6.29 6.59 6.77 BROUGHTONMILLCK 4570.00 7.64 5.97 6.38 6.59 BROUGHTONMILLCK 4860.00 7.08 5.32 5.88 6.17 BROUGHTONMILLCK 5068.00 5.64 4.53 4.77 4.94 BROUGHTONMILLCK 5342.00 5.02 4.23 4.20 4.44 BROUGHTONMILLCK 6260.00 4.75 4.01 3.51 4.15 BROUGHTONMILLCK 6508.41 4.65 3.99 3.30 4.11
3001049 B-2 Broughton Creek Flood Study –Final Draft Report, April 2007
Branch Chainage 2005 2002 1988 1974 BUNDEWALLAHCREEK -300.00 79.24 79.24 79.24 79.24 BUNDEWALLAHCREEK 0.00 73.91 73.35 73.57 73.53 BUNDEWALLAHCREEK 300.00 67.07 66.43 66.72 66.70 BUNDEWALLAHCREEK 600.00 62.01 61.13 61.37 61.34 BUNDEWALLAHCREEK 800.00 59.21 58.82 58.92 58.91 BUNDEWALLAHCREEK 1025.36 55.15 54.31 54.48 54.46 BUNDEWALLAHCREEK 1100.00 53.86 52.87 53.10 53.08 BUNDEWALLAHCREEK 1550.00 46.66 45.37 45.79 45.76 BUNDEWALLAHCREEK 2000.00 41.63 40.87 41.05 41.04 BUNDEWALLAHCREEK 2300.00 38.34 37.85 37.96 37.96 BUNDEWALLAHCREEK 2670.00 34.14 33.24 33.59 33.58 BUNDEWALLAHCREEK 2933.64 31.65 30.27 30.63 30.63 BUNDEWALLAHCREEK 3000.00 31.00 29.53 29.85 29.85 BUNDEWALLAHCREEK 3200.00 28.20 27.51 27.65 27.65 BUNDEWALLAHCREEK 3300.00 27.31 26.63 26.80 26.80 BUNDEWALLAHCREEK 3500.00 25.30 24.69 24.83 24.83 BUNDEWALLAHCREEK 3642.00 24.01 22.95 23.18 23.18 BUNDEWALLAHCREEK 3900.00 21.45 20.90 21.02 21.02 BUNDEWALLAHCREEK 4200.00 19.16 18.68 18.80 18.80 BUNDEWALLAHCREEK 4400.00 17.56 17.03 17.15 17.16 BUNDEWALLAHCREEK 4600.00 15.99 15.54 15.63 15.63 BUNDEWALLAHCREEK 4900.00 14.28 13.79 13.90 13.90 BUNDEWALLAHCREEK 5100.00 12.90 12.36 12.50 12.51 BUNDEWALLAHCREEK 5400.00 11.07 10.44 10.56 10.61 BUNDEWALLAHCREEK 5550.00 9.79 9.14 9.27 9.32 BUNDEWALLAHCREEK 5680.00 9.58 8.62 8.77 8.83 BUNDEWALLAHCREEK 5865.00 9.63 8.04 8.25 8.35 BUNDEWALLAHCREEK 5916.40 9.63 7.96 8.19 8.31
Water Level Branch Chainage 2005 2002 1988 1974 HITCHCOCKS_LANE_CK 0.00 50.01 50.19 50.21 50.21 HITCHCOCKS_LANE_CK 530.00 16.17 16.19 16.20 16.21 HITCHCOCKS_LANE_CK 914.00 9.00 9.00 9.02 9.03 HITCHCOCKS_LANE_CK 1200.00 6.25 6.25 6.43 6.47 HITCHCOCKS_LANE_CK 1225.00 4.73 4.73 4.75 4.75 HITCHCOCKS_LANE_CK 1400.00 4.31 4.01 3.75 4.05 HITCHCOCKS_LANE_CK 1626.25 4.31 4.00 3.72 4.04 HITCHCOCKS_LANE_CK 1630.00 4.31 4.00 3.72 4.04 HITCHCOCKS_LANE_CK 1740.00 4.31 4.00 3.71 4.04 HITCHCOCKS_LANE_CK 1810.00 3.98 3.90 3.11 3.91 HITCHCOCKS_LANE_CK 1900.00 3.98 3.90 3.11 3.91 HITCHCOCKS_LANE_CK 2174.98 3.98 3.90 3.11 3.91
3001049 B-3 Broughton Creek Flood Study –Final Draft Report, April 2007
Water Level Branch Chainage 2005 2002 1988 1974 HITCHCOCKS_LANE_TRIB_1 0.00 50.33 50.19 50.19 50.19 HITCHCOCKS_LANE_TRIB_1 530.00 46.21 45.86 45.86 45.86 HITCHCOCKS_LANE_TRIB_1 720.00 29.89 29.64 29.64 29.64 HITCHCOCKS_LANE_TRIB_1 990.00 21.54 20.95 20.95 20.95 HITCHCOCKS_LANE_TRIB_1 1400.00 14.90 14.50 14.50 14.50 HITCHCOCKS_LANE_TRIB_1 1600.00 12.40 12.13 12.13 12.13 HITCHCOCKS_LANE_TRIB_1 1762.00 9.85 9.10 9.10 9.10 HITCHCOCKS_LANE_TRIB_1 1890.00 9.83 8.39 8.39 8.39 HITCHCOCKS_LANE_TRIB_1 1930.00 8.49 7.99 7.99 7.99 HITCHCOCKS_LANE_TRIB_1 2100.00 7.09 6.60 6.60 6.60 HITCHCOCKS_LANE_TRIB_1 2300.00 5.80 5.16 5.16 5.16 HITCHCOCKS_LANE_TRIB_1 2400.00 5.14 4.73 4.73 4.73 HITCHCOCKS_LANE_TRIB_1 2500.00 4.34 4.00 3.72 4.04 HITCHCOCKS_LANE_TRIB_1 2756.18 4.31 4.00 3.72 4.04
Water Level Branch Chainage 2005 2002 1988 1974 Town Creek 0 54.01 54.01 54.01 53.69 Town Creek 285 53.66 53.66 53.66 53.51 Town Creek 450 44.95 44.95 44.95 44.83 Town Creek 600 37.41 37.30 37.34 37.25 Town Creek 985 30.55 30.32 30.42 30.38 Town Creek 1050 29.93 29.84 29.88 29.88 Town Creek 1509 23.92 23.66 23.77 23.82 Town Creek 1835 20.12 19.88 19.98 20.08 Town Creek 1869 19.84 19.50 19.65 19.76 Town Creek 1923 19.12 18.95 19.00 19.05 Town Creek 1992 18.38 18.19 18.25 18.31 Town Creek 2045 17.95 17.62 17.76 17.84 Town Creek 2075 17.90 17.59 17.72 17.79 Town Creek 2107 17.89 17.59 17.71 17.79 Town Creek 2140 17.89 17.59 17.71 17.79 Town Creek 2164 16.46 15.93 16.07 16.22 Town Creek 2227 16.10 15.42 15.65 15.85 Town Creek 2295 15.43 14.73 15.06 15.26 Town Creek 2357 15.12 14.26 14.77 14.96 Town Creek 2384 14.40 13.84 14.11 14.21 Town Creek 2401 14.33 13.73 13.95 14.08 Town Creek 2431 14.23 13.63 13.84 14.00 Town Creek 2464 13.68 13.39 13.50 13.57 Town Creek 2498 13.50 13.30 13.39 13.44 Town Creek 2516 13.33 13.07 13.17 13.23 Town Creek 2534 13.25 13.05 13.14 13.18 Town Creek 2566 12.86 12.36 12.67 12.75
3001049 B-4 Broughton Creek Flood Study –Final Draft Report, April 2007
Water Level Branch Chainage 2005 2002 1988 1974 Town Creek 2586 12.85 12.35 12.66 12.74 Town Creek 2605 12.64 11.88 12.45 12.53 Town Creek 2629 12.63 11.83 12.44 12.52 Town Creek 2662 11.85 11.10 11.32 11.53 Town Creek 2744 11.04 10.75 10.83 10.91 Town Creek 2823 10.20 9.96 10.00 10.03 Town Creek 2897 9.57 9.06 9.28 9.41 Town Creek 2919 9.46 9.02 9.20 9.32 Town Creek 2948 9.39 8.99 9.18 9.27 Town Creek 2993 9.35 8.98 9.16 9.26 Town Creek 3022 8.09 7.49 7.62 7.81 Town Creek 3074 7.41 7.12 7.20 7.27 Town Creek 3150 6.80 6.19 6.24 6.32 Town Creek 3212 6.78 5.77 5.84 5.93 Town Creek 3259 6.77 5.64 5.71 5.79 Town Creek 3286 6.76 4.83 4.91 5.05 Town Creek 3382 6.76 4.38 4.41 4.58 Town Creek 3590 5.63 4.07 3.85 4.44 Town Creek 3845 5.03 4.06 3.72 4.42 Town Creek 4761 4.75 4.01 3.51 4.15
3001049 B-5 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix C: Hydraulic Modelling Results for Design Events
1. Water Levels 2. Velocities 3. Flows
3001049 C-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix C1 – Water Levels
3001049 C-2 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix C2 – Velocities
3001049 C-10 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix C3 – Flows
3001049 C-24 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix D: DRAINS Model Results for Albert Street Stormwater Drainage
Subcatchment Characteristics for Drainage near Albert St Name Total Paved Grass Paved Grass Paved Grass Paved Grass Paved Grass Area Area Area Time Time Length Length Slope Slope Rough Rough (ha) % % (min) (min) (m) (m) % % C ALB-03/01 0.271 50 50 1 5 100 100 2 2 0.02 0.05 C ALB-01/05 1.2087 40 60 1 5 300 180 1.5 1.5 0.02 0.05 C ALB-01/01 10.9268 10 90 1 5 425 700 1.4 1.4 0.02 0.05 C ALB-01/02 0.2832 40 60 1 5 50 150 1.5 1.5 0.02 0.05 C ALB-01/03 0.5502 50 50 1 5 100 100 1.5 1.5 0.02 0.05 C ALB-01/3A 0.634 55 45 1 5 120 120 1 1 0.02 0.05 C ALB-01/3B 0.1057 50 50 1 5 C ALB-01/04 1.25 50 50 1 5 200 200 2 2 0.02 0.05 C ALB-02/01 1.7482 50 50 1 5 250 200 2 2 0.02 0.05 C ALB-05/1 2.4853 50 50 1 5 550 550 1.2 1.2 0.02 0.05 C ALB-05/2 4.0375 50 50 1 5 650 650 1.3 1.3 0.02 0.05 C ALB-04/1 1.0748 5 95 1 5 100 200 1.5 2 0.02 0.05 C ALB-06/1 0.4078 10 90 1 5 100 200 1.5 1.8 0.02 0.05 C ALB-06/2 0.3588 60 40 1 5 100 150 1 0.5 0.02 0.05
Pit Details for Drainage near Albert St Max Ponding Pressure Surface Pond Blocking Volume Change Elev Depth Factor
Name Type Family Size (cu.m) Coeff. Ku (m) (m) ALB-03/01 OnGrade NSW RTA Pits SA5 (Type 9) 3 8.82 0 ALB-01/05 OnGrade NSW RTA Pits SA5 (Type 9) 0 8.39 0.2 ALB-01/06 Node 8.17 ALB-01/01 Sag RSG RSG 1200 x 1200 20 1 14.12 0.5 0.5 ALB-01/02 Sag RSG RSG 1200 x 1200 10 0 14.2 0.3 0.5 ALB-01/03 Sag RSG RSG 1200 x 1200 5 1 13.18 0.1 0 ALB-01/3A Sag RSG RSG 1200 x 1200 10 0.5 11.884 0.15 0.5 ALB-01/3B Sag RSG RSG 1200 x 1200 10 0.5 11.533 0.15 0.5 ALB-01/04 OnGrade NSW RTA Pits SA5 (Type 9) 0 8.641 0.2 ALB-02/01 OnGrade NSW RTA Pits SA5 (Type 9) 2 8.87 0.2 ALB-05/1 OnGrade NSW RTA Pits SA5 (Type 9) 1 11.924 0.2 ALB-05/2 OnGrade NSW RTA Pits SA5 (Type 9) 0.5 11.95 0.2 ALB-04/1 OnGrade NSW RTA Pits SA5 (Type 9) 5 13.4 0.2 ALB-04/2 Illudas 0.5 13.42 ALB-06/1 OnGrade NSW RTA Pits SA5 (Type 9) 5 12.272 0.2 ALB-06/2 OnGrade NSW RTA Pits SA5 (Type 9) 1.5 12.57 0.2
3001049 C-25 Broughton Creek Flood Study –Final Draft Report, April 2007
Pipe Details for Drainage near Albert Street
Length U/S IL D/S IL Slope Dia I.D. Name From To (m) (m) (m) (%s) Type (mm) (mm) Rough PALB-03/01 ALB-03/01 ALB-01/05 15.562 7.975 7.6 2.41 Concrete 450 450 0.3 PALB-01/05 ALB-01/05 ALB-01/06 20.348 7.35 7.14 1.03 Box Culvert 2.5W x 0.8H 0.3 PALB-01/01 ALB-01/01 ALB-01/02 14.232 13.229 13.2 0.2 Concrete 750 750 0.3 PALB-01/02 ALB-01/02 ALB-01/03 106.107 13.2 11.63 1.48 Concrete 450 450 0.3 PALB-01/03 ALB-01/03 ALB-01/3A 126.871 11.61 10.09 1.2 Box Culvert 2.05W x 0.6H 0.3 PALB-01/3A ALB-01/3A ALB-01/3B 17.519 10.09 9.887 1.16 Box Culvert 2.05W x 0.6H 0.3 PALB-01/3B ALB-01/3B ALB-01/04 182.036 9.887 7.6 1.26 Box Culvert 2.05W x 0.6H 0.3 PALB-01/04 ALB-01/04 ALB-01/05 15.844 7.55 7.35 1.26 Box Culvert 1.75W x 0.8H 0.3 PALB-02/01 ALB-02/01 ALB-01/04 14.069 8.07 7.8 1.92 Box Culvert 1.05W x 0.35H 0.3 PALB-05/1 ALB-05/1 ALB-05/2 12.156 11 10.94 0.49 Concrete 450 450 0.3 PALB-05/2 ALB-05/2 ALB-01/3A 20.265 10.895 10.733 0.8 Concrete 450 450 0.3 P ALB-04/1 ALB-04/1 ALB-04/2 11.55 12.662 12.5 1.4 Concrete 450 450 0.3 P ALB-04/2 ALB-04/2 ALB-01/03 10.13 12.5 11.65 8.39 Concrete 450 450 0.3 PALB-06/1 ALB-06/1 ALB-06/2 15.679 11.736 11.29 2.84 Concrete 450 450 0.3 PALB-06/2 ALB-06/2 ALB-01/3A 75.857 11.324 10.733 0.78 Concrete 450 450 0.3
3001049 C-26 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix E: Flood Level Profiles
1. Historical Events
3001049 E1-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix E: Flood Level Profiles
2. Design Events
3001049 E2-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix F: Calibration Data
Results
Statistics for the differences between modelled and recorded levels (excluding the two floodmarks not within the flood extent) are: • average difference =0.18m • median difference = 0.13m • maximum difference = 0.52m These statistics indicate that on average the model replicates observed flood behaviour to within ±0.1 to ±0.2m.
For the 2005 event, the average difference is 0.15m and median is 0.08m.
These calibrated results were considered to be sufficiently accurate for the purposes of modelling design rainfall events.
June/July 2005 Event
Compared to the three other historical events, the 2005 event provided a larger number of floodmarks, offered a better representation of rainfall and was the largest event recorded. For these reasons more weight was given to these floodmarks during the calibration process.
24 floodmarks were recorded for the 2005 event, with the majority located within the town, although there were also four readings recorded for Broughton Mill Creek. Seven levels were recorded upstream of Queen Street, five upstream of Victoria Street, three upstream of Prince Alfred Street, two each upstream of Princess Street and at the sports field on North Street, and one recorded on the Princes Highway opposite Apex Park. See Figure 4b for the locations of the floodmarks.
Water level profiles are given in Appendix E1. The simulated profiles match closely at the majority of locations and with the exception of four floodmarks, these levels are all within 0.17m of recorded levels.
Upstream of Queen Street six of the seven floodmarks are matched to within 0.12m either above or below, although one of the floodmarks is anomalously high. 50% blockage was modelled in the pipes beneath Queen Street, since the modelled levels were too low in the unblocked case.
For the two floodmarks upstream of Princess Street, the roughness coefficient was increased to 0.08 and the pipes also blocked by 50% to more closely match these recorded levels. The modelled levels were between 0.05m and 0.39m lower than observed.
For the recorded flood levels further downstream between Princess Street and Victoria Street three of the five readings were matched to within 0.08m, while the other two floodmarks were significantly higher. One of these may have been due to local drainage effects. A good calibration was achieved by blocking the pipes by 50% and adopting roughness coefficients of 0.06-0.07 in this region.
3001049 F-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Upstream of Prince Alfred Street modelled water levels are 0.14-0.17m higher than recorded levels. This is in contrast to the 1988 and 2002 events at this location. For the 2005 event these levels are influenced by tailwater effects due to large overflows from Broughton Mill Creek.
The water profile modelled through the sporting field over North Street and the Princes Highway at Apex Park is within 0.08m of observed levels for all three floodmarks. At the bowling club however, modelled levels are about 0.4m higher. This could indicate that flows in Broughton Mill Creek are slightly overestimated, given that modelled levels at the downstream end of Town Creek were also high due to overflow from Broughton Mill Creek. However, weir flow over the railway at Broughton Mill Creek to a height of 1m was matched closely.
Further up Broughton Mill Creek the floodmark on Woodhill Mountain Road was matched to within 0.16m. Given that the 400m wide floodplain is approximately 0.8m lower than the floodmark, it is a surprisingly high observed level.
2002 Event
A total of ten floodmarks are available for the 2002 event throughout the town of Berry. Five levels were recorded upstream of Queen St. three on the Princes Highway near the smash repairers opposite Apex Park and one each at Prince Alfred St, and the corner of Princess and Albany Streets.
Water level profiles are given in Appendix E1. The simulated profiles match closely at the downstream end of Town Creek, while they are slightly high upstream of Queen St.
For the floodmark at Princess and Albany Streets, similar to the 1988 observation, it is separated from the main channel by a small pipe underneath Princess St and is likely to be influenced by the capacity of this pipe, rather than water levels from the floodway itself. Therefore, this floodmark was not used further for this calibration
Upstream of Queen St, the simulated peak water levels were between 0.19m and 0.75m higher than the observed levels. This was assuming 50% blockage in the pipes underneath Queen St. For the 2005 event the water levels match observed levels quite closely, which would suggest that the pipes may have been more blocked in the 2005 event than for the 2002 event.
For the remaining locations further downstream, all modelled levels demonstrated a close fit within 0.18m of observed levels.
1988 Event
There were four water levels recorded for this event. Three of them are along Town Creek just upstream of the culvert crossing under Prince Alfred Street. The other floodmark is on the south east corner of Princess and Albany Streets.
Observed levels are shown on the water level profile in Appendix E1. The modelled water levels are all lower than the recorded floodmarks.
The floodmark at Princess and Albany Streets is separated from the main channel by a small pipe underneath Princess Street, and it is likely that this level was influenced by the capacity of this pipe,
3001049 F-2 Broughton Creek Flood Study –Final Draft Report, April 2007
rather than water levels from the floodway itself. Therefore, this floodmark was not used further for this calibration.
For the floodmarks at Prince Alfred Street, the downstream pipes were blocked by 50%, and the roughness coefficient was increased in an attempt to match observed levels. This still did not result in water levels matching observed levels with the modelled levels lower than observed by between 0.13 and 0.61m. For the 2002 event at this same location water levels are also low, but for the 2005 event they are high. Tailwater effects due to overflow from Broughton Mill Creek influenced the water levels in the 2005 event. This could have had an effect in the 1988 and 2002 events. Roughness values of up to 0.08 were adopted within the overbank area, although there could be some justification for increasing this further. Increased flows down Town Creek would not have had a large impact at this location, since the level is controlled by weir flow over the road.
1974 Event
For the 1974 event are two recorded flood levels, both of which are located on the Princes Highway near the smash repairers opposite Apex Park. The locations of the floodmarks are shown on Figure 4b. The water level profile along Albert Street Bypass showing the observed floodmarks is found in Appendix E1. As seen on the profile, the modelled water surface is lower than both floodmarks by up to 700mm. At this same location there is a close fit with recorded data for both the 2002 and 2005 events. This difference could have been caused by either some previous obstruction to flow at that location or the rainfall could have been locally underestimated for the Broughton Mill Creek or Bundewallah Creek catchments.
Summary
Findings from the calibration of the hydraulic model are summarised as follows: • The observed data from past floods improved with the more recent events. Localised and variable data typified the 1974 and 1988 events, while the 2002 and 2005 events contained a much more widely spread and comprehensive data set. • The distribution of rainfall may have had a significant impact on the calibration especially near the confluence of Broughton Mill Creek, Bundewallah Creek and Town Creek. Since the rainfall pattern seems to be spatially variable, even within the catchment itself, this will have an impact on the relative size of flows for each creek or tributary. However, since local gauge data was available for the 2005 event it is likely that the rainfall distribution is better represented for this event than any of the previous historical events. • With changes to blockage of structures in the model the calibration of past events could be more closely matched (eg. Upstream of Queen Street for the 2002 event). • Given the obstruction to flow due to vegetation and fences through the town of Berry, high roughness coefficients and pipe blockages were adopted to achieve reasonable calibration. Any changes to channel or overbank roughnesses could significantly impact the flood levels through the town.
Since the results from the calibration process represent observed flood behaviour closely, the hydraulic model is considered to be suitable for estimating design flood events.
3001049 F-3 Broughton Creek Flood Study –Final Draft Report, April 2007
Summary of Roughness Coefficients
Chainage Extent (m) Roughness Coefficients Branch Start End Channel Left FP Right FP 0 500 0.058 0.040 0.040 Andersons Lane Creek 674 700 0.058 0.040 0.040 900 1556 0.040 0.050 0.050 0 570 0.050 0.080 0.040 Andersons Lane Trib 912 1077 0.040 0.040 0.040 1190 1406 0.040 0.050 0.050 430 1320 0.060 0.040 0.060 1600 1600 0.050 0.050 0.050 Broughton Creek 1830 1830 0.050 0.080 0.050 1961 1961 0.046 0.080 0.050 2800 5515 0.030 0.060 0.060 20 550 0.058 0.050 0.050 Broughton Trib 754 855 0.060 0.050 0.050 530 1400 0.040 0.040 0.040 1200 1200 0.040 0.060 0.040 Hitchcocks Lane Ck 1225 1400 0.040 0.040 0.040 1630 1740 0.050 0.050 0.040 1810 1900 0.040 0.050 0.050 0 990 0.060 0.080 0.050 Hitchcocks Lane Trib 1400 1762 0.040 0.040 0.040 1890 2500 0.040 0.050 0.050 1100 1950 0.050 0.040 0.040 2100 2700 0.052 0.040 0.040 2900 3400 0.045 0.050 0.080 Broughton Mill Creek 3700 4100 0.050 0.065 0.050 4300 4400 0.050 0.050 0.050 4570 4860 0.058 0.050 0.050 4915 6260 0.040 0.050 0.050 -300 800 0.040 0.050 0.050 1100 1550 0.052 0.060 0.040 2000 2670 0.046 0.050 0.050 Bundewallah Creek 3000 3200 0.055 0.060 0.040 3300 3642 0.052 0.060 0.040 3900 5100 0.052 0.060 0.050 5400 5865 0.055 0.060 0.050
3001049 F-4 Broughton Creek Flood Study –Final Draft Report, April 2007
Chainage Extent (m) Roughness Coefficients Branch Start End Channel Left FP Right FP 285 1050 0.080 0.040 0.080 1509 1509 0.060 0.040 0.060 1835 2045 0.060 0.060 0.060 2075 2140 0.050 0.040 0.050 2164 2164 0.050 0.080 0.100 2227 2227 0.060 0.080 0.060 2295 2295 0.080 0.080 0.100 2357 2357 0.060 0.040 0.100 2384 2401 0.060 0.060 0.060 2431 2498 0.040 0.070 0.040 2516 2516 0.040 0.070 0.060 Town (Capel) Creek 2534 2662 0.040 0.070 0.040 2744 2744 0.060 0.070 0.060 2823 2823 0.100 0.070 0.020 2897 2897 0.060 0.070 0.100 2919 2919 0.060 0.070 0.060 2948 2948 0.080 0.070 0.080 2993 2993 0.100 0.070 0.060 3022 3259 0.080 0.070 0.080 3286 3286 0.060 0.050 0.060 3382 3382 0.060 0.060 0.040 3590 3590 0.060 0.040 0.040 3845 3845 0.050 0.040 0.050
3001049 F-5 Broughton Creek Flood Study –Final Draft Report, April 2007
Calibrated Historical Flood Levels Ruoghness Historical Cross- Observed Flood Modelled level Modelled level Modelled peak Coefficient Event River Branch section level (m AHD) (m AHD) difference (m) flow (m3/s) Channel/O'bank Comments 50% blocked. Floodmark is upstream of local pipe 1988 Town Creek 2662 12.1 11.291 -0.81 6.4 0.07/0.04 & not directly within the flood extent. 1988 Town Creek 3212 5.965 5.839 -0.13 6.9 0.07/0.08 50% blocked 50% blocked. High floodmarks could be due to 1988 Town Creek 3259 6.233 6.32 5.711 -0.52 7.1 0.07/0.08 tailwater effects from Broughton Mill Creek. Low rainfall modelled in Broughton Mill & 1974 Albert Bypass 950 7.745 8.106 7.405 -0.34 56 0.03 Bundewallah sub-catchments or changed conditions. 2002 Town Creek 2045 17.429 17.619 0.19 3.4 0.06 2002 Town Creek 2075 17.223 17.15 17.587 0.36 3.4 0.04/0.05 2002 Town Creek 2107 17.268 16.834 17.586 0.32 3.4 0.04/0.05 50% blocked. Floodmark is upstream of local pipe 2002 Town Creek 2662 12.05 11.088 -0.96 3.7 0.07/0.04 & not directly within the flood extent. 2002 Town Creek 3212 5.947 5.77 -0.18 5.2 0.07/0.08 50% blocked 2002 Albert Bypass 918 7.439 7.336 7.372 -0.07 29 0.04 2002 Albert Bypass 950 7.232 7.243 0.01 29 0.03 2005 Town Creek 1992 18.502 18.38 -0.12 9.7 0.06 50% blocked 2005 Town Creek 2045 17.957 17.982 17.949 -0.01 10.1 0.06 50% blocked 2005 Town Creek 2075 18.342 17.896 -0.45 10.3 0.04/0.05 50% blocked. Floodmark is unusually high. 2005 Town Creek 2107 17.822 17.893 0.07 10.4 0.04/0.05 50% blocked 2005 Town Creek 2140 17.812 17.452 17.891 0.08 10.5 0.04/0.05 50% blocked 2005 Town Creek 2295 15.484 15.824 15.434 -0.05 9.7 0.08 50% blocked 50% blocked. High recorded level possibly due to 2005 Town Creek 2897 9.65 10.326 9.569 -0.08 15.2 0.07/0.06 local drainage effects. 2005 Town Creek 2919 9.475 9.534 9.457 -0.02 15.3 0.07/0.06 50% blocked 2005 Town Creek 2948 9.877 9.385 -0.49 15.5 0.07/0.08 50% blocked. Floodmark is unusually high. 2005 Town Creek 3259 6.588 6.767 0.18 17.7 0.07/0.08 2005 Town Creek 3286 6.612 6.76 0.15 23 0.05/0.06 2005 Town Creek 3382 6.61 6.76 0.15 164 0.06 2005 Broughton Mill 3200 11.877 11.717 -0.16 420 0.06/0.08 Water level impacted by bypass flows from 2005 Broughton Mill 4400 7.52 7.572 7.885 0.37 1092 0.05/0.04 Bundewallah Creek. 2005 Broughton Mill 4915 7.007 7.08 0.07 1090 0.05/0.04 2005 Albert Bypass 981 7.852 7.881 0.03 306 0.04 2005 Bund_Alb_OF 110 9.192 9.257 9.174 -0.02 306 0.08
3001349 F-6 Broughton Creek Flood Study –Final Draft Report, April 2007
Appendix G: Sensitivity Analysis
Since channel roughness and blockage rates can vary from one event to another, sensitivity runs were carried out to gain an appreciation of the potential effect on flood levels. The sensitivity of the hydraulic model was tested for roughness coefficients, blockage of structures, losses through bridges and the tailwater level. The 1%AEP flood event was used to determine the impact of these factors on the modelled water levels. The methodology and results are described below.
For the sensitivity analysis of roughness coefficients, values were varied by 20%. Roughness coefficients had most impact in Broughton Mill Creek, Broughton Creek and Bundewallah Creek, where water velocities are higher and structures are less of a constraint.
The Broughton Creek hydraulic model was run with a range of blockage amounts throughout the structures within the catchment. Pipe diameters were varied on the basis of cross-sectional area, while box culvert widths were reduced in proportion to the blockage. For instance, a 50% blocked pipe of 750mm diameter would have the equivalent flow area of a 530mm diameter pipe, while a 2m (w) x 1m (h) box culvert would be modelled as a 1m (w) x 1m (h) box culvert. Runs were done for the cases where structures were unblocked, 25% blocked, 50% blocked, 75% blocked or fully blocked. The results are shown in Appendix G Table (Page G-4) and a flood profile was also produced to demonstrate the impact on 50% and 100% blockage on structures through Town Creek in the PMF and 1% AEP events. This is shown in Chart 6.3. Sensitivity to blockage is most evident near Hitchcocks Lane and Andersons Lane where large culverts control the flow underneath a high level road. Blockage also impacts Town Creek, although overtopping occurs more frequently due to the shallow crossings.
Th bridge losses adopted from the calibration used a loss factor of 70. This factor was modified in the sensitivity analysis, to a high value of 105 and a low value of 35. Results demonstrate that the changes in pipe blockage have a greater impact on flood levels than the bridge resistance.
A tailwater was adopted at the lower end using an RL3.9 which corresponded with the 1974event. In addition to this the 1%AEP tailwater level of 5.0mAHD was increased and decreased by 1m to determine the impact on water levels further upstream. Flood levels along Broughton Creek, and in locations downstream of the railway were most affected.
The sensitivity of hydrological parameters was also tested. The storage parameter Bx was varied from 0.6 to 1.5, while the impact of infiltration was also changed from 10mm to 35mm for initial losses and 1.0mm/hr to 2.5mm/hr for continuing losses. The storage factor had a much larger impact on peak discharges.
3001049 G-1 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Roughness Parameters – 1%AEP Design Event
Water level (m AHD) Water Level Difference (m) 20% Increase 20% Decrease 20% Increase 20% Decrease in Roughness in Roughness in Roughness in Roughness Branch Ch Base Case Coefficient Coefficient Base Case Coefficient Coefficient town creek 1869 19.94 19.98 19.89 0 0.04 -0.05 town creek 2107 18.07 18.07 18.06 0 0.00 -0.01 town creek 2295 15.65 15.69 15.56 0 0.04 -0.09 town creek 2498 13.60 13.60 13.60 0 0.00 0.00 town creek 2744 11.19 11.23 11.14 0 0.04 -0.05 town creek 3259 6.76 6.83 6.68 0 0.07 -0.08 town creek 3382 6.75 6.82 6.67 0 0.07 -0.08 Bundewallah Ck 1550 46.78 46.94 46.63 0 0.16 -0.15 Bundewallah Ck 3300 27.35 27.45 27.24 0 0.10 -0.11 Bundewallah Ck 5400 11.47 11.60 11.37 0 0.13 -0.10 Broughton Mill Ck 1700 16.35 16.56 16.10 0 0.21 -0.25 Broughton Mill Ck 2700 12.55 12.70 12.42 0 0.15 -0.13 Broughton Mill Ck 3924 9.56 9.76 9.42 0 0.20 -0.14 Broughton Mill Ck 4570 7.57 7.72 7.43 0 0.15 -0.14 Broughton Mill Ck 5342 5.48 5.64 5.35 0 0.16 -0.13 Broughton Ck 1830 6.10 6.23 5.99 0 0.13 -0.11 Broughton Ck 3615 5.32 5.46 5.21 0 0.14 -0.11 Broughton Ck 5515 5.01 5.01 5.01 0 0.00 0.00 Hitchcocks Lane Ck 914 9.06 9.07 9.02 0 0.01 -0.04 Hitchcocks Lane Ck 1626 5.21 5.21 5.21 0 0.00 0.00 Hitchcocks Lane Ck 1900 5.03 5.05 5.02 0 0.02 -0.01 Hitchcocks Lane Trib 990 21.83 21.94 21.73 0 0.11 -0.10 Hitchcocks Lane Trib 1890 10.29 10.29 10.29 0 0.00 0.00 Hitchcocks Lane Trib 2500 5.21 5.22 5.21 0 0.01 0.00 Andersons Lane Ck 1065 6.43 6.47 6.40 0 0.04 -0.03 Andersons Lane Ck 1540 5.03 5.05 5.02 0 0.02 -0.01 Andersons Lane Ck 2554 5.03 5.05 5.02 0 0.02 -0.01
3001049 G-2 Broughton Creek Flood Study –Final Draft Report, April 2007
Water level (m AHD) Water Level Difference (m) 20% Increase 20% Decrease 20% Increase 20% Decrease in Roughness in Roughness in Roughness in Roughness Branch CH Base Case Coefficient Coefficient Base Case Coefficient Coefficient Andersons Lane Trib 570 20.29 20.43 20.18 0 0.14 -0.11 Andersons Lane Trib 1221 9.97 10.06 9.78 0 0.09 -0.19 Andersons Lane Trib 1800 5.03 5.05 5.02 0 0.02 -0.01 Bundewallah Trib 1 870 54.73 54.84 54.62 0 0.11 -0.11 Bundewallah Trib 1 1600 39.05 39.13 38.98 0 0.08 -0.07 Bundewallah Trib 2 590 71.28 71.43 71.13 0 0.15 -0.15 Bundewallah Trib 2 925 58.86 58.98 58.75 0 0.12 -0.11
3001049 G-3 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Culvert Blockage – 1%AEP Design Event
U/S Water Level (m AHD) Water Level Difference (m) Base Base Case Case Road No 25% 50% 75% 100% No 25% 50% 75% 100% Branch Ch Number Size (m) Level Blockage Blocked Blocked Blocked Blocked Blockage Blocked Blocked Blocked Blocked town creek 1852 4 0.45 19.7 20.19 20.20 20.20 20.20 19.98 -0.01 0.00 0.00 0.00 -0.22
town creek 2152 3 0.75 17.4 18.02 18.08 18.06 18.04 17.27 -0.04 0.02 0.00 -0.02 -0.79
town creek 2370 3 1.275 14.75 15.00 15.09 15.05 15.02 14.90 -0.05 0.04 0.00 -0.03 -0.15
town creek 2512 3 1.05 13.1 13.58 13.61 13.60 13.59 13.46 -0.02 0.01 0.00 -0.01 -0.14
town creek 2548 2 1.05 12.9 13.33 13.36 13.35 13.34 13.19 -0.02 0.01 0.00 -0.01 -0.16
town creek 2595 3 1.05 12.3 12.99 13.04 13.03 13.01 12.67 -0.04 0.01 0.00 -0.02 -0.36
town creek 2646 1 1.8 12.3 12.75 12.85 12.81 12.78 12.37 -0.06 0.04 0.00 -0.03 -0.44
town creek 2860 1 1.2 9.75 10.42 10.47 10.45 10.44 10.23 -0.03 0.02 0.00 -0.01 -0.22
town creek 3008 1 1.75 9 9.45 9.51 9.49 9.47 8.94 -0.04 0.02 0.00 -0.02 -0.55
town creek 3272 1 3.75 x 1.035 5.45 6.76 6.76 6.76 6.76 6.06 0.00 0.00 0.00 0.00 -0.70
Hitchcocks_Lane_Trib 1910 3 1.35 10.15 10.29 10.43 10.29 10.35 8.84 0.00 0.14 0.00 0.06 -1.45
Hitchcocks_Lane_Ck 1212 3 1.35 6.8 6.69 7.00 6.69 6.87 5.12 0.00 0.31 0.00 0.18 -1.57
Andersons_Lane_Ck 1205 2 1.05 5.7 6.24 6.25 6.24 6.25 5.23 0.00 0.01 0.00 0.01 -1.01
Andersons_Lane_Ck 685 2 2.4 x 2.4 9.25 9.29 9.64 9.29 9.54 8.24 0.00 0.35 0.00 0.25 -1.05
Andersons_Lane_Ck 1463 4 1.4 x 1.3 5 5.41 5.42 5.41 5.41 5.04 0.00 0.01 0.00 0.00 -0.37
Hitchcocks_Lane_Ck 1775 3 2.7 5.1 5.21 5.27 5.21 5.23 5.03 0.00 0.06 0.00 0.02 -0.18
3001049 G-4 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Bridge Resistance – 1% AEP Design Event
U/S Water Level (m AHD) Water Level Difference (m)
Base Case Base Case Bridge Bridge Lower Upper Bridge Resist Bridge Resist Bridge Resist Resist Value Resist Value Bridge Resist Branch Ch ID Chord Chord Value 70 Value 105 Value 35 70 105 Value 35
town creek 2410 Edward_St_Br 14.3 14.5 14.47 14.46 15.05 0.00 -0.01 0.58
BundewallahCreek 5750 Bundewallah_Br 9.4 10 9.71 9.71 9.70 0.00 0.00 -0.01
BroughtonMillCk 4200 Princes_Broughton_Br 10.5 11 8.55 8.62 8.31 0.00 0.07 -0.24
Broughton_Creek 1900 Beach_Rd_Bridge 4.6 5.75 6.37 6.35 6.40 0.00 -0.02 0.03
BroughtonMillCk 4940 Rail_Mill_Bridge 4.85 6 7.02 7.02 7.02 0.00 0.00 0.00
BroughtonCreek 1700 Rail_Broughton_Bridge 5.05 6.3 6.37 6.35 6.40 0.00 -0.02 0.03
town creek 3460 Rail_Town_Bridge 6.2 6.9 6.75 6.73 6.79 0.00 -0.02 0.04
Andersons_Lane_Trib 1765 Rail_Ander_Trib_Br 4 5.55 5.30 5.28 5.29 0.00 -0.02 -0.01
BeachRail 70 Rail_Beach_Br 6.45 7.9 6.37 6.35 6.40 0.00 -0.02 0.03
3001049 G-5 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Tailwater level - 1%AEP Design Event
Water Level (m AHD) Water Level Difference (m) Tailwater Tailwater Base Tailwater Tailwater Base Tailwater Tailwater Branch Ch RL3.9 RL3.9 RL5.0 RL4.0 RL6.0 RL5.0 RL4.0 RL6.0 (1974) (1974) town creek 3845 5.49 5.04 5.06 6.23 0.00 -0.45 -0.43 0.74 town creek 3590 5.80 5.60 5.60 6.33 0.00 -0.20 -0.20 0.53 town creek 3286 6.75 6.72 6.72 6.96 0.00 -0.03 -0.03 0.21 town creek 3022 8.52 8.52 8.52 8.53 0.00 0.00 0.00 0.01 Bundewallah Ck 5680 9.71 9.71 9.71 9.71 0.00 0.00 0.00 0.00 Bundewallah Ck 5100 12.99 12.99 12.99 12.99 0.00 0.00 0.00 0.00 Bundewallah Ck 3500 25.36 25.36 25.36 25.36 0.00 0.00 0.00 0.00 Broughton Mill Ck 5342 5.48 5.01 5.03 6.23 0.00 -0.47 -0.45 0.75 Broughton Mill Ck 4570 7.57 7.55 7.55 7.64 0.00 -0.02 -0.02 0.07 Broughton Mill Ck 4100 8.55 8.55 8.55 8.55 0.00 0.00 0.00 0.00 Broughton Mill Ck 3400 11.02 11.02 11.02 11.02 0.00 0.00 0.00 0.00 Broughton Ck 5689 5.00 3.90 4.00 6.00 0.00 -1.10 -1.00 1.00 Broughton Ck 5073 5.03 3.99 4.08 6.02 0.00 -1.04 -0.95 0.99 Broughton Ck 4519 5.12 4.23 4.30 6.06 0.00 -0.89 -0.82 0.94 Broughton Ck 3050 5.40 4.82 4.85 6.20 0.00 -0.58 -0.55 0.80 Hitchcocks Lane Ck 1900 5.03 3.99 4.08 6.02 0.00 -1.04 -0.95 0.99 Hitchcocks Lane Ck 1630 5.21 4.73 4.75 6.03 0.00 -0.48 -0.46 0.82 Hitchcocks Lane Ck 1225 5.22 4.83 4.83 6.03 0.00 -0.39 -0.39 0.81 Hitchcocks Lane Trib 990 21.83 21.83 21.83 21.83 0.00 0.00 0.00 0.00 Andersons Lane Ck 2554 5.03 3.99 4.08 6.02 0.00 -1.04 -0.95 0.99 Andersons Lane Ck 1550 5.03 3.99 4.08 6.02 0.00 -1.04 -0.95 0.99 Andersons Lane Ck 1215 5.41 5.35 5.35 6.03 0.00 -0.06 -0.06 0.62 Andersons Lane Trib 1800 5.03 4.02 4.09 6.02 0.00 -1.01 -0.94 0.99 Andersons Lane Trib 1406 8.27 8.27 8.27 8.27 0.00 0.00 0.00 0.00 Andersons Lane Trib 1077 12.63 12.63 12.63 12.63 0.00 0.00 0.00 0.00
3001049 G-6 Broughton Creek Flood Study –Final Draft Report, April 2007
3001049 G-7 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Storage Parameter Bx -1% AEP Design Event Peak Local Flow (m3/s) Difference (%) Label Adopted High Low High Low
Bx=1.0 Bx=1.5 Bx=0.6 Bx=1.5 Bx=0.6 BC-AL1 49 43 53 -12 8 BC-AL2 24 20 27 -17 13 BC-AL3 24 16 33 -33 38 BC-ALTrib1 50 45 56 -10 12 BC-BC1 70 58 81 -17 16 BC-BC2 135 109 171 -19 27 BC-BC3 272 248 312 -9 15 BC-BC4 133 121 154 -9 16 BC-BC5 179 163 204 -9 14 BC-BC6 98 61 152 -38 55 BC-BC7 46 38 54 -17 17 BC-BC8 44 39 51 -11 16 BC-BC9 40 33 46 -18 15 BC-BCTrib1 78 62 99 -21 27 BC-BM1 31 25 39 -19 26 BC-BM2 227 207 259 -9 14 BC-BM3 234 211 270 -10 15 BC-BM4 112 92 128 -18 14 BC-BM5 14 11 18 -21 29 BC-BW1 167 152 191 -9 14 BC-BW2a 22 20 23 -9 5 BC-BW2b 40 36 44 -10 10 BC-BW2c 87 70 111 -20 28 BC-BW3 19 16 23 -16 21 BC-CN1 160 141 183 -12 14 BC-CP1 16 14 18 -13 13 BC-CP2 27 25 27 -7 0 BC-CP3 6 5 7 -17 17 BC-HL1a 15 13 15 -13 0 BC-HL1b 5 5 5 0 0 BC-HL2a 15 13 17 -13 13 BC-HL2b 18 15 20 -17 11 Total Flow 2020 1826 2188 -10 8 @ Outlet
3001049 G-8 Broughton Creek Flood Study –Final Draft Report, April 2007
Sensitivity Analysis of Losses -1% AEP Design Event Peak Local Flow (m3/s) Adopted Low High Label IL=25, IL=10, IL=35, CL=2.5 CL=1.0 CL=2.5 BC-AL1 49 49 49 BC-AL2 24 24 24 BC-AL3 24 26 23 BC-ALTrib1 50 51 50 BC-BC1 70 72 70 BC-BC2 135 138 135 BC-BC3 272 276 272 BC-BC4 133 135 133 BC-BC5 179 182 179 BC-BC6 98 107 94 BC-BC7 46 47 46 BC-BC8 44 45 44 BC-BC9 40 41 40 BC-BCTrib1 78 80 78 BC-BM1 31 31 31 BC-BM2 227 230 227 BC-BM3 234 238 234 BC-BM4 112 114 112 BC-BM5 14 14 14 BC-BW1 167 170 167 BC-BW2a 22 22 22 BC-BW2b 40 41 40 BC-BW2c 87 90 87 BC-BW3 19 20 19 BC-CN1 160 162 160 BC-CP1 16 16 16 BC-CP2 27 27 27 BC-CP3 6 6 6 BC-HL1a 15 15 15 BC-HL1b 5 5 5 BC-HL2a 15 15 15 BC-HL2b 18 18 18 Total Flow 2020 2076 2013 @ Outlet
3001049 G-9 Broughton Creek Flood Study –Final Draft Report, April 2007