EXECUTIVE SUMMARY. Background. Dam operations

Transcription

1

2 EXECUTIVE SUMMARY Background This report has been prepared to describe the 1 May 2015 to 3 May 2015 Flood Event at North Pine Dam, in accordance with the requirements in Section 383, 384, and 385 of the Water Supply (Safety and Reliability) Act Dam operations A summary of dam operations over the period of this report is provided in Table E.1. Phase Time Brief Description Table E.1 North Pine Dam operating summary Flood Operations Centre in Alert Status Flood Event declared Flood Operations Centre STANDUP Status (FOC mobilised) First Situation Report Radial Gate Releases Radial Gates closed Flood Operations Centre demobilised notification 14:53 29/4/ :30 1/5/ :52 1/5/ :08 1/5/ :00 1/5/ :00 3/5/ :15 5/5/2015 Assessments and activation of ALERT status for the Flood Operations Centre (FOC). Declared in accordance with Manual notification for STANDUP status sent at 12:52. First Situation Report ed Dam was operated initially to requirements of Manual section 5.2, procedure 1C (4) (where the lake level is predicted to exceed EL 38.8) but releases maintained to a peak of 308 m 3 /s All radial gates closed and fish recovery completed. Closure implemented to meet Manual Procedure 2B. All radial gate operations and stakeholder communications completed for this event Table E.2 provides some key statistics for the flood event. Page i

3 Table E.2 Key event statistics Statistic Total Rainfall (4 days ending 16:00 03/05/2015) Units mm 187 Maximum Hourly Catchment Average mm/hr 29.9 Rainfall Intensity 1 Estimated Catchment Average Rainfall AEP AEP Approximately 1 in 5 for durations between 3 and 12 hours Start Dam level North Pine Dam mahd Peak North Pine Dam Level mahd Temporary Full Supply Level mahd Peak Inflow in North Pine Dam 2 m 3 /s 886 Peak Outflow North Pine Dam m 3 /s 308 Inflow Volume North Pine Dam 2 ML 29,800 Outflow Volume North Pine Dam ML 20,400 Dam level at gate closure mahd Based on constrained calendar hours 2 Determined from post event analysis Figure E-1 illustrates the actual catchment average rainfall, together with dam inflows, outflows and dam levels over the period covered by this report. Page ii

4 Figure E-1 North Pine Dam actual rainfall, modelled inflows, outflows and lake level Communications To assist with technical decision making, the Duty Flood Operations Engineers communicated regularly with the Bureau of Meteorology (BoM) and other key stakeholders including the Moreton Bay Regional Council over the course of the flood event. Direct communication lines between the Dam Operations staff and the Flood Operations Centre were in place at all times during the flood event. Situation Reports were issued at minimum frequency of twice daily throughout the flood event to communicate dam operations information to Local Disaster Management Groups and other stakeholder agencies in accordance with the Protocol. Event magnitude The May 2015 flood event was caused by rainfall generated primarily from an East Coast Low Pressure Weather System. The most severe weather conditions were observed in near coastal areas, between Brisbane and the Sunshine Coast. Catchment averaged rainfall intensities for this event were equivalent to the 1 in 5 Annual Exceedance Probability (AEP) estimates for the North Pine Dam catchment for rainfall durations between 3 hours and 12 hours. Page iii

5 Flood mitigation Significant flood mitigation was provided as a result of from North Pine Dam flood operations over the course of the Flood Event. The peak outflow from the dam during the event was 35% of the estimated peak inflow. The dam operations were highly effective in reducing flooding downstream of the dam. Systems review and compliance Hydrological monitoring and forecasting systems performed satisfactorily in the lead up to, and during, the flood event. Dam operations complied with the requirement of the Manual. Recommendations It is recommended that ongoing discussions with the BoM continue in relation as to the selection of the appropriate Australian Digital Forecast Database (ADFD) rainfall forecast products for use during flood event planning. For this weather event, post event analysis showed that a catchment average rainfall forecast based on the 25% ADFD exceedance estimate was a better estimate of actual catchment average rainfall. Page iv

6 CONTENTS 1. Introduction Report writing methodology Flood event key times and statistics Lead In Rainfall and forecasts preceding event Actual rainfall in the lead up to late April Forecast rainfall in week leading up to May 2015 Flood Event Catchment and dam status at flood event start Temporary FSLs Summary timeline of event lead up period Event Readiness Preparedness Statement of Preparedness Approved engineers Communications equipment Confirmed dam release infrastructure status Alert and mobilisation Staffing at the Flood Operations Centre Staffing at dams Flood Event Data Monitoring network Seqwater s ALERT network Seqwater s ALERT network performance Rainfall data checking during the Flood Event Forecast rainfall Rainfall Average catchment rainfall Catchment temporal patterns Gauging station hydrographs Flood Modelling Modelling systems Model runs Post event analysis Dam Operations Strategy timeline and selection Communications Overview Summary types of communication Statement of basis of reporting Communications Protocol Situation Reports Content and preparation Page v

7 7.2.2 Distribution of Situation Reports Situation Reports issued Other general communications Dam outflows information to the public Dam operators Flood Event Magnitude Rainfall Intensity-Frequency-Duration Catchment rainfall intensity Comparison with historical flood volumes Flood Attenuation Event Review Rainfall and catchment conditions preceding event API model Temporary FSL Event readiness Staffing Monitoring network Forecast rainfall Advice from the BoM Catchment runoff Model performance and ratings Forecasting systems Compliance with the Manual Record keeping Flood attenuation Review of the Manual Communications Dam Infrastructure Performance Recommendations References Page vi

8 FIGURES Figure E-1 North Pine Dam actual rainfall, modelled inflows, outflows and lake level... iii Figure 4-1 Rainfall gauge network Figure 4-2 River level and dam water level gauge network Figure 4-3 Actual catchment average rainfall (mm) for 24 hour period to 09:00 1/5/2015 (Source: FEWS).. 18 Figure 4-4 Actual catchment average rainfall (mm) for 24 hours period to 09:00 2/5/2015 (Source: FEWS) 19 Figure 4-5 Actual catchment average rainfall (mm) for 24 hours period to 09:00 3/5/2015 (Source: FEWS) 20 Figure 4-6 North Pine Dam catchment average rainfall temporal pattern Figure 4-7 Hydrographs at stations in North Pine Dam catchment Figure 4-8 North Pine Dam water level comparing ALERT data and gauge board readings Figure Progression of estimates of inflow volume Figure 6-1 North Pine Dam actual rainfall, inflow, water level and outflows Figure 8-1 North Pine River to North Pine Dam rainfall intensity analysis Figure 10-1 Model verification Page vii

9 TABLES Table E.1 North Pine Dam operating summary... i Table E.2 Key event statistics... ii Table 1.1 Key event times...1 Table 1.2 Key event statistics...2 Table 2.1 Actual rainfall statistics for lead up to conditions prior to May 2015 Flood Event...3 Table 2.2 Lead up period forecast rainfall for North Pine Dam catchment Default Forecast...5 Table 2.3 Lead up period forecast rainfall for North Pine Dam catchment High rain scenario...5 Table 2.4 Lead up period summary timeline...9 Table 4.1 Sensors identified as Out of Action at start of Flood Event Table 4.2 Potentially suspect gauge sensors identified after the Flood Event Table 4.3 Rainfall stations excluded from forecasting for the Flood Event Table 4.4 Flood Event period forecast rainfall for North Pine Dam catchment Table 7.1 Distribution of Situation Reports Table 7.2 Summary of Situation Reports Table 8.1 Comparison of historic flood event peak flow rates and volumes for North Pine Dam Table 10.1 Comparison of forecast rainfall and actual rainfall for North Pine Dam catchment Page viii

10 DOCUMENT HISTORY Document history Revision Date Issued Reviewed By Approved By Revision Type Rev A 29/5/2015 Senior Flood Engineers Internal draft Rev B 5/6/2015 Management review team Internal draft Rev 0 12/6/2015 CEO Seqwater Distribution of copies Revision Copy no Quantity Issued to Rev A Not controlled document Electronic Report review team Rev B Not controlled document Electronic Management review Rev 0 Not controlled document Electronic The Chief Executive, DEWS File name: _FER_NPD_RevC.docx Page ix

11 GLOSSARY In this report, the following terms are defined as below: Act means the Water Supply (Safety and Reliability) Act 2008; Acceptable Flood Capacity means the overall flood capacity required of a dam in accordance with DNRW (the then Queensland Department of Natural Resources and Water) Guidelines on Acceptable Flood Capacity, February 2007; ADFD means the Australian Digital Forecast Database which contains official weather forecast elements produced by the Bureau of Meteorology, such as temperature, rainfall and weather types, presented in a gridded format and covering the next 7 days; AEP means Annual Exceedance Probability, the probability of a specified event being reached or exceeded in any one year. This may be expressed as a ratio (e.g. 1 in Y) or a percentage; Agency includes a person, a local government and a department of State government within the meaning of the Acts Interpretation Act 1954; AHD means Australian Height Datum; ALERT means Automated Local Evaluation in Real Time System, a system of monitoring and displaying rainfall and water level data. It is a combination of field stations, communications networks and data collection software; AMTD means the Adopted Middle Thread Distance, which is the distance along the centre line of the mainstream from a junction, usually in kilometres; AR&R means Australian Rainfall and Run-off (Book 6), The Institution of Engineers Australia (Engineers Australia) national guidelines for the estimation of design flood characteristics; BCC means the Brisbane City Council; BoM means the Commonwealth Government agency, the Bureau of Meteorology; Chairperson means the Chairperson of Seqwater; CEO means the Chief Executive Officer of Seqwater; Chief Executive means the Director-General of the Department of Energy and Water Supply or nominated delegate; Controlled Document means a document subject to managerial control over its contents, distribution and storage. It may have legal and contractual implications; Dam Crest Flood means the flood event which, when routed through the storage with the storage initially at Full Supply Level, results in the still water level in the storage reaching the lowest point in the dam embankment, excluding wind and wave effects; Dam Operator means the duty officer on site at the dam; Dam Supervisor means the senior on-site officer at Somerset or Wivenhoe Dam as the case may be; DEWS means the Queensland Government department, the Department of Energy and Water Supply; DNRM means the Queensland Government department, the Department of Natural Resources and Mines; Page x

12 DTMR means the Queensland Department of Transport and Main Roads; Duty Flood Operations Engineer means a Flood Operations Engineer (or Senior Flood Operations Engineer) rostered on duty and with the responsibilities detailed in the Manual; Duty Senior Flood Operations Engineer means a Senior Flood Operations Engineer who is on duty and with the responsibilities set out in the Manual; EL means elevation in metres Australian Height Datum; Enviromon is the Bureau of Meteorology data collection software used to collect and display real time rainfall and water level data; ERRTS means Event Reporting Radio Telemetry System; Flood Event has the meaning set out in Section 4.2 of The Manual; FEWS is a software package developed by Deltares that incorporates a hydrological forecast and warning system; FFS means the Flood Forecasting System, being a suit of computer programs that utilise real time data to assist in decision making during Flood Events described in more detail in Appendix H of the Manual; Flood Officer means a person who: Provides assistance to the Duty Flood Operations Engineer during flood events as directed by the Duty Flood Operations Engineer; and Undertakes routine flood preparation duties between flood events. Flood Operations Centre or FOC means the office location used by Flood Operations Engineers during a flood event to manage the event; Flood Operations Engineer means a person means a person with the required qualifications, experience and training (set out in section 2.8 of the Manual) and who has been approved by Seqwater to fulfil the role of Duty Flood Operations Engineer under the Manual; Flood Operations Engineers means the collective group of persons who individually have designation as either a Flood Operations Engineer or a Senior Flood Operations Engineer; Flood Operations Manager means the person with designated responsibility for the overall management of the Flood Operations Centre leading up to or during a flood event; FSL or Full Supply Level means the level of the water surface when the reservoir is at maximum operating level, excluding periods of flood discharge; Gauge when referred to in (m) means river level referenced to or a local datum, and when referred to in (m 3 /s) means the estimated flow rate in cubic metres per second for the recorded level; ICC means Ipswich City Council; IFD means Intensity Frequency Duration and refers to the statistical analysis of rainfall intensities; Manual or Manual of Operational Procedures for Flood Mitigation at North Pine Dam means the current version (Revision 9, November 2014) of the Manual; OOA means out of action in relation to the operation of a rainfall or river height gauge that provides catchment data; Page xi

13 Protocol means Communications Protocol for Releases from Seqwater s Gated Dams (Wivenhoe Dam, Somerset Dam, and North Pine Dam) January 2015 Version 1.2; QPF means Quantitative Precipitation Forecast provided by the Bureau of Meteorology and is an estimate of the predicted rainfall in millimetres, usually in the next 24 hours. (This product is now superseded by ADFD forecasts and is mentioned in this report only for completeness of information available); Senior Flood Operations Engineer means a person with the required qualifications, experience and training (set out in section 2.8 of the Manual) and who has been approved by Seqwater to fulfil the role of Duty Senior Flood Operations Engineer under the Manual; Seqwater means the Queensland Bulk Water Supply Authority, trading as Seqwater; SRC means Somerset Bay Regional Council; SVW means Severe Weather Warning issued by the Bureau of Meteorology; URBS means Unified River Basin Simulator. Note: Levels in this document represented as metres (m) are metres Australian Height Datum or (m). Page xii

14 1. INTRODUCTION This report has been prepared to describe the 1 May 2015 to 3 May 2015 Flood Event at North Pine Dam, in accordance with the requirements in Section 383, 384, and 385 of the Water Supply (Safety and Reliability) Act Details of North Pine Dam and its operational procedures may be found in the Manual. 1.1 Report writing methodology This report was prepared considering the guidelines documented in the Seqwater procedure, Event Report Writing Methodology. This process was developed to address recommendation 16.2 in the Queensland Flood Commission of Inquiry Final Report, March The Report Writing Methodology provides guidance on: the legislative and Manual requirements for report content the target audience, which includes technical and non-technical stakeholders and reviewers the important principles of a flood event report recommended generic report structure and content the work flow methodology to prepare the report. 1.2 Flood event key times and statistics Key times and dates of the Flood Event are listed in Table 1.1, and key statistics in Table 1.2. Table 1.1 Key event times Milestone Temporary Full Supply Level (FSL) declared for North Pine Dam Event Modelling Start Date for use in the Flood Forecasting System (FFS) Time 8 December :00 29 April 2015 Flood Event declared 12:30 1 May 2015 Flood Operations Centre STANDUP status and mobilised 12:52 1 May 2015 Situation Report #1 ed 14:08 1 May 2015 Event releases commenced, North Pine Dam 18:00 1 May 2015 Event releases concluded and Flood Event declared ended at North Pine Dam 16:00 3 May 2015 Flood Operations Centre demobilised 16:00 5 May 2015 Page 1

15 Table 1.2 Key event statistics Statistic Total Rainfall (4 days ending 16:00 03/05/2015) Units mm 187 Maximum Hourly Catchment Average mm/hr 29.9 Rainfall Intensity 1 Estimated Catchment Average Rainfall AEP AEP Approximately 1 in 5 for durations between 3 and 12 hours Start Dam level North Pine Dam mahd Peak North Pine Dam Level mahd Temporary Full Supply Level mahd Peak Inflow in North Pine Dam 2 m 3 /s 886 Peak Outflow North Pine Dam m 3 /s 308 Inflow Volume North Pine Dam 2 ML 29,800 Outflow Volume North Pine Dam ML 20,400 Dam level at gate closure mahd Based on constrained calendar hours 2 Determined from post event analysis Page 2

16 2. LEAD IN This section discusses the actual rainfall, forecast rainfall, catchment and water storage conditions that preceded the declared Flood Event period covered by this report. Other intelligence about the potential for a Flood Event and a summary of actions taken are also described. 2.1 Rainfall and forecasts preceding event Actual rainfall in the lead up to late April 2015 Summary statistics of rainfall in the week, months, and water year leading up to late April 2015 are presented in Table 2.1. Table 2.1 Actual rainfall statistics for lead up to conditions prior to May 2015 Flood Event Catchment Average Rainfall (mm) Somerset Dam Catchment Wivenhoe Dam Catchment Lockyer Creek Catchment Bremer / Warrill Catchment Pine River Catchment 7 days to 24 April to 24 April Water Year to 24 April (from 1 October 2014) Note: Rainfall values sourced from Seqwater internal Weekly Rainfall Summary Report prepared on Friday 24 April There was little rain across Seqwater catchments in the lead in to and early part of the wet season before mid- January In mid-february 2015 rainfall from Ex Tropical Cyclone Marcia (Ex TC Marcia) produced runoff in the North Pine Dam catchment with observed rainfall depths being largest near the coast. The Ex TC Marcia rain event in mid February 2015 generated minor flood inflows into North Pine Dam that increased the volume stored within the dam from approximately 70% 1 of the water supply storage capacity to approximately 90% of the water supply storage capacity. This inflow did not require gated flood operations at North Pine Dam. After the Ex TC Marcia rain event, further small rainfall events occurred in late March and early April 2015 which produced some runoff in the North Pine Dam catchment. This resulted in a stored volume of approximately 95% of the water supply storage capacity in mid April but did not require flood operations Forecast rainfall in week leading up to May 2015 Flood Event Source of forecasts Several forecast rainfall products are available from the BoM. From late 2014, the Flood Forecasting System (FFS) used by the Seqwater Flood Operations Centre regularly imports the Bureau of Meteorology Australian Digital Forecast Database (ADFD) forecast rainfall grids. This forecast product is currently adopted by Seqwater based on BoM s advice that the ADFD contains official weather forecast elements produced by the BoM, such as rainfall, and the forecasts in the ADFD are quality controlled by the Bureau s Operational Meteorologists. Further information about the ADFD product is available at: 1 Percentage based on the water supply storage capacity with enacted temporary full supply level of 38.5 m AHD Page 3

17 The ADFD forecast product was promoted by BoM to Seqwater in late 2014 to replace the previously customised (Quantitative Precipitation Forecast, QPF) prepared twice daily by BoM meteorologists specifically for Seqwater. The QPF product is to be gradually phased out by BoM, but was still being received leading up to and during the May 2015 Flood Event. The ADFD forecast product suite supports the BoM MetEye webpage. The data spatial resolution is on a 6km x 6km grid. The specific forecast rainfall data accessed by Seqwater has a temporal resolution of mm/3hours for 0 to 48 hours, and mm/24hours for 0 to 192 hours. A significant difference in the ADFD forecast rainfall product compared to previous forecast rainfall products, is that the ADFD does not produce a single value estimate of rainfall depth for a defined point over a defined forecast period. The ADFD forecast products provide a range of estimates from 50% chance (equal likelihood above or below this amount) which is considered as a best equal chance estimate, together with 25% chance of exceedance and 10% chance of exceedance which provide estimates of potential higher rainfall. The higher rainfall scenarios (25%, and 10% chance of exceedance) are indicative of potential for higher point rainfall totals. When forecast rainfall values are accumulated from individual grid cells to represent rainfall over a catchment area the nominated chance of exceedance is not strictly maintained. This means that the chance of exceedance of catchment rainfall may not be identical to the chance of exceedance of rainfall at any of the individual points defined in the ADFD grid prepared by the BoM. This is similarly the case when forecast rainfall depths are accumulated from time intervals defined in the original ADFD grid to produce a seamless estimate of forecast across multiple days. To make practical use of the ADFD forecast rainfall information in the FFS, the 2 day (3 hourly) and 8 day (daily) forecast rainfall grids are merged to produce three forecast rainfall scenarios spanning 8 days: Default forecast scenario, based on the 50% ADFD forecast rainfall grids, High rainfall scenario, based on the 25% ADFD forecast rainfall grids, Very high rainfall scenario, based on the 10% ADFD forecast rainfall grids. Each of the forecast rainfall scenarios describes an aggregate of the official BoM forecast rainfall elements in space and time in a way that works with the hydrologic models in the FFS. These merged forecasts then do not represent a definable probability of catchment wide rainfall or a probability of event total rainfall. There is currently no accepted method available to adjust the probability defined by the ADFD grid chance of exceedance to a probability representing catchment rainfall chance of exceedance. For practical use, the catchment rainfall forecasts aggregated from the ADFD grids is considered as a scenario rather than a specific probabilistic forecast. The default forecast scenario is considered to represent the best available forecast. The high rainfall scenario and very high rainfall scenario provide an indication of potential for higher rainfall with lower probability of occurring. The FFS is currently configured to give the Duty Flood Operation Engineers the option to select any one of these rainfall scenarios to be applied to the hydrologic models of the FFS. Verbal advice from weather forecasters at BoM may lead to Duty Flood Operations Engineers selecting a higher rainfall scenario as a preferred forecast during a Flood Event. For the flood operations for North Pine Dam there is a single catchment model representing the area upstream of the dam delineated in the FFS to guide forecasting and dam operation decisions. The lead up period forecast rainfall for North Pine Dam is relevant for pre-event assessments of the possibility of inflows exceeding the temporary Full Supply Level and triggering the need for flood operations and declaration of a flood event. Page 4

18 Best estimate dam catchment forecast The default rainfall forecast scenario aggregated from the 50% chance of exceedance ADFD grids for the North Pine Dam catchment over the five days leading up to the May 2015 Flood Event is presented in Table 2.2. This forecast was indicating 40 to 50 mm catchment average event total for the dam catchment on Wednesday 29 April before the Flood Event. High rainfall scenario forecast The high rainfall forecast scenario aggregated from the 25% chance of exceedance grids for the North Pine Dam forecasting catchments over the five days leading up to the May 2015 Flood Event is presented in Table 2.3. This high rainfall forecast was indicating in the order of 140 mm catchment average event total rainfall on Wednesday 29 April before the Flood Event. The very high rainfall scenario aggregated from the 10% chance of exceedance grids was indicating potentially over 250 mm on Wednesday 29 April before the Flood Event, however this estimate cannot be defined as a 10% chance of exceedance of catchment average rainfall or event total rainfall. Comparison of the forecast rainfall to actual observed rainfall is discussed in Section 10.7 of this report. Previous (superseded) QPF forecast product The superseded 24 hour QPF forecast product was still being received in the lead up to and during the flood event. The 24 hour QPF forecast issued at 16:00 on 30 April 2015 stated NORTH PINE DAM CATCHMENT: Forecast of estimated catchment average rainfall for the 24 hour period to 4pm Friday: 60 to 120mm. Forecast Issue Date Forecast rain (mm) for 24 hours to 09:00 27/4/15 Table 2.2 Lead up period forecast rainfall for North Pine Dam catchment Default Forecast Forecast rain (mm) for 24 hours to 09:00 28/4/15 Forecast rain (mm) for 24 hours to 09:00 29/4/15 Forecast rain (mm) for 24 hours to 09:00 30/4/15 Forecast rain (mm) for 24 hours to 09:00 1/5/15 Forecast rain (mm) for 24 hours to 09:00 2/5/15 26/04/ /04/ /04/ /04/ /04/ /05/ Forecast Issue Date Forecast rain (mm) for 24 hours to 09:00 27/5/15 Table 2.3 Lead up period forecast rainfall for North Pine Dam catchment High rain scenario Forecast rain (mm) for 24 hours to 09:00 28/4/15 Forecast rain (mm) for 24 hours to 09:00 29/4/15 Forecast rain (mm) for 24 hours to 09:00 30/4/15 Forecast rain (mm) for 24 hours to 09:00 1/5/15 Forecast rain (mm) for 24 hours to 09:00 2/5/15 26/04/ /04/ /04/ /04/ /04/ /05/ Page 5

19 Severe Weather Warning The first official Severe Weather Warning from the BoM was received at the Seqwater FOC on at 11:27 on 30 April The warning stated 24 hour totals of 50 to 150 mm are likely over inland parts, increasing to 200 to 400 mm nearer to the coast with some isolated heavier falls possible. These estimates are not definitively a catchment wide forecast nor are they a definitive maximum point total forecast. The Severe Weather Warning was a generalised warning for South East Queensland (an area generally about 150km x 150 km) and not for specific river catchments. Page 6

20 2.2 Catchment and dam status at flood event start Up to the onset of rainfall around 29 April 2015, automated methods to estimate catchment initial loss (the amount of rain that will absorb in the ground before runoff occurs) indicated the initial loss could be as high as 120 mm for the North Pine Dam catchment (dam status report 30 April 2015). The automated assessment using an Antecedent Precipitation Index is known to have limited accuracy and is only suitable to provide an initial guide. The initial loss estimate from the automated method was deemed to be too high (unrealistic) and a revised estimate of initial loss based on professional judgment from recent rain event observations was used to adopt a conservative estimate of catchment initial loss of less than 40mm. As at 07:15 on 29 April, the North Pine Dam lake level was EL mahd (from gauge board reading), with the corresponding water storage volume at 93.8% of the full supply volume 2. Assessments of the catchment status, and dam status, undertaken by the Duty Senior Flood Engineer between 28 to 30 April using a prudent conservative estimate of catchment initial loss concluded that: If the rainfall scenario for event total rainfall in the order of up to 60mm eventuated it would be unlikely that gated dam flood operations would be necessary at North Pine; and If a higher rainfall scenario eventuated and catchment average rainfall exceeds 150mm, then gated dam flood operations at North Pine Dam would be a possible outcome, subject to actual rainfall totals, intensities, and actual catchment losses. The results of these assessments were compiled within Wet Weather Talking Points that were distributed to a wide range of personnel within Seqwater and representatives or general addresses at external agencies including: the Minister responsible for DEWS; the Director General, Deputy Director General, emergency address, Dam Safety Regulator, and others at DEWS; State Disaster Coordination Centre; DNRM; Queensland Treasury; Department of the Premier and Cabinet; DTMR; and communications staff from the SEQ Water Service Providers Partnership, including Queensland Urban Utilities, UnityWater, and the water businesses of the Gold Coast, Logan and Redland councils, as well as communication contacts from the following local councils: Brisbane, Ipswich, Somerset, Lockyer Valley, Scenic Rim, Gold Coast, Logan, Redlands, Moreton Bay, Noosa and Gympie. 2 Percentage based on a temporary Full Supply Level of EL 38.5 Page 7

21 2.3 Temporary FSLs The North Pine Dam Optimisation Study (DEWS, 2014) recommended a reduction in the full supply volume of North Pine Dam to achieve improved flood capacity and meet dam safety objectives for the dam. This recommendation was adopted on 8 December 2014 with the implementation of a temporary full supply level of 38.5 mahd for the dam as detailed in the Queensland Government gazette notice under the Water Supply (Safety and Reliability) Act 2008, entitled the Temporary Full Supply Level (North Pine Dam) Declaration Notice (No 01) A copy of the gazette notice is included in Appendix A. 2.4 Summary timeline of event lead up period In addition to the official forecast rainfall and status of dams, there are several other sources of information and actions taken that set the complete context for the situation development in the five days leading up to the flood event. A summary of the information, actions and guidance for the pre-event lead up is presented in Table 2.4. Page 8

22 Table 2.4 Lead up period summary timeline Date and Time Information / action / guidance 27 April Rainfall forecasts indicate in around 25 mm across the dam catchments 15:15 27 April Severe Weather Intelligence Briefing Number 1 issued by BoM. 15:15 28 April Severe Weather Intelligence Briefing Number 2 issued by BoM. 11:30 29 April Duty SFE participates in meeting with Seqwater Incident Team. 14:00 29 April Seqwater Wet Weather Talking Points prepared by Duty SFE to advise move to ALERT Status. This form of communication is used to provide easy reference information for the Minister for Energy and Water Supply and other internal and external stakeholders in responding to enquiries about the weather forecast and potential impacts on Seqwater operations. 14:53 29 April notification of ALERT Status for the Flood Operations Centre sent to all recipients of the Situation Report. This means more intensified monitoring of the situation. 16:30 29 April Severe Weather Intelligence Briefing Number 3 issued by BoM. Remainder of 29 April Negligible rainfall on the catchments to midnight. 11:28 30 April First Severe Weather Warning issued by BoM. 12:00 30 April Severe Weather Intelligence Briefing Number 4 issued by BoM. 13:30 30 April Teleconference with BoM, Brisbane City Council, Ipswich City Council. 24 hours to 00:00 1 May 07:00 to 13:00 1 May & ongoing 37 mm catchment average actual rain recorded in North Pine Dam catchment. Broad range of checks undertaken with gated dam and un-gated dam operators, contact with Moreton Bay Regional Council, and communications checks. 09:00 1 May Start of heavier rain in North Pine Dam catchments. 09:15 1 May Teleconference with BoM, Brisbane City Council, Ipswich City Council. 10:00 1 May Severe Weather Intelligence Briefing Number 5 issued by BoM. 11:00 1 May Teleconference with Moreton Bay Regional Council to discuss possible dam releases 12:30 1 May Duty Senior Flood Engineer declares Flood Event. Situation Report #1 prepared by Senior Flood Engineer to describe anticipation of potential gate releases later that night. Draft Situation Report distributed internally for checking and review. 12:52 1 May Senior Flood Engineer activates STANDUP status for the FOC. FOC formally mobilised through sent to all recipients of the Situation Reports advising of STANDUP Status and advising that first Situation Report will be issued shortly. 14:08 1 May Situation Report #1 ed. 15:00 1 May Contact from Moreton Bay Regional Council regarding the pending closure of Youngs Crossing. Crossing confirmed closed at 16:15. 13:00 to 17:00 1 May Ongoing forecasting, and initial Release Plan assessments, and discussions with local authorities. Refer Chapter 6 of this report. 17:57 1 May Situation Report # 2 issued by FOC with definitive time for commencement of gate releases. Page 9

23 3. EVENT READINESS This section describes Seqwater s preparation for the event, including staffing and the status of the gates and communication equipment at the start of the event. 3.1 Preparedness Statement of Preparedness In accordance with the Water Supply Safety and Reliability Act (2008), Seqwater must provide a detailed report to the Chief Executive by 1 September each year identifying the state of preparedness of the Dams, the Flood Operations Centre and the Flood Forecasting System to manage flood events in accordance with the Manual. This statement was provided to the Director-General of DEWS by the Chief Executive Officer of Seqwater on 29 August This statement included, in accordance with requirements of the Act: Details of Responsible Persons, including Flood Operations Engineers, Flood Officers, and Dam Operators The training and assessment of personnel responsible for dam operations The state of the FFS The state of communications equipment between the Flood Operations Centre and the dams Approved engineers The statement discussed in the above section contains the list of authorised Senior Flood Operations Engineers and Flood Operations Engineers. As at 1 September 2014 there were: Five trained and qualified Senior Flood Operations Engineers Four trained and qualified Flood Operations Engineers Eleven trained and qualified Flood Officers Fifteen trained and qualified Operators for North Pine Dam. Personnel responsible for flood operations undertook training before to the Flood Event as required by the Chief Executive. Further follow-up training of operators was undertaken in January 2015 for training in the revised procedures under the latest revision of the Manual. For the 1 May 2015 Flood Event, one of the Senior Flood Operations Engineers was on annual leave. This did not affect the adequacy of qualified personnel resources for the Flood Event Communications equipment The following methods of communication between the dam sites and FOC were confirmed as working before the flood event: Landline telephone Mobile telephones Facsimile Radio network Satellite phones Confirmed dam release infrastructure status All radial gates at North Pine Dam were operational before the commencement of the Flood Event. Page 10

24 3.2 Alert and mobilisation The FOC was mobilised and activated to Stand Up status with notification of this status sent at 12:52 1 May There was significant activity in monitoring and assessments prior to mobilisation as described in Section 2.2 and Section 2.4. This included activation of ALERT status on 29 April Staffing at the Flood Operations Centre Full-time staffing commenced at the FOC from about 07:00 1 May (prior to Mobilisation later that day), with at least one Senior Flood Operations Engineer, one Flood Operations Engineer and one Flood Officer on duty at all times. Staffing of the FOC continued on this basis until event de-mobilisation at 16:15 5 May Staffing at dams Staffing at North Pine Dam was in accordance with operational requirements over the duration of the Flood Event with a Dam Supervisor and backup Dam Operator on site from 16:00 1 May 2015 to 16:00 3 May 2015 (before first gate opening to final gate closure). Outside of these periods, a Dam Operator was stationed at the dam as part of routine dam operations from 07:00 to 15:00 on week days and for a two-hour period on weekends and public holidays. Page 11

25 4. FLOOD EVENT DATA This section describes the monitoring network and summarises the data collected during the Flood Event including forecast and recorded rainfall, recorded heights and estimated streamflow. 4.1 Monitoring network Seqwater maintains a real-time network to monitor rainfall and water levels in the dams catchments and to provide sufficient information that is both accurate and timely to allow informed decision making. The Seqwater network is part of a larger monitoring network in South East Queensland consisting of stations operated by other agencies such as Councils and BoM. Data from stations in the network is shared freely between co-operating agencies. Field stations, rainfall gauges and water level gauges, the radio network and data collection software is referred to as an ALERT system. ALERT has become a standard for flood warning systems in Australia and the United States of America, and is widely used by BoM and other flood warning agencies throughout the world. The ALERT system is the primary source of data for real time modelling of flows in Seqwater catchments using an advanced FFS. The FFS is described in the Manual and statement of preparedness referred to in Section A map of the rainfall gauge network showing Seqwater and other agency gauges is presented in Figure 4.1. The river level and dam water level gauge network is presented in Figure 4.2. Page 12

26 Page 13 Figure 4-1 Rainfall gauge network

27 Page 14 Figure 4-2 River level and dam water level gauge network

28 4.2 Seqwater s ALERT network The ALERT network consists of 364 rain sensors and 248 water level sensors at field stations throughout South East Queensland. Of this network, Seqwater operates 116 rainfall sensors and 81 water level sensors. Manual gauge board readings are taken at most dams including Wivenhoe, Somerset and North Pine dams to confirm the ALERT data, and form the basis for gate operations. 4.3 Seqwater s ALERT network performance At the start of the Flood Event, one Seqwater ALERT rain gauge was Out of Action (OOA) (Table 4.1). Since this site is a backup rain gauge and there is another rain gauge at Somerset Dam, this OOA rain gauge station did not impede forecasting and operations. All Seqwater ALERT river level and dam level gauges were operational at the start of the Flood Event. Table 4.1 Sensors identified as Out of Action at start of Flood Event Rain ALERT ID River ALERT ID Site Issue 6590 SOMERSET DAM AL-B Stopped reporting signals After the Flood Event two rain gauges and two river level gauges were identified as potentially suspect, as shown in the list in Table 4.2. Although these gauges were identified as suspect after the Flood Event, there was no evidence of erroneous readings during the Flood Event. In particular the Gregors Creek river level gauge in the Upper Brisbane River catchment had a primary and backup sensor that recorded near identical water levels during the event, so there was no reason to consider this data as suspect during the Flood Event. Rain ALERT ID River ALERT ID Site Issue Table 4.2 Potentially suspect gauge sensors identified after the Flood Event 6518 GREGORS CREEK AL - P Diurnal cycle drifting 6515 GREGORS CREEK AL - B Erroneous water levels 6736 KUSS ROAD AL Suspected as over-reporting 6705 WOODFORD AL P Suspected as under-reporting 4.4 Rainfall data checking during the Flood Event As data is imported and processed in the FOC, checking is undertaken to identify potentially suspect data at rain gauges as this will affect the recorded rainfall on the sub-catchments that are used for catchment flow forecasting in the FFS. All reporting rain gauges are considered, including gauges not owned by Seqwater. Data is usually identifiable as suspect in the FFS by comparison to nearby gauges, from a rainfall grid interpolation process between gauges, or clearly erroneous zero values. Suspect rain gauges are then marked OOA in the FFS so that these gauges are not included in the process of estimating rainfall on catchments. The rainfall stations that were marked OOA in the lead up to and/or during the Flood Event are summarised in Table 4.3. Page 15

29 Rain ALERT ID Table 4.3 Rainfall stations excluded from forecasting for the Flood Event Station Name Period Start Period End Time Identified 6255 Boonah AL 08:15 25/03/ :15 01/05/ :42 01/04/ Carrara AL 08:15 25/03/ :15 01/05/ :43 01/04/ Palen Creek AL 08:15 25/03/ :15 01/05/ :44 01/04/ Sheepstation Creek AL 08:15 25/03/ :15 01/05/ :45 01/04/ Laceys Ck AL 06:30 30/03/ :30 06/05/ :17 06/04/ Somerset Dam HW AL-B 22:00 18/04/ :00 04/05/ :52 27/04/ Brisbane City AL 09:45 22/04/ :00 30/04/ :00 30/04/ Perseverance Alert 16:30 23/04/ :30 30/05/ :40 30/04/ Cooby Creek Dam AL 16:30 23/04/ :30 30/05/ :44 30/04/ Ripley AL 08:15 25/03/ :15 30/05/ :33 30/04/ Opossum AL 20:15 23/04/ :15 30/05/ :33 30/04/ Churchill AL 11:45 19/03/ :15 30/05/ :37 30/04/ Dunwich AL 11:45 19/03/ :45 30/05/ :39 30/04/ Grandchester AL 11:45 19/03/ :45 30/05/ :41 30/04/ Goodna AL 11:45 19/03/ :45 31/05/ :42 30/04/ Bundamba AL (Hanlon 11:45 19/03/ :45 31/05/ :56 30/04/ Highvale AL 09:30 24/04/ :30 31/05/ :01 01/05/ Marburg AL 09:30 24/04/ :30 31/05/ :05 01/05/ One Mile Br AL 11:45 19/03/ :45 01/06/ :23 01/05/ Deception Bay (Creek Rd) AL 09:30 01/05/ :30 31/05/ :58 01/05/ Mapleton AL 12:00 02/05/ :00 05/05/ :33 02/05/ Old Gympie Rd AL 12:00 02/05/ :00 05/05/ :41 02/05/ Bellbird Park AL 20:15 23/04/ :00 01/05/ :54 03/05/ Somerset Dam HW AL-P 07:00 27/04/ :00 03/06/ :54 04/05/ Bega Rd Quarry AL 09:00 01/05/ :45 06/06/ :43 07/05/ Forecast rainfall A description of forecast rainfall products is presented in Section 2.1. The relevant rainfall forecasts for the North Pine Dam catchment in the lead-up to the Flood Event are presented in Section 2.1. The Flood Event was declared at 12:30 1 May Information on rainfall forecasts during the Flood Event is presented below. A summary of relevant forecast rainfall for the North Pine Dam catchment for the Flood Event period is presented in Table 4.4. The forecasts in this table indicate that little further rainfall was expected to occur after the 24 hours from 9:00 on 1 May Page 16

30 Table 4.4 Flood Event period forecast rainfall for North Pine Dam catchment Period of Forecast Default Forecast rain (mm) High Rain Scenario rain (mm) 24 hours total from 09:00 on 1/5/ day total from 09:00 on 1/5/ A discussion of the performance of the predicted rainfall during this period is presented in Section Rainfall The following rainfall maps show the rainfall recorded in the North Pine Dam catchment during the period covered by this report. This information was sourced from the Enviromon system and analysed in FEWS Average catchment rainfall In FEWS, the average rainfall for each sub-catchment is determined by fitting a gridded surface to the recorded station rainfalls and using a polygon outline of each sub-catchment to determine the average rainfall for the sub-catchment from the grid. The rainfall for the event is shown in Figure 4-3 to Figure 4-5 below. The full extent of South East Queensland is included in these figures to illustrate the spatial variability of rainfall through the event. Page 17

31 Figure 4-3 Actual catchment average rainfall (mm) for 24 hour period to 09:00 1/5/2015 (Source: FEWS) Page 18

32 Figure 4-4 Actual catchment average rainfall (mm) for 24 hours period to 09:00 2/5/2015 (Source: FEWS) Page 19

33 Figure 4-5 Actual catchment average rainfall (mm) for 24 hours period to 09:00 3/5/2015 (Source: FEWS) From these three figures it can be seen that: Catchment averages were greatest in the Caboolture River catchment for the 24 hours to 09:00 on 1 May Rainfall depths to this time were greatest in coastal areas between Brisbane and the Sunshine Coast For the 24 hours to 09:00 on 2 May 2015 the North Pine Dam catchment rainfall of 131 mm is less than the Caboolture River catchment to the north (211 mm) and the South Pine River catchment to the south (187 mm) The rain event cleared from most South East Queensland catchments prior to the 24hours to 09:00 on 3 May 2015, resulting in catchment average rainfall less than 5mm over this 24 hour period. Page 20

34 4.6.2 Catchment temporal patterns The catchment average hourly rainfall for the North Pine Dam catchment, shown in Figure 4-6 is determined using the FFS. The peak hourly rainfall intensity of 29.9 mm/hr occurred between 16:00 and 17:00 1 May This figure further illustrates the short duration of the rainfall in this event. Figure 4-6 North Pine Dam catchment average rainfall temporal pattern 4.7 Gauging station hydrographs The following figure presents the hydrographs of the water levels recorded at Seqwater-owned ALERT gauging stations upstream of North Pine Dam through this event. Water level data available at other ALERT stations in the basin operated by other agencies is not reported here. The four digit ALERT ID is shown as the station identifier. The recorded lake level at North Pine Dam is shown in Figure 4-8 and tabulated in Appendix B. This figure shows the telemetry captured ALERT data and the visually observed gauge board data were in good agreement for the duration of the event. Page 21

35 Figure 4-7 Hydrographs at stations in North Pine Dam catchment Figure 4-8 North Pine Dam water level comparing ALERT data and gauge board readings Page 22

36 5. FLOOD MODELLING This section describes the flood modelling systems used to estimate flows in the catchment during the period covered by this report. 5.1 Modelling systems Two hydrologic modelling systems were available in the FOC to generate estimates of inflows to the dam and downstream catchment flows: Primary System: Data from Enviromon is regularly imported into FEWS every 15 minutes. Within FEWS, URBS hydrological models can be run after checking of rainfall and removal of suspect rain gauge data. The software allows the user to modify model parameters, add forecast rainfall and run the hydrologic models. Output from the URBS models is stored and viewable in FEWS and then exported for input into a Gate Operations Model. Backup System: The Enviromon data collection system is linked directly to the URBS Control Centre which contains URBS hydrological models of all Seqwater catchments. The URBS Control Centre software allows the user to modify model parameters, add forecast rainfall and run the hydrologic models. Output from the URBS models is then input into a Gate Operations Module. For this Flood Event, the primary system using the FEWS FFS was functional at all times and it was not necessary to run the Backup System. 5.2 Model runs To account for rainfall that occurred before the time that the Flood Event was declared, simulation start times for all model runs used to undertake catchment flow forecasting and dam operations was set to 09:00 29 April A summary of the model runs undertaken during this Flood Event is presented in Appendix C. This list presents the model runs that were exported from FEWS to the Gate Operations Model. A total of 21 model runs were undertaken for the North Pine Dam catchment during this event. The process of model simulations to forecast the catchment flows (inflows into the dams, and downstream catchment flows) was continually repeated and updated during the course of the flood event as further gauge data became available. Ideally, for modelling estimates of the dam inflows the primary focus of calibration is to match the observed levels at the dams. This is because storage volume and spillway rating data for the dams are more reliable than calibration to upstream gauges which have some uncertainty in ratings and also due to the gauges not covering all of the catchment that produces inflows into the dams. However early in the Flood Event it is necessary to focus attention on the upstream river gauges as these provide a clear indication of the commencement of runoff before inflows reach the dams. When a substantial amount of the runoff volume arrives at the dam and there is sufficient response in the dam level data, it then becomes possible to place greater emphasis on calibration using the dam level data. For this flood event, there were significant rainfall losses (rain absorbed into the ground) and runoff rates were low. When there are high rainfall losses, the modelled inflow estimates are very sensitive to the rainfall loss value applied in the modelling. The significance of this for shorter duration rainfall events is that it may not be possible to get an accurate estimate of inflows even if the rain has finished, given there is still significant uncertainty for the rainfall losses. A good estimate of rainfall losses is only possible after catchment runoff arrives as inflows at the dam. The progression of estimated Flood Event dam inflow volume is shown in Figure 5-1. In this figure the estimates of inflow volumes were initially high (compared with the final post event estimate) from the start of the event until approximately 22:00 on 1 May At this time the lake rise observed in North Pine Dam was lower than that predicted in the FFS model estimates, leading to the adoption of an increased loss estimate and a corresponding reduction in event inflow volume. Page 23

37 Figure Progression of estimates of inflow volume A summary of the model scenarios archived during this event is attached as Appendix C. Note that the final operational estimate of the inflow volume of 31,300 ML compares favourably with the volume of 29,800 ML derived in the post flood analysis. 5.3 Post event analysis After the Flood Event, a reverse routed analysis was performed for North Pine Dam, using the known gate settings and observed lake levels, to derive a post-event estimate of the dam inflow hydrograph. This exercise provided a basis of comparison for inflow volume estimates derived from the FFS as the event progressed. The results of this analysis are discussed in Section 6 and 7 and presented in detail in Appendix B. Page 24

38 6. DAM OPERATIONS This section details the operations conducted at North Pine Dam for the Flood Event using procedures in the Manual. 6.1 Strategy timeline and selection A flood event was declared for North Pine Dam at 12:30 on 1 May 2015 as per section 4.2 of the Manual of Operational Procedures for North Pine Dam (Seqwater, 2014). At the time of flood event declaration the North Pine Dam lake level was approximately mahd and rising slowly in response to inflows at a rate of approximately 20mm per hour. This rate of lake level rise increased over the period from event declaration to when gated releases commenced at 18:00. During this period the catchment and lake conditions were closely monitored by the Flood Operations Centre. An initial release strategy was developed adhering to the operating procedures detailed in Section 5.2 of the Manual. In response to rising lake levels from catchment inflows, releases from North Pine Dam commenced at 18:00 on 1 May 2015 when the gauged lake level was mahd and rising. Lake levels were predicted, based on the observed rainfall on ground, to peak at approximately 39.2 mahd at 01:00 on 2 May Given these conditions, a gate opening strategy was initially adopted based on strategy 1C (4) of the Manual but with consideration for minimising peak outflow from the dam. By 19:00 1 May 2015 the release rate was 183 m 3 /s. By 20:00 1 May 2015 gated releases from North Pine Dam had increased to 300 m 3 /s with all gates open to three increments (a total of 15 open increments across five gates). The gates were maintained at this opening setting from 20:00 on 1 May 2015 to 01:00 at 2 May At this time the peak lake level was predicted to exceed 38.8mAHD (the differentiation level between two strategy procedures of the Manual). However, given the uncertainty in this estimate a release strategy was adopted that sought to minimise the peak outflow from the dam (as per procedure 1. 4(c) of the Manual). Hence, the 15 opened gate increments at the dam were maintained resulting in a peak outflow rate of 308 m 3 /s, consistent with an estimated peak lake level of less than 38.8 mahd. At 01:00 on 2 May 2015 an updated predicted peak lake level was estimated as mahd (which had occurred three hours earlier). This estimate indicated that the rainfall loss rates through infiltration in the catchment were higher than had been estimated earlier in the event. In response, releases from North Pine Dam were reduced to approximately 190 m 3 /s by maintaining all gates open two increments (a total of 10 open increments across 5 gates). The gates were maintained at this setting from 02:00 on 2 May 2015 to 11:00 at 2 May Observed lake levels peaked at North Pine Dam at 22:00 on 1 May 2015 at mahd and rainfall was observed to clear from the catchment late during 1 May 2015 into the early morning of 2 May In response to the observed clearing rainfall and the dam storage volume falling, the planning for the radial gate closure focussed on procedure 2 of section 5.2 of the Manual ( Check if rainfall event is nearing completion ). In returning the dam to near FSL (as outlined in procedure 2B), consideration was given to: 1). Minimising community disruption and limiting impacts on community safety; 2). Ceasing flood releases during daylight hours to allow for a safe and adequate fish recovery operation; and 3). Allowing for ongoing baseflow contributions to the dam when seeking to conclude dam releases near FSL. Progressive closure of gates commenced from the 10 open increments at 10:00 on 2 May 2015 to one open increment at 15:00 on 2 May During this period it was observed that ongoing baseflow and flows from the upper catchment would require continued gated releases beyond sunset on that day to meet the Page 25

39 requirements of point 3 above while also meeting the fish recovery requirements of point 2. As a result, releases were maintained at a rate of approximately 15 m 3 /s over the period of 15:00 on 2 May 2015 to 22:00 on 2 May 2015 and subsequently increased to approximately 45 m 3 /s until 05:00 on 3 May During this period the lake level reduced slightly from mahd to mahd, indicating that baseflows into the lake were very closely matching outflows. To meet the procedure point (3) as listed above and minimise the community disruption attributed to the closure of Youngs Crossing the releases were increased to a rate of 140 m 3 /s during the morning of 3 May 2015 so that gated releases could be concluded before the next day. This release rate was maintained until 12:00 on 3 May 2015, after which gates were progressively closed and releases concluded by 16:00 on the same day. At this time the lake level was mahd, to allow for ongoing baseflows into the dam and concluding the event near FSL. The gate closure sequence from 140 m 3 /s to gates closed was implemented over a five hour period to meet the following Flood Mitigation Objective: Minimise environmental impacts on river bank stability and riparian flora and fauna To assist in understanding the operational strategy, Figure 6-1 presents the catchment average rainfall, and dam inflows, levels and releases during the period covered by this report on a consistent scale. Reference to Figure 4-7, which shows flow hydrographs upstream of North Pine Dam, and Appendix B, which contains a detailed tabulation of gate settings, lake levels and release rates, may also assist in understanding the operational strategy. Table 1.2 provides a summary of the peak inflow, outflow and dam level for the Flood Event, sourced from Figure 6-1. A summary of the model scenarios that were archived during this event is attached as Appendix C. This Appendix contains a summary for each model scenario of: the forecast rainfall used (if any) the peak water level at North Pine Dam the peak inflow and outflow into North Pine Dam the total outflow volume estimated for North Pine Dam Please note that in some of these runs the Flood Engineer may only have completed planned actions in spreadsheet for the next few hours, and thus the forecast peak water levels, flows and the volumes listed should be used with caution. Page 26

40 Figure 6-1 North Pine Dam actual rainfall, inflow, water level and outflows Page 27