Agenda of Floodplain Management Advisory Committee Meeting

CONFLICT OF INTERESTS

What is a “Conflict of Interests” - A conflict of interests can be of two types:

Pecuniary - an interest that a person has in a matter because of a reasonable likelihood or expectation of appreciable financial gain or loss to the person or another person with whom the person is associated.

Non-pecuniary – a private or personal interest that a Council official has that does not amount to a pecuniary interest as defined in the Code of Conduct for Councillors (eg. A friendship, membership of an association, society or trade union or involvement or interest in an activity and may include an interest of a financial nature).

Remoteness – a person does not have a pecuniary interest in a matter if the interest is so remote or insignificant that it could not reasonably be regarded as likely to influence any decision the person might make in relation to a matter or if the interest is of a kind specified in the Code of Conduct for Councillors.

Who has a Pecuniary Interest? - a person has a pecuniary interest in a matter if the pecuniary interest is the interest of the person, or another person with whom the person is associated (see below).

Relatives, Partners - a person is taken to have a pecuniary interest in a matter if:

· The person’s spouse or de facto partner or a relative of the person has a pecuniary interest in the matter, or

· The person, or a nominee, partners or employer of the person, is a member of a company or other body that has a pecuniary interest in the matter.

N.B. “Relative”, in relation to a person means any of the following:

(a) the parent, grandparent, brother, sister, uncle, aunt, nephew, niece, lineal descends or adopted child of the person or of the person’s spouse;

(b) the spouse or de facto partners of the person or of a person referred to in paragraph (a)

No Interest in the Matter - however, a person is not taken to have a pecuniary interest in a matter:

· If the person is unaware of the relevant pecuniary interest of the spouse, de facto partner, relative or company or other body, or

· Just because the person is a member of, or is employed by, the Council.

· Just because the person is a member of, or a delegate of the Council to, a company or other body that has a pecuniary interest in the matter provided that the person has no beneficial interest in any shares of the company or body.

Disclosure and participation in meetings

· A Councillor or a member of a Council Committee who has a pecuniary interest in any matter with which the Council is concerned and who is present at a meeting of the Council or Committee at which the matter is being considered must disclose the nature of the interest to the meeting as soon as practicable.

· The Councillor or member must not be present at, or in sight of, the meeting of the Council or Committee:

(a) at any time during which the matter is being considered or discussed by the Council or Committee, or

(b) at any time during which the Council or Committee is voting on any question in relation to the matter.

No Knowledge - a person does not breach this Clause if the person did not know and could not reasonably be expected to have known that the matter under consideration at the meeting was a matter in which he or she had a pecuniary interest.

Non-pecuniary Interests - Must be disclosed in meetings.

There are a broad range of options available for managing conflicts & the option chosen will depend on an assessment of the circumstances of the matter, the nature of the interest and the significance of the issue being dealt with. Non-pecuniary conflicts of interests must be dealt with in at least one of the following ways:

· It may be appropriate that no action be taken where the potential for conflict is minimal. However, Councillors should consider providing an explanation of why they consider a conflict does not exist.

· Limit involvement if practical (eg. Participate in discussion but not in decision making or vice-versa). Care needs to be taken when exercising this option.

· Remove the source of the conflict (eg. Relinquishing or divesting the personal interest that creates the conflict)

· Have no involvement by absenting yourself from and not taking part in any debate or voting on the issue as of the provisions in the Code of Conduct (particularly if you have a significant non-pecuniary interest)

Committee members are reminded that they should declare and manage all conflicts of interest in respect of any matter on this Agenda, in accordance with the Code of Conduct.

RECORDING OF VOTING ON PLANNING MATTERS

Clause 375A of the Local Government Act 1993 – Recording of voting on planning matters

(1) In this section, planning decision means a decision made in the exercise of a function of a council under the Environmental Planning and Assessment Act 1979:

(a) including a decision relating to a development application, an environmental planning instrument, a development control plan or a development contribution plan under that Act, but

(b) not including the making of an order under that Act.

(2) The general manager is required to keep a register containing, for each planning decision made at a meeting of the council or a council committee, the names of the councillors who supported the decision and the names of any councillors who opposed (or are taken to have opposed) the decision.

(3) For the purpose of maintaining the register, a division is required to be called whenever a motion for a planning decision is put at a meeting of the council or a council committee.

(4) Each decision recorded in the register is to be described in the register or identified in a manner that enables the description to be obtained from another publicly available document and is to include the information required by the regulations.

(5) This section extends to a meeting that is closed to the public.

OATH AND AFFIRMATION FOR COUNCILLORS

Councillors are reminded of the oath of office or affirmation of office made at or before their first meeting of the council in accordance with Clause 233A of the Local Government Act 1993. This includes undertaking the duties of the office of councillor in the best interests of the people of Byron Shire and the Byron Shire Council and faithfully and impartially carrying out the functions, powers, authorities and discretions vested under the Act or any other Act to the best of one’s ability and judgment.

BYRON SHIRE COUNCIL

Staff Reports - Sustainable Environment and Economy 4.1

Staff Reports - Sustainable Environment and Economy

Report No. 4.1 Amendments to Byron Shire DCP 2014 Chapter C2: Areas Affected by Flood - Draft for Exhibition

Directorate: Sustainable Environment and Economy

Report Author: Alex Caras, Land Use Plannning Coordinator

Kristie Hughes, Natural Disaster Policy Planner

File No: I2024/661

Summary:

A report presenting draft amendments to the Byron Shire DCP 2014, Chapter ‘C2: Areas Affected by Flood’ was considered at the 18 April 2024 Council Meeting. The proposed changes to DCP 2014 Chapter ‘C2’ reflect current policies and legislation that should be considered when addressing ‘flood risk’ in planning decisions (both rezoning and development application assessment).

The report recommended that Council to place the document on public exhibition for a minimum period of 28 days, with engagement activities to include presentation of updates to the Floodplain Management Advisory Committee by the reviewing consultant, BMT.

A copy of the 18^th April council report and Draft DCP chapter C2 (marked up version) are contained in Attachments 1 & 2, respectively, as supporting reference material for BMT’s presentation to the Committee.

RECOMMENDATION:

That the Floodplain Management Advisory Committee:-

1. Note the information presented by BMT and as contained in the report attachments; and

2. Is invited to make a submission to the proposed amendments to Byron Shire DCP 2014, Chapter ‘C2: Areas Affected by Flood’, for Council’s consideration prior to final adoption.

Attachments:

1 Attachment 1 - copy of 18 April Report 13.13 - PLANNING - Amendments to Byron Shire DCP 2014 Chapter C2 - Areas Affected by Flood, E2024/50245 , page 18 ⇩

2 Attachment 2 - Amended Draft DCP chapter C2 - marked up version showing new additions in yellow highlight, deleted items in red strikethrough_7-12-23, E2023/129624 , page 20⇩

Report

Council engaged BMT WBM to review Chapter ‘C2 Areas Affected by Flood’ in Byron Development Control Plan 2014 (DCP) in order to:

· Ensure consistency of terminology

· Place greater emphasis on the safe occupation and efficient evacuation of people in the event of a flood

· Replace outdated flood study references

· Implement relevant actions (where possible) identified in North Byron Floodplain Risk Management Study.

Strategic Considerations

Community Strategic Plan and Operational Plan

CSP Objective	CSP Strategy	DP Action	Code	OP Activity
4: Ethical Growth	4.1: Manage responsible development through effective place and space planning	4.1.4: LEP & DCP - Review and update the Local Environmental Plan and Development Control Plans	4.1.4.2	Review and update Local Environmental Plan and Development Control Plans to reflect strategic land use priorities and/or legislative reforms

Recent Resolutions

21-285

24-182

Legal/Statutory/Policy Considerations

The review of the DCP planning controls will be used to inform Council’s future strategic land use planning and development control framework. The proposed amendments will be exhibited as per the statutory requirements.

Financial Considerations

This is a Council initiated DCP amendment that has been funded by Natural Disaster Funding grant. All other processing costs will be borne by Council.

Consultation and Engagement

In addition to BMT’s presentation to the Floodplain Management Advisory Committee, Council also resolved (Res 24-182) to arrange a community meeting with residents in the north of the shire to inform and discuss the draft DCP Chapter C2 proposal flood affected areas in the north.

BYRON SHIRE COUNCIL

Staff Reports - Infrastructure Services 4.2

Staff Reports - Infrastructure Services

Report No. 4.2 Flood Levee Raising Investigation - South Golden Beach

Directorate: Infrastructure Services

Report Author: Isabella Avelino Gianelli, Project Engineer

File No: I2024/161

Summary:

The report documents the constraints and feasibility assessment to improve the levee flood protection by raising the levee by 300mm or 600mm. It also presents high level costings to repair and remediate the levee in accordance with a recent levee audit (Engeny, 2022).

The findings of the Wilde Engineering Consulting (WEC)report indicate that the existing levee’s flood immunity exceeds the 1% Annual Exceedance Probability (AEP) event, which is high compared to other Northern Rivers levees. Raising the levee would only marginally impact the Average Annual Damage (AAD) caused by floods, as it would only improve protection against rare floods. Moreover, significant constraints suggest that the cost and complexity of raising the levee would significantly outweigh the benefits, resulting in a low cost-benefit ratio. Based on this, the report recommends no raising is undertaken.

The WEC report also provides cost estimates and probable funding source (Council or NSW Public Works Flood Levee Repair and Maintenance Program) to undertake the 20 action items identified in the 2022 levee audit and identifies 2 additional actions. The estimated annual cost to undertake all recommended works for Council-funded maintenance actions is $85,300. An additional one-off cost of $1,150 is needed for clearing a blocked flood gate. The NSW Public Works Flood Levee Repair and Maintenance Program can fund recommended levee actions totalling a one-off cost of $59,250.

RECOMMENDATION:

That Council, based on the reasons discussed in this report, it is recommended that raising the levee by either 300mm or 600mm is not undertaken.

Attachments:

1 P23008.RO1_SGB Levee Maintenance and Raising Investigation_001_FINAL, E2024/47780 , page 20 ⇩

Report

Background and Introduction

Following the 2022 floods, the NSW and Australian Governments announced funding for urban flood levees under the Disaster Recovery Funding Arrangements (DRFA). This program, involving 13 Local Government Areas including Byron Shire, aims to assess, repair, and improve levees. Council is considering using this funding to:

a) Repair and improve the SGB flood levee, which protects urban areas along the Capricornia Canal, in accordance with a recent levee audit (Engeny, 2022).

b) Raise the levee by either 300mm or 600mm to improve flood immunity of the area.

Current Flood Immunity

NSW Public Works undertook a levee survey in February 2023 which found that the eastern and western levee crests both fluctuate around the design level of RL 3.2 m AHD. The lowest crest levels, which determine flood immunity, are RL 3.01mAHD on the western levee and RL 3.08 on the eastern levee. The current 1% AEP flood level in the Capricornia Canal is 2.9mAHD, lower than both these crest levels. Therefore, the levee provides protection for the 1% AEP event with a freeboard of 110mm on the western side and 180mm on the eastern side, less than the design freeboard of 300mm.

It is recommended to review the survey and fill any areas where the levee crest elevation is less than RL 3.2mAHD. The 1% AEP protection level is considered good for the Northern Rivers area, matching the highest protection provided by any local levees, shown in table below.

Key issues

The investigation identified several constraints that will significantly impact the cost of raising the levee. These include:

1. The need to move, reconfigure, or reconstruct existing infrastructure such as foot bridges, footpaths, pump stations, driveways, roads, and fences.

2. The removal of many large trees along both levees for structural integrity, requiring substantial reconstruction of these levee sections.

3. Limited machinery access due to the levee’s proximity to private properties and dense vegetation, potentially necessitating costly barge use.

4. The need for steep batters or retaining walls due to the levee’s proximity to property boundaries, roads, and the Capricornia Canal, which may also require unpopular pedestrian barrier fences due to the respective safety requirements.

5. A complex approval process due to the disturbance of large mangrove areas, requiring NSW Fisheries permits.

Options

The flood levels of the 0.2% and 0.05% AEP events are not reported in the North Byron Floodplain Risk Management Study and Plan (FRMSP) prepared by WMA Water - 2020, however the Probable Maximum Flood (PMF) is reported as RL 5.2mAHD, significantly above the crest of the existing levee (3.2mAHD) and both proposed raising heights (3.5mAHD and 3.8mAHD). Therefore, the benefits of raising the levee will increase the flood immunity from 1% AEP to an event larger than the 1% AEP but less than the PMF, i.e. potentially 0.2% AEP or 0.05% AEP of the events modelled in the FRMSP.

The Average Annual Damage (AAD) approach, as outlined in the Flood Risk Management Manual (DPE, 2023), can be used to assess the benefits of the levee raising. This method estimates potential flood damage caused by a range of storm magnitudes (Annual Exceedance Probability - AEP), translates them into monetary values, calculates an average annual damage, and compares the AAD with and without the levee. The difference represents the levee’s annual economic benefit. A cost-benefit analysis then determines if the levee investment is justified. Rare events, for example >1% AEP floods, generally don’t significantly impact the AAD because they occur infrequently. Lower magnitude, more frequent events generally have a bigger baring on AAD over time and contribute more significantly to the expected annual damages. Therefore, although this exercise has not been undertaken for this study, the benefits of increasing the levee’s flood immunity to 0.2% or 0.05% are expected to be small relative to the costs of construction, which is expected to be large due to the constraints identified above.

Levee Raising Recommendations

Summarising the information presented above in the Levee Raising Assessment Section of the report (attachment 1)

· The current levee has a flood immunity greater than the 1% AEP event, which compared to other levees in the Northern Rivers is high.

· Raising the levee is not expected to have a significant impact on the AAD of the area, as it will only increase flood immunity for rare occurrence flood events.

· Significant constraints have been identified as part of the initial constraints study, indicating the cost and complexity of raising the levee would be high relative to the expected benefits.

· Due to the reasons stated above the cost-benefit ratio of the levee is expected to be low.

Based on the reasons identified above, it is recommended that raising the levee by either 300mm or 600mm is not undertaken.

Recommended actions

Levee Repair and Maintenance Works

After the 2022 floods, Engeny inspected the levee for Byron Shire Council, finding it in good condition with no structural integrity loss. They made 20 recommendations to maintain this condition: 2 high-priority items needing immediate action, 9 medium-priority items for action within a year, and 9 low-priority items for ongoing maintenance. The recommended actions, cost estimates provided by WEC, and funding sources are detailed in the report. Funding is based on the NSW Public Works Flood Levee Repair and Maintenance Program covering levee assessment, condition recording, repair planning, resilience improvements, and reliability evaluation. General maintenance costs are the Council’s responsibility.

The table summarising recommended levee works, including costings and proposed funding source, have been extracted from the South Golden Beach - Levee Maintenance and Raising Investigation (WEC, 2024) and are presented below.

Table 1: Recommended levee works including costings and proposed funding source

Strategic Considerations

Community Strategic Plan and Operational Plan

This investigation and report indirectly connect to the Drainage Upgrade OP activity for South Golden Beach as identified below.

CSP Objective	CSP Strategy	DP Action	Code	OP Activity
5: Connected Infrastructure	5.5: Provide continuous and sustainable water and sewerage management	5.5.3: Storm-water - Provide stormwater infrastructure to manage flood mitigation and improve social and environmental outcomes	5.5.3.8	Continue to progress South Golden Beach drainage upgrade program

Recent Resolutions

Legal/Statutory/Policy Considerations

Not Applicable

Financial Considerations

The estimated annual cost for Council-funded maintenance actions is $85,300. An additional one-off cost of $1,150 is needed for clearing a blocked flood gate. The NSW Public Works Flood Levee Repair and Maintenance Program can fund recommended levee actions totalling a one-off cost of $59,250.

Consultation and Engagement

Given this is a preliminary feasibility study, no consultation or engagement has been undertaken.

BYRON SHIRE COUNCIL

Staff Reports - Infrastructure Services 4.3

Report No. 4.3 Flood Gate Upgrade Options Investigation - South Golden Beach

Directorate: Infrastructure Services

Report Author: Isabella Avelino Gianelli, Project Engineer

File No: I2024/164

Summary:

JB Pacific was commissioned by Byron Shire Council staff to investigate potential upgrade options for floodgates at South Golden Beach NSW. The project scope includes twelve gates on the east bank, four gates along the west bank of Yelgun Creek and two along Redgate Road. The aim is to improve flood resilience of the area by investigating into the most effective upgrade options.

RECOMMENDATION:

1. That the Committee notes the Floodgate Upgrade Options Investigation prepared by JB Pacific March 2024– Attachment 1 (E2024/47404). In particular, the recommendations contained in Section 4.2 and 5 of the report.

Attachments:

1 Report_SGB_Floodgates_upgrade_options_investigation_JBPacific, E2024/47404 , page 20 ⇩

Report

The project location and extent has been shown in Figure 1-1.

Figure 1-1: Project site

In order to improve the floodgates, it is critical to understand the pros and cons of the current systems. Site inspection, made by JB Pacific, has revealed that floodgates with the following features have demonstrated notable effectiveness:

· Floodgates with grated pit upstream show significantly less debris accumulation inside of the pipes.

· Floodgates with upstream swale grassed (not planted with vegetation) show significantly less debris accumulation inside of the pipes.

Key issues

The main issues with the existing systems are:

1. Stagnant water rear of levee:
- Flood risk: the closure or difficulty to discharge water into Yelgun Creek may lead to increase in water level during flood events and result in water damage to residential properties.
- Hygiene, odour and aesthetic concerns: Stagnant water can be breeding ground for mosquitoes and attract various vectors which can transmit diseases to humans.

2. Flap gates unable to seal:
- Flood risk: the flap gates are supposed to be one-way systems allowing drainage into the creek only. As many of them are constantly open, they become two-way systems and would allow creek water to come over the levee and flood land behind.
- Flood risk: The flap gates unable to open.

The issues could exist simultaneously or even be of influence of each other, however, they are listed separately to facilitate proposal of solutions/options. Based on the present issues, the flap gates can be further grouped in Table 2-1, potentially requiring improvement in similar aspects.

The groups are:

· A - Water ponding rear of levee

· B - Large amount of debris coming through system, blockage at flap gate, unable to seal

· C - Large amount of debris on apron, flap gate unable to open

· D - No access due to overgrow

· E - No pressing issue.

Group D and E are advised to be monitored and no further options will be necessary until any issue with them become clear. Further options will be proposed for Group A to C. Further options will be proposed for Group A to C.

Table 2-1: Asset categorisation based on issue. (extract from attachment 1)

Group A - Stagnant water rear of levee

This has been observed along the west bank of Yelgun Creek and is considered likely to be the result of the following factors:

· Flap gates unable to seal due to rubber ring degradation.

· Flap gates unable to seal as they are jammed by debris.

· Flap gates unable to open as thick siltation and debris accumulating on the apron.

· Waterhead too small to flush debris out as longitudinal grade being too flat.

· Waterhead too small to flush debris out as insufficient maintenance and large volume of debris accumulation acting as natural log jams.

To avoid the ponding, upgrade options shall consider achieve at least one of the following:

· Ensure flap gates seal properly.

· Replace flap gates with another type of valve that seals properly with presence of debris.

· Increase waterhead.

Group B – blockage at flap gate

This has been observed at seven gates along the Yelgun Creek and is considered likely to be the result of the following factors:

· Dense vegetation growth in swales and on levee. Foliage, twigs and branches are main component of debris observed on site. Trees growing on the levee could compromise stability of the levee through their extensive root system. Piping could occur after mortality of trees and shrinkage of died root systems. Trees growing inside of swales are considered worsening the blockage.

· Lack of public awareness at locations. Residents utilise the swale as storage for green waste or compost.

· Absence of any sieve/grates at inlets.

· Waterhead too small or flap gates too heavy to be flushed open, resulting in water slowly drain out of a small opening and debris accumulating inside of the gates.

The blockage is considered a combined result of the above. Therefore, upgrade options shall consider achieve at least one of the following:

· Reduction in debris input into the systems.

· Replace flap gates with another type of valve that seals properly with presence of debris and allows water to drain freely during low tide times.

Group C - flap gate unable to open

This is a concern for nine gates which include gates experiencing blockage at flap gates. Large amount of debris accumulated at concrete aprons could make the opening of flap gates even more difficult resulting in loss of water head. Resolving the issues of Group B is expected to improve this issue at the same time. Apart from the above causes in Section 2.3, this is considered likely to be the result of the following factors:

· Outlet location experiences no flush from creek. Their locations are retrieved on riverbank and behind mangroves which further reduce flow.

The blockage is considered a combined result of the above. Therefore, upgrade options shall consider achieve at least one of the following:

· Reduction in debris input into the systems.

· Replace flap gates with another type of valve that seals properly with presence of debris and allows water to drain freely during low tide times.

· Extend outlets into the creek for flushing of concrete aprons.

Group D – no access and Group E – no pressing issue

No issues have been identified for seven gates which fall into Group D and E, either due to no access or flap gates are working properly.

Options

This section considers potential options for improvements for groups of outlets. Issues observed on site can be of the same cause as analysed above and same options will be proposed in such a case.

Option 1 – Maintenance work on existing system

The current systems have been in a good to fair condition after being in service for 50 years. The performance is reduced mainly due to lack of maintenance. Regular maintenance works are therefore worth considering, such as replacing degraded rubber ring, raking the pipes to remove excess debris, lubricating hinges for easier operation of flaps, pressure wash aprons and remove excessive debris etc. This option has minimum capital expenditure but requires long-term and continuous investment into maintenance. The maintenance level is considered medium to set a base-line case for this study.

Option 2 - Improving flap gates Option

2.1 – New flap gates: many improvements have been made to flap gates over the past 50 years. Replacing the existing gates with new designs will reduce head loss resulting in better drainage and seal. Comparing with the single hinge flap gates on site, double hung hinge flap gates have the benefit of less likelihood for sticking gates and reduction in head loss. Examples below shows a simple double hung flap gate and a Mueller hydro gate with an adjustable pivot lug. The latter can be adjusted for more sensitivity (less water to crack the gate open) which can result in less debris accumulating inside of the gates. Mounting new flap gates will only trigger a small amount of expense but it is likely they need to be imported from overseas. Locally in Australia, flap gates of lighter material are available such as High-Density Polyethylene (HDPE) which will be more sensitive than the current glass fibre reinforced polymer gates. This option also comes with a medium level or slightly lighter maintenance need.

At the same time, the current pipes seem to have a flush end, then connecting to a flap gate. This would result in flap gates to remain slightly open due to gravity. A schematisation of the situation is in Figure 3-2. This is considered a design defect or poor construction quality and should be remediated if confirmed through detailed geometry check of the flap gates.

Option 2.2 - Automated flap gates: automate the operation of flap gates to fully open and close can reduce head loss. This increases the likelihood of flushing debris out of the system, but requires establishment of new power supply, actuators and staff overwatching the operation which suggests a medium size capital expenditure and maintenance cost. The automated flap gates still require maintenance due to blockage by twigs and branches but is expected of less frequent due to less loss of water head. The actuators can be hydraulically or electrically operated. However, many gates at this site sits above tidal range suggesting the hydraulic operation is not available unless they are extended out into the creek, while electrical actuators need to be positioned above flood levels to avoid submergence. As these gates are customised, their fabrication price remains unknown. Existing flap gates cannot be recycled, and new gates are needed for automation.

Option 2.3 – New flushing system: a flushing system (likely consists of a hose, a water pump and a switch) can be incorporated inside of the pipe near its inlet to flush debris out and potentially clearing the concrete apron given enough pressure. This can largely reduce maintenance frequency, ensures the seal of flap gates at most times and reduce maintenance difficulty comparing with raking individual pipes. However, the flushing system requires new power supply, and water source. Its operation can be manually turned on by council staff (no telemetry required) or fully automated (with telemetry). Such system will be custom made which suggests a medium size capital expenditure but small maintenance fee on going.

Option 3 - Improving swales

Clearing out and restoring the swales to grass swales can significantly reduce the amount of debris going through the system. This includes clear out vegetations and reprofile swales for a 1% to 4% longitudinal grade. The system still requires maintenance but is expected of less frequent due to less debris coming through and greater waterhead to flush out them. A small capital expenditure and maintenance investment are expected, given the survey confirms the grade of existing swales are insufficient.

Option 4 - Replacing flap gates

Removing and replacing the existing flap gates with alternative one-way valves can improve performance and reduce maintenance requirements. Different valves are considered here.

Option 4.1 – Automated vertical rising gates: removing existing flap gates and replacing them with automated sluice gates (or knife gates, to retrofit onto existing pipes) that seals tight with minor leave debris present. Knife and sluice gates are vertical rising valves need to be lifted open through powered mechanic arms. Electrical actuators have been considered the most economic for our case by flap valve suppliers JBP approached.

The valves are off-shelf products, but the automation requires new power supply (with flood immunity) and actuators and operators as discussed before. The supplier has suggested the knife valves requires similar degree of maintenance as flap valves because they are unable to cut through twigs and branches.

Also note the knife valves require support from both sides therefore cannot be directly fitted on to the existing pipes. Likely works include cutting the concrete pipe; install the knife valve; rejoin the concrete pipe at both ends to provide stability for the valve. This is therefore high in capital and maintenance expenditure. Sluice gates can be mounted onto existing pipes (single side support) which saves on modification of concrete pipes.

With automation, a new risk to public safety will need to be managed by council by controlling unauthorised access to these valves. Closing of the knife valves could lead to death and serious injury of any person inside of the pipe. Full isolation of the system during maintenance works is also highly recommended for the safety of council staff.

Option 4.2 – Alternative one-way valves: there are other non-return valves available on the market that relies on hydrostatic pressure to operate. They eliminate the need for power supply and telemetry system which significantly reduce upgrade cost. Some examples include scissor gates, duckbill valves and in-line check valves.

Scissor gates rely on buoyance to open and close and can handle foliage debris. However, twigs and branches will still prevent it from sealing. The design is customised by HydroSlide (UK). The gate is of metal, which will have corrosion issue in our site and requires careful selection of material and corrosion prevention measures such as painting.

Duckbill valves have higher tolerance to debris comparing with flap gates, and are usually made of rubber. They are safer for fish and are claimed to be maintenance free (no moving mechanical parts), if given enough water head. More information on catchment area, longitudinal grade of each outlet would be required to determine if water head is sufficient to open them as they usually require higher head than flap gates.

In-line check valves can also seal better with minor foliage debris than flap gates but requires higher water head to open. They can be made of rubber and shares many pros and cons with the duckbill valves. Their application can result in a small to large capital expenditure, depending on how much work is required to increase water head to a satisfactory level. Based on observation on site, it is likely to require earthwork and replacing concrete pipes at a greater grade for this option to perform as intended. This suggests a large capital expenditure. However improved systems are expected to have less maintenance requirements.

Group B – blockage at flap gate, unable to seal

Option 3 and 4 discussed in Section 3.1.4 and 3.1.5 have been discussed above for Group A and are applicable to Group B with the same pros and cons. Hence it is not further discussed here.

Option 5 – Screens at inlet

Reduction in debris coming through the system reduces likelihood of blockage at flap gates. This can be achieved by installing screens/sieves/grates at inlets. The screens can prevent natural and man-made (plastic bags, cans) debris entering the creek and accumulate at locations that are easy to access and clear out. This is a value-add on cleaning the creek and allow safe removal of debris. There are many designs available depending on target debris size. Alignment of the screen can also vary from being perpendicular to the approach flow (susceptible to blockage but easy construction with off-shelf products) to being at an oblique angle to the approach flow to increase its effective area and reduce likelihood of blockage.

Without clearing of the swales, the debris are not removed from the system but simply accumulated upstream with less influence on seal of flap gates. However, the screens will change the hydraulic of the swale and suitability and design details should be confirmed through numerical modelling. The build-up requires clearing prior and after flood season to ensure minimum rise of water level in the swale and no increase in flood risk upstream.

The screens are easy to install, and swales are of good foot access. Therefore, this option has a small capital expenditure and a medium maintenance fee in long-run.

Group C – flap gate unable to open

The restriction on gate’s ability to open due to sedimentation on aprons can be resolved through:

· Careful design of Option 2 - Improving flap gates with sufficient clearance.

· Reducing debris load through Option 3 - Improving swales and Option 5 – Screens at inlet.

· Change of valve opening mechanism through Option 4 - Replacing flap gates. Duckbill valves have higher tolerance to debris and requires higher water head/ flow rate to open. Its design will not be blocked by accumulation of debris outside of the valve, and its release of water will have more volume hence better chance at flushing apron clean.

Multi Criteria Assessment

Methodology

Each option has been reviewed to establish their relative merits against a set of project objectives via a Multi-Criteria Analysis (MCA). The purpose of the MCA is to help determine the preferred options in a systematic way. It uses Technical, Environmental, Social and Economic categories, including several sub-categories to develop a scoring system. Table 4-1 MCA scoring criteria and results are presented in attachment 1.

Next steps

Exploring options to reduce maintenance frequency and difficulty reveals that automation, while initially appealing, adds complexity. It introduces additional electronic or mechanical components and specialized services along the levee. Automation may decrease outlet maintenance demand but requires regular upkeep by personnel with specific skills due to involvement with electricity, moving parts, and computer algorithms. O utsourcing this maintenance is an option but increases the maintenance budget. Moreover, in a marine environment with flood risk, electrical automation systems may necessitate monthly maintenance. Automation does not eliminate the need for regular maintenance tasks such as clearing swales, removing debris, and inspecting outlets, as automated systems may struggle with handling woody debris. Therefore, automation isn't recommended.

Upon review of available products and areas of improvements, a mechanical system relying on gravity/hydrostatic pressure just as the current flap gates remains council’s best choice for easy maintenance and low capital cost. However, improvements can certainly be made on the existing system.

JBP recommends taking the following measures:

1. Enhance seal/ water tightness: Consider adopting an improved design allows flap gates to close fully under gravity by extending the bottom of pipe to meet the gate as illustrated in Figure 3-2. Importing double hung hinged flap gates or bespoken flap gate design for Group A and B. Upgrade/ remediation priority will be on the gates along the western bank, 17924 to 17927, as the inlet invert is lower than the spring tide level, during high tide water will flow from the creek to inland.

Figure 3-2

2. Increase water head

Clear out swales of vegetation other than grass and re-grade them to ensure a good longitudinal profile, applicable to gates connected to swales. There are gates connected to open grass land which do not require further clearance.

3. Reduce debris coming into the system

(a) Install grates at inlets to further reduce debris coming into pipes. This may not be necessary if the swales are clear of debris. It is recommended to monitor the systems after clearing the swales before installing grates for gates without screens. If swales cannot to be cleared for any reason, priority should be given to floodgates that has dense vegetation or deciduous trees within 20m upstream of the inlet, and then gradually roll out to all inlets.

(b) Educate residents on the importance of maintaining the swales clear of foreign objects and avoid planting in or on the swale banks.

The measures are not listed in order of priorities but are recommended to be actioned at once to achieve the best outcome.

Yearly maintenance programme

Following CIRIA C7861 guidance and combining with specific site observations, a generic maintenance programme is developed to follow remediation works proposed above to further improve flood resilience of the site.

5.1 Activity

Expected maintenance activities for the remediated floodgates are:

1. Inspection. Council staff to inspect floodgates for abnormalities and identify triggers of further maintenance activities as below.

2. Removing sediment and debris from pipes through high-pressure jetting. This eliminates the need to feed a rake through the pipes and the need for personnel to enter the systems. The pressure should not be damaging to the concrete pipes but sufficient to flush debris directly out or at least to outlet points for easy removal.

3. Clearing debris from screens. Screens tend to block with debris and regular cleaning is needed to maintain hydraulic performance of them. As the floodgates in interest do not experience large head of water, manual raking is considered suitable. This activity should only be carried out in good sunny weather when the systems are dry. The debris should be removed from the site.

4. Maintaining flap gates. Flap gates operation relies on rubber rings and hinges. These parts should be examined and replaced timely. Lubrication of hinges should be conducted regularly to facilitate open and close of gates.

5. Controlling vegetation upstream. Swales feeding into the flap gates are to be cleared of debris and unnecessary vegetation that contributes to blockage.

5.2 Frequency

As the design/construction of these gates are not ideal, the below frequencies are recommended as a minimum:

· Inspection – Quarterly for any year. Recommended times are late October, late January, late April, and August based on ‘wet season’ from November to April.

· Activity 2, 3, and 5 – Biannually at late October (before start of wet season) and late April (drier time for easy access).

· Activity 4 – Likely to be every year but depends on manufacturer’s guidance.

Strategic Considerations

Community Strategic Plan and Operational Plan

CSP Objective	CSP Strategy	DP Action	Code	OP Activity
5: Connected Infrastructure	5.5: Provide continuous and sustainable water and sewerage management	5.5.3: Storm-water - Provide stormwater infrastructure to manage flood mitigation and improve social and environmental outcomes	5.5.3.8	Continue to progress South Golden Beach drainage upgrade program

Recent Resolutions

Legal/Statutory/Policy Considerations

Not applicable

Financial Considerations

This project has been funded under funding source - NRRRP Stream 1 - Increasing flood risk awareness. CSIRO ID NP10.

Indicative costs for construction works recommended in Section 4.2 have been developed as a guidance.

Table 6-1: Indicative construction cost (extract from attachment 1)

Yearly maintenance cost

Based on the frequency and activities proposed in Section 5, indicative costs for maintenance are as below.

Table 6-2: Indicative maintenance cost per year (extract from attachment 1)

Council do have an existing Maintenance Budget allowance for this area under the “North – Urban Drainage Maintenance” component of the Draft Operation Plan 2024/2025. Any upgrade items outlined in Section 4.2 and 5 and costs in Section 6 of this report would need to be reviewed and rationalised against the other priorities within that funding allowance.

Consultation and Engagement

Given this is an investigation study, no consultation or engagement has been undertaken.

BYRON SHIRE COUNCIL

Staff Reports - Infrastructure Services 4.4

Report No. 4.4 Post 2022 Event Flood Behaviour Analysis - Brunswick River , Belongil Creek and Tallow Creek - NSW Department of Planning & Environment

Directorate: Infrastructure Services

Report Author: Steve Twohill, Flood and Drainage Engineer

File No: I2024/676

Summary:

The NSW Department of Planning & Environment (DPE) – now rebranded to NSW Department of Climate Change, Energy, the Environment and Water (DCCEEW) have finalised and published Post 2022 Flood Analysis Assessments for the three (3) main catchments contained within Byron Shire Council.

These reports have been uploaded to the NSW State of Emergency Service – NSW Flood Data Portal. All these reports are available to be viewed and downloaded.

These assessment reports are outlined as:-

“Post 2022 Event Flood Behaviour Analysis - Brunswick River – Final Report – February 2024” – WMA Water - (E2024/51340). Download link at Post 2022 Event Flood Behaviour Analysis - Brunswick River Report - Datasets - NSW Flood Data Portal

“Post Event Flood Behaviour Analysis of the March 2022 Event – Belongil Creek – Final Report – 19 April 2024” – BMT - (E2024/51531). Download link at Post Event Flood Behaviour Analysis of the March 2022 Event - Belongil Creek Report - Datasets - NSW Flood Data Portal

“Post Event Flood Behaviour Analysis of the March 2022 Event – Tallow Creek – Final Report – 19 April 2024” – BMT - (E2024/51533). Download link at Post Event Flood Behaviour Analysis of the March 2022 Event - Tallow Creek Report - Datasets - NSW Flood Data Portal

Links to these reports have been included on the Byron Shire Council website.

In response to requests from the Committee, DCCEEW have provided an animation of the 2022 flood event for the North Byron catchment – refer document E2024/51367

RECOMMENDATION:

1. That the Floodplain Management Advisory Committee notes that the Department of Climate Change, Energy, the Environment and Water (DCCEEW) have finalised and published Post 2022 Flood Analysis Assessments for the three (3) main catchments contained within Byron Shire Council. These include the North Byron/Brunswick River, Belongil Creek and Tallow Creek catchments.

Attachments:

1 BSC Flood Mitigation Program, E2022/52007 , page 20⇩

Report

These reports have been uploaded to the NSW State of Emergency Service – NSW Flood Data Portal. All these reports are available to be viewed and downloaded.

These assessment reports are outlined as:-

Links to these reports have been included on the Byron Shire Council website.

These reports aim to understand the areas impacted by the recent 2022 flood event and determine the current approved flood model's ability to replicate the event. The common recommendation and finding from the analysis were that the existing Flood Studies have reached their use by date due to advances in modelling technology and techniques gained over the past five (5) years. Updates to all current flood studies are recommended.

While the Report’s findings provide various recommendation that Byron Shire Council support, we will not be making any changes to our planning instruments at this stage. To do this, we would need our own updated Floodplain Management Study and Plan/s for each of the catchments in the Shire. This would require updates to all Flood Models to then inform the Flood Risk Study and Plan process. That would include review of Development Controls, Fill Exclusion zones as examples. This approach is consistent with the mandated processes under the NSW Flood Risk Management Manual 2023 that Council shall comply with.

To support this approach in respect to updated development controls, the Brunswick River report compared the actual 2022 event to the adopted 2100 development flood controls that include 1% AEP, sea level rise and 20% increased rainfall intensity. It found that the 2022 event was either consistent or lower that these design controls.

In respect to the northern region of the shire, DCCEEW have provided an animation of the 2022 flood event for the North Byron / Brunswick River catchment – refer document E2024/51367.

There is an anomaly with the recreation of the flood pattern in the South Golden Beach area on the western side of the canal system. Flooding was experienced from the north in a manner not predicted by the design model. The post flood review raised concerns with the flood model limitation at the Kallaroo Bund Interface and interface with the Coastal Creeks of Tweed Shire.

In terms of updated flood studies, Council has been awarded DCCEEW grant funds to undertake the Belongil and Tallow Creek/s, works have been tendered with contract engagement expected to be issued by end of May 2024. Works were put on hold awaiting the updated the Light Detention and Ranging Survey (LIDAR) being undertaken by the CSIRO. To date no updated LIDAR data has been issued by the CSIRO. This project will also include updates to the Floodplain Risk Management Study and Plan/s for both catchments.

In respect to the North Byron Flood Study and associated Risk Management Study and Plan no budget has been allocated within the draft Operational Plan 2024/25 by Council for this work. Applications for the 2024-25 Floodplain Management Program close on 16 May 2024. This is a reoccurring annual grant; Council will seek funding to support an application in the 2025/2026 round.

Key issues

Not applicable

Strategic Considerations

Community Strategic Plan and Operational Plan

CSP Objective

CSP Strategy

DP Action

Code

OP Activity

Recent Resolutions

· 23-271, 23-094, 22-606, 22-352, 23-654

Legal/Statutory/Policy Considerations

The updated Floodplain Development Manual 2023 supports the policy and guides councils through the floodplain risk management process. The manual helps councils develop and implement local floodplain risk management plans and outlines the technical assistance provided by the NSW Government.

The manual details the roles and responsibilities of various NSW agencies and includes information on:

• the preparation of flood studies, floodplain risk management studies and plans

• floodplain risk management options

• flood planning levels and areas

• hydraulic and hazard categorisation

• emergency response planning.

The manual was originally gazetted in 2005 with a new updated manual being gazetted in 2023. It is the manual relating to the development of flood-liable land for the purposes of section 733 of the Local Government Act 1993.

Financial Considerations

There are no financial considerations in this instance as the report is being commissioned by NSW DCCEEW.

Consultation and Engagement

NSW DCCEEW have provided draft copies of the reports and briefing sessions to the committee in late 2023. The adopted reports are now publicly available with links on the Byron Shire Council website.

BYRON SHIRE COUNCIL

Staff Reports - Infrastructure Services 4.5

Report No. 4.5 Community Education Strategy and Review of Flood Options / North Byron Flood Investigations - Projects Update

Directorate: Infrastructure Services

Report Author: Steve Twohill, Flood and Drainage Engineer

File No: I2024/677

Summary:

This report provides an update to the Floodplain Advisory Committee requested in their recommendation of Report 4.2 tabled at the Friday 8 December 2023 committee meeting. This recommendation has not been ratified with a council resolution. However, Council staff provide this report in good faith to keep the committee informed of the responses to these matters acknowledging that the Committee will end in September under this current Council term.

The list of items is as follows and is discussed in this report: -

1. That the Floodplain Management Advisory Committee receive a further update on the ‘Community Education Strategy and Review of Flood Options’ project and a briefing on ways of further engaging community, for example with animations from existing and future flood models.

Consultants JBP have progressed this assessment and project since the public meeting held on 6 December 2023 and the ensuing Christmas holiday period. Council staff have met with the Consultant JBP in late December 2023 and February 2024 to discuss ways of further engaging the community in relation to improved flood awareness to this region.

In addition, Council sought permission from the NSW Department of Planning & Environment (DPE) to provide and release the confidential 2022 Flood event review report that was presented to the committee late last year. DPE have agreed to that request in late December 2023, this information has been provided to JBP.

This project has budgetary constraints that are already committed with an agreed scope. Staff have negotiated with the consultant JBP to undertake a review of the DPE 2022 flood event review report and integrate outcomes where appropriate in this assessment. The report is well underway however too premature to release for this committee meeting.

Animation and graphical recreation of the flood event are supported, however that aspect is not included in the scope for this project. Given that DPE has commissioned this review by WMA Water and the fact that it is their report and work, we recommend that DPE commission animation graphic models of the 2022 flood event and provide to Council to assist in future community engagement for this project.

We anticipate that the Final report will be presented to the committee at the next scheduled meeting in May 2024.

RECOMMENDATION:

That the Floodplain Management Advisory Committee:-

1. Note the update on the ‘Community Education Strategy and Review of Flood Options’ project which focusses on the Northern Byron Shire communities; and

2. Recommend that the NSW Department of Planning & Environment (DPE) be requested to commission animation graphic models of the 2022 flood event and provide to Council to assist in future community engagement.

Attachments:

1 JBP-Review Of Flood Studies North Byron Study Region - Draft Report - Feb 2024, E2024/47658 , page 20 ⇩

2 JBP-Executive Summary-Review Of Flood Studies North Byron Region - Draft - March 2024, E2024/47660 , page 20 ⇩

Report

This report provides an update to the Floodplain Advisory Committee requested in their recommendation of Report 4.2 tabled at the Friday 8 December 2023 committee meeting.

This recommendation has not been ratified with a council resolution. However, Council staff provide this report in good faith to keep the committee informed of the responses to these matters acknowledging that the Committee will end in September under this current Council term.

Background to this project is contained in the previous report table at the 8 December 2023 meeting – refer File I2023/1607.

Attachments 1 & 2 are provided for the committee’s information.

There are eight (8) interrelated flood related investigations in this study area that will be nearing completion. These other projects include: -

PM22_30091 - AGRN1012 - Local Government Recovery Grant Program

PM22_1486 - Flood Warning Systems (Gauges) Upgrade - Shire Wide

PM23_1513 - Flood Pump Generator Power Supply - South Golden Beach

PM23_1514 - Rear Drainage Easements Upgrade - South Golden Beach

PM23_1516 - Flood Pump Investigation for Western Levee - South Golden Beach

PM23_1517 - Drainage Easement Maintenance Access Upgrade - Narooma Drive

PM23_1519 - Flood Gate Upgrade Options Investigation - South Golden Beach

PM23_##### - Sky Pump Feasibility Investigation - South Golden Beach Canal system

Once all these investigations are complete, there is an opportunity to report all of these projects in a consolidated and integrated manner to the community June/July 2024.

Next steps

The Floodplain Advisory Management Committee will be updated as the project progresses. Committee members will be provided an opportunity to be further involved during the later stage of the project at an options workshop (date not yet confirmed).

Strategic Considerations

Community Strategic Plan and Operational Plan

CSP Objective		CSP Strategy		DP Action		Code		OP Activity
3: Nurtured Environment	3.3: Protect the health of coastline, estuaries, waterways, and catchments		3.3.2: Floodplain management - Mitigate the impact of flooding on private and public property		3.3.2.3		Floodplain Risk Management Committee coordination

Legal/Statutory/Policy Considerations

The study will align with the framework established by the NSW Floodplain Development Manual and national best practice as outlined in the Australian Institute for Disaster Resilience Handbook 7: Managing the floodplain: best practice in flood risk management in Australia (AIDR, 2017).

Financial Considerations

This is a grant funded project comprising consultancy fees only of $37,940 (excl. GST).

Consultation and Engagement

A Community and Stakeholder Engagement Plan (CSEP) has been developed for the project for implementation. The CSEP aims to collate community and stakeholder concerns and ideas and address all concerns after reviewing management options and data. The CSEP considers different approaches to communications and engagement, following the IAP2 Public Participation Spectrum. The key outcomes of the project is improved community and stakeholder understanding and education on flood risk and flood risk management, as such the below is proposed:

• Council Staff/DPE representatives are given a steering role (Empowered).

• Council’s Advisory Committees are Involved

• The community is Involved within the project. This is deliberately not at a level that would allow their request for new mitigation scenarios to be tested without checks from flood engineers to ensure they are viable; however, it will ensure they are a focus on this project.

Venue	Conference Room, Station Street, Mullumbimby
Date	Tuesday, 14 May 2024
Time	11.30am