Stormwater and Flood Mitigation Network

Asset Management Plan –Stormwater and Flood

Mitigation Network

Stormwater and Flood Mitigation Network

Wagga Wagga City Council // Asset Management Plan // Stormwater & Flood Mitigation Network //

This Supporting Section should be read in conjunction with Council’s Asset Management Plan, the Asset Management Policy (which sets out Council's philosophy of asset management) and Council’s Asset Management Strategy (which provides Council with a clear direction and goal for managing the community's $1.185 billion (as at June 2010) worth of assets).

Size of the NetworkThe stormwater and flood mitigation network managed by Council in the Wagga Wagga LGA comprises of 17.4km of levee banks, 10.6km of detention basin banks, 20.5km of open drains and 392km of stormwater pipes.

MapThe condition of Council’s assets has been audited as part of the asset inspection regime, rated against the asset condition reference sheet and captured in Council’s electronic mapping system. The condition of Council’s assets is rated from excellent to very poor. The colours on the following map indicate the condition of the asset, as detailed in the below table.

1 Excellent Dark Green

2 Good Green

3 Average Yellow

4 Poor Orange

5 Very Poor Red

Levee BanksThe following table lists the condition of the levees located in the Wagga Wagga Central Business District and in the rural village of Tarcutta from excellent to very poor.

Excellent 0% 0

Good 0% 0

Average 81.2% 14km

Poor 18.8% 3.3km

Very Poor 0% 0

1 Current Asset Base



The following map indicates the condition of the levee from excellent to very poor.



Stormwater Management System

The following map indicates the location of stormwater pipes and the below table details the proportion of the network in each condition.

Excellent 79% 288,177m

Good 11% 39,787m

Average 7% 27,160m

Poor 1% 2,433m

Very Poor 2% 7,464m



Challenges of the NetworkSome challenges facing the stormwater and flood mitigation network include:

The condition of the below ground stormwater infrastructure is largely unknown.

There are many areas of the City where the stormwater infrastructure, above and below ground, cannot contain the storm levels they were originally designed for because their hydraulic catchments have been extended without any upsizing of infrastructure lower in the catchment. This means that stormwater in these areas follow the natural overland flow path, usually through low lying properties.

Wollundry Lagoon and Tony Ireland Park receive much of the stormwater from the Central and South Wagga areas. The Wollundry Lagoon in particular is in need of desilting to free up air space which will accommodate increased stormwater volumes.

The top water level of the Wollundry Lagoon was raised by Council in the 1990’s to assist with the cooling of the Civic Centre. This has resulted in the level of the lagoon being above the discharge level for quite a few stormwater pipes which means that many of these pipes store water, significantly reducing the effectiveness of these systems.

Gross pollution systems in many of the detention basin in the City either do not exist or are in need of upgrading (particularly Bolton Park). This means that gross pollutants are not captured and cleanups are required after moderate to large storm events.

Council has a number of open drains, large diameter pipes and discharge points that can be accessed by the community during storm events which could result in serious injury or possible drowning.

Sediment and gross pollution control of stormwater must be assessed for environmental impact. The quality of stormwater discharged can be improved with engineering techniques.

Wagga Wagga is highly susceptible to urban salinity. Design efficient stormwater systems that do not exacerbate groundwater infiltration is an engineering challenge, particularly in some areas of the City were development is occurring.

The existing Main City Levee does not provide a level of protection against a modelled 1 in 100 year riverine flood event. The structural integrity of the levee has been audited, which shows the levee in some areas does not meet the engineering compaction standards.

The existing North Wagga Levee currently does not provide protection against a modelled 1 in 20 year riverine flood event. The structural integrity of this levee has been audited and shown that the levee in some areas does not meet the engineering compaction standards.

Council does not conduct community education for its stormwater system.

Council does not currently have a sufficient budget allocation to adequately maintain its ageing stormwater network.



Condition Ratings Reference SheetsThe condition of the stormwater infrastructure network is audited against a rating scale which ranges from excellent to very poor. This scale is used as the basis of all assessments of the stormwater infrastructure by Council’s Surveillance Team. The rating scale forms the Condition Rating Reference Sheet below.

Condition Rating Reference Sheet - Stormwater Pipes

2 Condition Assessment



Condition Rating Reference Sheet – Levee Banks



Risk and Condition Rating IndicatorsCouncil also uses Risk and Condition Rating Indicators to determine a prioritised works schedule for the maintenance, renewal and replacement of large asset categories. These indicators are used in addition to the Condition Ratings Reference Sheet to enable further analysis of the worst sections of the asset class. Risk and Condition Rating Indicators have been developed for the stormwater pipe network.

The Indicators are used to develop an overall Works Schedule Priority Rating for each individual asset or section of an asset. The first stage considers the risk the condition of the asset poses to the community. The following table details the Risk Rating Indicators for the stormwater network.

Stormwater Network Risk Rating Indicators

Weighting Location/Estimated Pedestrian Volume

1.2 Commercial Precincts (Central Business District, shopping malls)

1.1 Community Precincts (schools, churches, hospitals, clubs, community centres)

1.0 Residential Areas

Weighting Major Overland Flow Flood Study Priorities

1.3 High risk

1.2 Medium risk

1.1 Low risk



The second stage of the process considers the age of the pipe for the stomwater pipe network. This is the Condition Rating Indicator.

The older the stormwater pipe (or the closer the pipe is to the end of its design life), the higher the risk of failure due to internal and external pressure, cracking, root penetration and/or chemical corrosion. Each section of stormwater pipe is rated against the Condition Rating Indicators detailed in the below table.

Stormwater Condition Rating Indicator

Score Within percentage of its design life

1 30% of design life ending





The results of both these stages of the matrix process are combined to give an individual asset or section of the asset a Works Schedule Priority Rating. For example a section of stormwater infrastructure could be rated as follows:

Stormwater Infrastructure XYZ

Condition Rating Indicator (CRI) 4 (10% of design life ending)

Condition Rating (CR) 3 (Average)

Location (L) 1.1 (Community Precinct)

Major Overland Flow Flood Study Priority (MOFP)

1.2 (Medium Risk)

Works Schedule Priority Rating Formula

(CRI + CR)L x MOFP

Works Schedule Priority Rating Example

(4+3)1.1 x 1.2 = 9.24

The Work Schedule Priority Ratings for stormwater infrastructure are then ranked from highest to lowest to produce a prioritised schedule of works for maintenance, replacement and renewal of the network.



Intervention LevelsTo guide Council’s response to customer requests a set of reactive triggers have been developed for each asset category. These triggers are called intervention levels and include expected response times. The following tables detail the intervention levels and response times for maintenance of the stormwater and flood mitigation networks.

Stormwater and Flood Mitigation Infrastructure Intervention Levels

Blockages Inspection within one week. Corrective action undertaken within one month.

Batter Degradation Corrective action within one week.

Water diversion Corrective action within one week.

Condition Inspection RegimeThe condition and risk of the stormwater network will be assessed simultaneously as part of the Condition Inspection Regime. This inspection will audit the condition of each section of stormwater and flood mitigation infrastructure asset against the Condition Rating Reference Sheets and also assess the risk based on location and usage.

The entire stormwater pipe network will be audited via CCTV over the next 3 years. Until Council has completed a network wide surveillance of the stormwater pipe network it is difficult to accurately state a realistic interval for the frequency of these inspections. Subsequent revisions of this Asset Plan will identify the inspection frequency and regime once determined from the completed first surveillance.

It is proposed the inspection regime should address the pipe material most at risk of failure, for example clay, then by age of the pipe. Obviously the older the pipe, the closer it is to the end of its design life.

Pipes closer to the end of their design life need to be inspected more frequently. A new pipe or one less than 10-15 years old may only need to be inspected once during that time.

The levee will be audited every 3 months and after each significant rain event.

Ad hoc inspections will be conducted in response to customer requests, on an as needs basis and where the asset degrades due to un-foreseen or unusual circumstances, like a storm event. These inspections are done onsite by trained surveillance officers and the results are captured in Council’s electronic mapping system (ArcGIS).



3 Life Cycle ManagementLife cycle management details how Council plans to manage and operate the asset category at the agreed level of service while minimising life cycle coststhroughout the useful life of the asset.

For most local government assets there are four key phases to the life cycle, namely: acquisition, operation and maintenance, renewal, and disposal.

Costs occur in each phase of the asset life cycle. It is important to attribute these life cycle costs to each phase to allow for effective decision making about how the asset will be managed.

The life cycle costs of assets include:

initial capital investment

operation and maintenance

refurbishment and renewal

administration, overheads and taxes

depreciation

capital use rate charges or rate of return and

disposal of the asset at the end of its useful life

The initial capital or investment cost of a new asset is a significant cost and often dominates the decision as to whether to acquire the asset or expand the infrastructure network. However, it is important to include all the costs associated with each phase of the asset life cycle, including ongoing operation and maintenance, future renewal and disposal.



Target Maintenance EventsThe following tables detail the target maintenance events associated with the stormwater and flood mitigation network annually.

Flood Mitigation Target Maintenance Events

Event Target Maintenance Events per Year

Cleaning and minor repairs to flood gates, inlets and outlets

8 times per year

Cleaning and minor repairs to fixed flood pumps

8 times per year

Maintenance of temporary flood pumps 4 times per year

Cleaning and minor repairs to gross pollutant traps

52 times per year

Levee bank inspections 8 times per year

Levee bank minor repairs Once per year

Levee bank mowing 4 times per year

Drainage Network Target Maintenance Events


Cleaning lined open drains 4 times per year

Cleaning and re-grading unlined open drains Once per year

Jetting and root cutting pits, junctions, side entry pits and pipes

Once per year

Minor repairs of pits, junctions, side entry pits and pipes

Once per year

Cleaning and re-grading of stormwater sediment and detention basins

Once every 4 years



The following table details the target maintenance events associated with the salinity network annually.

Salinity Network Target Maintenance Events


Cleaning and minor repairs to bore pumps 4 times per year

Cleaning and minor repairs to salinity evaporation ponds

Every 2 years

Inspection and minor repairs to pipelines Once per year

General maintenance of pump station 4 times per year

Renewal A detailed work plan for the renewal of the stormwater infrastructure network is developed annually to support this Asset Management Plan. This renewal program is prioritised based on condition and risk.

Disposal Currently, Council includes the cost to dispose of an asset in the unit rate of that asset type. As Council moves towards strategic asset management this cost will be captured separately. The Asset Management Plan will be updated to reflect this change as it occurs across the asset types.



4 Level of ServiceThe Asset Management Plan for 2011 has been developed based on data collation, research outcomes and the results of Council’s internal stakeholder engagement process.

The next stage of the process is to ask the community to identify which asset condition is satisfactory to them. This will begin with an extensive community consultation process. The consultation will be in the form of a community survey which will be conducted online, at community gatherings, through focus groups and stakeholder meetings. The survey will use new technology, be based on images and a simple selection process. The outcomes of the consultation will form the foundation for true community engagement to occur in relation to the management of infrastructure across the Wagga Wagga Local Government Area, in particular the development of agreed levels of service, supported by Council and the community.

As Council gathers data from the community about the level of service for each asset category the outcomes will be integrated into the Asset Management Plan.

Until the outcomes of the community engagement are known, Council will provide costings to achieve an average condition for each asset category and use this as the satisfactory level of service.



5 Financial ConsiderationThe following graph details the proportion of stormwater pipes in each condition.

Council’s current liability in relation to the infrastructure network is the sum of all asset units which have a condition rating of poor and very poor. The current liability of the stormwater network is estimated to be $8,441,793 (in 2010 dollars). The following table provide details of the stormwater pipe network current liability.

RCP/FRCDiameter

Current Liability

300 $138,600

375 $140,749

450 $172,504

525 $38,600

600 $261,032

750 $128,084

900 $1,175,341

1200 $6,113,992

RCP - Reinforced Concrete Pipe FRC - Fibre Re-enforced Concrete



The following table continues to provide details of the stormwater pipe network current liability.

uPVC Diameter Current Liability

100 $140,068

150 $36,437

225 $96,386

uPVC – Unplasticised Polyvinyl Chloride

The following graph details the proportion of the levee infrastructure network in each condition.

The current liability of the levee infrastructure is the section of the levee which is rated as average or below. This current liability business rule is unique to the levee as its failure will have significant consequences to approximately 8,000 residents and commercial businesses, including possible loss of life. In addition, if the levee fails this failure puts enormous pressure on other parts of the levee resulting in further failures. The current liability of the levee is $19.9 million (in 2010 dollars). The following table provides the detail of the levee current liability.



Asset Condition Current Liability

3 - Average $15.9 million

2 - Poor $4 million

5 – Very Poor 0

Projected Annual Maintenance CostsFor Council to achieve the target maintenance events as detailed in Section 3 of this Asset Management Plan, the projected annual maintenance budget for the stormwater and flood mitigation networks is estimated to be $1,819,920 (in 2010 dollars). This estimate was developed by Council’s Asset Management Planning and Program Integration Teams in 2010. It is a first principle estimate and is expected to vary as Council improves its asset management process and strategies. The following table provides further details of the maintenance costs associated with maintaining the stormwater and flood mitigation network each year:

Stormwater and Flood Mitigation Network Annual Maintenance Costs

Event Maintenance Costs per Year

Cleaning and minor repairs to flood gates, inlets and outlets

$57,600

Cleaning and minor repairs to pumps $26,880

Cleaning and minor repairs to gross pollutant traps $31,200

Inspection – levee banks $38,400

Minor repairs to levee banks $300,000

Mowing levee banks $150,000

Cleaning of lined open drains $17,600

Cleaning and re-grading unlined open drains $75,000

Jetting and root cutting in pits, junctions, side entry pits and pipes

$90,000

Minor repairs to pits, junctions, side entry pits and pipes $105,000

Cleaning and re-grading of stormwater sediment and detention basins

$52,500

Camera inspections of the CCTV system $100,000

Cleaning and repairs to salinity bore pumps $4,320



The following table continues to detail the projected annual maintenance costs associated with the Stormwater and Flood Mitigation Network.

Cleaning and minor repairs of salinity evaporation ponds

$500

Inspection and minor repairs to salinity pipelines $9,000

General maintenance to salinity pump station $1,920

Required Increase to Annual Maintenance Budget perAdditional UnitAs the asset base increases it is important to ensure that the annual maintenance budget also increases. The following table details how much per unit the annual maintenance budget for the stormwater and flood mitigationnetwork should increase as it expands.

Required Increase to Maintenance Budget for Additional Stormwater and Flood Mitigation Infrastructure

Category Maintenance Costs per Year per Unit

Pits, junctions, side entry pits and pipes $1.80

Lined open drains $44

Stormwater sediment and detention basins $525

Unlined open drains $15

Flood gates, inlets and outlets $960

Fixed pumps $2,000

Temporary pumps $480

Gross pollutant traps $6,240

Levee banks $2.56 per m

Salinity bore pumps $480

Salinity pipelines $18

Salinity pump station $1,920

Salinity evaporation ponds $500



6 AssumptionsThere are some generic assumptions made in the management of assets in Wagga Wagga City Council, these are found in the Asset Management Plan. In addition, the following assumption has been made in relation to the stormwater and flood mitigation network:

Currently the open drains, flood gates and pumps, which are all part of the stormwater network are not condition rated and as a result are not included in the current liability. As Council continues to improve its asset management this will be completed.

Stormwater and Flood Mitigation Network

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