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12 Lincoln Stormwater Scheme

12.1 Scheme Summary

Description		Quantity
Scheme Area		2,022.12 ha
Scheme Coverage (as at 1 Jan 2021)	Rating numbers	2,541
System components	Piped (m)	75,140
	Swales (m)	12,377
	Drains (m)	9,399
	Manholes/Inspection Chambers (No.)	871
	Treatment	33 Wetlands / Infiltration basins 2 proprietary devices 3 silt traps 3 filter beds 1 oil trap
	Other	33 soakholes
Value ($)	Replacement Cost	$35,921,003
Value ($)	Depreciated Replacement Cost	$33,049,987
Financial	Operator cost (scheduled and reactive maintenance) per connection	$69.91/connection
Planning	Stormwater Management Plan	Yes
Planning	No. SDC stormwater consents	4
Demand	Mean Annual Rainfall (mm)	600
Demand	10% AEP (10 year) 1hr rainfall depth (mm)	18.2
Sustainability	Sustainable drain management practices	Adopted and Encouraged

12.2 Key Issues

The following key issues are associated with the Lincoln Stormwater Scheme. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.

Table 12‑1 Lincoln Scheme Issues

What's the Problem	What we plan to do
Requirement to pipe open drains in expanding urban areas leaving remnant short sections of open drain.	Council to budget to pipe sections of open drain remnants as required.

12.3 Overview & History

There are multiple waterways that flow through and/or border the township of Lincoln. These include:

The L-1 Creek which flows through the centre of the township;
The L-2 River which starts from a spring source at the eastern limits of the township
The Lincoln Main Drain on the western boundary; and
Todds Drain on the east, all of which discharge to the L2 river with the ultimate discharge to Lake Ellesmere (Te Waihora).

There are a large number of new stormwater facilities being installed in Lincoln within the new subdivisions including:

Te Whariki (Lincoln Land Developments) – Wetlands and Wet Ponds
Liffey Springs – Wetlands
Rosemerryn – Dry infiltration Basins
Flemington – Dry infiltration and discharge to drain.
BHL – To rapid soakage chamber

Figure 12-1
LINCOLN Stormwater - Scheme map
Open larger map: 'Stormwater Scheme'

Figure 12‑2 Scheme Schematic

12.4 Resource Consents

Council hold a global stormwater consent, CRC184822, for Lincoln. Previous resource consents were surrendered. All new subdivisions in Lincoln are required to obtain their own resource consent for construction and operation of their stormwater systems and subdivision and earthworks. Once installations are compliant and approved Council will bring them under global consent. Table 12‑2 shows the stormwater discharge and earthworks permitted by the resource consents for this scheme.

Table 12‑2 Resource Consents

Consent	Description	Location	Date Issued	Expiry Date
CRC111698 Issued - Active	To carry out works in and adjacent to a waterway, to install and maintain associated structures, and clear vegetation, associated with the construction and maintenance of the communal stormwater system	Global consent Lincoln area, bounded by Shands / Tancreds / Raineys / Ellesmere / Collin, LINCOLN	11/10/2011	7/10/2046
CRC111699 Issued - Active	To excavate land to construct stormwater treatment ponds	Global consent Lincoln area, bounded by Shands / Tancreds / Raineys / Ellesmere / Collin, LINCOLN	11/10/2011	7/10/2046
CRC111697 Issued - Active	To divert groundwater and surface water associated with construction and operation of the communal stormwater system	Global consent Lincoln area, bounded by Shands / Tancreds / Raineys / Ellesmere / Collin, LINCOLN	11/10/2011	7/10/2046
CRC184822	To discharge stormwater to land and surface water	Global, area bounded by Shands, Tancreds, Raineys, Ellesmere, Collin Roads, Lincoln	3/5/2018	7/10/2046

It is noted that there are five consents that Council is aware of with developers in this area.

12.5 Integrated Stormwater Management Plan

Environment Canterbury's Land and Water Regional Plan became operative on the 13th December 2018. Under policy 4.16, any reticulated stormwater system for an urban area requires a stormwater management plan. Additionally, from 1 January 2025, operators of reticulated stormwater systems will become responsible for the quality and quantity of all stormwater discharged from the reticulated stormwater system.

An Integrated Stormwater Management Plan (ISMP) was prepared for Lincoln in May 2007 and updated in 2011. This plan is titled 'Lincoln ISMP: Stormwater Management Options Report'. The plan was resubmitted to Environment Canterbury on 12^th March 2011 and consented on the 7^th of October 2011.

12.6 Scheme Assets

Council has a wide variety of stormwater assets within the district. A brief description of the assets within this scheme is provided below:

a) Swale (Grassed) – Is a longitudinal open channel which is lined with grass. The swale both conveys and treats stormwater.

b) Swale (Wetland) – Is a longitudinal open channel which is lined with wetland plant species. The swale both conveys and treats stormwater and is particular useful in areas with high groundwater tables.

c) Reticulated network – Includes pipes, manholes, sumps. The primary purpose of the reticulated network is to collect and convey stormwater. Historically these systems were designed for the 2 year storm event. Today's engineering standards require the piped network to be designed for a 10 year event with overland flow provision for up to the 50 year event.

d) Infiltration basin – is a stormwater management device which is used to store, treat and dispose of stormwater to the ground via soakage.

e) Wetland - is a stormwater management device which is used to attenuate, treat and dispose of stormwater. Discharge from a wetland is to surface water (open drains or streams). Wetlands have high biodiversity value and are best suited in areas where the ground water table is high.

f) Soakholes – Are used to dispose of stormwater to ground in areas where the ground water table is low and soil permeability is high.

g) Open drains – are channels used to convey stormwater. They are cost effective means to convey large volumes of water.

A summary of material and diameter for channels and pipes, where known, is shown below in Figure 12‑3 and Figure 12‑4.

Figure 12‑3 Pipe Material - Lincoln

Figure 12‑4 Pipe Diameter – Lincoln

12.7 Operational Management

The stormwater network is operated and maintained under two maintenance contracts as follows:

Contract 1241: Water Services Contract. Contract is with SICON who undertakes investigations, conditions inspections, proactive and reactive maintenance and minor asset renewals.
Contract 1202: Parks and Reserves Contract. Contract is with SICON who undertakes the maintenance of land scape features related to water services e.g. mowing, gardens etc.

Water quality sampling is completed under an agreement with Food and Health Ltd as required.

12.8 Photos of Main Assets

The photos below provide a summary of the types of assets found within this stormwater management area.

Photo 1: Wetland Swale

Photo 2: Dry Infiltration System

12.9 Rapid Flood Modelling

The Council has undertaken 'Rapid Flood Hazard Assessment' modelling for its main townships. The modelling uses DHI MIKE 21 to simulate rainfall on grid with the outputs processed through ArcGIS producing maps illustrating a range of flood deeps during different rainfall intensities and durations.

The rapid flood assessment has been generated to provide a high level summary of potential flood and ponding areas across the district during extreme rainfall events. The results from this study are not to be used to set floor levels. The results have not been ground tested and therefore are indicative only.

For a 50 year event, Figure 12‑5 shows the predicted flooding for Lincoln.

V4 Lincoln - Rapid Flood Modelling, Lincoln.jpg

Figure 12‑5 Rapid Flood Modelling, Lincoln

12.10 Risk Assessment

A risk assessment has been undertaken for the Lincoln scheme. The key output from the risk assessment is the identification of any extreme and high risks which need to be mitigated. In order to mitigate these risks they have been included and budgeted for in the projects within this LTP. Table 12‑3 details the risk priority rating, Table 12‑4 outlines the risks and the list of key projects is found in Table 12‑9.

Table 12‑3 Risk Priority Rating

Risk Score	Level of Risk	Risk Response
> 50	Extreme	Awareness of the event to be reported to Council. Urgent action to eliminate / mitigate / manage the risk. Document risk and action in the AMP.
35-50	Very High	Risk to be eliminated / mitigated / managed through normal business planning processes with responsibility assigned.
14-35	High	Manage risk using routine procedures.
3.5-14	Moderate	Monitor the risk.
< 3.5	Low	Awareness of the event to be reported to Council. Immediate action required to eliminate / mitigate / manage the risk. Document risk and action in the AMP.

Table 12‑4 Risks - Lincoln

Risk	Action/Project	Year Identified	2014 Risk Rating	2017 Risk Rating	Residual Risk Rating
Higher risk of pollution than anywhere else	Review spill control - buy spill kit	2014	6	6	6
Planting in wetland unsuccessful	Review wetland planting design approaches and maintenance needs	2014	12	2	2
Stormwater system discharges impact on ecology unknown	Invertebrate and Sediment sampling	2014	6	6	6
Stormwater system discharges impact on ecology unknown	Invertebrate and Sediment sampling	2014	6	6	6
Open drain safety - possible drowning	Pipe open drains	2014	7	2	2
Non-consented activities	Renewal of consents	2014	27	27	6

The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.

12.11 Asset Valuation Details

The total replacement value of assets within the Lincoln Stormwater Scheme is $35,921,003 as detailed in Table 12‑5 below.

Table 12‑5 Replacement Value, Lincoln

Asset Class 1	Asset Class 2	Sum of Replacement Value
Stormwater Reticulation	Chamber	$103,743
	Channel	$669,808
	Inlet-Outlet-Point	$700,651
	Lateral	$2,474,453
	Management Device	$6,101,090
	Manhole	$5,016,348
	Pipe	$20,769,152
	Soakhole	$38,622
	Valve	$47,136

12.12 Renewals

The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme are shown by Figure 12‑6 below. The majority of assets requiring renewal are culverts/pipes which occur in the period 2040-2046.

Figure 12‑6 Lincoln Stormwater Renewal Profile

12.13 Critical Assets

The criticality model for Lincoln has been updated for the 2021 AcMP. The methodology of the criticality model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the criticality has been calculated for the reticulation assets. Table 12‑6 and Figure 12‑7 below show the calculated criticality for all of the assets within this scheme that have a recorded known length.

Table 12‑6 Length of Assets per Criticality Level

Criticality Bands		Length (m)
5	Low	62,760
4	Medium-Low	6,826
3	Medium	8,676
2	Medium-High	5,064
1	High	112

Figure 12-7
LINCOLN Stormwater - Criticality map
Open larger map: 'Stormwater Criticality'

12.14 Asset Condition

The asset condition model was run for Lincoln in 2021. The methodology of the model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the model has been calculated for the reticulation assets (particularly pipes). Figure 12‑8 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.

Figure 12-8
LINCOLN Stormwater - Condition map
Open larger map: 'Stormwater Condition'

Table 12‑7 provides a description of the condition rating used within the condition model.

Table 12‑7 Asset Condition Grading

Condition Rating	Grading
1.0	Excellent
2.0	Good
3.0	Moderate
4.0	Poor
5.0+	Fail

12.15 Funding Program

The 10 year budgets are shown by Table 12‑8. Budgets are split into expenditure, renewals, projects and capital projects. Expenditure and renewals have been reported on a district-wide basis in Volume 1.

All figures are ($) not adjusted for CPI “inflation". They are calculated on historical data, and population growth where relevant.

Table 12‑8 Budget Summary

Years	Projects	Capital Projects
2021/2022	$30,000	$20,000
2022/2023	-	$20,000
2023/2024	-	$400,000
2024/2025	-	-
2025/2026	-	-
2026/2027	-	-
2027/2028	-	-
2028/2029	-	-
2029/2030	-	-
2031/2032	-	-
Total	$30,000	$440,000

An explanation of the categories within the budgets are as follows below:

Expenditure consists of operation and maintenance costs;
Renewals are replacement of assets which are nearing or exceeded their useful life;
Projects are investigations, decisions and planning activities which exclude capital works; and
Capital projects are activities involving physical works.

Table 12‑9 Key Projects

Account Label	GL	Description	Year 1($)	Year 2($)	Year 3($)	Years 4 to 10	Funding Split *
Capital Projects	-	New World pipeline	-	-	$300,000	-	TBC
Capital Projects	-	SCADA at Lincoln wetland outlets	$20,000	$20,000	-	-	TBC
Capital Projects	-	Ryelands Weird - Liffey engineering check	$30,000	-	$100,000	-	TBC

* Where LoS refers to Level of Service and G refers to Growth

The list of district wide projects can be found in 5Waters Activity Management Plan: Volume 1.

Discussion on Projects

Projects have been determined based on their:

Relevance to the scheme
Requirement to be completed under legislation
Ability to bring the scheme up to or maintain the Level of Service required under council's Asset Management Policy.

Many projects are jointly funded by more than one scheme and activity. Each scheme pays a pro-rata share only, equivalent to the number of connections.

Discussion on Capital and Projects

Where relevant, Capital (Levels of Service) and Capital (Growth) projects have been included in the scheme financial details.

Levels of Service Projects and growth splits have been provided to ensure the costs of population driven works are clear.

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