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21 Whitecliffs Stormwater Scheme

21.1 Scheme Summary

Description		Quantity
Scheme Area		29.22 ha
Scheme Coverage (as at 1 Jan 2021)	Rating numbers	91
System components	Piped (m)	200
	Swales (m)	120
	Drains (m)	1,667
	Manholes/Inspection Chambers (No.)	0
	Treatment	N/A
	Other	N/A
Value ($)	Replacement Cost	$80,781
Value ($)	Depreciated Replacement Cost	$80,781
Financial	Operator cost (scheduled and reactive maintenance) per connection	$3.58/connection
Planning	Stormwater Management Plan	Updated April 2017
Planning	No. SDC stormwater consents	1
Demand	Mean Annual Rainfall (mm)	900
Demand	10% AEP (10 year) 1hr rainfall depth (mm)	21.8
Sustainability	Sustainable drain management practices	Adopted and Encouraged

21.2 Key Issues

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

Table 21‑1 Whitecliffs Scheme Issues

What's the Problem	What we plan to do
Flooding from upper catchment	Work with the community to agree whether capacity increase of existing system or the development of a flood diversion channel can be funded.

21.3 Overview & History

The Whitecliffs stormwater management area is services by a network of open drains. The system works efficiently requiring minimal maintenance. The Council network discharged onto private property at the end of the network. This drain is steep and subject to erosion.

Figure 21-1
WHITECLIFFS Stormwater - Scheme map
Open larger map: 'Stormwater Scheme'

Figure 21‑2 Scheme Schematic

21.4 Resource Consents

Council have applied for a global consent for the Whitecliffs stormwater network. The application is in progress with ECan.

Table 21-2 Resource Consents

Consent	Description	Location	Date Issued	Expiry Date
CRC186178	To discharge stormwater to surface water from the existing stormwater network of Whitecliffs	Whitecliffs	TBC	TBC

21.5 Integrated Stormwater Management Plan

An Integrated Stormwater Management Plan was prepared for Whitecliffs in April 2017, and submitted to ECan as part of the application for consent CRC186178.

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

A summary of material and diameter for channels and pipes is shown in Figures 21-3 and 21-4 below.

Figure 21‑3 Pipe Material - Whitecliffs

Figure 21‑4 Pipe Diameter - Whitecliffs

21.7 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.

21.8 Photos of Main Assets

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

Photo 1: Typical Open Drain

21.9 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 21‑3 shows the predicted flooding for Whitecliffs.

Figure 21‑5 Rapid Flood Modelling, Whitecliffs

21.10 Risk Assessment

A risk assessment has been undertaken for the Whitecliffs 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 21‑3 details the risk priority rating and Table 21‑4 outlines the risks for this scheme.

Renewal of this consent is budgeted under district projects.

Table 21‑3 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 21‑4 Risks – Whitecliffs

Risk	Action/Project	Year Identified	2014 Risk Rating	2017 Risk Rating	Residual Risk Rating
Non-consented activities	Renewal of consents	2014	27	27	6
Drain scouring	Drain scouring	2017		9	2

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

21.11 Asset Valuation Details

The total replacement value of assets within the Whitecliffs Scheme is $80,781 as detailed in Table 21‑5 below.

Table 21‑5 Replacement Value, Whitecliffs

Asset Class 1	Asset Class 2	Sum of Replacement Value
Stormwater Reticulation	Channel	$80,781

21.12 Renewals

The renewal profile has been taken from the 2019 5 Waters Valuation. There are no renewals scheduled for this scheme.

21.13 Critical Assets

The criticality model for Whitecliffs 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 21‑6 and Figure 21‑6 below shows the calculated criticality for all of the assets within this scheme that have a recorded known length.

Table 21‑6 Length of Assets per Criticality Level

Criticality Bands		Length (m)
5	Low	1,774
4	Medium-Low	4
3	Medium	0
2	Medium-High	0
1	High	0

Figure 21-6
WHITECLIFFS Stormwater - Criticality map
Open larger map: 'Stormwater Criticality'

21.14 Asset Condition

The asset condition model was run for Whitecliffs 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 21‑7 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.

Figure 21-7
WHITECLIFFS Stormwater - Condition map
Open larger map: 'Stormwater Condition'

Table 21‑7 provides a description of the condition rating used within the condition model.

Table 21‑7 Asset Condition Grading

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

21.15 Funding Program

The 10 year budgets are shown by Table 21‑8. 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 21‑8 Budget Summary

Years	Projects	Capital Projects
2021/2022	$5,000	-
2022/2023	-	$40,000
2023/2024	-	-
2024/2025	-	-
2025/2026	-	-
2026/2027	-	-
2027/2028	-	-
2028/2029	-	-
2029/2030	-	-
2031/2032	-	-
Total	$5,000	$40,000

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 21‑9 Key Projects

Account Label	GL	Description	Year 1($)	Year 2($)	Year 3($)	Years 4 to 10	Funding Split *
Capital Projects	-	Culvert upgrade	$5,000	$40,000	-	-	100% LoS

* 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.