Assessment of Water & Sanitary Services...Stormwater Assessment of Water & Sanitary Services Report...

Stormwater

Assessment of Water & Sanitary Services Report 142

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Stormwater


17.0 Introduction Section 126(1)(a) of the Local Government Act 2002 provides that an assessment of water services must set out information about the means by which stormwater is managed within the district. The urban stormwater systems are well described in the Stormwater Asset Management Plan. The urban stormwater systems in the Hauraki District consist of a combination of open drains and piped reticulation networks in the three major towns, (Ngatea, Paeroa and Waihi), and in the smaller townships of Kerepehi and Turua. There is limited reticulation in the settlements of Mackaytown/Karangahake, and Waikino. In Whiritoa the network provides for the disposal of stormwater from the road surface only. On-site stormwater is disposed of by ground soakage, or retention for gradual release at a rate equivalent to the undeveloped ground. There is no piped reticulation in Waitakaruru which is served by the land drainage network of the Western Plains Drainage District. Council is responsible for the maintenance and operation of the piped reticulation in all areas, and for the maintenance of identified Council drains in all areas other than those in private property in Waihi. In the urban areas, the road network owns and maintains the collection sumps and the leads from the sumps to the stormwater pipes or drains. The eventual points of discharge of the stormwater systems are the streams and rivers in the district which are the responsibility of the river schemes of the Regional Council, Environment Waikato. Council holds four Comprehensive Stormwater Discharge Consents from the region. They are based on the geographic areas of Whiritoa, Waihi, Paeroa and the Plains. Council is currently undertaking the production of Stormwater Catchment Management Plans for the Paeroa and Waihi urban areas. These plans are intended to identify the extent and limitations of the existing systems and issues, and to provide strategies for the future development of the systems. The development of Catchment Management Plans for the other urban areas will follow the completion of the initial two plans. Because of the stage of development of the Catchment Management Plans, the public surveys were limited to the urban areas of Whiritoa and Waihi. These areas were identified as potentially having the most pressing issues with the stormwater system. The summary results of the surveys are attached as on under section 9.2.8. The overall result of the surveys was a general “Level of Satisfaction with the Stormwater services” of 58% of those who responded other than “Don’t know or Not Applicable”. The total for “Neither satisfied or dissatisfied” was 24%, and those “Dissatisfied” was 19%.

Stormwater


18.0 Stormwater Communities

18.1 Community Identification The communities identified for the stormwater function are as listed below: • Travelling public • Urban serviced

Stormwater


19.0 Assessment of Stormwater Services

19.1 Travelling Public

19.1.1 Description The travelling public community comprises non residential or residential public travelling through the Hauraki District utilising the district services.

19.1.2 Methods Used to Dispose of Stormwater Road kerb sumps collect runoff from the road surface, and deliver it to the piped stormwater network, which discharges to the receiving waters of a river or stream. In the case of Whiritoa and Waihi, this is solely by gravity to the seafront (in Whiritoa) or the Ohinemuri River (in Waihi). In Paeroa the main outfalls are to the Ohinemuri or Waihou Rivers via floodgated gravity outlets, supplemented by floodpumps when river flood levels prevent outflow. In Ngatea, the outflow to the Piako River is via floodgates and pumps. Kerepehi disposes stormwater by gravity to the land drainage network of the EPDD which is delivered to the Awaiti Canal via floodgates and pumps. Turua stormwater is disposed of via floodgated outlets to the tidal reach of the Waihou River.

19.1.3 Risks Attributable to the Absence of a Reticulated Stormwater Network Not required to be assessed due to this community having a reticulated stormwater network.

19.1.4 Assessment of the Quality and Quantity of Discharged Stormwater Water quality is sampled as a condition of the Comprehensive Stormwater Discharge Consents held by Council. The quantity of stormwater discharge is limited by the capacity of the network. This capacity is provided for in the District Plan which prescribes a level of service equivalent to the 10 year event for residential/commercial zones, and five years for industrial/reserve zones. (District Plan Section 9.3.10.4).

19.1.4.1 Collection and Treatment What type of collection and treatment is provided? Street kerb sumps and direct residential and commercial connections are piped to the reticulated network and discharged to the receiving waters. No treatment of stormwater is undertaken.

Stormwater


19.1.4.2 Operation and Maintenance

How is the system operated and maintained? Regular inspections of open drains for maintenance requirements. A programme of CCTV work to ascertain asset condition as outlined in the AMP is proposed.

19.1.4.3 Treatment Process Effects Are there any detrimental effects from the treatment process, e.g. odour? None.

19.1.4.4 Resource Consents Is there a requirement for the system to have a resource consent and if so, is it valid? Four Comprehensive Stormwater Discharge Consents issued by Environment Waikato are held for the urban stormwater networks in Whiritoa, Waihi Ward, Paeroa Ward, and Plains Ward. Detail is contained in the AMP.

19.1.4.5 System Capacity For Future Demands Is the system capacity adequate for the future planned demands? Capacity is currently being assessed as part of the Catchment Management Plans investigations.

19.1.4.6 Existing System Life Expectancy What is the estimated life of the existing system? The service life of the structures is 50-100 years plus, at which time they will most likely be replaced or upgraded in a similar configuration to the existing. The Hauraki District Council has no current intention of disposing of most of its stormwater assets. Apart from the surface drains, the assets are largely in-ground structures (pipes, manholes, floodgates and pump stations). Generally the parts of the pump station structures above ground are the control shed housing the pump motors and control gear. These components are not logically separable from the remainder of the structure. The one exception to the above is the disposal of the Paeroa Main Drain Pump Station to Environment Waikato.

19.1.5 Current and Estimated Future Demands This is currently being investigated and will be presented in the Catchment Management Plans.

Stormwater


19.1.6 Options to Meet Demands and their Suitability This is currently being investigated and will be presented in the Catchment Management Plans.

19.1.7 Intended Role of the Hauraki District Council in Meeting the Demands Hauraki District Council will continue to be the owner and operator of the urban stormwater network.

19.1.8 Hauraki District Council’s Proposal for Meeting the Demands This is currently being investigated and will be presented in the Catchment Management Plans.

Stormwater


19.2 Urban Serviced

19.2.1 Description Residents in the urban areas of Whiritoa, Waihi, Paeroa, Kerepehi, Turua, and Ngatea form the urban serviced community.

Table 3.2.1.1 – Plan of Hauraki District Council “URBAN SERVICED” community.

19.2.2 Methods Used To Dispose Of Stormwater Typically, stormwater disposal is provided by public reticulation network from the street sumps or private connections to the point of discharge to the receiving water of a river or stream. In the case of Whiritoa and Waihi, this is solely by gravity to the seafront (in Whiritoa) or the Ohinemuri River (in Waihi). In Paeroa the main outfalls are to the Ohinemuri or Waihou Rivers via floodgated gravity outlets, supplemented by floodpumps when river flood levels prevent outflow. In Ngatea, the outflow to the Piako River is via floodgates and pumps. Kerepehi disposes stormwater by gravity to the land drainage network of the EPDD which is delivered to the Awaiti Canal via floodgates and pumps. Turua stormwater is disposed of via floodgated outlets to the tidal reach of the Waihou River. In Whiritoa there is no provision for disposal of stormwater from the residential lots within the reticulated network. The pipe system is solely for the disposal of runoff from the road network.

Paeroa

Waihi

Whiritoa

Turua

Ngatea

Kerepehi

Stormwater


The method of disposal from residential lots is a combination of retention and ground soakage, depending on the soil conditions. Where soils are suitable for soakage, a soak pit of the required capacity is constructed to dissipate the runoff from developed areas at a rate dictated by the soil permeability. Where soil conditions are less permeable, a retention tank system may be employed to provide for interim storage and later release to ground. The principle of ‘hydraulic neutrality’ is employed, such that the increase in storm runoff due to development of buildings and paved areas does not exceed the rate of runoff from the undeveloped area. Generally retention tanks with reduced discharge lines are used. Often the detention volume is accommodated in the top section of a tank used to collect rain water for domestic use. In Waihi there is pressure on the reticulated network to accommodate flows from infill and new development. Where ground conditions are suitable, soakage is employed. Methods of retention are actively encouraged to reduce runoff rates. The incorporation of grassed swales in road berms is used to reduce runoff rates and to improve quality by providing a longer path over grass which acts as a filter. In Paeroa, Ngatea, Kerepehi and Turua, ground conditions are generally unsuited to soakage, so the discharge of stormwater to the reticulated network is accommodated. The discharge points to the receiving waters are monitored in accordance with the Stormwater discharge consents held by Council. Refer to the Stormwater Asset Management Plan for details. The floodgates and pump stations discharging to the Ohinemuri, Waihou and Piako Rivers are assets of the Waihou Valley and Piako River Schemes of the Regional Council (Environment Waikato). The structures have been built by the river schemes, are owned, maintained, and will be replaced by the Regional Council. Council’s responsibilities for these structures is limited to shared inspections, clearance of blockages, and in the case of the pumps, the payment of energy accounts for their running time, and the maintenance of the screens clear of weed during operation. The pumps have automatic start and stop levels, set in conjunction with the Region, reflecting ground levels within the catchment.

Stormwater


WHIRITOA STORMWATER NETWORK

Stormwater


WAIHI STORMWATER NETWORK

Stormwater


PAEROA STORMWATER NETWORK

Stormwater


NGATEA STORMWATER NETWORK

Stormwater


KEREPEHI STORMWATER NETWORK

TURUA STORMWATER NETWORK Refer to appendix B of the HDC Stormwater Asset Management Plan for detailed descriptions of the urban reticulation networks.

Stormwater


19.2.3 Risks Attributable to the Absence of a Reticulated

Stormwater Network • Not required to be assessed due to this community having a reticulated

stormwater network.

19.2.4 Assessment of the Quality and Quantity of Discharged Stormwater

19.2.4.1 Collection and Treatment What type of collection and treatment is provided? Street kerb sumps and direct residential and commercial connections are piped to the reticulated network and discharged to the receiving waters. No treatment of stormwater is undertaken.

19.2.4.2 Operation and Maintenance How is the system operated and maintained? Regular inspections of open drains for maintenance requirements. A programme of CCTV work to ascertain asset condition as outlined in the AMP is proposed.

19.2.4.3 Treatment Process Effects Are there any detrimental effects from the treatment process, e.g. odour? None.

19.2.4.4 Resource Consents

Is there a requirement for the system to have a resource consent and if so, is it valid? Four Comprehensive Stormwater Discharge Consents issued by Environment Waikato are held for the urban stormwater networks in Whiritoa, Waihi Ward, Paeroa Ward, and Plains Ward. Detail is contained in the AMP.

19.2.4.5 System Capacity for Future Demands Is the system capacity adequate for the future planned demands? Capacity is currently being assessed as part of the Catchment Management Plans investigations.

19.2.4.6 Existing System Life Expectancy What is the estimated life of the existing system? The Hauraki District Council has no current intention of disposing of most of its stormwater assets. Apart from the surface drains, the assets are largely in-ground structures (pipes, manholes, floodgates and pump stations). Generally

Stormwater


the parts of the pump station structures above ground are the control shed housing the pump motors and control gear. These components are not logically separable from the remainder of the structure. The service life of the structures is 50-100 years plus, at which time they will most likely be replaced or upgraded in a similar configuration to the existing. The one exception to the above is the disposal of the Paeroa Main Drain Pump Station to Environment Waikato.

19.2.5 Current and Estimated Future Demands This is currently being investigated and will be presented in the Catchment Management Plans.

19.2.6 Options to Meet Demands and their Suitability This is currently being investigated and will be presented in the Catchment Management Plans.

19.2.7 Intended Role of the Hauraki District Council in Meeting the Demands Hauraki District Council will continue to be the owner and operator of the urban stormwater network.

19.2.8 Hauraki District Council’s Proposal for Meeting the Demands This is currently being investigated and will be presented in the Catchment Management Plans.

Risk Management for Stormwater Types of Medium Risk Impact Probability ConsequencesSubsidence/Land movement 3 4 12 Development contribution/planning/customer demand/Land Dev./ Design/ Runoff co-efficient/Loss of ponding/Flooding of properties/Urbanisation etc 3 5 15 Loss of Knowledge 3 5 15 Rainfall Intensity 4 5 20 Open drains 3 4 12 Pollution/contamination 3 3 9

SUMMARY OF SURVEY RESULTS The returns from the newspaper questionnaire and the telephone surveys included with the water and wastewater surveys in Whiritoa and Waihi are attached.

Stormwater


The communities of Whiritoa and Waihi were surveyed selectively for the following reasons: Whiritoa has a reticulated network which provides for the disposal of stormwater from the road surface only. On site disposal and/or retention is required for the residential lots. Waihi has a network of open drains and piped systems which discharge to the receiving waters of the Ohinemuri River and its tributaries. There are no flood protection assets (stopbanks, floodgates, and pump stations) which control the discharge to the natural streams. Disposal of stormwater from the developed parts of Waihi is by a combination of on site disposal, some retention, and free discharge to the network. The maintenance of open drains in private property in Waihi is the responsibility of the landowner. This is not the case in the remainder of the District where Council maintains an extensive network of land drains in the rural drainage districts of the Plains and Paeroa Wards, and in the urban area of Paeroa. The graphs of the survey results follow. The overall level of satisfaction with the stormwater services is: Satisfied 40% Neither satisfied nor dissatisfied 28% Dissatisfied 16% Don’t know/not applicable 16%

Stormwater


AGE

46 28 15 11

47 19 15 19

26 43 14 17

48 28 16 8

32 23 19 26

0% 20% 40% 60% 80% 100%

% of Respondents

60 or older

50 to 59

40 to 49

30 to 39

18 to 29

Age

Satisfaction with the Stormwater Services

Satisfied Neither Dissatisfied Don't know/Not applicable

ETHNICITY

25 27 27 21

42 29 14 15

0% 20% 40% 60% 80% 100%

% of Respondents

Maori

Non-Maori

Ethn

icity



Stormwater


WARD-LOCATION

42 33 9 16

28 28 9 35

40 27 29 4

28 30 12 30

46 26 15 13

41 32 6 21

0% 20% 40% 60% 80% 100%

% of Respondents

Plains - Town

Plains - Rural

Paeroa - Town

Paeroa - Rural

Waihi - Town

Waihi - Rural

Loca

tion



WARD

39 32 9 20

36 28 24 12

45 27 13 15

0% 20% 40% 60% 80% 100%

% of Respondents

Plains

Paeroa

Waihi

War

d

Satisfaction with Stormwater Services


Stormwater


TOWN-RURAL

33 30 9 28

43 28 18 11

0% 20% 40% 60% 80% 100%

% of Respondents

Rural

Town/Settlement

Loca

tion



Stormwater


20.0 Conclusion This report is the first of the Assessment of Water and Sanitary Services report for Hauraki District Council. Considerable information has been collected, and there is considerable information to be collected as time allows for prior to the 2006 Long Term Council Community Plan. Further information on the water, wastewater, stormwater, cemeteries, public toilets assets can be found in the asset management plans available by calling 07 862 8609 or 0800 734 834 (from within the District).

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