SECTION 6 STORMWATER AND LAND DRAINAGE Final Version, Approved September 2003
Section 6 and Land Drainage Contents 6.1 PERFORMANCE STANDARDS... 2 6.1.1 General... 2 6.2 MEANS OF COMPLIANCE... 3 6.2.1 General... 3 6.2.2 Resource Consents... 4 6.2.3 Gravity Mains Layout... 4 6.2.4 Open Drainage... 5 6.2.5 Manholes... 5 6.2.6 Catchpits... 5 6.2.7 Super Modified Catchpits... 6 6.2.8 Service Connections... 6 6.2.9 Bedding and Protection... 6 6.2.10 Pipe Materials... 7 6.2.11 Connection to Council's System... 7 6.2.12 Testing and Acceptance... 7 6.2.13 Specific Ward Requirements Table 6.11... 8 Final Version, Approved September 2003 Page 2
6.1 Performance Standards 6.1.1 General A stormwater reticulation and disposal system that can be economically maintained and is adequate to safeguard people from injury or illness and to protect property and the natural environment from damage caused by surface water shall be provided. Council with input from Community Boards has developed and agreed on the Levels of Service to be provided for each stormwater scheme, which are within the Council s Areas of Benefit. All urban areas shall discharge as specified by the Levels of Service for each community (refer to table 6.11). generated by a property is required to be disposed of within the boundary of that property unless there is a sufficient capacity within the network and it is specifically authorised by Council s Representative disposal through soak-away pits is permitted provided the applicant can demonstrate that - they can be economically maintained, - the long-term soakage capacity is adequate 6.1.1.5 A stormwater and disposal system which incorporates detention ponds to minimise the impact of surface water runoff is permissible were authorised in Ward Specific Requirements (refer table 6.11), provided alternative arrangements do not satisfy the requirements and that these details are included in the resource consent applications. 6.1.1.6 Detention Basins are to be self-draining without the use of pumping equipment and are not permitted to permanently hold water or be used as a water feature. Detention basins are to be adequately landscaped and constructed to be economically maintained unless specifically approved. 6.1.1.7 Retention Basins are not permitted unless demonstrated to be absolutely necessary and shall be constructed with a controlled engineering outflow. Retention basins are to be adequately landscaped and constructed to be economically maintained. 6.1.1.8 All stormwater reticulation and disposal systems are to be constructed to convey surface water to an approved outfall, by means of gravity flow where possible. 6.1.1.9 Where pipes or lined channels are used the systems shall avoid the likelihood of blockages, leakage, erosion, penetration by roots or the entry of groundwater and shall be located to avoid the likelihood of superimposed loads or normal ground movements. 6.1.1.10 Self-cleansing velocities (minimum of 0.65m/s) are to be maintained within reticulation systems. Final Version, Approved September 2003 Page 3
6.1.1.11 Surface flows on carriageways are to be controlled in order to enable safe and comfortable vehicle and pedestrian access across and along road reserves. 6.1.1.12 systems shall be designed and installed to cater for full development in the catchment upstream of the subject site. Downstream effects are to be fully addressed. 6.1.1.13 Where any public main passes through privately owned residential, commercial or industrial complexes, then the main should be installed outside of the building envelope. If this is not achievable then an easement shall be provided in favour of the Thames- Coromandel District Council to allow access and repairs to the main at all times. 6.2 Means of Compliance 6.2.1 General 6.2.1.1 All primary land drainage systems shall be piped (where required by the Specific Ward requirements) unless otherwise approved, or the runoff constitutes an existing natural perennial stream. 6.2.1.2 The design events for which the stormwater systems shall be designed are specified in Table 6.11. 6.2.1.3 The stormwater system shall be constructed to contain the 2% AEP flood level with the freeboard to habitable floor as in Table 6.1: Table 6.1 Catchment Minimum Freeboard Less than 1 hectare 150mm 1 to 5 hectares 200mm 5 to 20 hectares 300mm Greater than 50 hectares 500mm 6.2.1.3 The design of the stormwater system shall generally be in accordance with the runoffs derived from the Rational Method for catchments less than 500 hectares and by the Modified Rational Method for catchments greater than 500 hectares. Other methods may be used to verify the results from the Modified Rational Method. Management Plans for some areas have been prepared. Rainfall data and design parameters are to be consistent with these plans. Refer to the Appendices for the Plans. 6.2.1.4 Systems shall be designed to cater for the peak design flow, without surcharge, based on a Colebrook - White pipe roughness coefficient Ks = 1.50 for pipes up to and including 1000mm diameter: and Ks = 0.60 for larger piped systems. 6.2.1.5 Lined channels shall be designed with the following Mannings n as in Table 6.2: Final Version, Approved September 2003 Page 4
Table 6.2 Lining Material Mannings n Dressed timber, joints flush 0.011 Sawn timber, joints uneven 0.014 Cement plaster 0.011 Concrete, steel trowled 0.012 Concrete, timber forms, unfinished 0.014 Untreated gunite 0.015-0.017 Brickwork or dressed masonry 0.014 Rubble set in cement 0.017 Earth, smooth, no weeds 0.020 Earth, some stones and weeds 0.025 Natural river channels: 0.025-0.030 Clean and straight Winding, with pools and shoals 0.033-0.040 Very weedy, winding and overgrown 0.075-0.150 6.2.2 Resource Consents 6.2.2.1 Resource Consents from may be required from Environment Waikato for the diversion and or discharge of stormwater. The applicant is responsible for making the necessary application and obtaining such Consents before the District Council will accept the completed works. 6.2.2.2 All developments within catchments where the Thames-Coromandel District Council have discharge resource consents will need to comply with any of the conditions that may apply to the proposed drainage system. In addition, any Catchment Management Plans recommendations must be adhered to. 6.2.3 Gravity Mains Layout 6.2.3.1 The cover to all pipes from finished ground level shall be a minimum of 600mm or as per the pipe manufactures specifications, which ever is the greater. Where this minimum cover cannot be achieved an approved concrete cover slab or other approved measures may be authorised by the Councils Representative. 6.2.3.2 All inlets (other than service connections) to the primary piped reticulation in urban areas where the pipe is greater than 450mm shall be either through a sump, or a headwall with a vertically grating. Outlets may be through a headwall with a hinged horizontal grating and appropriate energy dissipation for the outlet so that no soil erosion will take place. Outlet grates shall be hinged in urban areas where the pipe is greater than 450mm to allow flow pressures to open if the grates become blocked. Care is needed to ensure flows aren t going to surcharge upstream of blocked grates. 6.2.3.3 Flood gates shall be provided on the downstream end of all pipes discharging into the ocean, tidal channels or natural waterways where backflow is a potential problem, or with 600mm diameter or greater. Final Version, Approved September 2003 Page 5
6.2.3.4 Secondary overland flowpaths shall generally be aligned alongside the road network and reserve areas. Where such flowpaths are required to cross private property an appropriate easement in favour of the Council shall be provided to ensure its protection. It is preferred that secondary flowpaths on private property be on accessways. 6.2.3.5 Primary stormwater shall be piped across any footpath or berm. Unless specifically authorised. No building over primary pipe systems will be permitted. 6.2.4 Open Drainage Systems 6.2.4.1 Where natural open stream systems or formed drainage channels are to be incorporated in the land drainage system, they shall be of sufficient width to contain the full design flood flow together with the freeboard given in Table 6.1 and to ensure protection from unacceptable scouring. Sufficient access for maintenance shall be provided. 6.2.4.2 Open drainage systems may be subject to Environment Waikato resource consents. 6.2.4.3 The flow characteristics of natural open stream systems shall be based on the likely long term stream condition. Consideration shall be given to the density and suitability of vegetation and take due account of blockages under peak flood conditions. 6.2.5 Manholes 6.2.5.1 Accessible inspection chambers are to be provided at all changes of grade, direction and pipe size, and shall not exceed 90m spacing for pipelines up to 1000mm diameter, above which spacings may extend to 200m. Each branch line shall join a main line at a manhole junction. 6.2.5.2 Manholes shall be located on all drainage lines and at the end of all terminal lines greater than 50m in length. 6.2.5.3 All stormwater manholes shall be constructed as detailed on Drawings 600-303A. 6.2.5.4 Outlet pipes from manholes shall have a soffit level 20mm lower than that of the lowest incoming line, plus 5mm per 10 degrees of angle change between the two lines. Specific hydraulic design may be required for pipes where head losses are critical. 6.2.6 Catch-pits 6.2.6.1 Catch-pits (including back entry catch-pits) shall be constructed as on Drawings 600-321 to 600-324 and 600-326. Single and double catch-pits shall only be installed. Catchpits shall be fitted with grates and frames. 6.2.6.2 The maximum capacity of a single sump shall be taken as 30l/s and that of a double sump as 50l/s. 6.2.6.3 Catch-pits shall be designed to take at least the 20% AEP design runoff. 6.2.6.4 Catch-pits shall generally be located as follows: Final Version, Approved September 2003 Page 6
- On roads having a carriageway width up to and including 10m, a maximum channel run of 125m and on all roads with carriageways greater than 10m shall have a maximum channel run of 90m. - At all valley positions a double side entry sump is required. - As required for catchment areas. 6.2.6.5 Catch-pits shall be connected to the primary stormwater system by a pipe of at least 225mm diameter to an adjacent manhole (if the adjacent stormwater system is of greater size than 600mm diameter and the manhole is not conveniently located, the sump lead may be saddled directly to the pipe). 6.2.7 Super Modified Catchpits Super Modified Catchpits shall be installed where the gradient exceeds 1 in 20 or where there is a high possibility that a double catchpit is unable to manage the inlet flows equivalent to a 20% AEP event. (Refer Plan No. 600-321C) 6.2.8 Service Connections 6.2.8.1 Where service connections are approved, each residential lot shall include a lateral of at least 100mm diameter, which shall be extended from the main reticulation system to terminate at a minimum distance of 1.0m within the main body of the lot. Larger diameter service connections may be required for multi-unit or industrial lots. 6.2.8.2 Service connections shall be laid true to line and grade at right angles to the main line in an acceptable manner. 6.2.8.3 The connection point of the laterals to each lot shall be sited, when possible, in a location that will not reduce the building area available. This will generally be approximately 1.0m from a side boundary. 6.2.8.4 The connection point of the laterals to each lot shall be sited, when possible, on the low side of proposed sites having a cross fall greater than 1.0m. 6.2.8.5 Service connections shall be brought to between 0.6m and 1.2m of the final ground surface. Connections should be marked with stakes either tied with detector tape or stakes in contact with end caps, or with an identified concrete slab. 6.2.8.6 When the line is deeper than 4m, service connections will not be permitted directly to the line. 6.2.9 Bedding and Protection The pipe bedding shall be in accordance with the Concrete Pipe Selection & Installation Guide By The Concrete Pipe Association of Australasia and the manufactures guide to installation of PVC pipes. 6.2.9.1 The pipe bedding shall be in accordance with the Concrete Pipe Selection & Installation Guide By The Concrete Pipe Association of Australia and the manufactures guide to installation of PVC pipes. Final Version, Approved September 2003 Page 7
6.2.9.2 All drainage lines shall be designed and constructed to withstand all the likely loads they will be subject to during the life of the system. The load carrying capacity in relation to their installation conditions shall be calculated in accordance with NZS/AS 3725:1989 Loads on Buried Concrete Pipes and AS 2566:1998 Buried Flexible Pipelines, where appropriate. 6.2.9.3 For drainage lines laid at grades steeper than 10% (including service connections) the bedding and surround material shall be of a low-grade (7Mpa) weak concrete. For lines exceeding 20% in grade, anchor blocks located at pipe joints, not exceeding 6m spacing. 6.2.9.4 Where public drains are located within rights of way or private access legs, all other utility services such as power, telephone and gas shall be located 300mm clear of the pipe. 6.2.10 Pipe Materials Land drainage reticulation construction material shall be as defined in the Council s approved Materials Schedule. All public stormwater pipes shall have a minimum diameter of 300mm with the exception of catch-pit leads which may be 225mm. All joints on pipes and fittings less than 1050mm in diameter shall be factory made flexible type complying with the Council s approved Materials Schedule. 6.2.11 Connection To Council s System Only an approved contractor under the supervision of the Councils operators may make connections to Councils system with the appropriate approvals in place. 6.2.12 Testing and Acceptance Prior to acceptance of the completed land drainage system, the applicant s representative shall have supplied the Council with As Built drawings as per the Section 1 of this document and shall include any overland flowpaths and open channel systems together with certification. 6.2.12.2 The tests for drainage systems shall be a visual inspection of manholes and lines, inspection of secondary flowpaths, and a check on open water courses at the upstream and downstream boundaries. 6.2.12.3 When requested the Council may require each manhole structure to be tested in accordance with NZS 4452. 6.2.12.4 Flooding the channel shall test the effectiveness of the channels and sump. Any ponding of water in the channel greater than 3mm under a 3m straight edge shall render the work unacceptable. 6.2.13 Specific Ward Requirements Table 6.11 WARD Coromandel / Colville COMMUNITY FACILITY REQUIREMENT Final Version, Approved September 2003 Page 8
Coromandel Urban Properties Retention Ponds Open Water Courses Kerb Discharge Existing New Discharges Proposed Design generated on a property will be disposed of in a managed manner and authorisation of disposal will be required in each case. The on-site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Permitted. Any pond used as a retention pond or water feature will be subject to Management Plan approval. Permitted, subject to Design Constraints and Management Plan approval Not permitted unless otherwise authorised Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas capable of carrying a 5 year (20% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of carrying a 50 year (2% AEP) to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 9
WARD Thames COMMUNITY FUNCTION REQUIREMENT Thames Properties Retention Ponds Open Water Courses Kerb Discharge Existing New Discharges Proposed Design Constraints generated on a property will be disposed of in a managed manner and authorisation of disposal will be required in each case. The on-site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Permitted. Any pond used as a retention pond or water feature will be subject to Management Plan approval. Permitted, subject to Design Constraints and Management Plan approval Not permitted unless otherwise authorised Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas (other than Thames Central area) capable of carrying a 5 year (20% AEP) rain event Primary piped system in Thames Central Area (Refer Thames Central Area Plan) capable of carrying a 20 year (5% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of carrying a 50 year (2% AEP) to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 10
WARD Whangamata COMMUNITY FUNCTION REQUIREMENT Whangamata Properties Retention Treatment Ponds Open Courses Water Kerb Discharge Existing New Discharges Proposed Design Constraints generated by a property is to be disposed of within the boundary of that property unless otherwise authorised by the Council. The on site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Preferred for treatment. Not permitted to permanently hold water or be used as a water feature. Retention ponds to be self-draining. Subject to Management Plan approval. Permitted as provides some treatment, subject to Design Constraints and Management Plan approval. Not permitted unless otherwise authorised. Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas capable of carrying a 10 year (10% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of providing some treatment and carrying a 50 year (2% AEP) rain event to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 11
WARD Tairua/Pauanui COMMUNITY FUNCTION REQUIREMENT Pauanui Properties Retention Ponds Open Water Courses Kerb Discharge Existing New Discharges Proposed Design Constraints The strategy in Pauanui is to re-charge the water aquifer; hence stormwater generated by a property is to be disposed of within the boundary of that property unless otherwise authorised by the Council s Representative. The on-site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Permitted. Not permitted to permanently hold water or used as a water feature. Retention ponds to be self-draining. All ponds will be subject to Management Plan approval. Permitted, subject to Design Constraints and Management Plan approval. Not permitted without specific authorisation. Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas capable of carrying a 5 year (20% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of carrying a 50 year (2% AEP) to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 12
Tairua Properties Retention Ponds Open Water Courses Kerb Discharge Existing New Discharges Proposed Design Constraints generated by a property is to be disposed of within the boundary of that property unless otherwise authorised by the Council s Representative. The on-site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Permitted. Not permitted to permanently hold water or used as a water feature. Retention ponds to be self-draining. All ponds will be subject to Management Plan approval. Permitted, subject to Design Constraints and Management Plan approval. Not permitted without specific authorisation. Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas capable of carrying a 5 year (20% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of carrying a 50 year (2% AEP) to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 13
WARD Mercury Bay COMMUNITY FUNCTION REQUIREMENT Whitianga Matarangi Hahei Cooks Beach All Ward urban areas Properties Retention Ponds Open Water Courses Kerb Discharge Existing New Discharges Proposed Design Constraints generated by a property is to be disposed of within the boundary of that property unless otherwise authorised by the Council s Representative. The on-site system must be capable of carrying a 10 year (10% AEP) 10 minute rain event and must be maintainable. Permitted. Not permitted to permanently hold water or used as a water feature. Retention ponds to be self-draining. All ponds are subject to Management Plan approval. Permitted, subject to Design Constraints and Management Plan approval. Not permitted unless otherwise authorised Conditional on existing systems capacity and resource consent conditions. Subject to meeting Council s requirements relating to resource consent conditions. Primary piped system in all urban areas capable of carrying a 5 year (20% AEP) rain event Culverts in all areas capable of carrying a 20 year (5% AEP) rain event Open channels and overland flow-path capable of carrying a 50 year (2% AEP) to ensure that such surface water shall not enter buildings. Bridges capable of withstanding a 100 year (1% AEP) rain event. Final Version, Approved September 2003 Page 14