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Infrastructure Development Code

DS-6.4 Design

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City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:

    1. Consistency with any relevant structure or urban growth plan; and

    2. It is compatible with the design and construction of the existing wastewater network;

  2. Each wastewater management system shall be designed and constructed to ensure:

    1. All components of the wastewater management system shall be pre-approved by the Council and provide for an asset life that is suitable for its intended purpose;

    2. Gravity is used as the method of reticulation unless pump stations have been pre-approved by the Council;

    3. The upstream catchment is provided for and the downstream receiving network has the capacity and capability to cater for the design scenario; 

(Note: For the purpose of assessing this provision the downstream connection point shall be the nearest trunk sewer pipeline or receiving manhole of a pump station);

  1. The wastewater management system shall utilise a network of underground pipes and pump stations as its primary method of conveyance;

The following shall apply:

  1. Unless otherwise approved by Council, the design of the wastewater system shall be in accordance with the IDC but may be supplemented by the documents noted in DS-6 Apx A.1 General.
  2. A computer modelling system approved by Council may also be utilised.

Detailed design shall be required at the time of Development Works Approval. Where no Development Works Approval is required, Council approval shall be obtained at a time required by Council and before the construction of the system.

DS-6.4.1   Calculation of Flows

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:

  2. The following minimum peak hourly flow rates are achieved:

    1. 0.61 litres / second / hectare for Residential Zones;

    2. 0.7 litres / second / hectare for Commercial and Industrial zones.

The following shall apply:

  1. Wastewater flows are a function of water consumption, infiltration and direct entry of stormwater, which in turn are a function of the age of the system and the quality of maintenance. The wastewater system shall be designed to eliminate intrusion of stormwater & groundwater.
  2. Where part or all of the catchment is serviced or will be serviced by a trunk main to be constructed at a later date, Council may agree to this area being excluded from the calculation. The flow from all portions of the upper catchment within the Tauranga City boundary shall be calculated assuming full development to the zones potential.
  3. In residential areas, the wastewater system shall be designed and constructed using the following parameters:
    1. Population density of 50 people/ha.
    2. Average dry weather flow of 210L/person/day and a dry weather diurnal peak factor of 2.5.
    3. Dilution/infiltration factor of 2 for wet weather.
    4. Peak hourly flow 0.61 L/sec/ha.
  4. For design populations of 1000 people or more, a reduced peaking factor may be discussed and agreed with Council.
  5. In industrial or commercial areas, the wastewater system shall be designed using a discharge rate of 0.7 L/sec/hectare.
Explanatory Note:
These figures include both normal wastewater and trade wastes and include a peaking factor of 5 times average daily water flow (ADWF).
  1. Notwithstanding the above, provision for trade waste shall be made by arrangement with the Council and shall be subject to the provisions of the appropriate Trade Waste Bylaw. The industry type will not necessarily coincide with the zoning classification shown in the City Plan, but the zoning, particularly where effluent discharge is a performance standard, may be used to indicate the minimum design flow where more detailed information is not available.
  2. It may be desirable to provide additional capacity if the developer wishes to widen the range of industries to be located in a development area. However the capacity of the existing receiving facility may be a controlling factor and the final decision will rest with Council.
  3. The design of wastewater disposal systems for "wet" industries (very heavy water users) shall be based on the specific requirements for that industry.
  4. For commercial flows refer to DS-1 - Apx A.1 General.

DS-6.4.2   Hydraulic Design

The following shall apply:

  1. The hydraulic design of the system shall be designed such that maximum design flows can be accommodated without surcharging the pipe network.
  2. The hydraulic design of wastewater pipelines shall be based on tables for the hydraulic design of sewers and pipelines or on graphs or other representation of the same methods based on the Colebrook White or Manning's Formulae.
  3. The pipe roughness coefficient Ks used in the design shall be as shown in Table 6.1 Wastewater Pipe Roughness Coefficients

Table 6.1: Wastewater Pipe Roughness Coefficients

Material Colebrook White co-efficent Mannings roughness co-efficent
PVC-U 0.6 0.011
PE 0.6 0.011
GRP 0.6 0.011
Cement Lining 1.5 0.012
PE or Epoxy Lining 0.6 0.011

DS-6.4.3   Pipe Flow Velocity

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:

  2. The following pipe flow velocities are met:

    1. Maximum velocity: 3.0 metres / second for peak wet weather flow;

    2. Minimum velocity: 0.75 metres / second.

Where a steep grade that will cause a velocity greater than that specified is unavoidable, refer to the Water Services Association of Australia : Sewerage Code of Australia : WSA 02 – 2002 for precautions and design procedures.


Definitions in this section

City plan

Council

Design

Developer

Development works approval

IDC

Person

Stormwater

Wastewater

 

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