SuDS · Water Quality Calculator
SuDS Water Quality Treatment Device Calculator
Assess SuDS water quality treatment options using the SuDS Manual (C753) Simple Index Approach and generate an indicative treatment train from certified SPEL systems.
The SPEL SuDS Water Quality Treatment Device Calculator is a practical tool for engineers, designers and specifiers assessing surface water treatment requirements.
Enter the site Pollution Hazard Index risk level, catchment area and proposed treatment requirements to generate an indicative treatment train using SPEL water quality treatment systems.
The calculator is intended to support engineering assessment and product selection. Final system design, product sizing, hydraulic performance, site suitability and regulatory compliance must be independently checked before specification or installation.
SuDS Manual C753
Based on the Simple Index Approach.
Certified Treatment Solutions
Select from SPEL water quality treatment systems.
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SPEL Products
SUDs Water Quality – Treatment Device Calculator
This calculator helps engineers and specifiers to generate a compliant and certified treatment train in line with the SUDs manual (C753) ‘simple index approach’ SIA.
1 Site & treatment inputs
Enter a positive number of square metres.
Enter a positive flow rate in litres per second.
2 Generated treatment train
Sizing basis: each device is sized to the smallest model whose certified capacity meets or exceeds the site demand. Confirm against the modelled peak flow before finalising.
Important design notice
This calculator is provided as an indicative engineering aid only and does not replace professional engineering judgement or project-specific design.
Results depend on the accuracy and completeness of the information entered by the user. Incorrect, incomplete or inappropriate inputs may result in incorrect or unsuitable outputs.
All calculations, treatment selections, product sizes and specifications generated by this calculator must be independently reviewed and confirmed by a suitably qualified engineer and a SPEL Products technical representative before they are relied upon for specification, procurement, installation or construction.
SuDS Design Guidance & Help Notes
Practical guidance to help engineers and specifiers understand SPEL treatment options for different Pollution Hazard Index risk levels and treatment requirements.
Use the sections below to compare treatment systems and understand how SPEL products can form part of a SuDS water quality treatment train.
SPEL Smartceptor® Hydrodynamic Vortex Separator
The SPEL Smartceptor features a compact vertical design, making it particularly suitable where installation space is limited.
Its small footprint allows effective surface water treatment to be incorporated into constrained sites while maintaining convenient access for inspection and maintenance.
The SPEL Smartceptor can meet the Low Risk Pollution Hazard Index mitigation requirement within a single, offsite-built treatment unit, subject to appropriate selection and sizing.
Key benefits:
- Compact vertical design
- Small installation footprint
- Accessible for inspection and maintenance
- Offsite-built treatment unit
- Suitable for many space-constrained sites
SPEL ESR Treatment System
The SPEL ESR Treatment System is a horizontal water treatment device available in bypass and full-flow configurations and across a wide range of model sizes.
Its horizontal configuration can be particularly useful where a relatively shallow excavation is preferred.
The system also provides substantial hydrocarbon and silt storage capacity, helping to increase storage between maintenance events while supporting effective pollutant treatment.
The SPEL ESR Treatment System exceeds the Low Risk Pollution Hazard Index mitigation requirement within a single, offsite-built horizontal unit, subject to appropriate selection and sizing.
Key benefits:
- Horizontal installation
- Wide range of model sizes
- Available as bypass or full flow
- High hydrocarbon storage capacity
- High silt storage capacity
- Offsite-built treatment unit
Low Risk Pollution Hazard Index Areas
For low-risk sites, either a SPEL Smartceptor® Hydrodynamic Vortex Separator or a SPEL ESR Treatment System can provide the required mitigation within a single treatment device, subject to project-specific assessment and appropriate sizing.
Which solution should I consider?
Choose Smartceptor where space is limited
The compact vertical configuration can make Smartceptor particularly suitable where available installation footprint is restricted.
Choose ESR where storage capacity or shallow excavation is important
The horizontal ESR range provides substantial hydrocarbon and silt storage and a wide choice of model sizes.
Need help selecting a treatment device?
Every project is different. Speak to the SPEL technical team to discuss the proposed application, hydraulic requirements and treatment objectives.
Medium Risk Pollution Hazard Index Areas
Medium-risk sites require a higher level of surface water treatment than low-risk applications.
The most appropriate treatment solution will depend on the pollution risk, site characteristics, hydraulic design and potential for hydrocarbon spills.
Recommended SPEL Solution for Medium SuDS Risk
For many medium-risk applications, the SPEL ESR Treatment System is the preferred SPEL solution because the required mitigation can be achieved within a single below-ground treatment device, subject to appropriate sizing and project-specific design checks.
The SPEL ESR Treatment System is also certified to BS EN 858.
Using a single treatment device can simplify the treatment train, reduce the number of below-ground components and potentially simplify installation and ongoing maintenance.
SPELBasin
The SPELBasin can also achieve the required medium-risk mitigation within a single device, subject to appropriate selection and project-specific assessment.
Where expected pollutant loads are high, or where there is an increased likelihood of an oil or hydrocarbon spill, an ESR Treatment System should be considered because of its hydrocarbon and silt storage capacity and BS EN 858 certification.
Using Smartceptor for Medium SuDS Risk
Where a SPEL Smartceptor is selected as the primary treatment device for a medium-risk application, an additional downstream treatment stage will normally be required to achieve the required overall mitigation.
For this reason, an ESR Treatment System or SPELBasin will often provide a simpler single-device treatment solution for medium-risk sites.
Final selection should be based on the specific site design, pollution risk and hydraulic requirements.
Treatment Train Design for High SuDS Risk
High Pollution Hazard Index applications will often require more than one treatment stage to achieve the required overall mitigation.
The order of treatment devices can therefore have a significant effect on the calculated treatment performance of the complete treatment train.
Under the SuDS Manual Simple Index Approach, the effectiveness credited to subsequent treatment stages is reduced compared with the first stage.
For this reason, where a high-mitigation treatment device such as a SPEL ESR Treatment System is proposed, positioning it earlier within the treatment train can maximise the mitigation contribution available from that device.
Using Smartceptor within a High-Risk Treatment Train
Where a SPEL Smartceptor is selected as the first stage of treatment for a high-risk application, the downstream treatment stages must be selected carefully to ensure that the complete treatment train achieves the required mitigation indices.
Depending on the project, using a higher-mitigation treatment device such as the SPEL ESR Treatment System as the initial treatment stage may simplify the treatment train and improve the overall mitigation available through the Simple Index Approach.
The final treatment train must be assessed by the project engineer against the specific Pollution Hazard Indices and Mitigation Indices applicable to the development.
Full Flow vs Bypass SuDS Treatment Systems
SPEL ESR Treatment Systems are available in full-flow and bypass configurations.
Selecting the appropriate arrangement depends on the drainage design, treatment flow, site pollution risk and potential consequences of a hydrocarbon spill.
Full Flow Treatment Systems
A SPEL ESR Full Flow Treatment System treats the full design flow entering the treatment unit, subject to the hydraulic capacity of the selected model.
Full-flow systems include an automatic closure device designed to close the separator outlet in the event of a significant hydrocarbon accumulation.
This provides an additional level of protection against hydrocarbons passing into the downstream drainage network or receiving environment.
A full-flow treatment system should be considered where the potential pollution or spill risk warrants additional containment.
Bypass Treatment Systems
A SPEL ESR Bypass Treatment System is designed so that the treatment chamber processes the designated treatment flow, while higher storm flows bypass the main treatment chamber.
BS EN 858 provides for the use of bypass separators in applications where the risk of significant hydrocarbon contamination is low.
Where the consequences or likelihood of a hydrocarbon spill are greater, a full-flow treatment system should be considered.
Which system should I use?
The appropriate separator configuration must be determined by the project engineer based on the site risk assessment, drainage design, expected flows, pollution loading and relevant regulatory requirements.
Dissolved Metal Removal Requirements
Some planning authorities or project requirements may require additional treatment for dissolved metals and other dissolved pollutants beyond the standard SuDS Pollution Hazard Index assessment.
Where dissolved metal removal is required, SPEL recommends a treatment train incorporating primary sediment and hydrocarbon treatment followed by a dedicated polishing stage.
Recommended Treatment Arrangement
Stage 1:
SPEL ESR Treatment System
Stage 2:
Attenuation
Stage 3:
Flow Control
Stage 4:
SPELFilter System
Stage 5:
Final Discharge
The SPEL ESR Treatment System is positioned upstream of the attenuation system to provide primary treatment of sediment and hydrocarbons before runoff enters the attenuation system.
Following attenuation and flow control, the SPELFilter provides a final polishing stage designed to assist with the removal of dissolved pollutants before discharge.
This arrangement should be assessed against the specific planning conditions, pollutant requirements, hydraulic design and receiving environment for the project.
SuDS Calculator Disclaimer & Important Information
1. Purpose of the Calculator
The SPEL SuDS Water Quality Treatment Device Calculator is provided for general information and as a preliminary engineering aid only.
It is intended to assist suitably competent engineers, designers and specifiers in reviewing potential SPEL treatment options using information entered by the user and the treatment data incorporated within the calculator.
The calculator does not constitute a complete drainage design, engineering design, environmental assessment, planning assessment, regulatory approval or professional engineering advice.
2. Accuracy of User Inputs
Calculator outputs are dependent upon the accuracy, completeness and suitability of the information entered by the user.
SPEL Products does not independently verify the project information entered into the calculator.
Incorrect, incomplete, inaccurate or inappropriate input data may produce incorrect, incomplete or unsuitable results.
The user is responsible for checking all information entered into the calculator before relying on any resulting calculation or treatment recommendation.
3. Engineering Responsibility
The calculator is a decision-support tool and is not a substitute for professional engineering judgement.
The project engineer, designer and/or other responsible competent person remains responsible for determining:
- the applicable Pollution Hazard Index;
- the required Mitigation Indices;
- catchment characteristics and areas;
- design rainfall and hydraulic flows;
- drainage and hydraulic calculations;
- site conditions;
- ground conditions;
- installation requirements;
- structural requirements;
- maintenance requirements;
- treatment system configuration;
- product suitability;
- applicable planning conditions;
- applicable legislation, standards and regulatory requirements; and
- the suitability of the final treatment train for the intended application.
No project should be designed, specified, procured, installed or constructed solely on the basis of an output generated by this calculator.
4. Verification of Results
All calculator outputs, treatment trains, product selections, model sizes, calculations and generated specifications must be reviewed and verified before use.
Before specification, procurement, installation or construction, the proposed system must be confirmed by:
- a suitably qualified and competent engineer responsible for the project; and
- a SPEL Products technical representative.
Where project conditions differ from the assumptions used within the calculator, further assessment or an alternative treatment solution may be required.
5. Site-Specific Conditions
The calculator cannot account for every site-specific condition, design constraint, pollution source or project requirement.
Factors including unusual pollutant loads, industrial processes, spill risks, contaminated land, receiving-water sensitivity, hydraulic constraints, planning conditions and local authority requirements may require additional assessment or treatment.
Users should ensure that all relevant project-specific information has been considered independently of the calculator.
6. Product Information and Changes
Product information, technical data, standards, regulatory guidance and treatment recommendations may change over time.
Users must confirm that they are working from the latest available SPEL Products technical information and applicable guidance before finalising a design or specification.
SPEL Products reserves the right to amend product specifications, technical information and calculator methodology where appropriate.
7. Limitation of Reliance and Liability
To the fullest extent permitted by applicable law, SPEL Products accepts no responsibility for loss or damage arising solely from reliance on calculator results without the independent checks, professional assessment and confirmations described above.
Nothing in this disclaimer excludes or limits any liability which cannot lawfully be excluded or limited, including liability for death or personal injury caused by negligence, fraud or fraudulent misrepresentation.
8. Acceptance
By using this calculator, the user acknowledges that:
- the calculator provides indicative guidance only;
- outputs depend upon the information supplied by the user;
- calculator results may contain errors or may be unsuitable where the information entered is incorrect, incomplete or does not reflect actual site conditions;
- professional engineering judgement remains necessary; and
- all proposed specifications must be independently reviewed and confirmed before reliance, procurement, installation or construction.
If you are unsure whether a SPEL treatment system is appropriate for a project, contact the SPEL Products technical team before proceeding.
Selecting a SuDS Water Quality Treatment System
The appropriate SuDS water quality treatment solution depends on the pollution risk associated with the development, the characteristics of the contributing catchment, hydraulic conditions and any site-specific planning or environmental requirements.
The SuDS Manual Simple Index Approach compares the Pollution Hazard Indices associated with a development against the Mitigation Indices provided by the proposed treatment components.
SPEL Products offers a range of surface water treatment systems that can be incorporated into SuDS treatment trains, including hydrodynamic vortex separators, oil and silt treatment systems, attenuation systems, flow control chambers and filtration systems.
For complex sites, high pollution risks or projects with additional dissolved pollutant requirements, contact SPEL Products for technical support.
SuDS Water Quality Calculator FAQs
What is a SuDS Pollution Hazard Index?
The Pollution Hazard Index is used within the SuDS Manual Simple Index Approach to represent the potential pollution risk associated with runoff from different types of development.
The relevant Pollution Hazard Indices should be established by the project designer before selecting an appropriate treatment system.
What is a SuDS Mitigation Index?
A Mitigation Index represents the treatment performance attributed to a SuDS treatment component for particular pollutant categories.
The treatment system should be assessed against the Pollution Hazard Indices applicable to the proposed development.
Can the calculator design my drainage system?
No.
The calculator provides indicative water quality treatment guidance only. It does not undertake the complete hydraulic, drainage, structural, geotechnical or environmental design of a project.
Final design responsibility remains with the project’s suitably qualified engineering professionals.
Can I use the calculator output in a specification?
Calculator outputs can be used as a starting point when developing a project specification, but they must be independently checked before being relied upon.
Product selection, sizing and the complete treatment arrangement should be confirmed by the project engineer and SPEL Products before specification, procurement or installation.
What is the difference between a full-flow and bypass SuDS Treatment System?
A full-flow SuDS Treatment System is designed to treat the full design flow through the treatment chamber within the capacity of the selected system.
A bypass SuDS Treatment System treats the designated treatment flow while allowing higher storm flows to bypass the principal treatment chamber.
The appropriate configuration depends on the site drainage design and pollution or spill risk.
When might dissolved metal treatment be required?
Additional dissolved pollutant treatment may be required where specified by the planning authority, environmental regulator or project design requirements.
Where this applies, a dedicated polishing treatment stage such as SPELFilter may be incorporated into the treatment train.
Need expert advice on your project?
Every site is different.
The SPEL Products technical team can help you review treatment options, product sizing and project-specific requirements before the proposed solution is finalised.
