This document discusses using calibrated models to understand and control combined sewer overflows (CSOs) in urban drainage systems. It provides an example of calibrating a sewer model using flow and rainfall data collected from sensors in Kalundborg, Denmark. The calibrated model is then used to identify undersized pipes, flooded areas, CSO volumes and frequencies to ensure compliance with regulations. Calibrated models are a valuable decision support tool for capital planning, process optimization and evaluating strategies to manage flooding and CSOs before implementation.

1. UnderstandingCombinedSewer
Overflow(CSO)withCalibrated
Models
Nurudeen Adeyinka Salau
Project Manager/Engineer
Kalundborg Forsyning

2. www.kalfor.dk

3. www.kalfor.dk
Kalundborg Forsyning
supplies sewer system to the
48469 inhabitants in the
municipality of Kalundborg
and 5 other nearby villages
With 817km of sewer pipe
system, 328.3km of
wastewater network,
244.7km rain water and
244.1km of combined sewer
network

4. www.kalfor.dk
During heavy storms, the combined storm
and wastewater flow is a challenge, as it can
only handle a limited amount of rain
Solution in such circumstance is to provide
structures in the sewer diverting untreated
flow above a certain volume in the
combined sewer system into water bodies
These structures(weirs) are commonly used
to prevent flooding and to control the
untreated volume discharge to water
bodies.
The untreated discharge volume called
combined sewer overflows are a major
pollution concern in urban drainage
management
Calibrated Model is well suited to
understand and control CSOs

5. www.kalfor.dk
Initial Modelling set-up before
Calibration
Model Result does not fit reasonably
well with measured field data
A reason why it is important to
Calibrate the model

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Data Requirement for Calibration
Flow sensors and rain guage are
installed for Calibration e.g Byens
Mose Kalundborg as a case study
It is crucial for calculating model
reduction factor and initial loss

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Data are stored with a data logger and
transmitted via GPRS to the Blue
North Server
And thereafter they are exported to
Excel

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Analyses are done on the measured
flow and the raingauge to ensure
good quality of data for calibration

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A systematic method to avoid
over/under estimation of water in the
Model
Reduction factor calibration is an
approach that is based on a water
balance principle

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What is Model Calibration??
Making adjustment to the model with
the Calibrated reduction factor and
initial loss

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How is calibration accomplished??
Run simulation and compare Model
result to measured flow data

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Model is Calibrated…what next
- undersized pipes
Locate areas with poor turnover
- Flooded areas
- Combined sewer overflows

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Computed CSOs??
Results compared to legislational
requirement such as:
- Flooding on terrain (must not happen
more than once every n years).
- Flooding of basements (must not happen
more than once every n years).
- Discharge from CSO weirs to receiving
waters (must not happen more than n times
per year
-Total volume from CSOs (must not exceed
a certain threshold amount per year).

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Calibrated model afterwards for capital
Improvement planning , e.g
- Storage capacities for basins
- Pipe Dimensioning
- Green Infrastructure planning
- Process optimization and control of
pumps and treatment facilities

15. Conclusion
Calibrated models in utilities can create large value as a decision support tool
Based on models for Byens mose we have learned that
 Calibrated models can support operational strategies
 Provides understanding to support capital improvement planning
 Useful now and in the future and needs to be maintained and updated
 All planned activities at Kalundborg Forsyning can be tested with calibrated models before
implementation
CSOs and flood management strategies without a calibrated models might result in a
considerable waste of energy and resources

16. Thankyoufor listening
Nurudeen Adeyinka Salau
Project Manager/Engineer
Kalundborg Forsyning
Telephone Number: 29257609