Unidirectional Flushing - Ohiowater.org

UDF What Is it for Me & How
Does it Really Work
July 17, 2012
AWWA Distribution Workshop
By Bob McNutt, PE
Imagine the result

Main Points
• Your WDS needs flushed
• UDF is another tool, not a silver bullet
• Must define your goals, desired outcome

Outline
Define WDS flushing approaches
Advantages/Disadvantages for each flushing approach
How UDF works - Pilot studies and results
Lessons learned

Purpose of Flushing
1. What’s in your pipes

Define WDS
flushing
approaches

WDS Flushing Approaches
Conventional flushing
Spot flushing – water quality concerns
Unidirectional Flushing (UDF) approach

Conventional Flushing
Open hydrants "randomly"
Flush large quantities of water
Pulls water through many mains
No valve turning
Random or no water quality checking

Unidirectional Flushing (UDF)
Specific, orderly flushes, follow sequence, minimum # of
hydrants used
Higher flushing velocities to scour the water main
Pulls water thru one segment of main - moving from clean
thru the dirty pipes
Close valves to strategically direct the flow of water from
clean into dirty pipes deeper clean removing sediment,
tuberculation & biofilm
Significant water quality checking

Advantages and
Disadvantages
for each flushing
approach

Conventional – Advantages
• Familiarity of staff with program
• Simplicity of approach
• Provides adequate water quality short term
• Improves short term aesthetics of the water (taste, odor,
visual)

UDF - Advantages
• Typically saves 40% of water and 40% of labor vs.
conventional
• More control on direction, velocities, and thus results
• Hard flushes every 2 to 3 years vs 2X per year
• Scouring velocities remove sediment and deposits = clean
• Dislodges biofilm & curbs bacteria regrowth in WDS
• Restores hydraulic capacity
• Provides adequate water quality, longer term

UDF - Advantages
• Improves aesthetics of the water (taste, odor, visual)
• Improves water quality & reduces water age
• Reduces disinfectant demand and DBP concentrations
• Typically uses fewer fire hydrants
• Benefit of valve exercising during UDF
• Improves knowledge of WDS network and operations
• Minimum disturbance to customers and reduced dirty
water complaints following flushing

Conventional -
Disadvantages
• Does not scour WDS pipes, remove biofilm or sediments
adequately (inefficient cleaning)
• Does not exercise valves
• Uses more billable water than UDF
• Performed 2X annually (typically)
• Dirty water can be pulled into previously cleaned mains

UDF - Disadvantages
• More costly first year to develop the program
• Train staff
• Fix inoperable valves
• Implement program
• Operators must learn new program

How UDF works
– Pilot studies
and results

Case Studies –
Representative Clients
• Tallahassee, Florida (How it works)
• North Canton, Ohio
• Norwalk, Ohio
• Hudson, Ohio
• Streetsboro, Ohio

Tallahassee Model Background
1. Modeled in InfoWater
2. Created in 2009/2010
3. All pipes model
1. 1,218 miles of water mains
2. 41,000 pipes in the model
4. 28 ground water wells
1. Chlorine is added to well
discharge and pumping
directly into distribution
system
5. 8 elevated storage tanks
6. Two pressure zones

Why Flush in Tallahassee
- Iron Bacteria and Customer Complaints

Innovyze – InfoWater UDF Module

Flush Sequence Manager
- Sequence Setup

Flush Sequence Manager
- Sequence Setup

Flush Sequence Manager
- Results

Flush Sequence Manager
- Results

Field Journals

Results
• Program still requires lots of WDS knowledge
• Program does not tell you when pressures may be
excessively high
• WDS finds valves and/or other restrictions that were
previously unknown
• May result in MORE red water complaints

Results – Representative
Clients
• Tallahassee, Florida – high pressures
• North Canton, Ohio – replace bad water main instead
• Norwalk, Ohio – hidden hydraulic restrictions
• Hudson, Ohio – complete in-house, cost effective
• Streetsboro, Ohio – water quality model instead

Lessons Learned

Lessons Learned
• Evaluate the options available to resolve problem
• Not all situations need UDF, case by case review
• Program does not tell you when pressures may be
excessively high, care in choosing valves to close
• Operators find valves and/or other restrictions that were
previously unknown
• May result in MORE red water complaints

Lessons Learned
• Consider ROI as an evaluation method
• Cost savings not always enough to justify
• Save $4,350 annually vs. $30,000 UDF, 7 yr ROI
• In house versus consultant
• ROI may be too long, program too costly (purpose of
program not justified by cost of program)
• Non-cost issues, valve exercising, holistic knowledge of
WDS, etc, may sway decision to go with a UDF

Take Home Points
• Your WDS needs flushed
• UDF is another tool, not a silver
bullet
• Must define your goals, desired
outcome (case by case evaluation
of effectiveness for problem
resolution)

Imagine the result
CONTACT DATA:
Bob McNutt, PE
Ph: 330-515-5674
Cell: 330-697-0437
Bob.mcnutt@arcadis-us.com