Velocity Water Services Blog

A uni-directional flushing program is among the best ways for municipalities to preserve the high quality of water and keep the water distribution system reliable.

A uni-directional flushing program (or UDF) is a means of cleaning existing water mains using multiple flushing sequences, with the water being discharged through fire hydrants. A UDF program involves closing valves in a specific sequence to create water movement in one direction while opening specific hydrants at the end of that sequence. By directing water in a uniform direction, higher flow velocities can be achieved. The higher velocity creates better scouring of the pipe walls, and this scouring helps flush out sediment, biofilm, and corrosion byproducts.

A uni-directional flushing program usually does not cause a serious disruption of the water distribution. Some households only experience a temporary slight drop in water pressure or discolouration in cold water.

Let's dive into the process and learn what makes a uni-directional flushing program so important for municipalities.

What Factors Impact the UDF Program's Efficiency?

UDF programs can be perceived as asset management programs that hold a lot of long-term benefits, including the removal of unwanted tastes, odours, and discolorations of the water. However, there are a lot of factors that need to be considered for this complex process to be done right.

Before the UDF program's planning and execution, it's important for municipalities to assess all the available assets and conditions. If a proper asset assessment has not been done, the UDF program can worsen the quality of the water because it will simply stir up the sediment instead of removing it.

There are two main types of assets you need to consider to fulfil this step:

  • Business system assets, including GIS mapping and hydraulic models.

  • Physical assets such as pipes, valves and hydrants.

Knowing Your System

Having incomplete information may create some difficulties for the crew working on the project, such as inadequate water system pressure, incomplete flushing zones and more. To help eliminate these difficulties, here are some steps that can be taken.

  • Review the asset records and GIS data.

  • Provide the field team with as much data as possible to help them precisely determine the asset condition, age and operability. An important part of this assessment is fire hydrants flow testing. This step should not be skipped because fire flow testing helps determine pressure and flow-producing capabilities within the distribution system, as well as identify closed or partially closed watermain valves.

The Importance of Hydrant Inspections, Fire Flow Testing, and Valve Maintenance

Valves and fire hydrants are critical components when it comes to the proper execution of a UDF program. They are the main control points for water flow in the pipe network and therefore need to be operable for the successful execution of a UDF plan. Generally speaking, UDF sequences can be designed around inoperable valves or fire hydrants, but having those checked regularly is an essential part of the asset management program. Here are some more considerations to keep in mind about the fire hydrant maintenance plans and valve exercising programs:

  • An inoperable valve or fire hydrant can significantly impact the scouring abilities created by the required velocities.

  • To prevent unexpected issues, fire hydrants and valves should be checked and inspected before planning a UDF program.

  • Ideally, a full hydrant and valve inspection and maintenance program would be completed before the UDF program. This helps ensure all required assets are functional and that CAD/GIS programs are accurate.

At Velocity Water Services, we offer high-quality fire hydrant inspection and maintenance services for private, municipal and industrial clients. Give us a call today and let's discuss how we can help!

What Are the Key Benefits of a UDF Program?

A uni-directional flushing program is among the best practices for asset management because it cleans and maintains the water quality in the distribution system. Despite the main benefits of this program being obvious, let's talk about why these programs are so important for municipalities.

  • A uni-direction flushing program saves up to 40% of water compared to conventual flushing.

  • UDF program removes unwanted tastes, odours, or discolorations of the water.

  • It helps improve chlorine residuals.

  • It helps reduce turbidity.

  • Scouring velocities of 5 to 10 ft/s or more are achieved by cutting off other flows, compared to 1 to 3 ft/s achieved with conventional flushing.

  • The sediment, corrosion products, and biofilm are completely flushed out instead of just moved to another pipe run, as in conventional flushing.

UDF Program Execution Best Practices

The UDF program should be executed by an experienced team of experts who can determine any water distribution system issues. Some of the best practices that we, at Velocity Water Services, implement in our line of work are:

  • Minimum pressures should always be maintained within the system.

  • The length of flushing sequences is limited to maintain efficient and safe execution.

  • Stormwater drains can be used to discharge water to avoid the flooding of certain low-lying areas.

  • Testing turbidity levels before and after is done to help evaluate the water quality. Testing chlorine residuals can also indicate when complete water volumes have been displaced.

  • To protect receiving streams, discharged water is dechlorinated.

  • Notification of critical customers that will be affected by the program execution, such as hospitals, industrial customers, etc.

  • During the program's execution, it is common for residents to call with questions, concerns, or water quality complaints. Staff taking these calls should be well informed of the ongoing work and have up-to-date current information.

  • Ensuring traffic control to keep people safe is a number one priority.

At Velocity Water Services, we have extensive fire hydrant and water distribution system knowledge and expertise needed to identify and effectively resolve any water distribution issues. We help municipalities preserve the available assets more effectively and turn to a more cost-efficient preventative maintenance instead of implementing reactive measures. Learn more about our municipal fire hydrant inspection and maintenance services, and contact us to schedule your UDF program today!