County taps CAD app to keep water lines flowing

County taps CAD app to keep water lines flowing

Anne Arundel County, Md., county engineer Laura Layton uses WaterCAD software to make sure the county's water flows at the correct pressure.

Turn the tap, and water comes out in a reassuring whoosh. It's a part of daily life we all take for granted.

But a mysterious kingdom of pipes and pressure lurks behind the tap, presided over by the local public works department, to ensure our water is pure, potable and plentiful.

Anne Arundel County, Md.'s, Public Works Department distributed more than 11 billion gallons of water in 1999. It's utilities engineer Laura Layton's job to make sure the tap water comes out at just the right pressure, about 40 pounds per square inch (psi) during maximum demand times. She also needs to maintain fire flow requirements, which is the amount of water pressure a fire hose needs. Residential fire flow requirements are 1,000 gallons per minute; commercial fire flow requirements are 3,000 gallons per minute.

Layton determines if water mains have adequate capacity. To do this, she creates drawings of the pipes with WaterCAD Version 4.5 hydraulic modeling software from Haestad Methods of Waterbury, Conn. Anne Arundel County officials work with local real estate developers to make sure their plans meet the water flow requirements. 'Sometimes it might require curving the water main back in a loop,' she said.

The department has a four-user license for WaterCAD, which runs on Microsoft Windows NT.

Layton also uses the modeling software to predict where development will occur. 'It helps us see where water transmission mains will go and what size they have to be.'

One way down

The water division is also using the software to develop velocity requirements to clean out water mains through a process Layton called 'unidirectional flushing.'

Water mains build up mineral deposits and sediment that can eventually restrict water flow and erode the pipes. During a flushing session, water is forced through the pipes at a high velocity, which creates a scouring action. The water is then discharged through a hydrant. This removes mineral buildup from the pipe and contributes to the water's purity.

'Every year they pick a different part of the county system to target for flushing,' Layton said.

Layton uses WaterCAD to determine where the county's older pipes are. The buildup of minerals and sediment results in friction loss, which she called a 'low C factor,' a characteristic of older pipes. 'We can then target where our cleaning program should go.'

WaterCAD integrates with the county's geographic information system, which is built in ArcView Version 8.1 from Environmental Systems Research Institute of Redlands, Calif. Thomas Damm, a project manager with county contractor O'Brien & Gere Engineers Inc. of Landover, Md., exports system model data into the GIS. 'We use the data to plan zoning and land use,' Damm said.

Greg Landreth, a civil engineer with O'Brien & Gere, took a three-day training course in WaterCAD, which he described as 'really useful.'

'Anybody who's done any sort of hydraulic software modeling can pick it up and run with it,' he said.
WaterCAD comes with its own database. Users can import WaterCAD data into Microsoft Access and Excel spreadsheets, Landreth said.

How much do you need?

The county uses WaterCAD to sort out billing information, too. The county's billing database can pull data from WaterCAD models about water demand at certain points throughout the county. The county collects the water demand data from meters in the street and transmits it back into the billing database.

Hydraulic modeling takes away a lot of guesswork, Damm said. Say a four-inch pipeline runs in front of an apartment building. In the past, engineers would dig up the old pipe and install 8-inch pipe. Then they would find out they need 6-inch pipe, and have to repeat the process all over again, he said. With WaterCAD, the engineers could model the different sizes before making the investments of digging and fitting pipe.

About the Author

Trudy Walsh is a senior writer for GCN.


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