One of the most challenging and critical duties for the city of Garland, Texas’ water system operators is maintaining adequate pressure throughout the distribution system, which is composed of two pressure planes (east and west zones) and has elevation changes of up to 150 ft. Maintaining the minimum and maximum design pressure supplied to customers under specific demand conditions has for years been a delicate balancing act.
In the past, the only pressure points system operators could monitor were the pumping stations and elevated tower sites, leaving them virtually blind to what was actually happening farther within the distribution system. As a result, system operators had to set their operating parameters based on low-pressure complaints and water main breaks. Pressure estimation was being done manually, using outdated paper maps showing fire hydrant pressure readings for different areas of the distribution system.
In order to automate the process and better estimate pressure throughout the distribu- tion system without installing remote pressure transmitters or performing hydraulic analysis, City of Garland Water Utilities decided to bring a new concept to life by linking its SCADA system to the Geographic Information System (GIS) web map. This was accomplished by developing pressure equations for 152 strategic locations in order to estimate distribution system pressures based on measured pressures at facilities by SCADA equipment and mapping this information on the GIS Web map.
By integrating SCADA and GIS systems to offer a calculated estimate of pressures at 152 points throughout the system, operators can now monitor the conditions beyond the pump stations and adjust their operating param- eters based on the entire distribution system’s response to pump selection.
Development of Pressure Equations
The city’s water staff, with the assistance of Freese and Nichols Inc., selected 152 locations to provide the most representative system pressures. These points are distributed throughout the two pressure planes—with 71 points in the east pressure plane and 81 points in the west pressure lane—and are placed at or close to water hydrants.
Existing system average and maximum day model runs were used to determine the facility of greatest influence for each individual point, and the points were color-coded by the facility of greatest influence. Ground contours of 10 ft were utilized to assign elevations to each point. Equations to estimate pressure at each location were developed based on the elevation and pressure of the facility of greatest influence and the elevation of the pressure point location. The hydraulic model was used to compare the esti- mated pressures based on pressure equations to modeled pressures under average day and maxi- mum day demand conditions.
The majority of the calculated pressures fell within 5 psi of modeled pressures under average and maximum day demand conditions. Calculated pressures for the points farthest away from the facility of greatest influence were more than 3 psi above modeled pressures in average day demand conditions based on friction losses through the pipelines. The equations for these points were modified to account for estimated headloss based on model hydraulic grade lines under existing system average day conditions.
SCADA to GIS Integration
Once equations for all 152 points were developed, utility staff engineered a way to link its SCADA system to GIS without compromising integrity and security. One common factor between the two systems was the utility’s work management system (WMS) database, which already was receiving data from SCADA for other purposes.
The SCADA system database provides station “tag” (name) and pressure reading. That information is transferred to the WMS database, where the point-pressure calculation is made, stored and transferred to the GIS database for display on the Web map. A data transformation service has been set up, and data between all systems currently is being updated every three minutes.
By adding monitoring points, the utility sys- tem operators have better visibility of pressure estimates throughout the entire distribution system. This allows system operators to ensure that every customer has adequate pressure. Furthermore, they now have an extra tool to ensure that customers in the higher elevation areas have sufficient pressure, while customers in lower elevations do not have extreme pres- sures that could damage water heaters and other household fixtures, not to mention “wear and tear” key distribution system components like valves and fittings that may cause additional leaks or pipe breaks with subsequent repercussions on water quality.
With the ability to access SCADA and the GIS map information side by side, system operators and other utility staff quickly can deter- mine the estimated pressure and, because the information is constantly being updated as SCADA measures pressure data changes, more educated “pump run” decisions can be made. System operators hope this tool will help to better utilize pressure, either generated by pumping resources or generated by using elevated storage resources.
“GIS technology plays an important role in our operations, and pressure mapping is another useful GIS tool, in addition to automatic vehicle location, work orders and water and wastewater infrastructure mapping,” said John Baker, managing director of water and wastewater utilities for City of Garland Water Utilities.
The system currently is deployed, and water field crews, when performing routine fire flow tests, help system operators in the process of field-verifying estimated pressures at selected locations. At one current location, the difference between the pressure measured in the field and the estimated pressure shown in the GIS map was only 1.5 psi. Field verification allows water utility staff to tweak the pressure estimation formulas to better reflect measured pressures out in the distribution system.
In a recent preventive maintenance pump station shutdown, system operators at the con- trol center were able to monitor the estimated pressure points in that area to make sure those customers had adequate water pressure. Not a single low water pressure complaint from the affected area was reported to the Garland water utility.
This project has been successful due to the collaborative efforts of the city’s water utility staff, IT and GIS departments, and Freese and Nichols Inc.
Utility puts pressure on the map with SCADA and GIS integration