How do each of the LoadBuilder methods work?

Applies To
Product(s): WaterGEMS, WaterCAD, SewerGEMS, SewerCAD, HAMMER
Version(s): CONNECT Edition, V8i
Area: Modeling
Authors: Jesse Dringoli, Dan Iannicelli, Bentley Technical Support


How do each of the available LoadBuilder methods work and what types of files are required?

Below is a brief summary of the different LoadBuilder methods and how they work. Some methods are only available in either in the Water or the Storm-Sewer products. Such cases are noted below. More information on the different methods can be found in the Help documentation.

A Note on Service Area Layers

Note: some method require an additional service area layer. This is a shapefile with polygons, where each polygon is the area served by a particular node (such as a junction). The service area layer is used in some LoadBuilder methods to distribute loads based on areas associated with the nodes.

A tool called Thiessen Polygon is available from the Tools menu, which provides you with one method of generating these polygons which are associated with the nodes by using the ElementID of the nodes. The Thiessen method is just one possible way to generate a service area layer. You could in theory alternatively generate your own service area layer polygons in an external application such as ArcGIS, as long as your shapefile has a field that contains the elementID of the associated node (so that LoadBuilder knows which node each service area polygon refers to).

If you notice small inaccuracies where the polygons meet (such as a small space or small overlap) when zoomed far in, this may be due to the model being located at coordinated with a very large number (such as 2,000,000 ft, 7,000,000 ft). Our developers will look into improvements to the Thiessen Polygon calculations with large coordinates for a future release (reference # 471982)


Billing Meter Aggregation: This method assign all meters within a service polygon to a specified demand node, as shown in the screenshot below.

The service area is typically generated using the Thiessen polygon tool available in the product. Whatever billing meter points fall within the service area will be added as a demand to that service area’s corresponding junction. 

Here is a link with some example files: Billing Meter Aggregation Example Files. These can be used with the WaterGEMS and WaterCAD sample files Example3.wtg.

Nearest Node and NearestPipe: The Nearest Node method assigns loading data stored in a shapefile to the closest junction or hydrant in the model. The Nearest Pipe method assigns the loading data to the nearest pipe, and then distributes this data to the nodes based on criteria set by the user. The loading data shapefile can use either points or polygons. If it is a polygon, LoadBuilder will use the centroid to calculate proximity. The demand will be added to the junction that is closest to that point shapefile/centroid or to the junction or junctions connected to the pipe, if using nearest pipe.

Note: If you choose to use All Pipes and All Nodes for the layers, this will include inactive elements. If you do not want inactive elements, create a selection set and use this for Pipe Layer and/or Node Layer.

Flow Meter Distribution (SewerGEMS/SewerCAD only): The Flow Monitoring Distribution method assigns loading data from a point load monitoring layer to upstream loading nodes. It automatically identifies all the upstream manholes up to its adjacent next upstream load monitor, works out the subtotal load contribution of the manhole between the load monitors (i.e., the load difference between the monitors), and then equally distributes the effective load to all the contributing manholes. 

Detailed information on this method can be found here: Using the Flow Monitoring Distribution method in LoadBuilder.


Unit Line (WaterGEMS/WaterCAD/HAMMER only): The Unit Line method in LoadBuilder divides the total demand in the system (or in a section of the system) into two parts: known demand (metered) and unknown demand (leakage and unmeasured user demand). The known demands are included from existing Demand alternatives in the model. Unknown demand from leakage on only one side of the pipe (for example, pipes along a river), K is 0.5. If both sides of the pipe supply water to users, K is 1. The unknown demand is entered in a table in LoadBuilder. 

Detailed information on this method can be found here: How does the Unit Line LoadBuilder method work?


Equal Flow Distribution: This method equally divides the total flow contained in a flow boundary polygon and assigns it to the nodes that fall within the flow boundary polygon. For example, if the polygon represents 100 gpm and three junctions fall within it, they’ll get 33 gpm each.

Equal Flow Distribution Example files

Proportional Distribution by Area: Uses a service area layer (typically generated using the Thiessen polygon tool) which represents the service area around each junction, along with billing meter polygons with a single demand value. The demand assigned to the junction is based on how much of the flow polygon is overlapping it’s service area. For example, if 25% of the 100 gpm demand polygon falls within a junction’s Thiessen polygon, then that junction will get 25 gpm.

Proportional Distribution by Area Example

Proportional Distribution by Population: Requires Thiessen polygon (Service Area Layer), lump-sum demand polygon (Flow Boundary Layer) and population polygon. This method divides the lump-sum flow among the service polygons based upon one of two attributes of the service polygons: the area or the population. The greater the percentage of the lump-sum area or population that a service polygon contains, the greater the percentage of total flow assigned to that service polygon.

Note: The flow boundary layer should be a polygon shapefile that is divided into areas or zones (zone A, zone B, etc..) and will include a flow field that has the overall flow for that particular zone. For this method it helps to think of the Service Area Polygons layer as a cookie cutter that is going to be pressed through the population layer and the flow boundary layer. It’s a combination of the weighting of the population layer and zone flow layer data that will determine the loads that are assigned to your service area polygon layers.

Proportional Distribution by Population Example


Projection by Land use (Storm-Sewer products)/Load Estimation by Land Use (Water products): Uses a Thiessen polygon (service area layer) and layer of polygons that represent billing meter areas and their associated land use type. The user enters a guess of how much demand per acre is associated with each land use type and based on each polygon’s size, it will then have a specific demand value. This is distributed to the junctions in the same way as with Proportional Distribution By area. In the image below the portions of the purple land use areas that intersect the red Thiessen polygon service areas would determine the value of the demand that is applied to the nodes (junction, manholes, catch basins, etc.).

Projection by Land Use Example


Load Estimation by Population: This method is similar the one above, except you are making a guess at how much demand you think there is per capita, for each land use type. There is a field in the shapefile for population density, so based on the guess, each polygon will have a resulting demand value, which is distributed to the junctions in the same way as with Proportional Distribution By area.

Projection by Population Example

Video Demonstration

The below video demonstrates the use of various LoadBuilder Methods in WaterGEMS for ArcMap

See Also

You can also assign customer meters and property connections to elements through LoadBuilder. You can find more information on this here: 

Customer Meter Elements and the External Customer Meter Data Manager

Modeling Property Connections in the Storm-Sewer products

See Also

Troubleshooting and Understanding LoadBuilder