Fix Stormwater Network Gaps and Anomalies

Stormwater modeling in ArcGIS Pro often begins with datasets from various sources, including CAD drawings, field surveys, scanned as-builts, and spreadsheets—each with different formats and varying levels of accuracy. While these sources contain valuable information, they are rarely created with GIS-based modeling in mind. As a result, they often introduce issues like disconnected pipes, duplicate IDs, misaligned nodes, and missing attributes. These problems can lead to simulation instability, flawed analysis, and time-consuming rework. 

In practice, engineers rely on both CAD and GIS. CAD remains essential for design layouts and plan production, but GIS has become the preferred platform for stormwater model setup, asset integration, and spatial analysis. Professionals frequently convert CAD data into GIS to leverage tools like SWMM, HEC-HMS, HEC-RAS, and other modeling software for rainfall-runoff simulation, flow routing, and flood analysis. This transition, however, is not without challenges. As urban drainage systems grow more complex, GIS provides the spatial intelligence needed to manage large datasets, understand topographic flow paths, and coordinate asset records. GIS-based systems also support integration with field data, sensor readings, and inspection records, making them ideal for both long-term planning and emergency response. 

While ArcGIS Pro provides a robust environment for working with spatial data, transforming raw input into a fully connected, simulation-ready network requires extensive QA/QC. GeoSWMM’s Network Analysis Tool automates this critical step. It identifies common errors such as orphan nodes, missing links, invalid geometries, and attribute gaps, helping engineers efficiently correct problems and build model-ready sewer data. 

This article highlights the most common challenges found in storm sewer network datasets and explains how GeoSWMM streamlines the data cleanup process. 

Common Stormwater Network Issues in GIS-Based Modeling 

Bringing legacy infrastructure data or sewer data not specifically curated for SWMM model into ArcGIS Pro often reveals a range of hidden issues. These problems may not be immediately visible in basic mapping, but they may directly affect the integrity of hydrologic and hydraulic (H&H) models. Following are a few examples of typical data issues and how GeoSWMM’s Network Analysis Tool helps detect and resolve them. 

Missing Pipe Segments and Structures 

Critical gaps in the network, such as missing culverts and pipes between manholes, break hydraulic continuity. These gaps are often caused by incomplete CAD data, digitization errors, or inconsistencies across multiple data sources. GeoSWMM detects these discontinuities by analyzing both spatial geometry and attribute-based connectivity, flagging missing segments that disrupt flow paths and compromise model integrity. 

Orphaned Features and Network Disconnections 

It’s common to find manholes, inlets, or pipes that aren’t connected to the stormwater network, especially when working with CAD-based data sources. These disconnected features often result from non-topological CAD drawings or errors during CAD-to-GIS conversion. Since orphaned features are excluded from hydraulic analysis, they can lead to inaccurate estimates of system capacity and drainage coverage. GeoSWMM automatically identifies orphan nodes and links and highlights disconnected subnetworks, ensuring that all feature are properly integrated into the model. 

Incorrect Pipe Directionality 

When pipes are manually digitized without reliable topographic information, especially invert elevations or flow directions, they are often drawn in the wrong direction. This can result in unrealistic flow behavior, such as water appearing to flow uphill in the model. GeoSWMM checks pipe directionality by analyzing upstream and downstream relationships, flagging links that violate hydraulic principles, and guiding users to correct them before simulation. 

Attribute Errors and Inconsistencies 

Incomplete or inaccurate attribute data can undermine the reliability of a stormwater model. Common issues include incorrect or duplicate node and link IDs, missing invert elevations, and inconsistencies in pipe size and material. GeoSWMM performs comprehensive attribute validation, flagging missing, duplicated, or illogical entries that could affect hydraulic calculations and simulation results. 

Geometric and Spatial Anomalies 

Spatial errors, such as misaligned nodes, unsnapped links, or overlapping features, often arise from CAD drawings lacking proper topology or from merging datasets with inconsistent geometry. These issues may cause disconnected network segments and undermine model accuracy. GeoSWMM applies tolerance-based geometric checks to identify unconnected nodes, zero-length links, and poorly aligned features, ensuring a topologically sound and simulation-ready stormwater network. 

Smarter Modeling Starts with Clean Data 

A stormwater model is only as reliable as the quality of the data it’s built on. GeoSWMM’s Network Analysis Tool, natively integrated with ArcGIS Pro, eliminates the guesswork. By automating error detection and linking issues directly to problematic features, GeoSWMM accelerates QA/QC and improves model outcomes. 

With GeoSWMM, you can: 

• Reduce manual troubleshooting by pinpointing common and complex errors instantly 
• Improve model accuracy and reduce simulation errors with clean, validated network data 
• Collaborate more effectively by standardizing the modeling environment across teams 

Whether working with CAD imports, scanned plans, or spreadsheets, GeoSWMM helps transform fragmented inputs into connected, simulation-ready models. Designed specifically for drainage design engineers, it helps you spend less time fixing data—and more time solving real-world drainage challenges. With GeoSWMM, smarter stormwater modeling starts with clean, connected data, and that’s the foundation of reliable drainage design, capital planning, and regulatory compliance.