Published on June 21, 2025

An essential guide for municipalities, engineers, and field teams

Mapping a drainage system is a critical task for municipalities aiming to improve stormwater management, identify illicit discharges, support maintenance planning, and ensure regulatory compliance (e.g., MS4). A well-structured drainage system map reveals how stormwater flows through catch basins, pipes, culverts, channels, and outfalls, forming the backbone of effective stormwater asset management.

If your municipality falls within the jurisdiction of a Soil and Water Conservation District (SWCD), it’s highly recommended that you contact your local district office before beginning a new drainage mapping effort. Many SWCDs have already conducted comprehensive stormwater assessments and may possess valuable data on critical facilities such as culverts, outfalls, and drainage basins. They can provide guidance, existing maps, and possibly even GIS files or survey records that can save your team time and resources. In many cases, partnering with your SWCD ensures your mapping efforts align with regional watershed priorities and state reporting requirements.

 

Step 1: Define the Scope and Purpose

Before you begin mapping, clarify:

• What types of features you need to include (e.g., manholes, culverts, storm drains, open channels, outfalls)

• Why you're creating the map (e.g., compliance, maintenance, modeling, flood prevention)

• Who will use it (e.g., public works crews, engineers, planners)

A well-scoped project helps prioritize resources and data accuracy.

 

Step 2: Gather Existing Data

Collect all available resources that may inform your base map:

• As-built drawings

• Site or subdivision plans

• GIS shapefiles

• Maintenance records

• Aerial imagery

• LiDAR elevation data

• Parcel or utility maps

Many cities store this data in local or state-level GIS repositories or public works archives.

Reference:

• U.S. EPA MS4 Mapping Guidance: https://www.epa.gov/npdes/stormwater-maps-and-tools

• FEMA GIS Resources: https://www.fema.gov/gis

 

Step 3: Field Verification and GPS Data Collection

Because existing maps are often outdated or incomplete, field validation is essential. Equip your team with:

• GPS-enabled data collectors or smartphones with GNSS accuracy

• Asset ID system to track components

• Photo documentation

Survey key stormwater features:

• Catch basins and inlets

• Pipes (with diameter, material, flow direction)

• Manholes

• Headwalls

• Detention basins and BMPs

• Outfalls (especially priority for MS4)

Tip: Use consistent attribute fields and naming conventions. Many municipalities follow the NASSCO or EPA standards for asset data.

Reference:

• ESRI Field Data Collection Guide: https://www.esri.com/en-us/field-operations

 

Step 4: Build the Map in GIS Software

Use GIS software (such as ArcGIS, QGIS, or a stormwater-specific platform) to digitize the system:

• Layer structure: Separate layers for basins, pipes, outfalls, and surface flow

• Topology rules: Ensure connected flow (e.g., no dangling pipes)

• Symbology: Apply standard symbology for ease of interpretation

QGIS and ArcGIS both offer templates and plugins for utility mapping.

Reference:

• QGIS Stormwater Plugins: https://plugins.qgis.org/

• ArcGIS Utility Network Management: https://www.esri.com/en-us/arcgis/products/arcgis-utility-network

 

Step 5: Analyze Drainage Patterns and Watersheds

Overlay the infrastructure with elevation data (DEM/DTM) to model surface water flow:

• Delineate watersheds and subcatchments

• Determine flow direction and accumulation

• Identify low-lying or flood-prone areas

Tools like HEC-HMS or EPA SWMM can enhance modeling efforts when combined with your GIS map.

Reference:

• EPA SWMM: https://www.epa.gov/water-research/storm-water-management-model-swmm

• USGS National Map Elevation Data: https://apps.nationalmap.gov/downloader

 

Step 6: Document and Maintain

A drainage map should evolve over time. Be sure to:

• Version control: Archive historical versions of the map

• Update after new construction or repairs

• Link assets to inspection and maintenance records

Some municipalities integrate drainage maps into asset management systems or cloud-based field apps to streamline upkeep.

Reference:

• NACTO Urban Street Stormwater Guide: https://nacto.org/publication/urban-street-stormwater-guide/

• FHWA Hydraulic Engineering Circulars (HECs): https://www.fhwa.dot.gov/engineering/hydraulics/library_arc.cfm

 

Creating a detailed, accurate drainage system map requires a coordinated effort across data collection, GIS work, field validation, and long-term maintenance. For municipalities, this map is more than just a record. It’s a tool for smarter decisions, cleaner water, and safer communities.

Tagged: MS4 Compliance  MS4 Municipal Separate Storm Sewer System  Geographic Information System  SWCD  Stormwater Infrastructure  Soil and Water Conservation District 

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Grants, Budgets & Planning

Illicit Discharge & Pollution Control

Infrastructure Mapping

Maintenance & Compliance

Soil and Water Conservation

Stormwater Asset Management

System Components & Structures

Training & Field Operations