Mapping Culverts for 3D Hydrology and Stormwater Modeling

Understanding the importance of mapping our humble hydrologic helpers for creating 3D hydrology data and storm water modeling.


Why do we care about mapping water?

We want to create a watershed twin to help municipalities, organizations and citizens understand and participate in source water reduction to address combined sewer system overflows for the long term.

How does mapping culverts fit in?

Culverts, inlets, storm drains, grates, catch basins; no matter what you call our humble hydrologic helpers their importance in hydrologic mapping is on the rise. These man made structures are designed to intercept and redirect surface flow, at times contrary to the terrain.

These features are not easily identified using current 3D hydrology mapping techniques, but offer a unique opportunity for multi-dispciplanary approaches to mapping, categorizing, and assessing the water handling efficacy of these structures.

This talk will focus on field mapping approaches that leverage existing knowledge for collecting timely and structured data that assists with citizen science, watershed management, and structure vulnerability assessment.

What are some examples of this approach in action?

  1.  Past efforts in inlet mapping to align with recent imagery and elevation for use in storm water planning and water quantification in a PA urban watershed,
  2.  Current efforts to use existing culvert databases for peak flow calculations in a large NY watershed, and
  3. Future efforts to create culvert data products and workflows useful for asset inventory, 3D hydrology mapping and vulnerability assessment.

Past Project: Inlets in Nine Mile Run, Pittsburgh

Goal: Align stormwater infrastructure to current imagery.

Purpose: Upstream Pittsburgh has a history of embracing geospatial technology as a method to help further their mission. A key project was to leverage existing data products to build a 3D hydrologic dataset the organization can use to answer water quantity kinds of questions within the Nine Mile Run Watershed.

How: Upstream staff have deep knowledge of the Nine Mile Run watershed. Allegheny County provides publicly accessible high resolution and near contemporaneous high accuracy LIDAR data. 3RWW maintains a sewer infrastructure database for ALCOSAN compiled from input from the 83 member municipalities. Inlet location is critical in determining flow in urban areas. The alignment of the existing inlet data from 2 municipalities in the watershed with the imagery also meant that the inlets would be in the appropriate elevation value. The locations were used in the hydrology QA/QC to ensure flow lines follow curb lines and to identify locations of other surface flow modifications, such as reinforced open chanels, culverts, and tunnels. Together, these were taken into account when creating the hydrologic analytical surface.

Results: The Upstream staff analyzed over 1500 stormwater structure locations using the most currenlty available imagery. This ensured that the high resolution 3D hydrology developed for the project used these modified locations for checking water quantity calculations.

UPDATE: PWSA has now released the data for the locations of the stormwater inlets in their service region so we can complete the map now! https://pwsa-open-data-pwsa.hub.arcgis.com/

Catchbasin Mover Dashboard

NMR Watershed Explorer (click cancel if prompted for login)


Current Project: Road Crossings in the Hudson Valley

Purpose: The Hudson River Estuary Program has initiated a project to support culvert prioritization efforts for municipal-level road-stream crossings. Core to this project is the mapping of the road-stream crossings for the entire Hudson river watershed to a level that supports these assessments. The data will be provided to municipalites to assist with meaningful priotization of culverts within the context of the whole municipality.

How: CivicMapper has been working with Ground Point Engineering to support the geospatial workflow development for the running of the Cornell Culvert Capacity model at scale. The starting point for this project was the North Atlantic Aquatic Connectivity Collaborative (NAACC) database which provides a robust methdology for capturing information on simple and complex road crossing. NAACC provides a robust workflow for collection road crossing characteristics and an openly accessible database. This was an essential starting point as it provided a set of data points to be reviewed for data accuracy and completeness. These road crossings were used in conjunction with a hydrologic surface developed from the NYS high resolution DEM datasets to calculate peak flow metrics. These peak flow metrics were created using the modified road cross locations, the hydrologic surface, land cover data, and the Cornell Culvert Capacity model.

Results: The end product is a dataset of road crossing locations and the return interval of the storm where the capacity is expected to be exceeded. Culvert locations and their charactertics, both in 3D, have a massive impact on any peak flow location pre-processing. The horizontal accuracy directly affects the initial review and can be assisted greatly by using imagery in conjunction with GPS in the field to refine the locations. The hydrologic surface QA/QC was limited to the valid crossing records found, and surface modifications were imposed as necessary for flow modeling. The capacity calculations, as any with any model, are sensitive to the inputs, in this case the culvert characteristics.

HRE Road Crossings


Future Project: 'Culverts' for Western PA 3D Hydro

Purpose: There are several high-level efforts to tackle the problem of locating, documenting and maintaining an inventory of features needed for the nationwide creation of 3D hydrology. Th culvert topic has come up at local level meetings for stormwater efforts, state level data procurement discussions and at the national level. Experts at the USGS, NSGIC, PA Geologic Survey, and others, have all identified the need for a data model and field collection methodology for 'Culverts' to support multiple workflows: 3D hydrology development, capacity calculations, biotic assessment, and vulnerability ranking. Now that 3DEP high accuracy elevation data re available for all of Western PA, there is an urgent need for a complete, robust, and maintainable dataset for culverts to facilitiate the creation of large-scale 3D Hydrology Data.

Why: The term 'Culvert' has been adopted for this effort to describe any kind of structure that will affect the surface flow. To map these hydrologic structurs is a HUGE effort and the lift can be made easier by engaging those who are in proximity to these features (e.g., citizen scientists, watershed groups, etc.), leveraging existing data assests (i.e., local, state and federal government) and creating a low friction workflow for collecting and maintaining the data. Taking the lead from existing efforts like those at WI Coastal-Management Data Infrastructure, one goal is to extend the workflow to include active local watershed groups like the Negley Run Task Force as data collectors.

Anticipated Results: High accuracy publicly avaiable communally maintained mapped culvert database funded for eternity. .....Now the timeframe and probability.... The anticipated results of this movement will be to continue the conversation with the culvert cohort and begin to test some of the field collection methods. While there is currently no agreed upon tool or data model that can address all of the needs, the intersection of need, motivated citizen scientist,s and contribution of experts is encouraging.

Pittsburgh Urban Hydro Explorer


A whole bunch of 3D models of culverts

Full Metal Inlet

BKSQ : Find the culvert

Leafy and Beefy grate

iPhone 1Pro Max Resolution

Rehoboth Basin (now with bikes!)

(We Are) Penn Grate!

Inlet with paving lip

Street level inlet

Catch Basin and friend

Urban Geomorphology

Leafy inlet

BKSQ Stormwater Trenches

Grate by Snyder Hall


Unidentified Forged Object

Train (in vain) Bridge

lion egg

Beach Doge

Half Obelisk

Denver Pencils

Not creepy at all.

Credits and Thanks

Upstreampgh.org, groudpoint engineering, PGS, USGS, Hudson River Estuary Program

All rights reserved

CivicMapper 2023

Catchbasin Mover Dashboard