New Tool Release: Storm Sewer Network Analysis & Design
Designing a storm sewer network is a fundamental rite of passage for every civil engineer. But let's be honest: tracking cumulative drainage areas, calculating travel times, and finding the correct system Time of Concentration ($T_c$) across dozens of converging pipes in an Excel spreadsheet can quickly become a tangled, error-prone nightmare.
Today, I am incredibly excited to introduce a tool that completely automates this process: the Storm Sewer Network Analysis and Design Tool! 🏙️🌧️
This web-based worksheet uses a robust Directed Acyclic Graph (DAG) algorithm to automatically map your network topology. It routes your flows using the Rational Method ($Q=CiA$), auto-sizes your pipes using Manning's equation, and—best of all—generates a stunning, Civil 3D-style Hydraulic Grade Line (HGL) profile right in your browser!
Key Features of the Routing Engine
The beauty of the Rational Method lies in its simplicity. The complexity arises when you try to link those simple equations together across an entire city block. This tool takes care of the heavy lifting:
- Automated Network Sorting: You do not need to enter your pipes in order! Enter "Pipe 5" before "Pipe 1" if you want. The internal Directed Acyclic Graph (DAG) algorithm automatically sorts the network from upstream to downstream. It ensures a pipe is only sized after all its tributary flows and travel times have arrived.
- Bulk CSV Import/Export: Don't want to type in 50 pipes manually? Click the Template button to download a blank CSV. Fill out your Up/Dn Nodes, Areas, and Inverts in Excel, then click Import CSV to instantly load and route the entire network in milliseconds!
- Design vs. Assessment Modes: In "Design Mode," the tool calculates the theoretical required diameter and automatically rounds up to the next commercially available standard pipe size (e.g., 300mm, 375mm, 450mm). Switch to "Assessment Mode" to lock in your pipe sizes and check an existing system for surcharging.
The Crown Jewel: Civil 3D-Style Profile Viewer
Sizing a pipe is only half the battle. To ensure water actually stays in the ground and doesn't shoot out of a manhole cover, you must plot the Hydraulic Grade Line (HGL).
The tool now includes a dynamic, interactive longitudinal profile visualizer that renders exactly like standard AutoCAD Civil 3D plan & profile sheets. You select a flow path from the dropdown, and it generates the profile instantly, complete with a professional data band.
How the Backwater Engine Works
The profile viewer doesn't just draw lines—it actually runs a reverse-topological backwater calculation!
- It starts at the outfall (or most downstream node) and computes the Normal Depth ($y_n$).
- It moves upstream pipe-by-pipe. If a pipe is flowing partially full, the HGL tracks the physical water surface.
- If a pipe becomes surcharged (the required capacity exceeds the physical diameter), the engine calculates the Friction Slope ($S_f$) and plots the HGL above the pipe crown to represent the internal pressure head.
- It correctly splits the Data Band values at every manhole, showing the exact Invert Elevations and Water Depths for both the incoming and outgoing pipes!
How to Use the Tool
I built this worksheet to act like a dynamic, instant-feedback spreadsheet. Here is a quick step-by-step guide to routing your first storm sewer network:
Configure System Parameters
Set your preferred unit system (Metric or Imperial) and input your IDF curve coefficients ($A, B, C$).
Select whether you are in Design Mode (the tool will automatically size up your pipes) or Assessment Mode (the tool evaluates existing pipe sizes without altering them).
Input Your Pipe Network
In Section A, define the physical layout of your catchments. You can type the Upstream/Downstream nodes, Local Areas, Runoff Coefficients ($C$), and local $T_c$ manually.
Power User Move: Click the Template button to download a blank CSV. Fill out hundreds of pipes in Excel, then click Import CSV to load the entire network instantly!
Review Sizing Results
The routing engine will instantly populate Section B. The internal Directed Acyclic Graph (DAG) algorithm sorts your pipes from upstream to downstream automatically.
Review the computed system $T_c$, design discharge ($Q$), and the final pipe diameter. Keep an eye on the capacity! If a pipe is overloaded, the system will flag it in RED as surcharged.
Check the HGL Profile
Select a flow path from the dropdown in Section C to instantly plot the Civil 3D-style longitudinal profile.
The visualizer will plot the physical pipe walls, map the manhole inverts, and draw the Hydraulic Grade Line (HGL) backward from the outfall. Ensure your pressure head does not pop out of the manhole rims!
Export to CSV
Once your design is stable and free of severe surcharges, you are ready to report!
Click the Export Network button to download a complete, perfectly formatted CSV containing all your physical inputs, routing parameters, full/partial flow velocities, and calculated HGL elevations to attach to your final drainage report.
Pro Tips for Designers
Don't want to type in 50 pipes manually? Click the Template button to download a blank, properly formatted CSV. Fill out your Up/Dn Nodes, Areas, and Inverts in Excel, then click Import CSV to instantly load and route the entire network in milliseconds.
Keep an eye on the "Cap $Q_{full}$" column in the Results table. If your Design $Q$ exceeds this value, the row will highlight in bright red, indicating the pipe is surcharged. Switch over to the Profile Viewer to see exactly how high the HGL rises inside the upstream manhole—if it crosses the Existing Ground line, you have a flood on your hands!
Export and Report
Once your network is fully sized and your velocities are within self-cleansing limits, click the Export Network button. You will get a cleanly formatted CSV containing all routing parameters, travel times, cumulative areas, and calculated HGL elevations, ready to be attached to your final drainage report.
Head over to the tool page and try importing a sample network. Let me know in the comments if you want to see any additional features added in the next update!
Happy Designing!
- CivilSheets
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