New Tool Release: Detention Pond & Reservoir Routing
We have officially completed the core hydrology pipeline! I am incredibly proud to introduce the newest addition to the CivilSheets suite: the Detention Pond Routing Tool. 🌊
Over the past few weeks, we've built tools to analyze extreme rainfall, distribute that rain over time, and generate the resulting Runoff Hydrograph. But once that massive wave of water runs off your site, where does it go?
It usually hits a stormwater detention basin (or a massive dam reservoir). This new web-based workstation uses the industry-standard Level-Pool (Storage-Indication) Routing method to calculate exactly how a storage facility attenuates a flood wave, computing the Outflow Hydrograph and tracking the Water Surface Elevation (WSEL) minute by minute.
Why Level-Pool Routing is Essential
When an extreme storm hits a watershed, the water runs off rapidly, creating a dangerous "peak flow". The primary goal of stormwater management is to capture that massive wave of water in a pond, hold it temporarily, and release it slowly through a restricted pipe or weir.
This process is called attenuation. But calculating exactly how much the pond reduces the peak flow is complex, because the outflow rate constantly changes as the pond fills up and the water gets deeper (more head = more pressure = faster outflow).
The Level-Pool Routing (Storage-Indication) method solves this by using the Conservation of Mass:
Change in Storage = Inflow - Outflow
Tool Features & Capabilities
I designed this tool to be a highly visual, instant-feedback routing workstation. Instead of dealing with clunky desktop software, you can perform advanced routing right in your browser:
1. Universal Tabular Inputs
No proprietary file formats here. You simply paste your data directly from Excel.
- Stage-Area-Discharge Curve: Paste the geometry of your pond (Elevation vs Area) and the capacity of your outlet structure (Elevation vs Outflow). The tool automatically uses the mathematically superior Conic Method to calculate your incremental storage volumes!
- Inflow Hydrograph: Paste the time-series data you generated using our Runoff Hydrograph tool.
2. Beautiful Dual-Axis Visualization
Once you paste your data, the engine instantly calculates the routing and draws a stunning interactive chart. You can see the exact moment the Outflow Curve intersects the receding limb of the Inflow Curve (which is mathematically proven to be the moment of peak WSEL in level-pool routing!).
3. Automatic Overtopping Detection
Did you under-size your pond? If the routed Water Surface Elevation exceeds the highest elevation provided in your Rating Curve, the tool will instantly throw a red warning banner. The chart will also highlight the "overtopped" zone in bright red, so you know exactly when and for how long your dam is failing.
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 pond:
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Set Your Routing Parameters:
Define your simulation Time Step (Δt). Crucial: This must match the time step of your Inflow Hydrograph! Also, set the Initial Water Surface Elevation (WSEL) of your pond before the storm starts. -
Paste Your Rating Curve:
Copy three columns directly from Excel (Elevation, Area, Outflow) and paste them into the Stage-Area-Discharge box. The tool automatically computes the incremental storage volumes using the rigorous Conic Method. -
Paste Your Inflow Hydrograph:
Copy your two-column hydrograph data (Time vs. Inflow) and paste it into the Inflow box. You can easily generate this data using our Runoff Hydrograph Generator! -
Check for Overtopping & Export:
The chart will instantly draw. Check the summary stats for "Max WSEL" to ensure the water stays within your pond's physical limits. If it looks good, click the Export Routing Data button to grab your CSV report.
Pro Tips for Modelers
This tool isn't just for parking lot detention basins! The physics of Level-Pool routing apply perfectly to massive dam reservoirs as well. Just paste your river valley's bathymetry (Elevation vs Surface Area) and your spillway capacity curve, and you can route a Probable Maximum Flood (PMF) through a multi-billion gallon reservoir.
The Time Step you select in this routing tool must match the Time Step of the Inflow Hydrograph you pasted. If you generated a runoff hydrograph with 5-minute increments, make sure the routing engine is set to 5 Mins to avoid mathematical stretching.
Export and Report
When your design is finalized, click the Export Routing Data button to download a pristine CSV file containing your peak summaries, maximum WSEL, and the complete minute-by-minute routing timeline to include in your drainage report.
Head over to the tool page and try routing some flows. Let me know in the comments if you want to see a tool for calculating the Stage-Discharge curves for complex multi-stage outlet structures!
Happy Routing!
- CivilSheets
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