Every Service AI run that designs a stormwater network produces a capacity table: one row for every proposed pipe, showing its size, levels, cover, the flow it carries and where the water surface (hydraulic grade line) sits under the design storm. A Checks column flags the pipes that need attention.
Read the table with the Summary at the top. It counts the pipes with checks, so you can see at a glance whether anything needs your attention before reading a single row.
Where to find it
In Civil 3D — Tools panel ▸ Servicing ▸ Storm Capacity opens the table in a pane.
In the Allsite.ai web app — Design ▸ Design data ▸ Storm capacity, for the project's latest results.
As a spreadsheet — the download button saves the full capacity workbook for each subnet (a menu lists SW01, SW02 and so on). The workbook holds the full capacity assessment with its formulae, so every value can be reviewed in detail (see below). Where no workbook is available the button saves the table as a CSV instead.
Before you read the numbers
One row is one pipe. The table is a Summary followed by one table per subnet (SW01, SW02 …). Within a subnet the pipes run downstream first.
Check the units. They sit in each column heading. A metric project reports m, m RL and m³/s; an imperial one ft, ft RL and ft³/s.
Everything is for the first design storm. The flows, water levels and checks all use the first row of your design storm table. The other storms in that table are not shown.
Numbers are rounded for display to at most 3 decimal places. The spreadsheet carries the full values.
A dash means there is no value — for example Height on a circular pipe, or Inlet utilization on a pipe that has no inlet at its upstream end.
The Summary and the left-hand columns of SW01. Numbered markers: 1 Pipe, 2 Downstream link, 3 Diameter / width, 4 Grade, 5 US invert, 6 US cover.
The Summary
Item | What it tells you |
Network, Subnets, Pipes | What the table covers. A subnet is one connected run of pipes draining to an outfall. |
Total length | The combined length of all the pipes. |
Pipes with checks | How many pipes have anything in their Checks column. This counts pipes, not individual problems. |
Surcharged, Overflow | Pipes where the water surface rises above the top of the pipe, or above the ground. See Checks below. |
Cover outside limits, Clearance outside limits, Pipe clashes, Structure clearance outside limits, Pipe/structure clashes, Pipes under/over structures | The design checks from the cover and clearance review that runs when results are imported. Each is a count of pipes. |
Inlets over capacity | Pipes whose inlet is receiving more flow than it can take. |
If the cover and clearance rows are missing, that review did not run for this import. The Checks column will then show only the hydraulic findings (Surcharged, Overflow, Inlet over capacity), so a blank Checks cell does not prove the pipe is clear of clashes.
The pipe
Column | What it is |
Pipe | The pipe's number within the network. It is local to this table, not the Civil 3D handle. |
Downstream link | The pipe this one discharges into. A dash means it discharges to the outfall. |
Material, Shape | From the pipe parts catalogue. Circular and rectangular pipes are supported. |
Diameter / width | The diameter of a circular pipe, or the width of a rectangular one. |
Height | Rectangular pipes only. |
Length | Pipe length, centre to centre of the structures. |
Grade | The fall along the pipe as a percentage. Positive means it falls towards the downstream end. |
Levels and cover
Column | What it is |
US invert, DS invert | The level of the inside bottom of the pipe at its upstream and downstream ends (RL). |
US cover, DS cover | Ground level minus the top of the pipe, at each end — the depth of earth over the pipe's crown. This is the number to compare with your minimum cover. |
Flow and water levels
Column | What it is |
Design flow | The peak flow the pipe must carry for the first design storm, from everything that drains to it (the rational method by default). The pipe's own catchment plus all the pipes upstream. |
Velocity | How fast the water moves through the pipe at that flow. |
US HGL, DS HGL | The hydraulic grade line: the level of the water surface at each end of the pipe under the design flow. Compare it with the pipe's crown and with the ground. |
Minimum freeboard | The smaller of (ground − HGL) at the upstream end and (ground − HGL) at the downstream end. It is how far the water stays below ground at its worst point. Negative means the water level is above ground. |
The right-hand columns of SW01 (scrolled). Numbered markers: 1 Design flow, 2 US HGL, 3 Minimum freeboard, 4 Contributing area, 5 Inlet utilization, 6 Checks.
The catchment
Column | What it is |
Contributing area | All the area draining to this pipe: its own catchment plus the area draining to every pipe upstream of it. |
Impervious | The share of that area that is impervious, as a percentage. |
Time of concentration | The time for water to travel from the furthest part of the catchment to the downstream end of this pipe, in hours. |
AEP | The return period of the design storm, in years. A value of 10 means a 10-year storm. |
Inlet utilization | How much of the inlet's capacity the flow into it uses, as a percentage. Over 100 means the inlet cannot take the flow reaching it. A dash means the pipe has no inlet at its upstream end. |
Reviewing the workings in the spreadsheet
The table is a summary. The spreadsheet you download from the same button is the full capacity assessment for each subnet, and it contains the formulae, not just the results, so you can follow every number back to its inputs and review it in detail.
One workbook per subnet (SW01, SW02 …). Click into a cell and the formula shows how the value was worked out from the pipe's levels, size, roughness and flows.
The capacity assessment sheet lays the pipes out one per column, downstream first, with more rows than the table shows, including the node, catchment and head loss working behind the water levels.
The supporting reference data, such as the rainfall and coefficient tables the formulae look up, is on a second sheet.
Change an input in the workbook and the dependent cells recalculate, which is useful for checking a result or testing a what-if outside Allsite. It does not change your Allsite design.
Use the spreadsheet when you need to explain a result to a reviewer, check one pipe by hand, or see detail the table leaves out.
Checks
The Checks column lists every problem found on that pipe, separated by semicolons. A dash means none.
Check | What triggers it | What to do |
Overflow | The water level (HGL) at either end is higher than the ground. | The pipe cannot carry the flow without flooding the surface. Increase the pipe size, steepen it, or reduce what drains to it. |
Surcharged | The water level is above the top of the pipe at either end, but not above the ground. | The pipe is running under pressure. That may be acceptable by your standards, but it eats into freeboard — check Minimum freeboard. |
Inlet over capacity | Inlet utilization is over 100%. | Add inlets, or reduce the area draining to this one. |
Cover below minimum | Ground minus (invert plus the pipe's outside diameter) is less than the required cover at either end. | Lower the pipe, or raise the ground. The requirement is the carriageway cover under roads and the other-area cover elsewhere, unless the pipe has its own minimum. |
Pipe clash / Clearance below minimum | Two pipes cross without being connected and the gap between them is zero or less (clash) or less than the required clearance. | Both pipes are flagged. Change the level of one of them. |
Pipe/structure clash, Structure clearance below minimum, Pipe under/over structure | A pipe passes through, too close to, or directly above or below another structure. | Move the pipe or the structure. |
Every check is a strict comparison on the first design storm. A pipe sitting exactly on a limit passes. Short stub pipes and existing-to-existing crossings are not flagged.
Settings that change these numbers
If a figure looks wrong, it is usually a setting rather than the design.
Setting | What it changes |
Design storm sizing table (first row) | The return period, duration, flow method and whether node head loss is included. Drives every flow, HGL and check. |
Rainfall (IDF) data | The rainfall intensity used for the flow. |
Impervious and pervious runoff coefficients, Manning's n for impervious surfaces | Design flow and time of concentration. |
Pipe roughness (pipe parts catalogue) | Velocity and HGL. |
Carriageway cover, Other area cover and the clearance table | The Cover and Clearance checks, and the Summary counts. |
Project units | Every unit label and value in the table. |
These settings are described in Storm / Sanitary Networks.
Common questions
The page says “No Storm capacity data”.
No stormwater results have been imported for this project yet, or the latest Service AI run produced no stormwater network. Run Service AI and then import its results. If the page also says the report is not available yet, it has not been switched on for your environment — contact Allsite.ai support.
The table does not match my latest design.
The table shows the last Service AI results that were imported. If the most recent run finished as not viable, the previous run's table is kept. Re-run Service AI and import the results.
Why is the cover in the table different from the Cover check?
The table shows cover to the top of the pipe. The check allows for the pipe's wall thickness (it uses the outside diameter), so a pipe whose displayed cover looks just above the minimum can still be flagged.
Why does AEP say 10 when my storm is a 10% AEP?
The column gives the return period in years, so 10 means a 1-in-10-year storm.
The Time of concentration looks too short for the storm I set.
The column shows the time at the downstream end of the pipe. The flow is sized with the time at the upstream end, so the two will differ by the travel time through the pipe.
A tiny flow shows as 0 or looks coarse.
Values are shown to three decimal places. The spreadsheet holds the full values.
Where is the manhole or catchment detail?
In the spreadsheet. The table shows pipes only.
The Storm / Sanitary Networks article describes the network settings behind these results. For the equivalent table for sanitary pipes, which adds the dry and wet weather flows, see Interpreting Sanitary capacity table data. Contact the Allsite.ai support team if a value does not look right for your site.