ERROR 103:
Cannot solve KW equations for Link xxx.
Error 103 : The internal solver for Kinematic Wave routing failed to converge for the specified link at some stage of the simulation.
1. Description
ERROR 103 is a run-time Kinematic Wave routing error. It occurs when SWMM's internal numerical solver cannot solve the finite-difference continuity equation for the specified conduit during a simulation time step.
The link named in the message identifies where the numerical solution failed. However, the condition leading to the failure may originate in the adjacent flow path or from a rapid change in inflow or conduit losses. Because the simulation stops, investigate the cause and rerun the model before using the results.
2. Technical Background
Kinematic Wave routing solves the continuity equation together with a simplified form of the momentum equation in each conduit. It assumes that the water-surface slope equals the conduit slope, and the maximum conveyance is the full normal-flow value. This approach is efficient for dendritic drainage systems with positive slopes, but it does not represent backwater, flow reversal, pressurized flow, adverse slopes, or cyclic network loops. For more details, see the Flow Routing section of the Geo SWMM User's Manual and the SWMM Reference Manual, Volume II - Hydraulics.
For ERROR 103, SWMM's internal root solver fails while determining the conduit outlet area for the current routing time step. The calculation depends on current inflow, previous flow and area, conduit length, routing time step, cross-section hydraulic properties, full-flow capacity, barrel count, and applicable conduit loss rates. Therefore, abrupt inflow changes, unrealistic model data, or an inadequately resolved routing time step can contribute to the failure.
Before troubleshooting ERROR 103, review the report file for other errors and warnings. Invalid conduit length, roughness, barrel count, slope, or cross-section data, as well as cyclic loops or multiple outlet links, are reported separately by GeoSWMM and should be corrected first.
3. Resolution
Use the following sequence and make one documented change at a time so that its effect can be evaluated.
Table 1 : Troubleshooting steps
Step | Action | Why It Helps |
|---|---|---|
1 | Confirm the routing method and review the report file
| Separates this run-time convergence failure from model-definition errors that GeoSWMM reports under other error codes. |
2 | Identify the failure link and time
| Locates where the root solver failed and helps identify an upstream transient or adjacent condition affecting the calculation. |
3 | Review inflows, units, and conduit losses
| Current inflow and applicable conduit losses enter the Kinematic Wave continuity calculation. Abrupt or mis-scaled values can create a condition the solver cannot resolve. |
4 | Test a shorter routing time step
| The routing time step is part of the finite-difference continuity equation. A shorter step reduces the hydraulic change that must be resolved in one calculation. |
5 | Check the flagged conduit and adjacent data
| Conduit length, cross-section properties, and full-flow capacity are used directly in the Kinematic Wave solution. Inconsistent values can create an unrealistic normal-flow relationship. |
6 | Evaluate whether Kinematic Wave is appropriate
| Kinematic Wave does not represent these hydraulic conditions. Dynamic Wave is the appropriate method when downstream controls and pressurized or reversing flow are important |
7 | Rerun and verify the results
| A completed simulation does not by itself confirm that the correction is hydraulically defensible or that the results are numerically stable. |
MIN_SLOPE Caution:
MIN_SLOPE is the minimum allowed conduit slope. Use it only when a minimum modeling slope is technically justified and documented. Do not use it to override incorrect elevations, offsets, link directions, or surveyed adverse grades.
Do not correct ERROR 103 by making arbitrary geometry changes unsupported by survey, as-built, GIS, or design data. Document any assumption and confirm that the revised value remains hydraulically defensible.
✓ Diagnostic Tip
The error identifies the first conduit whose Kinematic Wave continuity equation could not be solved. Inspect the flagged link together with its upstream inflow path and any conduit loss or control change immediately before the failure. Changing the flagged link alone may not address the cause.