ERROR 109:
Invalid parameter values for Aquifer xxx.
Error 109 : The properties entered for an aquifer object were either invalid numbers or were inconsistent with one another (e.g., the soil field capacity was higher than the porosity).
Quick Fix — Start Here
First, check the soil-moisture relationship: Wilting Point < Field Capacity < Porosity. Open the Aquifer identified in the error message and verify these values first. Also confirm that Initial Upper-Zone Moisture falls between Wilting Point and Porosity.
Next, check how the moisture values were entered. Porosity, Field Capacity, Wilting Point, and Initial Upper-Zone Moisture should be entered as decimal fractions, such as 0.45 rather than 45.
In GeoSWMM, open the flagged Aquifer in the Aquifer Editor, correct the values, save the changes, and re-validate the model.
If ERROR 109 remains, continue to the full Data Review Checklist below. SWMM checks several additional Aquifer parameters and relationships that can also trigger this error.
1. Background Causes
SWMM represents groundwater using an upper unsaturated zone and a lower saturated zone. Aquifer properties define how much water can be stored in the soil, how water moves through the soil, how evapotranspiration interacts with groundwater, and the initial groundwater condition.
Before a simulation starts, SWMM validates the properties of each Aquifer against its input requirements and required parameter relationships. ERROR 109 means the Aquifer named in the message failed that check. It is an input-validation error, not a routing or numerical-solver problem, so the fix is always in the Aquifer's property values — never in solver settings or time-step adjustments.
One of the first relationships to check is soil-moisture hierarchy: Field Capacity equal to or greater than Porosity. Figure 1 illustrates a valid soil-moisture configuration and an example that fails because Field Capacity exceeds Porosity.
Figure 1. A valid Aquifer configuration keeps Wilting Point < Field Capacity < Porosity. In the invalid case, Field Capacity exceeds Porosity, and SWMM reports ERROR 109.
2. Data Review Checklist
Review the following validation conditions for the Aquifer identified in the error message. Work through the table from top to bottom before changing other model settings.
Parameter | Required Condition |
|---|---|
Porosity | > 0 |
Wilting Point / Field Capacity / Porosity | Wilting Point < Field Capacity < Porosity |
Initial Upper-Zone Moisture | Wilting Point ≤ Initial Moisture ≤ Porosity |
Saturated Hydraulic Conductivity | > 0 |
Conductivity Slope | ≥ 0 |
Tension Slope | ≥ 0 |
Upper Evaporation Fraction | ≥ 0 |
Lower Evaporation Depth | ≥ 0 |
Initial Water Table Elevation | ≥ Aquifer Bottom Elevation |
Upper Evaporation Pattern (if assigned) | Must be a monthly pattern |
Also confirm Porosity, Field Capacity, Wilting Point, and Initial Upper-Zone Moisture are entered as fractions, not percentages — enter 0.45, not 45.
3. Resolution
Work through the following steps in order. Do not change values solely to clear the error; trace each parameter to its source data, verify units and import mappings, correct the aquifer relationships, and rerun model validation.
Table 1 : Troubleshooting steps
Step | Action | Why It Helps |
|---|---|---|
1 | In GeoSWMM, locate the flagged Aquifer and record current values
| Isolates the object causing the failure and preserves a record of the original input. |
2 | Walk through the Data Review Checklist
| Provides a systematic review of the Aquifer inputs instead of troubleshooting individual values at random. |
3 | If values were imported, verify the source data and field mapping
| Helps identify import or mapping problems that may not be obvious from the displayed values alone. |
4 | Correct values in GeoSWMM using project data — not by trial and error
| Keeps parameter changes technically defensible and traceable. |
5 | Save in GeoSWMM and let the engine re-validate
| Confirms that the input problem has been resolved and supports subsequent model QA/QC. |
4. Example
Assume Porosity = 0.45 and Field Capacity = 0.50. This fails immediately because Field Capacity ≥ Porosity. Do not simply reduce Field Capacity until ERROR 109 disappears. First verify the intended values using the project's soil data or other documented sources. For example, assume the source data confirms the following:
Parameter | Invalid (fails ERROR 109) | Corrected (from soil data) |
|---|---|---|
Porosity | 0.45 | 0.45 |
Field Capacity | 0.50 | 0.30 |
Wilting Point | - | 0.15 |
Initial Upper-Zone Moisture | - | 0.25 |
Clearing ERROR 109 is not the same as a calibrated model
Clearing ERROR 109 confirms that the Aquifer has passed the applicable SWMM input-validation checks. It does not confirm that the groundwater parameters are appropriate for the watershed or that the groundwater model is calibrated.
After the simulation runs successfully, review groundwater continuity, water-table response, and groundwater exchange flows for hydrologic reasonableness. Any revised Aquifer parameters should be supported by project data, documented assumptions, or calibration results and recorded as part of the model QA/QC process.