Small Project Stormwater Management Program

Infiltration Trench Sizing Calculator

Enter the dimensions of your proposed impervious structure to calculate its area and the recommended infiltration trench size. Screenshot or save your result to submit with your permit application.

Structure dimensions

Design assumptions

Defaults assume clean AASHTO No. 3 stone (~40% void space) and a 3.5 ft. trench depth. Adjustments to either the trench depth or preferred trench width (ft.) based on field conditions.

If stone other than clean AASHTO No. 3 stone (~40% void space) is used this calculator cannot be used due to the change in void space.

Calculated results

Area 0.00 sq. ft.
Enter dimensions to see program status.
L: 0 ft. W: 0 ft.
Runoff volume (cu. ft.) 0.00
Required stone volume (cu. ft.) 0.00
Required footprint (sq. ft.) 0.00
Option 1 — Length × Width 0.00 × 0.00 ft.
Option 2 — Square trench (L = W) 0.00 × 0.00 ft.
Less than 400 sq. ft. — no Small Project Stormwater Management requirement. 400–1,000 sq. ft. — use this calculator. 1,000 sq. ft. or greater — full Ordinance 61 requirements apply. If your structure is not a rectangle, square, or circle, contact the Environmental Project Manager for assistance.