Infiltration Trench Volume Calculator
Calculate infiltration trench volume accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Formula
Storage Volume = Length x Width x Depth x Porosity | Rainfall Capacity = (Storage Volume / Drainage Area) x 12
The total trench volume is the rectangular excavation volume (length x width x depth). The effective storage volume is the total volume multiplied by the aggregate porosity, since only the void spaces between stones can hold water. Rainfall capacity in inches is calculated by dividing the storage volume by the contributing drainage area and converting to inches.
Worked Examples
Example 1: Residential Stormwater Trench
Problem: Design an infiltration trench 50 ft long, 3 ft wide, and 4 ft deep with 0.40 porosity aggregate to handle runoff from a 5,000 sq ft drainage area.
Solution: Total volume = 50 x 3 x 4 = 600 cu ft = 22.22 cu yd\nStorage volume = 600 x 0.40 = 240 cu ft = 1,795 gallons\nRainfall capacity = (240 / 5,000) x 12 = 0.58 inches\nGravel needed = 22.22 x 1.4 = 31.1 tons
Result: 240 cu ft storage, handles 0.58 inches of rainfall, requires 31.1 tons of gravel
Example 2: Commercial Parking Lot Trench
Problem: Calculate storage for a 100 ft x 4 ft x 5 ft trench with 0.35 porosity serving a 15,000 sq ft parking lot.
Solution: Total volume = 100 x 4 x 5 = 2,000 cu ft = 74.07 cu yd\nStorage volume = 2,000 x 0.35 = 700 cu ft = 5,236 gallons\nRainfall capacity = (700 / 15,000) x 12 = 0.56 inches
Result: 700 cu ft storage, handles 0.56 inches rainfall, requires 103.7 tons of gravel
Frequently Asked Questions
How do you determine the required size of an infiltration trench?
The required trench size depends on the drainage area, the design rainfall depth, and the soil infiltration rate. First, calculate the runoff volume from the drainage area for the design storm event. Then divide by the effective storage porosity of the aggregate fill to get the total trench volume needed. The trench dimensions must also ensure the stored water can fully drain within 24 to 72 hours based on the native soil infiltration rate.
What porosity value should I use for aggregate fill in an infiltration trench?
Clean, uniformly graded stone aggregate typically has a porosity between 0.35 and 0.40, meaning 35 to 40 percent of the trench volume is available for water storage. Crushed stone ranges from 0.30 to 0.40, while well-graded river gravel is typically 0.25 to 0.35. Manufactured plastic storage chambers can achieve effective porosities of 0.90 or higher, significantly reducing the required trench footprint compared to stone-filled trenches.
What soil types are suitable for infiltration trenches?
Infiltration trenches work best in well-draining soils such as sandy loam, loamy sand, and sand with infiltration rates of 0.5 inches per hour or greater. Clay soils with rates below 0.27 inches per hour are generally unsuitable. A percolation test or soil boring should be performed at the proposed trench location to confirm the infiltration rate. The seasonal high water table must be at least 2 feet below the trench bottom to prevent groundwater contamination.
How much gravel do I need for an infiltration trench?
The gravel quantity equals the total trench excavation volume since the entire trench is filled with aggregate. Calculate length times width times depth to get the total volume in cubic feet, then divide by 27 for cubic yards. To convert to tons, multiply cubic yards by approximately 1.4 for typical crushed stone. A 50 ft long by 3 ft wide by 4 ft deep trench requires about 22.2 cubic yards or roughly 31 tons of stone aggregate.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.