Designing a Drainage Trench System for a Flat 2-Acre Yard

Trench Width, Pipe Size, and Slope

• No gravel needed around pipe if using perforated pipe; water enters from soil directly.
• 4-inch trench OK for ≤3.5-inch pipe. For 8-inch main collector, use wider trench.
• Minimum slope: 1/16 inch per foot for 8-inch pipe; 1/8 inch per foot for 3–6 inch pipe.
• 110-foot main run is fine with proper pitch; ensure outlet is lower than all inlets.

Layout

Connect each low spot to the main trench with lateral lines. Use a laser level to set grades accurately. Consider a drywell or pop-up emitter at the terminus if no natural outlet.