Erosion Control & Drainage

Hydrology assessment is the foundation of effective drainage design. We walk the site during or after rain to observe flow paths, identify problem areas, and measure watershed areas contributing to the site. Soil infiltration rates, slope percentages, and existing drainage structures are documented. For larger projects or permit requirements, we perform rational method calculations to size culverts and channels for design storm events—typically 25-year storms for residential access, 100-year for major infrastructure.

Surface drainage design: We establish positive slopes (minimum 2%) to move water away from structures and toward controlled discharge points. Swales—shallow vegetated channels—catch sheet flow and convey it to culverts or natural drainage. Ditch grades are designed for non-erosive velocities (under 5 fps) or armored with riprap where velocities are higher. Berms and diversions redirect uphill water around building pads and prevent concentrated flow from crossing driveways.

Culvert sizing and installation prevent washouts and flooding. Culvert diameter is calculated based on watershed area, slope, roughness coefficient, and design storm intensity. We install HDPE, corrugated metal (CMP), or concrete pipe depending on load requirements and service life. Inlet and outlet protection—riprap aprons, headwalls, or flared end sections—prevent erosion and undermining. Culverts are bedded on compacted gravel, surrounded with backfill, and covered to design depth (typically 12-24 inches minimum under driveways).

Subsurface drainage systems: French drains and curtain drains intercept groundwater before it reaches foundations, retaining walls, or building pads. We excavate trenches, line with filter fabric, place perforated drain pipe, backfill with clean drain rock, and wrap with fabric to prevent siltation. Drains are sloped 1-2% and daylighted to safe discharge points—never into septic drain fields or storm sewers without permits. For retaining walls, we install back-drains with weep holes or collector pipes to relieve hydrostatic pressure.

Erosion control measures stabilize disturbed soils and protect water quality. Silt fencing and straw wattles trap sediment at site perimeters. Erosion blankets and hydroseeding establish vegetation on slopes. Riprap—angular rock 6-18 inches diameter—armors culvert outlets, ditch bottoms, and steep slopes against erosion. Check dams in swales slow water velocity and trap sediment. For sites over 1 acre, we prepare Stormwater Pollution Prevention Plans (SWPPP) and coordinate NPDES permit compliance.