Overland Park Drainage & French Drain Installation

Overland Park's detention code measures cumulative impervious area from September 1984, the effective date of the city's first detention ordinance. Everything platted before that date was built with no detention requirement at all. About 21.5 percent of the city's 89,184 housing units predate 1970, concentrated in the older northern grid, with 13 percent from the 1960s and 8.5 percent from the 1950s.

That is why drainage complaints cluster where they do. In the pre-1984 neighborhoods, upstream development sends water downhill at a rate nobody was ever required to slow, and the receiving lots were graded to a 1950s or 1960s standard. The city's own median year built is 1990, so the newer half of Overland Park operates under rules the older half never saw.

The dominant upland soils here are Sharpsburg and Grundy, both formed in loess and both smectitic, which is the technical way of saying they swell when wet and shrink when dry. Sharpsburg runs 36 to 42 percent clay and is moderately well drained. Grundy runs 42 to 48 percent clay, is classified somewhat poorly drained, and has a saturated hydraulic conductivity of only 0.1 to 1.0 micrometers per second.

The number that matters for a french drain is Grundy's seasonal saturated zone, which USDA places at 0.3 to 1.0 meter deep during wet periods, with linear extensibility greater than 6.0 centimeters in the upper meter of soil. Water does not percolate down through that. It perches and moves laterally, which is exactly the condition a properly built french drain is for and exactly the condition that defeats a shallow one. The Blue River itself begins in Overland Park, where Coffee Creek and Wolf Creek meet near the Arboretum in the south of the city.

Overland Park Public Works works from the Design and Construction Standards Manual, which adopts APWA Section 5600 as revised February 15, 2006, and then freezes it: any future revision of 5600 is not in force until the City Engineer adopts it in writing. Detention is not triggered by a flat threshold but by a downstream flooding test, with an allowance letting developments over an acre add a cumulative 8,000 square feet of impervious surface before detention is required.

The rule most homeowners have never heard of is OPMC 7.54.250: water from intermittent discharges such as sump pumps may not be discharged closer than five feet to any adjoining property line. The city's stated reason is that the discharge should percolate on your own ground, and constant discharge reaching a sidewalk or street becomes an abatable public nuisance. No Missouri-side city in this metro has an equivalent setback, so a contractor who works mostly in Jackson County will route a discharge line that does not comply here.