Yard Drainage & French Drains in Sammamish, WA

Because the absence of slope is the problem rather than the protection. Water arriving on sloped ground at least runs across the surface and away; water arriving on a level plateau simply stays where it lands. Underneath is glacial till, which passes water downward very slowly, so once the topsoil is saturated there is nowhere left for the next rainfall to go. Between October and March, when nearly all of our 38 inches arrives, the ground never gets a dry spell long enough to recover. It is not a fault in your garden — it is what a plateau does.

The Sammamish plateau carries genuine wetland and seasonally saturated ground scattered through it, some of it regulated as a critical area with its own rules on what can be built and how close. The difficulty is that several of these look entirely unremarkable in summer — ordinary lawn, ordinary planting, nothing visibly boggy. They reveal themselves between November and March. If part of your garden behaves differently from the rest through the winter, that is worth establishing properly rather than draining, because if it is regulated the approach is different.

Only if the drainage is fixed first, and this is the most common turf mistake we are called to correct on the plateau. Turf backing is permeable and passes water freely, so on ground that already fails to drain, water goes straight through the turf and then sits on the same hardpan it always did — except now it is trapped under a surface you cannot aerate or reseed. The result performs worse than the lawn it replaced. Built the right way round, with a proper drainage base and a real outfall underneath it, turf on a plateau lot is excellent, and it removes the winter mud problem outright.

The buried portion, generally not — once the surface is reinstated there is nothing to see. Where it can come up is anything visible: a catch basin grate in a front garden, a channel drain across a driveway, or a constructed outfall near a boundary. Klahanie, Trossachs, Sahalee and most of the newer plateau developments operate architectural standards that can reach those. We ask at the first visit and produce the layout in a form suitable for a submission where review applies, which in practice is usually a formality.