French Drains & Drainage Systems in Normandy Park, WA

Drainage & French drains in Normandy Park: what to know

The critical areas code is blunt about one thing: point discharges from surface water facilities and roof drains onto, or upstream from, an erosion or landslide hazard area are prohibited. The exceptions are continuous storm pipe downslope, discharge into an existing channel at predevelopment flow durations, and dispersal onto an adequate low-gradient buffer. A drain that ends at a slope edge fits none of them.

Creeks add context. Walker Creek runs through a ravine in the city, and King County’s photo tour shows a slowly eroding bank inside it and bank erosion downstream of SW 171st Street. Water sent toward those ravines adds to flows on banks that are already eroding.

Permits and rules in Normandy Park

The building code’s exemption lists do not name yard drains, and the grading exemption stops at 50 cubic yards and two feet deep. Drainage review applies to a permitted project that builds a pipe or ditch 12 inches or more in diameter or depth, or exposes more than 120 square feet of soil, under Ecology’s 2019 manual. We look up which of those your drain triggers, and whether the roadside ditch is an allowed outlet, before we quote.

Rules change and vary by parcel, so we confirm the current requirements with the city before we start.

How we approach it

Settle the outlet first: continuous pipe, existing channel, or dispersal onto a low-gradient buffer
Tightline downspouts in solid pipe instead of releasing them above a slope
Hold trench depth and soil volume under the grading exemption where possible
Never tie into the roadside ditch without confirming it is an allowed outlet

For the full process, see our Drainage Systems & French Drains page.

Questions from Normandy Park homeowners

Where can a French drain discharge on a sloped Normandy Park lot?

Near a slope, it is limited. Point discharges onto or above erosion and landslide hazard areas are prohibited except through continuous storm pipe, into existing channels, or dispersed onto a low-gradient buffer. On flatter ground, infiltration or dispersion on your own lot is the usual route. The mapping decides which applies.

Does Normandy Park require a permit for a yard drain?

It depends on depth and volume. The building code’s grading exemption covers excavation under 50 cubic yards and under two feet deep, and work beyond that, near a creek, or on a hazard slope can bring review. We confirm with Community Development before digging.

Can I run a drain into the ditch along my Normandy Park street?

Only if the city allows it. The right-of-way chapter will not grant a permit for a use that interferes with street and roadside drainage, and work in the right-of-way needs a permit. We ask the city whether your ditch is an allowed outlet.