Master drainage plan
What is the purpose of a master drainage plan?
A master drainage plan (MDP) is intended to prevent significant adverse impacts to the natural and human-made drainage system, both on- and off-site. A MDP is a comprehensive drainage control plan usually prepared during the Large Site Drainage Review process.
What activities require a master drainage plan?
A master drainage plan is required if:
- The project is a designated Urban Planned Development (UPD) on the King County Comprehensive Plan Land Use Map, OR
- The project, in full build-out, results in 50 acres or more of new impervious surface within a single sub-basin or multiple sub-basins that are hydraulically connected across sub-basin boundaries, OR
- The project is on a site of 50 acres or more (including opens space, critical areas, and growth reserve) within the recharge area of a sole-source aquifer as designated by the EPA and depicted as such on the "Areas Highly Susceptible to Groundwater Contamination Map" adopted as part of the King County Comprehensive Plan.
A MDP typically involves detailed sub-basin specific hydrologic data collection and modeling, however, a limited scope or special study may be appropriate for particular projects.
How much will it cost?
See the Permitting Department's current fee schedule for an estimate.
Where can I get application materials?
- Refer to the Master Drainage Plans Packet
- Request an application packet by mail, by calling the Permitting Department customer service at 206-296-6600 or
- Pick up an application packet at the Permitting Department in Snoqualmie (see map and directions).
How do I submit my application?
Notes / Comments
For more information, contact the Permitting Department at 206-296-6600.
Chapter 9.04* of the King County Code
The Department of Permitting and Environmental Review. For questions, please contact the customer service at 206-296-6600.