Zoning laws are founded in something that does make sense: that the community as a whole does have a
stake (and should therefore have a say) in what you do with your land. Without planning and zoning, you are perfectly privileged to build a inappropriate content shop next door to an elementary school, or a boiler factory next door to the hospital, convert a warehouse into low-income apartments with no place for the children of your tenants to play except in the parking lots of the properties next door....
They can tend to get very much out of hand -- for example, local zoning regulations that say what colors you may use to paint your house and trim, what objects are permissible in your yard, etc. But the basic principle is valid -- limited regulation to assure that the property owner's rights are not used in a way harmful to his neighbors and the community.
The Supreme Court has been very explicit that zoning is constitutional (
Euclid v. Ambler and subsequent cases) but that it cannot be used to deprive a property owner of any beneficial use of his property. The latter constitutes a
taking under the Fourteenth Amendment, and the property owner must be (1) permitted to use his property in reasonable ways and (2) be compensated for any complete deprivation of use. The leading case is
First English Lutheran Church v. California Coastal Commission, where (IIRC) the church's building was damaged in a storm and they were not permitted to rebuild in their lot owing to the "open space" requirements for the coastline imposed by the commission.
To require, on the other hand, that, e.g., 50% of a lot be kept "permeable" -- no structures or impermeable cover, such as a blacktop parking lot, be placed on it -- to allow safe drainage of stormwater, is quite legitimate.
A link to the King County Draft Environmental Impact Statement on the new proposal (table of contents; relevant text is in a series of PDF files linked to on the page).
Seattle Times article on the proposed law.
According to the Seattle Times article, the regulation affects
new construction (including replacement construction) within a couple hundred feet of certain streams and of wetlands in a rural area of the heavily-populated county. So it's not like it's making massive restrictions on all the land in the county. And a house and a driveway
will cover less than 10% of a five-acre lot, and most people wanting a large lot will want to preserve natural cover over much of it. It does not require that you cannot buy a smaller building lot somewhere else in the county; it restricts certain areas to large-lot keep-it-natural development. You could still even build a WalMart or other big-block store there -- at the cost of surrounding it with a
lot of natural area, to keep the store and parking lot within the 10% impermeable restriction and preserving 65% in its natural state.
