Can I Use this Wetland Inventory Map for My Project?

By Sam Payne

I love wetlands – the different soils and plants, all of it. But I understand that’s not true for most of our clients. Most are unsure about how critical areas fit into home building process and only aware of them because the city planner said they need a permit. They have a lot of questions, with one of the most frequent being:

I found this map of my property online that says I have a wetland on my property. Is that good enough?

Resources like King County iMap, Snohomish County’s PDS Map Portal, and Kitsap County’s Parcel Search provide a wealth of information about the region’s environments and land use types. It’s tempting to type in your address and believe you’re seeing an accurate snapshot of its history. However, the reality is you’re looking at more of a collage of different estimates performed over different years. For instance, the bright blue line representing a stream could be from a study made 20 years ago or drawn using low-accuracy topographic data. And if you’re looking at undeveloped property, the wetlands were most likely mapped from aerial imagery. 

 King County iMap.

King County iMap.

It’s tempting to believe you’re seeing a comprehensive snapshot; the reality is you’re looking a collage of different mapping estimates performed over different years by different authors.

 Three wetland indicators.

Three wetland indicators.

What are planning maps used for then?

Regional planning. For consultants like me, homeowners like you, and city planners, planning maps are a good first source of information before starting on a big project. Think of it liking checking the weather before you head out for the day. It might say cloudy with no chance of rain, but you won’t know for sure until you go outside.

I chance it sometimes.

That’s not the best idea with critical areas. A few months ago, a Seattle homeowner with a ravine on her property contacted us after receiving a violation notice from the City. A tree from the neighboring park fell and damaged the fence and retaining wall supporting her backyard. She hired a contractor to repair the wall without researching City requirements. Unbeknownst to her, the ground the contractor was digging into and filling in was inventoried by the City as a wetland. She was now facing a fine and requirement to assess and repair the damage done to the nearby ecosystem. A delineation was the first step.

It’s easy to see, from a distance, why someone could see a wetland when looking at the ravine on her property. However, when I checked it in-person, it was obvious the mapping was mistaken: the plants were not typical wetland plants and I found no sign of groundwater, even after digging three feet. Plus, the soil had a high chroma (reddish color) that is common in dry, well drained locations.

She was lucky. Ordinarily, after the delineation, the owner would be required to provide a mitigation plan, install mitigation planting and monitor the site for up to 5 years. These studies, in addition to violation fees, could have cost her tens of thousands of dollars. Yet, we have seen just as many clients who were not as lucky—or worse. It's not uncommon for landowners to buy a property with no mapped wetlands only to learn later it was totally encumbered by wetlands and a buffer.

Bottom line: Know Before You Start

Natural systems are forever changing: trees are grown and removed, water collects in a backyard and then channels down a driveway. A regional or city-wide inventory map isn’t going to give an accurate record. As a landowner—whether purchasing or looking to make a change--it’s in your best planning and financial interest to know what’s happening on your site before getting to work. (Plus, it provides for some fun landscape opportunities!)

Planning maps are a good first step, but the only way to be 100% certain about the presence of wetlands or streams on your property is to hire a wetland consultant who can advise you how to proceed in a way that works for you.

Have Questions About Your Property?

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