Should I Wait to Get a Wetland Delineation Until the Dry Season?

Written by Hugh Mortensen, PWS

Wow, nice weather lately. Here it is July 3rd and I woke up to clouds and rain for my drive to Kirkland. Seems like we’ve had a wet spring and early summer – better wait on that wetland delineation, right? All that rain might make the wetland bigger than it really is, huh?

Does rain make wetlands bigger?

 Checking a soil sample for wetland soil characteristics.

Checking a soil sample for wetland soil characteristics.

We get this question often from clients and it seems reasonable. Turns out wetland delineation is a bit more complicated than just how much water has fallen from the sky lately. While the presence of growing-season soil saturation is one wetland indicator, there are others that help avoid the "false positive" of lots of standing water. For example, to be included in the wetland, you also have to have the right type of plants. Many of our common non-wetland plant species can tolerate saturation for short duration, especially in the winter. Plants such as snowberry, bigleaf maple, and salal can take some short-term inundation. Soils are important too. Frequently, we will find inundated areas after a rainstorm that have bright soil colors, low organic content, and other "upland indicators."

Are wetlands smaller in the summer?

 A wetland biologist assessing a wetland in western Washington.

A wetland biologist assessing a wetland in western Washington.

Okay, so delineation after a storm still works. What about doing the work in August when the soil is really dry? You may not have a wetland at all, right? Well, it turns out that soil saturation leaves behind markers, or in the words of a wetland biologist: "hydrologic indicators." Also, be aware most wetland reviewers are skeptical about lack of hydrology when you have positive soil and plant scores. While hydrology drives these two other indicators, it is also the most difficult to assess because, unlike soils and plants, it can change dramatically over the short term.


Here at The Watershed Company, we strive to get it right the first time with wetland delineations and reconnaissance. Identifying the accurate boundary and classification is the first step in getting your project approved and built with minimal delay and maximum efficiency.