Hi! If you’ve bumped into my account, there’s a good chance you were looking at some water or wetlands in the Marysville watersheds. I noticed that a lot of the streams on OSM were sloppy, and a majority are just non-existent, so I’m fixing that. I have only mapped in Snohomish County, Washington and most of these maps are exclusive to here, but there are probably equivalents in other jurisdictions. Anyway, I’ll go through the government maps I use to accurately map waterways, and explain how I use them.

Snohomish County Maps

Snohomish County provides many different interactive maps for various uses, and several are very helpful for mapping water. This link goes to all of their interactive maps, which includes the maps below plus some others, which could be useful for other projects or neat to look at.

Aerial Imagery

Snohomish County provides the highest-quality imagery available for use, and It’s available in OSM already. I just wanted to mention it because it is the most detailed from what I can tell, and I want to encourage people to use it. In addition, there are two years available; one is from Winter (2022) and the other is from Spring (2020). This is very useful because it is much easier to see the ground and water when there aren’t leaves in the way. The summer imagery can also be useful since it’s a bit more bright and can show the outline of trees better.

*note: the link is currently broken, but you can paste this link into the custom background to get the 2022 map: https://gis.snoco.org/img/rest/services/Imagery/Aerial_2022/ImageServer/exportImage?f=image&format=jpg&bbox={bbox}&imageSR={wkid}&bboxSR={wkid}&size={width},{height} Thanks to archpdx on slack for getting the new link!

Historical Satillite Imagery

This tool lets you swipe between two satellite images from two different years, and can sometimes show why a reference map is wrong and outdated, or clarify something that used to be visible. For example, a ditch that used to exist was covered up by a farmer, and reference maps showed water there. I didn’t know if there was a pipe there or something, but using the historical imagery showed that it was gradually blocked, so there likely wasn’t anything put in. It can also erase newer bushes so you can see the paths of ditches better.

Snohomish Water Management Drainage Inventory

That may sound like a very boring name, but it is probably my favorite map. It contains ~90% of the culverts, ditches, and underground runoff water pipes in the entire county. It is probably the most critically important map other than the aerial imagery, because oftentimes culverts are not obvious, so it would otherwise be a complete guessing game. It also shows many drainage ditches, which can sometimes be parts of creeks. It’s missing most of the creeks and focuses on infrastructure, so just keep that in mind and don’t trust it for that. One more thing, though; all of the little stars around the map are sample data points that they took, so that is occasionally helpful for determining the center (thalweg) of a creek.

Snohomish and Marysville Watershed Maps

These are obviously quite handy for mapping water. They usually have the main streams drawn and labeled, and show you where to look. (I once spent half an hour looking for a connection when I was in the wrong watershed, lol.)

Nationwide and State Tools

Ok, enough of the hyper-specific maps, and on to the big ones.

USGS 3D Elevation Program

This map gives a Lidar view of the entire country. It is extremely helpful for looking at small streams in wooded areas since it penetrates trees and only looks at the surface. It lets you see where a valley is exactly and usually shows the exact dip where a stream is. It has been my only source for things at some points, so it’s very helpful, and it’s just a good guide when there are some tricky trees.

National Wetlands Inventory

This is a map that shows wetlands based on satellite imagery. It’s quite helpful and I’ve used it a lot, but it can miss areas at times, and I’ve gotten pretty good at identifying what is or isn’t a wetland by sight now, so I’ve been using it less. Still a great tool though to confirm what you think or call attention to an area you might have missed.

USGS Topo Map

The USGS topo map is a built-in background map for OSM, but I find the topoBuilder app to be easier to navigate and provide a bit more detail. It is one of the most detailed maps of creeks out there, but that’s not saying much, as it’s missing a few branches and can be slightly inaccurate at times. It’s a great map, but use it with caution and always cross-reference with sat images and other maps.

And that’s the list for now! I am brand new to this, so I will update this as I learn and grow as a mapper :)