When a Tree Falls… it’s LWD!

When a Tree Falls… it’s LWD!

This week, my partner Karl and I started our habitat mapping project in Redwood Creek. Our first task for the mapping project was to collect geographic locations at the edges of the water and along the banks, and most importantly, locate the large woody debris (LWD).

LWD is an important feature in creeks containing salmon or trout, because it improves habitat quality by creating shelter. When wood falls in the creek or is washed downstream, it creates large pools by diverting flows. These areas are used as a safe place for young fish to feed and grow. By mapping LWD, we can know where the best rearing habitat is for endangered Coho in Redwood Creek.  

We geared up with our handheld GNSS (Global Navigation Satellite System) unit and an extra antenna to help us get better satellite reception in the creek. Once one of us found a spot with good coverage, we could use the built in laser rangefinder to offset our position and collect many points along the creek without moving our antennae and losing our coverage.

To make using the rangefinder easier (and more fun!), Karl built a target which we attached to a wading staff. The target was placed over where we needed a point along the creek and the person using the GNSS unit would locate and shoot the target with the laser!


While target practice kept us entertained, the field days started to feel long when the machines misbehaved. This was a great reminder that field work requires patience, lots of trouble shooting, and a sense of humor.

On top of technical difficulties, many parts of the creek were newly rearranged after record rainfall this past April over Marin County. Some areas of the creek were messy with log jams made of new LWD that had just washed downstream, creating side channels and complicated flow patterns. But, while complex water systems might have frustrated novice cartographers like Karl and myself, this is exactly what fish need! Often times, in the stretches of the creek that were hard to map, just as we were getting frustrated, we would see a handful of young Coho swimming through submerged branches!


There is definitely some fish down there! 

Nature sure has an interesting way of working itself out, but it was only recently that natural resource professionals have really appreciated nature’s nuances when it comes to stream health. Up until the 1980s, LWD was removed from Redwood Creek to manage bank erosion and ensure fast flows through the channel. Today, we know the importance of LWD and allowing the creek to find new ways to meander through the watershed and form little pockets of shelter for fish. Moving through Redwood Creek today was, in parts, messy and complicated, but seeing baby Coho, it was hard not to appreciate all of nature’s messiness and complications.  

Hopefully by the end of the project we can create a map that shows all of Redwood Creek’s wild and meandering waterways!

… until, of course, the next big rain event when the creek decides to rearrange (again).

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