Nerd Terrarium warning: Some terminology and concepts may be considered nerdy.
My first thalweg survey was in a Forest and Range Hydrology class at Cal Poly San Luis Obispo. We were surveying San Luis Creek downstream of downtown San Luis Obispo. I remember we reached a big, deep pool, and as a taller person, I got to go into it with the survey rod because I could reach the deeper parts while still standing. I remember climbing onto a big log and reaching out into the pool to place the rod in what I thought was the deepest point.
And that is what a thalweg survey is. The thalweg is the deepest part of a channel. If you are in a boat and not wanting to run aground, you would typically follow the thalweg. If you were walking up or down a stream, unless you wanted to get really wet, you would typically avoid the thalweg. A survey of the thalweg is done in order to produce a profile view of the creek--from which you can see the slope and pools and riffles.
On Sunday I walked downstream. It was a hot day, but I wasn't prepared to go in too deeply or do too much climbing over debris because I was carrying my sleeping son in a carrier on my chest. Nevertheless, I got farther than the debris-jam and pool that stopped me last year. Peak flows during the winter cleared the jam and deposited sediment in the pool.
