Spread the Nerd

Here at the Nerd Nest, we’re big on nerd pride. We live in a world where it’s cool to be smart, and we want a space in that world where others can share their nerdy interests with you too. Welcome to Spread the Nerd, a guest series where awesome nerds like us tell you about their nerdy area of interest and teach you a little something too.


Today’s Spread the Nerd is brought to you by Serena of A Girl Named Sue.

Do you know how the Hulk bulks up and turns a lovely shade of green when he gets angry? I imagine that, in the seconds leading up to this explosion of awesome power, there is this tension and vibrational force at work inside him, ready to burst forth. That feeling pretty much describes me in the thick of research or a policy debate about the subject I’m about to tell you about, so I’m going to do my best to not let my nerd explode all over the page.

Hi, I’m Serena, and I’m a river nerd. I’ve been known to sometimes say that I spend a lot of time at work thinking and talking about dirt, and while I’m being a tad flippant and simplistic, you wouldn’t believe how much truth is hidden in that statement! What was that? What do rivers and “dirt” have in common? Fluvial geomorphology. Rivers, in addition to conveying water, move sediment (aka what I flippantly referred to as dirt), and fluvial geomorphology is the study of the movement and transport of sediment in river systems and the land forms these processes create or have created.

The first thing to know about sediment is that there are different types that range anywhere from sand and coarse gravel to clays and silts. Sediment is classified according this grain size (yep, a single particle). The image from the University of Michigan (below) does a great job of illustrating this. (Click on the image to view it larger.)

Fluvial Geomorphology | Spread the Nerd with Serena from A Girl Named Sue

The type of sediment you’re dealing with is important because they each affect physical (and biological) processes in different ways. For example, sands and gravels tend to be transported along the bed of a river channel and often comprise what we consider a river’s natural “load” (i.e., bedload). This type of sediment can contribute to better quality fish and bug habitat and is often cleaner due to the difficulty pollutants have in binding to it.

Your finer sediments, on the other hand, tend to comprise what we call suspended load. Because this sediment tends to be transported throughout the water column, it’s often why you have cloudy water that looks like chocolate milk. This sediment blocks light and decreases dissolved oxygen (DO) levels, two things critical to healthy fish populations. If DO levels get low enough, it can result in fish kills and harmful algae blooms. Also, unlike its coarser brethren, contaminants bind more easily to finer material.

Sediment can come from any number of sources! Small, headwater streams coming off mountains erode rock particles and accumulate a variety of rock, pebble, and sand that is transported downstream. These headwater streams join up with other tributaries, which eventually connect with our larger river systems. Runoff can be a significant source of finer sediment. An example of this is the soil at construction sites for new developments. These sites are pretty raw during construction, and if a storm hits, this material can be carried down onto the roads and into storm drains, eventually making its way into our rivers. I could go on, but I’m thinking Megan and Jake aren’t looking to publish a Spread the Nerd book.

Why should you care about fluvial geomorphology? You didn’t think I saw that questioning look, did you? The amount and character of sediment in a river directly affects the health and prosperity of fish and bugs (their food). If the fish aren’t healthy or abundant, what will the anglers catch? What will the cute little river otter or other wildlife eat? I haven’t even ventured into the topic of contaminated sediment, which is a whole other ball of wax.

The movement of sediment through a river system can also change the river’s form (i.e., shape and direction) over time. If an obstruction causes sediment build up on the right side of the river channel, the river could put additional stress along the left river bank, eroding it and potentially threatening infrastructure like roads, utility lines, or even your backyard. All of the things humans do to rivers–building cities and neighborhoods right up around them, damming and straightening them–impact a river’s natural processes.

The world of fluvial geomorphology is huge, and I’m just giving you the tiniest tip of the iceberg. You can always leave a comment or email me with questions if you want to know more.

Thanks so much to Megan and Jake for having me! I hope I did the nerds proud!


Serena spends her days working to restore damaged rivers as the director of river restoration at a national environmental group. However, in her free time, you can find her writing about books, travel, and sharing stories over at a girl named sue and probably rambling way too much on two podcasts, That’s What She Read and Friday Night Dinner: A Gilmore Girls Podcast.


Are you a nerd? Do you want to share your passion with the world? E-mail us and you could be the next person featured in Spread the Nerd!