Part of the Coronavirus pandemic experience for me has been the daily news briefings. There are days I try not to pay attention to them to keep my mind on tasks for work or just to avoid bad news to stay in a good mood. When I watch the briefings, as a scientist, I am drawn to the more technical aspects of the virus treatment and the outbreak management responses. Regardless of how you feel about it, it is a difficult task to communicate complicated technical information to an audience of various ages, educational backgrounds, and cultural perspectives. Often the comments I hear from people after the briefings are more about the people who delivered the information than the information itself. People trust certain types of personalities, backgrounds and communication styles and therefore are more likely to trust the information from people they trust, even if the information provided doesn’t match held-to beliefs or previous understanding. This is a time where it’s hard to believe in our public figures and the information they provide, or the information provided about them.
Thinking about this mistrust of science and trust/mistrust of the teacher made me think about how much I should trust my own observations. I wondered how much my observations are shaped by the science I have learned in school and throughout my career. I wondered how those observations have impacted how I fish. I haven’t written much about my job in my blog post, but maybe now is a good time to talk about my background in more detail.
I am a fluvial geomorphologist and environmental scientist professionally. I have studied and monitored streams for the past 25 years. Much of my career has been focused on stream restoration. Trout Unlimited, American Rivers, and many other organizations often participate in these types of projects that result in grading new alignments for stream channels, stabilizing banks, building instream and bank structures using large boulders and logs, and planting banks and riparian areas with trees, shrubs and grasses. I worked on many projects throughout the area including dam removals, fish passage structures, large wood structures, and floodplain modifications.
My understanding of streams has more of an academic bent than from many years spent fishing. I have struggled with intuition on when to change flies and when to change spots, but I think I can read the water reasonably well and I understand the physical properties of watersheds. I thought it may be of interest to expand on that scientific background.
Everything about streams that promotes their structure and the life that lives within them is based on water. The water that you see flowing through a stream is a result of a continual cycle of rain, infiltration, runoff, groundwater flow, and evapotranspiration. This is the water cycle and the study of the water cycle is the science of Hydrology. Hydrology, according to Webster’s dictionary, is described as: a science dealing with the properties, distribution, and circulation of water on and below the earth’s surface and in the atmosphere. For the fly fisher, hydrology is specific to the amount of water delivered to a stream from its watershed. A watershed is the area of land on which when rain falls, it drains to the same stream. Watersheds are separated by ridges. Watersheds are described on various scales of size such as the Yellow Breeches drains to the Lower Susquehanna River which drains to the Chesapeake Bay.
Once water reaches a channel the way at which it flows over the land is defined as Hydraulics. Hydraulics (again from Webster’s) is a branch of science that deals with practical applications (such as the transmission of energy or the effects of flow) of liquid (such as water) in motion. This field of science describes the various flow depths, velocities, and amounts of turbulence you observe in streams. When fly fishermen talk about reading a river, it usually means observing the hydraulic conditions matched with the physical structure you see. The saying of “home is the foam” and looking for perfect trout holding water often revolves around finding the “thalweg” of the channel. The thalweg is the lowest portion of the channel, in elevation, where the stream would have flow at the lowest discharge the channel experiences.
Flowing water is incredibly powerful. It shapes the ground over which it flows, leaving the largest particles it can’t lift or roll based on the speed and depth of the water. Steeper channels typically consist of larger boulders, and flatter channels often have sand bottoms. The channel bed and banks form a structure in which the water flows over and around.
Trout have adapted to the hydraulic conditions created by these flow patterns. As water flows towards and past an obstacle it accelerates and then experiences a hydraulic condition known as flow separation. Part of the flow that hits the obstruction slows down (sometimes this is called a pillow by fly fishermen) and part of the flow accelerates past the boulder forming a plunging jet. Downstream of the obstruction, turbulent eddies can sometimes form, which appear as swirling vortices. One particular eddy formation is called a Kármán vortex street (or a von Kármán vortex street). This is named after the fluid dynamics scientist Theodore von Kármán. This phenomenon which creates wakes behind flow obstructions also is responsible for the vibration of a car antenna at certain speeds.
Courtesy: Joseph Straccia
This phenomenon is important to fly fishers as trout species have adapted their body shapes and physiology to use this hydraulic pattern to their advantage. Trout have fusiform shaped bodies. Fusiform means their body shape resembles a torpedo, similarly to a tuna or striped bass, allowing for faster swimming in open water. However, the trout also is slightly compressed, allowing for quick darting movements and the ability to remain still for short periods of time. This body form adaptation is used by the trout to remain in a holding position behind a boulder by matching the curve of their bodies to the wavelength of the turbulent waves. There are some amazing videos of this by some amazing scientists at the Harvard Ecohydraulics Laboratory.
I came to fly fishing after having designed and managed the construction of fish passage structures that mimic natural riffle and step pool structures and understanding the complicated hydraulics required for migrating fish to navigate a stream. I hadn’t had years of fly-fishing observation and skills in my background. It was very reassuring for me though when I could match the observations of those people who were teaching me how to fly fish with the science and engineering principles of my education and profession.
Thinking back to the Coronavirus daily news briefings and the way in which many people doubt the information provided and analyze the ability of the politician, scientific advisor, or television personality to deliver the information, I am aware that most of the world doesn’t work in the same way as the fly fishing community. I wish that we could be provided truthful observations, critical thought, and clear reasoning in all aspects of our lives. But I am thankful that in my fly-fishing world, my teachers, my peers, and my scientific background have a lot of consistency and support those experiences and observations with sound science.
