How to Read a River
Reading a river is not a simple science. Throughout history, people have tried to develop ways to read rivers, to predict hazards, and plan the best routes to avoid them. There are many practical tips and tricks which have been passed on throughout the years. But much of modern river reading comes back to the study of fluvial geomorphology.
Fluvial geomorphology certainly sounds like a bit of a mouthful. So let’s break it down. Fluvial means the processes associated with running water, like in rivers. Geo means earth, and morphology refers to the shape of the channels. So fluvial geomorphology is just the study of the function and form of streams, and the landscapes around them.
If you’re still feeling a bit confused, think of it like this. The main principle of fluvial geomorphology is that water takes the path of least resistance. That means that if there’s a large boulder in the river, then water is likely to around it, as more and more water is pushed to the side by the object blocking its way.
The principle of water taking the path of least resistance explains most river hazards, most of the things you’ll be looking out for when you’re reading a river. The nature of water in this way explains why blackwater exists behind large submerged rocks. It explains why the current is strongest on a curve’s outside bank, as the water has more space to move and longer to travel.
Reading a river can add to your camping trip a knowledge of your surroundings, and will help make your boating, canoeing or kayaking trips even safer. Whether you’re going on an outdoors adventure in Illinois, Washington State, Pennsylvania, Michigan, or New England, there are rivers to read all over this great country! To understand how to read a river, we first need to know about how the flow of water works, and some of the relevant terms used in river reading.
Reading the current
Current happens when water flows downstream, down a river or stream. As the water is flowing downstream, through the current, it follows the path of least resistance. This means that it always finds the easiest route as it’s flowing, the clearest, most direct, steepest route so that gravity and less resistance helps it to flow faster.
The word velocity refers to the speed of the current as it travels. The velocity of the water is affected by the volume (or amount of flowing water, often measured in cubic feet per second (CFS)) of water flowing downstream in the current. It’s also affected by the width of the river and the gradient (the angle of the slope).
Volume is the amount of flowing water, often measured in cubic feet per second (CFS). Because of the way that gravity works, the higher the volume of the water, and this the heavier it is, the faster it flows. The speed at which the current flows is also affected by the gradient, or slope of the riverbed, of the traveling water. A riverbed with a high gradient often has fast-flowing shallow water. If the riverbed is wider, then the velocity of the current is often slower.
Following the path of least resistance
Friction happens when water comes to an obstacle, slowing its velocity. Because of friction, water at the bottom of the river bed often flows slower, whereas water at the top of the river flows quicker because there is less friction. This difference, between the speeds of water on the riverbed and at the surface of the current, is called laminar flow.
Similarly, near the banks of the river, the water is also slower because of friction on the river banks. This is called helical flow and produced a spiral current. Spiral current refers to the phenomenon where the slower water that’s been flowing leisurely next to the banks is drawn not the faster currents of the main body of water, towards the middle of the river. This water then spirals down to the bottom of the river, propelled by the water, and then moves over to the shore. Next time you’re next to a river, drop a stick into the water at the side of the river, and watch this movement in action!
Laminar and helical flow
Laminar flow is usually found at the center of the river. What it means is the fastest water traveling with no restrictions or obstacles in a straight line down a river. This is usually the easiest, and most convenient, part of the river to go boating, canoeing or kayaking. Helical flow, however, is found along a shoreline and is a current flowing in a corkscrew motion that is constantly rolling and pushing out into the laminar flow. Be careful of the helical flow: the spiral motion of the water flowing can sweep a person off their feet and potentially even push them into the main current of faster water or make swimming back to shore a challenge.
River left / river right
When we’re speaking about the flow of the rover and potential hazards on the river while river reading, there’s always one-way we see directions. Similarly to stage left or right. You always speak of the river looking downstream, meaning that river left is the left of the river, if you’re looking at it downstream!
Reading a river means knowing what to look for on the surface of the river, and what that indicates as to what’s happening below. Reading a river can be just as useful a safety precaution as wearing a life jacket. Here are some features that you should be looking for when you’re reading a river:
Strainers and the outside curve of the river
Strainers are things that often pile up in the curve of the river. On a river bend, the water usually moves faster and is deeper on the outside of the curve. Because of this, the water has an increasing amount of volume on the outside of the bend, which cuts into the bank.
This is where strainers can often be found. Strainers are debris such as tree limbs, which often trap solid objects such as trash, or even people! And be vigilant, because strainers aren’t always entirely visible. Sometimes they can be almost fully submerged. Watch out for bouncing twigs, as these can indicate a partially submerged strainer, and make sure to avoid these if you’re on the river in a boat, kayak or canoe.
When you’re reading a river, especially if you’re looking for a safe route to canoe or kayak, always avoid strainers. Avoid getting swept into the bank, too, by the stronger currents here, by avoiding the outside curves of river bends. It’s difficult to break free once you’re trapped in a strainer.
There’s a lot of water pressure on you, and on your boat or kayak, if you’re stuck in the bow of a tree and struggling to break loose! If you see a strainer coming up, try and aim around it, or back paddle a little to avoid it.
If you’re on the bank of the river, though, take a closer look at strainers. They play a valuable role in the form and function of the river. This is because the water moves at a 45-degree angle away from the obstruction, allowing a safe place for wildlife to rest, and room for fish to feed.
If you’re looking down a river, and you see what appears to be a light-colored pillow emerging from the water, then what you’re looking at is a pillow rock. A pillow rock is water, sheeting over a big flat rock which is close to the surface of the river. The slope of the rock forces the water passing over it to speed up, shooting off the edge.
If you see a pillow rock, avoid it at all costs. Try and maneuver around it, or back paddle and then take a different angle. If you hit a pillow rock in a canoe or a kayak, you risk damaging it, or if you hit the rock at a wrong angle, you could potentially capsize.
Make sure to always be on the lookout for pillow rocks. As you become more experienced at reading the river, you might even be able to take advantage fo the quicker water flowing past pillow rocks, to pick up a bit of speed.
A pillow is a different river hazard to a pillow rock. A pillow occurs when the water piles up on the upstream side of an obstruction, usually in a frothy foam of water as it hits the rock, thus resembling a pillow from afar. If you see a pillow, it usually means that the object is solid. If there isn’t a pillow in front of an object, usually a rock, then it means it is undercut (or the water can pass below the object or obstruction).
If you see a pillow in the river on a kayak or canoe, try and maneuver around it, or back paddle and then take a different angle. Just like if you hit a pillow rock in a canoe or a kayak if you hit a pillow, you risk damaging your canoe or kayak, or if you hit the rock at a wrong angle, you could potentially capsize. Make sure to always be on the lookout for pillows, as with all river hazards.
Eddies are another type of river hazard that we should be watching out for when reading a river. An eddy is a current created behind a rock or other obstruction in the river that flows in a circular upstream direction. The flow of the eddy is opposite to the direction of the main laminar flow.
This means that it hits the rock, tree branch, or other obstruction, and goes back in the opposite direction, then swerving around to pass past the obstruction. The visual separation between an eddy and the main current is the eddy line, the line where it ends to pass the obstruction on the other side.
Upstream Vs are formed by an obstruction, usually a lot smaller than the ones which cause pillows or are pillow rocks. Upstream Vs refer tot he shape made in the water of the river upstream, as a V-shaped white shape of foam or current is seen. The location of the upstream V depends on where the obstruction is located, in the river. It could be right on top of the obstruction if it’s just below the water’s surface. Or, if it’s much further back from the obstruction, this means that ti’s submerged far in the river.
A downstream V is formed when water is funneled, or constricted, traveling fast and low, between two obstructions. This then forms a V, deeper than the two obstructions, that points downstream. If you’re white water rafting then potentially this could give you the boost in speed you’re looking for. However, be careful with downstream Vs. They are river hazards, after all, so you shouldn’t brave them without training and the proper gear. Avoid them completely if you’re on your own, are less experienced, or you’re in a hard boat or kayak or canoe.
The inside of the river bend
Unsurprisingly, opposite to the outside of the river bend, the inside of the river bend is suavely where you find the slowest and shallowest water. This might be perfect for you if you’re paddling or just playing around in the water with your family.
However, we wouldn’t recommend going canoeing, kayaking, and especially not sailing in the inside of the river bend. This is because the water is often very shallow here. If you’re going boating, you’re more than likely to scratch or damage the underside of your boat in these areas.
Channels are created as water bounces off obstacles and flows around them, following the path of least resistance. Due to the velocity of the water, and how it flows quicker in the center of the river, in channels with deep water, a downstream “V” is formed as the currents meet in the channel. Rocks or shallow areas are on the sides of the river, meaning that there’s a safe channel down the middle, although it may be a lot faster. But, you need to be careful, as always when you are reading a river. Channels often flow very fast, so if there’s a rock at the end of the chute, it may be very hard to see. Always stay vigilant.
Low-Head dams should be avoided for obvious reasons if you’re boating, kayaking or canoeing, but they’re interesting where it comes to reading and understanding a river. Lots of people know about the dangers of going over the top of a low-head dam, but not many think about the dangers of canoeing or kayaking underneath it.
But it’s not something to be underestimated: A dam with a waterfall only of 6 inches can kill! It creates a back current that can be potentially fatal. This is how it works:
Low-head dams create dangerous recirculation currents at the base of the dam known as a hydraulic. As water flows over the dam, a depression is formed in the water. There’ Backwash which is water, which is flowing from the bottom back towards the dam face.
This is often bright wight in color, as it’s very aerated, from the impact of the water tumbling over the dam. Water downstream rushes back towards the dam face to fill in this depression, in what is called the boil line. And then the water flowing from the boil line and the backwash is what’s called the outwash, and this, of course then flows downstream.
Reading a river isn’t just about looking at the surface of the water to see what lies beneath. It helps us to know what potential dangers could lie ahead, or how best we can navigate a river to speed up or stay safe. It’s also a fascinating window into how fluvial geomorphology works, and how the geology of the world can be shaped by the movement and flow of water.
There are a few different variables that can affect how the river behaves and may change the way in which you read a river or the number of hazards you see. Features and hazards in the river look and act differently depending upon the water level. And the water level is of course, not at a constant. It can be affected by many different factors such as rainfall, snowmelt and flow adjustments at upstream dams, for example.
Many people take a huge amount of joy in the varieties of features which can be present in a river. Some features, which some kayakers see as hazards, might be a dream for someone who’s going white water rafting. If you’re thinking of making the most of the many features of a river in this way, then make sure you go with all the right kit, and a trained professional.
The more time you spend around rivers, the more you get to learn about their processes and watch them change and evolve. Think about buying a book on the science of fluvial geomorphology, or attending a course or doing an online quiz, to understand even further the processes of the river. Getting to grips with nature in this way will help you predict any potential hazards which might come your way, and can add to your enjoyment of wild rivers.
Bonus tip: If you’re interested in learning more about reading rivers, check out the video below. Like they say, reading a river is no different than reading a book!