The velocity of the water in a stream is defined as its velocity. Distance per time is the unit of measurement (e.g., meters per second or feet per second). The quantity (volume) of water moving past a particular site in a given length of time is referred to as stream discharge. Discharge can be estimated by measuring the volume of water flowing over a known distance during a specified period of time.

Stream velocity cannot be measured directly with instruments, but it can be estimated from measurements made at **one or more sites** within the stream. Stream discharge is the amount of water that flows past a given point in a specified time. Therefore, to estimate stream discharge, you first need to know how much water is flowing through the system per unit time. For most streams, this is expressed in cubic meters per second (m3/s).

The term "stream bed" is used to describe the bottom layer of a river or stream. This layer is composed of **rock fragments** that are smaller than sand but larger than clay. All the materials that fall into rivers and streams become part of **its stream bed**. As these materials move downriver, they can be carried away by future floods or deposited by gravity back into **the stream bed**. The process of erosion and deposition of material on the bed creates channels and valleys which influence how fast the water flows.

Stream velocity is usually less than 10 m/s, so most streams do not flow rapidly.

Because of friction, stream velocity is highest at the surface and slowest along the stream bed and banks. The average speed of streams across their entire length is about 1 m per second.

The rate that a stream flows into another body of water is called its discharge. The discharge is usually expressed in cubic meters per second (m3/s) but can also be expressed in gallons per minute (GPM), pounds per square foot (PSF), or other units. The discharge of a stream is the most accurate indicator of its size because it takes into account the area of land through which the stream flows.

The depth of a stream is the distance from the top of the water to the bottom of the channel. Generally, streams become deeper as you go downriver. However, some rivers have braided channels with **distinct upper and lower reaches**; in **these cases**, there is no single depth for **the whole river**.

The gradient of a stream is the ratio of the elevation gain to the elevation loss by **measure- ment**. Most streams have a gradual slope, which means that they are becoming more elevated as you go downstream. Only a few streams have very steep slopes, such as the Willamette River in Oregon and California.

The discharge of a stream is the product of **its velocity** (V-length of travel per unit of time, such as feet per second) multiplied by the depth of the water (D-unit of length) multiplied by the breadth (W of the water-units of length). For example, if the discharge of a stream is 100 gallons per minute and the depth is 6 feet, then the velocity is 60 miles per hour.

You can also use this formula to calculate velocity from discharge: V = D * W */ 1,000.

Where V is in feet per second, D is in feet and W is in feet wide. You can also view this on **Google Sheets** with Discharge vs Velocity.

This equation works because the volume of water flowing through a point in time is constant. So, if we know the discharge of a stream or river, we can calculate **its speed**. Speed equals distance divided by time. So, if we know the distance that the water flows in units of time, we can calculate its speed.

For example, if the distance that the water flows is 10 miles in 5 minutes, then it has a speed of 200 miles per hour. If the distance that the water flows is 12 miles in 6 seconds, then it has a speed of 167 miles per hour.

As you can see, this equation works very well for calculating speed from discharge.

(Be sure to express all three lengths in **the same unit**.) The formula for discharge is: Discharge (inches per second) = velocity (feet per second) x depth (feet) x width (feet).

For example, if your neighbor's stream flows at a rate of 40 inches per second, its depth is 20 feet, and its width is 5 feet, then it discharges 200 square feet per second. You can calculate this number using the formula for discharge and the appropriate measurements for your neighbor's stream.

Find the discharge of her stream using this formula and then compare it with the information provided on the U.S. Geological Survey website. If they don't match, that means there must be error in one or more of the measurements. Correct the measurement that isn't matching up and try again.

It's important to know the discharge of streams because changes to **their flow** may affect **other people** downstream. For example, if the discharge of a stream decreases, then the volume of water flowing through it will be reduced, which may cause problems for plants and animals dependent on the stream for survival. Streams are also used for recreation so reducing their discharge could have **negative effects** for users as well.

This is the rate at which the river's water flows, measured in metres per second. The volume of water flowing past **a certain location** in the river each second is referred to as the discharge. Thus, the discharge of a river is equal to the flow rate multiplied by the stream gauge height.

The discharge of a river is usually much smaller than its capacity because most of the time the river is not flowing at its maximum level. The ratio between the discharge and the capacity of a river is called its "fractional load". A fractional load of 1 means that the river is fully loaded, while **a fractional load** of 0 means that it is empty. Most rivers have a fractional load of less than 0.1, meaning that they are rarely if ever fully loaded.

The current speed at which the water is moving is called its velocity. If the river is wide enough, there will be more than one spot where the water is moving at the same speed. The distance between these spots is called the river's reach. At any given point on the river, the velocity of the water is typically higher near the source (where the river begins) than near the mouth (where it ends).

The distance over which the flow of **a river travels** is called its course. The course of a river is usually quite small compared to its reach.