Channel geometry and discharge govern aquatic habitat volume and connectivity. These factors directly influence organismal energetics, refuge availability, and community structure. Quantifying cross-sectional area and flow rate provides the physical basis for interpreting biological patterns and for calculating nutrient loads.

• Transect (at least as wide as the river)

• Meter stick

• Floating object (e.g., table tennis ball)

• Stopwatch

• Rope or marked pole (for reference points)

• Notebook and pen/pencil

1. Find a suitable section of the river where the banks are clearly defined and the flow is relatively uniform.

2. Stretch a transect across the river from one bank to the other at a right angle to the flow.

3. Record the total width of the river in meters (m).

1. Divide the river width into equal sections (e.g., every 0.5 m or 1 m).

2. At each interval, use a meter stick to measure the depth from the riverbed to the water surface.

3. Record all depth measurements in a table:
   
   Distance from Bank (m)              Depth (m)
   0.0 (Bank)                                                     0.00
   1.0                                                                     0.50
   2.0                                                                     0.80
   3.0 (Middle)                                                  1.00
   4.0                                                                     0.70
   5.0 (Bank)                                                      0.00                                                                     

1. Plot the depths across the river width to visualize the shape of the riverbed.

2. Use the trapezoidal rule or approximate as rectangles to estimate the total cross-sectional area (A) in square meters (m²).

Example Calculation:
If the river is divided into sections of 1 meter width:

A=∑[(Depth1+Depth2)/2×Width Interval)]

1. Choose a floating object that is visible and will move with the river's current.

2. Mark a starting point on the riverbank and measure a distance downstream (e.g., 10 meters).

3. Release the floating object at the starting point and start the stopwatch.

4. Measure the time (seconds) it takes for the object to travel the marked distance.

5. Repeat this process 3-5 times and calculate the average time.

6. Calculate velocity (V) using the formula:

V=Distance Travelled (m) / Time (s)

The river’s flow rate (discharge) is calculated using the formula:

Q=A×V

​

Where:

• Q = Discharge (m³/s)

• A = Cross-sectional area (m²)

• V = Average velocity (m/s)