The reaeration constant is a parameter used to quantify the rate at which oxygen is transferred from the atmosphere to a river through physical processes such as turbulence and gas exchange at the air-water interface.

Here's a step-by-step guide on how to estimate the reaeration constant:

1. Site Selection: Choose a representative reach of the river where you want to study reaeration. It should be free from significant inputs or outputs of water that could affect oxygen levels.

2. Sampling Equipment: You will need the following equipment:

- Dissolved oxygen (DO) probe: To measure the dissolved oxygen concentration.

- Flow meter: To measure the water velocity.

- Water sampling bottles: To collect water samples for laboratory analysis.

- Secchi disk: To measure water transparency (optional).

3. Sampling Frequency: Determine the sampling frequency based on the variability of the river and the desired level of accuracy. Typically, multiple sampling events are conducted at different times to capture diurnal and seasonal variations.

4. Field Measurements:

- Measure the water temperature, pH, and conductivity using appropriate meters.

- Measure the dissolved oxygen concentration at various locations along the reach using the DO probe. Take measurements at different depths to capture vertical variations.

- Measure the water velocity using a flow meter at each sampling point. Take measurements at different depths and calculate the average velocity.

- Measure water transparency using a Secchi disk if desired. This measurement can provide additional information about light penetration and algal biomass.

5. Laboratory Analysis:

- Collect water samples in clean sampling bottles for laboratory analysis. The samples should be representative of the river reach and cover various depths.

- Analyze the water samples for dissolved oxygen concentration using standard laboratory methods. This will provide more accurate and precise measurements compared to the field measurements.

6. Data Analysis:

- Plot the dissolved oxygen concentration against time or distance to observe the patterns and variations.

- Apply suitable statistical methods to estimate the reaeration constant. One common approach is to use the Streeter-Phelps equation or other empirical models that describe the relationship between dissolved oxygen and reaeration.

- Fit the model to the observed data and estimate the reaeration constant using regression techniques.

It's important to note that the actual calculation of the reaeration constant can vary depending on the model or method you choose to use. The steps outlined above provide a general framework for conducting the necessary measurements and analysis.

Remember to adhere to proper sampling protocols, maintain data accuracy, and consider any additional factors that may influence reaeration rates, such as wind speed, temperature gradients, and the presence of vegetation.

I hope this helps you get started with estimating the reaeration constant for your river!

See these 3 books (unfortunately just online )

1- Water and wastewater calculations manual

2- Water quality engineering: physical/chemical treatment processes

3- ] A procedure for estimating reaeration coefficients for Massachusetts streams

I agree with dear Mohannad Alobid. To calculate the reaeration constant for a river, conduct water sampling at various locations, considering flow conditions and pollution levels. Measure temperature, dissolved oxygen, BOD, and COD. Calculate oxygen saturation and use the Streeter-Phelps equation to determine the reaeration rate constant (K2). Employ a dissolved oxygen probe for field measurements. Validate results through statistical analysis, considering variations in flow and temperature. Interpret findings and document the methodology, results, and conclusions in a comprehensive report. Good luck!

Best,

Behnam