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Different Soil Erodibility Factor K Equation Calculation in MiTS to MSMA 2

In reference to the ESCP benchmark, the calculation of Soil Erodibility Factor (K) equation used in our programme MiTS is different from the equation shown in MSMA 2nd Edition Equation 12.3. After numerous testing on the equation given by the MSMA and based on other reliable sources, we believe that the equation shown in MSMA2 is incorrect, due to a typo. The sources will be shown in a later section. 

Equation 12.3 Soil Erodibility Factor (K) in MSMA 2

The equation used in our programme in MITS is as below. Although there is only a slight difference in terms of the decimal, it can cause a huge discrepancy in the result. 

Note that the MSMA manual lacks a ‘.’ in the “10” factor. 

Our references #

There are many research references with different equations regarding K calculations.  Below are the references that we refer to which shows the most similar equation as shown in MSMA2.  

Refer to page 802 Eq. 2

Refer to 39 Equation 3.8

Therefore, the equation used in MiTS is based on the equation as shown in the references above. 

MSMA2 Equation  #

However, if you must use the MSMA2 Equation 12.3, you can calculate the K manually and simply override the value in the box. 

Override the K value

We believe that the above sources and argument is sufficient to convince everyone that there is a typo in the MSMA manual.

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