Truncation error Analysis numerical methods

Hi i have developed the lax wendroff and lax friedrichs numerical methods to help approximate the one dimensional dam break problem using the st venant equation, i understand that the truncation error must be related to the numerical error produced so i have looped my code and found the greatest error for different space discretization and plotted the results on a log graph, it shows that with more space discretization the error becomes less, but how can i use this data to prove that each scheme is a 2nd and 1st order accurate respectively? Thanks for any help kyle :)