Abstract: Hydrochemical classification of water resource is one of the vital preconditions for water resource sustainable utilization.There are numerous methods with regard to hydrochemical classification for water resource,but the most effective and simplest method is the diagram method.As one of the most important diagram methods for hydrochemical classification,the Durov diagrams (including both the original type of Durov Diagram and the expanded Durov Diagram) are used widely not only because it can reveal the hydrogeochemical characteristics of water,but also because it can show the hydrochemical processes occurring within different hydrogeological systems.However,comparing with other diagrams (such as the Piper Diagram),these diagrams are very complex and difficult to plot.Few commercial software packages are designed to plot Durov diagrams,which limits researchers to use the diagrams.In this paper,we introduced both the original type of Durov Diagram and the expanded Durov Diagram,and we also compared the similarities and differences in them.To better understand the diagram,we interpreted the composition of the original type of Durov Diagram,especially the part of cation triangle,anion triangle and the square field.We also interpreted the composition of the expanded Durov Diagram,in which each of the cation and anion triangles is split into two subtriangles and a diamond,while the square field is split into nine fields.We stressed how to establish a coordinate to plot the original type of Durov Diagram and the expanded Durov Diagram respectively.And we deduced formulas to transform the hydrochemical data so that they can be projected into both the original type of Durov Diagram and the expanded Durov Diagram.Using these principles,we wrote programs for the output of both the original type of Durov Diagram and the expanded Durov Diagram based on Matlab.To test the validity of the programs,we plotted the original type of Durov Diagram with published data based on our Matlab programs.And we also plot the original type of Durov Diagram with the same data based on commercial software.The results showed that our program was as correct as the commercial software,which indicated our program is feasible.However,because none of commercial software packages we found has the function of plotting the expanded Durov Diagram,we compared the diagram plotted by our Maltlab program with diagram appearing in some classical literature that used the same data.The results also confirmed that our Matlab program is reliable.Both the original type of Durov Diagram and the expanded Durov Diagram plotted by Matlab will help researchers to interpret hydrochemical data in graphical methods conveniently.Especially,the expanded Durov Diagram provides a method to indicate hydrochemical processes.

Key words: hydrochemistry, the Durov diagrams, Matlab, plotting