Well,

Hydrograph is a plot of discharge against time(daily, monthly , annual).

Sincerely

Thank you for the information. Actually, I have to input a hydrograph in a simulation which has hourly ordinate. But, I have the four discharge value of different day in a month. Now, what can I do?

If you have only 4 consumption values, then there is not enough data.

But if for each date you have a series of observations of the flow rate, according to which it is possible to build single hydrograph for each date, there is a way out.

You can use the overlay principle:

  a hydrograph can be created by imposing unit hydrographs due to individual quantities of excess precipitation occurring in each unit period. This includes the principle of proportionality, according to which the ordinates of a hydrograph are proportional to the volume of excess precipitation.

Four values are not enough for build unit hydrograph. If you can have from those data, series of small step data it will be possible.

Depending on the purpose and degree of accuracy of your work, you can build a theoretical unit hydrograph of your watershed. But, for this option you need to master an appropriate empirical model.

Very dificult because each of dischages values are only one time, i suggest you should fine stage hydrographs for one peak occured and derive used rating curve or caliberation curve and you can plotting to build unit hydrograph

Unit Hydro-graph methods can be used to estimate flow hydro-graphs, even for un-gauged catchments. You may refer a suitable book. I recommend you 'Drainage Principles and Applications' by H.P.Ritzema, which can be downloaded from the internet. You may read pages from 133 to 143 to learn step by step procedure. I have published a paper 'Estimation of Direct Runoff and Flow Hydro-graphs in Ungauged Catchments' on the same subject in the 'Researchgate'. You may read the paper to study how to apply this procedure for practical purposes. I wonder whether your observations can be used to find 'Time of Concentration' (Tc) for your catchment. If you have catchment rainfall and observed hydro-graph for several events, you may find Tc more precisely with the help of your observations. That will be useful in constructing Unit Hydro-graph for the particular catchment more accurately.

If you still want to derive UH from stream flow data, the method (including the data requirement) has been clearly explained in the power point presentation "Unit Hydrograph Theory" -Researchgate. Otherwise you may use synthetic hydrograph methods which also have been explained in the same PPT.