Yes,u can use CN to calculate surface runoff. Best of luck

Dear Dr Abu Reza Md thank you very much your answer.

@Sujeewa Dissanayaka The Curve Number Method can be used to estimate the peak discharge of direct runoff for a rainstorm event, for an ungauged watershed. The area of the catchment area, the slope and length of the main channel can be determined by the use of GIS/remote sensing methods. Given the Curve Numbers for condition II (CNs for Hydrological Soil-Cover Complexes for antecedent wetness condition II of the catchment area Landcover) corresponding to the LULC and management practices of the study area, then, it is very possible to estimate the peak discharge of direct runoff for a rainstorm event for not just condition II, but for antecedent wetness conditions I & III of the catchment area. Use the antecedent wetness conditions and CN adjustment table to determine the corresponding CNs for conditions I & III.

Dear Nkpa M. Ogarekpe thank you so much for your information that was very important for me thanks again.

Dear D.M. Sujeewa Dissanayaka ,

I recommend you not to use SCS-CN in forested watersheds. Since in forested watersheds a large contribution is from baseflow of which the SCS-CN does not account for.

Dear Miyuru Bandara Gunathilake thank you very much for your information.

The Curve Number method was originally developed by the Soil Conservation Service, in the second half of the last century, for conditions prevailed in the USA. Later it was adopted to conditions in other parts of the world. It can be used in the catchments in Sri Lanka too. However, still there limitations in using this method. As you know, the factors affecting CN may vary in a short distance within a particular catchment. Further, In Sri Lanka, you cannot find catchments without man made reservoirs. Upper part of the catchment may be highly sloping.As such I recommend you to use the method only for small catchments and sub catchments. Secondly, you can find CN, from field observations, if you have rainfall - Runoff data with respect to several storm events in your catchment. I have explained the procedure of using CN method in my paper 'Estimation of Direct Runoff in Un-gauged Catchments' which has been published in Research-gate. You had better refer into 'Drainage Principles and Applications, ILRI Publication 16 (which can be downloaded from internet)' page number 121 to 143 for full procedure and limitations in using CN method.

Dear Madam,

Thank you for your information. This information is very useful for my study and many thanks again.

SCS CN Curve number method give you better result but it has some restriction it is applicable for small catchment and ungauged watershed.

Dear Stuti

Thank you very much for your information