Hi Nikhil,

Take a look at the Hydrology Toolset in ArcGIS:

http://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/identifying-stream-networks.htm

1) Calculate flow direction

2) Calculate flow accumulation

3) Check in the flow accumulation raster at which value (of flow accumulation) there still is a stream, which you can check by adding a Basemap (File > Add Data > Add basemap) following the link above.

4) Now you'll have your streams and can do some drainage intensity calculations (the number of 'stream' cells divided by surface area in a focal statistic for each cell [is that what you mean with 'each grided region'?])

You'll need the Spatial Analyst extension though. Otherwise you can consider using the Open Source SAGA GIS software.

Good luck,

Jelmer

Another option is to use Arc Hydro, a free extension for ArcGIS. You can download the latest version here: http://downloads.esri.com/archydro/archydro/Setup/10.5/

Versions are also available on the same server for earlier versions of ArcGIS. There are many tutorials for using Arc Hydro. The workflow is similar to what Jelmer recommends, but you may want to adjust the stream definition threshold to match topographic map(s), aerial imagery, or survey data.

- Adam

I've employed ArcHydro Tools for the drainage density calculations during my Master's Thesis. It's a handy extension to work with.

http://downloads.esri.com/archydro/ArcHydro/Tutorial/Doc/Arc%20Hydro%20Tools%202.0%20-%20Tutorial.pdf

Cheers!

-Indishe

I have calculated the lenght of the network using the Horton-Strahler system by taking into account all secondary small rivers.

Using the method described in the attached article, the problem can be solved easily.

Best regards,

Ion Zavoianu