I, in fact, encountered the same problem like yours .
I am working on sediment delivery distributed model (SEDD) which i believe , i should calculate the travel time of the eroded particles along the hydraulic path, from the considered area /cell to the nearest STREAM REACH as per the definition,.(as shown in the fig )
I used flow-length tool, however it gives a hydraulic path length down till to the outlet of the basin , Not to the Nearest stream reach .
I was having the same problem and after a lot of tries involving the optional weight raster as input for the Flow Length tool, I found that the only solution is to manipulate the Flow Direction raster such that is has NoData values where the streams are. Using that as the input for the Flow Length tool (and using no weight raster), I now get the desired flow lengths to the nearest stream.
Additionally, as I wanted to determine the longest flow path per subcatchment, I had to extract the flow direction raster for each subcatchment and then use the Flow Length tool on each of those individually. I used a python script to automate the process.
Sir;
Please i need help; i would like to know the process in arcmap to determinate the time travel (step by step) please
In the latest versions of ArcGIS Desktop and ArcGIS Pro, we have introduced a new tool in the Spatial Analyst Toolbox, Hydrology toolset that addresses this problem. Please take a look at the help topic Flow Distance—Help | ArcGIS Desktop for ArcMAP and Flow Distance—Help | ArcGIS Desktop for ArcGIS Pro.
This tool takes an 'input stream raster' that can be used as the destination for distance measurements.
You may calculate both vertical and horizontal distance to the stream from any cell within an 'input surface raster'. To compute distance following the steepest downslope path, provide an optional D8 'input flow direction raster' to the tool. This would limit the downslope path along which distance (horizontal/ vertical) is computed, to the D8 flow directions.
The tool requires an input surface for the entire catchment. However, if you are only interested in assessing the flow distance at catchment boundary cells, you may extract those values from the flow distance tool output using tools in the Extraction toolset An overview of the Extraction toolset—Help | ArcGIS Desktop