Hi all,
I am using ArcSWAT for GIS 10.2. I am trying to delineate watershed using ArcSWAT. The problem is the Delineation is successful when I select the outlet given by the SWAT itself. But when I try to delineate watershed for a user defined outlet, an error occurs. It would be really helpful if you know any solution for this. Thanks
Not knowing your specific situation or ARCSWAT specifically, the normal hydro-flow modeling is based in collecting and routing flow from pixel to pixel, based on the topographic DEM. Its not unusual for DEM information in relatively flat valleys to miss the actual channel or channels (if braided) location, especially in areas with dense canopy. And some stream types may shift channel location through time. Without spending the time to develop an improved topographic coverage and DEM, resulting in improved channel location perhaps utilizing LiDAR, or spending time to correct (edit) channel location, most will have to rely on the outlet selected by the model. In some instances, the topographic map DEMs and routing based on them can have errors. I collaborated on a few LiDAR papers that may help describe the dilemma and efforts made to address issues. If you select the wrong pixel, outside of the defined flow path for some user interfaces in other software, the software cannot pick up the channel system and the contributing area (hydrologic unit, such as watershed). In some instances, one must more or less burn the channel depth into the landscape, to help keep the flow path in the correct or desired location. If the flow model is diverted from the channel due to a road crossing or other abnormality and put on the valley surface, in all likelihood, the flow path will stay on the valley surface or floodplain until forced back such as by the next road crossing. In some coastal landscapes, substantial error may exist in not only channel location, but watershed size, which can be addressed more completely with LiDAR coverage and a lot of work (see our 2015 paper Maceyka and Hansen). If the program and user interface can show the flow path pixel(s), you need to select one or more pixels that cover the flow path at one location (outlet).
when you define the watershed outlet by yourself, can you zoom the outlet area and nearby and then define it ??
Miyuru Bandara Gunathilake Yes, I can zoom the area and the Outlet snaps to the stream line generated by SWAT.
Yeah sure, zoom it and then define, see whether the point you define intersects with the basin shape file and stream network
This might be a good resource for you:
https://sites.google.com/view/learnswat
