arcMap edit 4

open topology toolbar -> select all

topology edit tool -> select a edge -> shared tool

turn on terrain layer

select reshape edge tool from topology toolbar

turn on edge snapping -> draw a line following the river from divergence

right click -> finish sketch

open catalog -> right click on study area -> new topology

using default setting

drag and drop study area topology from catalog on the map

errors are displayed. topology toolbar -> error inspector -> search

zoom in error -> right click -> trim -> 3m

select undershot error -> right click -> extend -> 3m

click validate on topology toolbar to remove dirty area

right click on topology area -> error -> summary

reference:

https://desktop.arcgis.com/en/arcmap/latest/manage-data/editing-fundamentals/exercise-4b-using-geodatabase-topology-to-fix-line-errors.htm