The best replacement for runoff is run-off.

The best alternatives to runoff are rated as following:
★★★★★  run-off
★★  infiltration
★★  groundwater
★  1 rainfall
  run off

Your alternative for runoff is not listed? Suggest!
Speaking about runoff, one probably shouldn't forget about pta.

Other search terms related to runoff and their ratings are:
★★★★★ pta
★★★ water cycle
★★ balloon for claudication
You have in mind a companion for runoff and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of runoff in all years. Click on graph for more.
runoff
run-off
infiltration