The Modi Khola runs from the Annapurna Sanctuary, an area North of Pokhara where you can sit surrounded by the mighty peaks of the Annapurna Himal. The trek into the sanctuary follows the river and the descent of the river would be a great finish to the trek.
The river can be run from Landruk which is a day’s trek from Lumle. The valley then drops 540m from the put-in to the Kali gandaki confluence. The descent of the Kali gandaki would be the obvious end to the trip.