Pond with Sloped Bottom

I am using OpenRoads Designer Connect Edition 2021 Release 1.

I am trying to model a pond with a sloped bottom. I created a corridor around of the top of the pond and used a template with a constant slope and an end condition which extends to a bottom terrain. For my bottom terrain I created a sloped plane to mimic the desired bottom slope. After that I merged the terrains together to create a single pond terrain. While this method works it's difficult to be precise with the bottom of pond elevations.

Is anyone familiar with other methods for creating a pond with a sloped bottom? Thanks!