OptiSurface Designer has a Breakline feature allowing designers to add earthworks features like drains. It can easily design the side batters of a drain using the 'Batter Breakline' tool as shown here: 220.127.116.11 Batter Breakline
This feature was used in designs like the Queensland Melonhole and Canadian Cereals & Oilseeds but the cross section profiles shown have the vertical scale exaggerated so it does not represent what it actually looks like in real life. Here's what a 10% (1:10) side batter looks like in the software:
To better represent how these would appear in real life, see the illustrations below showing drain cross sections without vertical scale exaggeration and with different side batter slopes:
Side batters of 1:20 (5%) up to 1:10 (10%) can be farmed without issues and machinery can go over them and the slopes are generally barely noticeable at all.