We have similar slopes as you have, also heavy clay, very sticky when wet and very hard when dry. We have noticed that rainwater barely infiltrates in our soils if we do not break up the dense layers in the topsoil. Since we have to do that anyway in the areas we plant in, and we do not want to loose any rainwater, we terrace everything.
We're making small terraces, so that if maybe we'll have an accidental washout the damage is limited. All terraces we make have a slight angle, where the downslope side is higher than the upslope side. In heavy rains that means excess water won't flow over the edge, but it will flow to the backside of the terraces. Like this you can easily prevent erosion. We built stairways of rocks, which are also the spillways for excess water. When you try to retain rainwater it is very important to always have a way for excess water to escape.
The picture below shows how it looks after it's done. It works great, we also regularly have 100mm per 24 hrs rain (actually it falls in just a few hours) with one big event where we had 90mm in just 90 minutes, and we had NO runoff from the terraces. It all went into the soil. Very happy with that.