Garden Drainage Issue

[JoeGenoa]

We had a torrential downpour a couple of weeks ago and unfortunately this caused water leaking through to the neighbour's adjoining garage from the side of our garden. This was due to recently installed artificial grass being at too high a level against the wall. We dug down to its original level before the grass, and further still as shown in the pics. It's 2 bricks below the DPC.

 

The plan now is to have sleepers all the way across the wall and then deck boards on top to act as a lid. My question is should we add anything further to the trench to prevent any further issues? It's back at the level where there wasn't any issues but if we need to add gravel or a soakaway solution as well then we would definitely consider that. I'm thinking gravel would help more dirt falling into the trench over time?

 

Many thanks for any advice given.