We had 380mm of rain on Friday and at peak flow the drain running beside my driveway to take water away from the house needs to handle at least 0.5m x 0.5m of water moving down it once my neighbours drainage peaks and begins dumping water into mine. I'd like to add a little breathing room incase we ever get up to 500mm in a day sometime in the future, something like 1.5m or 2m wide x 0.75m deep concrete V drain seems like it would be best and embed gabion in the concrete to slow the water down. How thick would you want the concrete for something like this? 200mm work okay? And any recommendations or spacing of rebar on something like this? Ideally I'll get a concrete company to pour it but money is tight and not sure if insurance / EQC will pay out anything so it might just be a matter of paying drainlayer to dig the drain and lay a base and myself prepping the concrete and getting a concrete truck in and pouring it.

https://preview.redd.it/8pzrhyfkmeka1.jpg?width=1575&format=pjpg&auto=webp&s=ab46b51b7c6575011524e8ec0602360b97e51d42