Problem building drainage system on layout for residential plots.

[AbhinavSingh]

Trying to build a drainage system on a site meant for residential plots. It has 1 main road and 6 side roads. Drain has to flow from the back end of the site which has a closed boundary to the front side of the site...a length of 640 ft on the main road of the site. The six side roads are connected to this main road and will have drains too. Attaching site map for clarity.
The site had an uneven level from the ground surface. The back side of the site was at a much lower level than the ground surface mainly starting from around 300 ft of the site starting from front 0 to 640 ft at the end. Which means a negative slope considering setting up of drainage system. To address this negative slope extensive land filling was done because of big slope and large area of the site. To build drainage over these roads we made a plan of a slope of ~ 2 inches for 100 ft length of drain.
Now the situation is that the back side of the road has been elevated a lot for drain to set up over it with gradual slope downwards towards the front. And even with this the drain would go under the ground somewhere after 200 ft from the back side.
Is this the right approach for setting up the drainage? Any suggestions?

 

[TigerGuy]

I always start at the outlet elevation and work up from there. How much flow can you keep on the surface? When you start going underground with pipes, it can make things difficult to maintain flow and match flowline elevations.

 

[KaBone]

Sorry, I’m struggling to follow. With the drain slope you mentioned, in 200’ it dropped ~4”, and you’re saying it’s already under ground?
I see the bottle neck might be problematic. Looks like you need to bring all the runoff from a 3-ac(?) site through a corridor that’s 30’ wide. You have opportunities to deposit some volume at the various parks.

Side note: we are very spoiled in the US with our 50’ roads and 5000sf lots.