Started planning a new garden in my new backyard. Seeking advice on best practices.

I have a familiarity with designing raised beds and a working knowledge of construction techniques. What I'm lacking though, is knowledge about irrigation and drainage, so I'm seeking out advice from the internet. Here's the situation, my new backyard is slightly sloped towards the house with a raised car parking spot (see attached photo) and I want to design/construct a raised bed around the drainage pipes from the raised spot. What I need to decide is whether or not I should try to incorporate the drainage pipes into the raised bed irrigation or just divert a new drainage pipe(s) through the bed and create small rain garden to absorb excess rainwater? I'm planning on growing vegetables in the bed(s) and rotating them in succession with the seasons and leaving it dormant in the winter only. I've attached some sketches to this post as well to give you all an understanding of the idea I originally conceived. I'd love to hear how some things work vs. better ways to accomplish my goal. Additionally, I'll try to answer any questions about the environment/site, plans for veggie selection and/or design implementation. I hope to start construction in March 2019, so I still have a decent amount of time to figure out all of the details.

Thanks in advance for any feedback!

I want to see pics when you're done!

I wish I could draw like you, looks good!

I would tend to think that some type of extra irrigation would be a good thing for the raised beds.

Raised beds have the pros of being easy to access and well draining, however being higher up, they also loose that moisture quicker, so having an extra water source would be a great idea in my opinion to limit the amount of manual watering required.

@Steve Thorn Thanks for the feedback. I think my biggest concern is how I'm going to prevent soil from getting into the drainage pipe(s). Also I'm not certain about the wastewater that would be coming through the drainage under the raised parking spot. That's why I was considering running the drainage to a separate rain garden. Still not sure what direction I'll go, but hopefully the feedback on here will be beneficial!

Steve Thorn wrote:I wish I could draw like you, looks good!

I would tend to think that some type of extra irrigation would be a good thing for the raised beds.

Raised beds have the pros of being easy to access and well draining, however being higher up, they also loose that moisture quicker, so having an extra water source would be a great idea in my opinion to limit the amount of manual watering required.

Drainage would largely depend on what's in the bed, right?  How about making it a hugel-raised-bed - fill it most of the way with wood (already on its way to rotting if you want to get results from the bed sooner rather than later) and then cover it up with soil?  Wouldn't this give you a heck of a lot of water retention capabilities?

@Jean-Paul Calderone WOW I've never heard of this hugelkultur style of raised bed gardening. It's super interesting, I may have to find a way to incorporate this into my planning and design. So many great ideas right now, thanks so much

Drainage would largely depend on what's in the bed, right?  How about making it a hugel-raised-bed - fill it most of the way with wood (already on its way to rotting if you want to get results from the bed sooner rather than later) and then cover it up with soil?  Wouldn't this give you a heck of a lot of water retention capabilities?  

Great idea! Never thought of using hugelkultur in a regular raised bed, that would be perfect!

I think it depends on what is in the drainage water.  If it's often got oil or fuel drops creating a sheen on the water, I'd want to route that through the bed independently to a rain garden.  On the other hand, if it's cleanish water, I'd connect a perforated drain pipe up to the drains so they can add some water to the beds as the water flows through.  If it's raining enough for the drains to be draining, the beds should be getting some irrigation from the sky.  The thing to avoid is having a cloud give them 1/2" of rain and then have the parking spot deluge them with tons more water.  

Lacking any particular experience myself, I'd use perforated drain tile and arrange it relatively level through the bed.  When it gets to the near side, transition to non perforated and route it to another bed or rain garden.  Be wary of funneling too much water to those places in a 4" rain event.  This way when it's raining the perforated pipe will irrigate the soil some to assist with the rain that is falling from above.

If you're into tinkering (as I am), you could have the drain tile be horizontal in the bed and when it gets to the near side have a tee or other overflow that you can make an adjustable dam in.  So if you leave the dam out, the water will flow out and you'll only get the water through the perforations that decide to go that way.  If you raise the dam, adjust the overflow, or otherwise adjust it, you could hold back an inch or two or three of water in the horizontal drain tile as the rest overflows.  Then when the rain stops, that 1-3" of water wicks down into the bed.  This probably doesn't make any sense, sorry...

This also assumes decently well draining soil.  If you have clay in the beds, I wouldn't add any more water from the drainage pipes.