Reddit reviews Source 1 Drainage Trench & Driveway Channel Drain with Galvanized Steel Grate - 3 Pack

They sell drains that would go the whole length of the garage with grates on them. Something like this might help

Source 1 Drainage Trench & Driveway Channel Drain with Galvanized Steel Grate - 3 Pack https://www.amazon.com/dp/B006YVE71W/ref=cm_sw_r_cp_api_2pyRBb17CQHAK

Sorry in advance for the novel, unless you're into that kind of thing. Bear in mind again, this isn't professional advice by any means. I've just been researching this as we'll be planning and applying for a grant from our local sewer district very soon so I've been through a couple of courses and doing as much research as possible. In other words, I'm the most dangerous person on the internet and professionals hate me, but only because they have to fix what I've screwed up :).

We're also in the Midwest which means a good measure of rain in the spring. It looks as though you have a fair amount of roof to account for. You can use drainage guides like this to account for the ~exact amount of runoff your roof will yield during a storm. I've seen calculations where they say "take the square footage of your roof and multiply that by the number of inches rain you got and that's how much runoff you have!". It's not quite that simple as rain isn't (generally) an instantaneous figure but rather multiplied over time.

Q = (C x I x A) / 96.23 where

>Q = Storm Water Runoff (in gallons per minute, gpm)

>C = Coefficient of Runoff

>I = Rainfall Intensity (in inches per hour)

>A = Area of Drainage Zone (in square feet)

I like simple logic problems like this so if you DON'T, you can just take the square footage of your roof and multiply it by the average rainfall per rain event i.e. 600 square feet of roof x .5" rain = ~187 gallons of water :). This, in conjunction with the square footage per downspout, will give you a pretty good indicator of how much water you'll be dealing with on which parts of your property. The street is probably sloped from the center line down and you should also include your driveway and any applicable graded turf as most lawn turf isn't all that permeable in anything but the lightest misting.

Say for example your roof, driveway, street, and turf have a cumulative runoff of 500 gallons in a 1/2" rainfall. If ~200 of that comes from your roof, this is the water you can control. Depending on the number of downspouts you have in use, 2-4 50+ gallon rain catch barrels will easily soak up the 200 gallons in runoff just from your roof lines. Any overflow from those barrels can be run to that 4" pipe you mentioned which routes into the back yard.

Regarding the driveway, if you don't have them already I would look into trenched drainage systems. this would allow you to grade your driveway (per the image) from left to right so that any runoff from the street and drive routes to that pipe which runs along the side of your garage. Other than permeable pavement solutions ($$$$) there isn't much you can do with driveway runoff other than mitigate it. On that note, your 4" drain pipe may be sufficient but you can use calculators like this one to ascertain whether or not a larger 6" drain would be needed. Also keep in mind if you have silt or debris issues at the base of your drive where it meets the garage you'll need to get that addressed before you add any drains so you don't foul the pipes down stream with garbage.

Back to rain gardens. To use the 5'x20' example from my first post, a 100 square foot rain garden dug even 9" into the ground will give you ~75 cubic feet of reservoir or 100 cubic feet if you can make it a foot deep. This isn't just storage though as any plant matter you include in the garden will aid in slowing and soaking up storm water runoff. The average root depth of most turf grass is about as deep as the grass itself. However even smaller, decorative plants can have root structures many times their depth. These types of root structures will absorb an order of magnitude more runoff than turf grass and help maintain slope health of your yard (depending on the grade coming down from the street and whether or not you have erosion issues). You can either plant along side the driveway or plant parallel to the street so that the majority of the turf/street runoff is caught. Any rain garden requires an overflow which could then be tied into your driveway drain or drain on the other side of the driveway.

Since this will be a DIY scenario (as will ours) most of the cost will be in landscaping materials like plants and stone, but you can use the comparatively cheaper dry wells and rain barrels in conjunction with one another to form a kind of mesh runoff mitigation network. Say the rain barrels affixed directly to the gutters catch 200 gallons and you have a rain garden (or two or three, they don't have to be connected) which will collect another ~100. You could dig a dry well into series between the garden and the side drain to give another 50 gallon capacity or however many gallons you choose to utilize. Out of the original 500 gallon runoff (roof, driveway, street, lawn) these collection measures would 350-400 gallons not including the somewhat unquantifiable plant and root absorption as well as the driveway trench which will definitely aid in moving the water past your foundation.

Again, sorry for the novel :). Take what you need and ignore the rest. We don't have much of a grade at all in our land, but what little slope we do have near the foundation is unfortunately tilted towards the house and poorly drained at that and I'm realizing it's not going to be a simple task. There isn't one major resolution in most cases. I understand a rain garden solution isn't for everyone, but our orientations emphasized that while a metric ton of native plants is going to be more effective than fewer plants you can still get away with a modern looking landscape so your front lawn doesn't look like a prairie. Also, I would look into natural plant species as they're far more likely to thrive in your native soil and I personally prefer perennials so I don't have to replant every damn year. Feel free to PM me with any questions, or even to seek advice from a real professional :).