WOW! That's one heck of a Post! You're certainly on the right track of doing the job right. Since you did write a lot, I'll try to address your questions. If I happen to miss anything, just post back with, "Well, what about da-da-da-da-da ..." OK?
RE: The wall that leaks where there's a sidewalk - W/O seeing it I have to assume that it slopes towards the house. With that, no matter what you do to 'fix' that sidewalk-separation or bad slopage, water will still collect there in your 'best case, worst case' scenario. If water collects there (but doesn't get into the basement), it WILL get into the basement over time because of freezing and thawing. You either have to have the sidwalk fixed or you have to kinda 'allow' the water into the basement, and put in a perimeter drainage system. I don't like my latter suggestion because that invites other problems down the road. In short, you want to FIX the problem (by possibly getting a new sidwalk); not put a 'bandaid' on it (by installing a perimeter drain.)
RE: The Sidwalk (again) - You didn't mention if it's right up against the house, has a 'garden' between it and the house, and/or slopes towards the foundation. Nor did you mention what's on the other side of the sidewalk. Knowing these things may spawn new ideas. Come back on this if you want any ideas.
Very good in that you regraded and extended your downspouts. Now, what do you do w/all that water??? Yes, since this water is saturating your landscaping EVEN though it's sloped away from the foundation, you need to get rid of it. If you have enough slopeage where the extended downspouts currently 'termintate', you only need to bury the piping such that the TOP of the pipe is about 6" below ground. Even if you live in an area where the ground freezes, again, if there's enough slopeage, the drain tile doesn't have to be below frost line. HOWEVER, if you can only bury your tile where it slopes the MINIMUM of 1/4" per foot, then you want to install the pipe at that slopeage until you hit frostline. (The rest of the run of the pipe can be fairly level since the water won't freeze down there and it will 'rise' a little to drain out. Just make sure your pipe doesn't drain BACKWARDS, and you'll be fine.)
RE: Perforated vs. non-perforated - It depends on what you're trying to accomplish. Since you have a LOT of water, and have a past 'history' of water in the basement, I'd use non-perforated pipe. This will take ALL the water away. RE: Flexible vs. non-flexible - Well, that depends on the terrain you're digging into. If it's rocky and/or you have 'obsticles' to go around or over or under (like roots or other piping or the like), then you use the flexible piping. If you have a straight run, go w/the solid pipe. If you go w/the solid pipe, be sure to use the pipe that's rated for Below Ground Use. (There are a few types so just get the right kind. DWV pipe, or the like.)
So, dig your trench first to accommodate 3" of 1/2" crushed stone ESPECIALLY if all or part of the pipe is being installed AT or ABOVE frost line. (This will help handle the 'movement' in ground that moves when it freezes and thaws.) First, lay in your Filter Fabric or Landscape Fabric (NOT Weed Block Fabric), THEN lay in the 3" of gravel. Then, lay in your piping, then cover the pipe again until it's 1" below the top of the pipe. Then, wrap the gravel and pipe w/the 'excess' fabric. Then, cover w/6" of dirt.
Now, assuming the pipe is 5" in diamter, you'll need to dig 15" down (MINIMUM) to lay in your fabric, gravel, pipe, gravel, wrap-it-up, and dirt. (Of course, plant grass after that.) Remember, if you have fairly level ground, start w/a 1/4" slope until you hit frost line, then you can go fairly level. But watch out your piping doesn't run backwards. (See Landscape Drainage for more info. There's a link on how to construct a French Drain too.) Oh, IF you end up using perforated pipe, the holes face DOWNWARDS.
Instead of trying to come up with some sort of 'surface gutter', you can install a french drain with gravel being laid all the way to the surface of the landscape (along w/an underground perforated piping system.) Laying the gravel up to the surface will act as a 'gutter' where water would normally run across this point (if it wasn't there.) Instead of water running across this point, the water actually gets a straight run DOWNWARDS to the perforated pipe. So, you see, this method 'catches' the water and redirects it downwards to be carried to another location. You'd do this in a situation where there is really soft soil or where, say, a neighbor's water is running onto your lot and they won't / can't do anything about it. Or, for whatever other reason water is running where you don't want it to run. When the water runs down through the gravel, it will start to 'fill' down in the trench, and eventually rise up through the perforated holes and run out wherever you have the pipe running to. Kinda nifty, eh? I have 2 VERY important suggestions if you do this. 1) Be SURE to use Landscape Fabric or Filter Fabric, and wrap EVERYTHING up in it. If you use LF, I'd use 2 layers. If you use FF, you can use 1 layer. Be SURE you have enough 'excess' to overlay the 2 sides of the fabric w/each other. Don't skimp! 2) After you've layed the fabric, the gravel, the pipe, and more gravel, ONLY fill the trench to about 2" from the surface of the ground. At that point, cover the gravel w/the excess fabric, and trim and tuck any excess down the SIDES of the trench (a little). THEN, after that, lay 2" of plain gravel on TOP of what you just wrapped up. (You can even use that pretty Landscape Gravel if you want. I think it comes in GREEN if you want it to 'blend in' w/the grass. Color is apparently not a problem.) Covering at the 2" mark and covering w/gravel keeps the fabric down (and dirt out), AND it give you a 'way' to clean the gravel if, over time, it gets clogged w/dirt or leaves or dead grass or whatever (for whatever reason.) You see, IF you have to 'clean your trench, you only have to remove 2" of gravel, and then 'blow out' the dead stuff or dirt, then put the 2" back in. Kinda nifty, eh?
(WHEW!!!) Now, RE: Dry Well vs. just going to the street - The purpose of the drywell is to help drain the water if you have no other place to go, or to 'collect' it for some other purpose (like using it for watering the garden, or somethin'.) If you can get the water to the street, that's what I'd do. However, if it means busting up the curb or sidewalk, that's your call. Since I can't see the landscape from here, I don't know what else to suggest. IF you end up digging a drywell, you'll need to size it for a worst-case scenario. Remember, a LOT of water may end up in there. With that, you'd want to bury a tank vs. building a gravel-filled drywell. The latter is different, and is designed JUST like I described the french drain (w/o the pipe) where the gravel is laid right up to the surface. Water usually rises up and then runs out. This implies that the pipe feeding it is VERY high in the landscape, and that once the water rises up and out, it has some place to go. You COULD add a sump pump into the drywell to 'force' water somewheres else but this raises new 'issues' w/maintenance and electrical concerns. (I'll hold off on that unless you want to persue it ...)
I know I'VE said a lot about this. And I'm sure you'll have a question (or more.) Post back and we'll go from there.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!
[This message has been edited by Jay J (edited October 31, 2001).]