I'm wondering whether my house has a French drain to keep water away from the foundation. Is there a way to find out that doesn't involve digging up the yard? (I.e., would there be any above-ground indications?) Or do I just need to start digging and see what I find?
Water – Are there outward signs of a French drain
drainagewater
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I had to draw a small diagram to see how the area was around the house. I drew a swale in to show what is there already, or hopefully something that can be created
What looks troubling here is the concentration of runoff heading to the house IF there is no swale there, that is why I hope there is one there, if not you really need to get the flow away form the house. It is bad enough that it is sandy, the water can still perk into the foundation, though it will be minimized with a swale. The clay base on the north side, sounds exactly as you describe, a bowl.
You need to do whatever you can to minimize the water infiltration, to start. It may not require to pipe the downspouts away from the house to a drywell or into a French drain, well not a French drain as you may plan around the house. French drains return the water to the ground, and in turn the crawlspace. What I mean is terminating the downspouts into an in ground pipe that daylights downhill of the home. A drywell would work too, but it is much more than may be needed.
This is the minimum I would suggest, although it is still a lot to do. I would also consider waterproofing the foundation, it may work on most of the foundation, but I think the runoff would still migrate under the foundation on the south side since it is still on sand/ clay mix presumably.
All of this is still tempered by the symptoms created by the water in the crawlspace. If there is no evidence of black marks (mildew) or white fuzzy stuff growing in places from the excess moisture in the crawlspace, if none of these symptoms exist, al least extreme measures are not needed. Regrade if needed, would be the minimum, downspouts to daylight away from the house the next active remedy, drywell addition the next, and if you are doing all that digging, waterproof the foundation, all these measures combined are the extreme I mean.
Edit 1/26/13
Aside from the shape of the house and other extensions from it, it shows the same thing happening except your swale that exists is more of a collection point. It appears the rain runoff takes the same path, but the house is in the way. The swale in the above sketch I posted would divert the rain water before it gets too close to your home. Is this a possibility to happen? It can be done by lowering the grade or if the house is high enough above grade, the grade can be raised, but that has implications too. The water in the swale may be of no concern. I would draw more concern to the south and west side where the rain looks like it is path is unencumbered to the foundation.
I will edit your drawing to show a more accurate idea and post it.
Back at the downspouts that I mentioned earlier, if the grade looks like it can daylight a underground lead would help reduce the amount of water at the foundation. Yet the addition of the swale will redirect the downspout water as well.
Obviously, the soil needs to be graded away from the house (in the back yard). If that means you need a retaining wall, then you need a retaining wall.
Regarding the swale, improved drainage sounds helpful. The real question is, why isn't water shedding (what is the real issue)? I've had swale issues, and the problem in those cases, was not with my swale, but the neighbors'... so water backed up in my yard. In such a circumstance, you can talk to the neighbors about the issue, ask them to fix it, offer to help, and/or sue them for damages.
But if the neighbors aren't to be blamed, then another alternative to keep the grass cut very short (grass slows drainage). Or you could check into a trench drain (concrete ditch). This is just another option that I didn't see mentioned, although it may not be your best option. As Tester101 pointed out, being there to see the issue is probably necessary.
Regarding power outages, gasoline or propane generators are the most reliable answer. A moderate generator should be enough for a sump pump, the fridge, and should keep the toilet flushing too. As you know, the drawback with a battery bank is that once it discharges, then you don't have a simple solution, like getting more gas.
Edit- Here's a possible way to use a retaining wall to increase the grade away from the house.
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Best Answer
To tell the truth a really good French drain install will have no evidence with the exception of the water exit point. In some cases you may see a brown stripe through the lawn but not in all climate zones. A stripe that is brown is one way to tell but not always there. It is much like a leach field in some areas they are green above the drain field and some are brown it depends on the soil and local clean mate and rain / heat.