Water Drainage Tips
DEAR TIM: Spring is here and so are the incessant heavy rains. I have several places near my house where water ponds. This can't be a good thing for my house, as I constantly am battling water in my basement and part of the house that has a crawlspace under it. My lot isn't really that flat, so I'm at a loss as to what's going on. Do I have to call a professional to solve this issue, or can I just add soil to fill in the low spots? What are my options? Marion R., Evansville, IN
DEAR MARION: While I don't have accurate statistics to support my feelings, I suspect you're in a vast majority of homeowners who have varying degrees of poor drainage issues on their land or near their homes. You're correct in assuming that ponding water is not a good thing for houses.
My college degree was in geology. I gravitated to two disciplines within geology: geomorphology and hydrogeology. Geomorph, as we students affectionately called it, is the study of the Earth's surface features. Hydrogeology is the study of ground or subsurface water, or at least that's what we focused on the three years I was a geology student.
If you think about the Earth on a very large scale and take into consideration gravity, you quickly discover that Mother Nature is doing her best to constantly carry all soil, rock, your house, your car, your possessions and you down and into the oceans. She's a very patient woman, but she's also got a split personality as her evil twin is constantly building mountains where two crustal plates crash into one another. This is why the Earth has dry land that we build upon.
What does all this have to do with the water at and around your home? Simple. If you could look at a topographic map of your lot before it was developed, and in many locations these old maps are available, you'd see that your lot was shaped differently than it is now.
Your builder, or possibly the subdivision developer, undoubtedly moved dirt on your lot to prepare it for building your home. This process disturbed the natural slope of your lot as virtually no undisturbed land is perfectly flat. Almost all land has some natural fall to it that's caused by natural erosion. When you do encounter marshy land, it's because of some temporary geomorphological process. Lakes are a great example. You can find marshes next to lakes. Realize that lakes are temporary geological features. Mother Nature is constantly trying to fill lakes in.
Adding soil to the low spots is usually not a good method to fix poor drainage problems. Ponding water on your lot tells me that you don't have low-slope culverts surrounding your house like a moat surrounds a castle. These depressions, or culverts, should have been created by the builder so surface water always flows around your house to the towards the lowest spot of land on your lot.
To provide great drainage around your home, you should always have the ground slope away from your home. The building code used to require that the ground should have 6 inches of fall in the first 10 feet of horizontal run away from your home. That can be confusing to some.
All it means is that within 10 feet of your foundation, the ground should slope at least 6 inches. This change in elevation could happen within a foot, meaning it would be a very visible slope very close to your foundation walls.
The builder should have then created an artificial channel around and away from your home that also has a slope to it. The water flowing away from your foundation would enter this channel and then flow, by gravity, completely around your home. There should never be any ponding in this shallow channel. A slope of at least 1/8 inch per foot is required. More slope is better if you can tolerate it on your lot.
Surface water is but one challenge around your home. You also need to deal with subsurface water that flows through the soil towards your foundation and crawlspace walls. You can capture and divert this subsurface water by digging a narrow trench in the center of the artificial channel around your home.
This channel should be about 2 feet deep and 6 inches wide. The bottom of the trench should be parallel with the top of the artificial channel until it gets around your home. The trench extends past your home towards the lowest point of your lot. Once the trench passes your house, the slope can be reduced so the pipe eventually pops out of the ground.
You install a 1 inch layer of rounded gravel that's the size of large acorns into the bottom of the trench. Perforated drain pipe is laid on this gravel. The entire trench is then filled with the rounded gravel. This system readily collects subsurface water before it attacks your home. Water will flow from the end of the drainpipe where it eventually breaks through the surface of the ground.