Tuesday, April 12, 2011
Basement Groundwater Blues
Sometimes we need to be reminded that we live in the desert. It seems Mother Nature is more than happy to confuse the climatology of this region often enough to keep us on our toes. I had an RPR follower who is new to the area ask me to do a post on the subject of groundwater and basement flooding, and being somewhat knowledgeable on the subject (I'm a big nerd) I decided to oblige.
First of all, there is a huge difference between groundwater and a water table. I'll put some of your fears to rest that your collective basements are below the water table of either the Jordan River, or that salty monster west of us - most of them are not. There is a chance that if your home is West of the Jordan River and has a fairly deep subterranean basement, you could be below the water table during high run-off periods, but not during normal flow. Footings for a home could have never been successfully installed below an existing water table (total mud fest). If you look at the diagram below you'll gain a better understanding of what a "water table" is and how it would effect someone who's home is near a substantial body of water.
Now moving on to the real culprit of most of our spring flooding woes - groundwater. Groundwater is the water that is trying to make its way through the soil moisture belt, into the zone of aeration and eventually to the water table. Unfortunately, most of the "soil" in Rose Park was trucked in as top-soil and is only a few inches deep in most places. Below that are different layers of stratified clay and sediments. Clay is a notoriously difficult substance to permeate because of how dense it is, as opposed to sand which creates tiny air pockets for the water to seep through. What does this mean? It means that when a lot of rainfall comes all at one time, the water gets backed up as it waits its turn to seep below the water table. This backed up water is subject to gravity, just like you and me. It will find the path of least resistance to its final destination, even if it means going through your basement to get there.
What can I do to minimize my chances of flooding?
The good news is that all of you can do a few things to minimize your chances of flooding. I'll cover them one at a time in order of importance.
Number One, rain gutters can either be your best friend or your worst enemy. A properly installed rain gutter can flush your worries down the drain while an improperly installed or dysfunctional rain gutter can bring the problem to your doorstep, (or in this case - basement). Lets do some math. A home of 1,000 square feet with a roof pitch of 4/12 has 33% more surface area on the roof than the floor plan, making the roof 1,333 square feet of surface area. Each of those square feet has 144 square inches. Now, lets say an inch of rain falls in a day. That inch of rain is a measure of volume and therefore calculated by cubic inches. Each cubic inch occupies one square inch of your roof making your total roof rainfall (1,333 X 144) 191,952 cubic inches of rain. There are 231 cubic inches in a gallon of water making your roofs total diversion capability 830 gallons of water. That is a lot of water folks. If your rain gutters are not functioning properly, you could have just increased that little spot on your lawns annual rainfall from less than a gallon to a veritable deluge of biblical proportions and some of that water is going to make into your basement. Your rain gutter downspouts should be carried away from your house as far as they can, 4-5 feet at a minimum and preferably in excess of 10 feet during the wet season. There should also be plenty of them, for a 1,000 square foot home, 4 downspouts is the minimum. Another nifty arrangement would be to capture the rain from your downspouts in 50 gallon water barrels with only the overflow being diverted away from the home, that would prevent 200 gallons of water from saturating your soil and would go a long way toward responsibly watering your plants and garden over the next month. In fact, you can go much farther and purchase an underground cistern capable of holding thousands of gallons of water now that the state of Utah has made rain collection a legal homeowner enterprise.
Number Two, Make the grade - the grade away from your house that is. For the uninitiated, grade is another word for slope or level. In this instance, you want your soil to be sloped away from your foundation for 10 feet around the perimeter of your home. This can be as easy as adding a little top soil to your flower bed, or as complicated as changing the pitch of your driveway if it abuts your foundation. There are a lot of things one can do to help reduce water seepage between driveways and foundations. (Remember, a driveway is the same thing as a roof, if it drains all of its rainfall to one small area, you'll have a problem). The method I prefer for sealing these joints is a product called Sika Flex. You can buy it at Home Depot in various formulas but as long as it remains flexible, it will cope with the shifting driveway elevation when and if frost heave becomes an issue.
Number Three, Install a sump pump. A few things should be noted in regards to sump pumps. First, they do not make up for good drainage design and proper preparation. If they did, I would have listed them first. Second, though they can help, they are not a guaranteed fix for ground water seepage. Their location in the home will have an effect on how useful they are. If the pump is centrally located in the basement, it may not draw the water away from your footings and foundation walls the way you'd like it to. If you have a "problem area" in your basement, its due to numerous factors ranging from poor rainfall drainage to a cracked foundation wall. Once you have done all you can to fix the underlying problems, its wise advice to install a sump pump as close to that problem area as you can. By addressing both issues you stand a much better chance of not having any basement water seepage.
Number Four, Think long term and plant water needy plants in the high water drainage areas surrounding your house. Make sure you have a good idea where your water supply line comes in, but more importantly, where your waste line leaves your house. In the 1940's when our houses were constructed, the subterranean waste lines were made of clay pipe. In most cases, these pipes actually work very well but their weakness lies in their joints. The joints are large enough to allow tiny fibrous root material through the seam in search of the water you just flushed down your toilet. Plant a tree too close to this waste line and you'll be trading basement flooding for a clogged sewage main which requires professional help to maintain. However, do it right and you'll have a hand full of thirsty friends waiting for every drop that rolls off your roof. I have a Freemont Cottonwood tree in my backyard that drinks up to 300 gallons per day in the summer months! Tree Beard (as we call him) has kept our house from flooding since the day it was built. My parents have had similar results (with one or two minor exceptions) since planting a Black Walnut.
Conclusion, though the forecast keeps saying rain and many of you are dealing with flooded basements, there are things that can be done right now to improve your situation. Start with your rain gutters, they are the biggest cause of spot flooding in a home. When things ease up a bit, take a close look at how your homes water drainage system is designed and keep this in mind before you make any major changes to the landscaping or layout of your yard. When summer hits, make a few calculated changes to help protect yourself from future flooding.
If you have any further questions, post a comment and I'll do my best to answer them.