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How to mitigate ground water flooding

I need help! I live in Calgary Alberta, Canada. Our city was recently hit with a massive flood. Thousands of homes have been affected by this flood. My own house did not have overland flooding but did end up with 3 feet of water in the basement. The water entered the house through drain cut outs in the concrete floor. Unfortunately my house did not have a sump pump. The entire basement has been gutted with new water heater and furnace. I contacted a company about installing sump pumps. They have also suggested a system with internal "French drains" for around the perimeter of the basement. This would involve removing a 10 inch or so amount of the floor and part of the footing to mitigate water coming through the joint between the footing and the wall. My question is this a good idea? Are sump pumps enough? Will removing the concrete to put in the drain effect the footings so I later will have a problem there? During this flood I had no water coming in at the joint just through the cut outs in the floor. Can anyone give some advice? It will cost about 22K for the drain and sump pumps.



Re: How to mitigate ground water flooding

It sounds like your problem was not merely a high water table, but your sewers backing up. This is not uncommon in many areas of the country that are prone to torrential rains. It is also why in many areas, it is illegal to put downspout discharge and sump pump discharge into into normal sewers, rather than storm sewers. You might keep your house dry, but some poor snook downstream gets a flooded basement, and worse yet, it is not relatively clean run-off, but raw sewage mixed in! Most older areas of the country don't even have separate storm drains.

I don't think any normal sump pump is going to keep up with amount of water that comes bubbling up from a sewer. Worse yet, many times during these flood situations, the Edison power also goes out. Even if you have battery back up pumps, are they going to go on for a day or two pumping non-stop?

Sump pumps can keep the water table artificially drawn down, so long as they have power, or the battery powered back-up pumps hold out. My first home had a deep basement. After flooding twice in the same week-end. I bought a generator and a battery back-up pump.

I have seen devices that act as check valves to close off the floor drains or stand pipes which raise the flood level up several feet off the floor so that the water doesn't come out.

Re: How to mitigate ground water flooding

The next factor to consider ; how often does this happen?

Is it covered under flood insurance?

Re: How to mitigate ground water flooding

Thanks guys. Luckily there was no sewer back up on this flood, just the ground water. I will probably go with at least a sump pump but I'm really not sure about the perimeter drain. I was one of the few who was covered by insurance on this go round. In Canada there is no flood insurance available but as this was not considered "overland" flooding I was covered. This was supposedly the 1 in a 100 year flood so I'm really hoping it never happens again but have to plan for the you never know.

Re: How to mitigate ground water flooding

I'd go with a electrical mains powered sump pump with a mains water-operated back-up, and I would make sure all the plumbing drains had check-valves to prevent back-flow. There are ones for floor drains that replace the old one from the top so that you don't have to excavate a lot of concrete to fit a regular back-flow preventer valve. I'd pay special attention to sealing wherever I could, especially the drains in the floor, then I'd stop worrying and spending at that point.

First, you don't seem to need the perimeter french drain inside the basement- that type of drain belongs outside the foundation anyway. Cutting the floor open for it only opens up even more space for water to get in (and at a faster rate). There are good epoxy caulks for the wall-to-floor joint that will keep most if not all the water out. Second, you have good warning time of a possible flood (this is not always the case everywhere else) so you can move your valuables and irreplacables out of harm's way easily. Third, you've got insurance for this. Now having insurance doesn't mean that you should be irresponsible- that is not what I'm suggesting here. I'm just saying that this is a rare event and that is exactly what insurance is meant to cover. The steps I recommended are reasonable and cost-worthy where as an all-out war against water infiltration would cost you more than your next 100 year's flood insurance coverage so it makes little sense to go that far. And in doing those things the insurance company cannot claim negligence on your part to deny a claim later on.

I can't say for where you are, but where I am waterproofing contractors (along with some other [email protected] trades) tend to over-sell their products and services as much as they can to make for more work and more profit. Many times you don't really need all the 'extras' they want to sell you to make the job 'perfect' as they see things. And as always, get several opinions from different companies before making any decisions about anything.


Re: How to mitigate ground water flooding

Thanks Phil. Sounds like the most sensible thing to do.

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