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Landscaping & Design/Drainage - Hydrostatic pressure


3 times in the last 20 years my basement has flooded due to extremely heavy rain.  The sump pump could not keep pace with the rising water under the floor and hydrostatic pressure through the cinder block walls.

A waterproof contractor has suggested a deeper and more powerful sump pump, and french drains inside the basement.  It doesn't make sense to me to allow the water to enter the basement and then remove the water.  

The problem occurs because my backyard and 3 of my neighbor's yards all slope down away from our houses into a low circular area approximately 30' diameter on my property.  It is like a dry "pond", 5'-8' deep if completely full.  

Every spring water accumulates about 1 foot deep for a few days, but rarely any other time.  The good news is it provides natural collection of water runoff away from the house.  The bad news is that the horizontal hydrostatic pressure of 3-4 feet of water during these torrential storms combined with a high water table and saturated soil results in flooding.

I am thinking of installing a drywell outside the house, with a submersible pump to pump the collected water to the front yard, away from the house where it will drain away without problems.

Does this make sense?  To put my drainage in perspective, my neighbors all have sump pumps that run every 10 minutes, 24/7.


Drywells could be part of the solution but you will also need devices to direct the water away from your house and if that cannot adequately address the problem you may need to combine that with drainage devices in your basement. I would focus on using the circular area as a detention basin if you can find an adequate outfall for its water. Think about installing drain pipe under the water table.

The main objective in this case would be to lower the water table and that can be done with drain pipes underneath it or with special dewatering wells or with a dewatering trench. You may need a permit for a detention basin.

Mark Harshman  

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Design of landscape structures and design of planting arrangements in the landscape. I usually do not answer questions of a horticultural nature or about growing plants or gardening unless they are related to design. I will answer these questions at my discretion. I will answer maintenance questions at my discretion,usually when they are related to design. I am a landscape designer. I am not a contractor or a gardener. Although I will describe how something is built I do not provide detailed installation or construction instructions. Here are example categories of problems I can help you with: Design of residential walks,low walls,low retaining walls,fences,drainage systems,arbors,plant selection,xeriscapes (low water use landscapes),rain garden design,rain water harvesting,permeable paving,sustainable drainage. No advise on an architectural or engineering level. I DO NOT PERFORM ACTUAL DESIGN WORK THROUGH THIS SITE. I only provide suggestions and advice. For more comprehensive help check out my website at:


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