Will gravel inside brick patio cause a bowl effect?

chisey(TN)July 28, 2011

We're going to be making some changes to our patio area, which is currently just brick pavers. We intend to keep the brick pavers, but we need to pull them up and fix the grade a little to make sure it moves water away from the house. We also want to reconfigure and use them a little differently when we do that.

Because of ant issues we've decided that around the back of our house we're going to use a 3-4 foot wide bed of decorative gravel instead of mulch, and one idea we've had with the patio is to continue that bed around the house so that there's a strip of gravel between the brick pavers and the house. I'm going to have to play with the idea a little to see if I even think it will look good, but I have a bigger concern than that.

If the soil and sand under the patio is properly graded away from the house, with the gravel tend to let water sink in more than the pavers and thus result in a bowl effect? We need water to move away from the house and I'm concerned the transition from gravel to brick pavers will hold water back, below the brick line, and therefore against the house. Is this something I should be concerned about, or will water flow under and around the brick enough that I don't need to worry about it?

If it matters, we are not going to mortar the brick. They will just be butted up against one another.

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I'm not sure what you are asking... If the water is infiltrating through the gravel, then it should keep going down into the soil as well, at what rate depends on the vertical transmissivity of the lithology (soil formation) it passes through.

Whether the water, once it infiltrates flows horizontally vice vertically, which is demanded by gravity, depends on the differential transmissivity between the two possible flow direction. In general water flows downward unless it hits a "tight" formation in which case it may flow horizontally faster, but once it reaches the water table, it will flow in the prevailiring local/regional direction. Generally this is towards a water body like a stream or lake or ocean.

    Bookmark   July 31, 2011 at 8:57AM
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Consider a hard rain-- hard enough that the water would flow, to some degree, along the top of the soil before it has time to soak in. When such a hard rain hits gravel it will flow off the gravel and onto the sand or soil beneath rather quickly, then flow across the sand or soil. If it then runs into the side of a brick paver, will it pool up enough to create a "bowl" of water in the gravel area? The fact that the gravel area is next to the house is what has me concerned about this. I don't want the soil next to the foundation to be oversaturated.

I know this depends on soil drainage and a host of other factors but what I want to know is if you can envision conditions where the choice of gravel->brick alone could cause a drainage/moisture problem where a brick patio all the way to the house would not.

    Bookmark   August 1, 2011 at 10:42AM
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My experience is with groundwater plumes and not specific to landscaping design issues, so take this as very general observations. If the bowl fills up very rapidly, which it might do, because of the bricks concentrating the flow, then if the rate of filling > rate of infiltration the bowl will fill up and continue spilling over the top along the patio surface. Think of a puddle, put a hose into it so it's vertical flow rate is overwhelmed and it simply tops over and flows away.

    Bookmark   August 2, 2011 at 10:51PM
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