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Landscaping & Design/how to make clay soil more porous


our lawn is clay. we recently removed an old pool which left a layer of sand in the yard. i have researched enough to know that mixing sand with clay creates something less porous than clay. if i left the layer of sand without mixing it with clay, would the area drain. we are also going to build a berm at the back of our property to regulate water drainage from the property behind us. can we use sand, rocks, some fairly new pine chips, and clay. will the pine chips make the berm too porous as they decay thus defeating the purpose of the berm which is to hold back to redirect water.

Thank you


Depending on how fine or coarse,sand has relatively good drainage properties. A good method to make clay more porous is to add organic matter. A small amount of coarse sand or gravel should not cause any problems and certain types of crushed rock may be helpful.

Do not use pine chips in the berm or any other organic material. Organic material will interfere with compaction and could create voids and contribute to seepage through the berm. You are correct,it will increase porosity. Also,do not use sand or rocks in the berm. Do not use cracking clay. This is a clay that has a high shrink/swell potential. In other words,it changes volume too much between being wet and drying. Do not use topsoil or sodic soil. Sodic soil contains high amounts of sodium chloride or sodium carbonate and is found in semi-arid or arid regions. The sodium carbonate type is alkaline. This type of soil is unstable. Calcitic clay is also unstable.
Rock and sand will also lead to instability of the berm.  So,basically, do not use the following for the berm:

organic material




calcitic clay

cracking clay

sodic soil

fine silt

A good soil for the berm would be one with a relatively high and stable clay content. The clay will decrease the permeability of the soil. Some seepage may occur through the berm but depending on how long the water side of the berm is flooded,this may or may not be a problem. Riprap (stones placed on the water side of the berm) may be helpful in preventing erosion of the bank. A keyway at the base of the berm,consisting of impervious clay may be helpful in preventing seepage or a toe drain may be used. An alternative to a berm could be a concrete or masonry flood wall. An impermeable rubber lining may be helpful on the water side if suitable soil cannot be found to construct the berm. Other materials for the lining could include asphalt or concrete.

Plant a grass such as creeping bent or meadow grass on the berm to prevent erosion and to prevent deeper rooted weeds from moving in. These grasses are more suited to berms than ordinary lawn grass. Deep rooted plants such as shrubs are not desirable.

Before beginning work on this berm,be sure you can legally block water from your neighbors property. If this will cause flooding on your neighbors property or alter the natural drainage flow from your neighbors property,then you cannot legally alter the water flow. There are only limited circumstances where you can block water flow from a neighbors property,usually when the neighbor is causing water to be deposited on your property artificially,such as through a misplaced drain pipe. And sometimes even when the neighbor is in the wrong and is causing your property to be flooded,it is still not legal to block water flow,such as when a neighbor leaves a hill in an eroded condition causing excessive runoff onto your property. In this case,a court order must be obtained to have the neighbor correct the condition. Blocking water flow in such a case would cause flooding on the neighbors property by altering the natural flow of water. In general,always try to avoid flooding your neighbors property.  Good luck.

Mark Harshman  

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