Question
QUESTION: Hello Mark. I have drainage from one side of the house running down my 100 foot asphalt driveway that slopes downward and slightly away from the house.  On the slightly higher right side is grass and on the other slightly lower left side is mulch where buses run down my driveway.  Everything works well except for about a 20 foot area on the mulch side which always seems to form a four inch gully right along side the driveway after it rains. If I had Belgian blocks I wouldn't have an issue, as all the water would simply run down the driveway onto the street.  I plan on having them put in when it's time for a new driveway. I've tried putting pond stones under the mulch, but that still gets washed away with even a medium rainfall. Is there anything I can do or use that will allow proper drainage without the surface erosion in the interim?  Would gravel be a better option or would that get washed away as well. I originally used the pond stones because I thought with them being heavier, there would be no chance of them being carried away by the rain.

ANSWER: Hello:

A stone structure to control erosion known as "rip rap" can be used.  The stones should be a minimum of 8 inches in diameter but they should also rest on a foundation and not resting on a foundation is perhaps why your pond stones failed. Proceed according to the following instructions:

If the slope is less than 45 degree you can cover it with cobbles (rip rap) of about 8 inches in size.  Here are the steps to installing rip rap:

Clear the slope of all vegetation and compact the soil to a density similar to the surrounding undisturbed soil.

Layer the stone a mimimum of 9 inches thick.

Dig a keyway trench at the foot of the slope to hold the stone in place.

Lay filter fabric on the compacted slope and lay 6 inches of sand or gravel over the fabric and then lay the stone on top. The sand/gravel and fabric will aid in holding the underlying soil in place. Bury the fabric at the top of the slope and key it in at the bottom of the slope.

Install a drain at the bottom of the slope if needed to channel away water from the slope.

Planting shrubs at the top of the slope,immediately above the stone,will aid in further reducing erosion.

Plants suited for erosion control could also do the job. The roots will hold the soil in place.  This would also look less barren than all rip rap. It depends on how heavy the erosion is. A heavier volume and velocity of water would be better controlled by rip rap.

I would think about the consequences of using the driveway as a drainage channel. Will any adjacent area flood? Will the water have an outlet? None of the water will be soaking into the ground and so with a 100 feet driveway,you will be dealing with a substantial amount of water and also during rain you may not be able to use the driveway because it will be flooded. It is also not good for the road surface and will shorten its lifespan. Think about draining the water to the side of the driveway.


Mark Harshman
http://www.mahdrafting.com
Email: [email protected]

http://www.allexperts.com/ep/724-104627/Landscaping-Design/Mark.htm

---------- FOLLOW-UP ----------

QUESTION: Thanks Mark! The water travels down my driveway which slopes downward onto the street which slopes downward to the left. About a house down from mine is a sewer drain. No water ever builds up on my driveway or on the street, so flooding is not a concern. However, I am still a little confused by your answer because you mention creating a rip rap using stones 8 inches in diameter. But, then you say layer the stone 9 inches thick and also lay 6 inches of sand.  How do you lay 8 inch stones 9 inches? And is the sand only at the foot of the rip rap or do I put sand the entire length of the rip rap? I'm just looking for a solution that will not have my mulch and stones washed away when it rains. Thanks again.

Answer
Hello:

Thanks for pointing the dimensions of the stone out. These are only approximate dimensions. I should have said stone up to 9 inches in dimension but the individual stones can vary from approximately 4 to 9 inches in diameter. The point is,the stones should be relatively heavy,preferably angular in shape and form a layer approximately 9 inches thick.

The sand should form a continuous foundation for the rip rap. The sand acts to keep the soil beneath the stone from being washed out.

You might find plants to control erosion on the slope to be a cheaper and more aesthetically pleasing solution. You would have to first lay down an erosion control blanket and then plant in that. The blanket will protect the slope from erosion until the plants are established.

The purpose of the rip rap or erosion planting is not to protect mulch,it is to stop erosion. There is no way to hold mulch in place on an eroding slope. If you want to stop the erosion,you will have to rule out mulch.

If you dam water up by the use of the "Belgian Blocks" you will be putting additional water onto your driveway and the adjacent area. You will in effect be creating a small dam. The question is,will your property be able to accomodate this additonal water.


Mark Harshman


For more comprehensive help check out my website at:

http://www.prestoexperts.com/expert/markland