Erosion, flood plains, and other landscape disasters

Solutions for erosion and drainage problems in the landscape.

As a Master Gardener volunteer, one of my responsibilities was to answer landscape and gardening questions from metro Atlanta residents. Questions such as “what’s eating my peppers and tomatoes?” and “why won’t my hydrangea bloom?” were fairly easy to answer. Recommending insecticidal soap or horticultural oil spray for the edible plants and timely pruning and proper fertilization for the flowering shrubs provided a quick and easy fix for these landscape problems.

During dry spells, the number one question was how to maintain a viable garden when little water was available. After years of troubleshooting drought-related plant problems, we would have a wet summer, then the questions would center around what to do about too much water. What I quickly discovered, though, was that many new homeowners are saddled with serious landscape matters.

A good example of this is a discussion I had with a young woman from Kennesaw. She and her husband bought their home during a dry season, then researched, designed and installed a native wildlife habitat. They were thrilled with the results--a wonderful variety of beautiful, low-maintenance plants were planted and a vast array of birds and animals visited the yard regularly. Much time and money had been spent in their pursuit of perfect wildlife habitat, and it was an ideal landscape. Then came spring and summer with a record amount of rain, and previously dry topography became a muddy mess. A seemingly gentle slope served as the channel to a wide pool of standing water that took weeks to drain, causing the demise of many expensive plants (not to mention displacing the wildlife).

What to look for

Obviously, water can be a considerable problem in the landscape. Drainage and erosion problems go hand-in-hand—and the best time to avert this trouble is before the first planting hole is dug and the first pallet of sod is laid.

Flood plains

While it is impossible to predict every potential problem, there are indicators that can help homeowners identify current or possible problems. The first place to look is the survey or plat of your property. The young Kennesaw couple knew that a piece of their property was located in a designated flood plain, but didn’t really pay attention to that fact since their house would not be affected by floodwater. Based on their most recent experiences with the weather, they didn’t anticipate that the flood plain would affect their landscape plans - a costly mistake. Remember: if an area is a designated flood plain, at some point it will be inundated with water.

Another thing to keep in mind if you do have an area that is a designated flood plain on your property is that the soil in these areas is generally hydric—capable of holding water much more readily than most soils.  If this is the case, your choice of landscape plants will be limited to those that can survive in swampy conditions.

Drainage easements

The survey will also show drainage easements (labeled d.e on the map). Drainage easements are the paths that water will take across the land during a downpour. Erosion is frequently a problem along these easements, so it is important to be aware of their location when planning fences, structures or planting beds.

Creeks and stream banks

What about that creek that meanders gently through the back yard? While a creek is a seemingly desirable feature in the landscape, be careful when planning a landscape around it. Be conscious of the possibility of flooding during heavy rainstorms, resulting in unstable soil conditions and stream bank erosion problems. Take care to retain stream bank vegetation to help maintain the water quality and diminish the likelihood of future erosion, and if necessary, replace vegetation to discourage future erosion.

How the water flows

Examine your property carefully the next time it rains. Watch for run-off water from the roof, the gutters and hardscape areas (driveways, patios, sidewalks), as well as the water,  flow from neighboring yards. Does the water follow a neat pathway from the gutter downspout, along the driveway to the street, and into the storm sewer? Or does a sudden downpour create a reservoir in your front yard that takes days to drain away? Make note of your observations, so that you can make modifications to your property before you begin landscaping.

Drainage and erosion solutions

What can be done with drainage and erosion problems? Depending on the situation and the severity, there are a number of solutions.

• First, remember the laws of gravity, and that water will flow to the lowest point available. With that said, you must ensure that water flows away from your house, and does not pool or puddle around the foundation. Make sure that the ground slopes away from the house and the foundations, so that surface water runs away from the building. Take a look at the earth around your house, and if it doesn’t appear to be sloping at least slightly away, fix it.
• Make sure that gutters are kept clean, and that the downspouts pipe the water to a driveway, drainage easement or practical lower spot in the yard. This may require extra fittings or pipes be added to your gutter system.  It is well worth the money so that the foundation and surrounding areas will not be compromised. 
• The solution used to correct drainage problems depends largely on the extent of the problem. If it is not too severe, such as a small amount of excess surface water on the yard, improving soil structure alone may solve the problem. In our area, the heavy clay soil holds water and does not allow good drainage. Tilling the soil and adding organic material can be helpful, additionally providing a better environment for plant growth. For low spots in the lawn, leveling the area with additional topsoil may be the answer.
• Rain gardens are a low-maintenance addition to the landscape, intended to capture rainwater. Planted with vegetation that tolerates “wet feet,” it is located in an area that will absorb run-off and hold it for a short period of time. Rain gardens reduce flooding risks significantly, and allow excess rainfall to be used in a positive way.
• You may have a boggy area in your yard due to underground springs or a low water table. If this is the case, surrender to it and plant shrubs, trees, and perennials that love to get their feet wet.
• If you have more significant drainage dilemmas, soil improvement or leveling may not be enough. A diversion, such as a swale, could be constructed to channel the water to a more desirable spot and prevent pooling in the yard. A popular solution is to create a dry creek bed, which provides an interesting focal point to the landscape during dry weather and serves a useful purpose when the rainy season arrives. Both swales and dry creek beds also help significantly with erosion.
• If neither of these options is feasible in your landscape, subsurface drainage might be the answer. Underground collection pipes, catch basins and channel drains can be installed to remove large amounts of potentially damaging water. French drains are another alternative, particularly around the foundation, in raised beds or planting areas. These drains collect water and allow it to slowly seep back into the ground. In some situations, drain fields can be dug and filled with crushed rock to enable water to seep into the earth. While handy homeowners can install simple drainage systems, larger or more complicated jobs might be better suited to a landscape professional that is expert in grading and drainage work.
• What about erosion caused by drainage problems? Planting vegetation is often the best solution since the plants' roots will help to hold soil in place. Turf and groundcovers are excellent remedies for eroding soil, particularly on a gradual slope. For more steeply graded areas, terraces may be built to slow the water flow.  Terraces can also provide wonderful planting areas for the landscape. If there is a great deal of erosion present, it may be necessary for topsoil to be brought in to enhance the existing earth. Professionals who specialize in erosion and soil issues also have numerous products that can help to correct serious problems.

Sinkholes

Another landscape problem that has become more prevalent in metro Atlanta is the occurrence of sinkholes. Common in Florida due to developments built over underground limestone caves, sinkholes seemingly appear overnight, causing distress to homeowners. Unfortunately, the presence of a sinkhole is not easy to predict.

Most sinkholes occur where debris such as trash, stumps, tree branches and other building materials were buried during construction. Over a few years, the debris decays, leaving an empty cavity in the ground. Hidden under a layer of soil, the hole finally caves in, resulting in a sunken area in the landscape.

If you encounter a sinkhole in your yard, inspect it by enlarging the surface so that you can see inside with a flashlight. If you see building materials or decaying branches, it is a construction sinkhole. Poke into the hole with a stick, and determine if it is solid at the bottom and the sides. If so, you can probably fill the hole yourself, adding layers of soil, a foot at a time, and packing it firmly until filled. You can then safely plant turf or small plants in the area. If there is standing water or a pipe in the cavity, it may be a broken sewer line. If so, contact the county or city water department for guidance.

Do your homework

Just as in any home improvement project, research and proper planning before you start the task will ensure a successful final outcome. Take care of problems in the landscape before you plant, and in the long run, you’ll save time, money and lots of headaches!

Photo courtesy of Ed Castro Landscape

About the author

Mary Kay Woodworth is Executive Director of the Georgia Urban Ag Council. In her spare time, you can find her digging in the dirt, pulling weeds, and writing garden-related articles for publication.