Topography

Topography Drainage

Improper management of grades is one of the most common concerns for existing and new house lots. The resulting drainage problem can cause damage to structures, plants and human health. Water must be able to flow away from structures and be prevented from ponding (See Rain Gardens below for the exception). Principles for proper drainage include:

  • Slope soil and paving away from structures.
  • Slope paving to shed water to soil immediately in order to avoid water concentration.
  • As much as possible, direct rainwater to soil where it can be used by plants. Grade soil to sheet flow water so that excess water flows away and does not concentrate into ditches causing erosion.
  • Protect/restore soil quality to maintain its water absorbing properties. Soil can become compacted during construction. To avoid compaction, protect the soil or de-compact it when construction is complete. Small increases in organic material also exponentially increase soil’s ability to absorb and store water. Both are critical for successful plant growth.
  • Avoid French drains as much as possible. Over time, French drains will clog with leaves, silt and decomposed plant material. Maintenance can be time consuming, costly and is easily overlooked. Sloping the ground surface is a better and more permanent solution. It is also easier to detect an issue with surface flow before it becomes a problem.
  • For areas that cannot be sloped to drain naturally, use surface drains and pipe them to free draining areas or a rain garden.
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Walls and Terraces

The use of walls and terraces to manage slopes is centuries old. Farmers perfected and still use these methods to turn steep slopes into productive land and limit erosion. The principles perfected centuries ago apply today and are frequently used to create ornamental gardens and spaces.

  • Walls and terraces should fit the site naturally and avoid extreme conditions.
  • Terracing, the oldest method to deal with slopes, can allow you to avoid walls completely, making it the most cost-effective method.
  • Terraces need to be planted, making them much less intrusive than walls and easily blended into site design.
  • Walls in the city of Chattanooga require a permit to ensure they are properly engineered.
  • Grading should shed water evenly behind walls and over terraces to avoid concentration of water.
  • The improper location of walls and terraces can compound drainage problems if they create dams adjacent to structures.
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Best Management Practices

When grading or adjusting site topography, there are a number of best management practices to ensure healthy landscapes.

  • When grading lots, strive to balance the soil cut and fill in order to limit hauling away or bringing in soil thereby saving money and reducing the environmental impact.
  • For new construction or major exterior modification work, remove and stockpile the site’s existing topsoil for reuse in planted areas. This saves money, limits environmental impact, and usually provides for deeper topsoil and much better plant growth. It also reduces the likelihood of bringing in weeds.
  • Rain gardens allow rainwater to be held on your property instead of running off into the storm water system. They consist of slight depressions to hold water during rain and modified soil to ensure the water is absorbed within 36 hours.
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