How to Design a Retention Basin

In areas where excess water runoff is a problem, cutting through soil to cause erosion and flooding, retention basins are a first line of defense. Constructed geographically higher than the area of problem, retention basins gather water and disperse it through a controlled release system. Most retention basins are very large; but you can design one on a smaller scale. Read on to learn more.

Difficulty: Moderately Challenging

Instructions

1. Identify the main problem or goal. Sometimes it's obvious; homes are flooded, farm crops wiped out or bridges washed away. Other times it's more subtle such as when runoff creates deep ravines and transports water away quickly, leaving little for livestock or irrigation. Most basins are designed to utilize the geographic lay of the land.

2. Contact your state water authority before you begin your design. In some places you can plan a retention basin on a small scale without being required to get a permit, but in states where water quantity is an issue, it's often illegal to divert the natural flow without express permission.

3. Shoot grade. Used extensively by land survey crews, this means you measure the height of all the topography in the involved area to determine the exact pattern that water will follow when runoff occurs. Design your retention basin strategically to accumulate the runoff by placing it where it will gather the most water. You may have to incorporate some preliminary waterways before the basin diverts the flow where you want it.

4. Decide on your method of water release. Unless your basin will be very large, it will likely fill to capacity at some point and you will need to control the release of the water to keep it from going over or breaking the retaining walls. This can be as simple as an overflow made of non-porous material (like concrete or stone) or as elaborate as a mechanical release that opens when a pre-specified water level is reached. In any case, you must provide a place that is lower in grade to divert water from your basin.

5. Design the landscaping surrounding your basin. Provide the necessary access paths to reach the basin should you have to release the water by hand.

Tips & Warnings

• If you utilize a low area, your basin may need little more than a dam to hold water, as opposed to constructing retaining walls and digging if you're placing it in a higher area.
• Don't proceed without permission from your state's water authority. When you retain water, the property owner who lives geographically below you may be denied water he depends upon. Laws are on the books to regulate this issue.
• Don't neglect to incorporate a water release system. Even if you're just pushing up dirt to create a stock pond, when your basin fills, the runoff may begin to overflow which leads to a small trench. Very quickly, a small trench becomes a washed out retaining wall as the water rushes through.

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