Monday, May 19, 2014

Do Trees Reduce Flooding and Erosion?

Elsewhere on this site, the many benefits of trees have been discussed.  With a wet spring and recent tragic landslides in the national news, we thought we would discuss the positive effects of trees on flood control and erosion prevention.

Trees prevent flooding during heavy rains by several mechanisms.  First, broad leaf trees slow rainfall when rain hits their leaves and must slowly percolate to the ground.  This gives more time for the ground to absorb the water as the rain reaches the ground over a longer time period.  Just as leaves of a tree decrease vertical water speed, trunks and roots of the tree (and other vegetation) slow the horizontal speed of water once it has reached the ground.  This also gives the water more time to be absorbed into the soil.

The roots of the tree increase space between soil particles, allowing the water that does reach the ground to follow these root created channels to deeper water reservoirs.  Once rainfall does reach the roots of the tree, it is absorbed by the roots, and lifted by the tree into the canopy and atmosphere again in a process called evapotranspiration.  This process decreases the total amount of water with which our streams and rivers need to deal.

Trees also prevent erosion.  The most obvious way trees to this is through the binding effect of their roots, turning soil into a type of reinforced dirt.  As mentioned above, trees also slow water flows, which decreases erosion.  The canopies of trees also decrease wind speed, another cause of erosion when the soil is dry or being plowed for agriculture.  Trees planted as riparian buffers (along waterways) prevent soil erosion by fast flowing water already in the stream, as demonstrated by the image of a unforested waterway below.

A creek bank that has continually eroded due to the lack of stabilizing tree roots along it.  This creek will get ever wider (and shallower) until trees are planted.

How can the Groasis Waterboxx help with prevention of flooding and erosion?  Trees can be hard to establish, prone to death after transplant and during their critical first year.  When trees are bought from the big box stores they generally have fine canopies but very poor root systems, with a destroyed primary or tap root.  Because of their poor roots, these trees require frequent watering, and don't become well established and stabilize the soil for several years.  The Groasis Waterboxx allows smaller, bare root (with tap root intact) trees to be purchased (or found wild), and planted with the Waterboxx.  The Waterboxx requires watering only at initial set up, and never again.  Dew and rain water will fill the Waterboxx.  The Waterboxx slowly releases water to the roots of a growing tree, forming a water column in the soil beneath the tree that allows the tree's roots to get well established and grow straight down.  Once the tree's roots reach deeper water, you will see a growth spurt and the Waterboxx can be removed. The Waterboxx can be reused several more times (for up to ten years) on other trees.  Watch a video of the Waterboxx in action below

You can buy the Groasis Waterboxx in the United States from Dew Harvest. We would love to hear your comments below - to leave one, please click on "Comments".


  1. We have a little pond in our back yard and I was using erosion control products like coir logs and jute mats. I found them to be an inexpensive way to prevent erosion. You could try hay bales but bear in mind that when it rains, they can easily be washed away by runoffs.

  2. Seeing as how simple it is, sediment control is a great way to help protect the environment while keeping water supplies safe.

  3. Opponents of tree lopping point out that the damage can be irreversible. The tree may become weak, parasites and bacteria may infest the cuts, and the tree may start to rot and die. Sometimes, new branches will grow fast and the process will need to be repeated soon after. View publisher site

  4. Traditionally grown fruits and vegetables are dry and lack flavor because they do not have the trace minerals that are added to the soils in actual organic gardens. Light deprivation greenhouse