Monday, November 2, 2009

Keeping Our Streams Full

Constructing a rain garden is an excellent way to harvest rainfall that may otherwise become detrimental runoff. Generally a rain garden is a depression filled with plants that slows down stormwater and allows it to infiltrate into the soil. It is often referred to as a "passive" or "simple" rainwater harvesting system. Unlike "active" or "complex" systems, you are not using tanks, pipes, and pumps to collect and use water.

Many people can understand the benefit of reducing runoff that rain gardens provide. Slowing down the water's flow can prevent land from eroding and streets from flooding. However, there is a common misconception when it comes to the water's infiltration. Some believe that by preventing runoff, we are reducing a water source for river and streams.

The truth is in fact quite the opposite. Streams and rivers (especially in the West) receive a large portion of their flows from groundwater. This is called base flow and is why streams still run during droughts.

Rain gardens replenish aquifers with water which eventually contributes to streamflow. This may be delayed as it can take anywhere from days to decades for water to reach a stream after infiltrating into the ground.