So, the big question is, why do we need rain gardens? Why should we spend this money to dig up our yards and put some plants in it? This is why. Our waters are becoming polluted by surface runoff that is collecting chemicals, sediments, litter, nutrients, and waste. The more land we continue to urbanize, the more impervious surfaces we create. Impervious surfaces are nonporous materials that do not absorb water, so it prevents the land from absorbing water runoff and allows the water to retain the pollutants that it carries. Water that flows through the storm water systems in Hawaii is not filtered before it enters the ocean water. Not only are there tons of pollutants travelling through the runoff, it is also travelling fast as most of the storm water flows through manmade concrete channels. So, the ocean cannot filter it fast enough, which leads to coastal degradation of near shore waters and all that lives in it. To the right is a picture that displays storm water runoff simply.A rain garden helps to inhibit this pollution by using the process of infiltration. Infliltration is when water seeps through the pores and spaces of soil sediments and collects below a water table, which is the boundary between non-saturated and saturated soils. The water would naturally collect here in aquifers and the water is naturally filtered of all pollutants as it travels through the grains. However, now most of the land on the coast is covered in concrete or asphalt, which prevents the process of infliltration, depicted below.
Rain gardens act as a reservoir to hold the water that flows off of your roofs and some of your lawn. It holds the water after rain and gives the water the neccessary time to infiltrate into the ground rather than adding to the surface runoff and going straight into the ocean. The plants help by absorbing some of the water and later transpiring it after respiration as well as adding natural aesthetics to your yard. The plants also retain the soils with their root systems. Below, is a diagram of a common rain garden and an example of a residential garden version.
