CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is designing a bioretention area (rain garden) to manage stormwater runoff from a residential roof. Which of the following is the most critical characteristic of the soil media specified for the bioretention area?
- AHigh infiltration rate to quickly absorb runoff
- BNeutral pH to support a wide range of plants
- CHigh clay content for nutrient retention
- DLow organic matter content to prevent clogging
Show answer & explanationAnswer & explanation
Correct answer: A. High infiltration rate to quickly absorb runoff
The primary function of a bioretention area is to facilitate the infiltration of stormwater. Therefore, the soil media must have a high infiltration rate to quickly absorb and filter runoff. While nutrient retention and pH are important, the ability to infiltrate water is paramount for its effectiveness in stormwater management.
Why the other options are wrong
- B. A neutral pH is desirable for plant health, but the most critical characteristic for stormwater management is the infiltration rate.
- C. High clay content would reduce the infiltration rate, hindering the primary function of a bioretention area.
- D. While excessive organic matter can sometimes lead to clogging, a moderate amount is necessary for plant health and pollutant removal; 'low' is not the most critical characteristic.
Bioretention Soil Media Characteristic
The most critical characteristic of bioretention soil media is a high infiltration rate to quickly absorb and filter stormwater runoff.
- Allows rapid absorption of large volumes of water.
- Typically a custom-blended mix of sand, soil, and organic matter.
- Facilitates pollutant removal through filtration and biological processes.
Memory trick: Infiltration is the rain garden's main station.