Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations STORM WATER STORAGE AND TREATMENT Code Requirements Often a storm water management system is required to Restrict storm water runoff rate pre- development levels (quantity) Treat storm water so that runoff is relatively clean and free of toxins (quality) Project Lead The Way, Inc. Copyright 2010

Storm Water Management Devices Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Storm Water Management Devices Retention Pond (Wet Pond) Collects storm water in a permanent on-site pond Treats storm water by allowing pollutants to settle out or be removed by biological action Water can be reused for irrigation Limitations Difficult to maintain in arid and semi-arid climates Project Lead The Way, Inc. Copyright 2010

Storm Water Management Devices Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Storm Water Management Devices Detention Pond (Dry Pond) Extended detention basin that collects storm water and then slowly releases the water into the municipal storm water system Treats storm water by allowing pollutants to settle out Limitations Drainage area should be at least 10 acres, otherwise small release pipes clog Project Lead The Way, Inc. Copyright 2010

Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Detention Pond Retention Pond Project Lead The Way, Inc. Copyright 2010

Detention and Retention Pond Design Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Detention and Retention Pond Design DETENTION CAPACITY This slide illustrates structural differences between detention and retention ponds. A detention pond will allow a slow discharge of water (not to exceed the pre-development discharge) through piping at the bottom of the pond. This allows the pond to eventually empty after a storm. A retention pond maintains a permanent pool of water. Water is not drained from the pond; however, water can slowly infiltrate the soil. Both retention and detention ponds provide an overflow structure to allow controlled release when the pond capacity is exceeded. Courtesy DoD. Project Lead The Way, Inc. Copyright 2010

Storm Water Management Devices Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Storm Water Management Devices Underground Storage Tanks Variation of the detention pond Detains water for short periods before releasing it into municipal storm water system Limitations Expensive but can be used for smaller drainage areas Project Lead The Way, Inc. Copyright 2010

Storm Water Management Devices Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Storm Water Management Devices Storm water Wetlands (Constructed Wetlands) Storm water diverted to a permanent pool that incorporates wetland plants Pollutants removed through settling and biological activity Limitations Drainage area should be at least 25 acres Difficult to maintain in arid and semi-arid climates Project Lead The Way, Inc. Copyright 2010

Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Constructed Wetlands The image on the left is a subsurface flow constructed wetland (i.e., the water flows through a permeable layer below the surface, often soil, sand, or gravel). Free water surface systems like the one shown on the right are designed to simulate a natural wetland with shallow water flowing over the surface. This image shows constructed wetlands on a site formerly used as a dump in Orlando, Florida. Courtesy EPA Courtesy EPA Project Lead The Way, Inc. Copyright 2010

Size of Storm Water Ponds Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Size of Storm Water Ponds Rule of thumb: Reserve ten percent of development area for storm water pond Volume of storm water estimate V= Volume of storm water in acre feet A = Drainage area (area of site) in acres Project Lead The Way, Inc. Copyright 2010

Size of Storm Water Ponds Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Size of Storm Water Ponds Area of pond Ap= Area of pond V = Storm water volume in acre ft d = Average depth of pond Project Lead The Way, Inc. Copyright 2010

Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Pond Forms Project Lead The Way, Inc. Copyright 2010

Size of Storm Water Ponds Storm Water Storage and Treatment Civil Engineering and Architecture Unit 3 – Lesson 3.4 – Site Considerations Size of Storm Water Ponds Considerations: Soil characteristics Volume of water Contamination level Depth to water table Topography of site Project Lead The Way, Inc. Copyright 2010