Rain Gardens Reducing Stormwater

By May 14, 2015Blog

What do we think of when it rains? The sound of raindrops hitting the roof? The smell of the first spring rain? Meanwhile all of that rain has to collect and drain somewhere, right? That somewhere is our local storm sewer systems, ditch, and 1ultimately our streams. For some areas this stormwater falls in excess amounts, so much that existing ditches and stream cannot handle the volume. When this happens erosion and deposition can cause headaches for landowners such as the erosion (Picture 1) which then causes the deposition of material on a neighbor’s property (Picture 2). These problems are currently being experienced at the downstream outlet of the Saddle Hills 2neighborhood. To combat this problem the City of Omaha has built five demonstration project curb cut rain gardens within the neighborhood with help of a grant. A curb cut rain garden is a built depression where rain water is diverted off the street and into the garden alongside the road. The water is allowed to soak into the ground naturally with the help of native plantings. By holding and infiltrating water in the upper reaches of the 3watershed, the volume of water that reaches the downstream outlet is reduced and should help reduce the severity of erosion occurring on site. A rain garden is not: a pond, a mosquito haven or a wetland. When properly constructed the water within the rain garden drains away within 24 hours. The construction of these rain gardens in the Saddle Hills neighborhood was not only to reduce stormwater volumes but to also education the public on what rain gardens are and motivate them to construct one on their property. First a study was done to compile and narrow potential sites that were4 best suited for rain gardens (a priority location identified in Picture 3). After these sites were chosen, concept plans for each individual rain garden were developed and approved by the homeowners. The rain gardens were kept within the street right away as much as possible. Each garden layout included the overall footprint, a mulched planting area, and the extents of the 1’ deep water ponding area (Picture 4). Construction of the rain gardens started in October of 2014. As part of the design a net cu5t fill balance on earthwork was achieved to reduce costs. Excavated material was used to construct the earthen berm around the ponding area (Picture 5). After earthwork was completed the soil within the ponding area was amended with 2” of Oma-Gro compost and tilled in to a depth of 6”. The plantings and planting plans for the project were provided by the Nebraska Statewide Arboretum. The plants chosen were all native ones so that they could tolerate extended wet and dry periods.  6Picture 7 shows the rain garden functioning as planned during the first rain event. The final product of the rain garden does not only function to reduce stormwater volumes, it also is a great addition to the any homeowner’s landscape (Picture 8). As part of this project a community outreach workshop7 was performed. Participants helped with the plantings of the rain garden constructed in the Saddle Hills Park and were educated on how to construct a rain garden on their own property. To monitor the project’s effectiveness, the city of Omaha installed a flow sensor and rain gauge which has been collecting pre construction runoff data since 2011. This data will be compared to future monitoring data to quantify volume reductions. The demonstration approach was used to encourage additional rain gardens in the watershed8; we understand five gardens in an over 100 acre watershed will likely not produce a net effect sufficient to solve the downstream problems. But it is a fantastic first step and we look forward seeing the results of the monitoring data for the upcoming rain season! The City of Omaha also continues to pursue additional grants to implement additional gardens and infiltration solutions to build upon the progress already made. For more information about rain gardens in the Omaha area please visit: http://www.omahastormwater.org/

 

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– Dan Jones