A rain garden (bioretention area) is a man-made shallow depression that collects and stores stormwater runoff until it is absorbed into the ground. Usually bordered by berms and/or stone walls, it has a landscaped appeal using native plants adapted to both water-logging situations followed by drought. As well as eye-appealing in the landscape, it acts a wildlife habitat area.
To learn more about rain gardens, Texas Master Naturalist Beverly Guthrie of the East Texas Chapter hosted a seminar at the Hideaway Lake Clubhouse. Fouad Jaber, Assistant Professor and Extension Specialist with the Texas A&M System, led the half-day event. Jaber began with a slide-show description of various rain gardens around the North Texas area. These ranged from small backyard rain gardens designed to slow down stormwater runoff and reduce erosion to very large areas that capture debris and re-route fast moving water from parking lots.
After a brief break attendees car-pooled around Hideaway Lake. At each stop Jaber pointed out how a rain garden in that area would be beneficial. 
At one stop he noted that erosion could be avoided with a well placed rain garden. Another area contained a small drainage ditch that had filled with silt and grown over with grass. A small rain garden would allow better flow and control of stormwater runoff.
Regardless of size rain garden construction follows a specific plan. Once the site is located, the existing soil is excavated and replaced with layers of high-infiltration soils, gravel, and mulch. The size of the rain garden depends on the amount of runoff volume to be collected. Larger rain gardens often require the addition of a perforated under-drain pipe. The garden is then planted with native perennials, grasses, shrubs, and even trees. The possibilities are limited only by the plant’s resilience to the waterlog/drought cycle.
A residential rain garden will cost approximately $6/ft2 for a typical 200ft2 area. Operation and maintenance will cost your time and labor as any other garden. Chores like weeding, monitoring for insect infestations, regular aeration and composting, and removing sedimentation that may inhibit filtration are necessary. The upside, other than stormwater management is a beautiful garden area filled with blooms, insects, birds, and the occasional critter.
You can find out more from the sources as follows:
Your County Extension Agent
Texas Water Resources Institute
Texas A&M Agrilife Extension – Rain Gardens
and at the Bookstore
Wade Village 