Hidden Meaning

Nestled among century-old oak trees near the East Branch of the DuPage River in Illinois is the Bolingbrook Park District’s newest attraction and crown jewel–the Hidden Oaks Nature Center. The 7,000-square-foot, sustainably designed building provides numerous interactive learning experiences that promote interest in and respect for the natural world, while encouraging responsible environmental behavior.

Taking its cue from nature, the building is designed to be like a “tree house” and blend into its surroundings. The site is being returned to its former glory as oak/hickory woodland, one of the most endangered ecosystem types in the Midwest.

One of the more intriguing lessons visitors can study and learn relates to the value of rainwater and the importance of managing and minimizing stormwater runoff. Wight & Company–in collaboration with the park district–designed the nature center to serve as both a model and learning center for rainwater management.

This is especially important because of the nature center’s proximity to the DuPage River–a branch of the Chicago River–which flows into the Mississippi River and, eventually, the Gulf of Mexico. As rainwater passes over conventional surfaces–such as asphalt–it collects detergents, gasoline, oil, pesticides and other pollutants.

The water contains high concentrations of nitrogen and phosphorous, which each spring turn the Gulf into the perfect breeding ground for algae to spawn and grow the Gulf of Mexico Dead Zone–an 8,000-square-mile area equivalent to the state of New Jersey. In fact, the particulates stimulate such excessive algae growth that sunlight cannot penetrate the water. This in turn retards the growth of aquatic vegetation, depletes the oxygen supply, and kills the entire marine ecosystem.

To minimize its “water-runoff footprint,” the nature center incorporated Best Management Practices (BMPs) into the design, including a green roof, rain garden and the re-establishment of native flora. The guiding principle for these efforts was to reduce the amount of storm water that had to be managed at ground level.

Green Roof Absorbs Rainwater

That approach meant that the stormwater management BMPs started at the top of the building, and worked their way down. The first step was installing a semi-intensive green-roof system, which catches and holds some of the rainfall. In a light-to-moderate rainfall event, a green roof can absorb up to 75 percent of rainwater landing on it.

The green roof features a man-made soil medium suitable for both native and ornamental plants. Since the plants are adaptable to drought situations, they only require a temporary irrigation system to become established during their first year. Permanent irrigation is not needed, thus reducing the center’s use of potable water.

For water that does leave the roof, a rain garden on the north side of the building receives and filters the overflow. As water enters the garden, open graded rock in filter fabric below the soil pulls it down to slowly filter nutrients and other pollutants out of the system. In time, water will find its way to the adjacent hillside through limestone seams, recreating seeps of alkaline-based water for mesophytic plants on the north-facing slope.

Plantings around the nature center are comprised exclusively of native woodland wildflowers and grasses. Native plants, once established, will help absorb rain water, prevent erosion, and restore the ground vegetation within this endangered oak/hickory ecosystem. The dominant species within this restoration is oak sedge (Carex pensylvanica), a grass-like plant that turns humidity into tiny droplets of water for existing trees. It also carries autumnal fires–a key ingredient for combating non-native plants that can overwhelm this type of ecosystem–and provides soil organics for micro-organisms beneficial to native flora.

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