CASE STUDY: Dallas Street in Ennis, TX
Canopy and Root Management on Dallas Street in Ennis, TX
In anticipation of its future growth, the City of Ennis, along with MESA Design Group and Construction EcoServices developed a plan to serve as a road map for future development and economic revitalization. Dominated by vehicles, Dallas Street currently offers very little to the pedestrian experience. The design included an alley of Princeton American Elm trees along the street, providing a cathedral like corridor of cool dappled shade in the hot summer months, and allowing warm sunlight through in the cool winter months.
The average life of a tree in the urban environment is less than 10 years. The compacted soil from surrounding pavement and lack of nutrients decrease the lifespan and reduce the canopy size of trees. Root systems can damage the surrounding pavement and underground utilities, as it struggles to find the nutrients to survive. Shade cover created by healthy trees can help reduce the heat island effect, but most often urban trees never reach their full canopy size. If the City of Ennis was going to invest heavily into a pedestrian friendly roadway, they needed to ensure the trees would survive and reach full maturity.
MESA partnered with Construction EcoServices (CES) on a solution that would provide the trees with adequate soil volume and address the concerns with pavement heaving and underground utilities. The most common solution is CU soil, but that wouldn’t provide enough soil volume for the large Elm trees to survive the unpredictable Texas climate. Most of CU Soil consists of stone for structural support and not healthy soil. The more valuable solution came from Citygreen™. Their company manufactures structural soil cells (Stratavault™) that provide support for almost any traffic load and a 90% void space for healthy, uncompacted soil. MESA and CES took it one step further by using permeable pavers on top of the soil cells, which capture sheet flow from the buildings before entering the storm drain. Stormwater runoff provides water for irrigation, while the tree pits provide storage volume and remove pollutants. Healthier trees develop larger canopies for shade, which reduce the heat island effect and capture more rainfall. Trees aren’t typically thought of as infrastructure, but this application proved the value that multifunctional design can bring to the stormwater industry.