Natural Media Filter for Urban Green Stormwater Infrastructure

With rapid urbanization and development, the risk for increased urban flooding is a major threat to local waterways. Environmentally, urban settings introduce additional pollutants to water as well as a greatly increased flow regime that can overwhelm storm sewer systems. In cities with combined sewer systems this adds more of a burden on water treatment plants and the large amounts of public spending that are directed at water infrastructure. Flood damage alone can reduce a property’s value by 10-25% (11) and create overall degradation to a site. The implementation of green infrastructure can aid in minimizing storm water flooding and maximize the retention of stormwater. Through this study, a natural media filter was optimized using clay, sand, sawdust, and peat moss- all locally accessible materials to the site being analyzed in this study. Three successive 100-year storm events, 3.08 in/hr, were reproduced in the batch filtration and column filtration study, in order to be environmentally resilient. The batch filtration study tested the drainage and retention performance of varying percentages and layering of the materials being assessed. The optimal mixture was a two-layer mixture at a total depth of 5 cm containing 7% clay, 43% sand, 25% sawdust, and 25% peat moss. The optimal mixture was tested during the column study at a varying depth of 10 cm and at a higher flow rate of 2 mL/ min; in addition to the 5 cm and 0.55 mL/min flow rate that compared to the batch filtration study. The optimal mixture continued to prevent flooding when a higher flow rate was introduced. The column filtration study allowed for a constant flow rate of water into the system and had a smaller allowable surface area in comparison to the batch filtration study that had instantaneous water input at a larger surface area. The site area’s flow rate was linearly extrapolated from the volumetric flow rate of the two studies. The natural media filter design at a depth of 5 cm was sustainably assessed in comparison to the natural media filter at a depth of 10 cm and permeable pavers. Environmentally the permeable pavers had the greatest impact and the natural media filter at a depth of 10 cm had the highest energy implications. Economically, the natural media filter at a depth of 5 cm was the lowest initial capital. The social assessment determined that the public found the implementation of green infrastructure to be beneficial environmentally, economically, and socially. The optimal natural media filter mixture- 7% clay, 43% sand, 25% sawdust, and 25% peat moss at a depth of 5 cm- meets the needs of a sustainable design as well as meeting the performance goals.