Over the course of the past few decades, environmental sustainability has been a hot topic of conversation. Accelerating urbanization has exposed the fragile ecological future of cities and spurred extensive concerns about urban sustainability. Efforts to confront environmental challenges are increasingly reliant on largescale data sources and rapidly changing communication technologies for solutions. The “smart cities” movement in particular aims to connect urban transportation, energy, disaster preparedness, health emergency, and other systems of urban service delivery. The explosion of “big data” and real-time monitoring devices are also major features of recent efforts to enhance ecological sustainability. Urbanization presents one of the most pressing and complex challenges of the 21st century. How cities are designed, managed and used is likely to shift substantially based on demands created by two powerful trends. The first trend involves a growing awareness of a threat to the sustainability of the Earth’s natural environment; the second trend involves the rapid rise in the number of people moving into and living in cities. Combined, these trends call for massive development of new buildings and infrastructure, along with new social and cultural institutions in order to accommodate the vast numbers of city dwellers without irreparably harming the natural environment. In particular, rapid population and economic growth in the developing world pose profound implications for the future of human society. About 90% of urban growth worldwide occurs in developing countries, which are projected to triple their existing base of urban areas between 2000 and 2030. It is estimated that by 2025, China alone will add 350 million people to its urban population—more than the population of the entire United States today. One of the many products of urban population growth is an increase in the infrastructure that is built to accommodate the growing population. This bring me to the topic that I will be focusing my research on: stormwater management.

What happens to a drop of rain when it falls onto the ground? It may land on a tree and evaporate; it may land on a farm field and soak into the soil; or it may land on a rooftop, driveway or road and travel down the street into a storm drain or stream. Many familiarize rain with a calm, soothing aura. Unfortunately, rain is also familiarized with tremendous sadness, difficulty, and disaster. Rain, in all of its forms, causes billions of dollars in damage in the US every year. And every time it rains, all of those millions of gallons of water that tumble onto the ground need to go somewhere. In urban areas with an abundance of infrastructure, not all of it soaks into the soil below our feet. All that water that rolls off of your roof, through your yard, and over the street is called stormwater runoff. Stormwater runoff is rainfall that flows over the ground surface. It is created when rain falls on roads, driveways, parking lots, rooftops and other paved surfaces that do not allow water to soak into the ground. Agriculture is the leading source of NPS (nonpopint source) pollution in the United States. Agricultural activities that cause NPS pollution most generally occur in the absence of a conservation plan. Impacts can be generated from activities such as poorly located or managed animal feeding operations and manure, overgrazing, plowing too often or at the wrong time and the improper application of fertilizer. However, the built environment is also a major and growing contributor. Urban and suburban infrastructure developments usually reduce pervious surfaces, creating dramatic changes in the hydrologic regimes of whole watersheds. For example, impervious surfaces reduce local infiltration rates and groundwater percolation, resulting in higher surface water runoff, peak discharges, and the export of sediment and associated nutrients (e.g., nitrogen, phosphorous) into local tributaries.

Efforts to reduce the impacts of urban stormwater runoff have been happening for some time at federal, state, and local levels. The Clean Water Act (CWA) is the primary federal law that regulates the quality of the nation’s water bodies. The Clean Water Act, through the National Pollutant Discharge Elimination System (NPDES) program, establishes pollution limits for anyone discharging into streams and lake. In Wisconsin, NPDES permits are issued by the Wisconsin Department of Natural Resources (WDNR) which identify performance standards and limits for things like peak flow, runoff volume, phosphorus, and total suspended solids. As part of their permit, each city must prepare a management plan to meet these prescribed limits by implementing best management practices (BMPs). BMPs are practices, treatments, and technologies that can alleviate one or more of these negative effects.

Permeable pavement is one of these best management practices to improve water quality and reduce the impacts of urban runoff. Permeable pavement is a porous urban surface with an underlying stone reservoir. There are multiple types of permeable pavement, all of which are used for different purposes. These different types of permeable pavements include, but are not limited to; porous asphalt, plastic grids, porous turf, permeable interlocking concrete pavers, permeable clay brick pavers and bound recycled glass porous pavement. Permeable pavement catches precipitation and surface runoff, storing it in the reservoir while slowly allowing it to infiltrate into the soil below or discharge via a drain tile. The most common uses of permeable pavement are parking lots, residential roads and driveways, sidewalks, patios and swimming pool decks.

An additional factor to consider is that traditional asphalt gets very hot, creating a “heat island” effect in urban environments. A heat island, is essentially exactly what it sounds like- an area that becomes much warmer than its surroundings. Have you ever stepped barefoot onto black asphalt during the summer? That- is a the heat island effect. Many manufacturers believe green pavement (permeable pavement) can help to change all that. In addition to helping reduce stormwater runoff, green pavement also poses other positive contributions to the environment. In contrast to traditional asphalt, which requires a large amount of energy to produce and also emits a large amount of waste, companies can produce green pavement with recycled materials. Another thing to take note of in regards to permeable pavement is that it takes quite a lot for ice to build up on it in the winter due to the fact that water does not pool up on permeable pavement. Even in freezing temperatures, permeable pavement tends to be warmer due to the increased air circulation within the pavement. Thus, this provides a safer surface for walking and driving in harsh winter climates.

Another effective best management practice used in reducing stormwater runoff is the implementation of green roofs on top of buildings. A green roof is a roof a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. A green roof may also include additional layers such as a root barrier and drainage and irrigation systems. Container gardens on roofs, where plants are maintained in pots, are not considered to be authentic green roofs. Green roofs serve several purposes for a building. These purposes include; absorbing rainwater, providing a layer of insulation which helps to keep building cool in warm climates (which in turn reduces the heat island effect that I just discussed, and also provides savings on energy costs), creating a habitat for wildlife, and green roofs also increase the aesthetic appeal of a building. In addition, green roofs typically last longer than regular roofs.

Green roofs, without a doubt, serve many great purposes and have vast positive effects on both the economy, and the environment. A green roof is an excellent best management practice in combatting the issue of stormwater management. With green roofs, water is stored by the substrate and then taken up by the plants from where it is returned to the atmosphere though transpiration and evaporation. During summer-like climates, green roofs can retain 70-90% of the precipitation that falls on them. During winter-like climates, green roofs can retain between 25-40% of the precipitation that falls on them. Green roofs not only retain rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happen to run off. By green roofs effectively reducing the amount of stormwater runoff, this, in turn effectively helps to reduce stress on obsolete sewer systems at peak flow periods.

Unfortunately, the benefits of green roof technologies are poorly understood in North America and the market remains immature, despite the efforts of industry leaders. However, in Europe these technologies have become very well established. The reason for this is a direct result of government legislation and financial support. Such support recognizes the many tangible and intangible public benefits of green roofs. This support has led to the creation of a vibrant, multi-million-dollar market for green roof products and services in Germany, France, Austria, and Switzerland, among others.

In my opinion, the issue of stormwater management does not get nearly enough attention as it should. This is a pressing issue in our rapidly growing society, especially in urban areas. Humans use water for everything. I find it ridiculous that the issue of stormwater management is often overlooked by the masses. We must act swiftly on combating the issue of change, and I believe that green roofs and permeable pavement two best management practices which should be implemented everywhere around the globe.