Paving Surfaces: Reducing Water Pollution, How?

Paving surfaces can contribute to water pollution in several ways. When rain falls on paved surfaces, it washes pollutants such as leaked oil, pet waste, fertilizer, and road salt into storm drains, which then discharge into rivers and streams. This can harm aquatic life and contaminate drinking water supplies. Additionally, paved surfaces are impervious, meaning they prevent rainwater from naturally seeping into the ground. This can lead to increased water volume and speed, causing flash flooding and erosion, and reducing groundwater recharge. However, there are alternative paving solutions, such as permeable pavements, which can help mitigate these issues by allowing water to infiltrate and reducing runoff.

Permeable pavements can filter out pollutants

Permeable pavements are an effective way to filter out pollutants and reduce water pollution. They work by allowing stormwater to filter through surface voids into an underlying stone reservoir. This process helps to temporarily store or infiltrate the water, reducing the risk of flooding. The most common types of permeable pavement include pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). These materials are designed to replace traditional impervious surfaces such as low-speed roads, parking lots, driveways, sidewalks, and patios.

One of the key benefits of permeable pavements is their ability to reduce the amount of runoff that reaches water bodies. This, in turn, helps to decrease the levels of pollutants, such as nitrogen, metals, and process oils, that can be harmful to aquatic life. Additionally, permeable pavements can also reduce the need for de-icing chemicals and provide a durable and aesthetically pleasing surface.

The structure of permeable pavements plays a crucial role in their effectiveness. They typically consist of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains, and a geotextile layer over uncompacted soil subgrade. This combination of layers allows for the filtration and infiltration of stormwater, reducing the impact on the environment.

Research has shown that permeable pavements can effectively remove pollutants from stormwater. In a study by the U.S. Environmental Protection Agency, a parking lot surfaced with three types of permeable pavements was monitored for six years. The results indicated that the concentration of metals, such as barium, chromium, copper, and zinc, met both the groundwater effluent limitations and maximum contaminant levels in more than 99% of the samples.

In addition to their environmental benefits, permeable pavements are well-suited for high-density urban areas with limited space. They can be used to replace impervious surfaces and provide a more sustainable solution for managing stormwater runoff. However, it is important to consider the limitations of permeable pavements, such as their suitability for areas with high traffic or high-speed vehicles. Overall, permeable pavements offer a promising approach to reducing water pollution and promoting more sustainable urban development.

Permeable pavements can reduce the need for road salt

Permeable pavements can help reduce water pollution by infiltrating rainwater and snowmelt, allowing them to seep through the surface and into the underlying layers of soil and gravel. This prevents water from flowing over heated surfaces and into storm drains, which can increase the water temperature of bodies of water, negatively impacting dissolved oxygen levels and harming aquatic wildlife.

Permeable pavements can also reduce the need for road salt, which is commonly used to de-ice roads in winter. The pavement's porous voids and underlying crushed rock base allow melted water to infiltrate and warm up, preventing it from refreezing into slick, dangerous ice patches. Researchers at the University of New Hampshire found that permeable asphalt only needs 0 to 25% of the salt routinely applied to normal asphalt.

Additionally, the air trapped in the pavement can store and release heat, promoting the melting and thawing of snow and ice. This further reduces the need for road salt. In low-speed and low-frequency travel areas, such as parking lots or side roads, the environmental benefits of unsalted permeable pavement may outweigh the risk of ice.

However, one study found that snow and ice tend to last longer on permeable pavement due to the insulating effect of the air voids, which prevent heat from reaching the surface. This highlights the need for pavement professionals to weigh the priorities and consider the specific context when deciding whether to use permeable pavement.

Permeable pavements can reduce construction costs

Permeable pavements can help reduce construction costs in several ways. Firstly, they can lower material costs. Permeable pavers use interlocking grids that are laid over a prepared subsurface, such as compacted rock or limestone, and filled with gravel or crushed limestone. The cost of these materials is generally lower than that of concrete and similar to asphalt. Additionally, since the fill materials are sourced locally, shipping costs are reduced compared to transporting asphalt or concrete.

Secondly, permeable pavers can reduce labor costs. Installing asphalt or concrete surfaces requires a large team of experienced workers to run the paving equipment, transport materials, and finish the surface. In contrast, permeable pavers are quick and easy to install, requiring fewer skilled laborers.

Thirdly, permeable pavers can reduce equipment costs. Asphalt and concrete installations require specialized equipment, such as paving machines, concrete trucks, and rollers, which can be expensive. Permeable paver installations, on the other hand, require minimal equipment, as the same dump trucks and loaders used to install the subsurface can also be used to acquire and install the fill materials.

Finally, permeable pavers can reduce maintenance costs. Asphalt and concrete surfaces require expensive drainage systems to control stormwater and prevent flooding, erosion, and pollution. Permeable pavers, with their porous surface, eliminate the need for such drainage systems, as they allow water to drain through to the subsurface naturally. This reduction in drainage features leads to lower construction costs for residential and commercial developments.

Overall, permeable pavements offer a cost-effective and environmentally friendly alternative to traditional paving materials, contributing to reduced construction costs and helping to mitigate water pollution.

Permeable pavements can reduce flooding

The use of permeable pavements can play a crucial role in mitigating the risk of flooding, particularly in urban areas. Unlike conventional impervious pavements, permeable pavements are designed to allow water to pass through and absorb into the ground underneath. This feature offers a range of benefits, including a reduction in the volume of stormwater runoff, which is a significant contributor to flooding.

Reducing Flood Risk

Permeable pavements are an effective solution to manage stormwater runoff and reduce the risk of flooding. By allowing water to permeate through the surface and the underlying layer, typically made of crushed rock, permeable pavements prevent water from accumulating on the surface and overwhelming drainage systems. This absorption and retention of water help to slow down the rate at which water enters natural water bodies, reducing the risk of flash floods.

Comparison to Impervious Pavements

Impervious pavements, such as concrete or asphalt, act as barriers that prevent water from seeping into the ground. As a result, rainwater quickly flows over these surfaces and into storm drains, increasing the volume and speed of water entering streams and rivers. This sudden influx of water can lead to flooding, especially in urban areas where a significant portion of the land is covered by impervious surfaces.

Environmental Benefits

The use of permeable pavements offers additional environmental advantages. By reducing stormwater runoff, they help minimize the negative impact of increased water temperature on aquatic life. Permeable pavements also contribute to groundwater recharge, ensuring a consistent base flow for streams and maintaining the natural hydrologic balance. Additionally, they provide an opportunity for natural filtration as water passes through the underlying layers, helping to remove pollutants that would otherwise end up in water bodies.

Limitations and Considerations

While permeable pavements offer significant flood mitigation benefits, they do have some limitations. For example, they may not be suitable for heavy vehicular traffic due to their lower strength compared to conventional pavements. They are also more expensive to install and require regular maintenance to prevent clogging. Permeable pavements are most effective on level ground, as installing them on slopes can lead to water accumulation and defeat their purpose.

Permeable pavements can reduce water temperature

Permeable pavements can play a crucial role in mitigating water pollution and enhancing water temperature regulation. Here's how permeable pavements can reduce water temperature:

Impact on Water Temperature

Permeable pavements, by virtue of their porous nature, can effectively reduce the temperature of urban runoff. This is achieved through the process of slowing down the flow of stormwater, allowing it to cool before it reaches water bodies. This is particularly important as urbanized areas with extensive impervious surfaces contribute to the heating of water bodies. The sun's heat is absorbed by dark-colored roads and pavements, and when rainwater falls on these surfaces, it gets heated. This heated stormwater then flows into storm drains and ultimately enters streams, rivers, or lakes, increasing their water temperature.

Permeable Pavements to the Rescue

Permeable pavements, on the other hand, act as a natural buffer, slowing down the flow of stormwater and allowing it to infiltrate into the soil below gradually. This process naturally cools the water before it reaches the water bodies, reducing the thermal shock experienced by aquatic life. By reestablishing a more natural hydrologic balance, permeable pavements help mitigate the negative impact of increased water temperatures on aquatic ecosystems.

Benefits of Permeable Pavements

The use of permeable pavements offers multiple advantages. Firstly, they help reduce the volume of stormwater runoff by trapping and slowly releasing precipitation into the ground. This, in turn, reduces the risk of flash flooding and erosion. Secondly, they can physically, chemically, and biologically reduce the concentration of pollutants in stormwater. The pavement and soil can trap pollutants, while bacteria and other microbes can break them down. Additionally, plants growing between certain types of pavers can absorb and store pollutants.

Other Advantages

Permeable pavements also offer cold-weather benefits, such as a reduced need for road salt application during winter. The air trapped in the pavement can promote snow and ice melting, and the controlled runoff at the source can decrease the necessity for large-scale detention ponds. While concerns about the durability and maintenance of permeable pavements exist, the environmental benefits they offer, especially in reducing water temperature, are significant.

In summary, permeable pavements are a promising solution to mitigate water pollution and regulate water temperature in urbanized areas. By allowing stormwater to infiltrate into the ground and providing a natural cooling mechanism, permeable pavements help reduce the negative impact of urbanization on aquatic ecosystems.

Frequently asked questions