ENVIRONMENTAL IMPACT PAPER
The Impacts of Urbanization on Watersheds
Urbanization of Watersheds
Impacts of Urban Development on Watersheds
Global Wetland Loss
Causes of Wetland Loss
Figure 1. Climate change brings major flood risks to Louisville, as shown in this flood simulation map developed by the Army Corp of Engineers and Louisville/Jefferson County Metropolitan Sewer District.
A recent study conducted in Fairfax, VA indicated that climate change simulations showed that annual runoff volume could increase by 6.5% (Alamdari et al. 2017). Not only will urbanization and climate change result in higher runoff volume, but suspended solids, nitrogen, and phosphorous levels will increase as well (Alamdari et al. 2017). As a result, water treatment practices must be adjusted to deal with increasing urbanization and the impacts of climate change to meet water quality standards (Alamdari et al. 2017).
Combined Sewage Overflows
Solutions to the Urbanization of Watersheds
Figure 2. A stream restoration project in Louisville, Kentucky is an example of the practices of daylighting in which buried streams are removed from underground culverts and depaving in which impermeable surfaces are removed.
One solution to the problem of stormwater runoff and sewage overflow is the building of overflow basins in areas that most frequently have overflow problems during heavy rain events. These basins catch runoff and sewage overflow so that it can be treated rather than being funneled directly into urban waterways. The construction of combined sewer overflow and wastewater basins to prevent water contamination during storms has begun in areas across Louisville, Kentucky particularly prone to flooding and sewage overflows (Louisville/Jefferson County Metropolitan Sewer District 2020). Despite prior efforts to clean up the Beargrass Creek watershed, it has remained heavily polluted due to runoff and sewage overflow. The addition of overflow basins is projected to reduce pollution levels in the three forks of the creek that flow into the Ohio River (Louisville/Jefferson County Metropolitan Sewer District 2020).
Figure 3. Louisville/Jefferson County Metropolitan Sewer District construction of Portland Combined Sewer Overflow Basin to prevent overflow of sewage into local waterways.
Not only must existing wetlands be protected, but wetland restoration is critical to the future of these vital ecosystems and will mitigate some of the impacts of climate change (Kettenring & Tarsa 2020). According to the Ramsar Convention on Wetlands, the main goal of any restoration project “is to create resilient and sustainable ecosystems, as measured on a human timescale, in order to improve the ecological character and enhance the socioeconomic role that the wetland plays in the watershed.” (Zalidis et al. 2004). New tools, such as the Wetland Impact Assessment, can be used for wetland mitigation and restoration projects to minimize damage, restore or enhance wetlands, and even create new wetland environments (Kim et al. 2010).
Figure 4. The beginning stages of a stream and wetland restoration project along the Middle Fork of the Beargrass Creek in Louisville, Kentucky. This restoration will lessen urban flooding during extreme rain events.
Of all of the solutions to the urbanization of watersheds, wetland restoration is one of the most challenging (Zalidis et al. 1999). However, restoring wetland functions provides immediate benefits, from a reduction in pollution to an increase in biodiversity (Zalidis et al. 1999). Wetland restoration can even provide urban centers with economic benefits through a reduction in the costs associated with flooding and pollution control (Zalidis et al. 1999).
One of the challenges facing efforts to mitigate the impacts of urbanization on watersheds is the public perception of the problems and the willingness to allocate funding to these projects. In areas where the protection of water and avoidance of health and environmental risk is strongly valued, the public tends to be more willing to fund projects to reduce risks (Veronesi et al. 2014). Perceptions regarding climate change significantly impact willingness to fund restoration and mitigation projects (Veronesi et al. 2014). Public education will prove invaluable as climate change impacts grow, and urbanization threatens our most valuable and scarce resource - fresh water.
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