Stormwater Runoff
According to the Center for Watershed Protection, impervious surface cover has the most significant impact on watershed health at the small watershed level. As urbanization increases impervious surface cover, urban watersheds are faced with the compounding challenges of stormwater runoff. According to Charlotte- Mecklenburg Storm Water Services (CMSWS), one inch of rain on an acre of forested area produces little to no runoff. However, one inch of rain on one acre of impervious surface (concrete, asphalt, etc.) produces 27,000 gallons of stormwater. Since Charlotte has separate stormwater and sanitary sewer systems, every time it rains, runoff collects various forms of pollution as it flows into storm drains, which empty directly into Charlotte's creeks and streams (CMSWS, 2021). Urban stormwater runoff carries harmful pollutants including bacteria, trash, sediment, car oils, fertilizer, pet waste, and other forms of urban debris.
The Little Sugar Creek watershed is recognized as one of the most developed commercial and suburban watersheds in Mecklenburg County (CMSWS, 2021). Below are some photos I took along Little Sugar Creek showing normal conditions vs. conditions after an average rainfall event, highlighting the impacts of urban stormwater runoff, including heightened water levels, congregated debris, and increased turbidity.
Photo credits: Cecilia Kammire
In 2013, UNC Charlotte College of Arts + Architecture and UNC Charlotte Urban Institute partnered with numerous municipal, private, and non-profit groups to create KEEPING WATCH, a multi-year interdisciplinary project aimed at engaging the public in local environmental issues. In 2015, KEEPING WATCH focused their efforts on raising awareness of urban streams and water quality in Charlotte. Their research has been a central inspiration to this blog. Their "Worthless if Polluted" video below highlights the pivot role of creeks in Mecklenburg County, and how they need to be prioritized in planning for a sustainable future in Charlotte.
As the video mentions, most of Charlotte's creeks and streams are officially designated by the state as "impaired," meaning they cannot support diverse and abundant aquatic life. While pollution is a major part of the problem, stormwater runoff also dramatically alters the natural watershed hydrology in urban areas. Urbanization and increased impervious surface create compounding pressures on urban watersheds, causing several degrading impacts to occur:
Less rainfall infiltrates the soil, causing larger volumes of untreated stormwater to run directly into waterways, carrying various pollutants.
Less groundwater infiltration results in less available groundwater to replenish surface water supplies during drought events.
Larger volumes of stormwater entering streams causes higher peak flows, increasing flooding risks and property damage.
Higher storm flows also alter channel morphology through causing in-stream erosion, channel incision, increased turbidity, increased sediment loads, decreased aquatic habitat, and overall impaired aquatic biological health.
Climate Change
According to the U.S Climate Resilience Toolkit, one of the top future climate concerns for Charlotte, NC is extreme heat. If green-house gas emission continue at their current rate, in just thirty years, Charlotte is projected to have a 202% increase in extremely hot days per year (over 100°F), and a 3°F increase in average annual temperatures (U.S. Federal Government, 2023). Stormwater runoff from hot pavement in cities is already proven to raise water temperatures as it flows into waterways. Increased water temperatures will only heighten this effect, causing devastating and fatal impacts on aquatic life. Higher annual global temperatures have also been proven to drive more frequent and severe weather events, such as tropical storms and hurricanes, which can result in heavy flooding and even urban flash floods within Charlotte.
Within the next 30 years, Mecklenburg County is also projected to have a 12% increase in days with heavy precipitation and a 1.6" increase in average annual precipitation (U.S. federal Government, 2023). Increased annual precipitation acts as a stressor that contributes to sustained flooding and further worsens erosion in urban watersheds. Projected disruptions in seasonal patterns can also lead to longer dry spells in Charlotte, which severely threaten creeks and streams that already have reduced base-flow from urbanization. The compounding impacts of climate change and urbanization undoubtedly put the future of Charlotte's creeks at risk. Focusing on restoring and preserving the biological integrity of urban watersheds now is critical for building city-wide climate resilience in Charlotte.
Charlotte-Mecklenburg Storm Water Services. (2021, April). Sustainable Stormwater Management Strategy for a Thriving City. City of Charlotte. https://www.charlottenc.gov/files/sharedassets/city/v/1/services/stormwater/documents/about-us/charlottestormwaterservicesstrategicplanapril2021.pdf
UNCC Urban Institute. (2015, March 7). 2015 KEEPING WATCH on WATER: City of Creeks. [Video]. YouTube. https://www.youtube.com/watch?v=rysLmYVCsv0
U.S. Federal Government. (2023). U.S. Climate Resilience Toolkit Climate Explorer. Retrieved from https://crt-climate-explorer.nemac.org