Stormwater runoff occurs when rain or snowmelt flows over land surfaces instead of soaking into the ground. This water travels over paved areas like streets, parking lots, and rooftops. As it moves, it picks up debris, chemicals, and sediment. This mixture then flows into drainage systems or directly into natural waterways, often without treatment.
Environmental Degradation
Stormwater runoff introduces pollutants into natural ecosystems, impacting water quality. It picks up contaminants like fertilizers, pesticides, oil, grease, and trash from urban and suburban areas. Runoff also carries bacteria from pet waste and sewage overflows, degrading rivers, lakes, and coastal areas.
These pollutants cause harm to aquatic life, including fish, invertebrates, and plant species. Toxic chemicals from runoff can poison aquatic organisms and disrupt their reproductive cycles. Excess nutrients, particularly nitrogen and phosphorus from fertilizers, lead to rapid growth of algae, known as algal blooms.
When these algal blooms die and decompose, bacteria consume large amounts of dissolved oxygen. This oxygen depletion creates “dead zones” where aquatic creatures cannot survive. The volume and force of stormwater runoff can also cause erosion of stream banks and shorelines.
This erosion increases the amount of sediment carried into waterways, which can smother aquatic habitats, including spawning grounds for fish. Excessive sediment reduces water clarity, blocking sunlight necessary for underwater plants and affecting the food chain. Sediment particles can also harm fish by irritating or clogging their gills and making them more vulnerable to disease.
Community and Public Health Threats
Large volumes of stormwater runoff often overwhelm urban drainage systems, leading to widespread flooding. This happens when rainfall exceeds the soil’s absorption capacity and the infrastructure’s ability to manage the flow. Flooding causes property damage, disrupts daily activities, and creates public safety hazards like submerged roads and electrical risks.
Uncontrolled runoff can also damage infrastructure. Roads, bridges, culverts, and sewer systems can erode and sustain structural damage from the water’s force. This damage leads to costly repairs and disruptions to transportation and public services. Clogged storm drains, often filled with debris and sediment, worsen these issues by causing water to collect, leading to potholes, cracks, and sinkholes.
Contaminated stormwater runoff presents risks to human health. Pathogens, including bacteria and viruses from animal waste and sewage overflows, can enter recreational waters like beaches and swimming areas. Exposure to these contaminants can result in gastrointestinal illnesses, skin infections, and respiratory problems. Chemical pollutants in floodwaters can also pose health concerns for exposed individuals.
Economic Consequences
Stormwater runoff problems carry financial burdens. Expenses are incurred for cleaning up polluted waterways, removing debris, and restoring damaged ecosystems. These cleanup and remediation activities require investment to mitigate environmental harm.
Municipalities and property owners face costs for repairing infrastructure damaged by flooding and erosion. This includes repairs to roads, bridges, and drainage systems, as well as structural damage to buildings. These repairs are often complex and recurring, particularly in areas prone to frequent runoff events.
Recurrent flooding or proximity to polluted waterways can decrease property values. Homes in flood-prone zones can experience a reduction in market value ranging from 4% to 12%. This devaluation affects homeowners and can impact the economic stability of affected communities. Industries reliant on clean water, such as fishing, tourism, and recreation, also suffer economic losses due to degraded water quality. Beach closures or reduced fish populations impact revenue and livelihoods.