Flooding
Runoff water creates a lot of problems for urban areas. With a large percentage of land covered by hard, impermeable surfaces like pavement, parking lots, buildings, and sidewalks, rainfall cannot be naturally absorbed into the soil. This leaves a substantial amount that gathers into gutters and storm drains. However, everyone has seen storm drains backing up into the street when storms are intense or persist for many hours or even days. Flooding presents immediate danger to local populations and can cause damage to cars, buildings, and whatever those buildings contain. A mall in NC, for example, is regularly flooded during storm events when the adjacent creek overflows its banks, fed by sudden releases of municipal stormwater.
Unfortunately, changes in precipitation patterns, and less frequent but extremely intense storms are becoming common across the country. Control and containment protocols in both urban and rural areas were designed to handle rainfall that occured at predictable rates. In today’s climate, when several inches of rain are dumped in a matter of hours, these systems cannot handle the load. On a practical level, expanding and renovating an entire stormwater system to handle two or three annual events is prohibitively expensive, and even that won’t mitigate some of the fundamental problems with this practice.
Sedimentation
Stormwater that passes across any surface is likely to pick up particles of dirt, gravel, sand, or other solids that won’t dissolve but are carried along with the flow until the water’s velocity is reduced. Once the stormwater slows enough, larger suspended particles can settle out and come to rest along the bottom of the channel. Very small particles don’t settle as easily and may remain suspended indefinitely.
Some stormwater systems dump collected waters directly into local waterways and lakes, where sedimentation can cause significant problems, ranging from changing or interrupting the course of water flow, to disrupting local aquatic ecosystems. These ecosystems may provide recreational opportunities for local populations, food for local wildlife, or maintain the health of the entire waterway. Sediment originating from municipal or agricultural sources are typically overloaded with nutrients, which trigger destructive algae blooms. These blooms can suffocate fish and aquatic plants, and others can produce toxins that are deadly to wildlife, domesticated animals and humans.
Habitat Loss
When stormwater is dumped into surface waters, the resulting flooding, sedimentation, erosion, and contamination often leads to critical habitat loss. Plants and animals that dwell along the margins of waterways may be washed away and the conditions that allow them to thrive may be irrevocably changed. Riparian borders that provide critical filtration and nutrient uptake may be washed away, eliminating habitat for fish, reptiles, amphibians, crustaceans, insects, and countless invertebrates.
When aquatic ecosystems are damaged or destroyed, the wildlife that depends on them also suffer and may be driven out altogether. Eagles, songbirds, and migrating birds depend on healthy surface water. Wolves, raccoons, turtles, and black bears consume fish from rivers and streams and all wildlife needs safe water to drink. When aquatic ecosystems suffer, the repercussions are far-reaching.
Sewer Overflow
Older municipal stormwater systems create serious health hazards when they flood. In a vast number of cities across the US, stormwater systems were built to merge with sewer systems when they became overloaded. On a practical level, this management approach serves to mix raw sewage with the stormwater, which can flow back into the streets when the combined systems flood as well. It is not uncommon to see raw sewage flowing through downtown areas, residential neighborhoods, shopping centers, and even flowing into parks and ponds. Exposure to untreated sewage introduces the risk of diseases carried by fecal material, including hepatitis A, giardia, E. coli, and even encephalitis for those who are exposed to it; even after the water recedes.
Contamination
When contaminated water is mixed with raw sewage, in combined stormwater systems, urban populations are exposed to major health hazards. Yet, contamination due to flooding in rural areas can also be disastrous. Farms with moderate animal populations, like pigs, typically store animal waste in lagoons which allows the waste to naturally decay over time. When storms hit these areas, lagoons often overflow, spilling waste products which include urine, feces, and blood across agricultural fields, roads, and sometimes flowing all the way into rural towns and communities. If these communities aren’t equipped to divert and manage flood waters, this public health threat can persist for days. Worse, wastewater like this can infiltrate shallow wells and drinking water supplies, making it dangerous to consume.
Nutrient Pollution
Runoff from any source of disturbed or developed land will collect fertilizers, oil, pesticides, soil, bacteria, and other pollutants, whether it travels through rural ditches or urban stormwater systems. Excess nutrients from fertilizers and decaying organic matter are responsible for major disruptions to delicate aquatic ecosystems and can lead to repeated cycles of toxic algae blooms when this untreated water drains into our streams, rivers, lakes, and the ocean. In fact, nutrient pollution is identified as one of the most widespread, costly, and challenging threats to clean water supplies in the US.
