A watershed is defined as the area of land where all of the water that drains off of it or is underneath of it flows into the same spot. The water goes into the soils, groundwater, creeks, streams, rivers and eventually the sea. As the water travels, it is affected by everything that it touches. It can transport materials, such as metals, nutrients, sediments and pesticides. Land use and physical characteristics of the land affect the quality of water downstream. When a watershed is in a vegetated area, runoff seeps into the soil where it is stored as groundwater, then is eventually released through seeps and streams. Areas such as these often experience less flooding problems, due to the infiltration and water holding capacity of healthy soils. In urbanized areas, vegetation is replaced by impervious surfaces, such as buildings, roads and parking lots. These surfaces decrease the area for infiltration, causing runoff to enter the stream at a higher volume and faster rate. Furthermore, urban runoff contains pollutants such as nitrogen, phosphorus, pathogens, petroleum hydrocarbons and synthetic organics. Agricultural areas cause and experience their own issues, as well. According to the National Water Quality Assessment, nonpoint source pollution (pollution that comes from no obvious point of entry and more than one source) from agriculture is the leading cause of water quality issues on surveyed rivers and streams, the third largest source for lakes, the second largest source to wetlands, and a major contributor to estuary and groundwater issues (Environmental Protection Agency, 2015). Agriculture is the single largest user of freshwater sources, and damaging the water quality of these sources leads to problems with crop production (Global Agriculture, 2015).
Impacts of stormwater runoff on waterways encompass: Short- term impacts during and after storms, including temporary increases in concentration of toxins, pollutants or bacteria levels, long-term changes due to repeated storm events, and physical impacts caused by erosion and deposition associated with increased volume and frequency of runoff (Environmental Protection Agency, 1999). In Iowa, 736 of the 1,316 water bodies assessed by the Iowa Department of Natural Resources were determined to be impaired as of 2015. An impaired waterway is one that does not meet at least one of the Clean Water Act’s quality standards and is deemed too polluted for its designated use. Of the 736 impaired waterways, 571 of these are in Category Five, the highest category, meaning that they are impaired and need an immediate improvement plan. This is a 19 percent increase from the previous list compiled in 2012. The rest are in Category Four, meaning that they are impaired, but they either do not need an improvement plan or one is already in place. For Iowa’s streams, bacterial and biological impairments are most common, altering habitats and oxygen levels of the water bodies. Turbidity, meaning clouded water, and algae are the most common impairments in Iowa’s lakes (Iowa Department of Natural Resources, 2015).
The original objective of storm water management infrastructure was mainly to prevent flooding of urban areas; long term and environmental impacts were not often considered. Storm water management was designed town by town, city by city, rather than managing storm water by looking at the entirety of the watershed. The end goal was moreso to collect and get rid of the water, instead of managing storm water from a more biomimetic approach. This led to a fragmented and disorganized system, especially when it comes to agricultural runoff. Tiles are often used in farming areas in order to counteract low soil infiltration rates. These tiles are not regulated and dump large masses of nutrient and chemical- dense water into ditches, creeks and rivers. Furthermore, the expanses of monocrops in Iowa leads to poor soil infiltration, causing sediments from erosion to flow into water bodies. Fragmented storm water management infrastructure can lead to the destruction of both macro and microhabitats in the stream, as well as stream bank erosion.
As more data pertaining to the quality of water in creeks, rivers and lakes becomes available, the importance of a watershed-based approach is becoming clearer. Ecological literacy is the ability to understand how nature’s systems work, and how to mimic these systems in order to produce more efficient human technologies. When applying this to storm water management, this means finding the root of the cause- the problem areas- and implementing efficient technologies, such as rain gardens, rainwater catchment and green roofs. A rain garden is an attempt to mimic natural vegetation by creating a space for water infiltration through the use of a variety of native, deep-rooted plants (Iowa Stormwater Partnership, 2009). The application of Best Management Practices (BMP’s), such as rain gardens, green roofs and rainwater catchment, can effectively decrease runoff and improve an area’s watershed. A stormwater management BMP is defined as a practice or combination of practices that are effective and efficient (economically and technologically) at reducing or preventing the amount of pollution from stormwater runoff. Unless environmental and long-term impacts are taken into consideration when implementing BMP’s, as well as considering the effect on the entirety of the watershed, the success of these practices may fall short. Implementing a holistic, watershed-based approach could potentially improve stormwater management throughout the entirety of the watershed, and could lead to improvements downstream, as well. A watershed- based approach means moving away from a fragmented, “business as usual” system and moving towards a more integrative, efficient, and sustainable method of managing one of the world’s most valuable, yet often wasted, resource.