Urban runoff is the flow of stormwater, water from landscape irrigation and other human activities such as car washing which flow on the surface of impervious surfaces such as parking lots, roads and sidewalks created for the purpose by urbanization and development.

It is called URBAN because it is separate and distinct from similar activities which may be carried out in rural or farm areas where such waters are ordinary absorbed and reinfiltrated into groundwater and the water table by natural means. It is also distinct because unlike in rural areas, the flow in urban areas takes place on impervious surfaces such as concrete and asphalted surfaces which are constructed as a result of development and urbanization.

Urban runoff has become something of a hot topic in recent years because of its effect on natural water bodies close to urban areas which are affected by it as a result of the contaminants contained in the runoff such as chemicals, dirt and fertilizers from landscaped areas; lawns and gardens. These pollutants have proven dangerous to plant aquatic plant and animals life and by extension to human lives where these plants and/or animals and water are in turn depended on my humans for food and nourishment.

Incidents That Make Urban Runoff Quality Control Necessary

1. Water pollution: As we have already noted, major metropolitan cities have much of their land surface covered by structures and asphalt, which try not to permit downpour and snow melt to douse into the ground. All things considered, most of such urban areas depend on storm channels to convey a lot of overflow from rooftops and cleared regions to close by streams. The stormwater runoff carries poisons like oil, soil, synthetic compounds and manures straight to streams and waterways, where they truly hurt water quality.

We tend to mistake water pollution with pollution but plastic and visible materials alone. It is more than that.

Ephemeral streams—also known as watercourses that historically held little or no water during dry weather—are one of the most pronounced effects of urban runoff. At the point when a region around such a stream is urbanized, the resultant spillover makes an unnatural all year streamflow that harms the vegetation, untamed life and stream bed of the stream.

Urban runoff hurls down the stream channel, destroying natural features like meanders and sandbars and causing severe erosion—increasing sediment loads at the mouth while severely carving the stream bed upstream—despite containing little or no sediment in comparison to the historical ratio of sediment to water. For instance, at the mouth of a waterway on numerous beaches in Southern California, urban runoff can carry waste, pollutants, excessive silt, and other wastes and pose moderate to severe health risks.

This distortion of the water quality is further harmful to humans who depend on the aquatic life for food which would have become polluted.

2. Reduction in the water table: Urban areas are notorious for their abhorrence of usage of natural water sources such as rainwater and open wells. The burden of water supply to satisfy urban demand then rests on underground water which is drilled and supplied for domestic and industrial uses. When it rains and impervious surfaces prevent the water from being reabsorbed by the earth, underground water is not recharged thus water shortage becomes inevitable.

3. Urban flooding/erosion: Flooding occurs in situations of high precipitation such as rainfall or snowmelt, the available channels in the urban areas like stormwater drains and channels are usually overwhelmed in the moments immediately following them which could lead to water getting into properties like basements and low laying houses and where not effectively dealt with can lead to loss of lives and properties.

Flooding on the other hand occurs where runoff water manages to go beneath impervious surfaces and begin to chip, gradually, at the underlying soil. Initially, this is unobserved as the damage is unnoticed but as time goes on and water continues to seep beneath it, it could even lead to the impervious surface itself being destroyed. This is a direct consequence of uncontrolled stormwater and artificial runoff.

Purpose for Urban Runoff Quality Control

The aim of Urban Runoff Quality Control is to safeguard surface and groundwater resources and to improve on the mistakes that have already been made over the years by using engineering that is properly planned and implemented in such a way as to limit greater irresponsible runoff disposal but rather one that understands the shortfalls of traditional engineering and seeks to correct it such as WSUD (Water Sensitive Urban Design).

Simply put, the proper execution of designs, programmes and developmental engineering is to the end that anomalies which occurred as a result of the loopholes inherent in traditional engineering ideas are identified and effectively dealt with. For instance, traditional engineering depended on impervious surfaces in its design of urban areas, but it has been shown that impervious surfaces have disadvantages such as the depletion of underground water.

The effective application of modern design is to see how traditional engineering techniques are married with the old to see that the underground water is recharged with quality, pollution free water.

How to Mitigate the Effects of Urban Runoff and Ensure Better Quality Runoff

• The first stages in many techniques of improving the quality of urban runoff is the effective reduction of the flow of stormwater as well as going further to reduce the amount of pollutants being discharged into stormwater drains and channels. The techniques used to attain these goals are known as Best Management Practices for Water Pollution (BMPs). These techniques are usually water quantity or water quality control oriented and in some circumstances is a combination of both focuses.

• In the area of pollution control, techniques which are known as Green Infrastructure techniques which focus on sieving through pollutants according to their sizes like the Australian Water Sensitive Urban Design (WSUD), the UK’s Sustainable Urban Drainage Systems (SuDS) are the central focuses. These techniques seek to focus on the implementation of natural pollution control like the installation of green roofs and improving on the handling of chemical wastes like fertilizers, pesticides, and industrial wastes like oil and fuel.

Further techniques in the area of pollutant control are use and installation of techniques and infrastructure such as infiltration basins, bioretention suaves and systems and construction of wetlands.

• It could also be as far reaching as taking into account naturally occurring circumstances such as the temperature of the urban area, levels of precipitation and geographic location. It could also take into account airborne pollutant levels as all these different kinds of pollution could play their part in the increase of urban runoff and its quality.

Among taking cognizance of natural occurring activities and applying the gotten knowledge in dealing with runoff, stormwater harvesting is a credible tool. Much like harvesting rainwater reduces the volume of stormwater to be collected, harvesting grey stormwater directly from sources such as gullies and creeks which can then be reused for non-potable activities like irrigation of farms and gardens and flushing of toilet.

• Also, the human factor should not be overlooked as attention should be paid to human activities such as the rate of urbanization, choice of building materials and the trend in the use of land since as we have already noted, dependence on impervious materials only increase the runoff quantity of the immediate urban area.

Further along the line of human contribution to improving urban runoff with simple activities like road sweeps go a long way in reducing the amount of pollutant that is contained in the runoff as the vacuums used will be able to absorb the materials such as suspended solids which ordinarily are likely to end up storm channels.

• The place of education is also not to be overestimated as this is also a very effective tool in combating poor quality runoff from residential areas. In the use of education as a tool in controlling the quality of urban runoff, the focus should be on programs that educate people on the effects the harmless-looking runoffs from their houses have on the environment and what they can do by way of contribution to augment the corporate efforts being made by governments.

Incentives should also be put in place to encourage corporations to engage in discourses around urban runoffs and to encourage them to implement best practices in the regard. That way, efforts put into improving urban runoff by corporations does not feel forced and there is genuine interest in maintaining whatever good measures they must have put in place to achieve the said goals.

Urban runoff is inevitable. So long as precipitation occurs and rain continues to fall, stormwater becomes inevitable because rain and snowmelt all become stormwater which contribute to the runoff in urban places. What becomes an issue and makes it a viable environmental conundrum is the effect and quality of the runoff and the effect it has on the immediate environment, lands and surrounding water bodies. Effectively dealing with and improving the quality and reducing the volume of the runoff created is very crucial to any urban setting as it can be the difference between recurring illnesses and natural disasters such as flooding.