Week 11 - Mitigating Impact from Urban runoff

Have you found that chance of flooding after raining in urban area is increasing? Have you found that after raining, rivers, lakes and all sorts of waterway becomes turbid?

Of course, yes, we are familiar with these. What are the causes of these issues? Some might blame the factories discharging polluted water, some might blame the tossers tossing litters in waterways. They are all true. However, there might be one more culprit that we have never thought of - urban runoff.

Urban runoff, or in the other words, stormwater, is the water, usually rain water or irrigation water, that drained off from roof, urban land or road in urban area. If it is merely rainwater collected from the roof, it is usually cleaner without carrying all sorts of pollution to the ground. However urban runoff is creating severe environmental impact by polluting downstream waterways. Going through urban areas, there is no doubt that it carries dust, chemicals, litter, fertilisers from gardens and oils from the road. This is in some way breaking down the ecosystem.

Diagram Showing urban runoff in different areas.

Why is it a severe issue with all the grey/black water treatment system nowadays? In fact, generally there is no treatment available for urban runoff. In Australia, urban runoff is usually separated from sewage water treatment system. Urban runoff is therefore being discharged to waterways and sea without any treatment.

According to the diagram above, there is also an issue that urban runoff is increasing the risk of flooding by reducing draining surface in urban area.

There are heaps of known benefits if we could reduce urban runoff pollution, for example:

• Less polluted water being discharged into rivers, lakes and sea, providing a cleaner swimming environment
• Mitigating risks of flooding
• Cleaner water provided for human drinking purpose
• Healthier environment for ecosystem

There are a large amount of methods to deal with urban runoff issue. By doing it, urban runoff could possibly become a value in urban environment.

Knowing what is urban runoff, we can all contribute to mitigate the environmental impacts. Firstly, keeping pollutants out of stormwater is way more economically efficient than considering stormwater treatment. As individuals, for example, we can:

• Clean up/sweep waste on land and garden frequently to reduce waste pollution
• Retain vegetations and deep-rooted trees to preserve natural draining pattern
• Reduce usage of fertilisers or chemicals in your garden
• Reuse stormwater in irrigation to provide second time filtering
• Clean up storm drains more often

As organisations/governments, there are also heaps to do to reduce urban runoff:

• Promote permeable surface to provide a higher soak down rate than draining; minimise/grade impervious surfaces in urban design
• Design water sensitive roads, provide water catchment than redirect to proper filter/treatment systems
• Promote stormwater harvesting system for treatment or recycle
• Consider water sensitive urban design(WSUD)

There are a large amount of methods to reduce environmental impact from urban runoff. If all individuals contribute, we all can have a healthier sustainable environment to live in.





References:
http://www.yourhome.gov.au/water/stormwater
http://sustwatermgmt.wikia.com/wiki/File:Natural_Urban-Runoff-Rates.jpg
http://clean-water.uwex.edu/pubs/pdf/urban.pdf
https://www.smgov.net/uploadedFiles/Departments/OSE/Categories/Urban_Runoff/UR_Residential_Final.pdf