Storm water management in private lots and developments

This solution is tailored to local governments that have a mandate to approve and enforce municipal building regulations or bylaws that require and/or incentivize the use of SUDS and rain water harvest in private buildings and facilities in the city. It is applicable to new settlements as well as existing residential, commercial and institutional buildings and facilities.

The solution aspires to deal with surface run-off at the point at which it occurs. This would be achieved by: collecting, treating and infiltrating or reusing it where ever possible within the site or in the near vicinity through Sustainable Urban Drainage Systems (SUDS). SUDS are a combination of: decoupling of storm water drains (from waste water pipelines), green roofs, rain gardens, living walls, permeable pavements, rainwater retentions and reuse systems, and onsite infiltration systems [1].

To implement this solution, the local government should undertake: policy enactment, standardization, stakeholder involvement; community sensitization and mobilization, and monitoring and evaluation of interventions, including enforcement of regulations. To understand how this Solution articulates with city-level integrated storm water management see Package Sustainable Storm Water Management.

Motivation / Relevance

Rapid urbanization has increased impervious surface areas in cities resulting in increased surface run-off, causing water logging and floods. Around 70% of all land use in a city consists of residential, commercial, institutional areas of which, 30-35% constitute transport infrastructure. Various studies show that, highly impervious area (75 to 100%) can increase urban runoff by approximately 50% compared to a 10% from low impervious areas (10 to 20%) [2].

Traditional urban drainage systems (combined sewer networks) primarily focus on removal of storm water and wastewater away from urban settlements as quickly as possible. To reduce conveyance costs, storm water and domestic wastewater are transported together, ideally, to a wastewater treatment plant for clarification. However, such systems are often expensive to build operate and maintain, and also consume large amounts of energy. Additionally, combining storm water with wastewater especially during high rainfall events frequently exceeds the storage and treatment capacity. This result into discharging untreated storm water and raw sewage directly into receiving streams causing exceeded levels of pollution.

Moreover, changes in precipitation patterns as a result of climate change can have devastating consequences on cities in terms of heavy rainfall events or infrequent but high-intensity precipitation which can disrupt normal working in the city. Conversely, cities are also susceptible to water shortages and droughts. With increasing populations the demand for water in cities will also increase.

Furthermore, storm water is much less polluted than raw domestic sewage and if collected, treated and infiltrated separately, it can be utilized as an additional water resource for the city. In doing so cities can increase water security, reduce costs for expensive infrastructure and reduce the potential risk of flooding in cities. Additionally, creating building blue green infrastructure based on the principles of SUDS can negate het island effects, improve biodiversity and air quality, and improve the overall ascetic value of neighborhoods and quality of life for its citizens. This in turn can increase property values up to 28% higher [3].

Main impacts

  • Decrease the flood risk for low-lying urban areas
  • Decrease cost of sewer infrastructure
  • Provide water security for urban water uses
  • Improved urban resilience to climate change events (floods, droughts and heat waves)
  • Decrease the pressure on natural fresh water resources and ecosystems
  • Improve air quality in the surroundings
  • Reduction in greenhouse emissions from wastewater treatment plants
  • Improve urban biodiversity

Benefits and Co-Benefits

  • Decrease the costs for wastewater treatment, in some case by 50% [5]
  • Encourage non-potable water reuse (such as toilet flushing, car washing, gardening, etc.)
  • Reduce per capita consumption of water
  • Protect and / or enhance water quality
  • Increase trans-evaporation and reduce the heat island effect
  • Reduction in greenhouse emissions from energy consumption in wastewater treatment plants
  • Enhance aesthetic value of settlements and quality of life of neighborhoods in cities