Course contents Chapter 1 Introduction to Urban Drainage

Course contents • Chapter 1 – Introduction to Urban Drainage • Chapter 2 – Design of Sanitary Sewer system • Chapter 3 – Design of Storm Sewer system • Chapter 4 – Sewers and Appurtenances

Urban Drainage and Sewerage • Urban drainage may be used to describe the process of collecting and transporting wastewater, rainwater/stormwater or a combination of both. Ø Sewage being the liquid material and Ø Sewerage being the pipes, pumps and infrastructure through which sewage flows.

The urban drainage system Sewage retention Overflow structure Overflow Combined water storage WWTP effluent Receiving water

Purpose of urban drainage systems 1. Sewer system protect public health

Purpose of urban drainage systems 2. Sewer system prevent flooding

Purpose of urban drainage systems 3. Sewer system protect the environment

Function and goal of sewerage Goal : • Protect public health • Prevent flooding on the street Function • Collection of “water that one wants to get rid of: Domestic wastewater + rainfall • Transport of wastewater within the urban area (from there to WWTP)

Effects of urbanisation on drainage • Consequences of urbanisation • Less evapotranspiration • Less infiltration • A lot more runoff

Impacts

Faster -larger floods

Ground Depreciated of Water

Approaches to urban drainage • Type of system piped or natural

Natural drainage system • The movement towards making better use of natural drainage mechanisms has been given different names in different countries. • In the US and other countries, the techniques tend to be called ‘best management practices’, or BMPs. • In Australia the term ‘water sensitive urban design’ is often used to refer to the incorporation of natural drainage mechanisms in urban areas. • In the UK they are called Sustainable Urban Drainage Solutions (SUDS). • These techniques – including soakaways, infiltration trenches, swales, water butts, green roofs and ponds – concentrate on stormwater.

Types of piped sewer system Principle of collection • Combined • Separate • Above ground / underground Principles of transport • Gravity • Pressure • Vacuum

Combined systems • are large networks of underground pipes that convey domestic sewage, industrial wastewater and storm water runoff in the same pipe to a centralized treatment facility.

Combined system Urban Water Systems 10 Urban drainage

Combined systems • In dry weather, the system carries wastewater flow. During rainfall, the flow increases as a result of the inflow of stormwater. • The stormwater flow exceeds the wastewater flow even under light rainfall conditions. During heavy rainfall, storm water flow exceeds wastewater flow by a factor of 100 to 1000 or more. • It is not economically feasible to provide capacity for the Total flow under these conditions. Therefore, in combined systems so-called combined sewer overflows are installed to discharge excess water that cannot be transported towards the wastewater treatment plant, to surface water.

Combined system Groundwater , Drainage, … Rain water clean polluted Domestic and industrial sewage Comb syst CSO Groundwater , Drainage, … WWTP Rain water clean polluted Domestic and industrial sewage Comb syst Infiltration Groundwater aquifer Urban Water Systems CSO 10 Urban drainage WWTP © PK, 2005 – page 24

Separate Sewers • Separate sewer systems are designed to convey wastewater and storm water in separate pipes. • Sanitary sewer systems collect and transport wastewater • Storm sewer systems collect and transport stormwater runoff

Separate system Urban Water Systems 10 Urban drainage © PK, 2005 – page 27

Separate Sewers • Wastewater, washing water and rain water through three separate conduits.

Separate vs. combined system

Separate vs. combined system

Simplified and Condominal Sewers • Describe a sewer system that is constructed using smaller diameter pipes laid at a shallower depth and at a flatter gradient than conventional sewers • Allows for a more flexible design associated with lower costs and a higher number of connected households • Because the sewers are more communal, they are often referred to as condominal sewers

Simplified sewerage • Simplified sewerage system – conveys unsettled wastewater – Essentially conventional sewerage without conservative design features and rules of thumbs

Simplified and Condominal Sewers

Solids-free Sewers • These are similar to conventional sewer systems, except that the wastewater is pre-settled and solids removed before entering the system • As solids are removed, sewer diameter can be much smaller and they can be constructed using less conservative design criteria (lower gradients, fewer pumps, less pipe depth, etc. ) resulting in significantly lower investment costs • Due to the simplified design, solids-free sewers can be built cheaper

Solids-free Sewers

Pressurised Sewers

Pressurised Sewers

Pressurised Sewers – cost consideration