Download
1 / 27
270 likes | 468 Views
GEOG 442. Day 12 : Infrastructure Planning. Water, Sewer and Stormwater Systems.
E N D
GEOG 442 Day 12: Infrastructure Planning
Water, Sewer and Stormwater Systems • Municipal water and sewer systems are expensive, and thus have to be planned carefully. They are essential preconditions for new urban development, and can also and often do stimulate such development once in place. • Demand for land uses has to be coordinated with infrastructure provision (i.e. location, type, quality, use and capacity). • Their capacity thresholds have to be respected or they will break down. • For decades, these systems were supplied free to developers, but now there is trend towards cost recovery though not on an equitable basis.
Water Supply Systems • Two types of water, though most municipal systems do not distinguish: potable (for drinking) and non-potable (for agricultural and industrial use). A potable system addresses acquisition, treatment and delivery. • The source of potable water is either surface water or an underground aquifer. (Two million Canadian urban residents rely on groundwater.) Water is treated for use by physical (filtration and sedimentation) and chemical means (chlorination and flouridation; sometimes ozonation). • The water is then stored underground or above ground for peak use and to maintain pressure (“head”). • Water is delivered through a branch or a loop system of pipes, the latter providing more consistent pressure.
Water Supply Systems • Different land uses generate different levels of demand. To meet this demand, we need to know the system’s yield capacity, storage capacity, location of mains, and distribution pipe sizes and locations. We also need to know current and projected demand, consumer preferences, and government policies and regulations. Overall issues concern quantity, quality, and pressure. What are desirable and undesirable qualities possessed by potable water? • The design standard for municipal water in North America is 150-300 gallons (570-1140 litres) per person. In Canada, actual consumption is 650 litres. 35% or higher is for domestic use, 50% for non-domestic and public uses, and 15% unaccounted for losses and leaks. Older systems lose up to 50% in transit.
Water Supply Systems • Water quality standards are set by the province, but usually accord with the Canadian Drinking Water Standards. 30 lbs. per square inch (psi) is needed for fire-fighting, and 50-75 is optimal for domestic purposes. • Municipal water systems are economically justified at 1000 persons per square mile or at 0.6 dwellings per acre gross. While urban redevelopment is desirable from an infrastructural efficiency standpoint, if the system is too old the extra demand could cause pipe rupture.
Water Supply Systems • There is an increasing trend towards demand management instead of increasing supply. What are some of the ways of decreasing or stabilizing per capita demand? • Another challenge for supply is when sources are compromised. Can you think of examples, and cite the kinds of things that can compromise water sources?
Walkerton Water Tragedy (2000) Walkerton criminal charges met with anger WALKERTON -- At a news conference marked by angry outbursts from residents, Ontario Provincial Police announced yesterday they have charged the two brothers at the centre of the Walkerton tainted water tragedy. Stan Koebel, manager of the Walkerton Public Utilities Commission when the E. coli disaster hit in 2000, faces seven criminal charges. His brother, Frank, PUC foreman at the time, faces five criminal charges.
Walkerton Water Tragedy (2000) Seven people died and more than 2,000 were sickened by E. coli contamination of Walkerton's water system in May 2000. "After a very extensive investigation, the OPP investigators have determined these are the charges that are supported by the evidence," acting OPP Det. Supt. Paul Chaytor told a news conference packed with media and about a dozen Walkerton residents.
Municipal Wastewater Systems • As of 1994, 75% of Canada’s population was serviced by municipal wastewater treatment systems. These operate mostly on the basis on gravity-fed collection pipes. • Once collected the sewage is treated according to one or more of the following standards: primary, secondary, or tertiary.
Municipal Wastewater Systems • Primary treatment involves screening and sedimenting techniques for removing solids and organics. • Secondary treatment involves using biological means to digest the waste, and • Tertiary treatment involves using bio-chemical means to remove phosphorus and nitrogen that contribute to eutrophication. • Some communities are turning bio-solids into fertilizer.
Municipal Wastewater Systems • In 1994, 39% of the population with municipal systems were receiving primary treatment, 31% secondary, and 39% with tertiary. There are a few significant municipalities that have no treatment at all. Can you name them? • Different land uses place different demands on the sewage treatment system, including in relation to peak demand. Systems, once put in place, offer little flexibility.
Municipal Wastewater Systems • For planning purposes, one needs to know the location, size, and age of the collection and treatment components, current demand and remaining capacity, characteristics of the waste stream, and policy and regulations regarding effluent and sludge disposal. (In some cases, the sludge is landfilled; in other cases, it is used as a soil conditioner.)
Wastewater Systems • Between 65% and 85% of municipal water supply is cycled into the wastewater (sewer) system. The U.S. EPA suggests an expected per capita production of 100-125 gallons – 60% domestic, and the remainder commercial, industrial, and institutional. One can also calculate expected volumes based on population density and per capita production rates (see table on p. 161 for residential wastewater flows).
Wastewater Systems A sewerage impact analysis would look at location and amount of projected development, the possible need for new treatment methods, and new regulatory standards. This would help determine service areas, trunk extensions, and technologies to be used. Increasingly, developers are being required to pay for new wastewater systems through development charges (DCCs or DCLs).
Wastewater Systems • Isolated developments can use self-contained communal systems. One example, both of a self-contained and of an alternative sewage treatment system, is the solar aquatics system in a trailer park in Errington. • In rural areas, the tendency is to rely on septic systems (bacterial action and tile beds to percolate the effluent into the soil). Depending on soil conditions, the lots have to be big enough to ensure separation between the house, well, and septic bed – not to mention neighbours’ wells. In extreme cases, this could be one acre configured as follows: 150 feet by 300 (50 metres by 100).
Stormwater Management The hydrological cycle consists of: • precipitation • infiltration • transpiration • evaporation, and • run-off/ stream flow The cycle is very much affected by human activities and structures, especially the urbanization process. Why is this so?
Stormwater Management • Urban development increases the amount of impervious surfaces (roofs, roads, and parking lots) and reduces vegetation. This reduces infiltration and evapo-transpiration and increases the speed and volume of run-off, which can lead to erosion and flooding. • The run-off picks up pollutants from urban surfaces, such as roads, and discharges them into receiving waters, unless they are treated by various means. Some pollutants are deliberately dumped into storm sewers. This kind of “diffuse” pollution is called non-point source pollution.
Stormwater Management • Urban run-off often contains organic matter (e.g. feces), bacteria, dust and dirt, nitrogen, phosphorus, chlorides (from road salt), metals, oil and grease, and much more. It can and often does have a very negative impact on fish and fish habitat, water supply, and recreation areas, while adding sediments and algae to rivers and lakes.
Stormwater Management • A stormwater system consists of surfaces and channels and/or underground pipes. In some municipalities there are combined storm and sanitary systems where stormwater is channeled to sewage treatment plants, but in the event of “major weather events,” the sewage pipes overflow into storm sewers and discharge raw sewage into receiving waters.
Stormwater Management To calculate appropriate channels and conduits and flood prevention measures, one must know how much run-off can be expected. There are two methods for doing this: • The rational method examines the amount of run-off for a given land use (the coefficient [C]) – see p. 162 for a list – and multiplies that by the intensity [I] of rainfall and the size of the area [A] to be drained.
Stormwater Management • This is also calculated based on the biggest likely storm event for a given period – anywhere between two and ten years, depending on the property value and liability issues associated with the area. • The hydrograph method is best used for flood control and retention/ detention measures where one looks at flow rates at key “points of interest”.
Stormwater Management • There is a new trend towards requiring developers to employ best management practices (BMPs) to create zero discharge increase with new developments. This means ensuring that baseline run-off conditions are not made worse in any way. • There are a number of ways of managing run-off in more proactive ways:
