Wastewater transport and urban drainage Prof Em Oddvar
Wastewater transport and urban drainage Prof. Em. Oddvar Lindholm Norwegen University of Life Science oddvar. lindholm@nmbu. no
Outline § Introduction § Design aspects § Infiltration and leakages § Rehabilitation § Storm water management and floods § Climate Change impacts § Sustainable urban drainage systems (SUDS) § Sewer modelling tool - SWIMM Wastewater transport and urban drainage 2
Wastewater collection and transport § From urban centres, wastewater must be collected and transported to WWTPs, which could be tens of km away. . Wastewater transport and urban drainage 3
Typical components of a sewer system § Pumps § Pipes (sewers) – combined, storm water, wastewater § Weirs § Valves § Manholes § Retention tanks § Overflow discharge § Surveillance systems (quantity and quality) § Control systems (pumps and valves) § Sewer models Wastewater transport and urban drainage 4
Wastewater transport and urban drainage © virginiaplaces. org 5
Statistics about sewers § Need to supplement with EU++ statistics Wastewater transport and urban drainage 6
A sewer pipe normally uses gravity. If ascending terrain; pump the sewage? Is it possible to avoid pumping? Maybe it is possible to dig a deep ditch for a quite small distance, until normal inclination of the terrain is obtained? An economic calculation will decide. Wastewater transport and urban drainage 7
Typical sewer placement in ground Wastewater transport and urban drainage 8
Double manholes for water, storm runoff and sewerage Wastewater transport and urban drainage 9
Storage tank for combined sewer overflows Wastewater transport and urban drainage 10
Cross section of a road with pipes and sand catch basin Wastewater transport and urban drainage 11
Catch basin for storm water runoff Wastewater transport and urban drainage 12
Retention tanks for reducing the storm overflow or high peaks in discharge Used in combined sewerage systems and at combined storm overflows (CSO) Installed inline with continues throughflow Combined sewer overflow. Tank is installed in parallell, and fills only in wet weather Wastewater transport and urban drainage 13
Water flows without retention and with a retention basin The retention basin are dampening the maximum flow in the system The area between the inflow and outflow curve represent volume Wastewater transport and urban drainage 14
Retention basin (in combined sewerage system) with ”toblerone floor” to get self cleansing conditions during emtying. Water for flushing is added. Wastewater transport and urban drainage 15
Retention basin under Tokyo From TIME-magazine April 9, 2007 Wastewater transport and urban drainage 16
Pump station for sewage Wastewater transport and urban drainage 17
Partly gravity sewer lines with a pump station Wastewater transport and urban drainage 18
Pressure sewerage system with pumps in every house Wastewater transport and urban drainage 19
Pressure sewerage system Wastewater transport and urban drainage 20
Pressure sewerage system and a pump with a grinder Wastewater transport and urban drainage 21
An outfall for treated sewage with a manhole and pipe Wastewater transport and urban drainage 22
The effluent jet should be located under or in thermocline Brackish water Thermocline Heavy sea water Density of water Wastewater transport and urban drainage 23
Sewer design in general Wastewater transport and urban drainage 24
Wastewater from a typical European household Item WC Water use liters/person day 30 Kitchen 30 Laundry of cloths 40 Shower, bathing, etc 50 Sum 150 Wastewater transport and urban drainage 25
Example of variations of wastewater during a day Wastewater transport and urban drainage 26
Variation factors f and k • fmax = Q daily max / Q daily average • fmin = Q daily min • kmax = Q hourly max • kmin = Q hourly min Wastewater transport and urban drainage / Q daily average / Q hourly average 27
Dimensioning for maximum wastewater Qmax = (P ∙ qspes ∙ fmax∙ kmax + P ∙ qleak )/( 24∙ 60) + Qind Qmax P qspes Qleak Qind fmax kmax = Max dimensioning discharge in liters/sec = Number of person units = Specific wastewater production (l/p day) = Specific infitration person (l/p day) = Industry (l/s) = Daily max factor = Hourly max factor Wastewater transport and urban drainage 28
Requirements for sewage pipes • No 1: High enough capacity to transport Qmax = P ∙ Qspec ∙ Fmax ∙ Kmax + Qinfiltration • No 2: Avoid clogging of pipes (self cleaning) (At least a velocity of 0, 7 m/s once each day at peak hour) Or else, sediments will build up in the pipes and become clogged. Wastewater transport and urban drainage 29
Number of blockages per year (clogging) in sewer pipes in municipalities in Norway. Renewal of old pipes has reduced the number of blockages 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 2002 2004 2006 2008 2010 2012 2014 2016 Year Wastewater transport and urban drainage 30
Infiltration and leakages Wastewater transport and urban drainage 31
Leakages and sewer renewal Wastewater transport and urban drainage 32
We assume that ca 50 % of leakages from the drinking water pipes infiltrates into the sewers Water pipe Sewage pipe Left: ground water table is higher than the pipes are. Right: ground water table is lower than the pipes are. Wastewater transport and urban drainage 33
Definition of Inflow/Infiltration (I/I) Infiltration - Water other than sanitary flow that enters a sewer system (including sewer service connections and foundation drains) from the ground, through means which include defective pipes, pipe joints, connections, or manholes. Infiltration does not include, and is distinguished from inflow. Inflow - Water other than sanitary flow that enters a sewer system (including sewer service connections) from sources which include roof leaders, cellar drains, yard drains, area drains, drains from springs and swampy areas, manhole covers, cross connections between storm sewers and sanitary sewers, catch basins, storm waters, surface runoff, street wash waters, or drainage. Inflow does not include, and is distinguished from, infiltration. The total amount of inflow is equal to the sum of the delayed inflow and direct inflow. Wastewater transport and urban drainage 34
What is I/I (Inflow and infiltration)? Source of I/I Sewer pipe in separatsystem Combined sewer pipe Drainage water from buildings Illegal connection Planned Storm runoff from surfaces Illegal connections Planned Not planned Groundwater leaking into pipes or manholes Leakages of drinking water from water supply systems Wastewater transport and urban drainage 35
What is the problem with the I/I ? Type of problem Sewage pipes in separate systems Combined sewer pipes Occupy hydraulic capacity in the pipes Yes No usually not Increased discharge via the CSO No Yes Increased discharge via the emergency outlets in pumping stations Yes Increased load on the hydraulic capacity in the WWTPs Yes Transports pollution out via the effluents in WWTPs Yes Yes Increased costs for O & M in WWTPs and pumps Wastewater transport and urban drainage 36
Calculation of % I/I to a WWTP using a simple dilution formula Wastewater transport and urban drainage 37
Example of rain derived I/I (Massachusetts 1993) Wastewater transport and urban drainage 38
Infiltration/Inflow to sewer pipes in Oslo • I/I = 1, 5 l/s km of pipes as an average • 1490 km of sewer pipes in Oslo • 650 000 persons • This amounts to ca. 300 l/ p d in I/I • Real sewage in Oslo = 166 l/ p d Total waste water = 300 + 166 = 466 l/p d • This tallies up to 63 % I/I (of total waste water) Wastewater transport and urban drainage 39
Renewal of an old pipe by pulling a new pipe into the old one New pipe of PEH-material The old pipe is cracked up by the «torpedo» in front Pulling machine To avoid digging up streets to replace old dilapidated sewers, «No Dig» has become widely used in cities. This is must faster, cheaper and less disturbing of city life. One of this methods is «Pipe cracking» or «Pipe bursting» , shown here. Wastewater transport and urban drainage 40
Sewer rehabilitation Wastewater transport and urban drainage 41
Relining an old sewer with a hose impregnated with a plastic material. The hose is rolled into the old pipeline and cured in place (CIPP) www. olimb. no Wastewater transport and urban drainage 42
Cured in place pipe (CIPP) www. trenchlesstechnology. com Wastewater transport and urban drainage 43
Inserting the hose via a pipe shaft and pushing in the hose with pressure from water pumped in behind the front of the hose SSTT 2008 SSTT (2008) No-dig Handbook. Scandinavian Society for trenchless technology, Drammen/ København, 2008 Wastewater transport and urban drainage 44
No Dig methods for renewal of sewer pipes www. trenchlesstechnology. com Wastewater transport and urban drainage 45
Storm water management and floods Wastewater transport and urban drainage 46
A convective rain cell. This type of rainstorm occurs in summer and has normally the highest rain intensity Wastewater transport and urban drainage 47
The Rational Formulae for calculation of storm runoff Q= A I Q = Storm runoff in liter per second (liters/s). = Runoff coefficient. A = Area. Catchment that contributes to runoff (ha). I = Rainfall intensity (l/s ha). Wastewater transport and urban drainage 48
Wastewater transport and urban drainage 49
Rainfall intensity in Bergen - l/s ha vs. rain duration (min) and return period Green is 100 year return periode Wastewater transport and urban drainage 50
Maximum storm runoff occurs when: The rain duration = the time of concentration for the area Train = tc Time of concentration (tc) is the time the runoff uses from the far edge of the actual drainage area to the point of dimensioning tc = ts + tp = time on the surface + time in the pipes ts Wastewater transport and urban drainage = ca. 5 – 7 minutes in cities 51
Example: Calculate time of concentration for an area in a city. The length of the pipe is 1260 meter. Solution: Time on the surface ts is estimated to 6 min. Velocity in the pipes is estimated to 1, 5 m/s. Time of flow in the pipe tp = 1260/1, 5 = 840 sec Time of concentration is tc = tp + ts = 840/60 + 6 = 14 + 6 = 20 min Wastewater transport and urban drainage 52
Problems when pipes have to small capacity m 530 Flooding on the surface 528 526 524 Flooding of basements? 522 520 Wastewater transport and urban drainage 53
A small increase in the hydrograph / rain may cause a much bigger increase of the problems and flooding Storm water discharge Capacity of the urban drainage Time after start of the rainfall (min) Wastewater transport and urban drainage 54
Sustainable urban drainage systems (SUDS) Wastewater transport and urban drainage 55
Storm runoff discharge (l/s) Capacity of the drainage network (liters / sec) Time after start of the rain (minutes) The effect of delaying the storm runoff over a longer time, is a less Qmax. Can be achieved by using retention and infiltration of storm runoff. These methods are called SUDS (Sustainable Urban Drainage Systems) Wastewater transport and urban drainage 56
Discharge as little as possible of storm water to the drainage network! Storm runoff should be infiltrated into the ground or handled at the surface, if possible. (SUDS) SUDS = Sustainable urban drainage systems Wastewater transport and urban drainage 57
Installations for handling of storm runoff must be introduced early in the area planning stage. Wastewater transport and urban drainage 58
Measures could be enforced by the Plan and Building Act • Saving and strengthen the vegetation like trees, grass areas, etc. • The width of the roads. • Permeable road and parking surfaces. • Use of infiltration solutions. • Infiltration trenches and ponds. • Maximum allowable discharge to the pipe network. • Use of swales instead of conventional gutters. • Use of “green” roofs. • Cisterns for collection of runoff from the roofs. • Use of detention in open dams and ponds. • Etc. Wastewater transport and urban drainage 59
Principles for handling of storm runoff 3 -stages strategy The numbers are examples and must be locally adjusted Wastewater transport and urban drainage 60
The first stage in the 3 -stage strategy could have the measures shown in the figure: Haven. dk 2010 Wastewater transport and urban drainage 61
Design rains and floodings- example Wastewater transport and urban drainage 62
Recommended design rain return periods Example: Norway Dimensioning return periods for the critical level (The basement floor): In housing areas: 1 time every 20 year In town centers: 1 time every 30 year Wastewater transport and urban drainage 63
Open flood ways (The 3 rd stage) The capacity of the open flood ways should be calculated and recorded on maps. Lower lying areas must be able to receive the discharge. Streets, roads, park areas etc. may be a part of the flood way. Flood ways should only pass public areas. If the flood way must pass private ground, this should be incorporated in the area planning process and deals should be negotiated with the owners of the area. Flood ways should slow down and retain water as much as possible. Terrain models need to be used when calculating directions of the flood ways, flood levels and the flooded areas. Wastewater transport and urban drainage 64
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The challenge of climate change A «monster rain» hit Copenhagen 2 th of July 2011. It was a 1000 years event according to old statistics. The 3 hour long rain caused damages for 1000 million Euro. Wastewater transport and urban drainage 66
IPCC - UNs Panel for climate change Wastewater transport and urban drainage 67
“…This means that cloudbursts that could have been expected once in 20 years will now become a one-in-5 -year occurrence”. IPCC 2013 Wastewater transport and urban drainage 68
Wastewater transport and urban drainage 69
Sewer design & modelling tool Introduction to USEPA SWMM 70
Hydrologic Modeling Features § Spatially and time varying rainfall § Evaporation of standing surface water § Snow accumulation and melting § Interception from depression storage § Infiltration into soil layers § Percolation into shallow groundwater § Interflow between groundwater & channels § Nonlinear routing of overland flow 71 Wastewater transport and urban drainage 71
What Is SWMM? SWMM is a distributed, dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and 72 quality from primarily urban areas.
Flow Routing Algorithms in SWMM 5 § Steady Flow • simple hydrograph translation • applicable only to branched networks § Kinematic Wave • gravity force balanced by friction force • attenuated & delayed outflow due to channel storage • applicable only to branched networks § Dynamic Wave • solves full St. Venant eqns. • accounts for channel storage, backwater effects, pressurized flow, and reverse flow • applicable to any network layout • requires smaller time step 73 Wastewater transport and urban drainage 73
Flow Routing Algorithms in SWMM 5 § Steady Flow Routing • Actually just sums instantaneous subcatchment runoff for all subcatchments upstream of the selected channel § Kinematic Wave • Uniform, unsteady flow • No backwater, no surcharge, tree branch systems only unless flow splits are input § Dynamic Wave • Non-uniform, unsteady flow • Backwater, surcharge, looped or parallel sewers, street routing of flooded sewer manholes 74 Wastewater transport and urban drainage 74
Schematic Illustration of SWMM Routing Algorithm 75
SWMM’s Process Models 76
Hydraulic Modeling Features § Handles drainage networks of any size § Accommodates various conduit shapes as well as irregular natural channels § Models pumps, regulators, storage units § Allows external inflows from runoff, groundwater, RDII, sanitary, DWF, and user-supplied time series § Uses flexible rule-based controls for pumps and regulators § Models various flow regimes, such as backwater, surcharging, reverse flow, and surface ponding 77 Wastewater transport and urban drainage 77
Water Quality Modeling Features § Pollutant buildup over different land uses § Pollutant washoff during runoff events § Reduction in buildup from street cleaning § Reduction in washoff from BMPs § Inflows from user-defined sources and sanitary DWF § WQ routing through the drainage network § User-defined treatment functions 78 Wastewater transport and urban drainage 78
Typical Applications of SWMM § Design and sizing of drainage system components including detention facilities § Flood plain mapping of natural channel systems § Control of combined and sanitary sewer overflows § Generating non-point source pollutant loadings for wasteload allocation studies § Evaluating BMPs and LIDs for sustainability goals 79 Wastewater transport and urban drainage 79
Limitations of SWMM § Not applicable to large-scale, non-urban watersheds § Not applicable to forested areas or irrigated cropland § Cannot be used with highly aggregated (e. g. , daily) rainfall data § Its an analysis tool, not an automated design tool 80 Wastewater transport and urban drainage 80
Structure of SWMM 5 81
SWMM 5’s Visual Objects 82
Node Flooding Options 83
Surface Routing of Flood Flows Surface Gutter (NN) Zp(NN, 1) Zp(NN, 2) Conduit ( N) JN 84 J N+1
Orifices and Weirs 85
Representation of Weirs 86
Representation of Pump 87
EPA SWMM Web Site http: //www. epa. gov/ednnrmrl/swmm/ 88
The SWMM-USERS List Server List servers provide a means for subscribers to get quick answers to questions and participate in discussions relating to the list server topics. Subscription is free, and subscribers receive all the e-mail that is sent to the list and can in turn send e-mail to the list. The SWMM-USERS list server is a forum for users of the public-domain USEPA SWMM program to share ideas and ask questions on issues related to stormwater management modeling. A searchable archive of past questions and answers is available through our SWMM Q&A database. To subscribe to a list, send an email to listserv@listserv. uoguelph. ca. Do not put anything in the subject line and, in the body of the message, include the following line (with NO other text and no brackets): SUBSCRIBE SWMM-USERS [first name] [last name] For example, SUBSCRIBE SWMM-USERS JANE DOE 89
SWMM Wrappers With GIS Interfaces § XP SWMM – XP Software (www. xpsoftware. com) § Mike SWMM – DHI (www. dhisoftware. com) § Info. SWMM - MWH Soft (www. mwhsoft. com) § PC SWMM – CHI (www. computationalhydraulics. com) 90 Wastewater transport and urban drainage 90
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