SANITARY ENGINEERING LESSON 10 / SUMMARY · PDF fileSaimel (Pombalino) Cascões. SANEAMENTO / FEVEREIRO DE 2012 83 WASTEWATER DRAINAGE SYSTEMS HISTORICAL ASPECTS IN PORTUGAL Higyenist

SANEAMENTO / FEVEREIRO DE 2012 80

SANITARY ENGINEERINGLESSON 10 / SUMMARY

LESSON 10

WASTEWATER DRAINAGE SYSTEMS

� Wastewater drainage systems evolution;

� Current situation in Portugal;

� Components of the systems;

�Examples of existing wastewater systems (components and layout);

�Types of systems. Advantages and inconvenientes;

�Plant layout.



A BIT OF HISTORY

3000 AC: Mohengo-Doro (Hindu civilization, nowadays Pakistan);

1000 a 3000 AC – Cnosso, Crete;

500 AC: Roman Cloaca Maxima (cloacarium e curatores clocarium);

1650 DC: 1st buried collecting pipe (London);

1800 DC: Collecting pipes/tunnels of Paris;

1870 DC: 1st separative systems (Lenox e Memphis, USA).

Public latrine ruins in Ephessos, Turkey (1st century)

Boat trip to Paris sewages, 1896



HISTORICAL ASPECTS IN PORTUGAL

D. João II (1400 DC): Pipes cleaning;

1755: Methodical pipeline-collecting mesh;

Lisbon: “cascões” collecting pipes;

1950 – Setúbal: “canecos” in front of houses to collect “excreta”.

Saimel (Pombalino) Cascões




Higyenist line of thought

� Concerns about effluent treatment and public health;

� Analogy between city network infrastructures (water supply andwastewater drainage) and body circulatory system (arteries and veins).Ecology and urban metabolism.

Urban water cycle

� Urban metabolism (entry of water, chemicals, materials and energy, andoutput of liquid, solid and gaseous wastes). Open system and closedsystem (effluent reuse, eco-efficiency)

Ceramic material Cast iron




Séc. XX – Construction of separative Systems

1930: Porto;

40s: part of Barreiro;

50s: Beja, Caparica, Setúbal, …; Costa de Caparica: first network in the countrywith fiber cement pipes and watertight seals;

60s: Viseu, Tomar, …;

60s, 70s: Lisboa, Elvas, …;

80s: Alcanena (collection of effluents from tanneries, Alviela decontamination);

90s e 2000s: Estoril Coast system, large systems in the Lisbon region:Alcântara, Chelas e Beirolas, Frielas, S. João da Talha, Quinta da Bomba, Portinho daCosta, Mutela, Vale do Ave, SIMRIA, ….



HISTORICAL EVOLUTION OF SYSTEMS

Former pluvial network (until XIX century)

Former pluvial network (until XIX century)

Wastewater treatment inserted in a unitary system (XX century)

Drainage basin

Sewage network

Emissaries

Receiving environment

Buildings

Treatment

CSOs

Industries

Rainwater

Domestic and Industrial WW

Mix

Exutor



HISTORICAL EVOLUTION OF SYSTEMS

Drainage basin

Sewage network

Emissaries


Buildings

Treatment

CSOs

Industries

Rainwater

Domestic and Industrial WW

Mix

Rainwater separative system with eventual treatment

Separative system of domestic wastewater, with mandatory treatment and exutor conveniently inserted

Exutor

Separative wastewater system with pre-treated industrial wastewater connection



COMPONENTS OF WASTEWATER DRAINAGE SYSTEMS

1. Buildings interior networks

a1) Stormwater

a2) Domestic, industrial and commercial wastewater

2. Branches to connect to the main public network

3. Main network components: pipes, manholes, storm drains (in combined or separative

networks);




4. Pumping stations and other elevation devices

5. Collection and transport pipes

6. Sand and/or fact retention chambers, upstream the drainage network:



7. Weirs for control of overflows;

8. Inverted shyphons

9. Special works: crossings, bridge-channel, damping and retention reservoirs;

.




10. Tunnels

11. WWTP

12. Marine outfalls



WASTEWATER DRAINAGE SYSTEMSEXAMPLES OF SYSTEMS

COSTA DO ESTORIL SANITATION SYSTEM

�Population: 900 000 inhab.

�Main interceptor: ø 1,5 m a ø 2,5 m, em 25 km.

�Several pumping stations (in lower elevation areas) and emissaries affluent to the

general intercetor

�WWTP (two phases)

Liquid phase (underground), near Guia (Cascais) in improvement;

Solid phase (sludge treatment) on the surface, in Outeiro da Lota, 4 km away.

�Marine outfall with two diffusers 400 m, for release into the sea (with 2700 m long, 40 m

deep).

�WWTP (physico-chemical treatment, following filtration and disinfection by UV, during

bathing season)



Service area of the wastewater drainage system of Costa do Estoril (Counties of Oeiras,

Cascais and part of Amadora and Sintra)


SIMBOLOGY

Interceptor system

Eduction pipe

Pumping station

Main



Schematic representation of Costa do Estoril drainage system, with interceptor, affluent

emissaries (Jamor, Barcarena, etc..) and pumping stations in areas with lower elevations

(▲)




S. JOÃO DA TALHA SANITATION SYSTEM

Location: Loures County (Freguesias de Bobadela, Sta Iria da Azóia e S. João da Talha);

North Interceptor: L= 3,8 km;

DN 315 a 800 mm (connecting section to WWTP : L = 8 m;

DN = 1000 mm);

South Interceptor: L= 2 km;

DN 400 a 600 mm;

WWTP Physico-chemical and biological treatment (activated sludge);

Operating since 1997;

Project population= 130 000 equivalent habitants;

Qhousehold (average)= 5 980 m3/day;

Qtotal (average)(industrial+household) = 12 582 m3/day.

(65% of the pollution load from industrial sources)



SCHEMATIC REPRESENTATION OF S. JOÃO DA TALHA SANITATION SYSTEM






TYPES OF SYSTEMS

Decree nº23/95 – Article 116º

�Combined systemsConsisting of a single network where stormwater and household,commercial and industrial wastewater are all accepted; they collect anddrain all types of wastewater produced.

�Separative systemsComposed of two distinct networks, one for the drainage of household,commercial and industrial wastewater, and another to the drainage ofstormwater and alike.

�Mixed systemsConsisting of the combination of the two previous types in witch part of thecollectors network operates as a unitary system and the rest as a separativesystem.

�Partialy separative systemsWhere it is accepted, in exceptional conditions, the connection of rainwater from interior courtyards to the collector of household wastewater.


WASTEWATER DRAINAGE SYSTEMSTYPES OF SYSTEMS: ADVANTAGES AND DISADVANTAGES

COMBINED VERSUS SEPARATIVE SYSTEMS

� Advantages of combined systems

� Cheaper

� Easier to build

� Allows the treatment of part of stormwater flows

� Disadvantages

� The over flow that occurs when it rains and the WWTP capacity is exceeded, is amix of stormwater and community wastewater (combined sewage overflow). So,when discharged into the receiving environment, can lead to pollution andcontamination problems;

� Adequate hydraulic conditions are hard to maintain during dry weather periods(sedimentation of suspended solids, risk of formation of hydrogen sulfide, odorsand corrosion of the material collectors)

� When the first rainfall event occurs, after a prolonged drought, the WWTPreceives high pollutant loads (First flush effect)


WASTEWATER DRAINAGE SYSTEMSTYPES OF SYSTEMS: ADVANTAGES AND DISADVANTAGES

COMBINED VERSUS SEPARATIVE SYSTEMS

� Disadvantages (cont.)

� Some components need to have a syphon to prevent odour disturbances (guttersand other components at the network inlet);

� In unitary systems, mains, even short ones, can have large diameters. Inseparative systems a shorter pipe can be installed, as long as the discharge ismade in a nearby water line;

� In separate stormwater systems the pipes do not need to be protected againstcorrosion, since they only carry runoff water, with practically no corrosive effects;

� In unitary systems the WWTP capacity is 2 to 3 times higher than in separatesystems



REGULATION FOR NEW SYSTEMS


1. When designing a public wastewater drainage system in new urbanization areas, a

separative system should be adopted;

2. The household and industrial drainage systems must be designed together, as well

as the stormwater system (independently of being built in different stages).

Decree nº 23/95 – Article 120°: Remodeling existing systems

3. When remodelling existing systems, a transition to a separate systems should be

considered.



SYSTEM DESIGN CONSIDERATIONS

Decree nº 23/95 – Article 118º

1. For the design of the wastewater drainage system, the final effluent disposal should be

considered, both in terms of natural resources protection, public health and economic

aspects;

2. The drainage network should cover the entire service area, as much as possible by

gravity flow.



PLANT LAYOUT DESIGN

�In urban areas the pipes and manholes should be under the street.

�Outside urban areas the collection and transport pipes should develop allong valey

lines or allong the shore.

�The design depends on the final destination of the effluents.

GENERAL PRINCIPLES

a) Distance to urban centers

A1) Layout along valleys (rivers);

A2) Layout along the coast, such as pumping stations (near the ocean or sea);

b) Discharge away from bathing áreas;

c) Discharge should be made in areas with good dilution and dispersion conditions.



PLANT LAYOUT DESIGN

river

ocean

WWTP

WWTP

Example 2

Example 3

Example 1

ocean



LESSON 11

� System design steps

� Design flows and hydraulic criteria

� Sewer profile

� Sewer installation. Manholes



DESIGN MAIN STEPS

� Collection of necessary data;

� Collection of information about possible restrictions and covered area;

� Choose the most suitable drainage system, how it will process the wastewatertreatment and final disposure, as well as all the system componentes;

� Analysis of economically viable alternative solutions;

� Hydraulic/sanitary design of all collectors (diameter and inclination), and all othersystem components, for the design flow;

� Delivery of reports and drawings



DESIGN MAIN STEPS

1. Use adequate cartography: topographic mapping scale 1/1000 or 1/2000 of the current

urbanized area and the future expansion area, where all the proper information

appears(water lines, etc..).

2. Plant layout should take into account topography of the zone (gravity flow) and soil

nature, overlapping with other networks and relevant infrastructures

3. After the first plant layout, visit the area in order to collect more detailed information,

including:

a) best location of branch lines (front versus rear);

b) nature of the terrain (sand, clay or hard/soft rock);

c) type of flooring (asphalt, pavement, macadam …);

d) Watercourses crossing (bridges, viaducts, ... etc..).



DESIGN MAIN STEPS

e) Outfalls layout

f) Groundwater levels (problems in executing the works and calculation of the

infiltration flow);

g) If pumping stations are planned, examine whether there is enough power and

study the resource manifold location;

h) Even if the project does not include the study of the treatment plant, analyze its

possible location;

4. Location of manholes.



PLANT LAYOUT CONSTRAINS


1. Pipes should be placed on the axis of the paved area

2. In large streets with large sidewalks the pipes can be

placed outside the paved area, while respecting the

minimum distance of 1m in relation to property

boundaries

3. Pipes can be installed in both sides of the street more economic.

4. The placement relative to water supply systems must be ensured.



PLANT LAYOUT CONSTRAINS


5. In order to minimize the risk of undue connections in the

network, the sewage pipe should be installed to the right of

the stormwater pipe, considering the flow direction;

6. No infrastructures can be built over drainage pipes;

7. If the previous rule is impossible to ensure, infrastructures

built over drainage pipes should be done ensuring a good

functioning of the pipes as well as a full access and water

tightness


WASTEWATER DRAINAGE SYSTEMSPROJECT ASPECTS

1. It is mandatory to implement manholes:

a) in pipe junctions;

b) where pipes change direction, slope and

diameter;

c) in straight line pipes manhole distance should

not exceed 60 and 100 m for pipes that cannot

and can be visited, respectively.

MANHOLE LOCATION CRITERIA


2. Maximum distances referred previously can increase depending on the cleaning

methods available for the firs case and exceptionally for the second


SEWER SYSTEM

PHASES OF THE STUDY: SYNTHESIS

1.Plant layout of the drainage system

2.Determine design flows

3.Draw longitudinal profile and determine hydraulicconditions


SEWER SYSTEM

DESIGN FLOWS

Decree nº 23/95 – Artigo 132º: Design flows

1. On sewer systems, for domestic or indutrial wastewater, the design flows that

considered correspond to the ones predicted for the design life, this is, it should be

considered the average annual flow affected by a peak factor, to which the infiltration flow

is added

3. For the year of commencement of operation of the system, the hydraulic-sanitary

conditions of the system’s flow should be verified (height and velocity).

Decree nº 23/95 – Artigo 123°: Inflow coeficient

1. The inflow coeficient is the value by which the per capita water demand should be

multiplied as to have the wastewater production per capita

2. The network Inflow coefficient should be discriminated according to identic

characteristic areas, that depend on the extension of green and gardened areas or

agricultural land and habits of the population, values vary usually between 0.7 and 0.9.


DESIGN FLOWS

1.Determine the population that is connected to each stretch

2.Determine the accumulated population associated with each stretch

3.Determine design flow

Qtotal = Q domestic+ Q industrial + Q inflow

where:

Qtotal - total flow to be transported

Q domestic - flow due to population activities

Q industrial - flow from industries

Q infiltration - infiltration form groundwater and storm water

SEWER SYSTEMDESIGN FLOWS


DESIGN FLOWS

4.Determine infiltration flow

Common use: 0 < Qi < Qm

According to the Article 126º do DR 23/95: for D ≤ 300 mm then Qi = Qm

5.Determine peak flow

Q domestic= Fh x ( ∑ Kr x Population x Per capita water demand)

Fh - instant peak factor (varies with the population as

seen in Artigo 125º do DR 23/95) |

Kr - infiltration coefficient usually varies between0,70 a 1,0, as not all the water that is used is drained to the sewers (losses, irrigation, washing, etc.)

Pop

601,5Fh +=

SEWER SYSTEMDESIGN FLOWS


SISTEMAS DE DRENAGEM DE ÁGUAS RESIDUAIS

HYDRAULIC DESIGN CRITERIA

� Minimum diameter (Artigo 126º do DR 23/95) |

D min = 200 mm

� Maximum flow height (Artigo 133º do DR 23/95): |

a) domestic wastewater flows

D ≤ 500 mm y máx / D = 0,50

D > 500 mm y máx / D = 0,75

b) combined wastewater or storm water flows

y máx / D = 1

� Maximum velocity (Artigo 133º do DR 23/95): |

V máx = 3 ms-1 domestic wastewater flows

V máx = 5 ms-1 combined wastewater or storm water flows

SEWER SYSTEMHYDRAULIC DESIGN CRITERIA




� Minimum and maximum slope, for constructive reasons [Artigo 133º do DR 23/95] |

J mín = 0,3%

J máx = 15%

Slopes inferior to the prescribed minimum may be admitted, as long as the leveling and

the transport power are guaranteed and, in case slopes higher than the maximum are

necessary, special anchoring devices should be provided

� J mín = 1/ D (mm) European guidelines





Self-cleaning

Self-cleaning conditions must be ensured for year 0 and maintained in order that the solids

settled during low flow hours are dragged during peak hours.

� self-cleaning criteria (velocity in year 0) [Artigo 133º do DR 23/95]:

V Auto-limpeza = 0,6 ms-1 domestic wastewater flows

V Alimpeza = 0,9 ms-1 combined wastewater or storm water flows

When these limits are not achieved, as it happens on the top of the network, the slopes

should ensure that the minimum is met for a full section flow.


MP1

Slide 120

MP1 colectores de cabeceiraMafalda Pinto; 11-06-2014


1º Each stretch between manholes should be dimensioned starting upstream todownstream. No downstream stretch can be dimensioned before the previousupstream stretches have been determined;

2º Diameter and slope should be selected according to the longitudinal profile, in orderto minimize land movement;

3º Slopes must respect maximum and minimum values due to constructive reasons

4º Hydraulic conditions, flow height and velocity, must be checked for peak flow on thedesign year regarding transport capacity (h/D and Vmax)

5º Velocity and transport capacity should be equal or superior to the minimum required(self-cleaning), for the peak flow on the year of commencement of operation

HYDRAULIC DESIGN STEPS



ANALYTIC METHOD

Known I pipe, D e Q dim :

a) calculate θ (iteratively);

b) Determin y, S e V (by the continuity equation).

Q = Ks x S x R 2/3 x J 1/2

Q = 2 -13/3 x Ks x θ -2/3 ( θ – sin θ ) 5/3 x D 8/3 x J 1/2 4,06,1

6,0

1 063,6 n

s

nn DJK

Qsen θθθ −

+

+=

SEWER SYSTEMHYDRAULIC DESIGN


Known I pipe, D e Q dim :

a) Calculate Q f e V f

b) determine the relation Q dim / Q f

c) use the abacus of the hydraulic properties of

the circular sections :

Q-curve

Q dim / Q f y / D y

V-curve

y / D V / V f V

GRAPHICAL METHOD



Strecht Population [hab] Q m f p Q inf Q dim D I y/D V real τreal Q sc V sc

[-] Affluent Accumulated [L/s] [-] [L/s] [L/s] [mm] [m/m] [-] [m/s] [N/m2] [L/s] [m/s]

1-2

2-3

...

HYDRAULIC CONDITIONS

�1 Table for design for Qpeak for Year 40

�1 Table for verifying for Qpeak for Year 0



ISSUES TO CONSIDER WHEN DESIGNING THE LONGITUDINAL PROFILE

1. Whenever possible, adopt slopes that minimize the depth of excavation (use minimum

depth in the downstream manhole when possible)

2.Comply with minimum and maximum slope

3. Minimum depth of 1,0 m, measured to the top of the pipe (can be lower in special

circumstances)



ISSUES TO CONSIDER WHEN DESIGNING THE LONGITUDINAL PROFILE

5. Pipe alignment on the longitudinal profile:

a) Align pipes by the upper part

b) The energy line upstream of a manhole equals the downstream energy line

added to the specific energy of the drop in the manhole

c) Diameter size must not decrease from upstream to downstream

6. Diâmetro mínimo regulamentar (estipulado pelo Regulamento em 200 mm) |

minimum diameter of 200 mm.



If i ideal < i mín ⇒ i mín(*)

If i mín < i ideal < i máx ⇒ i ideal

(*) I ideal - slope obtained by linking the bottom of the upstream manhole to the bottom ofthe downstream manhole defined with the minimum depth

SELECTING THE SLOPE OF THE PIPES

iground < imin

imin < iground < imáx

i = iground

Min. depth


i = iground

Min. depth


If i ideal > i máx ⇒ i máx

Install a manhole with a drop.

If the upstream manehole has depth higher

that the minimum, choose a slope that installs

the downstream manhole at the minimum

depth, taking into consideration the minimum

acceptable slope

SELECTING THE SLOPE OF THE PIPES

iground > imáx

i = imáx

i = icalculated

> Min.depth

Min.depth

Min.depth



STRETCHES THAT BEGIN WITH MINIMUM DEPTH

i ground< i mín ⇒ i mín

common rule

i ideal < i mín ⇒ i mín

EXAMPLES



stretches that begin with minimum depth and

(i mínima < i terreno < i máxima

i mín < i ground < i máx

For those cases, chose ⇒ i terreno (iground)

Common rule: i mín < i ideal < i máx Choose⇒ i ideal

EXAMPLES



Choose ⇒ i mín

Choose ⇒ i máx


EXAMPLES


SEWER LONGITUDINAL PROFILE



1. Diameter size in wastewater separate systems must not decrease from upstream to

downstream

2. For unitary or storm water separated systems, the reduction of the section downstream

may be reduced, as long as the transport capacity is maintained

[Decreto Regulamentar nº 23/95 – Artigo 159º]

� the insertion of one pipe into another must be done according to the flow direction;

� pipes with different diameter must be aligned by the upper part (to avoid hydraulic

jump, clogging and ensure the continuity of the flow)

� Soft drops (gap≤0,5 m) or guided drops (gap>0,5 m)

� if the depth of a manhole is >5m a platform must be built halfway, with non matching

stairs or passage.

DIAMETERS AND OTHER RULES FOR THE DESIGN OF THE LONGITUDINAL PROFILE




1. Minimum depth of pipes is 1m and it is relative to the top of the

pipe.

INSTALLATION AND LAYOUT OF PIPES


The mentioned minimum depth can be increased depending on traffic demands or due to

the connection to households or other infrastructures.

Only for exceptional situations depths lower than the minimum may be allowed as long as

the protection of the pipes is guaranteed


3. Water distribution pipes must be placed at least 1 m above wastewater drainage pipes,

in order to prevent contamination. If this is not possible, adequate protection must be

ensured.

SEWER SYSTEMLOCATION AND LAYOUT OF PIPES


� On top view, the wastewater pipe and the storm water must maintain the

same relative position (wastewater pipe to the right or to the left of the

storm water pipe)

� In the longitudinal profile the lower part of the storm water pipe must be

placed at a higher elevation than the upper part of the wastewater pipe.

� In the cross-sectional profile minimum distances must be set between the

wastewater pipe and the storm water pipe, both horizontally and vertically.

� In crossings, junctions and direction changes the manholes should be

placed according to the Figure on the lower left.

LOCATION AND LAYOUT OF PIPES

SEWER SYSTEMLOCATION AND LAYOUT OF PIPES



Normalized manholesManholes for large diameters

MANHOLES

[Decreto Regulamentar nº 23/95 – Artigos 155º a 160º]

SEWER SYSTEMMANHOLES


Manholes with inner diameter (D i) depending on

the dept (H)

H < 2,5 m D i = 1,00 m

H > 2,5 m D i = 1,25 m

MANHOLES: BODY AND OPENING



MANHOLES: BOTTOM, SOFT DROPS AND GUIDED DROPS


Initial or passage manhole

Circular manhole for direction change without drop

Rectagular manhole for direction change without drop



MANHOLES: BOTTOM, SOFT DROPS AND GUIDED DROPS

Passage manhole with a drop Junction chamber with drop


MANHOLES: CLOSING MECHANISM AND NORMALIZED STEPS



MANHOLE WITH A SWEPING FLOW




CONSTRUCTION DETAILS

[Decreto Regulamentar nº 23/95 – Artigos146º a 154º]

SEWER SYSTEMCONNECTION BRANCHES


Lesson 12

SANITARY ENGINEERINGLESSON 11 / SUMMARY

STORMWATER DRAINAGE SYSTEMS AND WATER QUALITY

�Main system components

�Plant layout. Source control techniques

�Design steps: baselines, design flows

�Hydraulic design

�Common and special infrastructures of stormwater systems

�Kinds of pollutants and effluents on receiving waters


infiltração

no solo

armazenamento

em depressões

intercepção +

evapotranspiração

escoamento

superficial

intercepção +

evaporação

escoamento

em colectores

evaporação

STORMWATER PLANNING AND DESIGN

ORIGIN AND DESTINATION

a) A fraction does not reach the ground(is intercepted or evaporate)

b) Another fraction reaches permeable soil

. Part infiltrates

. Part evaporates (after puddling)

. Part flows (direct runoff)

c) The remaining portion falls into impervious area (roads and pavements, pavements and roofs)

STORMWATER DRAINAGE SYSTEMSStormwater origin in urban areas

Interception + Evaporation

Interception +

Evapotranspiration

Evaporation

Superficial

evaporation

Water puddle

Infiltration

Pipe flow


� Concerns in urban areas

a) Pollutant load of stormwater

► Heavy metals(Fe, Pb, Zn,…)► hydrocarbons► Suspended solids► CBO5 (organic matter)

► Unitary systems ⇒⇒⇒⇒ “first flush” effect (resuspension and transportof pollutants previously decanted into collecting)

b) Unitary behaviour of domestic (even when conceived as separative)

c) Large range and variability of flows

► Stormwater peak flows >> household flows► Strong relationship between soil occupation and flow

– � impermeable areas– Artificial water channels

► Transient flow in pipes

PROJECT MORE COMPLEX AND EXPENSIVE

Increased flows

STORMWATER DRAINAGE SYSTEMSStormwater origin in urban areas


MAIN GUIDELINES FOR STORMWATER DRAINAGE SYSTEMS

a) Goal 1- Reduce peak flow

b) Goal 2 – Water quality control

Main goal: Reduce the risc of flooding in urban areas

STORMWATER DRAINAGE SYSTEMSDesign and establishmentof systems

a1) Increase interception

a2) Increase filtration

a3) increase storage and detention

a4) increase flow travel time

a5) apply adequate operational and management techniques

b1) Avoid discharge in sensitive areas

b2) treat flows ⇒⇒⇒⇒ overland flowpond/constructed wetlands systemshydrodinamic separators/physico-chemical systems/UV desinfection


Examples of flooding in Portugal

Flooding in Albufeira, Oct. 2009 and

Alcântara, in Lisbon, Feb. 2008

Flash floods in Madeira, February 2010

STORMWATER DRAINAGE SYSTEMSManagement of urban drainage systems - challenges and perspectives


CONTROL PROCEDURES (QUANTITY AND QUALITY)

STORMWATER DRAINAGE SYSTEMSDesign and implementation of systems

a1) Vegetation

a2) Introduce green areas in the the middles of paved areas

• Use of pourous materials in pavments

• Use drains

• Use draining chambers

a3) Use retention and detention basins

• Use storage tanks at dwelling level

a4) Reduce the lenght of pipes and increase the travel time in the upper catchments (with limitations)

a5) Real time control (use the installed storage capacity)


The design should begin at an initial stage of urban planning, especially in critical areas

CONCERNS IN CRITICAL AREAS

a) Plain áreas (with low gravitational potential) to ensure runoff;

b) Areas close to water lines or the sea (collectors subject to the effects of floods and

tides);

c) Areas downstream large watersheds;

d) Intensively urbanized áreas.



• Reduction of pipe lenght and diameters (Decree nº23/95 – Article 118°°°°; point 3 and 4)

a) Maximize the surface path (especially in the headwaters)

b) Promote the integration of permeable areas (green areas, porous pavement ...)

• Concern about the quality of the receiving water bodies (due to pollution transmitted by the stormwater flows, especially after dry periods)

GENERAL CONCERNS:



• Adoption of non conventional drainage solutions

SOURCE CONTROL TECHNIQUES

Vegetated swales Retention /infiltration basin

(Regateira, Almada).

Infiltration trenches

STORMWATER DRAINAGE SYSTEMSSource control techniques


Wet detention basin Dry detention basin

Pourous pavements

STORMWATER DRAINAGE SYSTEMSSource control techniques


PLANT LAYOUT AND CATCHMENT LIMITS

� Pipes intalled in the middle of the street (as household collectors)

� Carefull delimitation of subcatchments affected to each network section

Upper subcatchment

subcatchment

Stormwater Collector


STORMWATER DRAINAGE SYSTEMSPlant layout


STEPS OF THE DESIGN PROCESS

1. Definition of baselines

2. Calculation of design flows

3. Hydraulic design

1. DEFINITION OF BASELINES

• Delimitation of the basin limits and sub-basins affected to each network section

• Definine the return period T (normally varies between 2 and 25 yrs) –

• Determination of local rain regime ⇒⇒⇒⇒ IDF curves

• Characterization of subcatchments (area, runoff coeficiente, slope, soil type, % impervious áreas, etc)

• Determine initial concentration times tc

(Decree nº 23/95 –Article 130°°°°)

STORMWATER DRAINAGE SYSTEMSDesign steps


• Identify constraints:

- Elevations and water level in the receiving environment;

- Elevation of the lower areas to drain;

- Crossings and intersections with other infrastructure.

2. CALCULATION OF STORMWATER DESIGN FLOWS

� Rational Method (semi-conceptual; Mulvaney, 1851 e Kuickling, 1889)

Qstw = C x I x A

sendo:

Qstw - Stormwater flow to be drained by the collector (m3/s)

C - runoff coeficient (-) ⇒

I - precipitation intensity (m3/(ha.s))

A - área of the catchment (ha)

(Decree nº 23/95 – Article 129°°°°)

STORMWATER DRAINAGE SYSTEMS


Precipitation Intensity

I = a . t b

with:

t - subcatchment concentration time

a, b - parameters of IDF curve

(Decree nº 23/95 – Article 128º)

STORMWATER DRAINAGE SYSTEMSDesign Steps

REGION

T (YEARS)


� Método Racional Generalizado (Costa, 1956, D.R. nº 23/95-Anexo X)

AICt

t

V

V Q

c

⋅⋅⋅⋅⋅⋅= γ1

2

sendo,

V1 - volume corresponding to the rising part ofthe hydrograph (m3)

V - total volume of the hydrograph (m3)t - duration of the design precipitation (h)tc - concentration time of the catchment (h)γ - Backwater coefficient.

2 V1/V - Represents the retention and storage: minimal in natural catchments and maximal for impervious catchments (=1).

t/tc - Represents the lag between the end of the precipitation and the instant of peak flow: itis minimal in natural catchments (=0,7) and it is assumed equal to 1 for impervious catchments or highly piped.


= C1 I A


Global reduction coefficient of the generalized rational method (Qp = C1 I A):

C1 = C (2 v1/v) (t/tc)



3. HYDRAULIC DESIGN

• Maximum flow depth ⇒⇒⇒⇒ (h/D) ≤≤≤≤ 1

• Maximum flow velocity ⇒⇒⇒⇒ Vmáx = 5 m/s (for unitary or separative stomwatercollectors)

• Minimum flow velocity ⇒⇒⇒⇒ Vmín = 0,9 m/s

Self-cleaning criteria

• Minimal depths (Art. 137) ⇒⇒⇒⇒ Depths ≥ 1 m

• Minimum diameter (Art. 134) ⇒⇒⇒⇒ Dmín = 200 mm

• Minimum and maximum slopes ⇒⇒⇒⇒ 0,3% e 15% (por razões construtivas)

A – PROJECT CRITERIA:

J mín = 1/ D (mm) Norma Europeia

When these limits are unviable, (common in

the upper subcatchments) the slopes should

be chosen to ensure these limits for full section

flow

(Decree nº 23/95 – Article 133º)



B – CALCULATION STEPS

1 - Analyse the project area and the network plan layout.

Identify constraints ⇒⇒⇒⇒ (Elevations and water level in the receiving environment; Crossings and intersections with other infrastructures …)

2 - Define the return period, T.

3 - Select the IDF curve for the study area and the chosen return period.

4 - Define subcatchments for each design section ⇒⇒⇒⇒ calculate the respective area A

5 - Determine the overall average weighted coefficient for the catchment for each design section:

C = (∑i CiAi) / ∑i Ai

6 - Determine initial concentration times, t c

pe c t t t +=t

L

Vp

j

j

= Σ

STORMWATER DRAINAGE SYSTEMSCalculation Steps

Land SlopeA I < 50% A I > 50%

(min) (min)

very high 5.0 5.0

high 10.0 7.5

medium and plain 15.0 10.0


I = a . t b

7 - Determine the average precipitation intensity, I, for a duration equal to tc (based on IDF curves)

8 - Calculate design flow, using the following expression (rational method):

Q p = ∑i C i x A i x I

9 - Choose a diameter and the pipe slope:

minimize costs; minimal seating depth; verify hydraulics criteria

10 - Determine the velocity, flow depth and the drag tension in the collector;

11- Determine the travel time, tp, for the section considered on the previous point;

12- Add the tp calculated with the concentration time calculated on step 6;

13- Repeat all the steps starting at step 5, from upstream to downstream for each section.

STORMWATER DRAINAGE SYSTEMSCalculation Steps


COMMON COMPONENTS OF STORMWATER SYSTEMS

1- Public sewers (circular, in concrete or PVC)

2- Manholes (for inspection, operation and maintenance)

3- House connections

4- Inlets

Gutters Floor drains Combined gutter-floor drain systems

a) Straight lines between manholes

b) Implementation of water distribution pipelines within the paved driveway, in the middle of the street ( Pimin = 1 m)

c) Smaller lenghts than domestic network

d) Final disposal (river, …)

STORMWATER DRAINAGE SYSTEMSFittings and accessories


Curb inletDrain inlet



SPECIAL COMPONENTS

1- Retention Ponds

2- Infiltration chambers

3- Sand Traps

- conventional (rectangular)

- non conventional (circular, …)

4- Pumping Stations

Should be avoided when possible Construction and exploration costs;

Magnitude and randomness of flows.

(D50 ≥ 0,2 mm), (V = 0,30 m/s)


HEADWORKS OUTLET WORKS

INTERNAL CHANNEL


RETENTION BASIN

�Objectives

• Reduce risk of floods

• Creation of recreational areas (for fishing and boating…)

• Creation of water reserves (agriculture, fire fighting, industries, irrigation…)

• Protection of the environment (reduction of TSS e organic mater)

(Decree nº23/95 – Article 176°°°°)

STORMWATER DRAINAGE SYSTEMSRetention Basins

� Types of basins:

- underground basins (reservoirs)

- open basins - dry

- with permanent water level

WATER POLLUTION AND PUBLIC HEALTH:

POLLUTION:

Presence of substances in water that interfere in its use .

WTP:Ensure water quality for human consumption.

WWTP:

Ensure that the effluent is compatible with the capacity of the receiving water.

Receiving waterIntake ofwater

Discharge

WWTPWastewatertreatment plant

WTPWater treatmentplant

Water Supply Network SewerageNetwork

ReservoirWater Consumption(households, industries,...)

Sanitation [166]

SANITARY ENGINEERING LESSON 10 / SUMMARY · PDF fileSaimel (Pombalino) Cascões. SANEAMENTO / FEVEREIRO DE 2012 83 WASTEWATER DRAINAGE SYSTEMS HISTORICAL ASPECTS IN PORTUGAL Higyenist

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