urban water systems10 urban drainage© pk, 2005 – page 1 10urban drainage 10.1 rain...

Urban Water Systems 10 Urban drainage © PK, 2005 – page 1

10 Urban Drainage

10.1 Rain characterisation

10.2 Rain-runoff process

10.3 Sewer structure elements

10.4 Stormwater concepts

Technische Universität Dresden

Department of Hydro Science, Institute for Urban Water Management

Peter Krebs

Urban Water Systems


10.1 Rain characterisation

10 Urban drainage


Rain-runoff process

Rain Runoff

Not predictable

Can be analysed statistically

Affected by systematic changes

Cannot be analysed statistically

Models

Measurements Dimensioning


• Stormwater runoff decisive for pipe diameter

• WWTP operation is disturbed for longer than the rain duration

Significance of stormwater

• Contaminated after surface runoff

• Erosion of sewer sediments

• Sewage overflow due to stormwater runoff


Rain measurement

Syphon Weighing Tipping bucket


Description of rain events

From Dyck and Peschke (1989)

Long duration event

Intense event


Rain measurement

Defined opening area of 200 cm2

Normalised shape in vertical section

Measurement error depending on

Wind velocity field

Rain or snow

Wind protection shield


Description of rain (precipitation)

Rain height hR in mm

Rain duration tR in min

Rain intensity in mm/min, l/(s·ha), m/s R

R

th

r

Rain intensity

Time t tR

r Area = hR

Block rain


Resolution in time

0

100

200

300

400

500

0 5 10 15 20 25

0

100

200

300

400

0 5 10 15 20 25

0

100

200

300

400

0 5 10 15 20 25

0

100

200

300

400

0 5 10 15 20 25

Time (min) Time (min)

r (

l/(s

·ha)

)r

(l/

(s·h

a))


Resolution in time Runoff


Resolution in time retention volume

Date of rain event

Retention volume in m3

t = 5 min t = 10 min

29.08.1964

07.07.1965

17.07.1963

19.05.1964

1890

1792

1232

1089

1886

1772

1225

1075

From Krejci et al. (1994)


Resolution in space


Assignment of rain gauges to sub-catchments

Thiessen-Polygon (from Dracos, 1980)


Extreme value frequency

3690

938 41

115 ./

zt

rrR

ztR min

min(Reinhold, 1940)

0

1

2

3

4

0 15 30 45 60

Rain duration t R (min)

rel.

Ra

in i

nte

ns

ity

rtR

(z)

/ r

15

(1)

(-)

0.25

z = 1

5

10 20


Reference rain intensity r15(1) in l/(s·ha)

Baden-Baden 120

Berlin 94

Bonn 108

Bremen 108

Dortmund 120

Dresden 102

Essen 96

Flensburg 100

Frankfurt/Main 120

Garmisch-Patenkirchen 200

Göttingen 98

Hamburg 99

Hannover 100

Köln 97

Konstanz 150

Krefeld 112

Lübeck 106

Mainz 117

München 135

Münster 100

Oldenburg 108

Osnabrück 150

Passau 123

Saarland 135

Stuttgart 126

Tübingen 200

Ulm (Donau) 140

Wetzlar 122

Wilhelmshaven 85

Wolfsburg 112


Frequency analysis

sfhh KPmzP ,z-years event

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Year j

Max

imu

m r

ain

dep

th

hj (

mm

)

hPm

tR = 30 min

s

s


Frequency analysis

sfhh KRmzR ,z-years event

n

hh

n

jRj

Rm

1

Mean value

21

1

2

1

/

n

hhs

n

jRmRj

Standard deviation

Frequency factor fK = f (duration of data

collection, frequency)

from tables


Return period for sewer design

Return period (a)Catchment

Mixed structures

City centre, important industry area

Streets, not in cities areas

Street underpass, underground

1 – 2

1 – 5

1

5 – 20


Historical rain events

Significance

Critical impacts to receiving waters

Less significance for sewer design

Prerequisites for data collection

Measuring time period

Resolution in time

Resolution in space

Time synchronisation

Data bank systems


10.2 Rain-runoff process

10 Urban drainage


Peak runoff factor

Runoff durationRain duration

r·A

QRrmax·A

QP

ArQP

P

max


Peak runoff factor P and coefficient P

Surface material PHousing density

P

Metal and Stone roof 0,95 Class I 350 Inh/ha

0,8Roofing tile and felt 0,90

Flat roof 0,50 – 0,70 Class II 250 Inh/ha

0,60 – 0,65Asphalt road 0,85 – 0,90

Rough road surface 0,75 – 0,85 Class III 150 Inh/ha

0,40 – 0,52Gravel road 0,25 – 0,60

Gravel path 0,15 – 0,30 Class IV 100 Inh/ha

0,25 – 0,46Unpaved area 0,10 – 0,20

Park and Garden 0,05 – 0,10 Class V no housing

0,05 – 0,35Meadow, Forest 0


Peak runoff factor = f(rain intensity r, slope J)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,2 0,4 0,6 0,8 1

Impervious area (-)

Pea

k ru

no

ff f

acto

r

P

(-)

r = 225 (l/(s·ha))r = 180 (l/(s·ha))r = 130 (l/(s·ha))r = 100 (l/(s·ha))

4% < J < 10%


Dry- and wet-weather runoff

Population density e = 100 Inh/ha

DrWa-consumption

Rain intensity

Peak runoff factor

q = 100 l/(Inh·d)

r15(1) = 100 l/(s·ha)

P = 0,4

hasl

dInhl

120100100 ,qeQDW

hasl

hasl

4010040115 ,rQ PWW

DW

WW


Rain-runoff-process in two steps

Runoff production

Runoff concentration

Time

r·A

Q


Losses and runoff production

Permanent losses

Infiltration losses

Depression storage

Runoff

Wet

ting

loss

es

Rain duration

Rai

n in

tens

ity


Pervious area


Surface runoff and infiltration


Surface classification


tR tC

ra

tR < tC C

Ra t

tAr

tC

rb

tR = tC Arb

2 tC

Rain duration to produce maximum runoff

C

N

tt

A

A

Qa

Qb


tR

rc

tR > tC Arc

tR+tC

A

Concentration time = surface runoff time + flow time in sewer

Qc

Rain duration to produce maximum runoff


Assumption of decisive rain duration with a lack of information

Class Sloppe Impervious fraction tR

1 < 1% 50% 15 min

1

2

3

4

< 1%

1% - 4%

4% - 10%

> 10%

> 50%

> 50%

> 50%

50%

10 min

4 > 10% > 50% 5 min


Rationale method

3

4 5 621

111 FSR ttt

2112 FFSR tttt

333 FSR ttt

243 RR tt ,

43324 ,QQQ

kritQQ 5

666 FA ttfQ

566 QQQ tot ,

Iteration with effective concentration time tC

for Point 3

for Point 4


Rationale method Section 1 2 3 4 5 6 Comments

L reach (m) 120 180 60 180

v (m/s)

Flow time (min)

tR = tsur + tflo (min) tA = 5 min

r (tR, z) (l/(s·ha)) (Reinhold, 1940)

Ai (ha) 2 3 1 3

P (-) 0,4 0,6 0,6 0,5

Ared,i (ha)

Ared,i (ha)

QRain (m3/s) QRain = r·Ared,i

const. Q (m3/s)

QRain,tot (m3/s)

QDW (m3/s)

Qm (m3/s)


Application of rain-runoff models

Rationale method

Detailed numerical simulationen

Maximum flow rate

Extreme rain event as input

Dimensioning of sewer cross section

Flow as a function of time at every point in the system

Measured rain events as input

Evaluation of functionality of sewer system

Optimisation of operation and control

Estimation of impact to receiving water


10.3 Sewer structure elements

10 Urban drainage


Groundwater , Drainage, …

Rain water

CSO WWTP

Domestic and industrial sewage clean polluted

Comb syst

Groundwater , Drainage, …

Rain water

CSO WWTP


Comb syst

Infiltration

Groundwater aquifer

Combined system


Combined system


(DIN 1998)

No access for rehabilitation

Combined system

Cross section through street underground

Gully Manhole

House connection


Separate system

Groundwater, drainage, …

Rain water

Storm sewer

WWTP


Sewage sewer

Rainwater treatment

Groundwater, drainage, …

Rain water

Storm sewer

WWTP


Sewage sewer

Infiltration

Groundwater aquifer

Rainwater treatment


Separate system


DIN (1998)

Separate system

Cross section through street underground

Gully Manholes

House connection: sewage

Street water

Roof water


Comparison of combined and separate system

Target Combined system Separate system

• Distinct load variation WWTP

Receiving water

Sewer system

• Storage tanks needed

• Increased design requirements

• Theoretically relatively homogeneous loading re. both flow and load

• CSO includes part of the sewage

• Time delay before combined water is discharged

• Stormwater discharge untreated

• No sewage directly to river

• No retention, quicker discharge

• Lower contruction costs

• Space requirements in the region of retention tanks

• 2 sewers, more expensive• More space requirement in

the ground

• Not retention tanks needed


Target Combined system Separate system

• Frequent self-flushing Sediments

Maintenance

House connection

• Rel. small slope needed

• More susceptible to sedimentation

• Less cleaning required

• Better air exchange

• More cleaning required

• Increased total sewer length

• No mis-connections

• Backwater effect to cellars

• Mis-connections

• No backwater effects

Pumping

• Higher slope needed

• High pumping performance needed which is used only seldomly

• If possible only sewage has to be pumped

Comparison of combined and separate system


Sewer cross sections


„Other“ sewer profile


Elements of stormwater treatment

Function Element Applied in

• CSO structure Overflow

Combined water retention

Stormwater treatment

• Sewer overflow

Combined system

• First flush tank

• Flow-through tank

Pollutants retention • Sewage retention tank

• Combined tank

• Storage channel

Combined system

Separate system

Stormwater retention Comb., sep. system

• Gully

Upstream comb. Syst.

Comb., sep. system


Operation of combined water oberflow structures

River

CWRT combined water retention tank

WWTP wastewater treatment plant

SO sewer overflow

CSO CSO structure

CSO WWTP

CWRTR Weak rain

CSO

moderate

rain

CSO

rain intense

CSO

event Extreme-

SO

SO

SO

SO

CWRTR

CWRTR

CWRTR

WWTP

WWTP

WWTP


Overflow structure with side weir

Overflow at

hasl

minmin

15120

120

fcrit t

r

Throttle flow iThimpcritDWTh QArQQ ,24

Mixing ratio 724

24 DW

DWThCSO Q

QQm

resp.

mg/lmg/l

60180 DW

CSOc

m with cDW > 600 mg/l


„Leaping Weir“, bottom outlet


Combined water retention tank

First flush tank

Flow-through tank

Combined tank

First flush characteristics

Short concentration time (< 15 min)

Moderate slope

Continuous settling of suspended solids

Combination of first-flush storage and settling part


First flush tank

WWTPSO

CSO

WWTPSO, CSO

Off-line In-line

Emptying with pump

Separate flow to WWTP

Emptying through slope

Flow to WWTP through tank

Total stored volume is directed to WWTP!


Flow-through tank

Off-line In-line

Emptying with pump

Separate flow to WWTP

Emptying though slope

Flow to WWTP through tank

Sugnificant part of overflow flows through tank!

WWTPSO

CSO

WWTPSO, CSO


Storage channeloverflow

overflowManhole


Dimensioning of CWRT (ATV A128)

Goal for annual COD load

„Overflow + WWTP effluent Storm water load“

SFo + SFWWTP SFSt

StStWWTPStoSt cVQceVQceVQ 00 1 c COD concentration e0 annual overflow rate

WWTPo

WWTPSt

cccc

e0 mit cDW : cSt : cWWTP = 600 : 107 : 70

1

CSO

DWStCSOo m

ccmc

*

sedimentsrain, pollution,acc DWDW *

m mixing ratio


Specific retention volume and overflow rate

0

5

10

15

20

25

30

35

40

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2

mittlere Regenabflußspende q r (l/(s·ha))

sp

ezi

fis

ch

es

Sp

eic

he

rvo

lum

en

Vs (

m3/h

a)

e 0 = 75

70

65

60

55

50

45 40 35 30 e 0 = 25 %

Vs,min

red

DWWWTPSt A

QQq 24

Specific stormwater runoff to WWTP qSt (l/(s·ha*red))

Sp

ecifi

c st

ora

ge

volu

me

VS

p (

m3/h

a re

d)


WeirBaffle Weir

CSO First-flush tank Throttle

Pump

First-flush tank

Throttle CSO

Baffle Weir CSO

Weir to first flush tank emptyingFirst flush tank off-line

Section

Top view


First-flush tank

Baffle Weir

CSO

Throttle

Dry-weather flume

CSO

Weir

Baffle

First-flush tank in-line

First-flush tank

Throttle

Cross section

Longitudinal section

Top view


Flow-through tank off-line

Section I

Section II

Top view

Effluent weir

Flow-through tank

Pump

Baffle Weir CSO

Weir to flow-through tank

emptying

Throttle

Weir CSO

Baffle Weir to tank

Throttle Flow-through tank

Cleaning device

Cleaning device

Effluent weir


Flow-through tank in-line

Section

Top view

Flow-through tank

Flow-through tank

Throttle

Throttle

Cleaning device

Effluent weir

Baffle Weir CSO emptying

Baffle

Weir CSO Cleaning device

Effluent to receiving water


Combined tank

off-line

Section Baffle Weir CSO

Flow-through tank

First-flush tank

Pump

Top view

emptyingWeir to first-flush tank

Weir to flow-through tank Baffle

Baffle

Weir CSO

Weir to FFT Weir to FTT

Flow-through tank

First-flush tank

Throttle

Baffle

Effluent weir


Circular tank in-line

Section

Top view

Baffle Weir CSO emptying

Throttle

Throttle Dry-weather flow

Baffle

Weir CSO


Cleaning device


Design of stormwater retention tank

Estimation with rectangular rain graph

3690min9

min38 41115 ,

z

trr

NIntensity

Return period z = 5 a

Impervious area Ared = 3 ha

Duration tN = ??

Inflow volume

Outflow volume

Storage volume

Rredtin tArVR

RRoutaus ttQV sm310,

ztVVV RoutinSRT ,fmax


Design of stormwater retention tank

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60

Rain duration tR (min)

Wat

er v

olu

me

(m

3)

0

50

100

150

200

250

300

350

Rai

n i

nte

nsi

ty

r (

l/(s

·ha)

)

Inflow volume

Outflow volume

Retention volume

Rain intensity


Decentralised stormwater retention

Green roof, flat gravel roof

Biotope

Retention channel

Parking lot as a retention area

Stormwater use


Sewage retention tank

Overflow

Receiving water

CSO

Combined water retention

WWTP

WWTP effluent



0

0,2

0,4

0,6

0,8

1

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00

N-l

oad

(g

N/s

)

Event 9 �� CSO without retention

—— combined water retention tank

------ Sewage retention tank

Effects of combined water an sewage retention tank

Long event with rel. low intensity

Short event with moderate intensity

0

1

2

3

4

7:00 7:15 7:30 7:45 8:00 8:15 8:30

N-l

oad

(g

N/s

) Event 13 �� CSO

—— CWRT

------ SRT


0

1

2

3

4

2:50 3:20 3:50 4:20 4:50 5:20

N-l

oad

(g

N/s

) Event 11Short event with high intensity

Acute reveiving water impact is reduced at short events with moderate intensity

WWTP load is reduced during critical phase for N-Elimination

Combined water retention tank


Effects of combined water an sewage retention tank

�� CSO without retention

—— combined water retention tank

------ Sewage retention tank


Retention of solid matter

Gully pot

Related catchment app. 200 m3

Withdrawal zone

Sediment zone, largely variable

Water depth 80 – 100 cm

Volume 280 – 380 l


Stormwater infiltration

Means

Conditions

Effects

Establish pervious and semi-pervious surfaces

Collecting e.g. roof water in infiltration devices

Land use of sub-catchment

Composition of soil

Distance to drinking water extraction

Reduction of runoff

Reduction of loads in CSOs

Increase of groundwater recharge (small)


Optimum range for infiltration

10-10 10-8 10-6 10-4 10-2 1

Gravel

Fine gravel

Sandy gravel

Coarse sand

Sand

Fine sand

Loamy sand

Loam

Clayey loam

Clay

High infiltration capacity High sorption capacity


Trough infiltration U

pper

laye

r w

ith

low

per

mea

bilit

y lo

wer

laye

r w

ith

high

per

mea

bilit

y

Bank protection

Frost protection

Filter layer, sand, h = 50 cm

Humus, h = 30 cm

ev. overflow

Max. water level

Maximum groundwater level m

in. 1

m


Infiltration pipe


Infiltration shaft


Trough-trench system


Trough-trench syestem

Sieker (2001)


vortex drop shaft


outflow inflow

10m

Dry-weather pipe

Wet-weather pipe

flushing

Low passage, change to pressurised flow


House connection, sparate system

private public

sewagestormwater


„vacuum“ drainage

Hauptleitung Vakuum-station

Kläranlage

Connection density

Branch length (m) Length of

total network

(P/m) DN 65 DN 80 DN 100 DN 125

0.04 – 0.06 200 m 800 m 1000 m < 5000 m

0.06 – 0.12 150 m 650 m 900 m 300 m < 4000 m

0.12 – 0.20 100 m 300 m 300 m 800 m < 3000 m

WWTP

Vacuum stationMain collector


10.4 Stormwater concepts

10 Urban drainage


Stormwater retention; green roof


Biotope for stormwater retention


Infiltration


Stormwater runoff at surface


Retention and infiltration pond


Stormwater use

urban water systems10 urban drainage© pk, 2005 – page 1 10urban drainage 10.1 rain...

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