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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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 2
10.1 Rain characterisation
10 Urban drainage
Urban Water Systems 10 Urban drainage © PK, 2005 – page 3
Rain-runoff process
Rain Runoff
Not predictable
Can be analysed statistically
Affected by systematic changes
Cannot be analysed statistically
Models
Measurements Dimensioning
Urban Water Systems 10 Urban drainage © PK, 2005 – page 4
• 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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 5
Rain measurement
Syphon Weighing Tipping bucket
Urban Water Systems 10 Urban drainage © PK, 2005 – page 6
Description of rain events
From Dyck and Peschke (1989)
Long duration event
Intense event
Urban Water Systems 10 Urban drainage © PK, 2005 – page 7
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 8
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 9
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))
Urban Water Systems 10 Urban drainage © PK, 2005 – page 10
Resolution in time Runoff
Urban Water Systems 10 Urban drainage © PK, 2005 – page 11
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)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 12
Resolution in space
Urban Water Systems 10 Urban drainage © PK, 2005 – page 13
Assignment of rain gauges to sub-catchments
Thiessen-Polygon (from Dracos, 1980)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 14
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 15
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 16
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 17
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 18
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 19
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 20
10.2 Rain-runoff process
10 Urban drainage
Urban Water Systems 10 Urban drainage © PK, 2005 – page 21
Peak runoff factor
Runoff durationRain duration
r·A
QRrmax·A
QP
ArQP
P
max
Urban Water Systems 10 Urban drainage © PK, 2005 – page 22
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 23
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%
Urban Water Systems 10 Urban drainage © PK, 2005 – page 24
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 25
Rain-runoff-process in two steps
Runoff production
Runoff concentration
Time
r·A
Q
Urban Water Systems 10 Urban drainage © PK, 2005 – page 26
Losses and runoff production
Permanent losses
Infiltration losses
Depression storage
Runoff
Wet
ting
loss
es
Rain duration
Rai
n in
tens
ity
Urban Water Systems 10 Urban drainage © PK, 2005 – page 27
Pervious area
Urban Water Systems 10 Urban drainage © PK, 2005 – page 28
Surface runoff and infiltration
Urban Water Systems 10 Urban drainage © PK, 2005 – page 29
Surface classification
Urban Water Systems 10 Urban drainage © PK, 2005 – page 30
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 31
tR
rc
tR > tC Arc
tR+tC
A
Concentration time = surface runoff time + flow time in sewer
Qc
Rain duration to produce maximum runoff
Urban Water Systems 10 Urban drainage © PK, 2005 – page 32
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 33
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 34
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)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 35
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 36
10.3 Sewer structure elements
10 Urban drainage
Urban Water Systems 10 Urban drainage © PK, 2005 – page 37
Groundwater , Drainage, …
Rain water
CSO WWTP
Domestic and industrial sewage clean polluted
Comb syst
Groundwater , Drainage, …
Rain water
CSO WWTP
Domestic and industrial sewage clean polluted
Comb syst
Infiltration
Groundwater aquifer
Combined system
Urban Water Systems 10 Urban drainage © PK, 2005 – page 38
Combined system
Urban Water Systems 10 Urban drainage © PK, 2005 – page 39
(DIN 1998)
No access for rehabilitation
Combined system
Cross section through street underground
Gully Manhole
House connection
Urban Water Systems 10 Urban drainage © PK, 2005 – page 40
Separate system
Groundwater, drainage, …
Rain water
Storm sewer
WWTP
Domestic and industrial sewage clean polluted
Sewage sewer
Rainwater treatment
Groundwater, drainage, …
Rain water
Storm sewer
WWTP
Domestic and industrial sewage clean polluted
Sewage sewer
Infiltration
Groundwater aquifer
Rainwater treatment
Urban Water Systems 10 Urban drainage © PK, 2005 – page 41
Separate system
Urban Water Systems 10 Urban drainage © PK, 2005 – page 42
DIN (1998)
Separate system
Cross section through street underground
Gully Manholes
House connection: sewage
Street water
Roof water
Urban Water Systems 10 Urban drainage © PK, 2005 – page 43
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 44
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 45
Sewer cross sections
Urban Water Systems 10 Urban drainage © PK, 2005 – page 46
„Other“ sewer profile
Urban Water Systems 10 Urban drainage © PK, 2005 – page 47
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 48
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 49
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 50
„Leaping Weir“, bottom outlet
Urban Water Systems 10 Urban drainage © PK, 2005 – page 51
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 52
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!
Urban Water Systems 10 Urban drainage © PK, 2005 – page 53
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 54
Storage channeloverflow
overflowManhole
Urban Water Systems 10 Urban drainage © PK, 2005 – page 55
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 56
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)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 57
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 58
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 59
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 60
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 61
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 62
Circular tank in-line
Section
Top view
Baffle Weir CSO emptying
Throttle
Throttle Dry-weather flow
Baffle
Weir CSO
Urban Water Systems 10 Urban drainage © PK, 2005 – page 63
Cleaning device
Urban Water Systems 10 Urban drainage © PK, 2005 – page 64
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 65
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 66
Decentralised stormwater retention
Green roof, flat gravel roof
Biotope
Retention channel
Parking lot as a retention area
Stormwater use
Urban Water Systems 10 Urban drainage © PK, 2005 – page 67
Sewage retention tank
Overflow
Receiving water
CSO
Combined water retention
WWTP
WWTP effluent
Sewage retention tank
Urban Water Systems 10 Urban drainage © PK, 2005 – page 68
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 69
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
Sewage retention tank
Effects of combined water an sewage retention tank
��� CSO without retention
—— combined water retention tank
------ Sewage retention tank
Urban Water Systems 10 Urban drainage © PK, 2005 – page 70
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 71
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)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 72
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 73
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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 74
Infiltration pipe
Urban Water Systems 10 Urban drainage © PK, 2005 – page 75
Infiltration shaft
Urban Water Systems 10 Urban drainage © PK, 2005 – page 76
Trough-trench system
Urban Water Systems 10 Urban drainage © PK, 2005 – page 77
Trough-trench system
Urban Water Systems 10 Urban drainage © PK, 2005 – page 78
Trough-trench syestem
Sieker (2001)
Urban Water Systems 10 Urban drainage © PK, 2005 – page 79
vortex drop shaft
Urban Water Systems 10 Urban drainage © PK, 2005 – page 80
outflow inflow
10m
Dry-weather pipe
Wet-weather pipe
flushing
Low passage, change to pressurised flow
Urban Water Systems 10 Urban drainage © PK, 2005 – page 81
House connection, sparate system
private public
sewagestormwater
Urban Water Systems 10 Urban drainage © PK, 2005 – page 82
„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
Urban Water Systems 10 Urban drainage © PK, 2005 – page 83
10.4 Stormwater concepts
10 Urban drainage
Urban Water Systems 10 Urban drainage © PK, 2005 – page 84
Stormwater retention; green roof
Urban Water Systems 10 Urban drainage © PK, 2005 – page 85
Biotope for stormwater retention
Urban Water Systems 10 Urban drainage © PK, 2005 – page 86
Infiltration
Urban Water Systems 10 Urban drainage © PK, 2005 – page 87
Stormwater runoff at surface
Urban Water Systems 10 Urban drainage © PK, 2005 – page 88
Retention and infiltration pond
Urban Water Systems 10 Urban drainage © PK, 2005 – page 89
Stormwater use