2. General objectives of the Zagreb
project
Phase I - create and verify model of the present state, clarify
system’s pattern of performance, clarify reasons for
missbehaviour, check system as a system
Phase II - create Master Plan, design GIS cadasdre define
short term remedial measures, define new measurement
system, …
Phase II a - define relevant parameters for the future
sewerage system performance w.r. to WWTP, and other
infrastructure projects
Subsequent phases … WQ, Scada, RTC
3. Rainfall analysis
Check applicability of traditional approaches based on IDF
relations and Rational formula vs. HD models and resulting
sewer’s dimensions
Produce flooding maps based on IDF curves and relate them
to historical rain data simulations
Check system’s performance on historical rain records
Perform rainfall-runoff measuremnts and calirate/verify model
Check applicability of historical rain data for design purposes
and relate to flooding frequencies
Propose guidelines for design of the Zagreb sewer system
4. General data
Zagreb sewerage serving 1 M inhabitants + Industry
Catchment >200 km2, 30 km from W to E
>180 M m3 average yearly volume of waste water
~1400 km of sewers
2 M m3 retention capacity of sewers
2 combined systems separted by the river Sava
no CSO allowed by authorities so far
6 small rivers introduced into the sewer system
no WWTP
5.
6. Traditional values
(valid for Zagreb)
RAINFALL ANALYSIS
– IDF relationship valid for Zagreb derived as a complex
empirical formula ...
– Design IDF values i=140 l/sec/ha, D=25 min F=3 y.
RUNOFF ANALYSIS
– all assumptions inherent to Rational formula
7. IDF relations developed for ZAGREB
HTP curves for Zagreb IDVOGZ 1992.
0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
160,00
180,00
200,00
10 15 20 25 30 40 50 60 120 240 300 360 720 1080 1440
Time (min)
Rainstomrdepth(mm)
P = 1 god
P = 2 god
P = 3 god
P = 4 god
P = 5 god
P = 10 god
P = 15 god
P = 20 god
P = 25 god
P = 30 god
P = 40 god
P = 50 god
P = 100 god
P = 1000 god
P = 10000 god
9. Hydrological interest
Investigate influence of FRC and SRC
Investigate influence of hydrological memory of
the catchment
investigate spatial and temporal rain pattern
Define contributing factors of water balance in
yearly waste water production on the catchment
Investigate overload duration and frequency vs.
untreated volume for hypothetical WWTP
USE HISTORICAL RAIN SERIES RECORDS and
CONTINOUS MODELLING APPROACH !!!
10. Rain + relevant data
Historical rain series from 11 r-g with 5 min time
inc. measured by National Weather Institute
(“DHMZ”)
Rain data from measuring campaign at 3 locations
with 2 min resolution --> on-line (+simultaneous
runoff at strategic places in sewers)
potential evaporation
temperature
11. 6 of 11 rain gauges taken in 2nd round from the
National Weather Service
Year /
R.gauge
YEARLY
AVERAGE BIJENIK BORČEC GRIČ MAKSIMIR PUNTIJAR RIM
1984 1023,0 923,0 579,8 730,7 726,2 628,5 440,1
1985 918,0 785,8 488,7 651,6 621,4 368,4 380,2
1986 896,2 822,7 564,3 825,4 736,0 539,1 419,6
1987 977,7 872,4 559,1 755,8 790,9 522,4 218,6
1988 878,2 697,3 420,6 527,9 743,6 564,5 406
1989 1044,4 958,1 642,7 880,1 883,4 895 525,9
1990 779,8 730,6 271,8 644,6 610,6 232,5 438,4
12. Permanent rain gauges / temporary flow
monitors
PER M A N EN T R A IN G A U G ES (“D H M Z”)
TEM PO R A R Y R A IN G A U G ES (“A D S”)
PER M A N EN T LEVEL/ VELO C ITY M O N ITO R
TEM PO R A R Y LEVEL / VELO C ITY / FLO W M O N ITO R S
Z A G R E B SE W E R A G E SY ST E M - M O N I T O R I N G L O CA T I O N SZ A G R E B SE W E R A G E SY ST E M - M O N I T O R I N G L O CA T I O N S
18. Extreme event analysis - HD simulation
NO. DATE 1-HOUR PEAK
RAIN VOLUME
(MAX. OF 3 R.GAUGES)
MM
AVERAGE
RAINFALL
DURATION
HOURS
AVERAGE
TOTAL
RAINFALL
VOLUME
MM
1. 03.07.1989. 27.3 10.58 96.2
2. 25.08.1989. 21.6 7.42 38.6
3. 29.05.1985. 33.7 2.05 19.8
4. 23.06.1989. 27.6 1.75 27.60
5- 08.08.1989. 39.5 10.36 65.37
6. 27.09.1987. 17.2 18.39 77.23
7. 23.09.1991. 26.5 5.81 37.37
8. 14.06.1990. 18.4 1.33 17.37
9. 14.06.1986. 31.1 6.61 40.27
10. 06.08.1985. 19.1 9.22 39.07
19. Flooding map
FL O O D M A P I L L U ST R A T I N G T H E FR E Q U E N CY O F FL O O D I N G R E CU R R E N CEFL O O D M A P I L L U ST R A T I N G T H E FR E Q U E N CY O F FL O O D I N G R E CU R R E N CE
FL O O D E D O N CE I N 10 Y E A R S
FL O O D E D 2 - 3 T I M E S I N 10 Y E A R S
FL O O D E D 4 O R M O R E T I M E S I N 10 Y E A R S
BA SE D O N T H E “PI L O T ” SI M U L A T I O N S (1984. - 1993.) E X PE R I E N CE D
CR I T I CA L A R E A S
A N D PO SSI BL E
FL O O D I N G Z O N E S
20. Conclusions
Use IDF curves … YES when designing secondary
sewers, and as a initial step before use of historical
rain records for final solutions
Use Rational Formula … NO
Use Historical rain series … YES when designing
system’s performance pattern, Master Plan, detailed
insight in generation of surcharge and flooding,
structures, input to WWTP, etc.
21. More conclusions ...
SRC component (rain induced infiltration) important
Catchments sensitive to hydrological history … i.e. to
catchment’s hydrological memory
Majority of relevant rain events come from N, problem
arrives when it comes from W --> E
Time difference is important for rain events coming
from W --> E
Spatial and temporal differences subject to further
investigation (current)
22. Contributing factors in water balance
KEY NUMBERS - FLOW COMPONENTS IN GOK
Yearlyaveragecontributions
Sanitary+ Industrial
Flow
53%
SurfaceRunoff
6%
InflowfromCreeks
36%
GroundWater
Infiltration
5%
23. More conclusions ...
WWTP loadings for different volume of untreated water, overload frequency
and duration
0
2
4
6
8
10
12
14
16
18
20
6 9 12 15 18
WWTP capacity m3/s
milionam3/god.
0
10
20
30
40
50
60
OverloadFrequencyandDuration
Netretirani volumen (miliona m3/god)
U~estalost preoptere}enja (doga|aj/godi{nje)
Trajanje preoptere}enja (dana/godi{nje)
24. KEEP IN MIND
DON’T LOOSE TOUCH OF WHAT IS
THE PURPOSE AND OBJECTIVE OF
RAINFALL ANALYSIS
DECISION MAKERS (MONEY
HOLDERS) WILL EASE YOUR
PROBLEMS - THEY WILL IMPLICITLY
DEFINE RELEVANT RAIN INPUT