Risk Assessment Methodology forHydraulic Overloading of Urban Drainage Networks and Flooding of Urban Areas               ...
CASE STUDY•   The town is situated in the middle north part of Bulgaria•   The climate in the region is typical continenta...
RAINFALL INTENSITY AND RETURN              PERIOD• Definitions for the term “intensive rainfall”• Inability to accept univ...
RAINFALL INTENSITY AND RETURN              PERIOD• The existing combined sewer network is designed for 2 years  return per...
HYDRAULIC MODELLING• Exiting urban drainage network was performed by means of  MOUSE software, based on the available elec...
HYDRAULIC MODELLING•   The hydraulic model comprises of:•   241 manholes•   236 pipes•   67 catchments with total drainage...
HYDRAULIC MODELLING       manhole             pipeweir                       Legend:                           Diameters o...
COMPUTER SIMULATIONS    Design rainfall•   Return period P=1 year•   Rainfall duration 30 minutes•   Rainfall intensity 10...
COMPUTER SIMULATIONS•   Depth of cover over sewer pipes lower than the minimum admissible•   Sewer pipes with steep slope ...
5.11.2009 г. 12:30:10COMPUTER SIMULATIONS
Methodology for Risk Assessment of Hydraulic     Overloading and Flooding of Urban Drainage      System Based on the Fuzzy...
Methodology for Risk Assessment of Hydraulic  Overloading and Flooding of Urban Drainage   System Based on the Fuzzy Set A...
Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban  Drainage System Based on the Fuzzy Set     ...
Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban  Drainage System Based on the Fuzzy Set     ...
Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban  Drainage System Based on the Fuzzy Set     ...
Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban  Drainage System Based on the Fuzzy Set     ...
Risk          R            1                    0                                                                         ...
Methodology for Risk Assessment of Hydraulic  [m]0.0         Overloading and Flooding of Urban Drainage System            ...
CONCLUSIONSRisk/reliability of hydraulic overloading of the urbandrainage networks can be adequately assessed only byapply...
THANK YOU FOR YOUR     ATTENTION!
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3-1_2. ywp 2012 igneva

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3-1_2. ywp 2012 igneva

  1. 1. Risk Assessment Methodology forHydraulic Overloading of Urban Drainage Networks and Flooding of Urban Areas T. IGNEVA-DANOVA University of Architecture, Civil Engineering and Geodesy Sofia, Bulgaria
  2. 2. CASE STUDY• The town is situated in the middle north part of Bulgaria• The climate in the region is typical continental – cold winters, springs with intensive rainfalls and hot summers• The town is built on relatively steep terrain with considerable displacement between its upper and lower parts• The drainage area is approximately 75 ha• The urban area is drained by combined sewer system with total length of nearly 8 km• The total number of the population is approximately 4 000 people• Existing sewer pipes and joints are in relatively good technical condition• Existing combined sewer system after rehabilitation is planned to be exploited as storm system
  3. 3. RAINFALL INTENSITY AND RETURN PERIOD• Definitions for the term “intensive rainfall”• Inability to accept universal border of intensity and duration of these rains• Standards for modelling hyetographs - “intensive rainfalls” are accepted to be these with intensity more than 30 l/s.ha (0,18 mm/min) regardless to their duration.• For the area of the town intensive rains with duration of 5 minutes (independently from its intensity) are 30 cases per a year and these with duration from 10 to 17 minutes – 17 cases per year. The number of heavy rains with duration of 30 minutes is 5 to 6.• The probability of occurring heavy rains with 60 minutes duration is about 60-70% per year• Return period P is considered in accordance with type of sewer system
  4. 4. RAINFALL INTENSITY AND RETURN PERIOD• The existing combined sewer network is designed for 2 years return period• About 67% of the total drainage area is taken by yards• On the territory of the two districts there are no underground warehouses, stores and business buildings.• Eventual flooding with waste waters in basements would not cause so many damages in comparison with flooding in town centre• During the past 20 years no actual damages due to hydraulic overloading of sewer network were recorded• The design return period of the storm water system is diminished to 1 year
  5. 5. HYDRAULIC MODELLING• Exiting urban drainage network was performed by means of MOUSE software, based on the available electronic cadastre• Imperviousness is precisely defined in accordance with surface type and information from the cadastre. The mean percentage of imperviousness in the considered districts is 33%• New storm water collectors• The influence of these seven newly designed collectors on the conveyance of the existing network is examined through the computer model• Two of the sewer overflows are planned to be used as dividing chambers and the excess storm water is going to be discharged to the river. The third sewer overflow will be reconstructed as a manhole with no direct discharge to the river
  6. 6. HYDRAULIC MODELLING• The hydraulic model comprises of:• 241 manholes• 236 pipes• 67 catchments with total drainage area of 50,3 ha• 2 outlets• 2 dividing chambers• The total length of the modelled network is 7740 m
  7. 7. HYDRAULIC MODELLING manhole pipeweir Legend: Diameters of pipes: --- 0,3 – 0,5 m --- 0,5 – 0,6 m --- 0,6 – 0,8 m --- 0,8 – 1,2 m outlet Δ - outlet  - weir  - manhole
  8. 8. COMPUTER SIMULATIONS Design rainfall• Return period P=1 year• Rainfall duration 30 minutes• Rainfall intensity 100 l/s.ha
  9. 9. COMPUTER SIMULATIONS• Depth of cover over sewer pipes lower than the minimum admissible• Sewer pipes with steep slope followed by pipes with flat slope. Reducing of velocity is precondition for backflow and pressure conditions in sewer pipes.• Higher velocity in secondary sewer collectors at the point of attachment to main sewer than in the main collector. This non-compliance with design criteria leads to backflows at three certain sewer sections.• Pressurized sewer pipes - total length is 455 m or 6,2 % of the whole sewer network.• No surface flooding occurs during the simulated event.• Despite the mentioned above design shortcomings, the existing sewer network possesses relatively good hydraulic capacity and can be exploited without serious problems.• Pressurized regime in storm water sewers is not so dangerous because there is no potential threat of basements’ flooding.
  10. 10. 5.11.2009 г. 12:30:10COMPUTER SIMULATIONS
  11. 11. Methodology for Risk Assessment of Hydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach Fuzzy Set Theory• Zadeh – 1965• Application in physically controlled systems, different engineering problems, statistics, medicine, biology• No information for application of this theory in risk assessment for hydraulic overloading of urban drainage networks is available for author’s best knowledge
  12. 12. Methodology for Risk Assessment of Hydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach1. Area of absolutely safety (normal performance of the sewer pipe) ►2. Area of decreasing safety (increasing risk – the sewer pipe is pressurized) ►3. Area of absolute risk (the water level is above the terrain - flooding) ►4. Area of external load to the sewer pipe (rain with a definite return period – P, at witch in this example the water level rises up to 2 m above the sewer pipe invert) ► ►
  13. 13. Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach ► ► ►
  14. 14. Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach 1. External Load of the system - L Its membership function µL is changing in the interval (0,1) at maximum µL = 1 at a head/depth of 2 m, for this example ► 2. Response of the system – R µR – increasing the pipe depth from D to terrain surface, the membership function is changing from 1 to 0 linearly ►
  15. 15. Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach _ _ _ Reliability measure M = R− L ∫µ h >0 M _ (m)dm Reliability of the system Re = ∫µ h _ M (m)dm
  16. 16. Methodology for Risk Assessment ofHydraulic Overloading and Flooding of Urban Drainage System Based on the Fuzzy Set Approach Dependence between Risk and Reliability Re + Ri = 1 Ri = 1 - Re
  17. 17. Risk R 1 0 1 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 R 30 1 R 31 1 R 57 1 R 77 3 R 22 3 R 31 4 R 32 4 R 33 4 R 34 4 R 35 4 R 36 4 R 37 4 R 38 4 R 39 4 R 40 R R441 43 4 3- 42 W R eir 4 R 44 4 R 45 4 R 46 4 R 47 4 R 48 4 R 49 4 R 50 4 R 51 4 R 52 4 R 53 4 R 54 4 R 55 4 R 56 4 R 57 4 R 58 O 45 ut 9 le t2 R 46 R 0 4Manhole ID R 61 4 R 62 4 R 63 4 R 64 on return period P 4 R 65 4 R 66 4 R 67 4 R 68 Risk of hydraulic overloading and flooding O 46 ut 9 le t1 R 60 R 6 4 R 70 4 R 71 4 W 72 P=5 years P=2 years e P=40 years P=30 years P=20 years P=10 years R i r1 47 R 4 4 R 75 4 R 76 4 R 77 4 R 78 4 R 79 4 Based on the Fuzzy Set Approach R 80 4 R 81 Risk of overloading and flooding of the sewer network depending 4 R 82 4 R 83 4 R 84 4 R 85 4 R 86 4 R 87 48 8 Methodology for Risk Assessment of Hydraulic Overloading and Flooding of Urban Drainage System
  18. 18. Methodology for Risk Assessment of Hydraulic [m]0.0 Overloading and Flooding of Urban Drainage System Diameters0.0 Based on the Fuzzy Set Approach0.0 Map of risk - spatial distribution of reliability over the territory of the0.0 town of Novi Iskar before and after the reconstruction0.00.00.00.00.00.00.00.0 Legend:0.0  Ri 0 – 0,25  Ri 0,25 – 0,50.0  Ri 0,5-0,75  Ri 0,75 - 10.00.0
  19. 19. CONCLUSIONSRisk/reliability of hydraulic overloading of the urbandrainage networks can be adequately assessed only byapplying the appropriate approaches, models and softwareIn our view the most appropriate approach for assessmentof the hydraulic overloading/flooding of the sewer networkshould be one, based on the Fuzzy Set TheoryThe proper assessment of the hydraulic capacity of sewernetworks includes not only simulations with design rainfall,but also giving quantitative assessment of risk for differentrain events
  20. 20. THANK YOU FOR YOUR ATTENTION!

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