Technische Universität Dresden Peter Krebs Department of Hydro Science, Institute for Urban Water Management Urban Water Systems 10 Urban Drainage 10. 1 Rain characterisation 10. 2 Rain-runoff process 10. 3 Sewer structure elements 10. 4 Stormwater concepts Urban Water Systems 10 Urban drainage 1
10 Urban drainage 10. 1 Rain characterisation Urban Water Systems 10 Urban drainage 2
Rain-runoff process Rain Not predictable Can be analysed statistically Measurements Urban Water Systems Runoff Affected by systematic changes Cannot be analysed statistically Models 10 Urban drainage Dimensioning 3
Significance of stormwater • Stormwater runoff decisive for pipe diameter • Contaminated after surface runoff • Sewage overflow due to stormwater runoff • Erosion of sewer sediments • WWTP operation is disturbed for longer than the rain duration Urban Water Systems 10 Urban drainage 4
Rain measurement Syphon Urban Water Systems Weighing 10 Urban drainage Tipping bucket 5
Description of rain events Intense event Long duration event From Dyck and Peschke (1989) Urban Water Systems 10 Urban drainage 6
Rain measurement Defined opening area of 200 cm 2 Normalised shape in vertical section Measurement error depending on Wind velocity field Rain or snow Wind protection shield Urban Water Systems 10 Urban drainage 7
Description of rain (precipitation) Rain height h R in mm Rain duration t R in min Rain intensity in mm/min, l/(s·ha), m/s Rain intensity r Area = h. R Block rain Urban Water Systems 10 Urban drainage t. R Time t 8
r (l/(s·ha)) Resolution in time Time (min) Urban Water Systems Time (min) 10 Urban drainage 9
Resolution in time Runoff Urban Water Systems 10 Urban drainage 10
Resolution in time retention volume Retention volume in m 3 Date of rain event t = 5 min t = 10 min 29. 08. 1964 1890 1886 07. 1965 1792 1772 17. 07. 1963 1232 1225 19. 05. 1964 1089 1075 From Krejci et al. (1994) Urban Water Systems 10 Urban drainage 11
Resolution in space Urban Water Systems 10 Urban drainage 12
Assignment of rain gauges to sub-catchments Thiessen-Polygon (from Dracos, 1980) Urban Water Systems 10 Urban drainage 13
Extreme value frequency (Reinhold, 1940) Urban Water Systems 10 Urban drainage 14
Reference rain intensity r 15(1) in l/(s·ha) Baden-Baden 120 Göttingen 98 Oldenburg 108 Berlin 94 Hamburg 99 Osnabrück 150 Bonn 108 Hannover 100 Passau 123 Bremen 108 Köln 97 Saarland 135 Dortmund 120 Konstanz 150 Stuttgart 126 Dresden 102 Krefeld 112 Tübingen 200 96 Lübeck 106 Ulm (Donau) 140 Flensburg 100 Mainz 117 Wetzlar 122 Frankfurt/Main 120 München 135 Wilhelmshaven 85 Münster 100 Wolfsburg Essen Garmisch-Patenkirchen 200 Urban Water Systems 10 Urban drainage 112 15
Frequency analysis z-years event Maximum rain depth h j (mm) 70 t R = 30 min 60 50 s 40 s 30 h Pm 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Year Urban Water Systems 10 Urban drainage j 16
Frequency analysis z-years event Mean value Standard deviation Frequency factor f. K = f (duration of data collection, frequency) from tables Urban Water Systems 10 Urban drainage 17
Return period for sewer design Catchment Return period (a) Mixed structures 1 – 2 City centre, important industry area 1 – 5 Streets, not in cities areas 1 Street underpass, underground Urban Water Systems 10 Urban drainage 5 – 20 18
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 19
10 Urban drainage 10. 2 Rain-runoff process Urban Water Systems 10 Urban drainage 20
Peak runoff factor r·A QR rmax·A QP Rain duration Urban Water Systems 10 Urban drainage Runoff duration 21
Peak runoff factor P and coefficient P Surface material P Metal and Stone roof 0, 95 Roofing tile and felt 0, 90 Flat roof Asphalt road Rough road surface Gravel road Gravel path Unpaved area Park and Garden Meadow, Forest Urban Water Systems Housing density P Class I 350 Inh/ha 0, 8 0, 50 – 0, 70 Class II 0, 85 – 0, 90 250 Inh/ha 0, 60 – 0, 65 0, 75 – 0, 85 Class III 0, 25 – 0, 60 150 Inh/ha 0, 40 – 0, 52 0, 15 – 0, 30 Class IV 0, 10 – 0, 20 100 Inh/ha 0, 25 – 0, 46 0, 05 – 0, 10 Class V no housing 0 0, 05 – 0, 35 10 Urban drainage 22
Peak runoff factor = f(rain intensity r, slope J) P (-) 1 0, 9 4% < J < 10% 0, 8 Peak runoff factor 0, 7 0, 6 0, 5 r = 225 (l/(s·ha)) r = 180 (l/(s·ha)) r = 130 (l/(s·ha)) r = 100 (l/(s·ha)) 0, 4 0, 3 0, 2 0, 1 0 0 0, 2 0, 4 0, 6 0, 8 1 Impervious area (-) Urban Water Systems 10 Urban drainage 23
Dry- and wet-weather runoff Population density e = 100 Inh/ha Dr. Wa-consumption q = 100 l/(Inh·d) Rain intensity r 15(1) = 100 l/(s·ha) Peak runoff factor P = 0, 4 DW WW Urban Water Systems 10 Urban drainage 24
Rain-runoff-process in two steps r·A Runoff production Q Runoff concentration Time Urban Water Systems 10 Urban drainage 25
Losses and runoff production Wetting losse Rain intensity s Permanent losses Infiltration losses e torag s sion s epre D Runoff Rain duration Urban Water Systems 10 Urban drainage 26
Pervious area Urban Water Systems 10 Urban drainage 27
Surface runoff and infiltration Urban Water Systems 10 Urban drainage 28
Surface classification Urban Water Systems 10 Urban drainage 29
Rain duration to produce maximum runoff ra Qa t. R < t. C t. R t. C A rb Qb t. R = t. C Urban Water Systems 10 Urban drainage 2 t. C 30
Rain duration to produce maximum runoff A Qc rc t. R > t. C t. R+t. C Concentration time = surface runoff time + flow time in sewer Urban Water Systems 10 Urban drainage 31
Assumption of decisive rain duration with a lack of information Class Sloppe Impervious fraction t. R 1 < 1% 50% 15 min 1 2 3 4 < 1% 1% - 4% 4% - 10% > 10% > 50% 10 min 4 > 10% > 50% 5 min Urban Water Systems 10 Urban drainage 32
Rationale method 3 1 2 4 5 6 for Point 3 for Point 4 Iteration with effective concentration time t. C Urban Water Systems 10 Urban drainage 33
Rationale method Section L reach (m) 1 2 3 120 180 4 60 5 6 Comments 180 v (m/s) Flow time (min) t. R = tsur + tflo (min) t. A = 5 min r (t. R, z) (l/(s·ha)) (Reinhold, 1940) Ai (ha) 2 3 1 3 P (-) 0, 4 0, 6 0, 5 Ared, i (ha) QRain (m 3/s) QRain = r· Ared, i const. Q (m 3/s) QRain, tot (m 3/s) QDW (m 3/s) Qm (m 3/s) Urban Water Systems 10 Urban drainage 34
Application of rain-runoff models Rationale method Maximum flow rate Extreme rain event as input Dimensioning of sewer cross section Detailed numerical simulationen 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 35
10 Urban drainage 10. 3 Sewer structure elements Urban Water Systems 10 Urban drainage 36
Combined system Groundwater , Drainage, … Rain water clean polluted Domestic and industrial sewage Comb syst CSO Groundwater , Drainage, … WWTP Rain water clean polluted Domestic and industrial sewage Comb syst Infiltration Groundwater aquifer Urban Water Systems CSO 10 Urban drainage WWTP 37
Combined system Urban Water Systems 10 Urban drainage 38
Combined system Cross section through street underground Gully Manhole House connection No access for rehabilitation (DIN 1998) Urban Water Systems 10 Urban drainage 39
Separate system Rain water clean polluted Groundwater, drainage, … Storm sewer Domestic and industrial sewage Sewage sewer Rainwater treatment WWTP Rain water Groundwater, drainage, … Domestic and industrial sewage clean polluted Storm sewer Sewage sewer Infiltration Rainwater treatment Urban Water Systems Groundwater aquifer 10 Urban drainage WWTP 40
Separate system Urban Water Systems 10 Urban drainage 41
Separate system Cross section through street underground Gully Manholes Street water House connection: sewage Roof water DIN (1998) Urban Water Systems 10 Urban drainage 42
Comparison of combined and separate system Target Combined system WWTP • Distinct load variation • Storage tanks needed • Increased design requirements Receiving water Separate system • Theoretically relatively homogeneous loading re. both flow and load • CSO includes part of the sewage • Stormwater discharge untreated • Time delay before combined • No sewage directly to river water is discharged • No retention, quicker discharge Sewer system • 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 43
Comparison of combined and separate system Target Combined system Separate system Sediments • Frequent self-flushing • Rel. small slope needed • More susceptible to sedimentation • Higher slope needed Maintenance • Less cleaning required • More cleaning required • Increased total sewer length • Better air exchange House connection • No mis-connections • Mis-connections • Backwater effect to cellars • No backwater effects Pumping • High pumping performance • If possible only sewage has needed which is used only to be pumped seldomly Urban Water Systems 10 Urban drainage 44
Sewer cross sections Urban Water Systems 10 Urban drainage 45
„Other“ sewer profile Urban Water Systems 10 Urban drainage 46
Elements of stormwater treatment Function Element Applied in Overflow • CSO structure • Sewer overflow Combined system Combined water retention • • Combined system First flush tank Flow-through tank Combined tank Storage channel Stormwater treatment Separate system Stormwater retention Comb. , sep. system Pollutants retention Urban Water Systems • Sewage retention tank • Gully 10 Urban drainage Upstream comb. Syst. Comb. , sep. system 47
Operation of combined water oberflow structures River CWRTR CSO SO Weak rain WWTP CWRTR moderate rain CSO SO WWTP CWRTR CSO SO intense rain WWTP CWRT combined water retention tank WWTP wastewater treatment plant CWRTR CSO Urban Water Systems SO Extreme event WWTP 10 Urban drainage SO sewer overflow CSO structure 48
Overflow structure with side weir Overflow at Throttle flow Mixing ratio resp. Urban Water Systems with c. DW > 600 mg/l 10 Urban drainage 49
„Leaping Weir“, bottom outlet Urban Water Systems 10 Urban drainage 50
Combined water retention tank First flush characteristics Short concentration time (< 15 min) Moderate slope Flow-through tank Continuous settling of suspended solids Combined tank Urban Water Systems Combination of first-flush storage and settling part 10 Urban drainage 51
First flush tank Off-line SO In-line WWTP SO, CSO WWTP CSO 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 52
Flow-through tank Off-line SO In-line WWTP SO, CSO WWTP CSO Emptying with pump Separate flow to WWTP Emptying though slope Flow to WWTP through tank Sugnificant part of overflows through tank! Urban Water Systems 10 Urban drainage 53
Storage channel overflow Urban Water Systems Manhole 10 Urban drainage 54
Dimensioning of CWRT (ATV A 128) Goal for annual COD load SFo + SFWWTP SFSt „Overflow + WWTP effluent Storm water load“ c COD concentration e 0 annual overflow rate mit c. DW : c. St : c. WWTP = 600 : 107 : 70 m mixing ratio Urban Water Systems 10 Urban drainage 55
Specific storage volume VSp (m 3/hared) Specific retention volume and overflow rate Specific stormwater runoff to WWTP q. St (l/(s·ha*red)) Urban Water Systems 10 Urban drainage 56
Section Baffle Weir CSO Weir to first flush tank First-flush tank emptying First flush tank off-line Throttle Pump Top view Baffle Weir CSO Urban Water Systems Weir First-flush tank Throttle 10 Urban drainage 57
Cross section First-flush tank in-line First-flush tank Longitudinal section Baffle Weir First-flush tank CSO Throttle Top view Throttle Baffle Weir CSO Urban Water Systems Dry-weather flume 10 Urban drainage 58
Section I Flow-through tank off-line Cleaning device Effluent weir Flow-through tank Pump Section II Baffle Weir CSO Weir to flowthrough tank emptying Throttle Top view Baffle Weir CSO Weir to tank Throttle Flow-through tank Cleaning device Effluent weir Urban Water Systems 10 Urban drainage 59
Section Baffle Weir CSO emptying Cleaning device Flow-through tank in-line Effluent weir Flow-through tank Throttle Top view Flow-through tank Baffle Weir CSO Cleaning device Throttle Effluent to receiving water Urban Water Systems 10 Urban drainage 60
Section Baffle Weir CSO Weir to flow-through tank Baffle Weir to first-flush tank emptying Combined tank Pump Flow-through First-flush tank off-line Top view Baffle Weir CSO Weir to FTT Weir to FFT Throttle Flow-through First-flush tank Baffle Effluent weir Urban Water Systems 10 Urban drainage 61
Circular tank in-line Section Baffle Weir CSO Top view emptying Dry-weather flow Throttle Baffle Weir CSO Urban Water Systems Throttle 10 Urban drainage 62
Cleaning device Urban Water Systems 10 Urban drainage 63
Design of stormwater retention tank Estimation with rectangular rain graph Intensity Return period z = 5 a Impervious area Ared = 3 ha Duration t. N = ? ? Inflow volume Outflow volume Storage volume Urban Water Systems 10 Urban drainage 64
Design of stormwater retention tank Inflow volume Outflow volume Retention volume Rain intensity Water volume (m 3) 700 350 300 600 250 500 200 400 150 300 100 200 50 100 0 Rain intensity r (l/(s·ha)) 800 0 0 10 20 30 40 50 60 Rain duration t. R (min) Urban Water Systems 10 Urban drainage 65
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 66
Sewage retention tank Overflow CSO Combined water retention Urban Water Systems WWTP effluent Receiving water 10 Urban drainage 67
Effects of combined water an sewage retention tank N-load (g. N/s) 1 0, 8 0, 6 CSO without retention —— combined water retention tank ------ Sewage retention tank Long event with rel. low intensity Event 9 0, 4 0, 2 0 0: 00 1: 00 2: 00 3: 00 4: 00 5: 00 6: 00 7: 00 8: 00 N-load (g. N/s) 4 3 2 Event 13 CSO —— CWRT ------ SRT Short event with moderate intensity 1 0 7: 00 Urban Water Systems 7: 15 7: 30 7: 45 8: 00 10 Urban drainage 8: 15 8: 30 68
Effects of combined water an sewage retention tank N-load (g. N/s) 4 3 2 CSO without retention Event 11 —— combined water retention tank ------ Sewage retention tank Short event with high intensity 1 0 2: 50 3: 20 3: 50 4: 20 4: 50 5: 20 Combined water retention tank Acute reveiving water impact is reduced at short events with moderate intensity Sewage retention tank WWTP load is reduced during critical phase for N-Elimination Urban Water Systems 10 Urban drainage 69
Retention of solid matter Gully pot Related catchment app. 200 m 3 Withdrawal zone Water depth 80 – 100 cm Volume 280 – 380 l Sediment zone, largely variable Urban Water Systems 10 Urban drainage 70
Stormwater infiltration Means Establish pervious and semi-pervious surfaces Collecting e. g. roof water in infiltration devices Conditions Land use of sub-catchment Composition of soil Distance to drinking water extraction Effects Reduction of runoff Reduction of loads in CSOs Increase of groundwater recharge (small) Urban Water Systems 10 Urban drainage 71
Optimum range for infiltration Gravel Fine gravel Sandy gravel Coarse sand Sand Fine sand Loamy sand Loam Clayey loam Clay 10 -10 10 -8 High sorption capacity Urban Water Systems 10 -6 10 -4 10 -2 1 High infiltration capacity 10 Urban drainage 72
Trough infiltration Frost protection Urban Water Systems Bank protection Maximum groundwater level min. 1 m lower layer with high permeability Upper layer with low permeability ev. overflow 10 Urban drainage Max. water level Humus, h = 30 cm Filter layer, sand, h = 50 cm 73
Infiltration pipe Urban Water Systems 10 Urban drainage 74
Infiltration shaft Urban Water Systems 10 Urban drainage 75
Trough-trench system Urban Water Systems 10 Urban drainage 76
Trough-trench system Urban Water Systems 10 Urban drainage 77
Trough-trench syestem Sieker (2001) Urban Water Systems 10 Urban drainage 78
vortex drop shaft Urban Water Systems 10 Urban drainage 79
Low passage, change to pressurised flow outflow inflow 10 m flushing Dry-weather pipe Wet-weather pipe Urban Water Systems 10 Urban drainage 80
House connection, sparate system private public sewage Urban Water Systems 10 Urban drainage stormwater 81
„vacuum“ drainage Vacuum station Main collector WWTP Connection density (P/m) DN 65 DN 80 0. 04 – 0. 06 200 m 0. 06 – 0. 12 – 0. 20 Urban Water Systems Length of total network DN 100 DN 125 800 m 1000 m < 5000 m 150 m 650 m 900 m 300 m < 4000 m 100 m 300 m 800 m < 3000 m Branch length (m) 10 Urban drainage 82
10 Urban drainage 10. 4 Stormwater concepts Urban Water Systems 10 Urban drainage 83
Stormwater retention; green roof Urban Water Systems 10 Urban drainage 84
Biotope for stormwater retention Urban Water Systems 10 Urban drainage 85
Infiltration Urban Water Systems 10 Urban drainage 86
Stormwater runoff at surface Urban Water Systems 10 Urban drainage 87
Retention and infiltration pond Urban Water Systems 10 Urban drainage 88
Stormwater use Urban Water Systems 10 Urban drainage 89
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