03 Stormwater management-Hydrological analysis runoff PDF

EAH 417 (2) Click to edit Master title style Urban Water Management Click toSemester edit Master subtitle style I 2024/2025 Hydrological analysis Runoff 10/20/2024...

EAH 417 (2) Click to edit Master title style Urban Water Management Click toSemester edit Master subtitle style I 2024/2025 Hydrological analysis Runoff 10/20/2024 1 1 Runoff  Introduction Introduces methods and procedures for the estimation, routing and attenuation of peak flows and flow volume from sub-catchment as a prerequisite to the design of stormwater conveyance system. Runoff Estimation A graph showing the rate of Catchment Area flow (discharge) versus time past a specific point. Receiving Waterbody Discharge point / River Discharge Runoff Hydrograph Time Runoff Estimation Requires calculations of the following main components: Catchment properties (Area, Slope, Length, etc.) Design rainfall (Storm duration, ARI, IDF, etc.) Time of Concentration - (tc = to + td)  travel time of runoff flows from the most hydraulically remote point upstream in the contributing catchment area to the point under consideration downstream Hydrograph (RM, RMHM, Time Area, etc.)  a graph showing the rate of flow (discharge) versus time past a specific point. Runoff Estimation Determine catchment area, slope, length, etc. Catchment Area Calculate tc = to + td Main Drain Select design storm ARI and Receiving storm duration and compute Waterbody / River design rainfall from IDF curves Estimate runoff using RM, RHM, Time-Area, etc. Runoff Estimation Minor system Major system Ponds, lakes Culverts, larger pipes Natural river, channels Time of Concentration (tc) Flow Time Component for Time of Concentration Flow Type Components Method Overland/sheet flow Natural surfaces Friend Formula - Landscaped surfaces Empirical Equation Impervious surfaces Roof to drain system Residential roofs Minimum 5 minute Commercial/industrial roofs Open channel Curb and gutters Curb & gutter – used Open drains empirical equation Roadside drains Monsoon drains Manning’s Equation Engineered channels Natural channel Underground pipe Downpipe to street gutter Pipe flow within lots Pipe flow chart Street drainage pipe flow (chapter 25) Time of Concentration (tc) Table 2.1: Equations to Estimate Time of Concentration Travel Path Travel Time Remark Overland * 1/ 3 t o = sheet flow travel time (minutes) 107.n. L to = L = sheet flow path length (m) Flow S1/ 5 for Steep Slope (>10%), L ≤ 50 m for Moderate Slope ( 10 ARI) year ARI) Residential Bungalow 0.65 0.70 Semi-detached Bungalow 0.70 0.75 Link and Terrace House 0.80 0.90 Flat and Apartment 0.80 0.85 Condominium 0.75 0.80 Discharge Estimation – Rational Hydrograph Method (RHM) RHM extends the Rational Method to the development of inflow hydrograph for on-site detention and small detention pond. Not recommended for complex drainage system and high-risk areas. d Two types of hydrographs: d tc tc tc tc  Type 1: d > tc Discharge Discharge  Type 2: d = tc Q Q Time Time a) Type 1 (d>tc) b) Type 2 (d=tc) Hydrograph type in the RHM is determined by the relationship between rainfall duration and the time of concentration of the sub-catchment. Given the hydrograph type, the peak discharge is determined using the Rational Method Worked Example Develop the runoff hydrograph using the RHM based on 10- and 45-minute durations design storm for a major drainage of medium density residential area of 10 hectares in Bunan Gega, Sarawak. Assume 80 m of overland flow followed by 400 m of flow in an open drain. Catchment area average slope = 0.5%. Solution: tc = 15 minutes. d = storm duration 7 7 tc tc tc tc 6 6 5 5 Q (m3/s) Q (m3/s) 4 4 3 3 2 2 1 1 0 0 0 5 10 15 20 25 30 35 0 10 20 30 40 50 60 70 Time (min) Time (min) For d = 10 min, d < tc For d = 30 min, d > tc Discharge Estimation – Time-Area Method This method assumes that the outflow hydrograph for any storm is characterised by separable sub-catchment translation and storage effects. Pure translation of the direct runoff to the outlet via the drainage network is described using the channel travel time, resulting in an outflow hydrograph that ignores storage effects. q j = I j. A 1 + I j −1. A 2 +....... + I 1. A j (2.5) where, qj = Flow hydrograph ordinates (m3/s); Ij = Rainfall excess hyetograph ordinates (mm/hr); Aj = Time-area histogram ordinates (ha); and j = Number of isochrone contributing to the outlet. Discharge Estimation – Time-Area Method 4 ∆t Rainfall intensity,I ∆t The catchment is first divided into a number of Isochrones 3∆ A4 isochrones or lines of equal t travel time to the outlet I1 I2 I3 I4 Area A1 2∆ (Figure 2.6b). ∆t t 0 ∆t 2 ∆t 3 ∆t 4 ∆t The areas between Time t A2 A3 isochrones are then determined and plotted against the travel time as (a) Rainfall Histogram (b) Catchment Isochrones shown in Figure 2.6c. The translated inflow Cumulative Area hydrograph ordinates qi q2 Runoff Flow (Figure 2.6d) for any q3 selected design hyetograph can now be determined. q4 q1 ∆t q5 0 ∆t 2 ∆t 3 ∆t 4 ∆t Time t Time t (c) Time-Area Curve (d) Runoff Hydrograph Figure 2.6: Time–Area Hydrograph Method Discharge Estimation – Time-Area Method (Concept) # Isochrone, from the Greek root words iso (equal) and chrone (time) Catchment area is divided into sub-catchments based Isochrone line on the travel time of the runoff to the outlet. Isochrones are lines representing equal travel time for the rainfall runoff (excess rainfall) to the outlet. A4 P4 G A3 A2 F P3 E P2 Lo D A1 C P1 Ld B A 1 2 3 4 5 6 7 Lo = length travelled overland Ld = length travelled through channel to = Lo / V = time travelled overland td = Ld / V = time travelled in drain V = velocity of flow Discharge Estimation – Time-Area Method (Concept) Assumption : same unit rainfall over The principal of linear superposition is hydrograph can be used catchment area for all sub-catchments assumed valid in time-area method. and catchment area. Each sub-catchment will have a A4 hydrograph at its own outlet (P1, P2, P3 or P4) if we consider each sub- P4 catchment as independent entity. A3 A2 P3 Rainfall intensity,I ∆t Hydrograph at P4 P2 A1 I1 I2 I3 I4 q(τ) A 0 ∆t 2 ∆t 3 ∆t 4 ∆t P1 Time t q j = I j. A 1 + I j −1. A 2 +....... + I 1. A j Hydrograph at P3 (a) Rainfall Histogram Hydrograph at P2 Hydrograph at P1 Discharge Estimation – Time-Area Method (Concept) A4 Isochrones A3 P4 A2 P3 A1 P2 P1 q(t) Time Discharge (m3/s) 0 Qo 0 5 Q1 I1A1 + 0 A2 + 0 A3 + 0 A4 10 Q2 I2A1 + I1 A 2 + 0 A3 + 0 A4 15 Q3 I3A1 + I2 A 2 + I1 A 3 + 0 A4 20 Q4 I4A1 + I3 A 2 + I2 A 3 + I1 A 4 25 Q5 I5A1 + I4 A 2 + I3 A 3 + I2 A 4 … … … … … … 55 Q11 I11 A1 + I10 A2 + I9 A 3 + I8 A 4 60 Q12 I12 A1 + I11 A2 + I10 A3 + I9 A 4 I1 I2 I3 I4 I5 I6 I7 I8 I9 I10 I11 I12 65 Q13 0 A1 + I12 A2 + I11 A3 + I10 A4 70 Q14 0 A1 + 0 A2 + I12 A3 + I11 A4 75 Q15 0 A1 + 0 A2 + 0 A3 + I12 A4 80 Q16 0 A1 + 0 A2 + 0 A3 + 0 A4 Discharge Estimation – Time-Area Method Runoff Losses Total Rainfall should be deducted by losses, initial or continuous, to calculate the rainfall excess (RE), which will result in the surface runoff hydrograph. Rainfall/Loss Initial Loss The rainfall losses can be assumed constant (for Rainfall Excess (RE) simplicity) or decaying (to be more practical). Continuous Loss The parameter values are given in Table 2.6. Time Figure 2.7: Initial and Continuous Loss Concept for Runoff Estimation Table 2.6: Recommended Loss Values for Rainfall Excess Estimation Catchment Initial Loss Continuous Loss Condition (mm) (mm/hr) Impervious 1.5 0 Pervious 10 (i) Sandy Soil: 10 - 25 mm/hr (ii) Loam Soil: 3 - 10 mm/hr (iii) Clay Soil: 0.5 - 3 mm/hr Worked Example Using the time-area hydrograph method, calculate a 20-year ARI runoff hydrograph from a 97 ha mixed urban area located in Wangsa Maju, Kuala Lumpur. A B C D E F G H I J K L M 1 2 74 100 23.6 21.0 25.9 109 165 23.3 3 21.4 8.6 12.6 24.6 71 20.7 75 16.9 118 139 22.0 4 5 8.6 71 15.7 10.5 20.7 72 76 85 1.3 7.3 5.0 14.2 22.5 19.5 96 21.0 5 71 71 71 8.9 18.4 75 15.1 103 117 86 11.0 2.8 11.4 11.6 8.9 18.5 20.4 21.4 6 71 12.8 10.4 15.4 18.2 16.5 158 7 12.6 16.9 84 133 18.4 143 20.8 22.3 24.7 71 71 14.1 20.3 115 8 18.4 14.5 95 21.5 142 22.4 150 31.9 11.4 11.6 22.3 15.1 90 19.8 9 12.9 10.0 96 21.6 104 113 115 15.5 15.9 14.4 30.5 31.2 16.9 71 71 15.1 71 82 89 96 114 11.6 75 20.0 11.7 20.2 21.3 19.9 23.0 25.7 29.9 10 71 Legend 15.1 75 80 85 100 Drain 23.9 19.4 19.8 24.9 23.2 26.4 27.2 105 29.5 107 11 Catchment Contour 22.4 26.2 75 100 28.7 20.4 25.6 125 12 Building 13 0 100 200 300 Refer MSMA 2nd Edition - 2.F2 Time-Area Hydrograph Method (Page 2-103) Worked Example 1) Determine ARI and duration of rainfall design. 2) Design rainfall STEP 1 Determine ARI (average recurrence interval) and duration of rainfall for design ARI (years) 20 Duration (min) 30 Location Ibu Pejabat JPS, Kuala Lumpur STEP 2 Design Rainfall Design rainfall intensity, i mm/hr Reference 61.967 0.5 0.818 0.145 0.122 141.1 Table 2.B1 Total design rainfall 70.54 for 30 min = Worked Example 3) Determine the temporal rainfall pattern STEP 3 Rainfall Temporal Pattern Normalized-rainfall temporal pattern ( for 30 mins duration, Appendix 2.C5) Rainfall temporal pattern Reference Time Rainfall (mm) (min) (mm) 0-5 6.84 0.097 5-10 11.36 0.161 10-15 28.22 0.400 15-20 11.57 0.164 Appendix 2.C5 20-25 7.48 0.106 25-30 5.08 0.072 Total 70.54 1.000 Worked Example 4) Determine the rainfall excess STEP 4 Rainfall Excess (Runoff) Rainfall Time Rainfall Losses excess Reference (min) (mm) (mm) mm mm/s 0-5 6.84 4.90 1.94 0.006476 5-10 11.36 0.32 11.04 0.036803 10-15 28.22 0.30 27.92 0.093058 Table 2.6 15-20 11.57 0.28 11.29 0.037620 20-25 7.48 0.27 7.21 0.024037 25-30 5.08 0.23 4.85 0.016153 Infiltration losses Estimation of losses based on Table 2.6 Pervious area Impervious area (40%) (60%) Catchment Initial Loss Continuous Loss (loam soil) Total loss Condition (mm) (mm/hr) Initial loss Continuous loss Initial loss Continuous loss Impervious 1.5 0 mm mm/hr mm mm mm/hr mm mm 10.00 0.00 10.00 1.50 0.00 1.50 4.90 Pervious 10 (i) Sandy Soil: 10 - 25 mm/hr 0.00 9.50 0.79 0.00 0.00 0.00 0.32 (ii) Loam Soil: 3 - 10 mm/hr 0.00 9.00 0.75 0.00 0.00 0.00 0.30 (iii) Clay Soil: 0.5 - 3 mm/hr 0.00 8.50 0.71 0.00 0.00 0.00 0.28 0.00 8.00 0.67 0.00 0.00 0.00 0.27 0.00 7.00 0.58 0.00 0.00 0.00 0.23  Worked Example Areas between Isochornes ID Isochrones Area (m2) 5) Establish hydrograph by superposition A1 0-5 44,449 A2 5-10 79,304 A3 10-15 229,404 A4 15-20 213,852 A5 20-25 160,342 Information required A6 >25 45,306 STEP 5 Hydrograph Area of Time Rainfall 0-5 5-10 10-15 15-20 20-25 25-30 isochrone Hydrograph excess 2 (I1) (I2) (I3) (I4) (I5) (I6) (m3/s) min m (mm/s) 0.0064759 0.0368030 0.0930585 0.0376195 0.0240366 0.0161528 0 0 A1 5 44449 0.287845136 0.2878 Q1 A2 10 79304 0.513560949 1.635856049 2.1494 Q2 A3 15 229404 1.485586301 2.918624224 4.136357058 8.5406 Q3 A4 20 213852 1.384873854 8.442752844 7.379910912 1.672150873 18.8797 Q4 A5 25 160342 1.038351026 7.870392762 21.34799106 2.983379891 1.068403383 34.3085 Q5 A6 30 45306 0.293394941 5.901064831 19.90074534 8.63007264 1.906199507 0.717973646 37.3495 Q6 35 1.667396211 14.92118525 8.045013575 5.514095023 1.280977795 31.4287 Q7 40 4.216108188 6.031992063 5.140277628 3.705505777 19.0939 Q8 45 1.704390817 3.8540785 3.454298187 9.0128 Q9 50 1.08900276 2.589964461 3.6790 Q10 55 0.731816554 0.7318 Q11 60 0 Q12 Worked Example Hydrograph at outlet 40 35 30 Discharge (m3/s) 25 20 15 10 5 0 0 10 20 30 40 50 60 Time (minute) Hydrologic Pond Routing To account for the changes to the hydrograph which take place during the passage in the flow system. Three types of flow routing:  Catchment routing  Channel routing  Reservoir routing The most commonly used method for routing inflow hydrograph through a detention pond is the Storage Indication or modified Puls method. Flow routing is a procedure to determine the time and magnitude of flow at a point on a watercourse from known or assumed hydrographs at one or more points upstream. It is a technique to trace the flow (its characteristic) through a hydrologic system. Hydrologic Pond Routing The most commonly used method for routing inflow hydrograph through a detention pond is the Storage Indication or modified Puls method. This method begins with the continuity equation which states that the inflow minus the outflow equals the change in storage (I-0=∆S). By taking the average of two closely spaced inflows and two closely spaced outflows, the method is expressed by Equation below : ∆S I1 + I 2 O1 + O2 = − ∆t 2 2 I1 + I 2 = I (t ) = Inflow discharge inflow 2 Volume O1 + O2 increment = O(t ) = Outflow discharge 2 ∆S = Change in storage volume ∆t = Time interval outflow Hydrologic Pond Routing Storage Indication Method Pond routing conforms to the Continuity Equation. ∆S I1 + I 2 O1 + O2 = − ∆t 2 2 Figure 2.11: Development of the Storage-Discharge Function for Hydrologic Pond Routing Hydrologic Pond Routing inflow outflow Hydrologic Pond Routing Continuity Equation ∆S I1 + I 2 O1 + O2 = − unknown known known unknown known ∆t 2 2 unknown known Storage Storage indicator indicator number number Worked Example Given is a triangular inflow hydrograph with Qp = 10.93 m3/s at tc = 11.65 min (Figure 2.G1). Determine the outflow hydrograph from a storage pond using the routing procedure in Section 2.5. Given are pond stage-storage (Figure 2.G2) and stage- discharge curve of the outlet structure, orifice and spillway combined (Figure 2.G3). 9000 12 8000 7000 Figure 2.G2: Stage-storage Curve 11 Qpost=10.93m3/s Storage (m³) 6000 10 5000 4000 9 3000 2000 8 1000 Flowrate, Q(m3/s) 7 0 31.00 31.50 32.00 32.50 33.00 33.50 34.00 6 Stage (m) 5 2.5 4 Figure 2.G3: Stage-discharge Curve 2.0 3 (Composite) Outflow (m³/s) 2 1.5 Orifice + Spillway 1 1.0 0 Orifice 0.5 0 5 10 15 20 25 30 Time of Concentration, tc (minutes) 0.0 31.00 31.50 32.00 32.50 33.00 33.50 34.00 Figure 2.G1: Triangular Hydrograph Stage (m) Worked Example Solution: Step 1: Develop storage indicator curve For each stage point determine storage(S) and discharge (O) For each discharge point determine storage indicator (S2/∆t + O2/2) Discharge, Storage Volume, Stage O 2/ 2 S2/ ∆t S2/ ∆t + O2/ 2 O2 S2 (m) (m3/s) (m3) (m3/s) (m3/s) (m3/s) 31.00 0.000 0.000 0.000 0.000 0.000 31.50 0.217 486.838 0.109 3.246 3.354 32.00 0.376 1216.161 0.188 8.108 8.296 2.5 32.50 0.485 2228.079 0.243 14.854 15.097 33.00 0.574 3562.700 2.0 0.287 23.751 24.038 Outflow O2 (m³/s) 33.50 0.651 5260.137 0.326 35.068 35.393 1.5 34.00 2.131 8489.051 1.065 56.594 57.659 1.0 0.5 Figure 2.G3 Figure 2.G2 (∆t = 2.5 min. or 150 sec) 0.0 0 5 10 15 20 25 30 35 40 45 50 55 60 Indicator Numbers (S2/ t + O2/ 2) (m³/s) Worked Example Time Inflow (I) (I1 + I2)/2 S1/ ∆t + O1/ 2 Outflow (O1) S2/ ∆t + O2/ 2 Outflow (O2) Solution: (hr) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) 0.00 0.000 0.000 0.000 0.000 0.000 0.000 Step 2: Calculate O2 0.04 2.350 1.173 0.000 0.000 0.08 4.690 3.520 0.13 7.040 5.866 0.17 9.390 8.212 0.21 10.140 9.761 0.25 7.790 8.963 0.29 5.440 6.617 0.33 3.100 4.270 0.38 0.750 1.924 0.42 0.000 0.375 0.46 0.000 0.000 0.50 0.000 0.000 0.54 0.000 0.000 0.58 0.000 0.000 Worked Example Time Inflow (I) (I1 + I2)/2 S1/ ∆t + O1/ 2 Outflow (O1) S2/ ∆t + O2/ 2 Outflow (O2) Solution: (hr) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) 0.00 0.000 0.000 0.000 0.000 0.000 0.000 Step 2: Calculate O2 0.04 2.350 1.173 0.000 0.000 1.173 0.078 0.08 4.690 3.520 0.13 7.040 5.866 0.17 9.390 8.212 0.21 10.140 9.761 0.25 7.790 8.963 0.29 5.440 6.617 0.33 3.100 4.270 0.38 0.750 1.924 0.42 0.000 0.375 0.46 0.000 0.000 0.50 0.000 0.000 Discharge, Storage Volume, Stage O2 0.54S 0.000 O2/ 20.000S2/ ∆t S2/ ∆t + O2/ 2 2 (m) (m3/s) (m3) (m3/s) (m3/s) (m3/s) 0.58 0.000 0.000 31.00 0.000 Linear 0.000 31.50 0.217 Interpolation 3.354  Worked Example Time Inflow (I) (I1 + I2)/2 S1/ ∆t + O1/ 2 Outflow (O1) S2/ ∆t + O2/ 2 Outflow (O2) Solution: (hr) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) 0.00 0.000 0.000 0.000 0.000 0.000 0.000 Step 2: Calculate O2 0.04 2.350 1.173 0.000 0.000 1.173 0.078 0.08 4.690 3.520 1.173 0.078 4.614 0.463 0.13 7.040 5.866 4.614 0.463 10.017 0.715 0.17 9.390 8.212 10.017 0.715 17.515 0.904 0.21 10.140 9.761 17.515 0.904 26.371 1.040 0.25 7.790 8.963 26.371 1.040 34.295 1.142 0.29 5.440 6.617 34.295 1.142 39.770 1.669 0.33 3.100 4.270 39.770 1.669 42.372 1.971 10.0 0.38 0.750 1.924 42.372 1.971 42.324 1.966 8.0 0.42 0.000 0.375 42.324 1.966 40.734 1.781 40.734 1.781 38.953 1.574 Discharge (m³/s) 0.46 0.000 0.000 6.0 Inflow 38.953 1.574 37.379 1.391 0.50 0.000 0.000 0.54 0.000 0.000 37.379 1.391 35.988 1.229 4.0 0.58 0.000 0.000 35.988 1.229 34.759 1.148 2.0 Outflow 0.0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 Time (hr)  Thank You Presented by Ir. Ts. Dr. Chang Chun Kiat | River Engineering & Urban Drainage Research Centre (REDAC) Discharge Estimation – Time-Area Method (Concept) The total discharge at main outlet P1 is obtained by rainfall over superimposing all the hydrographs. However, each catchment hydrographs has to be time-lagged as their outlets area A4 (P1, P2, P3, P4) are located at different isochrones P4 from the main outlet A3 = I 4. A1(τ)+q q4 q(τ)=q 1 + I 32(τ)+q. A2 +3(τ)+q + I1. A 4 I 2. A43(τ) P3 A2 P2 A1 P1 q(τ) q3(τ) Superposition of hydrographs from each sub-catchments q4(τ) q2(τ) Each hydrographs from sub-catchments arrived Hydrograph at P2 Hydrograph at P3 q1(τ) at P1 at different time t t-3∆t t-∆t t t=τ t-2∆t Hydrograph at main outlet P1 (with superposition) Hydrograph at P1 Hydrograph at P4 Procedure Isochrones G Create grid system over F A4 catchment area in drawing A3 P4 E D A2 P3 Determine Lo and Ld from A1 drawing P2 C P1 q(t) B Cumulative time-area diagram Assume flow velocity v and Contributing area to outlet discharge (cumulative area) A therefore calculate tc=to+td 1 2 3 4 5 6 7 A4 Or directly Establish isochrones based on tc , determine to and td A3 A3 therefore create sub-catchments from Table 2.1 Lo = length travelled overland Measure area A of each sub- Ld = length travelled through channel A2 A2 A2 catchments tc = time of concentration to = Lo / v A1 A1 A1 A1 td = Ld / v time Procedure Design rainfall intensity Total design rainfall over catchment Determine rainfall temporal pattern by using temporal rainfall for the catchment area Temporal rainfall for whole catchment Hydrograph at outlet based on total amount of rainfall over the whole catchment area Determine loss, excess rainfall and excess rainfall intensity I. Excess rainfall See Eq. (1) intensity I q(t) Excess Calculate discharge at main Superposition of rainfall from rainfall outlet of catchment area q(t) all sub-catchments with appropriate time-lagged Infiltration Infiltration rate curve loss  Time Inflow (I) (I1 + I2)/2 S1/ ∆t + O1/ 2 Outflow (O1) S2/ ∆t + O2/ 2 Outflow (O2) Solution: (hr) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) 0.00 0.000 0.000 0.000 0.000 0.000 0.000 Step 2: Calculate O2 0.04 2.350 1.173 0.000 0.000 1.173 0.078 0.08 4.690 3.520 1.173 0.078 4.614 0.463 0.13 7.040 5.866 4.614 0.463 10.017 0.715 0.17 9.390 8.212 10.017 0.715 17.515 0.904 0.21 10.140 9.761 17.515 0.904 26.371 1.040 0.25 7.790 8.963 26.371 1.040 34.295 1.142 0.29 5.440 6.617 34.295 1.142 39.770 1.669 0.33 3.100 4.270 39.770 1.669 42.372 1.971 10.0 0.38 0.750 1.924 42.372 1.971 42.324 1.966 8.0 0.42 0.000 0.375 42.324 1.966 40.734 1.781 40.734 1.781 38.953 1.574 Discharge (m³/s) 0.46 0.000 0.000 6.0 Inflow 38.953 1.574 37.379 1.391 0.50 0.000 0.000 0.54 0.000 0.000 37.379 1.391 35.988 1.229 4.0 0.58 0.000 0.000 35.988 1.229 34.759 1.148 2.0 Outflow 0.0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 Time (hr) Urban Stormwater Management Design Requirements & Criteria MSMA Quantity and Quality Management Strategies Discharge Time MSMA Quantity and Quality Management Strategies 1.2.1 Peak Discharge Control The level of runoff quantity control required is dependent on the type of development proposed, new development or redevelopment. Flow control requirements shall be stipulated as the following: Runoff quantity control requirement for any size of development or re-development project is “Post development peak flow of any ARI at the project outlet shall be less than or equal to the pre- development peak flow of the corresponding ARI (Qpost ≤ Qpre)”.  MSMA Quantity and Quality Management Strategies On-Site Detention Control at source Community Pond Treatment Train Sustainability LEVELS On-site Community Regional Regional Pond