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Hydrology/Hydraulic Model for South Boston CSO Project

D
dingfangliu

The document discusses modeling of wet weather flow for a sewer separation project in South Boston, Massachusetts. It summarizes modeling of existing conditions, calibration of the model, and modeling of future conditions under various levels of sewer separation. The modeling found that a 92% separation level is needed to meet long-term water quality goals of less than 3 combined sewer overflows per year with volumes under 1.5 million gallons each.

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* The photo is cropped from MWRAs Combined Sewer Overflow Control Plan-Annual Progress Report 2006. Reserved Channel Pleasure Bay North Dorchester Bay Modeling the Wet Weather Flow for Reserved Channel Sewer Separation in South Boston Dingfang Liu, PhD, P.E., Al Carrier, P.E., Rick Moore, P.E.
Background Boston Harbor Case Boston Harbor Water Quality Meet SB Class Standard MWRA CSO Long-term Control Plan 35 sewer improvement project Reserved Channel CSO Control Project BWSC manage the project under MOU with MWRA Storage-Deep ground tunnel Source Reduction-Sewer Separation SB cso 314 CMR 4.00 Surface Water Quality Standards
Project Area
MWRAs System Wide Model InfoWorks CS model > 11,000 nodes Covers 430 square miles service area Take 24 hours to complete one run Too Big to be used for design purpose!
MWRAs Collection System Model in the Project Area Reserved Channel Pleasure Bay 83 sewer nodes, 78 conduits, and 39 subcatchments. No enough detail for design purpose Need update to reflect recent changes on the sewer and drain system
Catchment Area Delineation Topographic - BWSC GIS Topo points - Slope analysis Building and Parking Lot Connection Field Investigation - windshield survey - dye test - facility inspection - building inspection
Imperviousness Ref: Mass GIS 1 meter imperviousness map Total % of impervious area: 87%
Existing Condition Model
Flow Metering Locations
Storm Events for Model Calibration 1 : return period is determined by comparison with IDF curves derived from NRCC data HIGH 6 months 2.41 0.96 14 10/28/06 HIGH < 3 months 1.32 1.48 10 10/11/06 Tidal conditions (high/low) Return Period 1 Total Rain (in) Peak Intensity (in/hr) Duration (hrs) Date
Sensitivity Analysis 40 14.039 2 40 14.039 3 Hortonian infiltration decay rate ( k , 1/hour) 40 14.039 0.1 40 14.039 0.2 Hortonian constant infiltration rate ( f C , inches/hour) 40 14.039 0.8 40 14.039 1 Hortonian initial infiltration rate ( f 0 , inches/hour) 40 14.106 0.013 40 13.201 0.017 50 11.531 0.021 Mannings Roughness Coefficient ( n ) 40 10.43 0.52 25 13.507 0.7 50 15.436 0.88 Runoff Coefficient for impervious Surface 30 13.397 Observed FWHP (minutes) Peak flow (mgd) Values Parameter
Dry Weather Flow Calibration Average daily diurnal curve from the flow metering data Address count to determine population density Apply a daily per capita wastewater flow to diurnal distribution curve Result: 63 gpd per capita
Model Calibration RE is relative error; O i is observed data point at time ( t i ); S i is simulated data point at time ( t i ); N is the data population. 28.60% 21.70% 0.55 0.75 25.60% 21.60% 0.65 0.85 27.60% 35.90% 0.75 0.95 29.00% 44.90% 0.85 1 n/a n/a Observed 10/28/07 10/11/07 Pavement Surface Rooftop Surface Relative Error Runoff Coefficient
Model Calibration
CSO at Existing Condition MWRAs typicalized yearly storm series MWRAs System-wide InfoWorks Model with modification in the project area Dynamic tidal condition CSO criteria: > 1,000 gal sewer spill Long-term CSO control goal: 3 CSO/yr with volume < 1.5 million gallon 29.26 10.22 1.73 8.82 8.49 Volume (MG) 36 36 16 21 27 CSO Activation Calibrated model 37.11 12.16 1.59 7.31 16.04 Volume (MG) 35 35 8 18 27 CSO Activation Original 2006 condition model Reserved Channel Total BOS080 BOS079 BOS078 BOS076
Storm Drain Model Design for 100% separation level Determine building/parking lot disconnect 10 Year Type III design storm (NRCC) Design storm peak coincided with spring high tide (13 ft BCB) Surcharge shall be more than 2 ft from rim elev.
Storm Drain System During 10 year Storm Coincide with Spring High Tide
Building Inspection
Levels of Separation 95% 17 89% 40.5 83% 63.1 365 Total 95% 2.3 88% 5.8 79% 9.8 47 BOS080 93% 2.7 81% 7.8 65% 14.3 41 BOS079 95% 5.4 88% 12.1 83% 17.8 102 BOS078 96% 6.7 92% 14.8 88% 21.3 175 BOS076 (%) (Acres) (%) (Acres) (%) (Acres) (Acres) Separation Remain Connected Separation Remain Connected Separation Remain Connected *Level C (Orange) *Level B (Yellow) *Level A (Green)
Future Condition < 1.5 < 3 Target 0.04 2 Level C (Orange) 0.65 5 Level B (Yellow) 2.57 9 Level A (Green) 29.26 36 Baseline Condition (2006) Volume (MG) Annual CSO Activation
Storm Drain System during Extreme Storm Events During 25 year storm During 50 year storm During 100 year storm
Design Conclusion A separation level of 92% is needed in order to meet the long-term control goal The future sanitary sewer system have enough capacity for storm events up to 25 year return frequency coincide with spring high tide. Upgrade existing outfall system is needed for a 10 year design storm coincided with spring high tide.
Acknowledgement Boston Sewer and Water Commission Ed Duggan Massachusetts Water Resource Authority Wenley Jiang HDR- New York Office Guy Apicella, Frank Brihante, Jee Kyung Ko Tetra Tech Rizzo Water/Wastewater Group Stuffs Melissa Recos, Billy Kwong, Alfred Navato
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Hydrology/Hydraulic Model for South Boston CSO Project

  • 1. * The photo is cropped from MWRAs Combined Sewer Overflow Control Plan-Annual Progress Report 2006. Reserved Channel Pleasure Bay North Dorchester Bay Modeling the Wet Weather Flow for Reserved Channel Sewer Separation in South Boston Dingfang Liu, PhD, P.E., Al Carrier, P.E., Rick Moore, P.E.
  • 2. Background Boston Harbor Case Boston Harbor Water Quality Meet SB Class Standard MWRA CSO Long-term Control Plan 35 sewer improvement project Reserved Channel CSO Control Project BWSC manage the project under MOU with MWRA Storage-Deep ground tunnel Source Reduction-Sewer Separation SB cso 314 CMR 4.00 Surface Water Quality Standards
  • 4. MWRAs System Wide Model InfoWorks CS model > 11,000 nodes Covers 430 square miles service area Take 24 hours to complete one run Too Big to be used for design purpose!
  • 5. MWRAs Collection System Model in the Project Area Reserved Channel Pleasure Bay 83 sewer nodes, 78 conduits, and 39 subcatchments. No enough detail for design purpose Need update to reflect recent changes on the sewer and drain system
  • 6. Catchment Area Delineation Topographic - BWSC GIS Topo points - Slope analysis Building and Parking Lot Connection Field Investigation - windshield survey - dye test - facility inspection - building inspection
  • 7. Imperviousness Ref: Mass GIS 1 meter imperviousness map Total % of impervious area: 87%
  • 10. Storm Events for Model Calibration 1 : return period is determined by comparison with IDF curves derived from NRCC data HIGH 6 months 2.41 0.96 14 10/28/06 HIGH < 3 months 1.32 1.48 10 10/11/06 Tidal conditions (high/low) Return Period 1 Total Rain (in) Peak Intensity (in/hr) Duration (hrs) Date
  • 11. Sensitivity Analysis 40 14.039 2 40 14.039 3 Hortonian infiltration decay rate ( k , 1/hour) 40 14.039 0.1 40 14.039 0.2 Hortonian constant infiltration rate ( f C , inches/hour) 40 14.039 0.8 40 14.039 1 Hortonian initial infiltration rate ( f 0 , inches/hour) 40 14.106 0.013 40 13.201 0.017 50 11.531 0.021 Mannings Roughness Coefficient ( n ) 40 10.43 0.52 25 13.507 0.7 50 15.436 0.88 Runoff Coefficient for impervious Surface 30 13.397 Observed FWHP (minutes) Peak flow (mgd) Values Parameter
  • 12. Dry Weather Flow Calibration Average daily diurnal curve from the flow metering data Address count to determine population density Apply a daily per capita wastewater flow to diurnal distribution curve Result: 63 gpd per capita
  • 13. Model Calibration RE is relative error; O i is observed data point at time ( t i ); S i is simulated data point at time ( t i ); N is the data population. 28.60% 21.70% 0.55 0.75 25.60% 21.60% 0.65 0.85 27.60% 35.90% 0.75 0.95 29.00% 44.90% 0.85 1 n/a n/a Observed 10/28/07 10/11/07 Pavement Surface Rooftop Surface Relative Error Runoff Coefficient
  • 15. CSO at Existing Condition MWRAs typicalized yearly storm series MWRAs System-wide InfoWorks Model with modification in the project area Dynamic tidal condition CSO criteria: > 1,000 gal sewer spill Long-term CSO control goal: 3 CSO/yr with volume < 1.5 million gallon 29.26 10.22 1.73 8.82 8.49 Volume (MG) 36 36 16 21 27 CSO Activation Calibrated model 37.11 12.16 1.59 7.31 16.04 Volume (MG) 35 35 8 18 27 CSO Activation Original 2006 condition model Reserved Channel Total BOS080 BOS079 BOS078 BOS076
  • 16. Storm Drain Model Design for 100% separation level Determine building/parking lot disconnect 10 Year Type III design storm (NRCC) Design storm peak coincided with spring high tide (13 ft BCB) Surcharge shall be more than 2 ft from rim elev.
  • 17. Storm Drain System During 10 year Storm Coincide with Spring High Tide
  • 19. Levels of Separation 95% 17 89% 40.5 83% 63.1 365 Total 95% 2.3 88% 5.8 79% 9.8 47 BOS080 93% 2.7 81% 7.8 65% 14.3 41 BOS079 95% 5.4 88% 12.1 83% 17.8 102 BOS078 96% 6.7 92% 14.8 88% 21.3 175 BOS076 (%) (Acres) (%) (Acres) (%) (Acres) (Acres) Separation Remain Connected Separation Remain Connected Separation Remain Connected *Level C (Orange) *Level B (Yellow) *Level A (Green)
  • 20. Future Condition < 1.5 < 3 Target 0.04 2 Level C (Orange) 0.65 5 Level B (Yellow) 2.57 9 Level A (Green) 29.26 36 Baseline Condition (2006) Volume (MG) Annual CSO Activation
  • 21. Storm Drain System during Extreme Storm Events During 25 year storm During 50 year storm During 100 year storm
  • 22. Design Conclusion A separation level of 92% is needed in order to meet the long-term control goal The future sanitary sewer system have enough capacity for storm events up to 25 year return frequency coincide with spring high tide. Upgrade existing outfall system is needed for a 10 year design storm coincided with spring high tide.
  • 23. Acknowledgement Boston Sewer and Water Commission Ed Duggan Massachusetts Water Resource Authority Wenley Jiang HDR- New York Office Guy Apicella, Frank Brihante, Jee Kyung Ko Tetra Tech Rizzo Water/Wastewater Group Stuffs Melissa Recos, Billy Kwong, Alfred Navato