Ellis Y. Byeon, PE Bryan VanderGheynst, PE 1

Transcription

1 Ellis Y. Byeon, PE Bryan VanderGheynst, PE 1

2 Background Information: City of Trenton, Mercer County Assunpink Creek, Pond Run and Delaware River Lower 2.5 miles of the Assunpink Creek Lower 0.6 miles of Pond Run 30 bridges/culverts Route 29 MP 3.22 to MP

3 Delaware River overflowing its banks along Route 29 (April 4, 2005) Assunpink Creek Synopsis: NJDOT completed the Route 29 Drainage Improvements Concept Development Study in January 2012 focused on addressing flooding problems at Route 29 due to the adjacent Delaware River. However, in August 2011, the effects of Hurricane Irene resulted in major flooding of Route 29 caused by overflow from the Assunpink Creek. While the source of flooding at Route 29 is frequently attributable to the Delaware River, floodwaters from the Delaware River did not inundate Route 29 during Irene. 3 Image Source: nj.usgs.gov/hazards/flood/flood0405

4 OnAugust28,2011,Route29withinthesouthernsectionofthestudyareawas flooded because of overflow of Assunpink Creek and Pond Run into the Northern Corridor rail line. None of the proposed alternatives[evaluated] would have alleviated this problem. InordertomitigatefloodingsimilartotheeffectsofIrene,DPMisproposingtoconductaseparate Concept Development study along the Assunpink& Pond Run to determine the needed improvements along the study reach that would keep the Assunpink and Pond Run within their banks and alleviate the flooding such as the Irene flooding. 4 Image Source(s):

5 Assunpink Creek contributing DA 91.7 square miles Pond Run contributing DA 9.8 square miles Delaware River contributing DA 6,780 square miles Meandaily discharge recorded based on 88 years of recorded data 100 cfs Peakdischarge recorded during Hurricane Irene 5,820 cfs (new record) USGS Gage : Assunpink Trenton, NJ (continuous operation since 1932) Image Source(s): & USDA/SCS April

6 Market Street Culvert (1,140 ) Lincoln Ave. Bridge Confluence Capital District Route 29 reported flood location during Hurricane Irene ( MP 3.90) Trenton Transit Center and Retaining Walls (1,490 ) Former Freight Yards 6

7 North East Corridor & Trenton Transit Center 7 Image Source(s):

8 Image Source: Critical Path to Route 29 8

9 Image Source: Critical Path to Route 29 (cont.) 9

10 Image Source: NJ Governor s Office (Tim Larsen) Critical Path to Route 29 (cont.) Total Travel Path 0.92 mi 10

11 Former Freight Yards Lincoln Ave. Bridge 11

12 NJ Transit Retaining Wall U/S face of Market Street Culvert D/S face of Market Street Culvert Assunpink Creek D/S of Market Street 12

13 Additional Notes: FIS flows very close to USGS Gage Data (FIS flows slightly more conservative) Notable Events: Irene 2011 Peak Q = 5,820 cfs(record) July 1975 Flood Peak Q = 5,450 cfs Floyd 1999 Peak Q = 4,510 cfs USGS

14 Additional Note: 50-year flood elevation selected as the worst-case scenario for hydraulic evaluations USGS

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16 Profile Market Street Culvert (1,140 ) Lateral Weir: The Freight Yards Lateral Weir: Low lying Lincoln Ave. Bridge Lateral Weir: Trenton Transit Center Retaining Wall (1,490 ) Lateral Weir: Localized location D/S of S. Clinton Ave. Bridge Plan Notes: Aerial survey + field surveyed crosssections and structures 227 cross-sections & 27 bridges/culverts modeled Key overtopping locations modeled as lateral weirs in HEC-RAS to quantify the discharge leaving the Assunpink Creek floodplain 16

17 ** Critical to account for all potential overtopping locations in order to understand the complete dynamics of the watershed ** 17

18 ** All overtopping locations occur upstream of the Market Street Culvert ** Market Street Culvert 18

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20 3-Way Balance delicate balance required so that any improvement alternatives will not worsen the condition of flooding within the Assunpink Creek floodplain and to prevent any adverse impacts U/S and D/S of where improvement alternatives are proposed. 20

21 Notes: Narrowed down to four main conceptual improvement alternatives for evaluation Improvement Alternative 1 = NO BUILD Several other alternatives were initially evaluated including variations of levee/containment options; dredging variations; multiple Market Street Culvert opening variations; and consideration for a detention system within former Freight Yards Ruled out as various scenarios worsened flooding conditions elsewhere (three-way balance) or provided little to no benefits to Route 29 This process was critical in understanding the complete dynamics of the system 21

22 Improvement Alternative 2 Dredging/Channel Improvements 22

23 Improvement Alternative 3 Market Street Culvert Improvements 23

24 Improvement Alternative 4 Bypass Relief Culvert 24

25 Notes: ALT 2 benefits observed at upstream overtopping locations as dredging/channel improvements provide increased channel capacity thereby lowering flood elevations. HOWEVER, this benefit is balanced out by increases in overflow at the two downstream locations (constriction of flow at Market St. Culvert) ALT 3 a more balanced reduction is achieved compared to ALT 2, HOWEVER, significant overflow would still occur under larger flood events ALT 4 no reductions to overflow provided (comparison based on maximum discharge capacity of the 60 bypass culvert not acting under pressure conditions) 25

26 Challenges faced in heavily urbanized watersheds Climate Change Regional involvement by all affected parties Level of Risk Reality of Cost $ Contact Information: Ellis Y. Byeon, PE Senior Engineer RBA Group ebyeon@rbagroup.com Bryan VanderGheynst, PE Associate/Supervising Engineer RBA Group bvandergheynst@rbagroup.com 26