Environmental Protection (NJDEP) The Louis Berger Group, Inc.

Transcription

1 Hydraulic Modeling for Preliminary Evaluation of Potential Flooding Impacts for Various Dredging, Capping and Armoring Scenarios of The Lower Passaic River Restoration Abdulai Fofanah, PE, D.WRE, CFM Murat Utku, PE, PhD Michael Burlingame, PE Steve Rock Stephen Trainor, PE Ellis Byeon, EIT The Louis Berger Group, Inc. The Louis Berger Group, Inc. New Jersey Department of Environmental Protection (NJDEP) The Louis Berger Group, Inc. The Louis Berger Group, Inc. The Louis Berger Group, Inc.

2 Definition of Terms Overview Remedial Scenarios Modeling Methodology Preliminary Results Preliminary Conclusions

3 Dredging (Environmental): The removal of contaminated sediments from the waterway Capping (In-situ): Leaving contaminated sediments in place and placing a layer of sand and/or other material over it Armoring: Placing a layer of material (gravel, riprap, etc.) over a cap to prevent erosion Armored surface substrate

4 Dredging (Navigational): Removal of sediments from the channel to allow boats to pass FFS: Focused Feasibility Study which presents the remedial alternatives in detail Alternatives from June 2007 DRAFT FFS were grouped and evaluated in 3 remedial scenarios All alternatives have been substantially changed since then, in response to stakeholder comments and additional technical work

5 General purpose of the modeling was to provide a preliminary assessment of potential flooding impacts resulting from various draft 2007 FFS remedial alternatives Seven remedial alternatives for the lower 8 miles of the Passaic River study area were modeled

6 Draft 2007 FFS remedial technologies included various combinations of: Dredging Capping Armoring Each technology could result in activity subject to the NJDEP Flood Hazard Area Control Act Rules (N.J.A.C 7:13) (the Rules) Modeling was performed to determine compliance with substantive requirements of the Rules

7 Evaluating alternatives for compliance with the NJDEP Rules Evaluate potential flooding impacts Flood storage Obstructions to flow Protect public safety Construct new structures above flood hazard area elevation Provide healthy riparian corridors Preserve vegetation Protect habitat

8 All seven alternatives were modeled by NJDEP/Berger using tools that NJDEP typically relies upon (i.e. HEC-RAS, flooding modeling) EPA also performed flood modeling using a hydrodynamic model developed under the CARP program Presentation focuses on three scenarios that are representative of all seven alternatives modeled

9 Dredging to navigational depths

10 Capping and armoring

11 Capping and armoring with dredging less than for navigation

12 Hydrologic Engineering Center River Analysis System (HEC-RAS) model used Model developed by US Army Corps of Engineers The HEC-RAS system contains four onedimensional river analysis components for: Steady flow water surface profile computations Unsteady flow simulation Movable boundary sediment transport computations Water quality analysis Study based on steady flow component to assess potential changes in water surface profiles due to channel modifications associated with each remedial alternative

13 HEC-RAS model input data River and floodplain cross sections

14 HEC-RAS model input data Structures River and floodplain roughness

15 HEC-RAS model input data Upstream boundary conditions Upstream Boundary Fluvial Peak Flows Q 10-YR Q 50-YR Q 100-YR Q 500-YR (cfs) (cfs) (cfs) (cfs) 15,300 25,300 31,800 46,200 Downstream boundary conditions Tidal Elevations Coincident Storm Surge Mean High Water T 10-YR T 50-YR T 100-YR T 500-YR MHW (ft. NGVD29) (ft. NGVD29) (ft. NGVD29) (ft. NGVD29) (ft. NGVD29)

16 Modeling performed for all four upstream boundary conditions with their associated storm surge downstream boundary conditions Modeling also performed for all four upstream boundary conditions with a mean high water downstream boundary condition Modeling was performed assuming a sub-critical flow regime

17 Preliminary results assessment focused on coincident storm surge downstream and upstream peak flow boundary condition

18 Dredging to navigational depths scenario could result in water surface elevation decrease of between 0.0 ft ft Effects of water levels above 8 miles need further study

19 Capping and armoring scenario could result in water surface elevation increases of between 0.0 ft to 1.4 ft

20 Capping and armoring scenario with dredging less than for navigation could result in zero to only minor (i.e. within error band of the model) water surface elevation increases of between 0.0 ft to 0.1 ft

21 Dredging to navigational depths could result in water surface elevation decrease by an estimated 0.7 ft during peak flooding, but further study would be needed to confirm this. Capping and armoring [without dredging] could potentially result in increased water surface elevations during flood events Modeling indicates zero to negligible water surface elevation increases for the capping and armoring with dredging less than for navigation

22 As remedial alternatives for the Lower Passaic River are further developed, additional flood modeling by NJDEP and EPA would appear to be appropriate Although comparison to and reconciliation with more sophisticated modeling efforts may be required, the HEC-RAS modeling conducted for this study was seen as an acceptable means of identifying preliminary order-of-magnitude flooding impacts

23 QUESTIONS?