AmyMarie Accardi-Dey (The Louis Berger Group, Inc.)

Transcription

1 Correspondence Date: January 27, 2010 To: From: Re: Scott Thompson (The Louis Berger Group, Inc.) AmyMarie Accardi-Dey (The Louis Berger Group, Inc.) Details on Net Suspended Sediment Estimation by Plume-Width Basis and Cross-sectional Area Method Environmental Dredging Pilot Study; On May 14, 2009, the United States Army Corps of Engineers New York District (USACE) and their consultants met with the Lower Passaic River Cooperating Party Group (CPG) to discuss the revisions to the Environmental Dredging Pilot Study (herein referred to as the Pilot Study) 1. During this discussion, the CPG requested details on the net suspended sediment flux calculations [in units of kilograms per second (kg/s)] for the very near-field (defined as the region approximately 60 to 300 feet from the dredge operation). The following memorandum describes the two methods used to calculate the net suspended sediment fluxes in the very near-field that are presented in Table 8-3 of the Environmental Dredging Pilot Study Report (anticipated in 2010), and where applicable, back-up material is attached to this memorandum. While a dredge-related plume was identified in the very near-field, plumes were not discernable from background in the near-field (approximately 400 feet from the dredging operation), indicating that dredgerelated solids settle out of the water column or are dispersed between the very near-field and the near-field. Refer to Section 8 in the main report (Environmental Dredging Pilot Study Report) for data evaluations and conclusions. Cross-Section Basis Method As part of the Pilot Study, Earth Tech, Inc. conducted a pairwise data analysis on the Acoustic Doppler Current Profiler (ADCP) data that were collected on the R/V Caleta. This analysis identified pairs of ship-board surveys that were collected upflow and downflow of the dredging operation that corresponded to the tracking of an ideal particle across the dredging operation (i.e., accounting for time of travel). The pairwise analysis resulted in total suspended solids (TSS) fluxes, which were then adjusted to account for the fact that (1) the R/V Caleta surveys did not span the entire width of the river and (2) the water flux and TSS flux at an upflow pass were not necessarily equivalent to water flux and TSS flux at the downflow pass. Methodology and data results were provided in a memorandum from Serkan Mahnutoglu (Earth Tech, Inc.) to Scott Thompson on August 2, 2007 and are included as an attachment to the Environmental Dredging Pilot Study Report (anticipated in 2010). 1 The Pilot Study was conducted between December 5, 2005 and December 10, 2005 in the Lower Passaic River.

2 January 27, 2010 Page 2 of 3 Using the data provided by Earth Tech, Inc., The Louis Berger Group, Inc. calculated a net suspended sediment flux (assuming a constant water flux) for the identified 18 matched-pairs as follows: data provided in column 3, TSS Flux per Water Flux, Difference (kg/m 3 ), which represents the difference in the TSS flux upflow and downflow of the dredging operation in the matched pair, were multiplied by the downflow water flux data provided in column 2, Water flux (m 3 /s). This process generated the net suspended sediment fluxes (Column 4) labeled Cross-section Basis in Table 8-3 of the Environmental Dredging Pilot Study Report (refer to Attachment 1) and also presented below. Table A: The Louis Berger Group, Inc. Calculated Net Suspended Sediment Flux based on Earth Tech, Inc. Data (Column 1) Date (Column 2) Water Flux (m 3 /s) (downflow) From Earth Tech, Inc. (Column 3) TSS Flux per Water Flux, Difference (kg/s) From Earth Tech, Inc. (Column 4) The Louis Berger Group, Inc. Calculated Net Suspended Sediment Flux in the Very-Near Field (assuming a constant water flux) 12/5/ :42:43 PM /5/ :57:51 PM /5/2005 3:21:52 PM /5/2005 4:22:45 PM /6/2005 2:55:09 PM /6/2005 3:36:48 PM /7/2005 9:28:04 AM /7/2005 9:57:28 AM /7/2005 4:02:10 PM /8/ :16:29 AM /8/ :13:12 PM /8/ :14:24 PM /10/2005 8:53:23 AM /10/2005 8:54:55 AM /10/2005 9:07:38 AM /10/2005 9:34:47 AM /10/ :57:29 PM /10/2005 1:58:22 PM Plume Width Basis Method As part of the Pilot Study, Dr. Robert Chant of Rutgers University developed a MATLAB model to estimate net suspended sediment fluxes in the very near-field of the dredging operation using the data collected on the R/V Caleta. Output from this model was provided to Lisa Baron (USACE) in August 2007 and is included as an attachment to the Environmental Dredging Pilot Study Report (anticipated 2010). In this work, Dr. Chant identifies 27 matching ADCP cross-section pairs, which provide two-dimensional estimates of suspended sediments upflow and downflow of the dredging operation. The difference of these two values represents the net suspended sediment flux. However, in

3 January 27, 2010 Page 3 of 3 this evaluation, a dredge-related plume was evident for only 8 of the 27 match crosssection pairs. When reviewing these MATLAB model runs, The Louis Berger Group, Inc. observed that when a plume was identified, it was generally observed between the horizontal positions of 30 to 70 meters. The Louis Berger Group, Inc. then estimated the net suspended sediment flux by determining a matching upflow load and by normalizing for flow within the width of the plume. This calculation was repeated for the 19 matched cross-section pairs originally presented by Dr. Chant, in which he did not identify a dredge-related plume plus three additional pairs identified by The Louis Berger Group, Inc. (a total of 22 matched pairs). The model outputs are provided in Attachment 2. In these figures, the top left graphic shows the positioning of the two boat-based ADCP surveys and the river flow direction. One survey track is positioned upflow of the dredging operation while the other track is positioning downflow. The bottom two graphics show the estimated suspended sediment concentration in units of kilograms per second (kg/s) for the two boat-based ADCP survey tracks where the y-axis is the depth in the water column, the x-axis is the river cross-section distance (from the southern to northern bank), and the color-scale represents the suspended sediment concentration in two-dimensional space. The top right graphic shows the integrated suspended solids concentration for the river cross-sectional distance. The value in the top right graphic represents the net suspended sediments flux for the apparent plume width. The net suspended sediment flux calculated by The Louis Berger Group, Inc. for the 22 matched pairs plus the 8 matched pairs identified by Rutgers University are listed in Table 8-3 (refer to Attachment 1) rounded to two-decimal places. Attachment 1: Net Suspended Sediment Flux Estimated by Plume-Width and Cross- Section Methods (Table) Attachment 2: TSS Flux Estimated by Plume-Width Basis (Figures showing MATLAB model outputs)

4 Net Suspended Sediment Flux Estimated by Plume-Width and Cross Section Methods from R/V Caleta Date Military Time Method Used Net Solids Flux (kg/s) December 5, :19 Plume Width Basis December 5, :18 Plume Width Basis December 5, :42 Cross-section Basis 2.40 December 5, :57 Cross-section Basis 0.42 December 5, :00 Plume Width Basis 0.07 December 5, :46 Plume Width Basis 1.31 December 5, 2005 * 13:47 Plume Width Basis 0.90 December 5, 2005 * 14:25 Plume Width Basis 2.00 December 5, :21 Cross-section Basis 2.45 December 5, :22 Cross-section Basis 1.23 December 6, :59 Plume Width Basis December 6, :17 Plume Width Basis 0.26 December 6, 2005 * 14:02 Plume Width Basis 4.30 December 6, 2005 * 14:51 Plume Width Basis 1.80 December 6, :55 Cross-section Basis 2.93 December 6, :53 Plume Width Basis 1.43 December 6, :36 Plume Width Basis 0.95 December 6, :36 Cross-section Basis 1.58 December 7, :18 Plume Width Basis December 7, :28 Cross-section Basis December 7, :46 Plume Width Basis 0.42 December 7, :57 Cross-section Basis December 7, :03 Plume Width Basis 0.34 December 7, :38 Plume Width Basis 0.16 December 7, :04 Plume Width Basis 0.11 December 7, :40 Plume Width Basis 0.03 December 7, :50 Plume Width Basis 0.68 December 7, :04 Plume Width Basis 0.81 December 7, :01 Plume Width Basis 0.70 December 7, :02 Cross-section Basis 0.87 December 7, 2005 * 16:10 Plume Width Basis 1.50 December 8, :05 Plume Width Basis 0.77 December 8, :16 Cross-section Basis December 8, 2005 * 11:41 Plume Width Basis 1.00 December 8, :13 Cross-section Basis 0.61 December 8, :14 Cross-section Basis 0.93 December 8, :54 Plume Width Basis 0.10 December 8, :44 Plume Width Basis 0.15 December 10, :52 Plume Width Basis December 10, :34 Plume Width Basis December 10, :53 Cross-section Basis 0.15 December 10, :54 Cross-section Basis 0.22 December 10, :07 Cross-section Basis December 10, :34 Cross-section Basis 0.26 December 10, 2005 * 12:47 Plume Width Basis 2.10 December 10, :57 Cross-section Basis 0.22 December 10, 2005 * 13:38 Plume Width Basis 2.70 December 10, :58 Cross-section Basis 1.04 Notes: * Surveys with observed plume (refer to Appendix G) kg/s= kilograms per second

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12 1.426 Net Suspended Sediment Flux Estimated by Plume Width Basis Figure 8

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