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Sedimentshed Delineation

Sedimentshed Delineation. Chesapeake Bay Program Sediment Workgroup. Background: Current Sediment Cap Load Allocation. Understanding of… sediment sources and their impact on the Bay is not yet complete land based sediment and stream erosion is still basic

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Sedimentshed Delineation

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  1. Sedimentshed Delineation Chesapeake Bay Program Sediment Workgroup

  2. Background: Current Sediment Cap Load Allocation Understanding of… • sediment sources and their impact on the Bay is not yet complete • land based sediment and stream erosion is still basic • nearshore sediment transport from shoreline erosion and shallow-water resuspension is even more limited Therefore… • Sediment load allocations are currently focused on land based sediment loads by major trib basin Source: Setting and Allocating the Chesapeake Bay Basin Nutrient and Sediment Loads, 2003

  3. Background: Current Sediment Cap Load Allocation • Current water quality model is not capable of providing a reliable understanding of the sediment loads effect on water clarity (p. 104) • Since no reliable tool existed, sediment cap load allocations were based on reductions from implementing land-based phosphorus controls (p. 104) Source: Setting and Allocating the Chesapeake Bay Basin Nutrient and Sediment Loads, 2003

  4. Significance of Tidal Erosionin the Chesapeake (From Tidal Sediment Report)

  5. Sedimentshed • Definition: Area, including nearshore, that contributes the sediment loads that directly influences water clarity in specific adjoining shallow water habitats in a reasonable management timeframe • Purpose: Set appropriate geographic frame of reference for setting/revising sediment cap allocations by 2010 • Reasoning: Impacts from sediment on Bay water clarity and SAV growth are predominately localized (CBP, 2003)

  6. Area of influence • Shallow Sater SAV habitat– defined as the shallow-water SAV habitats most directly influenced by sediments from the surrounding sediment-shed (also called Designated Use Areas)

  7. Sedimentshed • Breaking new ground…

  8. Sediment Sources • Upland • Above fall line (sediment allocation defined in tributary strategies) • Below fall line (considered upland in model) • Shoreline and Bay • Shoreline erosion • Shallow water wave resuspension • Deep water resuspension (least important to SAV) • Resuspended primary producers (dead) in the water column • Oceanic Input

  9. Natural delineations of a Sedimentshed • It is expected that sediment sheds will likely be from single or multiple collections of CB segments • CB Segments group similar regions to define a range of objectives, target specific actions and monitor response (p. 1) • Hierarchy of considerations (p. 8) • Salinity (TF, OH, MH, PH) • Natural geographic partitions and features • Original segmentation boundaries Source: Chesapeake Bay Program Analytical Segmentation Scheme, 2004

  10. Questions to Group • Should we use the current model framework to identify sediment sheds? • What can we do with and what are the advantages with respect to sediment transport of the Phase V modeling framework in identifying sediment sheds? • What is the logical process to define a sedimentshed? • What can we do with the information currently available (independent of the WQM)? Meeting: 12/15/2005

  11. Sedimentshed - Proposed Approach • Define area of influence (SAV) • Locate ETM – Set “boundary” • Location? • Is it a true boundary? • Locate natural geographic partitions • Tribs to bay (CB Segmentation, 2004) • Compare WSM model segmentation with the new national watershed segmentation data • Locate nearshore vs. deep water • Model tracer study using only spike along shoreline? • Moving down the Bay • Sediment distribution (Newell et. al., 2004) • Soils (bottom type)

  12. Model Tracer Study • Phase V model framework • CBP modeling staff momentum is toward new model development • WSM accounts for the “partial area concept” • Suggested tracer scenarios • Above fall line (major tributary inputs) • Shoreline (high erosion areas) • Open bay • Set up future meeting to define scenarios and get committee agreement

  13. The ETM • Is it really a “boundary”? • Should it be an RFP? • Proposal: • Can we use the 20+ year record of TSS concentrations in tidal Bay waters in combination with the river flow record to determine is there a magnitude of storm event/level of river flow that disrupts the otherwise effective barrier in place with the estuarine turbidity maximum?

  14. The ETM - Cont • How much credit should ETMs be given for holding back sediments from upstream river basins? • Are there clear locations and documentation of the ETM locations? • Analysis by CBP in January and February • Report in the early spring 2006 • Require five independent reviewers

  15. Where do we go from here…

  16. Sediment Shed Report • Timeline: Dec 2005 – Dec 2006 • Assignment of sections??? • Proposed outline • Acknowledge the existing info on sediment transport and destination • Sediment shed • Definition • Natural “barriers” • Area of influence – shallow water habitat (SAV)

  17. Sediment Shed Report - Cont • Outline • Sediment mass balance • Sediment sources • Application of mass balance based on clarity • Tracer study • Design • Recommended scenarios to define sediment shed • Preliminary model results expected late 2006

  18. Sediment Workgroup Task Timeline Task Timeline General report Vol I: Up to scenario Jan 2006 – Dec 2006 Vol II: Sedimentshed Jan 2007 - 2009 Define Sediment Sheds 2006 - 2007 Delineate Sediment Shed Determine Budgets 2007 - 2009 Support for Scenarios to restore SAV 2008 - 2009 Expanding on compilation of menu of sediment BMP present - 2009 practices and benefits

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