Update on Chesapeake Bay Airshed and Water Quality Modeling

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• Update on Chesapeake Bay Airshed and Water
  Quality Modeling

Briefing to the Water Resources Technical
Committee July 10, 2008 Presented by Steve
Bieber Metropolitan Washington Council of
Governments
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Overview

• CBP Modeling Framework
• Chesapeake Bay Airshed Model
• Chesapeake Bay Water Quality Model
• Potomac Estuary Modeling Effort

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Previous Modeling Structure
Overview of the Assessment Tools
A Regression Model of 15 monitoring sites over 10
simulation years. Changes in air quality
management simulated with the Regional Acid
Deposition Model (RADM) with a domain covering
the Eastern states and limited grid capabilities
Watershed Model Phase 4.3 94 model segments, 9
land uses, 20 calibration sites, 10 simulation
years, fixed annual land use
Chesapeake Bay Water Quality Model Hydrodynamic
Model, Sediment Benthic Model, and Submerged
Aquatic Vegetation, 10 simulation years, 13,000
model cells
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New CBP Modeling Structure
Overview of the Assessment Tools
Nitrate and ammonia deposition from improved
Daily Nitrate and Ammonium Concentration Models
using 35 monitoring stations over 18 simulation
years. Adjustments to deposition from
Models-3/Community Multi-scale Air Quality
(CMAQ) Modeling System
Phase 5 Watershed Model Year-to-year changes in
land use and BMPs 899 segments 24 land uses
296 calibration stations 18 simulation years
sophisticated calibration procedures calibration
demonstrably better in quality and scale
Chesapeake Bay Estuary Model Detailed sediment
input Wave model for resuspension, Full sediment
transport Filter feeder simulation Simulation
of Potomac algal blooms 54,000 model cells 18
simulation years
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Why is the CBP Upgrading their Modeling Tools?

• The Tributary Strategy nutrient and sediment
  reductions are estimated to achieve the DO and
  chlorophyll water quality standards, but not the
  clarity standard.
• The upgraded water quality model will allow the
  CBP to complete a suspended sediment budget from
  all sources for the first time, and will provide
  a sound foundation for sediment allocation
  decision-making.
• fall lines of major rivers
• local watershed inputs
• shore erosion and
• sediment resuspension.

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Why is the CBP Upgrading their Modeling Tools?

• Develop a Bay watershed TMDL
• Subject to the terms of consent decrees in
  Virginia and the District of Columbia and a
  Maryland/EPA MOU.
• EPA and the Bay states must complete those TMDLs
  by May 1, 2011.
• The Chesapeake Bay and its tidal tributaries
  (including the Potomac) were part of the lawsuit
  settlement.
• Reevaluate and potentially change allocations for
  nitrogen, phosphorus, and sediment.

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Bay Water Quality Model

• The Estuary Model, commonly referred to as the
  Water Quality Model, examines the effects of the
  loads generated by the Watershed Model on Bay
  water quality.
• The Estuary Model is built on two submodels the
  hydrodynamic submodel and the water quality
  submodel.

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Key Improvements

• Potomac Upgrade
• Better spatial scale to simulate water quality
  responses to management efforts at a local scale.
• Better simulation of algal species and their
  impacts on water quality.
• Sediment and pH-alkalinity dynamics critical to
  the Potomac and Anacostia have been modeled.

• Chesapeake Bay Upgrade
• Sediment types and physical processes affecting
  sediment loads will be incorporated.
• Water quality responses to sediment control
  actions will be more accurately reflected.
• Expert quantification of bank loads. Time
  variable input based on erosion events.

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Shoreline Sediment Inputs are Estimated To Be
About Equal to Watershed Inputs Estimated Tidal
Sediment Inputs for 1990
Shoreline inputs Watershed
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Observed and simulated hourly wave heights at
Poplar Island between October 27 to November 10,
1995. The wave simulation is applied to every
shallow water cell in the WQSTM.
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The Bay Model Provides Simulation of the Effect
Oyster and Menhaden Filter Feeders Have in
Reducing Suspended Sediment Loads

• The Water Quality Model will incorporate the
  effect of oyster and menhaden filter feeders as
  well as four other generalized filter feeder
  groups to provide assessments of
• The synergy between health living resources and
  improved clarity conditions, such as healthy SAV
  beds reducing sediment resuspension.
• The contribution filter feeders play in reducing
  suspended sediment and algae, and improving water
  clarity in shallow waters.

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The Bay Model will allow a substantial
reassessment of the table below which shows
nonachievement of the clarity water quality
standard in most of the Bay even under full
application of the Tributary Strategies.
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A decision will need to be made on the role
filter feeders play in attaining the SAV/clarity
water quality standard
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Key Improvements to the Potomac Model

• New coding that relates pH to nutrient loading,
  primary production, and other factors in the
  Potomac portion of the Bay model has also been
  implemented.
• Improvements to the representation of algal
  speciation in the Potomac portion of the Bay
  model will be completed by the end of 2008.
• More detailed segmentation and updated
  calibration to Potomac data.
• A new estuarine phosphorus model has been
  developed, which is key to predicting frequency
  and severity of harmful algae blooms.

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New Potomac Model Segmentation
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Bay Water Quality Model Status

• The revised model is essentially complete.
• The most critical need is to finalize
  hydrodynamics based on Watershed Model flows. It
  is not possible to calibrate tidal fresh waters
  or small tributaries without these flows.
• July 2008 is the deadline for model completion.
• Scoping management scenarios are scheduled to
  begin then.

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CMAQ Airshed Model

• CMAQ The Community Multi-scale Air Quality
  (CMAQ) modeling system
• Replaces Regional Acid Deposition Model (RADM).
• Provides estimates of nitrogen deposition
  resulting from changes in precursor emissions
  from utility, mobile, and industrial sources due
  to management actions or growth.
• Provides estimates of the influence of source
  loads from one region on deposition in other
  regions.

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Regression Model Estimated Atmospheric Deposition
NH4 Wet Deposition (kg/ha) Mean annual
(1985-2001)
NO3- Wet Deposition (kg/ha) Mean annual
(1985-2001)
Estimates produced by applying daily ammonium and
nitrate concentration model to grids of estimated
daily precipitation from the National Weather
Service Climate Prediction Centers U.S. Daily
Precipitation Analyses.
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CMAQ Scenarios to be run by the CBP

• Current funding allows for about ten CMAQ
  scenarios. The following list of key air
  scenarios have been identified by the CBP
  Modeling Subcommittee
• 2015 CAIR (all current national air regulations
  included).
• 2020 CAIR (all current national air regulations
  included).
• 2020 CAIR with additional, aggressive utility or
  electric generating units (EGU) controls.
• 2030 CAIR with aggressive EGU controls.
• 2020 CAIR with additional, aggressive EGU,
  industry, and mobile source controls (to
  approximate a Limit of Technology future).
• Allocation of Bay State responsibility to
  watershed deposition for PA, VA, MD, DE, WV, NY
  (each State requires a separate scenario).

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Any questions?