1. Marjorie Friedrichs, Raleigh Hood and Aaron Bever
Comparison of Shallow-water Models for Use in Supporting Chesapeake Bay Management Decision-making
Marjorie Friedrichs, Raleigh Hood and Aaron Bever
Model Comparison Team
SCHISM team
Joseph Zhang
Harry Wang
ROMS-GL team
Dick Zimmerman
John Klinck
Chuck Gallegos
Victoria Hill
Mike Dinniman
ROMS-RCA team
Jeremy Testa
Damian Brady
Ming Li
FVCOM & CH3D team
Richard Tian
Ping Wang
Advisory Team:
Lewis Linker
Carl Cerco
Larry Sanford
Kevin Sellner

2. Shallow Water Multiple Model Effort
Chesapeake Bay
Shallow Water Multiple Model Effort
Why focus on the shallow waters of the Chesapeake Bay?
This is where we have seen degradation of water quality
This is where we are likely to see early responses to management actions
Why do we need improved shallow water models?
We depend on models to assess the impacts of alternative management strategies
Current models (e.g., CH3D) don’t resolve shallow waters very well.
Why do we need multiple models of these waters?
To increase scientific, management, and stakeholder confidence in the tools used to support and inform partnership collaborative decision making.

3. Challenges of Modeling Shallow Waters
Challenging waters to model!
Complex linkages between shallows & land, sediment and open Bay waters
Processes vary on small time & space scales, requiring high resolution models
Systems respond strongly to distant forcing: multiple spatial/temporal scales

4. Outline Study site: Chester River tributary
Cruise and continuous monitoring data
Four participating models
Similarities (forcing) and differences (grids)
Model performance:
hydrodynamics (T, S)
water quality (DO, chl, TSM)
Sensitivity experiments
Outer Boundary Conditions (OBC)
Freshwater discharge
Summary
TSM = Total suspended matter = Total Suspended Solids = TSS

5. Study Site: Chester River
Chesapeake Bay
Study Site:
Chester River
Study site location
Chester River

6. Observations: 2003-2006 A CHE0348 B XIH0077 C XHH4916
ET4.1
B XIH0077
= biweekly
cruise data
A, B, C = continuous
moored data
Data available. Today we will be showing results only from 2003, since this is the only year that we have results from all the models.
C XHH4916
= CBP WQM
data
ET4.2
salinity, temperature, oxygen, chlorophyll, TSM

7. Horizontal resolution
Participating models
All models use consistent winds, boundary conditions, freshwater & nutrient discharge
Model grids differ considerably
Participating model
Horizontal resolution
Horizontal
grid
Vertical
CH3D-ICM*
low
structured
z-grid
FVCOM-ICM
medium
triangular
sigma
ROMS-RCA
high
SCHISM-ICM
hybrid
*CH3D is the regulatory model currently used for management decisions in the Chesapeake Bay
*CH3D-ICM is the regulatory model currently used by the CBP for management decisions in the Chesapeake Bay

8. CH3D Low res. 190 pts FVCOM Medium res. 8349 pts SCHISM Medium res.
ROMS
High res.
38432 pts
Note that FVCOM has more resolution along coastline and SCHISM has more resolution in main channel

9. Channel depths also differ among models
Bottom Depth [m]
Note that we are going to show lots of plots that look like this – transects from the Chester River mouth to upstream.
data
Bay
upstream
SCHISM channel depths closely follow DEM; FVCOM & CH3D-ICM are shallower.

10. Simulation Experiments
Three simulations for hydrodynamics (S, T) and water quality (chl, DO,TSM):
Base Case (CH3D OBC)
10% reduction in watershed inflow
SCHISM Outer Boundary Condition (OBC) in place of CH3D OBC

11. Simulation Experiments
Three simulations for hydrodynamics (S, T) and water quality (chl, DO,TSM):
Base Case (CH3D OBC)
10% reduction in watershed inflow
SCHISM Outer Boundary Condition (OBC) in place of CH3D OBC
Can our shallow water models reproduce observed hydrodynamics and water quality in the Chester River?
How sensitive are the simulations to input fluxes from the rivers and at the Chester mouth?

12. Part 1: Hydrodynamic (T & S) multiple model comparisons
Color scheme!

13. Multiple model comparison:
temperature
Generally models simulate T well throughout transect, regardless of model resolution
Surface Temperature
All models get T
July 15, 2003 – Sep 15, 2003
Sep 15, 2003
– Nov 15, 2003
Bay
upstream
Bay
upstream

14. Multiple model comparison:
Surface Salinity
Summer 2003
Fall 2003
Main point is ICM overestimates S in upstream portions of river; only works for the first 40km into the Chester.
Bay
upstream
Bay
upstream
ICM overestimates surface salinity in upper half of Chester
FVCOM is always saltier than SCHISM
Summer: ROMS performs best; Fall: FVCOM and SCHISM perform best
results (not shown) indicate that ICM does best in lower Chester, SCHISM does best in mid-Chester and FVCOM does best in upper Chester

15. Multiple model comparison: Salinity Stratification
Summer 2003
Stratification = bottom S minus surface S
Bay
upstream
ICM overestimates stratification in the channel and upstream
ROMS & SCHISM often underestimate stratification
FVCOM does best?

16. Multiple model comparison: S Stratification in Channel
Summer 2003
Stratification = bottom S minus surface S
We don’t have data all along the channel, but we can still compare the models and see that ICM has much higher stratification in the channel than the high resolution models. In reality, stratification is probably less than ICM and greater than the high res models.
ICM generates much more stratification throughout Chester

17. Part 2: Water Quality (Chl, DO, TSM) multiple model comparisons
(A work in progress!!)
(New – under development!)
Color scheme – note that these results are preliminary! Especially the new ICM results
No results for ROMS yet.

18. Multiple model comparison:
Surface Chlorophyll
Summer 2003
TMDL WQSTM
(phase 5.3.2)
“new” WQSTM
(work in progress)
Surface Chl (ug/L)
Bay
upstream
Lots of variability between models
SCHISM produces low Chl near ~50km (improved coastline and bathymetry -> longer residence time)

19. Multiple model comparison: Surface Total Suspended Matter
Summer 2003
TMDL WQSTM
(phase 5.3.2)
“new” WQSTM
(work in progress)
Surface Total Suspended Matter (mg/L)
Bay
upstream
Models generally underestimate suspended matter
“New” WQSTM represents improvement throughout most of Chester

20. Multiple model comparison:
Bottom DO
Summer 2003
TMDL WQSTM
(phase 5.3.2)
“new” WQSTM
(work in progress)
Bottom DO (mg/L)
Bay
upstream
High resolution models show much improved bottom DO in upper Chester and at Chester mouth
ICM models often show too much bottom DO depletion (too much stratification?)

21. Multiple model comparison:
Surface DO
Summer 2003
TMDL WQSTM
(phase 5.3.2)
“new” WQSTM
(work in progress)
Surface DO (mg/L)
Bay
upstream
Models perform more similarly for surface DO
Surface DO in upper Chester for “new” WQSTM needs investigation

22. Sensitivity Experiments
 10% decrease in freshwater inflow
 SCHISM vs. CH3D Outer Boundary Conditions

23. Multiple model comparison: Effect of changing OBC on surface salinity
Summer 2003
Tidally-averaged surface salinity (PSU)
Bay
upstream
Effect of change in OBC is felt 45 km up the tributary

24. Multiple model comparison: Effect of 10% change in freshwater input
Summer 2003
Tidally-averaged surface salinity (PSU)
Bay
upstream
Effect of 10% change in freshwater input on salinity is negligible
10% change in nutrient inputs has negligible effect on water quality too (not shown)

25. Summary Models simulate hydrodynamics relatively well
All models reproduce temperature well
Low resolution CBP model only works ~40km into the tributary; higher resolution models are needed to reproduce upstream salinity (~0psu) and weak stratification
Models are very sensitive to bathymetry
Water quality is more challenging to simulate
Very preliminary results indicate that:
High resolution models produce much better DO in
upstream Chester (and at mouth)
High resolution bathymetry and coastline affects residence time which may improve chlorophyll simulation
All models underestimate TSM; “New” WQSTM simulation seems to produce higher (more realistic) values
Sensitivity experiments:
10% reduction of freshwater/nutrient inflow has negligible effect on water quality & hydrodynamics (compared to changing models)
Change in salinity OBC affects salinity ~45km up Chester River

26. Future Work Continue work on 2003-2006 base case comparisons
(focusing on water quality)
Examine sensitivity to alternate bathymetry
Use new FEMA bathymetry
Nutrient reduction scenarios ( )
Historically high loads – “1985”
Lowest loads ever seen – “all forest” = 90% reduction
2025 reductions – “TMDL” = 50% reduction
We have seen that models produce very different water quality results in the shallow Chester River.
Do the models produce equally different improvements resulting from nutrient reductions?