Nearly 30 scenarios completed for NAB and CBP over a years effort Report on application of CBEMP in preparation October time frame for draft Targeted management scenarios in progress Dredging remove 3 ID: 271087
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Slide1
Status
Nearly 30 scenarios completed for NAB and CBP over a year’s effort.
Report on application of CBEMP in preparation. October time frame for draft.
Targeted management scenarios in progress:
Dredging, remove 3
mcy
. Completed.
Dredging, remove 3
mcy
with sediment bypass. Mid-September.
Dredging, remove 31
mcy
, equivalent to 1996 bathymetry. Completed. Slide2
Scenario Procedure
The CBEMP is run for 1991 – 2001.
Today’s runs are based on Chesapeake Bay TMDL loadings.
Loads from a major scour event in January 1996 are added to the WSM loads.
Scour is computed by ADH applied to 2008 – 2011 hydrology including TS Lee. We obtain 1996 scour by a scaling procedure.
Nutrient composition of solids is based on observations during TS Lee.Slide3
Conceptual Model of Sediment Movement through Conowingo Reservoir
Sediment and nutrient releases are event-oriented.
WIPS decrease sediment loads. Also decrease deposition.
Sedimentation rate is largely independent of bathymetry.
Scour is strongly dependent on bathymetry.
Erosion event increases depth, diminishes subsequent erosion events.
Water Column
Bed Sediments
Conowingo
Dam
Upstream Reservoirs and WatershedSlide4
1996 Scour Loads for Three BathymetriesSlide5
Model Results
We’re going to concentrate on difference plots.
Dredging 3
mcy
(LSWRA28) – TMDL with existing bathymetry (LSRWA21).
Dredging 31
mcy
(LSRWA13) – TMDL with equilibrium bathymetry (LSWRA19).Slide6
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide7
Dredge 3 mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide8
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide9
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide10
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide11
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide12
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide13
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide14
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide15
Dredge 3
mcy
Dredge 31
mcy
Decrease Increase
Decrease IncreaseSlide16
Conclusions
Dredging 3
mcy
will improve summer-average bottom DO in the deep trench of the bay, Potomac River, and Baltimore Harbor by 0.02 to 0.04 mg/L based on a 1996 scour event.
Dredging
31
mcy
will improve summer-average bottom DO in the deep trench of the bay, Potomac River, and Baltimore Harbor by 0.04
to 0.06 mg/L based on a 1996 scour event.Slide17
Conclusions
Dredging 3
mcy
will reduce SAV growing-season chlorophyll by 0.02 to 0.05 in a large expanse of the bay, extending from Baltimore harbor past the mouth of the Potomac River, based on a 1996 scour event.
The magnitude of chlorophyll reduction from dredging 31
mcy
is comparable to dredging 3 mcy
, based on a 1996 scour event. The improvement is more extensive and prolonged, however.Slide18
Conclusions
Improvements in SAV growing-season light attenuation obtained by dredging are limited, generally less than 0.01 / m.
These results are influenced by the timing of the scour event, January 1996. Most solids have settled out by the subsequent SAV growing season.