Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 1 September 24 , 2010 

### Appendix P

. Setting the SAV/Water Clarity Criteria Based Sediment Allocations



### Introduction

The scale of the Chesapeake Bay Program partnership’s models extend from the extreme of the continental scale of the Community Multiscale Air Quality Bay Airshed Model and watershed

wide scale of the Phase 5.3 Bay Watershed Model to the other extreme of th e narrow ribbon of shallow water adjacent to the Bay’s over 11,000 miles of tidal shoreline. The ribbon of shallow water of 2 meters or less in depth is the region where the jurisdictions’ SAV/water clarity criteria are applied to assess protection of the shallow

- water bay grass designated use. This region of a convoluted shoreline is spatially and temporally more heterogeneous than the rest of the Chesapeake Bay Water Quality and Sediment Transport Model domain covering the open and contiguous waters of t he Chesapeake. Episodic loads from shoreline erosion, resuspension and watershed inputs all transit this narrow band of land and water interface.

The challenge of assessing SAV and water clarity criteria at these scales has only recently been taken up by the Chesapeake Bay Program partnerships in the past five years. Monitoring, modeling and research in these shallow

- water systems is in its relative infancy compared to the more mature environmental science surrounding dissolved oxygen in eutrophic estuari ne ecosystems. In addition, while moving toward these finer scales, the retention of system

- wide representation of loading sources, boundary conditions must be preserved.



### Key Model Refinements in the Simulation of Water Clarity

- SAV

The Bay Water Quality M odel used in setting the 2003 Chesapeake Bay nutrient and sediment allocations (Cerco and Noel, 2004; Linker et al., 2000; Cerco et al., 2004) was refined to include full sediment transport of four classes of inert particulates approximating the settling a nd transport behavior of sand, silt, clay, and a sediment fraction of slowly settling clay. The resulting Chesapeake Bay Water Quality and Sediment Transport Model was capable of resolving turbidity maximum zones in the Bay and appropriately setting the b oundary conditions for the shallow water region of the SAV/water clarity criteria. Resuspension of sediment was generated by currents, both tidal and residual, and by waves. Additional refinements included high resolution at half meter depths of the shal low water SAV grow areas (Figure P

- 1), a advanced optics model of underwater light attenuation, improvements to the SAV simulation,

and refinements to shoreline erosion. These model refinements and additions are shown schematically in Figure P

- 2.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 2 September 24 , 2010 Source: Carl Cerco, 2009. Presentation at CERF Conference.

Figure P

- 1. A schematic of the half meter depths of the SAV sub

- grid unit cells mapped to the WQSTM grid cell which provides light attenuation and other model state variables the SAV growth cell.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 3 September 24 , 2010 Source: Cerco 2009.

Figure P

- 2. A schematic of the Water Quality and Sediment Transport Model refinements applied for the simulation of the SAV/water clarity water quality standard.



### Refinements to Shore Erosion Estimates

Consistent temporal and spatial data for erosion rates, bank heights, shoreline protection, and sediment type were needed for the entire Chesapeake Bay to better estimate the role of shoreline

erosion in the overall sediment budget ( Hennessee et al., 2006; Hardaway et al., 1992). The refined shoreline sediment load estimates included both bank load (e.g. fastland e rosion) and

nearshore e rosion ( Figure P

- 3 ) . S patially explicit erosion rates by ―reach‖ that allowed for

variance with bank height, shoreline orientation, and sediment composition were calculated.

Best estimates of the actual shoreline lengths were used , including reduced erosion rates for

enclosed minor inlets where reduced wave and current erosion would be expected. The different

shoreline l oading estimates were the n incorporated into the appropriate Water Quality and Sediment Transport Model cells

.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 4 September 24 , 2010 Figure P

- 3. Example of fastland and nearshore components of the shoreline sediment loads.

Source: Hopkins and Halka (2007).

For unprotected shorelines the shoreline erosion computation was as follows:

- Eroded Fastland Volume = Shoreline Len gth x Elevation x Erosion Rate/D ay

- Total Eroded (Fastland + Nearshore) = Fastland Mass/0.65

- Eroded Silt/Clay Mass = Total Eroded Volume x Bulk Density x Silt Clay %

- Different silt/clay proportions for bank and marsh sources ( Applied to Maryland portion

tidal shoreline only)

- Different silt/clay proportions for north and south banks of each major river (Applied to Virginia tidal shoreline only)

For protected shoreli nes everywhere the assumption was that fastland erosion was eliminated

, but that nearshore erosion continued. Nearshore erosion was estimated for protected shore lines by using adjacent or nearby unprotected shoreline.



### Simulation of SAV

The unit SAV simulation c omputes SAV density (mass/unit area) as a function of irradiance and

nutrients for SAV shoot and roots as shown in Figure P

- 4

. Irradiance and epiphytes are calculated separately and the SAV model fully i nteracts with water column and bed sediments (see Figure P

- 2).Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 5 September 24 , 2010 Source: Cerco 2009.

Figure P

- 4. The Chesapeake Bay Water Quality and Sediment Transport Model’s SAV unit model.

The current simulation of SAV considers light to be the sole determinant of SAV abundance , but

other factors such as composition of bottom substrate, SAV community structure and seed bank availability are significant. These factors not explicitly simulated in the Water Quality and Sediment Transport Model but are accounted for via an empirical ―probabili ty of suc cess ‖

.

The probability function was empirically set to best represent SAV biomass under current nutrient loads and adjusted to improve the probability of SAV growth under conditions that are more representative of mid

- 1900s Chesapeake nutrient loads (Hagy et al., 2004). The use of the empirically set probability function for SAV allowed appropriate SAV levels to best simulate water clarity, which was solely used to assess the water clarity criteria. Moving forward, in the next generation of th e Bay Model the probability function will be replaced with salient first principal forcing functions.



### Process of Assessment of the Water Clarity

- SAV Criteria

There are three methods to assess attainment of the Bay jurisdictions’ SAV/water clarity water

q uality standards. Either one of the following three methods can be used to determine whether the SAV and water clarity goal is achieved. The SAV/water clarity criteria assessment applied to the Bay Water Quality and Sediment Transport Model scenario outp ut is always on the combined SAV and water clarity criteria assessment method.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 6 September 24 , 2010 Using only acres of SAV coverage : A segment attains if the SAV acreage of single best year in the segment is met in the preceding 3 years (including the current year) (USEPA 2003b).

Using only water clarity acres : A segment attains if the single best year water clarity acreage in the preceding 3 years exceeds 2.5 times the SAV restoration acreage. The water clarity acres for a year are assessed based on the arithmetic mean o f monthly water clarity in the criteria months that meets the water clarity criteria (see Table 3

- 5) (USEPA 2007).

Using combined SAV and water clarity achievement : This method considers both the achieved SAV acreage and water clarity acre in a segment . In the assessment, the water clarity acre can

be converted to an SAV

- equivalent acre by dividing 2.5 of the water clarity acre, which will be credited along with the SAV coverage estimated by regression model.

Estimation of SAV/Water Clarity in a WQS TM L oading Scenario

In the combined SAV and water clarity assessment , both the SAV acres and water clarity acres needs to be estimated in load reduction scenarios. The light extinction coefficient, Ke, is the metric used to measure water clarity. The Ke in a load reduction scenario is estimated using the Chesapeake Bay W ater Quality and Sediment Transport Model (WQSTM). The SAV area in a load reduction scenario is estimated from a regression model.

Ke A ssessment by the WQSTM The simulated Ke in the WQSTM is based on the amounts of simulated clay, silt, sand, organic

pa rticulates, and dissolved organic matters in a model cell. Since the simulated Ke is an imperfect representation of the observed Ke, a data correction method is used to obtain adjusted scenarioed Ke in each shallow cell for the target loading scenario. W hile several more sophisticated data correction methods were tried a simple proportional adjustment of the shallow water Ke to the nearest observed water quality monitoring station was found to provide the best

shallow water data correction as determined b y independent shallow water monitoring sites.

The shallow water bay grass designated

- use habitat is considered located between the 2

- meter depth contour and the adjacent shoreline. A segment consists of Bay Water Quality and Sediment Transport Model c ells. Due to inconsistency between the model cell boundary and the

2

- meter contour area, EPA remapped and extended the model cells to cover tidal water up to the shoreline, and subdivided the area into 0

- 0.5 m, 0.5

- 1.0 m, 1.0

- 1.5m and 1.5

- 2.0m depths. For

each half

- meter contour area we apply corresponding Ke criteria (see Section 3, Table 3

- 5).

Note that the areas of defined no

- growth zone are excluded from the cell/segment area in the

assessment.

Credit of SAV A rea Based on Observed SAV Area

The projected SAV acreage in a target scenario is based on a regression of observed SAV in the Bay segments which, together, compose the major tributaries and the nutrient and sediment loads from each corresponding land basin (i.e., the major sub

- watershed) of the Chesapeake Bay watershed which provides loads to those collective set of segments (Table P

- 1).Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 7 September 24 , 2010 Through the Baywide SAV aerial survey, the partners have access to annual SAV distribution and abundance data for almost every year in the past 30 year s. The attached Excel file, Appendix P SAV Coverage 1971

- 2009 Spreadsheet.xls, shows observed SAV for Bay segments

in 1971

- 2009. The observed SAV areas from 102 segments are aggregated into SAV areas for the 8 tidal basins for each year.

TN, TP, a nd TSS loads from the 8 major basins are estimated from the Phase 5.3 Chesapeake Bay Watershed Model’s progress scenarios under years 1985, 1987, 1992, 1998, 2002, 2005, 2007 and 2009 management conditions.

Linear regression of SAV versus load of TN or TP or TSS, respectively, is conducted for each basin, yields:

SAV = m Load + b

where, coefficient m is slope and b is intercept from the linear regression. The results are presented in Table P

- 1.

Table P

- 1 . Results of linear regression of SAV versus TN, TP

, and TSS loads for 8 major basins

. Basin Component R2 Slope Intercept Susq uehanna TN 0.8983

- 4.16E+02 6.43E+04 Susquehanna TS 0.8049

- 2.77E+01 9.11E+04 Susquehanna TP 0.6847

- 8.54E+03 5.12E+04

Pot omac TN 0.9068

- 2.85E+02 2.82E+04

Potomac TS 0.8769

- 2.13E+01 6.83E+04

Potomac TP 0.8449

- 1.28E+04 7.04E+04

York TN 0.0468 1.09E+03 1.79E+03

York TS 0.8948

- 8.81E+01 2.65E+04

York TP 0.7539

- 9.38E+03 1.79E+04

Eastern Shore TN 0.1615

- 1.87E+03 7.69E+04

East ern Shore TS 0.5769

- 2.29E+02 1.20E+05

Eastern Shore TP 0.3518

- 2.18E+04 8.09E+04
Rappahannock TN 0.5900

- 6.93E+02 6.57E+03
Rappahannock TS 0.5425

- 8.42E+00 7.88E+03
Rap pahannock TP 0.6609

- 5.44E+03 7.68E+03

James TN 0.9624

- 8.54E+00 3.81E+02

James TS 0.8763

- 3.59E

- 01 5.89E+02

James TP 0.7467

- 3.27E+01 2.21E+02

MD Western Shore TN 0.5437

- 2.35E+02 6.11E+03

MD West ern Shore TS 0.7106

- 4.79E+01 1.49E+04

MD Western Shore TP 0.5361

- 3.50E+03 5.17E+03

Patux ent TN 0.5940

- 2.02E+02 9.31E+02

Patuxent TS 0.5693

- 3.66E+00 7.66E+02

Patuxent TP 0.3253

- 1.38E+03 6.89E+02Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 8 September 24 , 2010 For individual basin, we use the regression of SAV with Load component TN or TP or TSS, which has the highest R2 of regression.

The Bay TMDL’s critical period of 1993

- 1995 is our reference for the TMDL. The load in the reference year for each basin can be estimated from Bay Watershed Model calibration, and the corresponding SAV is known from the observation. They also have the relationship:

SAV_ref = m Load_ref + b.

A projected SAV of the basin in a load reduction scenario is:

Proj_SAV = m Proj_load + b

Therefore, Proj_SAV

– SAV_ref = m (Proj_load

– Load_ref).

We can calculate the ratio:

Rate = Proj_SAV / SAV_ref = (Proj_SAV

– SAV_ref) / SAV_ref + 1 = m (Pro j_load

– Load_ref) / SAV_ref + 1 = (m (Proj_load

– Load_ref) + SAV_ref ) / SAV_ref

Thus, the projected SAV of this basin for the target loading scenario can also be estimated by:

Proj_SAV = Rate * SAV_ref.

We assume that the rate calculated fr om a basin is applicable to individual segments in this basin. We use this rate to calculated projected SAV in the reference hydrology year for each segment in this basin:

Proj_SAV (seg) = Rate * SAV_ref (seg).

The projected SAV in segments is us ed for SAV credit in the assessment.

Assessing Attainment of the SAV/Water Clarity Standard Before the assessment, EPA converted the SAV restoration goal acreage (see Section 3, Table 3.6) with a factor of 2.5 to establish the water clarity acre for ea ch Bay segment.

For individual months, EPA compared the monthly average Ke in a cell at 4

- depth

- interval areas (0

- 0.5, 0.5

- 1.0, 1.0

- 1.5, and 1.5

- 2.0) with the applicable water clarity criterion for the 4 application depths (i.e., 0.5, 1.0, 1.5, and 2.0 ), respectively. If it meets the criterion for that depth, the area is accounted. Adding the area achieving the water clarity criterion for each depth of all cells in the segment, yield the total area achieving the water clarity criterion for the month. Averaging (using arithmetic mean) the monthly achieving areas in the criteria months (i.e., SAV growing seasons

— see Section 3, Table 3.5), we get the water clarity acres for that year for each segment. If the water clarity acre is smaller than the SAV ar ea, we use 2.5 of the assessed SAV area as the total water clarity acre from this combined SAV/water clarity assessment in the year.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 9 September 24 , 2010 If the water clarity acre is greater than the SAV area, we credit 1.5 of the assessed SAV area, into

the total water clari ty acre of this year for this combined SAV/water clarity assessment.

Finally, the water clarity acre in single best year of the 3 consecutive assessment years (i.e.,

1993

- 1995 hydrology years) is regarded as the achieved water clarity acreage. If th e achieved water clarity acre was greater than the water clarity acre goal (i.e., 2.5 times SAV acre goal), then the combined SAV/water clarity criteria were projected to be achieved in this segment under model loading scenario. Otherwise, i.e., the achie ved water clarity acre is less than the water clarity acre goal, a percent violation is calculated:

100 * (water clarity acre goal

– water clarity acre) / water clarity acre goal.



### References

Cerco, C

. F.

, M

. Noel, and L

. Linker, 2004. Managing for water clarity in Chesapeake Bay. ASCE Journal of Environmental Engineering 130:6, pp1

- 12.

Cerco, C

. F. and M

. R. Noel, 2004. The 2002 Chesapeake Bay Eutrophication Model U.S. EPA Chesapeake Bay Program Office 349 pages, July 2004 , Annapolis, MD http://www.chesapeakebay.net/pubs/subcommittee/mdsc/doc 2002_Eutrophication_Model.pdf

Hagy, J.D., W.R. Boynton, C.W. Keef e, and K.V. Wood . 2004. Hypoxia in Chesapeake Bay,

1950

– 2001: long

- term change in relation to nutrient loading and river flow. Estuaries 27:

634

– 658.

Hardaway, C. S.; Thomas, G. R.; Glover, J. B.; Smithson, J. B.; Berman, M. R.; Kenne, A. K.

1992. Bank Erosion Study

. Spe cial Report in Applied Marine Science and Ocean Engineering Number 319. Virginia Institute of Marine Science 73 pages. April, 1992 Gloucester Point, VA

Hennessee, L

., K

. Offerman, and J

. Halka, 2006. Suspended Sediment Load Contributed by

Shore Erosion Chesapeake Bay, Maryland. M aryland G eological S urvey . C oastal and

E stuarine G eology F ile R eport N o . 06

- 03

. June 2006. 21 pages. Baltimore, MD

.

Hopkins, K. and J. Halka. 2007. Developing Shoreline Sediment Erosion Estimates for the Chesapeake Bay. C oast al and Estuarine Research Federation 2007 Conference.

Linker, L

. C.

, G.W. Shenk, R.L. Dennis, and J.S. Sweeney

. 2000

. Cross

- Media Models of the Chesapeake Bay Watershed and Airshed. Water Quality and Ecosystem Modeling. 1:1

- 4 pp 91

- 122 March

- December, 20 00.

U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries

.Draft Appendix P

– Chesapeake Bay TMDL for Nutrients and Sediment

P

- 10 September 24 , 2010 EPA 903

- R

- 03

- 002. U.S. Environmental Protection Agency, Region 3, Chesa peake Bay Program Office, Annapolis, MD.

U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identification of Chesapeake Bay Designated Uses and Attainability . EPA 903

- R

- 03

- 004. U.S. Environmental Protection Agency, Region 3, Chesa peake Bay Program Office, Annapolis, MD.

U.S. Environmental Protection Agency. 2007. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries

— 2007 Addendum . EPA 903

- R

- 07

- 003. CBP/TRS 285

- 07. U.S. Environmental Protection Agency, Region 3, Chesapeake Bay Program Office, Annapolis, MD.

U.S. Environmental Protection Agency. 2008. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapea ke Bay and Its Tidal Tributaries

– 2008 Technical Support for Criteria Assessment Protocols Addendum . EPA 903

- R

- 08

- 001.

CBP/TRS 290

- 08. U.S. Environmental Protection Agency, Region 3, Chesapeake Bay Program Office, Annapolis, MD.