noaa National Oceanic and Atmospheric Administration

U.S. DEPARTMENT OF COMMERCE

National Ocean Service

Center for Operational Oceanographic Products and Services

NOAA Technical Report NOS CO-OPS 076

Water Level Variations at Poplar Island, MD

Silver Spring, Maryland

April 2015
Center for Operational Oceanographic Products and Services

National Ocean Service

National Oceanic and Atmospheric Administration

U.S. Department of Commerce

The National Ocean Service (NOS) Center for Operational Oceanographic Products and Services 

(CO-OPS) provides the National infrastructure, science, and technical expertise to collect and 

distribute observations and predictions of water levels and currents to ensure safe, efficient and 

environmentally sound maritime commerce. The Center provides the set of water level and tidal 

current products required to support NOS’ Strategic Plan mission requirements, and to assist in 

providing operational oceanographic data/products required by NOAA’s other Strategic Plan 

themes. For example, CO-OPS provides data and products required by the National Weather 

Service to meet its flood and tsunami warning responsibilities. The Center manages the National 

Water Level Observation Network (NWLON), a national network of Physical Oceanographic 

Real-Time Systems (PORTS®) in major U. S. harbors, and the National Current Observation 

Program consisting of current surveys in near shore and coastal areas utilizing bottom mounted 

platforms, subsurface buoys, horizontal sensors and quick response real time buoys. The Center 

establishes standards for the collection and processing of water level and current data; collects 

and documents user requirements which serve as the foundation for all resulting program 

activities; designs new and/or improved oceanographic observing systems; designs software to 

improve CO-OPS’ data processing capabilities; maintains and operates oceanographic observing 

systems; performs operational data analysis/quality control; and produces/disseminates 

oceanographic products. 
NOAA Technical Report NOS CO-OPS 076

Water Level Variations at Poplar Island, MD

Jena Kent

April 2015

U.S. DEPARTMENT OF COMMERCE

Penny Pritzker, Secretary

National Oceanic and Atmospheric Administration 

Dr. Kathryn Sullivan, NOAA Administrator and Under Secretary of 

Commerce for Oceans and Atmosphere

National Ocean Service

Dr. Russell Callender, Acting Assistant Administrator

Center for Operational Oceanographic Products and Services 

Richard Edwing, Director
ii

NOTICE

Mention of a commercial company or product does not constitute an 

endorsement by NOAA. Use of information from this publication for 

publicity or advertising purposes concerning proprietary products 

or the tests of such products is not authorized. 
iii

TABLE OF CONTENTS

NOTICE.......................................................................................................................................... ii

TABLE OF CONTENTS...............................................................................................................iii

INTRODUCTION .......................................................................................................................... 1

PROJECT INFORMATION........................................................................................................... 2

MONTHLY WATER LEVEL PROCESSING .............................................................................. 4

TIDAL DATUMS........................................................................................................................... 7

GEODETIC ELEVATION REFERENCES TO TIDAL DATUMS.............................................. 7

PREDICTED AND OBSERVED TIDE COMPARISON ............................................................. 9

FREQUENCY OF HIGH WATER ELEVATIONS AND DURATIONS OF INUNDATION ........ 11

RELATIONSHIP OF DURATION OF INUNDATION VS. ELEVATION ABOVE MEAN 

HIGH WATER DATUM.............................................................................................................. 14

COMPARISON OF MONTHLY MEANS .................................................................................. 17

LONG TERM SEA LEVEL TRENDS......................................................................................... 19

EXTREME WATER LEVELS AND EXCEEDANCE PROBABILITY.................................... 21

SUMMARY.................................................................................................................................. 27

ACKNOWLEDGEMENTS.......................................................................................................... 29

REFERENCES ............................................................................................................................. 29

APPENDIX 1. Benchmark Sheet ................................................................................................. 30

APPENDIX 2. Harmonic Constants from Poplar Island, MD...................................................... 35
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TABLE OF FIGURES

Figure 1. Site map displaying water level stations at U.S. Academy in Annapolis, MD and 

Poplar Island, MD. The inset depicts a more detailed image of Poplar Island.............................. 1

Figure 2. The benchmark network for station 8572271, Poplar Island, MD and a table of values 

for the initial, annual, and closing leveling in units of feet............................................................. 3

Figure 3. Monthly high and low tabulations for Poplar Island, January 2007............................... 4

Figure 4. Tabulated high and low, and monthly means for January, 2007. This tabulation shows 

the time and height of every high and low water level in relation to station datum (STND)......... 5

Figure 5. Tabulated hourly heights for January, 2007. This tabulation shows the hourly heights 

in relation to station datum (STND). .............................................................................................. 6

Figure 6. Accepted tidal datum elevations (in meters) for Poplar Island, MD, relative to station 

datum based on the 1983-2001 NTDE. Accepted ranges of tide, maximum and minimum 

observed water levels, highest and lowest astronomical tides, and Greenwich time intervals have 

also been calculated. Although not shown, NAVD88 was estimated to be 0.346 meters (1.135 

feet). ................................................................................................................................................ 8

Figure 7. Relationship of geodetic datum elevations and local mean sea level at Poplar Island... 9

Figure 8. Plot of Poplar Island, MD observed (blue) and predicted (red) water levels............... 10

Figure 9. Difference of Poplar Island, MD observed and predicted water levels (residual). ...... 10

Figure 10. Frequency of high water elevation relative to MHW at Poplar Island, MD on station 

datum............................................................................................................................................. 11

Figure 11. Frequency of high water elevation relative to MHW at Annapolis, MD on station 

datum............................................................................................................................................. 12

Figure 12. Frequency and duration of water at Poplar Island, MD above MHW on station datum.

....................................................................................................................................................... 13

Figure 13. Frequency and duration of water at Annapolis, MD above MHW on station datum. 14

Figure 14. Poplar Island, MD duration of inundation................................................................... 15

Figure 15. Annapolis, MD duration of inundation. ..................................................................... 16

Figure 16. Poplar Island, MD tide predictions and observed hourly water levels relative to 

MLLW during the Veteran’s Day Nor’easter............................................................................... 16
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Figure 17. Regional comparison of monthly MHW relative to 1983-2001 NTDE MHW datum.

....................................................................................................................................................... 17

Figure 18. Regional comparison of monthly MLLW relative to 1983-2001 NTDE MLLW 

datum............................................................................................................................................. 18

Figure 19. Regional comparison of monthly MSL relative to the 1983-2001 NTDE MSL datum.

....................................................................................................................................................... 19

Figure 20. Mean sea level trend for Annapolis, MD. .................................................................. 20

Figure 21. Mean sea level trend for Cambridge, MD.................................................................. 20

Figure 22. Exceedance probability for Annapolis, MD............................................................... 21

Figure 23. Exceedance probability for Cambridge, MD.............................................................. 22

Figure 24. Extreme water levels at Annapolis, MD..................................................................... 23

Figure 25. Annual exceedance probability curves for Annapolis, MD. ...................................... 24

Figure 26. Extreme water levels at Cambridge, MD. .................................................................. 25

Figure 27. Annual exceedance probability curves for Cambridge, MD. ..................................... 26
vi
1

INTRODUCTION

Poplar Island, once on the verge of disappearing due to sediment erosion and sea level rise, is 

today a national model for habitat restoration and the beneficial use of dredged material. Just off 

the Chesapeake Bay coastline, about 34 miles south of Baltimore in Talbot County, MD, Poplar 

Island is returning to its former size and will again serve an important ecological function while 

helping to ensure the economic vitality of the region.

The U.S. Army Corps of Engineers (USACE) are working in partnership with the Maryland Port 

Administration and other Federal and State agencies, to restore Poplar Island by using dredged 

material from the Baltimore Harbor and Channels Federal navigation projects. Approximately 

68 million cubic yards of dredged material will be placed to develop 737 acres of wetlands, 840 

acres of uplands, and 138 acres of open water embayment. The Poplar Island water level station

is located on the east coast of Poplar Island, and was established in 2006 through a partnership 

between NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS) and 

the Baltimore District, USACE (USACE, 2013).

The purpose of this report is to provide an analysis of water level data and tidal datums observed 

from Poplar Island, Maryland. For context, the analyses include comparisons with the nearby 

long-term water level station in Annapolis, Maryland and Cambridge, Maryland (Figure 1). This 

report includes comparative analyses of regional sea level trends, frequency and duration of 

inundation, and exceedance probabilities at these locations.

Figure 1. Site map displaying water level stations at U.S. Academy in Annapolis, MD and Poplar Island, MD. The inset depicts 

a more detailed image of Poplar Island. 
2

PROJECT INFORMATION

The Poplar Island, Maryland water level station was installed in October 2006 by the U.S. Army 

Corps of Engineers (USACE), in consultation with CO-OPS. CO-OPS’ Coastal Oceanographic 

Applications and Services of Tides And Lakes (COASTAL) Program along with NOAA’s 

National Geodetic Survey (NGS) and NOAA’s Office of Coast Survey (OCS) comprise a TriOffice initiative that provided USACE with an integrated suite of data products to help guide the 

reconstruction of Poplar Island in a manner that will provide sustainable wildlife habitat for years 

to come. CO-OPS’ role included processing three years of data from the Poplar Island, MD 

water level station to calculate datums. 

Land subsidence, rising sea level, and wave action are causing valuable remote island habitats 

to be lost throughout the Chesapeake Bay. As a result of the loss of these habitats, on May 12, 

2009, President Barack Obama issued Executive Order 13508 on Chesapeake Bay Protection and 

Restoration. In the Executive Order, the President declared the Chesapeake Bay a "national 

treasure" and ushered in a new era of federal leadership, action, and accountability. The Paul S. 

Sarbanes Ecosystem Restoration Project at Poplar Island coordinated by USACE directly 

supported the Executive Order 13508 goals to recover habitat and sustain fish and wildlife

(Federal Action Plan, 2012).

Actions planned by USACE at the nation’s premier island habitat restoration site, Poplar Island, 

included developing 111 acres of wetland and tidal gut habitat to allow inflow of dredged 

material, and began the design of the expansion of the Poplar Island project. Fifty-five of 111

acres of wetlands were opened to fish and natural tidal flow in late 2014, and the remaining 56 

acres are scheduled to be open in late fall 2015, increasing the area of fully restored/developed 

wetlands to 287 acres (Federal Action Plan, 2012).

The water level station for Poplar Island (Station ID: 8572271) was located on the east side of 

Poplar Island, MD on the USACE personnel pier. Five (5) bench marks located on the island 

were selected as tidal bench marks. The benchmarks were located along the islands perimeter 

road and cross dikes. The water level station is located at the southeast end of the personnel pier 

T-section. The gauge consists of a primary water level acoustic sensor and a data collection 

platform (DCP). The Poplar Island water level station was established and operated following 

CO-OPS specifications (CO-OPS, 2013).
3

Figure 2. The benchmark network for station 8572271, Poplar Island, MD and a table of values for the initial, annual, and 

closing leveling in units of feet.

The tidal benchmarks were established for each station to preserve the elevations of the tidal 

datums and their relationship to geodetic (land-based) datums by periodic leveling and GPS 

surveys if the station was removed or destroyed. The primary benchmark is CM-3 TRUE and is 

at the northeast corner of cell 4D, 15.68 meters (51.44 feet) east of the east corner of the Murden 

Memorial monument stone, 10.62 meters (34.84 feet) WSW of the west corner of the landing 

craft ramp, and 1.02 meters (3.35 feet) NNW of a wooden bollard. The benchmark is set 15 

centimeters (0.49 feet) below ground, crimped to an aluminum rod driven to an unknown depth 

to substantial resistance, and encased in a 5-inch logo cap. The locations of the remaining

benchmarks are shown in Figure 2; descriptions of these locations can be found on the 

benchmark sheet (Appendix 1). Constructed cells at Poplar Island can be designed based on 

accurate relationships between land elevations and water levels within a consistent reference 

frame. This information is critical because the frequency and duration of flooding are both 

dependent upon elevation. The elevation and relative water levels of Poplar Island can be reobserved to a high level of accuracy because of the baseline elevation data collected. This 

information is cirtical in monitoring the impacts of change (inland elevation or water level) over 

time and projecting the long-term sustainability of the restoration project (NOAA’s 

Contributions to the Poplar Island Restoration Project: A Chesapeake Bay Executive Order 

FY11 Accomplishments Report, 2011). 
4

MONTHLY WATER LEVEL PROCESSING

The Poplar Island, MD water level data were processed by the CO-OPS Data Processing Team. 

The data were reviewed, outliers were removed, and gaps were filled where needed. Once the 6-

minute interval water level data were processed other products could be generated. The typical 

monthly water level processing outputs were tabulated high and low waters, and hourly heights.

(Figures 3, 4, and 5). Note that these products are shown relative to station datum (STND), 

which is an arbitrary zero point set low enough in the water such that the water level will never 

be below this point. 

Figure 3. Monthly high and low tabulations for Poplar Island, January 2007.

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Elevation Relative to Station Datum (meters)

8572271 Poplar Island, MD – January 2007

8572271 - Water Level - Six Minute - WL 8572271 - Highs - WL

8572271 - Higher Highs - WL 8572271 - Lows - WL

8572271 - Lower Lows - WL
5

Figure 4. Tabulated high and low, and monthly means for January, 2007. This tabulation shows the time and 

height of every high and low water level in relation to station datum (STND).
6

Figure 5. Tabulated hourly heights for January, 2007. This tabulation shows the hourly heights in relation to 

station datum (STND). 
7

TIDAL DATUMS

Accepted tidal datums have been calculated for Poplar Island relative to the current 19-year 

National Tidal Datum Epoch (NTDE) of 1983-2001 using a standard NOAA simultaneous 

comparison procedure (CO-OPS, 2003) of three years of data (October 2006-February 2010)

with the long-term control station at Annapolis, which has been continuously operating since

1928. For marine applications, a vertical datum is a base elevation used as a reference to 

determine heights and depths (NOAA, 2001). A vertical datum is referred to as a tidal datum 

when defined by a certain phase of the tide. It is determined by measurements from a water level 

station. For example, Mean High Water (MHW) is the mean elevation of all the high waters 

observed over the NTDE. Mean Lower Low Water (MLLW) is the mean elevation of all of the 

lower low waters observed each day over the NTDE and is the U.S. nautical chart reference 

datum (CO-OPS, 2001). 

The tides at Poplar Island and Annapolis are classified as semi-diurnal (two high tides and two 

low tides per day with one high being slightly higher than the other and one low being lower than 

the other). The water levels in the Chesapeake Bay are influenced by atmospheric forcing 

(winds), as much as the astronomical tides. The mean range of tide (Mn), defined as the 

elevation difference between Mean High Water (MHW) and Mean Low Water (MLW), is 0.336 

meters (1.102 feet) at Poplar Island. The Great Diurnal Range of Tide (GT) is 0.468 meters 

(1.535 feet) and is the elevation difference between Mean Higher High Water (MHHW) and 

Mean Lower Low Water (MLLW). Figure 6 shows the elevation relationships of tidal datums 

and ranges of tide for Poplar Island, MD. 

GEODETIC ELEVATION REFERENCES TO TIDAL DATUMS

For land-based reference, a geodetic datum is a fixed reference that is developed and maintained 

by the National Geodetic Survey (www.ngs.noaa.gov). The North American Vertical Datum of 

1988 (NAVD88) is the existing geodetic vertical reference datum for the United States and is 

the vertical reference for most modern topographic elevation sources such as the United States 

Geological Survey (USGS) National Elevation Database (NED) (NOAA, 2003). GPS surveys 

have been made at some of the tidal benchmarks on Poplar Island, but published NAVD88 

elevations are not yet available. GPS surveys require occupying various tidal bench marks for

several hours with a survey-grade static GPS receiver. Orthometric geodetic elevations, such as 

NAVD88 are obtained using the NGS OPUS software (http://www.ngs.noaa.gov/OPUS/). When 

available, relationships between tidal and geodetic datums can be determined; otherwise, 

geodetic datum relationships can be estimated using the NOAA VDatum tool 

(www.Vdatum.noaa.gov) with the Chesapeake Bay VDatum grid (Figure 7). Using VDatum for 

Poplar Island, NGVD29 was estimated to be 0.166 meters (0.545 feet) above station datum and 

NAVD88 was estimated to be 0.346 meters (1.135 feet) above station datum. This means 

NGVD29 was 0.150 meters (0.492 feet) below MSL and NAVD88 was 0.030 meters (0.098 feet) 

above MSL at Poplar Island.
8

Figure 6. Accepted tidal datum elevations (in meters) for Poplar Island, MD, relative to station datum based on the 

1983-2001 NTDE. Accepted ranges of tide, maximum and minimum observed water levels, highest and lowest 

astronomical tides, and Greenwich time intervals have also been calculated. Although not shown, NAVD88 was 

estimated to be 0.346 meters (1.135 feet).
9

Figure 7. Relationship of geodetic datum elevations and local mean sea level at Poplar Island.

PREDICTED AND OBSERVED TIDE COMPARISON

Tidal predictions were generated for Poplar Island using the harmonic constants derived from a 

least-squares harmonic analysis for one-year of observed hourly heights (see Appendix 1). 

Figure 8 is a three year comparison plot of observed and predicted water levels that shows the 

large annual variations and the extent of the differences between observed and predicted high 

and low tides. There was a signficant amount of variability in the observations that was not 

present in the predictions due to the effects of atmospheric influences. Figure 9 shows the time 

series of the residual differences between observed versus predicted water levels. The standard 

deviation of these differences 0.17 meters (0.56 feet) was a signficant percentage of the observed 

mean range of tide 0.34 meters (1.12 feet). In this region of the Chesapeake Bay, the effects of 

the winds can have just as much influence on the water levels as the tidal forcing.
10

Figure 8. Plot of Poplar Island, MD observed (blue) and predicted (red) water levels.

Figure 9. Difference of Poplar Island, MD observed and predicted water levels (residual).

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Water Levels (Meters)

Date and Time (GMT)

8572271 Poplar Island, MD

Observed and Predicted Hourly Water Levels on MLLW

8572271 - Water Level - Hourly - WL 8572271 - Water Level - Hourly - PR

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Hourly Height Difference (Meters) 

Date and Time (GMT)

8572271 Poplar Island, MD

Difference between Hourly Heights Obs.-Pred. Values on MLLW 

Mean: 0.123

Standard Deviation: .170 
11

FREQUENCY OF HIGH WATER ELEVATIONS AND DURATIONS OF 

INUNDATION

A frequency and duration of inundation analysis was used to generate statistics of the elapsed 

time the water elevation was at or above a user defined threshold for each tabulated high tide. 

Six-minute data above the defined threshold before and after the time of each tabulated high tide

was used in this analysis. For this study, the frequency and duration of inundation of high water 

elevation relative to MHW for the Poplar Island and Annapolis water level gauges were 

analyzed. MHW is often used as a threshold for habitat restoration and inundation studies, as it 

often approximates the natural break in marsh vegetation between upland and lower marsh 

species. Sustained marsh health is also often dependent on the frequency and duration of 

inundation. Figure 10 is a histogram of the frequency of high water elevations above MHW at 

Poplar Island for all high waters measured during the operation of the station from October

2006-Feburary 2010. The histogram shows a decreasing distribution of tides, with 90% of the 

distribution being within 0.301 meters (0.988 feet) above MHW. The highest elevation was 

approximately 0.701 meters (2.299 feet) above MHW. The histogram in Figure 11 shows the 

histogram distribution for Poplar Island for the same time period. The distribution at Annapolis 

is very similar to Poplar Island, with the only difference being a slightly lower maximum 

elevation at Poplar Island due to their geographical locations on opposite sides of the bay.

Figure 10. Frequency of high water elevation relative to MHW at Poplar Island, MD on station datum.

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Cumulative Percent

Frequency

Elevation above MHW Datum (Meters)

8572271 Poplar Island, MD

Frequency of High Water Elevations Relative to MHW Datum (0.482 Meters)

Oct 01, 2006 To Feb 28, 2010

Frequency

Cumulative Frequency

1337 Tides Analyzed
12

Figure 11. Frequency of high water elevation relative to MHW at Annapolis, MD on station datum.

The frequency of the duration of inundation above MHW at Poplar Island over the 2006 to 2010 

time period is represented in Figure 12. The duration is defined as the length of time the 6-

minute water level data is above the user threshold for each high water event, which is used to 

determine the total elapsed time the water level was at or above the threshold. Using MHW as 

the threshold elevation, the histogram was normally distributed, with 90% of the high waters 

having durations less than 10 hours. For the more extreme high storm tides, durations were over 

15 hours. 

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Frequency

Elevation above MHW Datum (Meters)

8575512 Annapolis, MD

Frequency of High Water Elevations Relative to MHW Datum (1.741 Meters)

Oct 01, 2006 To Feb 28, 2010

Frequency

Cumulative Frequency

1182 Tides Analyzed
13

Figure 12. Frequency and duration of water at Poplar Island, MD above MHW on station datum.

Figure 13 illustrates a histogram of duration of inundation for the same time period observed at 

Annapolis. The distributions in these figures are similar to the distributions for the frequency of 

high water elevations. This agreement in the statistical distributions implies that the stations 

have similar tidal and nontidal signals. Statistical analyses from the long term record at 

Annapolis could therefore be used as a proxy for the long term statistics at the Poplar Island

station location, which only has a three year record.

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Frequency

Duration above MHW Datum (Hours)

8572271 Poplar Island, MD

Frequency of High Water Durations Relative to MHW Datum (0.482 Meters)

Oct 01, 2006 To Feb 28, 2010

Frequency

Cumulative Frequency

8556.6 Total Hours 
14

Figure 13. Frequency and duration of water at Annapolis, MD above MHW on station datum.

RELATIONSHIP OF DURATION OF INUNDATION VS. ELEVATION 

ABOVE MEAN HIGH WATER DATUM

The relationship of the frequency of elevation and frequency of duration can provide information 

that can be used to model and extrapolate the inundation statistics. In general, the higher the 

elevation of the tide above a threshold value, the longer the duration of inundation for that tide. 

However, as shown in Figures 14 and 15 for Poplar Island and Annapolis, it is not a linear 

relationship, but rather a complex multi-tiered curvilinear relationship which is not easily 

modeled. For instance, at Poplar Island (Figure 14), for elevations above 0.16 meters (0.52 feet)

MHW, a second systematic tier of inundation durations centered around 20 hours occurs. This 

means that during these wind-driven events, the inundation above MHW lasts through two 

succesive high tides and the intervening low tide. Due to their close proximity, Poplar Island and 

Annapolis exhibit a similar response to these events. For extreme events, the events with the 

longest durations are not ncessarily those with the highest elevations.

A notable event that affected both Poplar Island and Annapolis was the Veteran’s Day Nor’easter 

on November 10, 2009. The Veteran’s Day storm was attributed to the remnants of Hurricane

Ida which made landfall as a tropical storm along the U.S. Gulf Coast on Tuesday morning, 

November 10. Tropical Storm Ida weakened quickly into a remnant low which was located near 

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Cumulative Percent

Frequency

Duration above MHW Datum (Hours)

8575512 Annapolis, MD

Frequency of High Water Durations Relative to MHW Datum (1.741 Meters)

Oct 01, 2006 To Feb 28, 2010

Frequency

Cumulative Frequency

9947.4 Total Hours Inundated
15

the North Carolina coastal waters. The interaction between the low and a strong high pressure 

system located over eastern Canada produced an intense pressure gradient over the mid-Atlantic 

region, which persisted for several tide cycles. The Nor’easter generated a prolonged period of 

strong onshore winds of 39 miles per hour which persisted for more than 30 hours in some 

locations. The combination of the prolonged northeast flow, a long fetch over the bay, and the 

proximity of a new moon on November 16, produced large wave heights and strong wave action 

at the shore (NOAA, 2009). Moderate to severe tidal flooding also occurred along both the 

Atlantic coast and the back bays. Flooding on some barrier islands was worse on the bay side 

than on the ocean side because of the build up of water between tidal cycles. This extreme event 

resulted in Annapolis experiencing a duration of inundation of 103.7 hours at an elevation above 

datum equaling 0.506 meters (1.660 feet). The event was also observed at Poplar Island. Poplar 

Island experienced a duration of inundation of 81.8 hours at an elevation above datum equaling 

0.529 meters (1.736 feet). Figure 16 captures this anomalous event and shows the deviation of 

water level observations from tide predictions at Poplar Island due to the landfall of the remnants 

of Hurricane Ida on November 10, 2009 to November 14, 2009. The elevation of the water 

levels remained above MHW for several tidal cycles.

Figure 14. Poplar Island, MD duration of inundation.

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120.0

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800

Duration of Inundation (hours)

Elevation above MHW Datum (Meters)

8572271 Poplar Island, MD

Duration of Inundation vs. Elevation above Datum

(MHW Datum = 0.482 Meters)

Oct 01, 2006 To Feb 28, 2010

November 16, 2009
16

Figure 15. Annapolis, MD duration of inundation.

Figure 16. Poplar Island, MD tide predictions and observed hourly water levels relative to MLLW during the 

Veteran’s Day Nor’easter.

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Duration of Inundation (hours)

Elevation above MHW Datum (Meters)

8575512 Annapolis, MD

Duration of Inundation vs. Elevation above Datum

(MHW Datum = 1.741 Meters)

Oct 01, 2006 To Feb 28, 2010

November 16, 2009
17

COMPARISON OF MONTHLY MEANS

Figures 17, 18, and 19, show comparisons of the monthly means for MHW, MLLW, and Mean

Sea Level (MSL) for the stations at Poplar Island, MD, Annapolis, MD, and Cambridge, MD

relative to the long term MHW for the 1983-2001 NTDE. Over the period from 2006 thru 2010, 

the seasonal and annual variations are highly correlated, demonstrating similar regional response 

to seasonal weather patterns and longer periods of sea level change. 

Figure 17. Regional comparison of monthly MHW relative to 1983-2001 NTDE MHW datum.

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Elevation Relative to MHHW Datum 1983-2001 NTDE (meters)

(Month)

8572271 Poplar Island, MD

8571892 Cambridge, MD

8575512 Annapolis, MD

8572271 - MHW - WL 8571892 - MHW - WL 8575512 - MHW - WL
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Figure 18. Regional comparison of monthly MLLW relative to 1983-2001 NTDE MLLW datum.

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2-10

Elevation Relative to MLLW Datum 1983-2001 NTDE (meters)

(Month)

8572271 Poplar Island, MD

8571892 Cambridge, MD

8575512 Annapolis, MD

8572271 - MLLW - WL 8571892 - MLLW - WL 8575512 - MLLW - WL
19

Figure 19. Regional comparison of monthly MSL relative to the 1983-2001 NTDE MSL datum.

LONG TERM SEA LEVEL TRENDS

Since the Poplar Island, Annapolis, and Cambridge water level station records exhibit similar

monthly and seasonal variations over the five year period, it is reasonable to assume that the long 

term relative sea level trends for Annapolis and Cambridge can be used as guidelines for long 

term trends at Poplar Island. Relative sea level trends reflecting changes in local sea level over 

time are critical for many coastal applications. These sea level trends were computed from 

monthly averages of hourly water levels observed at Annapolis and Cambridge (Zervas, 2009). 

Annapolis’ mean sea level trend is 3.44 millimeters/year (0.14 inches/year) with a 95% 

confidence interval of +/- 0.23 millimeters/year (0.01 inches/year) based on monthly mean sea 

level data from 1928-2013 which is equivalent to a change of 0.35 meters (1.15 feet) in 100 

years (Figure 20). Cambridge’s mean sea level trend (Figure 21) is 3.48 millimeters/year (0.14

inches/year) with a 95% confidence interval of +/- 0.39 millimeters/year (0.02 inches/year) based 

on monthly mean sea level data from 1943-2013 which is equivalent to a change of 0.37 meters 

(1.21 feet) in 100 years. It is likely that Poplar Island has experienced very similar mean sea 

level changes, although local changes in land motion (such as marsh subsidence) may create 

small local variations.

-0.400

-0.300

-0.200

-0.100

0.000

0.100

0.200

0.300

10-0612-06

2-074-076-078-07

10-0712-07

2-084-086-088-08

10-0812-08

2-094-096-098-09

10-0912-09

2-10

Elevation Relative to MSL Datum 1983-2001 NTDE (meters)

(Month)

8572271 Poplar Island, MD

8571892 Cambridge, MD

8575512 Annapolis, MD

8572271 - MSL - WL 8571892 - MSL - WL 8575512 - MSL - WL
20

Figure 20. Mean sea level trend for Annapolis, MD.

Figure 21. Mean sea level trend for Cambridge, MD.
21

EXTREME WATER LEVELS AND EXCEEDANCE PROBABILITY

CO-OPS has statistically analyzed the historical monthly and annual highest and lowest observed 

tides over the period of observation (Zervas, 2009). The results are a set of annual high and low 

exceedance probability levels relative to tidal datums and the geodetic North American Vertical 

Datum (NAVD88). The 1%, 10%, 50%, and 99% exceedance probability levels relative to Mean 

Sea Level (MSL) at the Annapolis and Cambridge stations are shown in Figure 22 and 23 

(CO-OPS, 2015). 

Figure 22. Exceedance probability for Annapolis, MD.
22

Figure 23. Exceedance probability for Cambridge, MD.

The probability levels are in meters relative to the National Tidal Datum Epoch (1983-2001) 

Mean Sea Level. The values in the left column are the exceedance probability levels for the midyear (1992) of the current tidal epoch. In the right column, projected exceedance probability 

levels and tidal datums assuming continuation of the linear historic trend are provided. For 

instance, the 1% annual exceedance probability level for Annapolis increases from 1.73 meters 

(5.68 feet) above Mean Sea Level (MSL) to 1.81 meters (5.94 feet) above MSL based on the 

current trend. Similarly, the 1% annual exceedance probability level for Cambridge increases 

from 1.46 meters (4.79 feet) above Mean Sea Level (MSL) to 1.54 meters (5.05 feet) above MSL 

based on the current trend.
23

Figure 24. Extreme water levels at Annapolis, MD.

Figures 24 and 25 show exceedance probabilities above MHHW and below MLLW using the 

Generalized Extreme Value (GEV) probability distribution function applied to annual maximum 

or annual minimum data (Zervas, 2005). The monthly extreme water levels include a Mean Sea 

Level (MSL) trend of 3.44 millimeters (0.14 inches) (see earlier discussion of sea level trends). 

The figures show the monthly highest and lowest water levels with the 1%, 10%, 50%, and 99% 

annual exceedance probability levels shown in red, orange, green, and blue. The plotted values 

are in meters relative to the Mean Higher High Water (MHHW) or Mean Lower Low Water 

(MLLW) datums established by CO-OPS. On average, the 1% exceedance probability level (red) 

will be exceeded in only one year per century, the 10% level (orange) will be exceeded in ten 

years per century, and the 50% level (green) will be exceeded in fifty years per century. The 99% 

level (blue) will be exceeded in all but one year per century, and it is assumed that it could be 

exceeded more than once in any year. Of note in the top panel of Figure 24, the most extreme 

high water events that occurred during the period of record are the 1933 Hurricane and Hurricane 

Isabel in 2003. Both of these events exceeded the 1% level. 
24

Figure 25. Annual exceedance probability curves for Annapolis, MD.

The 1% annual exceedance probability levels are 1.52 meters (4.99 feet) above Mean Higher 

High Water and 1.10 meters (3.61 feet) below Mean Lower Low Water for Annapolis. The 

curves were calculated using the CO-OPS Extremes Toolkit software package which fits the 

three parameters of the GEV probability distribution function to annual maximum or annual 

minimum data using an iterative maximum likelihood estimation. The spread of the 95% 

confidence intervals depends on the variability of the source data and the length of the series 

used. The level of confidence in the exceedance probability level decreases with longer return 

periods and should always be used in conjunction with the confidence interval in the application 

of these data. For instance, in the upper panel of Figure 25, the 95% confidence intervals have a 

large spread [approximately 1.0 meters (3.28 feet)] above and below the estimate for high water 

extremes and in the lower panel, the spread is approximately 0.600 meters (1.97 feet) for low 

water extremes. The estimated uncertainty in the elevation of the tidal datums (MHHW and 

MLLW) is less than 0.01 meters (0.03 feet). The annual exceedance probability curves and 

statistics at Annapolis are transferable to Poplar Island.
25

Figure 26. Extreme water levels at Cambridge, MD.

Similarly, Figures 26 and 27 show exceedance probabilities above MHHW and below MLLW 

for Cambridge using the GEV probability distribution function applied to annual maximum or 

annual minimum data using interactive maximum likelihood estimation. Due to the shorter 

record length and the presence of a multi-year gap, the annual exceedance probability curve and 

statistics determined at Cambridge are not transferable to Poplar Island. The monthly extreme 

water levels include a Mean Sea Level (MSL) trend of 3.48 millimeters/year (0.14 inches/year) 

with a 95% confidence interval of +/- 0.39 millimeters/year (0.02 inches/year) based on monthly 

MSL data from 1943 to 2006 which is equivalent to a change of 1.14 feet (0.35 meters) in 100 

years. The top panel of Figure 26 (above), the most extreme high water event occurred during 

Hurricane Isabel in 2003. This event exceeded the 1% level.
26

Figure 27. Annual exceedance probability curves for Cambridge, MD.

The 1% annual exceedance probability levels are 1.15 meters (3.77 feet) above Mean Higher 

High Water and 0.85 meters (2.79 feet) below Mean Lower Low Water for Cambridge. In the 

upper panel of Figure 27, the 95% confidence intervals have a large spread [approximately 1.2

meters (3.94 feet)] above and below the estimate for high water extremes and in the lower panel, 

the spread is approximately 0.30 meters (0.98 feet) for low water extremes. Estimated 

uncertainty in the elevation of the tidal datums (MHHW and MLLW) is 0.00 meters (0.00 feet).
27

SUMMARY 

The water level station at Poplar Island, MD is a long term station established and operated by 

the USACE to support their project operations in building the island. CO-OPS analyzed 

approximately three years (October 2006-February 2010) of data for the purpose of establishing 

accepted NOAA tidal datums, publishing benchmark elevations, and performing frequency and 

duration of inundation analyses for use by USACE. The data and metadata were quality 

controlled and documented to meet NOAA standards. The observations at Poplar Island were 

compared with the two closest NOAA NWLON stations at Annapolis, MD and Cambridge, MD. 

Although they each have slightly different ranges of tide and times of high and low waters, the 

water levels at all three locations have very similar responses to regional atmospheric forcing due 

to changes in wind and barometric pressure. The statistical distributions of the frequency and 

duration of inundation above MHW are very similar at all three locations. Based on these

comparisons, it is recommended that the longer term sea level trends and statistical distribution 

for inundation and for extreme water levels observed at Annapolis and Cambridge can be used as 

a proxy for Poplar Island. 

USACE’s goal was to ensure that all elevations on the island could be accurately related to 

elevations of surrounding land masses, as well as tidal characteristics derived from nearby water 

level stations. This information is critical because the frequency and duration of flooding are 

both dependent upon elevation. The tidal datum elevations and the frequency and duration 

statistics are specifically being used to design the wetlands and marsh surfaces in specified 

project areas on the island. This information is also essential for monitoring the impacts of 

change (in land elevation or water level) over time and projecting the long term sustainability of 

the restoration project. NOAA products and services will help inform wetland restoration in the 

face of rising sea levels in this area.
28
29

ACKNOWLEDGEMENTS

The author gratefully acknowledges Stephen Gill (CO-OPS Chief Scientist), who provided 

guidance in the analysis and interpretation of data associated with the work contained in the 

technical report. I would also like to thank Allison Allen, Gerald Hovis, Christopher Paternostro, 

and Patrick Burke for technical editing. 

The author also would like to thank Brenda Via for production assistance in preparing this report.

REFERENCES

CO-OPS, 2013. CO-OPS Specifications and Deliverables for Installation, Operational, and Removal of 

Water Level Stations, Updated October 2013, http://tidesandcurrents.noaa.gov/publications/COOPS_Specifications_and_Deliverables 

_for_installation_operation_and_removal_of_water_level_stations_updated_October_2013.pdf (October, 

2013).

CO-OPS, 2003. Computational Techniques for Tidal Datums Handbook, NOAA Special Publication 

NOS CO-OPS 2, 

http://www.tidesandcurrents.noaa.gov/publications/Computational_Techniques_for_Tidal_Datums_hand

book.pdf, (September, 2003).

CO-OPS, 2001. Tidal Datums and Their Applications, NOAA Special Publication NOS CO-OPS 1, 

http://www.tidesandcurrents.noaa.gov/publications/tidal_datums_and_their_applications.pdf, (February, 

2001).

Federal Action Plan, 2012. Federal Leadership Committee for the Chesapeake Bay. Action Plan, Strategy 

for Protecting and Restoring the Chesapeake Bay Watershed, 

http://executiveorder.chesapeakebay.net/EO_13508_FY13_Action_Plan_2012-11-14.pdf (November, 

2012).

NOAA, 2009. NOAA’s National Weather Service Forecast Office Philadelphia/Mount Holly (2009). 

Veteran’s Day Storm, http://www.erh.noaa.gov/phi/storms/2009/vds/veteransday2009_sum.pdf (June, 

2014).

USACE, 2013. Poplar Island, US Army Corps of Engineers, Baltimore District. 

http://www.nab.usace.army.mil/Missions/Environmental/PoplarIsland.aspx (October, 2013).

Zervas, C., 2005. Response of Extreme Storm Tide Levels to Long-term Sea Level Change. 

http://tidesandcurrents.noaa.gov/est/050415-53.pdf (October, 2013).

Zervas, C., 2009. Sea Level Variations of the United States 1854-2006, Technical Report NOS CO-OPS 

053, http://tidesandcurrents.noaa.gov/publications/Tech_rpt_53.pdf (October, 2013).

CO-OPS, 2013. Sea Level Trends. http://tidesandcurrents.noaa.gov/sltrends/sltrends.html (October, 

2013).

CO-OPS, 2013. Extreme Water Levels. http://tidesandcurrents.noaa.gov/est/ (October, 2013).

CO-OPS, 2013. Datums. http://tidesandcurrents.noaa.gov/datums.html?id=8572271 (October, 2013).

CO-OPS, 2013. Benchmark Data Sheets. 

http://tidesandcurrents.noaa.gov/benchmarks.html?id=8572271. (October, 2013).

CO-OPS, 2013. Harmonic Constituents. http://tidesandcurrents.noaa.gov/harcon.html?id=8572271. 

(October, 2013).
30

APPENDIX 1. Benchmark Sheet

 U.S. DEPARTMENT OF COMMERCE

 National Oceanic and Atmospheric Administration

 National Ocean Service

 

Station ID: 8572271 PUBLICATION DATE: 03/09/2012

Name: POPLAR ISLAND 

 MARYLAND

NOAA Chart: 12270 Latitude: 38° 45.5' N

USGS Quad: CLAIRBORNE Longitude: 76° 22.5' W

This station was installed in support of a project with the U.S. Army Corp of

Engineers (USACE). Due to the special nature of this project, the bench mark

are described in terms specific to the project. To reach the tidal bench mark

from Lowes Wharf in Sherwood, MD, proceed west by boat for 4.3 km (2.7 miles) to

the personnel pier at Poplar Island. The bench mark are located along the

islands perimeter road and cross dikes. The tide gauge is located at the SE end

of the personnel pier T-section.

 T I D A L B E N C H M A R K S

 PRIMARY BENCH MARK STAMPING: USACE CM3 2004

 DESIGNATION: CM-3 TRUE

MONUMENTATION: Bench Mark disk VM#: 19749

AGENCY: USACE PID: 

SETTING CLASSIFICATION: Aluminum rod driven to the ground

The primary bench mark is a disk at the NE corner of cell 4D, 15.68 m (51.4 ft)

east of the east corner of the Murden Memorial monument stone, 10.62 m (34.8 ft)

WSW of the west corner of the landing craft ramp, and 1.02 m (3.3 ft) NNW of a

wooden bollard. The bench mark is set 15 cm (0.5 ft) below ground, crimped to an

aluminum rod driven to an unknown depth to substantial resistance, and encased

in a 5-inch logo cap. 

 BENCH MARK STAMPING: NONE

 DESIGNATION: SP-6

MONUMENTATION: Pipe Cap VM#: 19750

AGENCY: USACE PID: 

SETTING CLASSIFICATION: Driven to the ground

The bench mark is a 2-inch capped pipe at the NE corner of cell 3A, 12.20 m

(40.0 ft) ENE of the SE sluice gate operator for spillway #6, 5.55 m (18.2 ft)

SE of the SE railing of the gangway for spillway #6, and 3.47 m (11.4 ft) SW of

the centerline of the perimeter road. The bench mark is set 30 cm (1.0 ft) below

the road grade, driven to an unknown depth to substantial resistance, and

encased in a 12-inch steel casing. 

 
31

 

 U.S. DEPARTMENT OF COMMERCE

 National Oceanic and Atmospheric Administration

 National Ocean Service

 

 

Station ID: 8572271 PUBLICATION DATE: 03/09/2012

Name: POPLAR ISLAND 

 MARYLAND

NOAA Chart: 12270 Latitude: 38° 45.5' N

USGS Quad: CLAIRBORNE Longitude: 76° 22.5' W

 T I D A L B E N C H M A R K S

 BENCH MARK STAMPING: USACE CM1 2004

 DESIGNATION: CM-1

MONUMENTATION: Bench Mark disk VM#: 19751

AGENCY: USACE PID: 

SETTING CLASSIFICATION: Aluminum rod driven to the ground

The bench mark is a disk at the NE corner of cell 3C, 9.99 m (32.8 ft) ESE of

the south sluice gate operator for spillway #5, 4.55 m (14.9 ft) south of the

south railing of the gangway for spillway #5, and 5.03 m (16.5 ft) west of the

centerline of the perimeter road. The bench mark is set 15 cm (0.5 ft) below

ground, crimped to an aluminum rod driven to an unknown depth to substantial

resistance, and encased in a 5-inch logo cap.

 BENCH MARK STAMPING: NONE

 DESIGNATION: SP-8

MONUMENTATION: Pipe Cap VM#: 19752

AGENCY: USACE PID: 

SETTING CLASSIFICATION: Driven to the ground

The bench mark is a 2-inch capped pipe at the approximate midpoint of the cross

dike, 3.66 m (12.0 ft) NE of the centerline of the cell 1A-3D cross dike, 0.93 m

(3.1 ft) SE of the northernmost of two wooden bollards, and 0.91 m (3.0 ft) NNE

of the other wooden bollard. The bench mark is set 9 cm (0.3 ft) below ground,

driven to an unknown depth to substantial resistance, and encased in a 12-inch

steel casing.

 
32

 U.S. DEPARTMENT OF COMMERCE

 National Oceanic and Atmospheric Administration

 National Ocean Service

 

 

Station ID: 8572271 PUBLICATION DATE: 03/09/2012

Name: POPLAR ISLAND 

 MARYLAND

NOAA Chart: 12270 Latitude: 38° 45.5' N

USGS Quad: CLAIRBORNE Longitude: 76° 22.5' W

 

 T I D A L B E N C H M A R K S

 BENCH MARK STAMPING: PIP 1 2002

 DESIGNATION: PIP-1

MONUMENTATION: Bench Mark disk VM#: 19753

AGENCY: USACE PID: 

SETTING CLASSIFICATION: Aluminum rod driven to the ground

The bench mark is a disk at the south edge of cell 3A, 20.12 m (66.0 ft) NNE of

the NE corner of a metal shed, 7.94 m (26.0 ft) NW of the center of an abandoned

electric box, and 3.93 m (12.9 ft) ENE of the island's well. The bench mark is

set 6 cm (0.2 ft) below ground, crimped to an aluminum rod driven to an unknown

depth to substantial resistance, and encased in a 4-inch PVC pipe with concrete

kickblock.
33

 U.S. DEPARTMENT OF COMMERCE

 National Oceanic and Atmospheric Administration

 National Ocean Service

 

 

Station ID: 8572271 PUBLICATION DATE: 03/09/2012

Name: POPLAR ISLAND 

 MARYLAND

NOAA Chart: 12270 Latitude: 38° 45.5' N

USGS Quad: CLAIRBORNE Longitude: 76° 22.5' W

 T I D A L D A T U M S 

Tidal datums at POPLAR ISLAND based on:

 LENGTH OF SERIES: 3 YEARS

 TIME PERIOD: March 2007 - February 2010

 TIDAL EPOCH: 1983-2001

 CONTROL TIDE STATION: 8575512 U.S. NAVAL ACADEMY, SEVERN R., CHES. BAY

Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:

 HIGHEST OBSERVED WATER LEVEL (12/26/2009) = 1.081

 MEAN HIGHER HIGH WATER MHHW = 0.469

 MEAN HIGH WATER MHW = 0.402

 MEAN SEA LEVEL MSL = 0.236

 MEAN TIDE LEVEL MTL = 0.233

 MEAN LOW WATER MLW = 0.065

 MEAN LOWER LOW WATER MLLW = 0.000

 LOWEST OBSERVED WATER LEVEL (01/03/2008) = -0.830

Bench Mark Elevation Information In METERS above:

 Stamping or Designation MLLW MHW

 USACE CM3 2004 1.508 1.106

 NONE 2.042 1.640

 USACE CM1 2004 2.064 1.662

 NONE 2.215 1.813

 PIP 1 2002 2.773 2.371

Foot Notes:

Bench mark PIP 1 2002 is based on one differential leveling connection and does

not meet the quality control standards of the NOS. Therefore, caution should be

used when deriving elevations for this mark.
34

 U.S. DEPARTMENT OF COMMERCE

 National Oceanic and Atmospheric Administration

 National Ocean Service

 

 

Station ID: 8572271 PUBLICATION DATE: 03/09/2012

Name: POPLAR ISLAND 

 MARYLAND

NOAA Chart: 12270 Latitude: 38° 45.5' N

USGS Quad: CLAIRBORNE Longitude: 76° 22.5' W

 D E F I N I T I O N S

Mean Sea Level (MSL) is a tidal datum determined over a 19-year National Tidal

Datum Epoch. It pertains to local mean sea level and should not be confused

with the fixed datums of North American Vertical Datum of 1988 (NAVD88).

NAVD88 is a fixed datum derived from a simultaneous, least squares, minimum

constraint adjustment of Canadian/Mexican/United States leveling observations.

Local mean sea level observed at Father Point/Rimouski, Canada was held fixed as

the single initial constraint. NAVD88 replaces NGVD29 as the national

standard geodetic reference for heights. Bench mark elevations relative to

NAVD88 are available from NGS through the World Wide Web at 

National Geodetic Survey.

NGVD29 is a fixed datum adopted as a national standard geodetic reference for

heights but is now considered superseded. NGVD29 is sometimes referred to as

Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological

Survey Topographic Quads. NGVD29 was originally derived from a general

adjustment of the first-order leveling networks of the U.S. and Canada after

holding mean sea level observed at 26 long term tide stations as fixed.

Numerous local and wide-spread adjustments have been made since establishment in

1929. Bench mark elevations relative to NGVD29 are available from the National

Geodetic Survey (NGS) data base via the World Wide Web at 

National Geodetic Survey.

NAVD88 and NGVD29 are fixed geodetic datums whose elevation relationships to

local MSL and other tidal datums may not be consistent from one location to

another.

The Vertical Mark Number (VM#) and PID# shown on the bench mark sheet are unique

identifiers for bench mark in the tidal and geodetic databases, respectively.

Each bench mark in either database has a single, unique VM# and/or PID# assigned.

Where both VM# and PID# are indicated, both tidal and geodetic elevations are

available for the bench mark listed.

The NAVD88 elevation is shown on the Elevations of Tidal Datums Table Referred

to MLLW only when two or more of the bench mark listed have NAVD88 elevations.

The NAVD88 elevation relationship shown in the table is derived from an average

of several bench mark elevations relative to tide station datum. As a result of

this averaging, NAVD88 bench mark elevations computed indirectly from the tidal

datums elevation table may differ slightly from NAVD88 elevations listed for

each bench mark in the NGS database.
35

APPENDIX 2. Harmonic Constants from Poplar Island, MD

Station Metadata 

Station Id : 8572271

Station Name : Poplar Island

State : MD

Latitude : 38.7583

Longitude : -76.375

Time Zone : LST

Unit : Meters

Center for Operational Oceanographic Products and Services

Name -- Description

Cst# -- Constituent Number Order in which NOS lists the constituents

Name -- Common name used to refer to a particular constituent, subscript 

 refers to the number of cycles per day 

Amplitude Phase -- One-half the range of a tidal constituent

 -- The phase lag of the observed tidal constituent relative to the 

 theoretical equilibrium tide

Speed -- The rate change in the phase of a constituent, expressed in

 degrees per hour. The speed is equal to 360 degrees divided by 

 the constituent period expressed in hours

Cst# Name Amplitude Phase Speed

1 M2 0.156 117.1 28.9841042 

2 S2 0.024 142.9 30.0000000 

3 N2 0.031 94.9 28.4397295 

4 K1 0.053 269.3 15.0410686 

5 M4 0.004 135.3 57.9682084 

6 O1 0.041 285.3 13.9430356 

7 M6 0.002 13.5 86.9523127 

8 MK3 0.003 227.9 44.0251729 

9 S4 0.000 0.0 60.0000000 

10 MN4 0.002 103.8 57.4238337 

11 NU2 0.007 102.2 28.5125831 

12 S6 0.000 0.0 90.0000000 

13 MU2 0.001 190.4 27.9682084 

14 2N2 0.004 51.4 27.8953548 

15 OO1 0.002 257.9 16.1391017 

16 LAM2 0.004 137.7 29.4556253 

17 S1 0.017 226.6 15.0000000 

18 M1 0.002 316.5 14.4966939 

19 J1 0.002 241.0 15.5854433 

20 MM 0.010 49.2 0.5443747 

21 SSA 0.037 61.7 0.0821373 

22 SA 0.113 134.0 0.0410686 

23 MSF 0.006 236.0 1.0158958 

24 MF 0.009 330.3 1.0980331 

25 RHO 0.004 280.9 13.4715145 

26 Q1 0.009 267.2 13.3986609 

27 T2 0.002 121.1 29.9589333 

28 R2 0.002 315.1 30.0410667 

29 2Q1 0.003 260.8 12.8542862 

30 P1 0.018 255.1 14.9589314 

31 2SM2 0.001 85.8 31.0158958 

32 M3 0.001 189.1 43.4761563 

33 L2 0.010 142.0 29.5284789 

34 2MK3 0.003 221.1 42.9271398 

35 K2 0.006 137.6 30.0821373 

36 M8 0.000 0.0 115.9364166 

37 MS4 0.001 185.4 58.9841042 
36