The shorelines of Maryland's portion of the Chesapeake Bay exhibit seasonal changes in direction of littoral transport and resulting beach width. Observation and study of this process at selected locations emphasizes the necessity of study for a complete year's seasonal cycle before stating erosion rates of an area to be protected by structures and the cyclincal presence or absence of beaches. Seasonal beach conditions at four selected sites are described along with resulting physical changes to protective structures. Through the use of ERTS-1 multi-spectral photography, it will be possible to make widespread predictions elsewhere in the Bay as a direct aid in protective structure design

Slaughter, T. H.

English

NASA Technical Reports Server

Paper M 1 
SEASONAL CHANGES OF LITTORAL TRANSPORT AND BEACH WIDTH 
AND RESULTING EFFECT ON PROTECTIVE STRUCTURES 
Turbit H. Slaughter, Geologist, Maryland Geological Survey, The Johns 
Hopkins University, Baltimore, Maryland 
ABSTRACT 
The shorelines of Haryland's portion of the Chesapeake Bay exhibi t  
seasonal changes i n  direction of l i t t o r a l  transport  and resul t ing beach 
width, Observation and study of this process a t  selected locations 
emphasizes the necessity of study f o r  a complete years seasonal cycle 
before s ta t ing  erosion r a t e s  of an area t o  be protected by st ructures  
and the  cyclincal presence or absence of beaches. 
a t  four selected sites and resul t ing physical changes to protective 
structures. 
sites and of ERTS-1 underflight photography of these sites. !&rough 
the  use of ERTS-1 nnilti-spectral photography, it will be possible to 
make widespread predictions elsewhers i n  the Bay as a direct e i d  
protective s t ructure  design, 
The purpose of t h i s  paper i s  to  describe seasonal beach conditions 
The seasonal changes will be shown by 35m slides of the 
1. ZNTRODUCTION 
Aerial photography is  available to the public from the U. S. Depart- 
ment of Agriculture, Agricultural Stabi l izat ion and Conservation %mice, 
flown generally during warn weather months, The photography i s  panchro- 
matic, showing a l l  objects in v-g shades of gray. 
of t ide  on the beach is not distinguishable, however, shallow offshore 
s t ruc tura l  features  are discernable. 
necessarily include all seasons and the  position of t ide  along the 
shoreline should be mapable f r o m  photography. 
has estabUshed a geologic baseline reference of the shoreline environ- 
ment of the Chesapeake Bay, and the Atlantic coast, 
me purpose of this paper i a  to discus8 i n  some d e t a i l  one discipl ine 
application of the Maryland Geological Survey 's Coastal-Estuarine Geology 
program, re la t ing  accumulated pre and current ground t ru th  t o  ERTS-1 low 
a l t i t ude  color I R  and color posit ive film. 
The precise l i n e  
L i t to ra l  transport  s tudies  nnast 
Seasonal ERTS-1 underflight color I R  and color posit ive photography 
The Survey has been act ively gathering physical data on the Chesapeake 
Bay nearshore environment since 1963. As a consequence, it has become 
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https://ntrs.nasa.gov/search.jsp?R=19730019609 2020-03-17T08:52:50+00:00Z
apparent t ha t  l i t t o r a l  transport direction i s  seasonal, with a net 
direction and is related d i rec t ly  to seasonal prevailing winds, t o  
intenee loca l  weather occurrences, and t o  zhe geographic location of 
the shore t o  prewailing wind direction. 
siographic un i t  is vital  t o  the total eros5.on-deposition budget of the 
unit ,  however, it becomes apparent t ha t  the nearshore shallow env5ronment 
must contribute a share of the t o t a l  E-R budget, To comprehend fully 
the offshore-onshore erosional depositional relationship, Mr, Randall T. 
Kerhin, geologist with the Maryland Survey, i s  studying i n  detail the 
offahore bar and trough structure and composition, The locations of 
areas t o  be described are shown i n  Figure 1. 
The geology of an eroding phy- 
Figure 1, Incations of amas discussed 
1260 
A study of the geomorphologic problem of a former s p i t  that  now 
8emes a8 a barr ier  beach extending along the southern boundary of 
Jane8 Island State Park, Somerset County, extends slightly sotlI%eastward 
of Island Point a distance of 4,800 feet, disclosed two apparent but 
different types of litploral data. 
blowing f r o m  the southwest across Tangier Sound moved sand northward to 
a cove bordered by scrub size trees, There was no beach i n  front of the 
thick deep rooted organic marsh vegetation, Wave action would break 
chunks of the vegetation ~ias8 up aad through #em up on the shore. D w h g  
the wSnter month8 the winds from the northwest would move the sand south- 
ward and by late spring there would be a sand beach completely covering 
and protecting the summeme eroding marsh shore edge, The erosion rate 
of t h i s  location is  1.5 fee t  a year, a relatively low rate, but under- 
standably 80. 
During the summer months, due to uinds 
A time sequence of April and July, is shown by Figures 2, 
and 3. 
danes Island State Park - Island Point, - Looking Mom 
Mgure 2 April 29, 1971 
facts  are documented 
underflight mission 
973, I.espectively. 
o r t u n a b l y  flights e le, The fall- 
ter l i t t o r a l  t m s p o  October 20, as  
deflaitely delineates 
e color positive f i l m  
shows the offshore the color IR does not. 
i 
Figure 5.  Janes Island 
Underflight Jan. 16, 1973 
1262 
1 263 
Another area of interest is located iarrasdiately north of the U. S. 
Navy Research Laboratory tower, south Tilghmn Island, Talbot County. 
Although the property is  now privately owned, the State of &@,and 
acquired shore property having 3,800 f e e t  of shoreline i n  1963. Erosion 
at  the rate of 16 feet per year of the area north of the protected Navy 
property was endangering a county road paralleling the shoreme.  As a 
consequence the State provided i n  1965, a sum o f  $!50,000 t o  be used i n  
constructim of appro*ately 1,100 fee t  of protective structures which 
were considered m a  "ahow case test site". 
Constructdon was begun in April, 1966 and completed in September, 
1967. The first section of structure was keyed t o  the northern end of 
the Navy steel lmlkhead and consi.irts of 270 feet of timber bulkheading, 
reinforced a t  the toe with 1/L ton rip-rap. The remining 730 feet was 
protected by a sloped revetment of interlocking concrete blibcks. "he 
use of concrete blocks i n  revetment design has been documented by Hall, 
J, V. and Jachasski, R. A. (1964) and Hall, J. V. (1967). The revetment 
a t  'pilghlnan has been described by Mohl, E. V. and Brown, J. D. (1967) and 
Slaughter, T. H. (1967). 
Background knouledge of offshore and onahore conditions of the area 
indicated a high hydrodynamic environment, with l i t t le  o r  no beach during 
most of the year. The offshore was shallow cored, i n d i c s t h g  a predominent 
sandy bottom which could serve as  a source of l i t t o r a l  material, especi- 
a l l y  during the winter months. 
that f o r  a number of reasons, the northern 200 feet of the concrete 
block revetment was in trouble, the toe of the structure was being under- 
mined. Aa a re su l t  of toe  undermining, the structure failed along this 
section. (Figure 10 ehows the northern end of fhe stwtnre on September 
26, 1967 Bhortly after completion. Figure 11 shower the same location on 
October 4, 1972.) 
By the spring of 1971 it was apparent 
Fig- 10. S o  Til&tla~~ Island Figure 11. S. Tilghman Island 
26, 1967 O c t o  4, 1972 
1264 
Inspection of ERTS-1 low alt i tude f l igh t  filn, Color IR of October 
20, 1972, Figure 12 and January 16, 1973, Figure 13? and color posit ives 
of January 16, 1973, does not show arry beach for the 3,800 feet under 
consideration, The lack of winter sand accumulation as shown by the 
Jmuary 16, 1973 flight may not be the  usual s i tuat ion as somethies is 
the case, but it emphasizes the f a c t  that there  is  very l i t t l e  beach 
sand t o  be counted on t o  protect the toe of the r e m b n t .  
Figure 12. 
S. Tilghman 
Underflight 
ERTS-1 M i d  
Oct, 20, 
Island 
.on 16 
1972 
S. Tilgban 
ERTS-1 Miss& 
Underflight 
Jan. 16, 
The last area t o  be described is the  beach a t  Ocean City, Maryland? 
specifically the beach between 12th and 27th Streets,  and 73rd and 78th 
Streets, These are two areas of Ocean Ciw beach groin f i e l d  systems. 
The groins i n  the southern field were erected over the period 1938 t o  
1961. 
Of concern is the effectiveneas o r  non-effectiveness of the groin 
fields and individual groins, 
of the beach and i n  some cases the dune is under ex%ren~e high tide attack. 
(Ffw 3.4 dated February 7, 1973, shows weak beach conditiona a t  the 75th 
Street groin. 
Ihe northern groin f ie ld  was erected i n  1961. 
Winter northeast winds take their t o l l  
IS 
on 
1 
,land 
226 
.973 
Figure 4. Ocean City, 75th Street February 7, 1973 
1265 
1 
i 
i 
r 
Figure 15 shows the beach cronditions a t  13th Street on October 17, 
1972, The groin i n  the foreground is completely exposed and high t i de  
reached under the base of the boardwalk. 
i 
Figure 15. Ocean City, 13th Street October 17¶ 1972 
Avaflable offshore profiled data obtained by the  U, S, Army Corps of 
Engineers along Ocean City beach show the nearshore bar t o  vary iri width 
and height and distance from shore. 
summer beach SKfmmiRg conditions, documents t h e  existence of r i p  currents, 
when along shore currents are increased. 
film of mission 210 on Augu8t 12) 1972, disclosed very clearly, the 
apparent relationship of the offshore bar t o  the beach. 
fairly normal m e r  day weather-wise, winds s ta r ted  off i n  the morning 
from the north and mung around t o  the southeast later i n  the day. 
mum wind was 6 t o  10 mph. 
the day disclosed t h a t  where the waves break the shoreline is fa r ther  
eastward than the offshore area8 tha t  do not have breaking waves facing 
them. 
from shore creates a cusp condition of varying width and depth of enlarge- 
ment. 
pointers indicate s t r ee t s  12 and 27, the location of the southern groin 
field.  Figure 17 points t o  the location of the northern groin field,  
specifically a t  75th Street. 
Mission 226 low a l t i tude  underflight of January 16, 1973, duplicates 
Personal knowledge of Ocean City 
ERTS-1 underflight low a l t i tude  
The day was a 
Maxi- 
The minimal offshore wave breaking pattern of 
The offshore bar being non uniform on width, height, and distance 
Figure 16 reproduces mission 210 of August 12, 1972. The numbered 
the essence of August 12, 1972 f l igh t ,  except the wave pattern of the 
January f l i g h t  i s  a l i t t l e  more intense, therefore, exact wave breaking 
patterns are not discernable. 
1266 
16. South Ocean City Mgum 17. South Ocean City 
ERTS-1 Hssion 210 ERTS-1 Mission 210 
Underflight August 12, 1972 Underflight August 12, 1972 
ow level underfUght multi-spectral photography has proven 
study of l i t t o r a l  transport of selected , and of geohydrodynamic processes along t o  be a most productive a i d  areas within the Chesapeake 
Maryland rs Atlantic Coast . 
, J, V, and Jachowski, R. A. 4), Concrete Block Rsvstment Near 
Benedict, Maryland: U. S. Coastal Zngineering Research Center, 
ems Paper NO. 1-64 
Hall, J. 8. (1967), Wave Tes n t  Using Machine-Producted Inter- 
locking Blocks: U e  S e  Engineering Research Center, 
d Brown, J. D. ( 9671, Flexible Revs 
Blocks, Tilghnan sland, Maryland: a1 of t h e  American 
n t  Using Interfocking 
Shore and Beach Prese 
1967 
Association, Vole 35, No, 2, October, 
tures in the Maryland 
and Beach Preserva- 
1267 


Seasonal changes of littoral transport and beach width and resulting effect on protective structures

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