moar ce ‘ TP 80-5 WHOIK DOCUMENT COLLECTION / Experimental Dune Restoration and Stabilization, Nauset Beach, Cape Cod, Massachusetts by Paul L. Knutson TECHNICAL PAPER NO. 80-5 AUGUST 1980 2m : BS N es yy, Ay ®ERinG B® Approved for public release; distribution unlimited. U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING fA RESEARCH CENTER 729 Kingman Building Fort Belvoir, Va. 22060 Reprint or republication of any of this material shall give appropriate credit to the U.S. Army Coastal Engineering Research Center. Limited free distribution within the United States of single ras of on eee Has yao made by this Center. Additional copies are National Technical Information Service ATTN: Operations Division 5285 Port Royal Road Springfield, Virginia 22161 Reet, eA construed as an official partmen oH the Army position unless so designated by other UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) READ INSTRUCTIONS REPORT DOCUMENTATION PAGE BEFORE COMPLETING FORM 1. REPORT NUMBER 2. GOVT ACCESSION NO, 3. RECIPIENT’S CATALOG NUMBER TP 80-5 4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED Technical Paper EXPERIMENTAL DUNE RESTORATION AND STABILIZATION, NAUSET BEACH, CAPE COD, MASSACHUSETTS 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(s) 8. CONTRACT OR GRANT NUMBER(s) Paul L. Knutson 10. PROGRAM ELEMENT, PROJECT, TASK 9. PERFORMING ORGANIZATION NAME AND ADDRESS AREA & WORK UNIT NUMBERS Department of the Army Coastal Engineering Research Center (CERRE-CE) Kingman Building, Fort Belvoir, Virginia 22060 CONTROLLING OFFICE NAME AND ADDRESS Department of the Army Coastal Engineering Research Center Kingman Building, Fort Belvoir, Virginia 22060 14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office) 631533 12. REPORT DATE August 1980 13. NUMBER OF PAGES 42 15. SECURITY CLASS. (of this report) UNCLASSIFIED DECL ASSIFICATION/ DOWNGRADING SCHEDULE 15a, 16. DISTRIBUTION STATEMENT (of this Report) Approved for public release; distribution unlimited. - DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report) - SUPPLEMENTARY NOTES - KEY WORDS (Continue on reverse side if necessary and identify by block number) Beachgrass Dune stabilization Cape Cod, Massachusetts Dunes Coastal ecology Nauset Beach, Massachusetts Dune restoration Sand fence 20. ABSTRACT (Continue on reverse side if necesaary and identify by block number) In April 1970, experimental plots were established on a baymouth bar at Nauset Harbor on Cape Cod, Massachusetts. On the bar both sand fences and American beachgrass (Ammophtla breviltgulata) were tested as alternative techniques for creating and stabilizing dunes. Elevational profiles were made periodically in the test plots from April 1970 to November 1977. The study concluded that sand fences initially capture sand more rapidly than newly planted beachgrass. Once established, however, beachgrass plantings (continued) FORM DD , jan 73 1473 EDITION OF 1 Nov 6515 OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) UNCLASSIFIED ee ee eee SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered) trap sand at a rate equivalent to multiple lifts of sand fence. Using either sand fence or beachgrass, a dune growth rate of more than 11 cubic meters per linear meter of beach per year was sustained. increased 0.25 meter per year. Crest elevation @ UNCLASSIFIED —_—- SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered) PREFACE This report, which describes the methods, materials, results, and con- clusions of an experimental dune restoration and stabilization study on Nauset Beach, Cape Cod, Massachusetts, is published to assist engineers, municipali- ties, and private property owners in designing and maintaining dune restoration and stabilization projects on the North Atlantic coast. The work was carried out under the coastal ecology research program of the U.S. Army Coastal Engi- neering Research Center (CERC). The report was prepared by Paul L. Knutson, a CERC coastal ecologist, under the general supervision of E.J. Pullen, Chief, Coastal Ecology Branch. The author expresses appreciation to R. Savage and D. Woodard, who initi- ated the experiment and monitored the early progress of the work, and S. Onysko of the U.S. Army Engineer Division, New England, who managed, inspected, and maintained the project throughout the experimental period and reviewed the final draft. AK. Hurme of CERC conducted periodic site inspections and A. Meyer, J. Ford, and D. Knight, CERC, performed much of the data reduction. Dr. WeW. Woodhouse, North Carolina State University at Raleigh, reviewed and commented on the original manuscript. U.S. Army Engineer Division, New England, acknowledges the cooperation and assistance in this experiment by personnel of other Federal offices and agencies, by State, municipal and local authorities, and by other individuals, particu- larly the following: U.S. Department of Interior, National Park Service, Cape Cod National Seashore; U.S. Department of Interior, Wellfleet Job Corps; U.S. Department of Agriculture, Soil Conservation Service, Hyannis, Massachusetts; Stephen L. French Forestry Camp, Nicherson State Park, East Brewster, Massa- chusetts; Selectmen, Towns of Orleans, Eastham, and Chatham; G. Munsey, R. Frostholm, W. Goff, and E.M. Richardson; Town of Orleans; and R.C. Kelsey, aerial photographer, Chatham, Massachusetts. Comments on this publication are invited. Approved for publication in accordance with Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. Colonel, Corps of Engineers Commander and Director CONTENTS CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI). ..... I IORAURLONDLOKIHON Gg GN Go. GG Geovo 0 ooo O40 0 910 0 0.56.0 5.0 0 1. General... era To LeCuiG Wi CMCMED not rO= a | DeLO- os Gato. GoD ic 2. Study Goveceuwesr CER cb ies Touatte: aetbvelbice et relltas: NetPro Maton noah: Mtrsiton te S) 5) PIgENALOKS Wifohclie Go, so ao G0 6 010 0 9°60 0 6 a1'0 6 6 ICIE IDA GRIGALILON CLF! ISI SURO NG VANS Gud) 6 oto 6 0 0 6 6!)'5) 6 Oo 6 1. Geography and eee 0 00 0D 0 BO oo Go 6 Qn Gletmate wen eke aay 6 6 a0 0 6 6 0 60°60 10 SHO A Raye VeYe} As OE ee aU Bil GG GM Chuan On Gor rau cu 45 IEIGIL METHODSPWANDSEROGED URES Mi nicnit 56 0 6 o ool ol dlold o 86 & Growth characteristics of four lifts of straight fencing, plot 4, IMVOS7Y 6s So 16 @ 0 6.6 66 5°65 5 5 6 0 oO 6 015 6 G 6 6 o Growth characteristics of American beachgrass planting, plot 5 @0=centimeterispacinie)F Hal 7O=7i7i) ree. cali elon oh 4 Med lel une Width of American beachgrass in beachgrass plots, October 1977 . Sand accumulation and increase in crest elevation in American beacherassipillotisrmyire oi acie es cited leone) Meterlheh i cMlcodmed ied tte) Ml -Mirey iii Sand accumulation and increase in crest elevation in spur and SERA Ane TESS LOSS GalGNaieo AG. o.6 awe” omc Guid hoo) dia By OS Comparison of annual sand accumulation and dune growth rates in Massachusetts, North Carolina, Texas, and Oregon. ...... FIGURES Location of study area at Cape Cod, Massachusetts. ..... . inlotrateNauseerharbor.OCtOber L969) mei mcmrciem ciel tyne) Men ie) (1 (ol el re Nauset Harbor (north spit) abandoned test site, October 1969. . Nauset Harbor (south spit), October 1969... Location of fine test plots at Nauset Beach. . ......2. Fence configurations in plots 2 and 4. ........ Gross=sectional. profile locations. . . . . 295 « » «s+... - Pilot 5 Mey lO G6 66 G6 6 6-6 3 6 6 a lo 6 o26 616 6 0G 6 Jc Surveys of profile line 1 at plotl........ Plot mlemOctobervl97 7" tkmeeanas em MeUEas NERUNI R sods Rent. Pile Qe Wereeay AoA GSB! 6G dos G08) GO Go SoS for 6% Sunveyssor- protien ines seat) plot miele Monel i lelt lle init | (ls Sunveysporuprorile: dune 4) atu pilots 2 grea elie pile iron isl i=liftei is) en) cee Plot 3, May 1973; recent planting by local volunteer groups evident. Sunveys von procilemhine (sat plot) Si. Var cya vere eh ot fon ss) Pilot A, Ween MOk Ss vaio iol) 6 tole 6! oslo Bio Nol 6 1a 6 |b 16 Vo ic Pilot 45) Magy WO7Siag WG 686! ooo Solaire. S Nomioia oo oie Sunveys of profileslinem/acatuplot (4 None). eile jiatieie eles iielts Milo S, Men NOV 6 Ma Veto Gros 6 aoe) GONG! oa 6% Sunveys o£ protile dine’ 9 ‘at plot Si) 25.) 2) i) vere es jel el CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI) UNITS OF MEASUREMENT U.S. customary units of measurement used in this report can be converted to metric (SI) units as follows: Se OOOO \|_\_\__swonnanaoa oa. 0 Oooo Multiply by To obtain ee EEE inches 25.4 millimeters 2.54 centimeters square inches 6.452 square centimeters cubic inches 16.39 cubic centimeters feet 30.48 centimeters 0.3048 meters square feet 0.0929 square meters cubic feet 0.0283 cubic meters yards 0.9144 meters square yards 0.836 square meters cubic yards 0.7646 cubic meters miles 1.6093 kilometers square miles 259.0 hectares knots 1.852 kilometers per hour acres 0.4047 hectares foot-pounds 1.3558 newton meters millibars 10197) ) t ; = Oo First Lift @ 5 fo ieee | Plot 2. Straight Fence With Side Spurs (ee ehcurtg a=) Second Lift ea Ba celeron ee RN LE AS A hg ee SINS A ee SE CONGALT EN eMNaN Le LAU = ' § S First Lift = on; § a j Third Lift —_~ —<—— Plot 4. Straight Fence 6(m) Figure 6. Fence configurations in plots 2 and 4. 3. Maintenance. Parts of the planting areas in which survival was low were routinely re- planted: plot 1, remedial planting in October 1971 and April 1972; plot 2, remedial planting in April 1973; plot 3, remedial planting in October LO 7s pilloit 4, remedial planting in April 1973; and plot 5, remedial planting in October 1971 and April 1972. Although experimental planting was discontinued after 1973, local volunteer groups have continued to provide periodic maintenance. | 14 Commercial fertilizer was applied to the surface of the fence and beach- grass plots as needed to encourage growth. Table 2 is a summary of fertilizer applications. Application rates varied from 5 to 25 kilograms per hectare of nitrogen. It is not known whether local groups have continued fertilizer applications. Table 2. Fertilizer applications. Types of fertilizer | Plots fertilized Slow release Slow release Slow release 30-10-10 NPK* 30-10-10 NPK 30-10-10 NPK 30-10-10 NPK 30-10-10 NPK 30-10-10 NPK INitrogen, phosphorous, potassium. 4, Monitoring. a. Elevational Surveys. A permanent base line was established roughly parallel to the long axis of the 150-meter test plots. Two cross-sectional profile lines were made across each of the plots during 11 survey periods: April 1970; January, April, and October 1971; February and October 1972; April and June 1973; April 1974; September 1975; and November 1977. Elevations were recorded to the nearest 3.6 centimeters. Profile lines are numbered consecu- tively from south to north. Lines 1 and 2 traverse plot 1, lines 3 and 4 traverse plot 2, etc. (Fig=7). The survey data were analyzed for sand accumulation rates, elevational pro- file changes, and shoreline migration. As a standard for direct comparison of plots, sand accumulation was calculated for an area 23 meters landward and seaward of each plot centerline for surveys up to April 1974 and 30.5 meters from each centerline for 1975 and 1977 surveys. In addition, for the beachgrass plots 1, 3, and 5 lateral spread of vegetation was measured and sand accumulation beneath vegetation was calculated. b. Field Observations. Observations of plant growth and the condition of sand fences were recorded during each profile survey. Special damage estimates were also made following severe storms. IV. RESULTS During this 7-year study (1970 to 1977), Nauset south spit elongated at a rate of more than 100 meters per year. Detailed information on long-term ie) Line 8 Line 7 W 2 : = 5 150 (m) S ® Scale is) jaa) Line 6 Line 5 Line 4 Line 3 ---4 Plot Centerline — Profile Line Line 2 Line | Figure 7. Cross-sectional profile locations. patterns of erosion and accretion on the spit as well as changes associated with severe storms is given in Appendix B. The remainder of this section focuses on changes that occurred within the boundaries of five test plots. 1. American Beachgrass with 45-Centimeter Spacin Pilot 2): a. Installation, Damage, and Repair. Plot 1 was planted with American beachgrass sprigs on 45-centimeter centers, three to five sprigs per hill in 1970. Survival of plantings during the first year was 85 percent. Bare areas were replanted in October 1971. A severe storm in February 1972 deposited 0.3 to 0.7 meter of sand in the entire planting area. Plants were observed emerg- ing through the deposit by April 1972. It was not possible to measure the overall survival of the buried plants because bare areas were replanted in April 1972 in keeping with study objectives to provide plant cover in the test plots. Of importance, however, is that American beachgrass did emerge through at least a 0.3-meter washover deposit and did survive saltwater inundation. b. Short-Term Dune Growth. At the end of the first complete growing sea- son (October 1971), the crest elevation of the planted area had increased only 16 0.1 meter and sand accumulation was negligible. By October 1972, crest elevation had increased an average of 0.5 meter and sand accumulation was approximately 16.3 cubic meters per meter of beach. Figure 8 is a photo of the plot in May 1973. Figure 8: Plot 1 (American beachgrass on 45-centimeter spacing), May 1973. c. Long-Term Dune Growth. Growth of the dune at profile line 1 through November 1977, 7 years after planting, is illustrated in Figure 9. Dune width along profile lines 1 and 2 averaged about 61 meters by 1977. The landward and seaward slope along these profile lines averaged 1 on 9.5 and 1 on 15.6, respec- tively. Dune growth was generally in a seaward direction. The seaward shore- line showed slight accretion until 1973; thereafter, slight erosion returned the shoreline to near its original location. By 1977 the crest elevation had reached 5.5 meters mean sea level (MSL), 1.8 meters above the original planting elevation. Total sand accumulation during seven complete growing seasons was 55 cubic meters per linear meter. Figure 10 is a photo of the plot in October OT) « d. Performance Summary. Table 3 summarizes growth characteristics of the dune in plot l. ELEVATION ( WN) SS SHORELINE POSITION VERTICAL DATUM [S MSL HORIZGNTAL CATUM IS BASE LINE o DATE < « SNOV77 x 1SEP75 + 12JUN73 + 1APR7O N SEAWARD [eS o N -150 -10c °-50 10} so 10¢ 150 200 OISTANCE (fh) Figure 9. Surveys of profile line 1 at plot 1 (American beachgrass). Figure 10. Plot 1 (American beachgrass), October 1977. 18 Table 3. Growth characteristics of American beachgrass planting, plot 1 (45- centimeter spacing), 1970-77. Parameter Time interval by Value ' growing season -2.5 m3/lin m 16.3 m3/lin m 55.0 m3/lin m Sand accumulation or loss Increase in crest elevation 3 Dune slope Landward Seaward plot centerline; average of profile lines 1 and 2. 2Volume calculated for area 30.5 meters landward and seaward of plot centerline; average of profile lines 1 and 2. 3Average of profile lines 1 and 2. 2. Sand Fence with Side Spurs (Plot 2). ae Installation, Damage, and Repair. A single, straight sand fence with side spurs was constructed in plot 2 in April 1970. Additional lifts of fence were constructed in January 1971 (second lift), April 1971 (third lift), and January 1972 (fourth lift). In April 1972 after the fourth lift had filled with sand, the plot was planted with American beachgrass on 60-centimeter centers, three to five sprigs per hill. The first lift of fencing filled by December 1970, 8 months after instal- lation. One year later washover damaged the southern 30 meters of fencing. The area was again overwashed in February 1972 at which time the southern 53 meters of lifts one, two, and three were destroyed in several places. The damaged fences were not repaired. By August the weakened southern section was again overwashed, and the beachgrass planting survival was lowe In the north- ern half of the plot, however, plant survival was high. A remedial planting in the northern section was made in April 1973. be Short-Term Dune Growth. During the first 8 months, the first lift of fencing accumulated 11.3 cubic meters per linear meter. After 1 year the first two lifts (Fig. 11) had trapped 13.8 cubic meters and after 18 months three lifts had trapped 17.5 cubic meters. Subsequent winter storms, however, removed all accumulated material from the damaged southern section of the plot and removed about 0.9 cubic meter from the northern half. Thirty months (October 1972) after initial installation, an average of 21.3 cubic meters had been trapped by the fences and newly planted (April 1972) beachgrasses. ce Long-Term Dune Growth. Figures 12 and 13 depict dune growth in plot 2 along profile lines 3 and 4 from 1970 to 1977. Note on these figures that a well-developed dune ridge existed landward of this plot when the study was initiated. Despite earlier damage to the southern section, by 1977 both 19 Figure 11. Plot 2 (sand fence with side spurs), March 1971. “> sHoreLine POSITION VERTICAL DATUM IS MSL HORIZONTAL DATUM Is BASE LINE o DATE zt @ SNOV77 x LSEP7S ae + 12JUN73 Z » 1APR70 f= c > os w SEAWARD —_— > Oo N -150 -100 -S50 c so 109 15¢ 200 OISTANCE ( MM) Figure 12. Surveys of profile line 3 at plot 2 (sand fence with side spurs). 20 NS SHORELINE POSITION VERTICAL DATUM IS HSL HORIZONTAL OATUM [8 BASE LINE o DATE = @ §NOV77 x 18EP75 fa ¢ s%2JUN73 z 2 SAPR7O e Do w SEAWARD _ o ay -150 -100 -50 0 50 100 180 200 DISTANCE ( AD Figure 13. Surveys of profile line 4 at plot 2 (sand fence with side spurs). segments of the plot had trapped similar amounts of sand, 30 and 35 cubic meters. Final crest elevation in the southern section was somewhat lower than the northern section, 4.9 versus 5.3 meters. Dune slope of the southern sec- tion was 1 on 15 landward and 1 on 18 seaward. Dune slope in the undamaged section was twice as steep, 1 on 7./ landward and 1 on 7.9 seaward. Base width of the dune in 1977 was about 41.2 meters in the southern section and about 32.9 meters in the northern section. While the bayward shore remained stable, the seaward shore retreated about 25 meters during the 8 years of observation. d. Performance Summary. Table 4 summarizes dune development from 1970 to IO 3. American Beachgrass with 60-Centimeter Spacing (Plot 3). a. Installation, Damage, and Repair. Plot 3 was planted in 1970 with American beachgrass on 60-centimeter centers, three to five sprigs per hill. Survival was initially very low (about 10 percent as measured in June 1971) because of the migration of a storm berm into the planting area. The plot was replanted in October 1971. Much of the replanted area was buried with sand during a February 1972 storm and survival of the second planting was less than 20 percent the following year. Observations in May 1973 indicated that the area was replanted, possibly by local volunteer groups, though no additional planting was made as part of this study (Fig. 14). The presence of the storm berm in the planting area and evidence of overwash were observed in October 1973 and May 1974. After 1973, two washover areas became natural pathways for foot and vehicular traffic. These two thoroughfares, lying east-west, con- nected the seaward beach with a pathway running north-south that roughly bisected the dune longitudinally. Neither of the plot 3 profile lines (lines 5 and 6) coincide with the east-west thoroughfare; however, the north-south 2| Table 4. Growth characteristics of four lifts of spur fencing, plot 2, 1970-77. Parameter Time interval (mo) Sand accumulation Increase in crest elevation 3 Dune slope Landward em Allo” Seaward ion 269 Base Pen SG ian lyolumes calculated for area 23 meters land- ward and seaward of plot centerline; average of profile lines 3 and 4. 2Volume calculated for area 30.5 meters land- ward and seaward of plot centerline; average of profile lines 3 and 4. 3average of profile lines 3 and 4. Figure 14. Plot 3 (American beachgrass on 60-centimeter spacing), May 1973; recent planting by local volunteer groups evident. 22 pathway is seen in profile line 5 (Fig. 15). Although the dune continued to accumulate sand both seaward and landward of the north-south pathway, the elevation of the path remained constant over the 5-year period from 1973 to OYA @Q Ne SHORELINE POSITIGN VERTICAL DATUN IS HSL HORIZONTAL OATUM IS BASE LINE ao Foot and Vehicular Pathway ~ DATE = * e@ 9NOV77 = x 1SEP75S = + 12JUN73 o o 1APR70 = c > a us Seaward ——>— oOo -2 Je -159 -100 -50 4 50 100 159 200 OISTANCE { A} Figure 15. Surveys of profile line 5 at plot 3 (American beachgrass). be Short-Term Dune Growth. By the end of the second growing season (October 1972), an average of 31.3 cubic meters per meter had accumulated in the planting area.e Much of this material was deposited by waves rather than by the wind. Crest elevation of the dune was 4.1 meters, 1.1 meters above the original planting surface. ce Long-Term Dune Growthe An average of 51.3 cubic meters per meter of sand had accumulated by November 1977. Crest elevation was 4.6 meters MSL, 1.5 meters above the original planting surface, and the base width of the dune averaged 81.7 meters. The landward and seaward slopes were 1 on 21.2 and 1 on 29.7, respectively. The landward shore remained relatively stable during the study period; the seaward shore retreated about 15.0 meters over the 8 years. d. Performance Summary. Table 5 summarizes growth characteristics for DIlOE Si. 4. Straight Fence (Plot 4). ae Installation, Damage, and Repair. A single, straight sand fence was constructed in plot 4 in April 1970. Additional lifts of fence were con- structed in January 1971 (second lift), April 1971 (third lift), and January 23 Table 5. Growth characteristics of American beachgrass planting, plot 3 (60- centimeter spacing), 1970-77. Parameter Time interval by growing season Sand accumulation Increase in crest elevition 5 Dune slope Landward Seaward lyolume calculated for an area 23 meters landward and seaward of plot centerline for profile line 6; no data available on profile line 5 for this survey period. 2Volume calculated for an area 23 meters landward and seaward of plot centerline; average of profile lines 5 and 6. 3Volume calculated for an area 30.5 meters landward and seaward of plot centerline; average of profile lines 5 and 6. ‘Calculation based on profile line 6. Saverage of profile lines 5 and 6. 1972 (fourth lift). In April 1972 after the fourth lift had filled with sand, the plot was planted with American beachgrass on 60-centimeter centers, three to five sprigs per hill. This fence plot sustained little damage during the experiment. be Short-Term Dune Growth. The first lift of fence trapped approxi- mately 12.5 cubic meters per meter by January 1971 when the second lift was installed. After 1 year, a total of 21.3 cubic meters per meter had been trapped by the first two lifts (Fig. 16). By May 1973 the four lifts of fencing in combination with the beachgrass planted in April 1972 had trapped 42.5 cubic meters per meter. Figure 17 shows the plot in May 1973, 30 months after initial installation. ce Long-Term Dune Growth. Figure 18 illustrates the continued growth of the straight fence dune through November 1977. Although the crest elevation continued to increase, there was little net accumulation after October 19/72. In general, the dune became progressively narrower due to erosion of the shoreline. By 1977, crest elevation was 3.1 meters above the plot elevation in 1970. Dune width was only an average of 30.1 meters and the landward and seaward slopes of the dune were a steep 1 on 5.8 and 1 on 4.3, respectively. The seaward shore retreated approximately 21.0 meters during the 8 years of observation. d. Performance Summary. Table 6 summarizes dune development from 1970 to MOAT 6 24 Figure 16. Plot 4 (straight fencing), March 1971. Figure 17. Plot 4 (straight fencing), May 1973. 25 ELEVATION ( A) -2 NS SHORELINE POSITION VERTICAL DATUM IS ASL HORIZONTAL DATUM IS BASE LINE OATE 9NOV77 1SEP75 12JUN73 LAPR70 brtxe -150 -100 -$0 tt} 50 100 160 200 DISTANCE ( A) Figure 18. Surveys of profile line 7 at plot 4 (straight sand fence). Table 6. Growth characteristics of four lifts of straight fencing, plot 4, 1970-77. Parameter Time interval (mo) Sand accumulation 8, 12.55 m?/m 12 21.3 m°/m 18; 21.3 m°/m 30, 42.5 m°/m 65, 48.8 m>/m 90 45.0 m?/m Increase in 3 30 2Oe mn crest elevation 90 3.1m Dune slope Landward 90 eon D6 Seaward 90 Ones 3 Base width 90 30.2 m IVolume calculated for area 23 meters landward and seaward of plot centerline; average of profile lines 7 and 8. 2Volume calculated for area 30.5 meters landward and seaward of plot centerline; average of profile lines 7 and 8. 3Average of profile lines 7 and 8. 26 5. American Beachgrass with 90-Centimeter Spacing (Plot 5). ae Installation, Damage, and Repair. Plot 5 was planted in 1970 with American beachgrass on 90-centimeter centers, three to five sprigs per hill. Planting survival in June 1971 measured 60 to 70 percent. Bare areas were replanted in October 1971. The severe storm of February 1972 deposited a veneer of sand over the plantings. Areas of low survival were replanted in April 1972. be Short-Term Dune Growth. Sand accumulation was negligible at the end of the first growing season. After two growing seasons 10 cubic meters per meter had accumulated and the crest elevation was 2.9 meters, 0.9 meter above the initial planting surface (Fig. 19). Figure 19. Plot 5 (American beachgrass on 90-centimeter spacing), May 1973. ce Long-Term Dune Growth. Figure 20 illustrates the growth of the dune from 1970 to 1977. A small secondary dune ridge had formed landward of the test area by 1973. After seven growing seasons, 55 cubic meters per meter had accumulated and the crest elevation was 3.9 meters, about 2.0 meters above the original planting surface. Most of the sand accumulation was seaward of the centerline of the plot. Base width of the dune in 1977 was very broad, aver- aging 96.3 meters. The landward and seaward slopes of the dune were 1 on 8.7 and 1 on 9.8, respectively. The bay shoreline remained relatively stable dur- ing the experiment; the seaward shoreline receded approximately 28.5 meters. d. Performance Summary. Table 7 summarizes the growth characteristics of plot 5. 27 ELEVATION ( mM) -2 -150 -100 -50 Me SHORELINE POSITION VERTICAL DATUM IS) MSL HGRIZONTAL DATUM IS BASE LINE DATE SNOV77 1SEP75 12JUN73 1APR70 b-+x@ Seaward ——>- 0 §0 100 159 200 DISTANCE ( N) Figure 20. Surveys of profile line 9 at plot 5 (American beachgrass). Table 7. Growth characteristics of American beachgrass planting, plot 5 (90-centimeter spacing), 1970-77. Parameter Sand accumulation or loss Increase in 3 crest elevation Dune slope Landward Seaward 3 Base width Time interval by growing season lyolume calculated for area 23 meters landward and seaward of plot centerline; average of profile lines 9 and 10. 2Volume calculated for area 30.5 meters landward and seaward of plot centerline; average of profile lines 9 and 10. 3average of profile lines 9 and 10. 28 V. DISCUSSION 1. Comparison of American Beachgrass Spacing Schemes. American beachgrass plots were planted to a standard width of 15 meters. Plants in plot 1 were spaced 45 centimeters apart; plants in plots 3 and 5 were spaced 60 and 90 centimeters apart, respectively. In October 1977, the lateral growth of vegetation was measured along each profile line. Table 8 summarized the observations made at each beachgrass plot. Table 8. Width of American beachgrass in beachgrass plots, October 1977. Description Profile | Width! American beachgrass (45- by 45-centimeter spacing) American beachgrass (60- by 60-centimeter spacing) American beachgrass (90- by 90-centimeter spacing) lafter seven growing seasons. Woodhouse, Seneca, and Broome (1976) report that in North Carolina, American beachgrass spreads in the direction of sand supply at a rate of 2.4 to 3.0 meters per year. This spreading rate was exceeded in two of the three beachgrass plots in the Nauset experiment. Vegetation in plots 1 and 5 ex- tended laterally an average of 3.8 and 4.9 meters per year. Vegetation in plot 3 spread more slowly. Plot 3, which has the foot and vehicular pathways, was badly damaged in 1971 and 1972; survival of the initial and followup plantings was only 10 to 20 percent. Initial survival in plots 1 and 5 was high, 70 to 85 percent, which accounts for the greater spread observed in these plots. Seaward spread of the vegetation in the three plots averaged 2.4 meters per year; landward spread was 4.8 meters per year. Winds are predomi- nantly from the west during the growing season; therefore, vegetative spread was greatest in the windward direction. This observation supports that of Woodhouse, Seneca, and Broome (1976) concerning the rapid spread of American beachgrass in the direction of sand supply. Table 9 summarizes the volume of sand accumulated under beachgrass and the overall increase in crest elevation after seven growing seasons at each beach- grass plot. The sand volume and the elevation increase in each plot are close- ly related to the width of vegetation in each plot (Table 8). The greatest lateral spread of vegetation and largest sand accumulation occurred in plot 5, the plot with the greatest exposure to windblown sand. In addition to landward and seaward beaches which contributed sand to all plots, plot 5 benefited by 29 Table 9. Sand accumulation under beachgrass and increase in crest elevation in American beachgrass plots. Increase in crest elevation (n) Sand accumulation (103 /m) Description American beachgrass (45- by 45-centimeter spacing) American beachgrass 1.6 (60- by 60-centimeter spacing) American beachgrass (90- by 90-centimeter lafter seven growing seasons. the elongation of the spit which provided an almost limitless supply of sand from the northern quadrant. Supporting this contention is the fact that twice the amount of sand was accumulated by the beachgrass in the northern half (profile line 10) of plot 5 as compared to the southern half (profile line 9), 100.1 versus 56.3 cubic meters per meter. Sand accumulation in the southern half of plot 5 was very similar to that in plot 1 (51.4 cubic meters per meter). From this experiment, there is no evidence to support that close (45 by 45 centimeters) or wide (90 by 90 centimeters) spacing measurably influ- enced dune growth. Zak (1967) also concluded that 90-centimeter spacing was adequate except in areas of severe erosion. 2. Comparison of Sand Fence Schemes. Table 10 summarizes sand accumulation and increase in crest elevation in the spur (plot 2) and straight (plot 4) fence sections. Table 10. Sand accumulation and increase in crest elevation in spur and straight fence plots. Time Sand Increase in interval accumulation | crest elevation (mo) (m3/m) (m) Sand fence with side spurs (Jan. 1971) 18 (Oct. 1971) 90 (Nov. 1977) Sand fence 8 with straight (Jan. 1971) sections 18 (Oct. 1971) 90 (Nov. 1977) 30 The first lift of fencing was constructed in each plot in April 1970. Eight months after installation, sand accumulation was slightly higher in the straight fence plot (plot 4). In January and April 1971, lifts two and three were installed. By October 1971 the straight fence plot had trapped about 20 percent more material and its crest elevation had increased 10 percent more than the spur plot (plot 2). This inequity between plots may not be the direct result of fence performance. Note in Figure 13 that a secondary dune line formed landward of the spur fence plot. It is likely that the secondary dune reduced the volume of sand available from the landward beach. In October 1971, the spur fence plot was damaged by overwash, whereas the straight fence remained intact. Comparison of the performance of the two fence schemes is meaningful only during the 18-month period before the damage occurred. During this period, there was no evidence that side spurs improved trapping efficiency or fence stability, but use of the side spurs did increase construction cost of the fence by about 20 percent. A fourth lift of fencing was added to both plots in January 1972, and both plots were planted with American beachgrass in April 1972. By September 1975, 5 years and 5 months after installation, the straight fence plot had trapped 48.8 cubic meters per meter. This represents an annual accumulation rate of 9.0 cubic meters. Between 1975 and 1977, a slight loss of material occurred due to shoreline recession. By 1977, crest elevation in the straight fence plot had increased 3.0 meters or an average annual growth rate of 0.4 meter. 3. Comparison of American Beachgrass and Sand Fence. Sand accumulation was negligible in the three American beachgrass plots during the first growing season (Tables 3, 5, and 7). The 20 cubic meters per meter of accumulation in plot 3 resulted from the migration of the storm berm into the planting area. Sand accumulation in the fenced plots was very high during the first year, averaging 11.9 cubic meters. The undamaged straight fence plot trapped sand at a rapid rate of 9.0 cubic meters per year for the first 5.5 years. Though initially slow, the beachgrass plots trapped an average of 8.3 cubic meters per meter per year over seven growing seasons. These observations support conclusions by Savage and Woodhouse (1968): (a) Sand fences initially trap more sand than newly established stands of beachgrass, (b) multiple lifts of sand fencing can sus- tain dune growth, and (c) once established beachgrass stands trap sand at rates comparable to multiple lifts of sand fence. There are two striking differences between the sand fence and beachgrass dunes--final base width and crest growth (Tables 3 to 7). Base width of the fence dunes was only 30 to 3/7 meters. The beachgrass dunes were 61 to 96 meters, two to three times the width of the fence dunes. However, crest growth was 1 meter greater in the straight fence plot than in the most suc— cessful beachgrass plot. 4, Comparison with Previous Studies. Table 11 provides a comparison of annual sand accumulation and dune growth rates observed in this study and rates observed in previous studies at Ocracoke Island, North Carolina, Padre Island, Texas, and Clatsop Plains, Oregon. Cape 3| Cod and Ocracoke Island appear to be comparable dune-building environments. Growth rates observed in the Padre Island and Clatsop Plains studies were somewhat higher. Dune growth rates are likely to be greatly influenced by the broadness of the beach as a source of sand and the direction and severity of local winds. Table 11. Comparison of annual sand accumulation and dune growth rates in Massachusetts, North Carolina, Texas, and Oregon. Location Crest growth | Sand accumulation (m) (m3/m) Nauset Beach, 1 Cape Cod, Mass. Ocracoke Island, N.C. 4 Padre Island, Tex. laverage of American beachgrass plots 1, 3, and 5 in Table 9 (7 years growth). 2Woodhouse, Seneca, and Broome (1976) (10 years growth). 3Table 1, sections 12, 13, 14, and 16 in Savage and Woodhouse (1968) (3 years growth). ‘Dahl, et Eula: (less SMeyer and Chester (1977) (30 years growth). Savage and Woodhouse (1968) calculated the volume of sand accumulated in four lifts of sand fence over a period of 5 years and 8 months. Annual accu- mulation during this period averaged 6.6 cubic meters per meter. The four lifts of straight fencing at Nauset Beach trapped 9.0 meters per meter per year over a comparable period. VI. CONCLUSIONS 1. American Beachgrass. ae American beachgrass was found to be effective for building dunes and stabilizing sand on Cape Cod. b. American beachgrass spreads laterally at rates up to 4.9 meters per yeare Previous studies in North Carolina reported spreading rates from 2.4 to 3.0 meters per year. Lateral spread was greater in the direction of prevail- ing winds. Prevailing winds are from the west on Cape Cod during the growing season. ce American beachgrass is capable of surviving when buried to a depth of 0.3 meter by washover deposits. Beachgrass is also tolerant to saltwater in- undation while dormant. 32 d. Average annual sand accumulation in 15-meter-wide plantings of American beachgrass was 8.3 cubic meters per linear meter during seven growing seasons. Dune height increased an average of 0.25 meter per year. These are similar to growth rates reported for North Carolina. e. A 15-meter-wide planting, three to five sprigs per hill and 90 cen- timeters between hills, formed a dune 2.0 meters high and 96 meters wide at the base in seven growing seasons.- The 90-centimeter spacing is both econom- ical and effective. f. Foot and vehicular traffic can damage American beachgrass plantings and prohibit growth in footpaths and wheel tracks, thereby reducing or pre- venting sand accumulation. 2. Sand Fence. ae Multiple lifts of sand fence are effective for dune building on Cape Cod. b. Four lifts of straight sand fence trapped sand at an annual rate of 9.0 cubic meters per meter of beach over a 5-year and 5-month observation period. ce. Four lifts of straight fence formed a dune 3.0 meters high and 30.2 meters wide in 7 years. d. Adding side spurs to straight fencing does not measurably improve long-term fence performance and increases construction costs by about 20 percent. 3. American Beachgrass Versus Sand Fencing. a. American beachgrass plantings trap little sand during the first growing season. Sand fences initially trap sand at a high rate, about Mike) cubic meters per meter. b. American beachgrass plantings, once established, trap sand at a rate comparable to multiple lifts of sand fence. 33 LITERATURE CITED BIRKEMEIER, W.A., “The Effects of the 19 December 1977 Coastal Storm on Beaches in North Carolina and New Jersey,” Shore and Beach, Jan. 1979 (also Reprint 79-2, U.S. Army, Corps of Engineers, Coastal Engineering Reseach Center, Fort Belvoir, Vae, NTIS AO70 554). BRODHEAD, J-M., and GODFREY, P.J., “Off Road Vehicle Impact in Cape Cod National Seashore: Disruption and Recovery of Dune Vegetation,” Internattonal Journal of Btometeorology, Vol. 21, No. 3, 1977, pp. 299-306. DAHL, Be et ale, “Construction and Stabilization of Coastal Foredunes with Vegetation: Padre Island, Texas," MP 9-75, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va-, Sept. 19/5. KNUTSON, P.L., “Planting Guidelines for Dune Creation and Stabilization, “CETA 77-4, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Vae, Sept. 1977. MEYER, NEI and CHESTER, A.L., "The Stabilization of Clatsop Plains, Oregon,” Shore and Beach, Oct. 1977, pp. 34-41. PORE, NeA., “Marine Conditions and Automated Forecasts for the Atlantic Coastal Storm of February 18-20, 1972" Monthly Weather Review, Vol. 101, No. 4, Apr. 1973. SAVAGE, R.P., “Experimental Study of Dune Building with Sand Fences,” Proceed- tings of the Eighth Conference on Coastal Engineering, Mexico City, 1963. SAVAGE, ReP., and WOODHOUSE, W.W., Jr., “Creation and Stabilization of Coastal Barrier Dunes,” Proceedings of the 11th Conference on Coastal Engineering, American Society of Civil Engineers, Sept. 1968 (also Reprint 3-69, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., NTIS 697 532). U.S. ARMY ENGINEER DIVISION, NEW ENGLAND, "Pleasant Bay, Chatham, Orleans, Harwich; Massachusetts,” Survey Report, Waltham, Mass., Nov. 1968. U.S. NAVAL WEATHER SERVICE COMMAND, "Summary of Synoptic Meteorological Obser- vations,” Vol. 2, Area 13 - Charleston, S.C., May 1975. WOODHOUSE, W.W., Jre, “Dune Building and Stabilization with Vegetation,” SR-3, Stock No. 008-022-00124-7, U.S. Government Printing Office, Washington, D.C., Sept. 1978. WOODHOUSE, W.W., Jr.e, SENECA, E.D., and BROOME, S.W., “Propagation and Use of Spartina alterntflora for Shoreline Erosion Abatement,” TR 76-2, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., Auge 1976. ZAK, JoM., “Controlling Drifting Sand Dunes on Cape Cod,” Bulletin 563, Univer- sity of Massachusetts, Amherst, Mass., Mar. 1967. ZEIGLER, J.M., “Beach Studies in the Cape Cod Area,” Reference No. 58-26, Woods Hole Oceanographic Institution, Woods Hole, Mass., May 1958. ZEIGLER, J.M., “Beach Studies in the Cape Cod Area," Reference No. 60-20, Woods Hole Oceanographic Institution, Woods Hole, Mass., Apr. 1960. 34 APPENDIX A SUMMARY OF SAND STABILIZATION FIELD TRIALS ON CAPE COD, MASSACHUSETTS The following summary describes sand stabilization field trials in Cape Cod, Massachusetts, sponsored or initiated by the Massachusetts Department of Public Works, the Massachusetts Beach Buggy Association, the U.S. Army Engineer Division, New England, and the Coastal Engineering Research Center (S. Onysko, U.S. Army Engineer Division, New England, personal communication, 1979). 1. Massachusetts Department of Public Works. In the early 1960's the Massachusetts Department of Public Works and the U.S. Bureau of Public Roads, in cooperation with the University of Massachusetts, initiated definitive studies on the use of American beachgrass for stabilization on Cape Cod. These studies found that beachgrass was effective in restoring damaged dunes and that plant spacing of 45 by 90 centimeters was adequate except in areas of severe erosion (Zak, 1967). 2. Massachusetts Beach Buggy Association (MBBA). In 1963, MBBA obtained permission from the towns of Orleans and Chatham to erect 1,500 feet of sand fences on Nauset Beach to prevent overwash from cutting a channel into Pleasant Bay (Fig. A-1l). The fence collected considerable sand and was successful for about 2 years. However, subsequent storms destroyed the project. 3. U.S. Army Engineer Division, New England. In October 1965, the New England Division experimented with sand fences on Nauset Beach in conjunction with their Pleasant Bay navigation study (Fig. A-2), to determine if the dunes could be restored to prevent sand from washing into proposed navigation channels for the bay. The fence, which consisted of cedar piles tied securely with twine, was erected in a single line parallel to the beach but back from the high waterline in an attempt to build the dune forward. Sand was building slowly until a northeast storm hit the area on 9 January 1966, causing breakthroughs in the southern section amounting to about 7 percent total damage to the fence. Total sand accumulation for the entire length of fence, excluding the breakthroughs, amounted to about 15,000 cubic meters. This amount was collected over a 2.5-month period, but the bulk of it was collected during and right after the January storm. The cost of the fencing and posts was about $1,200 (1966). Volunteer labor was provided by the Wellfleet Job Corps. The estimated cost of collecting the sand was $0.50 per cubic meter. A second row of fencing, with front spurs only, was constructed at the northern end of the project on 17 August 1966, about two-thirds of the way up the front slope of the new dune. By 11 January 1967, that fence was almost filled. By May 1967, the northern end of the sand fencing had created an artificial sand dune almost 2.3 meters high. Field visits in 1969 found beach- grass growing back naturally on the artificial dunes. 4. Coastal Engineering Research Center (CERC). The original CERC experimental project was first established on Nauset Harbor north spit (Fig. A-3). The project was started in May 1969 and consisted of alternating plots of straight sand fence, grass plantings, fabric fence, and sand fences with spurs, each plot approximately 122 meters long. The straight oS) “(99ZET “ON “(QHZET “ON 34eYD TeOTINeU SON) UOTIeOOT |RTS uoTIeZFT JAeYO TBOTINEU SON) WOFIBIOT |IFS UOTFIeZTTTGQeIs pues *7-Vy eINnsTy -Tqeqs pues uofzepoossy A38ng yoeog sjqasnyoesseW E96] ‘“[-V 21N3TY Tate) d ° ) — Pere eu Hy cs As) W Oc NO9 Deeg} (2) 14 99 Ss 3 e@ - ac, (y3MOL >” KDBM BuIwVI0Y ouay \ . JdIdONVIS ‘ Se Kh 3dIdONVIS 3 130g wey $103 Awiy ‘Ss ‘f aul yo uoisiaig pudjbuZ man aS uooII0SSy Abbng yo0ag sjjasnyoossoW 36 sections of fence collected very little sand due to the influence of existing dunes, which appeared to alter the wind patterns. The planted beachgrass plots had a 95- to 98-percent mortality. The fabric fence collected sand initially but later failed structurally. The fence section with side spurs was destroyed due to the inlet shifting to the north during a coastal storm in November 1969. The CERC project was relocated to the Nauset Harbor south spit (Fig. A-3) in April 1970. * fs Casey yp ay ee ee BS a ° Salt Pond \S) - Bay CERC Experimental Dune Stabilization Site a (North Spit Site ) ys SN anding ae x. ae : E 4 ce CEC Experimental Dune AFx( Stabilization Site eH (South Spit Site ) , : -y a Nauset — Nicights \ aumento | WS 2. DS 17 \} Mill Pond AA ELA > Ges TaN Bsvese mes il Ore Na 1] (e fete he Oi ON ole Me SN Figure A-3. 1969 north spit and 1970 south spit CERC experimental dune stabilization sites (U.S. Geological Survey). 37 APPENDIX B EROSION AND ACCRETION AT NAUSET BEACH, CAPE COD 1. Storm Erosion. a. Storm of February 1972. (1) Description. The most severe storm encountered during the 8-year monitoring period (1970-1977) occurred 18 to 20 February 1972. Because of its intensity and long duration, the storm caused extensive damage along beaches from Long Island to New England. Storm surge reached its greatest height in the early morning hours of 19 February 1972. Surge levels of 1.3 to 1.4 meters were reported on Cape Cod (Pore, 1973). The peak storm surge was nearly coinci- dent with high tide which intensified shore damage. Shipboard observers reported waves from 3.0 to 3.5 meters during the storm (Pore, 1973). (2) Impact. Profile surveys were made in the study area on 14 February 1972, 4 days before the storm, and again on 6 March 1972, 14 days after the storm. Though a survey was conducted relatively soon after the storm, it should be noted that significant changes in the shore and beach may occur immediately following severe storms. For example, Birkemeier (1979) recently studied beach changes during an 18 to 20 December 1977 storm on Long Beach, New Jersey. He found that about one-half of the material eroded from the beach during the storm was returned to the beach within 2 days. The February and March 1972 profile surveys provide data on the storm impact on dunes during early stages of devel- opment. Figure B-l depicts the prestorm and poststorm profiles on the spit. Major accretion of sand occurred along the seaward shore of profiles 1 to 4. In this area, the beach advanced from 15 to 40 meters. Though data are incom- plete for profile lines 8 and 10, there appeared to be some erosion along profile lines 5 to 10, up to 15 meters at profile line 9. During the storm the beachgrass plots (profile lines 1, 2, 5, 6, 9, and 10) were buried with overwashed sand. Plot 1 was buried by 0.3 to 0.7 meter, plot 3 by 0.03 to 0.7 meter, and plot 5 by 0.2 to 0.5 meter of sand. Plants were observed emerging in all plots by April 1972. It was not possible to measure the overall survival of the buried plants because bare areas were replanted in April 1972 in keeping with study objectives to provide complete plant cover in these areas. However, American beachgrass did emerge through at least a 0.3- meter washover deposit in plot 2 and did survive saltwater inundation. S.P. Leatherman and P.J. Godfrey (Institute for Man and Environment, National Park Service Cooperative Research Unit, University of Massachusetts, personal communication, 1979) have recently made similar observations on Nauset Beach. However, they note that saltwater inundation and overwash during the growing season can cause total mortality in American beachgrass stands. The growing season for American beachgrass is roughly from March through November (R. Zaremba, Institute for Man and Environment, University of Massachusetts, personal commu- nication, 1979). Crest elevations in the fenced plots were nearly 1 meter higher than the beachgrass plots before the storm. Consequently, less overwash occurred in these plots. The only major overwash occurred in plot 2. About 30 meters of the fencing in plot 2 had been damaged by a storm during the previous year. The earlier damage probably provided a natural pathway for overwash during the 38 @ HORELINE POSITION - eee DATUA Hepes HORI Pat OATUM BASE NE T SURVEY ( 14FEBTZ ) S. FIR SS E8xD SURVEY ( BAARTZ ) ELEVATION ¢ H) 14 18 18 12 10 “160 -120 -80 ~B0 -30 Q 30 8a a0 120 150 180 216 OIBTANCE (¢ A) Figure B-l. Profile comparison for surveys of 10 profile lines at Nauset Beach, after February 1972 storm. February 1972 storm. In all, 50 meters of the southern end of fence lifts one, two, and three were destroyed and lift four was damaged by the storm. Profile line 3 crosses the damaged section of plot 2 (Fig. B-1). Landward of the fences about 0.3 meter of sand was deposited. Little overwash occurred in the northern end of plot 2, profile line 4 (Fig. B-1). The straight fence section (plot 4) did not sustain damage during the February 1972 storm. b. Storm of February 1978. (1) Description. Though no elevational profiles were made after November 1977, seven observations were made after the severe storm on 6 and 7 February 1978. This storm tested the overall effectiveness of the dunes at Nauset Beach. The storm was the most severe to attack the northeastern 39 seaboard since March 1962. According to the New England Division, this storm has a recurrence interval of 75 years. Storm surge was recorded at Provincetown, Massachusetts, at 1.1 meters above a spring high tide of about 3.4 meters (G. Geise, Provincetown Center for Coastal Studies, personal com- munication, 1978). Breaking waves of 2./ meters were observed on the U.S. Coast Guard Beach, 3 kilometers north of the test area. (2) Impact. A field inspection in February 1978 revealed massive erosion on the seaward face of the experimental dunes. Of particular impor- tance, however, is the fact that the plots were overwashed at only one loca- tion, the center of plot 3. Plot 3 was bisected by two foot and vehicular thoroughfares that had persisted since 1973. Figure B-2 is a ground photo of plot 3, showing the traffic area, taken in 1977, 4 months before the storm. Figure B-2. Plot 3 (American beachgrass on 60-centimeter spacing), October 1977. Note foot and vehicular pathway through plot. 2. Long-Term Erosion and Accretion. a. Shore Migration Adjacent to Test Plots. Figure B-3 compares the initial (April 1970) and final (November 1977) elevational profiles along the 762-meter test section at the south spit of Nauset Harbor. During the 91 months of moni- toring, the landward shoreline in plots 1, 2, and 3 remained stable. The landward shoreline of plots 4 and 5 retreated about 15 to 18 meters, an annual erosion rate of about 2 meters per year. Erosion on the seaward shore followed the same general pattern. Annual erosion was less than 1 meter per year in plot 1 and more than 3 meters per year in plot 5. In general, the spit was relatively stable near its southern apex, while erosion was greater on both the seaward and landward shores of its more northern extremities. 40 ~sk. Shoreline Position Vertical Datum is MSL Horizontal Datum is Base Line “Ss. First Survey (1 Apr. 1970) ™~\ Second Survey (9 Nov. 1977) Elevation (m) a -150 -120 -90 -60 -30 0 30 60 90 !20 150 180 210 Distance (m) Figure B-3. Profile comparison for surveys of 10 profile lines at Nauset Beach for survey period, 1970-77. b. Spit Migration. From 1856 to 1940, Nauset Inlet opened at the south end of Nauset Harbor. During this period the south spit was either quite short or completely absent (Zeigler, 1960). Since 1940 the south spit has elongated, though there have been several periods of retreat and progression. In October 1969, 6 months before the start of the experimental study, the length of the south spit was about 914 meters. By November 1977, the spit had increased to a length of 1,972 meters (Fig. B-4). 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