Summary of 20-years of Shoreline Monitoring Between Maryland Avenue, Point Pleasant Beach, Bay Head, Mantoloking, Brick Township, to 1 st Avenue in Normandy Beach, Ocean County, New Jersey & an Evaluation of Shoreline Change Between 1920, 1994, and 2005 Beach, dune and development in the Borough of Mantoloking as of January 1920. Prepared for The Borough of Mantoloking: April 2, 2008 Prepared by the Richard Stockton College Coastal Research Center Dr. Stewart Farrell & Mr. Daniel Barone
Introduction: In 1985 Hurricane Gloria inflicted serious damage along the entire NJ coastal oceanfront. Following the settlement of issues raised by the Federal Emergency Management Agency (FEMA) the State of NJ instituted a program of coastal beach/dune monitoring between Raritan Bay and Delaware Bay including at least one survey site in every oceanfront municipality. Initial surveys were conduced at each site every fall until 1994 when the State instituted a survey series every spring as well. The second mode of study was the use of aerial photography from 1920, 1994 and 2005 to generate comparison graphics showing the nature and amount of advance or retreat in the Mantoloking shoreline for 1920 to 2005 and for 1994 to 2005 with a view to understanding where sand has been going and an idea of why the observed changes have occurred. Graphics include views of the entire Northern Ocean County shoreline. For the purpose of part one of this study, the Borough of Mantoloking site, located at 1117 Ocean Avenue (Mant-3) in the municipal profile series, was extracted from the NJ State 20-year report along with the two sites north and south of the Borough. The data from the five locations is reproduced below and can be summarized as follows: Summary of the 5 New Jersey Beach Profile sites centered on the Borough of Mantoloking shoreline Figure 1: A view of New Jersey, highlighting the northern Ocean County barrier-spit (outlined in red). Each site is approximately 6,000 feet apart and begins at Maryland Avenue in Point Pleasant Beach. Each survey begins behind the dunes and extends across the beach, out into the water to a depth of 15 to 16 feet. The repetitive nature of the surveying allows calculation of change in terms of sand volume and growth or loss in any portion of the surveyed area. The shoreline position is taken as the zero elevation for the North American Vertical Datum(1929) that was initially used to establish engineering elevation control at each site. There is a series of timber and rock groins in the Borough of Bay Head that extends south from the Point Pleasant Beach boundary to Chadwick Street about the middle of Bay Head s oceanfront. From there south there are no further oceanfront structures perpendicular to the shoreline. Sand is free to move north or south along the entire shoreline from Chadwick Street in Bay Head, south into Lavallette. There are six groins between Osborne Avenue at the Point Pleasant Bay Head border and Chadwick Street. The Maryland Avenue site is located two blocks north of the Bay Head municipal boundary. While none of these six groins are particularly large structures, the sand does collect at each and form pronounced littoral drift offsets in the shoreline position from time to time especially when the sand transport direction is strongly one way or the other for a protracted period of time (six weeks). 1. The Maryland Avenue site saw two minimum years for the shoreline position in 1994 and 1997 retreating about 75 feet to the minimum value, then recovering nearly all the lost distance. The dune was substantially enhanced by natural accretion over the 20 year period. 2
2. The Johnson Avenue site lies 1,125 feet south of the Chadwick Street groin and shows oscillatory behavior in the position of the shoreline from year to year. This is especially true between 1997 and 2004. The range of shoreline position shifts was about 170 feet and represented about 50% of the normal width of the beach and dune system. Since 2003 the shoreline advanced 50 feet by 2006 and a post-1992 storm dune system was established that buried the rock revetment that exists along this segment of the Bay Head beach. 3. The Mantoloking site is positioned nearly in the center of the Borough shoreline and has been remarkably stable with a minimum position just 35 feet landward of the beginning and ending shoreline positions. A shoreline retreat and dune loss followed the December 1992 northeast storm. Only the shoreline recovery was complete about a year later. The erosion and retreat in the dune has remained. Two subsequent shoreline retreat episodes occurred 1997 and 2002, but the trend has been positive since returning the shoreline position to that present in 1986 (-0.3 foot of shoreline retreat since 1986). 4. The shoreline trends for Brick Township Public Beach #3 were similar with very small excursions in the location of the shoreline. The most recent two years in the series showed the largest retreat followed by recovery in 2006. The dune added a large volume of sand however. 5. The southern site in this set is located at 1 st Avenue in Normandy Beach. Here the shoreline retreated 50 feet between 1986 and 1993 then stabilized at that position for the next 13 years. The total retreat was 39 feet since 1986. Changes to the Northern Ocean County Shoreline since 1920: The Coastal Research Center performed a shoreline change analysis in northern Ocean County, New Jersey (Fig. 1) to study the sand budget for the entire barrier spit, with a focus on Mantoloking, NJ (Fig. 2). Shoreline change analyses allow scientists and coastal researchers to study the effects of natural events such as northeasters and hurricanes as well as study the long term effects that shore structures (i.e. groins, jetties) have on beach-dune systems in terms of advancement and retreat of shorelines. The utilization of Geographic Information Systems (GIS) allows for regionalscale assessments of beach-dune systems and aids in determining areas of greatest change between shorelines between various years. Methods Individual northern Ocean County shorelines were analyzed between the years of 1920 and 2005, and 1994 and 2005. The shorelines were delineated from georeferenced aerial photography and LiDAR elevation data using Geographic Information Systems (GIS). Since shorelines delineated from aerial photography (1920 and 1994) were derived from features (i.e wet-dry line on the beach face), the shoreline delineated from LiDAR data (2005) was derived from creating a digital elevation model (DEM), then converting the data in a hillshade raster grid. The hillshade raster allowed for the delineation of the beach berm crest, which, in most cases can easily be defined as the wet-dry line on a beach face due to the sharp change in beach slope at the berm crest position (Figure 4). 3 Figure 2: A view of the northern Ocean County barrier-spit, highlighting the Borough of Mantoloking (displayed in red).
To analyze the changes between shorelines from different time periods, two shorelines were overlain on an aerial photograph in ArcGIS. The lines were then merged and converted into polygons. Transect lines, perpendicular to the shoreline, spaced 250 feet apart, and running parallel to the shoreline from Manasquan Inlet to Barnegat Inlet were then overlain over the polygons created from the delineated shorelines. The transect lines were clipped at the extent of the shoreline polygons and the lengths for each transect were calculated using the spatial analyst in ArcGIS. Once the lengths of the clipped transects were calculated, it was determined whether the lengths of transect lines represented an advance or retreat of the shoreline between the years being analyzed (Figure 5). The results of the shoreline change analysis are represented as four graphical representations. The first two representations display the shoreline changes for the entire northern Ocean County barrier-spit between the years of 1920 and 2005, and 1994 and 2005 (Figures 6 & 7). The second two representations focus on the borough of Mantoloking, also displaying shoreline changes between the two pairs of years (Figures 8 & 9). Figure 3: A zoom-in of Seaside Heights, New Jersey displaying the delineated wet-dry line Figure 4: A zoom-in of Mantoloking, New Jersey displaying the delineated berm, or wet-dry line (red) from hillshade raster derived from LiDAR 2005 data. Figure 5: A zoom-in of Island Beach State Park displaying clipped shoreline transect lines (black) overlain on advancement and retreat polygons. 4
Summary of the Shoreline Changes in Northern Ocean County Since 1920: 1920-2005 Shoreline Changes, Northern Ocean County: At the northern and southern ends of the barrier spit (Manasquan and Barnegat Inlets), the shorelines have advanced dramatically due to the construction of jetties at both inlets between the shoreline years studied (1930 s). The jetties have prevented the littoral transport of sand into the inlets, resulting in major shoreline advances proximal to the inlets in Point Pleasant (north) and Island Beach State Park (south). The center of the study area (Berkley, Seaside, Dover), has shown and overall gain in shoreline, while the surrounding areas, the center of Island beach and Mantoloking, have shown losses. The center of Island Beach State Park shows a tremendous loss due to change in the shoreline position near the southern end of the park. In Mantoloking, the shoreline appears to be in a constant state of flux. This is probably related to large variations in the width of the beach, which change locations over shorter time periods along the Mantoloking shoreline. 1994-2005 Shoreline Changes, Northern Ocean County: During the approximately 10-year time span, the northern end of the barrier spit retreated approximately 50 feet, while the southern end of the barrier-spit advanced approximately 50 feet. In the middle of the study area (Berkley, Seaside, Dover), the shoreline remained relatively stable, showing gains and losses within the area. The areas that showed the greatest losses were in the middle of Island Beach State Park and the boroughs of Mantoloking and Bay Head. The losses in Island Beach State Park can be attributed to continued advance of the shoreline at the southern end of the park. The losses in Mantoloking appear to be generated by the groin field existing in Bay Head. 1920-2005 Shoreline Changes, Mantoloking: As described in the summary of the northern Ocean County analysis (1920-2005), the shoreline appears vary between advance or retreat over shorter distances (about 2,000 feet). When looking closer, the areas where the most retreat occurs are in the northern end of the municipality (north of Lyman). The areas where there have been mainly advances in shoreline position are in the southern end of the municipality (south of Herbert). The center of the municipality shows gains and losses related to lobes of sand that move laterally over moderate time periods. These lobes move along the shoreline slowly and create zones of narrow beaches alternating with zones of wider beaches. The near equilibrium between the shoreline positions at the end member years emphasizes the lobate differences as undulating zones of gain or loss along the shoreline. 1994-2005 Shoreline Changes, Mantoloking: In the past ten years, the municipality has seen an overall shoreline retreat, primarily in the northern half of the town. There is an area in the southern section (between Downer and Carpenter) where there is a minimal advance in the shoreline. The results of this analysis coincide with the analysis from 1920 to 2005, where the northern section of the municipality experiences more shoreline retreat than the southern section of the municipality. As described in figure 7, losses in Mantoloking seem to be generated by the groin field existing in Bay Head. A second piece of evidence is the sudden shift between deposition in Point Pleasant Beach to erosion at the first groin in Bay Head. Retreat of the Bay Head shoreline declines away from the Chadwick Street groin south toward Mantoloking making the case for sand trapping by those six groins and a significant impact for 5-6,000 feet south of the structures. 5
Conclusion: Since the New Jersey beach monitoring program was established in 1986 the segment of shoreline representing the Borough of Mantoloking and the two community beaches north and south demonstrate relative stability along the entire reach with definite dune growth from natural sand transport without a significant retreat in the shoreline position or a decline in the volume of sand present on the beach. Any loss to the beach has been compensated for by growth in the dunes. The absence of significant storm activity since 1992 is largely responsible for this performance and its persistence depends on the continued absence of such activity. In the absence of a serious storm or a series of minor events occurring over a short time interval, the Mantoloking beachfront is generally stable as evidenced by 88 years of aerial photographic comparison. This evidence also says that should a Borough-wide beach restoration project be conducted to at least half the sand volume proposed by the US Army Corps of Engineers for the community, it would remain largely in place for sufficient time to be worth the effort and costs involved in getting the job done. Addition of sand for maintenance would most likely be required on a 5-year interval (longer if the storm pattern presently ongoing continues). The aerial photography, which goes back to 1920 (covering 88 years) shows the substantial impact of jetty construction at the boundary inlets. These structures curtailed sand movements into or out of the inlet shoal systems producing dramatic advances in the adjacent shorelines, but a pronounced retreat trend to the beaches located a mile or so north and south of each jetty. Sand also gathered in the center of the Northern Ocean County shoreline since 1920. In the 10 years between 1994 and 2005 the shoreline retreated modestly most of the reach, with Mantoloking situated with half its shoreline in the shadow of the pattern cast by the groin structures in Bay Head. 6
Shoreline Trends at Maryland Avenue, Point Pleasant Beach, NJ 500 400 Feet from Reference Position 300 200 100 Largest Annual Advance in the Shoreline Two Minimum Years in Shoreline Position 0-100 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year Annual Shoreline Position Shoreline Position Trend Poly. (Shoreline Position Trend) Figure 76 Site 155. This profile well south of the Manasquan Inlet, the beach behaved more in tune with the general climate for the interval. Storms produced retreat in 1991 to 1993 followed by slow recovery to the 2005 position. Both 1987 and 2005 showed nearly the same maximum advance position in the shoreline. The minimum was seen in 1994 and 1997. There has been no influence by beach nourishment activities from here south along the northern Ocean County shoreline. 7
A. B. C. 20-Comparison Photographs Site 155, Maryland Avenue, Point Pleasant This shoreline segment is protected by a massive dune in terms of both width and height (C, taken in 2006)). Established prior to monitoring in 1986, this feature has gained sand volume in spite of a relatively narrow beach. The beach width improved since 1986 but not in a steady fashion. In 2005, there was a substantial advance in the position of the shoreline coupled with a wider berm. Photos A and B show the beach conditions in 1990 and 2006, respectively. 8
30 New Jersey Beach Profile Network #155 -Maryland Avenue, Point Pleasant, Ocean County Line Survey Date 20 155 01 12 Dec 86 155 33 26 Oct 06 10 Elevation, Feet 0-10 -20 Figure 77: This massive dune has slowly increased in sand volume over 20 years. The crest elevation remained constant as did the dune width footprint. The beach is slightly wider as sand accumulated offshore and on the berm. Located over a mile and a half from Manasquan Inlet, sand movement from the Monmouth County project is possible but unlikely. -30 0 100 200 300 400 500 600 700 800 Distance, Feet 9
Shoreline Trends at Johnson Avenue Bay Head, NJ 300 250 200 Peak Period in Shoreline Position Feet from Reference Position 150 100 50 0 Large Variations in Shoreline Position due to the Impacts of the Bay Head Groin Field -50-100 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year Annual Shoreline Position Shoreline Position Trend Poly. (Shoreline Position Trend) Figure 78 Site 154. In Bay Head the variations in shoreline position were quite large with a 20-year trend of seaward advance. The 1992 Storm caused shoreline retreat with serious overwash of the tiny dune exposing the rock seawall core. Fortunately, the rock revetment extended across about 1,600 feet of shoreline and prevented extensive damage to properties and infrastructure. This structure was exposed and scoured on both sides as waves overtopped the feature sending water and sand into the streets and adjacent 10
properties. A dune was rebuilt after the storm to a more reasonable size and has grown larger from natural aeolian processes since. There was a yearly oscillation in shoreline position between 1997 and 2004 significant in that it represents changes in the direction of longshore transport by waves whether toward the groin field (north) or away from it (south). This produces large shifts in the shoreline depending on the direction of dominant drift for sand. 20-Year Comparison Photographs Site 154, Johnson Avenue, Bay Head The revetment is partially shown on the left side of the 1991 photograph (left side) and lies directly under the photographer s feet and extends north and south in the 2006 photograph (left). Exposed completely in December of 1992, the beach was deeply scoured directly seaward of the rocks and overwash topped the rock crest and washed all the dune sand down the street into route 35. Reconstruction initiated development of a substantial dune today (right) enhancing storm protection, but fortunately similar intense storm events have not occurred along the Jersey shore since. 11
30 New Jersey Beach Profile Network #154 - Johnson Avenue, Bay Head, Ocean County Line Survey Date 20 154 01 12 Dec 86 154 33 27 Oct 06 10 Elevation, Feet 0-10 -20-30 -100 Figure 79: In 1986 there was no dune at Johnson Avenue, but there is a rock revetment that lies below the thin wedge of the artificial dune present in 1986. Dune enhancement efforts during the 1990 s generated a reasonable width and height dune following an overwash event in December 1992. Sand accreted on the beach from offshore with an advance of 73 feet in the shoreline as well as 27.86 3 yds /ft of sand that was added to the dune and berm. 0 100 200 300 400 500 600 700 Distance, Feet 12
Shoreline Trends at 1117 Ocean Avenue, Mantoloking, NJ 350 Feet from Reference Position 300 250 200 150 100 50 Peak Year in Shoreline Position Duplicated 4 More Times Largest Annual Retreat in the Shoreline 0-50 -100 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year Annual Shoreline Position Shoreline Position Trend Poly. (Shoreline Position Trend) Figure 80 Site 153. The Mantoloking Borough has no hard structures in its beach; therefore the shifts in shoreline position are far more muted and related to individual storm impacts and seasons with higher than average storm activity. The long-term trend is nearly flat over 20-year study period, a fairly rare occurrence along the NJ ocean coast. 13
20-Year Comparison Photographs Site 153, 1117 Ocean Avenue, Mantoloking The 1992 northeast storm damaged the dune severely enough to erode through the crest. Restoration efforts have continued to date (right). The linear vegetation boundary represents the 2005 2006 winter erosion of the dune with the dune slope sand put back using a bulldozer to harvest sand from the storm recovery deposit on the beach. The 1992 scarp was about 25 feet landward of the most recent storm activity. Although the shoreline position has been relatively stable the beach width is insufficient to support further dune growth and marginally sufficient for supporting the current dune system, resulting in frequent erosion and vertical scarping of the seaward slope even during modest to moderate storm events. 14
30 New Jersey Beach Profile Network #153-1117 Ocean Avenue, Mantoloking, Ocean County Line Survey Date 20 153 01 12 Dec 86 153 33 25 Sep 06 10 Elevation, Feet 0-10 -20 Figure 81: Located in front of a private residence, this Mantoloking site s dune retreated dramatically during the December 1992 northeast storm. Recovery did not return the width of the dune or its height back to pre-storm values. The beach remained essentially the same, offering some protection to dune erosion during minor storms. This site saw a 5.68 yds 3 /ft. sand volume loss with a shoreline retreat of only 0.3 feet. -30 0 100 200 300 400 500 600 700 800 Distance, Feet 15
Shoreline Trends at the Public Beach #3, Brick Township, NJ 450 400 Peak Year in Shoreline Position Feet from Reference Position 350 300 250 200 150 100 50 Largest Annual Retreat in the Shoreline 0-50 -100 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year Annual Shoreline Position Shoreline Position Trend Poly. (Shoreline Position Trend) Figure 82 Site 152. The lack of hard structures in Brick Township continued the trend of minimal shoreline shifts from year to year. The site showed a retreat of about 15 feet in 20 years with no observable pattern. In fact, the best and worst years in terms of shoreline position occurred in 2004 and 2005. 16
20-Year Comparison Photographs Site #152, Public Beach #3, Brick Township The 2006 view from the dune crest in front of the public use building for the beach (right). The dune was built naturally as a result of sand accumulation around snow fencing erected as the facility was opened in 1986 (left). Today a substantial dune and generous beach exists at this public use area. The beach s width has not changed significantly during the 20-year time interval. 17
30 New Jersey Beach Profile Network #152 - Public Beach #3, Brick Township, Ocean County Line Survey Date 20 PAVILION 152 01 11 Dec 86 152 33 09 Oct 06 10 Elevation, Feet 0-10 -20 Figure 83: The Brick Township dune was created when the public recreation area was built about 20 years ago. Dune accumulation amounted to a gain 3 of 23.23 yds /ft while the beach remained essentially constant. The public works effort expended to build this dune was limited to the initial grass planting and several installations of dune fencing. -30 0 100 200 300 400 500 600 700 800 Distance, Feet 18
Shoreline Trends at 1 st Avenue, Normandy Beach, NJ 250 Peak Year in Shoreline Position 200 Feet from Reference Position 150 100 50 0 Largest Annual Retreat in the Shoreline -50-100 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year Annual Shoreline Position Shoreline Position Trend Poly. (Shoreline Position Trend) Figure 84 Site 151. The beach at Normandy s First Avenue saw a rapid shoreline retreat that stabilized by 1992/93 and subsequently advanced slightly until 2006. The largest retreat occurred in 1989; a year with no significant storms. 50-foot shoreline retreats along the Ocean County shoreline are by no means rare, but do demand attention if not reversed almost immediately because of the narrow beaches. 19
20-Year Comparison Photographs Site 151, 1 st Avenue, Normandy Beach The dune toe lies within easy reach of ocean waves during a storm. The 1992 storm caused seaward slope erosion and overwash that pushed sand onto the landward slope. Fortunately there have been few storms since 1992 and the dune has not been called upon to defend the development positioned landward of the feature. No sand has been placed on this beach during the past 20 years. The pictures above depict the beach conditions in 1991 (left) and 2006 (right). 20
30 New Jersey Beach Profile Network st #151-1 Avenue, Normandy Beach, Ocean County Line Survey Date 20 151 01 11 Dec 86 151 33 09 Oct 06 10 Elevation, Feet 0-10 -20 Figure 85: Changes at this site were relatively minimal. The entire profile, defined by the extent of the 1986 survey, resulted in a loss of 12.95 3 yds /ft. The dune grew slightly, but the shoreline retreated by 39 feet. The 1986 survey methodology did not permit reaching more than wading depths at low tide so details on the offshore bars is lacking. -30-100 0 100 200 300 400 500 600 700 Distance, Feet 21
Figure 6. This graph represents the changes in shoreline positions per 250-foot beach segment for the entire northern Ocean County barrier-spit between the years of 1920 and 2005. At the northern and southern ends of the barrier spit (Manasquan and Barnegat Inlets), the shorelines have advanced dramatically due to the construction of jetties at both ends in the 1930 s. The jetties have prevented the littoral transport of sand into the inlets, resulting in major shoreline advances proximal to the inlets in Point Pleasant (north) and Island Beach State Park (south). From the graph, in the center of the study area (Berkley, Seaside, Dover), has shown an overall advance in shoreline, while the surrounding areas, the center of Island Beach Park and Mantoloking have shown losses. The center of Island Beach State Park shows a tremendous loss due to change in the shoreline position near the southern end of the park. In Mantoloking, the shoreline change appears as a series of waves of advance or retreat spaced regularly along the beach. This is due to the lobate nature of an un-structured sand beach exposed to littoral currents parallel to the shoreline. The near coincidence of the two shorelines emphasizes these undulating excursions in the beach. 22
Figure 7. This graph represents the changes in shoreline positions per 250-foot beach segment for the entire northern Ocean County barrier-spit between the years of 1994 and 2005. During the approximately 10-year time span, the northern end of the barrier spit retreated approximately 50 feet, while the southern end of the barrier-spit gained approximately 50 feet. In the middle of the study area (Berkley, Seaside, Dover), the shoreline remained relatively stable, showing gains and losses within the area. The areas that showed the greatest losses were in the middle of Island Beach State Park and the boroughs of Mantoloking and Bay Head. The losses in Island Beach State Park can be attributed to advancement of the shoreline at the southern end of the park. The losses in Mantoloking seem to be generated by the groin field existing in Bay Head. Note the abrupt shift to erosion at the Bay Head border with Point Pleasant Beach with the erosion shadow declining in magnitude to the south into Brick Township. 23
Figure 8. This graph represents the changes in shoreline positions per 250-foot beach segment for Mantoloking, New Jersey between the years of 1920 and 2005. As described in figure 6, the shoreline appears as undulating waves of erosion and deposition. This is partially due to the construction of the jetty at Manasquan Inlet and the presence of a groin field in Bay Head. When looking closer, the areas where the most retreat occurs are in the northern end of the municipality (north of Lyman). The areas where there have been mainly advances in shoreline position are in the southern end of the municipality (south of Herbert). The center of the municipality shows oscillating gains and losses with a 1,500 to 2,000-foot interval. 24
Figure 9. This graph represents the changes in shoreline positions per 250-foot segment of beach for Mantoloking, New Jersey between the years of 1994 and 2005. It is clear that in the past ten years, the municipality seen an overall shoreline retreat, primarily in the northern half of the town. There is an area in the southern section (between Downer and Carpenter) where there is a minimal advance in the shoreline. The results of this analysis coincide with the analysis from 1920 to 2005, where the northern section of the municipality experiences more shoreline retreat than the southern section of the municipality. As described in figure 7, losses in Mantoloking seem to be generated by the groin field existing in Bay Head. 25