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Beach Grading Summary and Discussion
In the 2009 assessment, the beaches in southern Maine showed relatively good recovery from the Patriots' Day Storm of 2007, scoring an overall grade of a B/B-. Many beaches saw substantial recovery by 2008. In fact, for many locations, 2008 appeared to be the most accretive year of the past four years of profile collection. This was an extremely positive sign, as it showed that the profiles, which underwent massive erosion caused by the Patriots' Day Storm, could recover within one year of the storm.
For many locations, this recovery occurred into 2009, though some areas started to see a reversal in profile growth, and started to experience erosion. For these profiles, this may have resulted from impacts from a series of spring storms in 2009. Similarly, in February and March 2010, a series of very strong northeast storms caused large amounts of erosion at many of the profile locations. This was evident in some of the winter profile shapes, but also carried over into the summer with lean recovery of many of the profiles.
For example, profile HI02 at Higgins Beach in Scarborough showed very good recovery in the last assessment, scoring a B, with good profile recovery through April of 2009. However, by April of 2010, the profile underwent massive erosion due to the winter storms of 2010. This erosion was followed by very poor recovery in the summer of 2010, so the profile was set up for a very tough winter of 2011. Sure enough, the April 2011 profile shape showed little recovery from the severely eroded shape of April 2010. As a result, this profile scored an F for its summer and winter shapes.
Of course, one of the limitations of using "snapshot" points in time (such as the same month through consecutive years, as is the case in this report) is that the analysis may miss, or overly weigh, a certain profile shape that was influenced by an event immediately preceding the recording of the beach profile, when a month later, the profile may show full recovery.
The 2011 Highs and Lows
The Maine beaches, in 2011, scored an overall C, with a numerical grade of 77. This is down from the 2009 assessment, in which the beaches averaged a low B.
Table 4 shows the final scores for each beach, based on their summer and winter scores, ranked by the high score to low score, including the numerical score. Each numerical score has been color-coded to represent the corresponding grade: green (A or B); yellow (C); and red (D or F). Table 5 shows the overall averaged letter grades from 2011 in comparison with 2009 scores and indicates the trend from 2009-2011 for each beach.
Based on winter profile shapes through the winter of 2011, the top scoring beaches were East Grand Beach in Scarborough, Goose Rocks Beach in Kennebunkport, and Kinney Shores in Saco and Long Sands Beach in York (tied for third). However, based on summer profile scores, the top three beaches include East Grand Beach in Scarborough, Goochs Beach in Kennebunk, and Wells Beach, Wells. Overall (including both winter and summer profile analysis), the top three scoring beaches were East Grand Beach (92, A-), Kinney Shores (83, B), and Goose Rocks Beach (81, B-). Note: it is important to note that results at Goose Rocks may be inaccurate due to profile starting point relocation for several of the pins in 2010.
Review of the data indicates that only one beach had all profiles score an excellent (A) for both summer and winter profiles - that was East Grand Beach in Scarborough. Situated at the northern end of Saco Bay, this section of the shoreline underwent substantial dune and berm growth, and relatively stable berm and beach formation from year-to-year. As noted in the previous assessment, this beach is fortunate enough to be the recipient of sediment migrating from the southern portion of the bay. The next closest beaches in terms of overall score were Kinney Shores (83, B), Goose Rocks Beach, and Goochs Beach, which both scored a low very good (B-). This concerns us, since these are all lower levels of what we would consider to be "very good" on the scale.
The majority (11 of 13 or 85%) of beaches scored in the green range in the 2009 assessment - that is, an A or a B. The remaining 2 beaches scored in the yellow range. In the 2011 assessment, only 4 beaches of 12 (33%) scored in the green range, while 5 beaches (42%) scored in the yellow range, and 3 beaches (25%) in the red range. Of all the beaches, only one had an increase in score (East Grand Beach), and only 2 stayed the same, with similar scores from 2009 (Kinney Shores and Goose Rocks Beach, see Table 5). The rest of the beaches had scores in 2011 that were lower than in 2009.
The beaches with the biggest changes in overall grades from the 2009 assessment were: Higgins Beach (B to a C-); Laudholm Beach (B to a C-); Drakes Island Beach (B- to a D+); Wells Beach Beach (A to a C+); and Ogunquit Beach (B- to a D).
Beaches with only minor, yet decreasing trends in grades were: Scarborough Beach (C+ to a C); Ferry Beach (C- to a D); Goochs Beach (B to a B-); and Long Sands Beach (B to a C).
Analysis of seasonal profiles, winter vs. summer, showed that in general, winter profiles maintained a low, concave up shape, with sand in the offshore. Conversely, in the summer, a berm typically developed, and sand moved up the beach profile, forming a more convex shape. This was especially notable in the profiles that scored higher (East Grand Beach, Kinney Shores, etc.), as opposed to those that scored lower. This seasonal shift is very important, and the ability of a profile to lose sand in the winter, and gain it back in the summer, lends itself to a healthy beach system. When sediment is lost in the winter, and not regained in the summer, the berm has difficulty forming, and the profile will undergo erosion, especially in comparison with the previous summer's shape.
This is evidenced in the seasonal data in this assessment. Although the overall grades were the same for winter and summer (an average of 76), an interesting finding was that, in general, many profiles scored slightly better for their winter shapes, as opposed to their summer shapes. This may be due to the fact that in the winter, the profiles were eroded to nearly the same point, bringing them slightly closer to an erosional equilibrium point, with less room for great variability. When the summer returned, the profile did not have the same amount of sand returning as the previous summer, resulting in a worse summer score.
This was mainly due to the fact that the summer berm, apparent in previous years, was small or absent coming into the summer of 2010 at many beaches. For example, Kinney Shores in Saco scored more poorly based on its summer shapes, than it did its winter shapes. Again, we feel this is likely due to the winter 2010 storms, which eroded many profiles quite deeply. It will be interesting to compare summer 2011 profiles with those of 2010, to see if beaches that have not fared so well have recovered by this summer.
Also, it is possible that profiles, in the winter, are reaching a ravinement (erosional) surface or underlying geology (historic peat surface or rock outcrops); because these surfaces do not erode easily, they give a sense of profile stability in the winter. This may explain why some beaches, such as Long Sands Beach in York, and at Wells Beach in Wells, have exhibited better winter stability and scores than summer stability and scores.
One of the lows of this assessment was the overall trend of ongoing erosion, of both dunes and summer berms, over a period of a few years (e.g., 2008-2010, or 2008-2011). It seems like the 2008 year produced many of the profiles with the most sediment, and thus, the most healthy shapes. The recent trend of erosion in 2009 that has continued into 2010, and for some locations into 2011, is very concerning.
Sea Level Impacts?
As noted throughout this report, the winter storms of February and March 2010 had significant impacts on the shapes of beaches going into the spring and summer. This led to many low-scoring summer beach profile shapes.
We took a closer look at recent sea level trends in order to investigate whether or not sea level may be influencing the recent erosion. Historically, based on yearly averaged sea level measurements, Maine has been recording sea level change rates similar to that of the global ocean over the past century (around 1.8 mm/year), as measured by the tide gauge in Portland (Figure 97). Satellite altimetry measurements of the global oceans from 1993 through 2011 indicate that there has been an acceleration in the rate of sea level rise over the last 18 years to around 3.1 mm/year (Figure 98). Based on yearly sea level data from 1993 through 2009, Maine had not yet seen this acceleration, and was trending near 1.9 mm/year.
However, taking into account newer data from 2010 and 2011, it is clear that the Portland tide gauge recorded higher water levels in 2010 than in any of the previous years (Figure 99). Over this 18 year period, Portland's averaged annual sea level rise rate increased to almost 4.2 mm/year (or around 1.4 feet per century), over double the historic trend over the past 100 years.
Looking even closer at this sea level data on a monthly basis since January 2007 through June 2011 (Figure 100), one can see that the highest sea level measurements over this time period corresponded with the February and March 2010 storms. It is clear that this was the highest average monthly water level recorded in the past 100 years. It is also noteworthy that previous winters (2007, 2008, and 2009) had monthly sea levels below the trend of the linear regression. So the winter sea level of 2010 was on the order of 0.6 to 0.9 meters (2 to 3 feet) above that in the previous three winters. The winter of 2011 saw monthly sea levels fall to below the regression line. The higher sea levels from December 2009 through March 2010 most likely exacerbated beach erosion caused by the February and March 2010 storm events.
It is certain that the high surge from the February storm helped elevate the sea levels that are graphed, but we cannot conclude that was the only cause at this time without an analysis of residuals of tidal anomalies down to the day-to-day level. During June-July of 2009, there was also a period of relatively high sea levels (Figure 100) that was documented along the east coast, including Maine (Sweet and others, 2009). However, this period of anomalously high tides coincided with low wave heights and fewer storms, so had little impact on Maine beach erosion.
Seawalls and Natural Dunes
Profiles adjacent to seawalls generally show a more concave up shape, and undergo less overall profile change, in general, from season to season, than profiles at natural dunes. This is evident by looking at berm formation at areas like Goochs Beach, which is backed by seawalls, and areas like Scarborough Beach, which has a natural frontal dune ridge.
We investigated the average scores for summer and winter profiles at locations that start at a seawall, versus starting at a natural dune. Interestingly, both scored about the same. However, there was one important distinction. Using winter profiles only, those that profiles located adjacent to a seawall had a slightly higher average score (a 77, C+) than those profiles located at a natural starting point (average score of 76, C). Conversely, for summer beach profiles, the reverse was the case; the natural beach profiles had a slightly higher average score (77), as opposed to the profiles starting at a seawall (76).
These summer vs. winter values are so close that it is difficult to draw a strong conclusion. Intuitively however, this result makes some sense, although we would expect a slightly larger difference in the scores. That is, in winter, when profiles erode, the beaches with seawalls have less sediment available in the profile to begin with (thus the concave shape), and thus undergo slightly less change in response to winter storms, thus scoring higher. The natural profiles, which typically have more sand, undergo more erosion (including frontal dune erosion) in the winter months, thus scoring lower. Conversely, in the summer, the natural profiles typically see more sand return to form a better defined summer berm, indicating recovery, while beaches "stabilized" with seawalls only see a slight return since they don't undergo as much change.
Last updated on July 14, 2011
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