The objectives of the project are 1) to quantify the occurrence of hotspots, 2) to provide preliminary guidance to Corps engineers, and 3) to provide a classification system and database from which to identify candidate cases for further study on the causative processes. Information regarding various hotspots in the US was collected from Corps Districts through an online questionnaire (http://www.vims.edu/physical/hotspot/survey.html or the "Questionnaire" link above). The data have been categorized and are presented here. You will find charts and graphs that attempt to constrain the general character exhibited by hotspots and the conditions in which they occur. Hotspot characteristics reported include the following:

• Size
• Erosion types and rates
• Wave dynamics
• Bathymetry
• Geomorphology
• Beach state
• Presence and Type of Engineering Structures
• Modeling/Mitigation Success

The data presented begin to elucidate characteristics that are common to most hotspots and to highlight those qualities that are more specific. We hope more specific characteristics will give clues to the primary mechanisms responsible for the observed hotspot behavior. It should be noted that the data are from only 6 questionnaires. We expect as more questionnaires are answered, results will become more definitive. The following figures should demonstrate what will be done with the information received and its usefulness in characterizing hotspots and the environments in which they occur.

Figure 1:  "Hotspot Size and Erosion Characteristics"
Figure 2:  "Oceanographic Characteristics"
Figure 3:  "Geologic Characteristics"
Figure 4:  "Geologic Characteristics, continued"
Figure 5:  "Nearshore Bars and Underlying Geology"
Figure 6:  "Modeling and Mitigation"

               "Other Findings"

The hotspots for which we have information are the following: Miami Beach, FL; Sea Gate/Coney Island, NY; Surfside, CA; Monmouth Beach, NJ; Ocean City, NJ; and Spring Lake, NJ. Most of the hotspots reported were greater than 750m in length along the shoreline. A large percentage of the hotspots experienced both chronic and post-storm erosion, demonstrating the importance of investigating hotspot behavior over short (weeks to months) and long (years to decades) time scales. In all reported cases, the long-term (annual) erosion rate at the hotspot was greater than that of the surrounding beach. On average, the erosion rate was 14.3 m/yr (± 13.7) higher at the hotspot. It is also interesting to note that short-term erosion rates (m/day) were not reported from any of the sites.

While tidal ranges and wave periods were widely variable from one hotspot to another (0.5->2m and 5-14.99s, respectively), wave heights at the reported hotspots were all between 0.5-1m. In almost all of the sites (5), wave refraction had been modeled but not observed. Bathymetric highs and lows were reported at almost all of the sites. No variable bathymetry was also reported in the vicinity of one of the hotspots, suggesting that bathymetric variations and resulting wave refraction may not be the only controlling factor.

Four of the hotspots were located on barrier islands while the other two were located on mainland beaches. The upper beaches around the hotspot were mostly flat or had a single, primary dune. A bluff or scarp was reported for Surfside, CA, which coincides with the extremely high erosion rate reported for the hotspot in that area (35m/yr). The beaches at the location of the hotspots were often straight or had beach cusps.

Information on beach slopes was also collected. Most of the beaches that reported hotspots had slopes in the 5-9.99 degree range. It should be noted that the actual slopes were 5, 5.4 and 5.7 degrees, so the presentation of the data (at this stage) may be a little misleading. A very complete range of engineering structures are located around the hotspots, except at the Miami Beach hotspot, which reported no engineering structures. The structures reported were those within 1 kilometer of the center of the hotspot. The "Other" category included the following structures: buried wooden groins, stone dikes, bulkheads, and a pier.

None of the respondents had information about whether or not the underlying geology seaward of the hotspot had been surveyed. The presence of outcropping geology (hardbottom, peat, etc) in the nearshore close to the hotspot was unknown. If in fact underlying geology does play a role in shoreline behavior (See Ongoing Research link), the nearshore subbottom in the areas of the reported hotspots should be investigated. The presence of a single, shore parallel bar and the lack of any sand bar (planar) were the most common nearshore settings reported for the hotspot sites.

At half of the sites, sediment transport/shoreline change was both modeled and observed. In all cases the processes had been quantified either by modeling and/or observation. The dominant sediment transport model used was GENESIS. Others include MIKE21 and CERC. Those that modeled using GENESIS, MIKE21, or CERC (3 sites) reported accurate reproduction of the erosion at the hotspot. The success of mitigation of erosion at the hotspot sites (which mainly involved beach fill projects) was mixed or unsuccessful. To quote a response from Miami Beach, the engineers were "unable to hold [the] design template in [the] hotspot area." This statement encapsulates the motivation for hotspot research and suggests that hotspots should be better understood so that coastal engineering endeavors may be more effective and financially efficient.

All hotspot sites had a history of beach fill, the most recent fills occurring in 2001, 2000, and 1997 at various sites. None of the sites reported rapid recovery (heightened accretion) after erosion events, suggesting that fills will have to continue if the beaches are to be preserved. In almost all cases the grain size of the beach fill was similar to or exactly the grain size of the native sediment.