Photogrammetric Monitoring of Dolos Stability, Manasquan Inlet, New Jersey

Abstract

Photogrammetry has been applied as a technique to monitor the stability of dolosse on the Manasquan Inlet, New Jersey jetties. These jetties were rehabilitated between 1979 and 1982 with 16-ton steel-reinforced dolosse. The jetties have been exposed to a number of storms since 1982, including a design-level storm in March 1984. The photogrammetric measurements have provided a detailed record of the magnitude and direction of dolos movements in response to these storm events. Standard leveling techniques have been used to check the accuracy of the elevation data derived from photogrammetry. This paper describes the methods used in this monitoring effort and the results obtained from the photogrammetric measurements. Also presented are data on the structural integrity of the steelreinforced dolosse.

Analysis of 42-Ton Dolos Motions at Crescent City

“…While breakage has typically been associated with some amount of movement, either of the dolos which breaks or of adjacent units, it has not necessarily been associated with significant movement and vice versa. At the Manasquan Inlet jetties, Gebert and Clausner (1984) also observed that the largest displacements experienced were by dolosse which did not break. The dolosse at Manasquan Inlet weigh 14.6 metric tons (16 tons).…”

“…To date, the dominant dolos movement has been upslope with slight settling plus rotation about the vertical or z-axis (yaw). Yaw was also the predominant dolos rotation observed by Gebert and Clausner (1984) at the Manasquan Inlet jetties. This type of rotation probably occurs more frequently because the upper layer dolosse are not constrained laterally as much as they are vertically; note that the settlement shown in Table I is a relatively small component of the total translation experienced.…”

“…If, in the future, a more refined and three-dimensional assessment of the movements of non-targeted dolos is deemed necessary, such an assessment can be made using the photography already taken by preparing photomaps outlining all visible dolosse using the same stereo model set up for the targeted dolosse. This photomapping approach was used to monitor dolosse movements on the jetties at Manasquan Inlet, New Jersey (Gebert and Clausner;1984}. The twenty-six dolosse which have been marked in this monitoring project are shown in Figure 1. Eighteen of these are located in the instrumented section and eight are distributed uniformly throughout the remainder of the dolos field.…”

“…Considering the structure slopes at Crescent City (typically flatter than 4H:1V in the zone of wave impact), the observed upslope movement of the dolosse is not surprising. Other recent full-scale monitoring of smaller dolosse on the East Coast and Great Lakes of the United States has documented downslope movements (wave run-down dominated) at structures with slopes ranging from 1.5H:1V to 3H:1V (Pope and Clark, 1983;Gebert and Clausner, 1984;Pope, 1988;Gebert, 1988). Full-scale observations of dolosse within the United States appear to support Jensen's conclusion that the critical slope which determines whether armor will move upslope with wave run-up or downslope with wave run-down is near 3.5H:1V.…”