U.S. ARMY CORPS OF ENGINEER PERMIT NUMBER 960100004
SPECIAL CONDITION 3
This document is the second in a series of monitoring reports required by the USCOE pen-nit which was issued to IOTA Partners, Inc. for the archeological excavation of the SANTA MARGARITA, a Spanish galleon which sank on Rota's fringing reef in 1601. According to IOTA Partner's on-site archeologist, Mr, Robert Reedy, this particular wreck has historical significance as it is one of the few "early" Manila wrecks that have been, or are in the process of being excavated.
The initial compliance report (dated 19 June 1999) addressed the turbidity component of Special Condition 3. The turbidity issue is more completely detailed in the Section 401 Water Quality Certification (Section 401 WQC) which the DEQ issued on 5 February 1999. In keeping with the sampling scheme developed by the DEQ, turbidity data is collected daily from two sampling sites whenever excavation occurs and FAXed to DEQ. Compliance with the Section 401 WQC is based on the results of this turbidity data.
As previously discussed in the initial report, four coral reference sites were identified and marked with rebar: two sites were positioned up-current from the "project site area" (ie., sand pit) while two sites were situated downcurrent. These sites were further delineated into shallow and deep water. Photographs of the coral colonies at each site were photo-documented for future comparison of coral health.
The results from this July survey were compared with those from the initial report. This series of reference coral photographs were taken on 16-17 July 1999, approximately 62 days after the initial photographs were obtained. The reference coral photographs taken for this report are shown in Figures 1, 2, 3 and 4.
The following qualitative assessment is based on visual observations, followed up by photographic documentation, and discussion on the probable cause of any observed impacts.
UP-CURRENT SHALLOW:
Photographs of the corals at this reference site are shown in Figure 1. It appears that no project related impacts have occurred to these corals or the general surrounding reef area.
UP-CURRENT DEEP:
Photographs of the corals at this reference site are shown in Figure 2. It appears that no project related impacts have occurred to these corals or the general surrounding reef area.
DOWN-CURRENT SHALLOW:
Photographs of the corals at this reference site are shown in Figure 3. It appears that no project related impacts have occurred to these corals or the general surrounding reef area.
DOWN-CURRENT DEEP:
Photographs of the corals at this reference site are shown in Figure 4. Two corals in the immediate area of the rebar station marker have been impacted and perished. Although the coral monitoring design does not actually validate a cause and effect relationship between the excavation project and coral health, it is an excellent indicator of possible problems. However, in this particular case, I was present during the initial problems with sediment plume control and can attest to its impacts on these corals.
The first, a columnar/corymbose coral (Acropora sp.) is shown in the following photographs displayed in Figure 4: TOP ROW(left and right), MIDDLE ROW (right) and BOTTOM ROW (left). This coral is "bright" white in color and is identified by an arrow. Although not readily apparent in the photograph, the central portion (approximately 30%) of the coral contained sparse algal growth while the remaining coral was completely algae free and may be assumed to have recently died.
The second coral, a low convex encrusting Favia sp. is identified by the arrow in the MIDDLE (left) photograph, While this specimen appears to be partially dead and/or severely distressed, a healthy example of Favia sp. can be seen in the BOTTOM (right) photograph and is found within the reference coral grouping. These two corals, as well as others in the general surrounding area, were impacted by sediment plumes generated from the excavation project. The mitigative measures which IOTA Partners immediately implemented to rectify this problem are discussed in Sections III and IV.
Other general observations made on the surrounding corals in the area of impact are as follows. Not surprisingly, not all coral species were affected by the sediment plume. The branching coral Stylophora sp. appeared to be the most resistant. Very little sediment collected on the coral and evidence of mucus secretion was not common.
Acropora sp. appeared also to be doing well, although more evidence of mucus secretion was evident. impacts occurred primarily to those colonies that had a corymbose or shelf type morphology as the sediment collected in between the spaces of the upward protruding columns- Large branching Acropora (cf.) palifera (brown colored) trapped sediment on certain portions of its branches. When the sediment was swept away (by hand), the coral was bleached where the sediment had collected.
Five Fungia sp. colonies were observed in a relatively open area (approximately 2 square feet). Four appeared to be healthy while one had recently succumbed. Favia sp. corals appeared to be easily affected due to there encrusting type morphology and usual location of low-lying places. Additionally, the corallites, with their somewhat elevated ridges, tended to trap sediment particles. Although one Favia sp. coral died at a reference site, the sediment impacts did not appear to detrimentally affect all colonies of this species. Other structurally similar corals, Oulophyllia sp. and Galaxea sp., appeared to have the same affinity for trapping sediment.
After the project commenced excavation, I received a call from Mr. Tom Cusack (IOTA Environmental Officer) asking for assistance in examining environmental effects and controlling the sediment plume being generated from the excavation.
The first mitigative measure that was attempted involved extending the discharge hoses to the adjacent larger sand pit which lies northward and in deeper water. The coral growth appeared to be less and the sand pit was larger and therefore offered a larger area for the sediment plume to settle. Unfortunately, when the discharge hoses were extended to the larger sand pit, water velocity decreased to a point where the suction was not efficient. To remedy this problem, the Operations Manager installed booster pumps on the system, but it was still not enough power for the eductor system to work. Design criteria for this equipment requires that water velocity be maintained above 10 feet per second. If the velocity falls below this threshold, sand and limestone rocks will settle out in the hoses and cause blockage. This shortcoming seriously limits the length of discharge hoses, Since the discharge could not be transported further away from the project site, the only other alternative discharge area was to utilize the sand pit immediately adjacent to the excavation site. Traditional silt curtains were discussed as an option, but with the water depth at 40 feet and longshore currents, we believed it would be impractical. The first effort at controlling the sediment plume was to install a tarpaulin over the end of the discharge pipe to slow the sediment plume velocity and allow for some settling of particles. The tarp was promptly buried and failed to control the sediment plume.
Because one tarpaulin was not adequate to control the discharge flow, the IOTA crew connected three tarpaulins and formed a loose "tent" over the discharge point, This was more successful, however a bit difficult to manage as the tarpaulins kept getting dislodged by the current and buried. To keep the tarpaulin from being buried, the aluminum frame (approximately 16-foot square) supporting the shade cloth was removed from El Cazador and placed on the bottom directly fronting the discharge pipe. A second tarpaulin was connected to the rear of the alummum frame and weighted down on the outside comers for stabilization. This second tarpaulin also dampened the effects of the silt plume. Photographs of this equipment is shown in Figure 5 below. This is currently the design being utilized to control sediment plumes.
At the same time a mitigation measure was being developed for controlling the sediment plume, the reef area surrounding the project site was qualitatively surveyed for sediment related impacts to coral resources. General observations included looking for stressed corals either secreting mucus and the obvious silting over of corals.
The general area surrounding the down-current deep coral reference site was impacted by the sediment plume during the initial excavation work. Sediment appeared to collect more on certain species and forms of corals while other corals were observed secreting mucus, a natural defense mechanism for ridding itself of sediment. After discussing the sedimentation problem with Mr. Jack Harbeston, he decided to shut down the project and utilized the entire crew to clean corals. IOTA first attempted to utilize the 6" eductor to "wash" the sediment off corals, but the hose could not be easily controlled by divers and it ended up resuspending the sediment. The current was not very strong so the sediment settled back down on the corals that IOTA was attempting to clean. IOTA staff then hand swept sediment off affected corals. This methodology was very specific toward affected corals and did not unnecessarily re-suspend any additional sediment. The following several days, excavation times were decreased while the silt control measures were being developed as discussed in Section III. Additional time was spent hand sweeping corals on a as needed basis.
Special Condition 3 (USCOE 4960100004) established a monitoring plan to examine the health of adjacent corals throughout the duration of the project. The purpose of this condition was to be able to identify early on, impacts to reference corals and determine whether the impacts were originating from project related activities. Results from this survey indicated that impacts to two corals in the downcurrent deep reference site were related to the sediment plume generated from the excavation.
Immediately upon becoming aware of the sediment plume problem, IOTA PARTNERS acted in good faith and started developing mitigative measures to address the problem. The sediment plume dilemma was attacked on two fronts, the design of a mechanism to help control the sediment plume and sweeping sediment from coral colonies. Further modifications to these mitigative measures will likely be forthcoming and may include the addition of more tarpaulins to the alummum frame tent.
As coral related impacts were limited to one reference site, widespread impacts from the sediment plume are not occurring. The logical explanation for this is that the longshore current moves the plume away from the discharge site (ie., sand pit) in a westerly direction, thus impacting one general area.
The Operations Manager and Environmental Officer are working with Mr. James Reedy, IOTA Archeologist, to minimize the effects of any sediment plume that is generated from project related activities. As the excavation gradually uncovers the SANTA MARGARITA additional mitigative measures may have to be implemented which will dependent upon the particular circumstances surrounding the excavation related impact. The IOTA crew will need to be flexible and imaginative to address these unique problems should they present themselves.
