2003-066 - Laserfiche WebLink

Home Browse Search

Task 1 . 1 .2 Sub-Bottom Profiling Sub-bottom profiling will be performed to assess the substrate thickness, consistency and condition . An EdgeTech , Inc. X-Star Full Spectrum Digital Sub-bottom Profiler will be utilized for data acquisition . The frequency of operation of the EdgeTech system will be in the range of 2 kHz to 16 kHz . The lower acoustic frequency range will allow penetration into the sub-bottom . Sub-bottom profiling will occur at locations equivalent to those investigated in task 1 . 1 . 1 . A trackline spacing of five hundred (500) feet on-center in the shore normal direction , and ' cross ' lines at three hundred (300) feet shore-parallel is proposed . The first shore-normal truckline shall commence directly offshore from DEP monument R-86 at an approximate water depth of 12 feet (MLLW) and shall extend 2 , 000 feet offshore . Shore-normal tracklines for sub-bottom profile data acquisition will be conducted as described in Task 1 . 1 . 1 , with the requisite 19 shore-normal tracklines allowing for 7 .2 line-miles of seismic data acquisition . The shore parallel tracklines shall be conducted beginning offshore of R-86 at an approximate water depth of 12 feet (MLLW) . The shore parallel tracklines shall be taken every 300 feet and shall extend a maximum of 2 , 000 feet offshore . Shore-parallel tracklines shall extend alongshore to R-95 (a total shore parallel length of approximately 8 , 500 feet) . The 7 shore-parallel tracklines shall cover approximately 11 . 93 line-miles . Sub-bottom profiles will be taken at the same time as the bathymetric survey, Task 1 . 1 . 3 Jet Probes to Assess Substrate Thickness As detailed in the " Indian River County Sectors 1 &2 Beach Restoration Project Mitigation Plan" (2002) candidate areas will be surveyed with towed array sub-bottom profiling equipment to evaluate sand layer thickness , consistency and condition (Task 1 . 1 . 2) . These results will require limited groundAruthing by diver-operated jet probes . Three jet probes shall be preformed along each transect line at R-86 , R-881 R-901 R-92 and R-95 (coincident with the bathymetric and sub-bottom survey areas) . The jet probes shall occur along each profile line at 500 ft offshore of the MHW line , 1 , 500 ft offshore of the MHW line, and 2 , 000 ft offshore of the MHW line , for a total of 15 jet probes . The depth of the jet probes will be in the range of 6 to 10 feet, with the intent of locating planform areas sufficient to accept mitigative reef unit placement with limited unit differential settlement (ideally, a maximum of 3 feet of sand overburden prior to encountering subsurface rock/refusal , indicating a stable platform for reef construction) . The exact spacing of the jet probes will be subject to the field reconnaissance and exact locations noted as the work is performed . Task 1 . 1 .4 Interpretation and Presentation of Bathymetric, Jet Probe and Sub= Bottom Profiling Data To assist with determining the location of existing hardbottom to be avoided for mitigative reef siting , the County-acquired 2001 aerial photographs acquired by Indian River County will be utilized . It is understood that, while the 2001 aerials are not rectified , the imagery provides sufficient resolution and reasonable confidence in the location of the exposed reef resources to allow the proper siting of mitigative reef units without C1WINDOWSITEMPWnbersend Post-ConsUmbon Services Contract Amendment #6 - Reduced Scope 03.12.03.doc 3