Corpus Christi Ship Channel Deepening Project: Approach to Assessing Project Impact
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Corpus Christi Ship Channel Deepening Project: Approach to Assessing Project Impact Prepared for Port of Corpus Christi Authority (PCCA) 222 Power Street Corpus Christi, Texas 78403 June 26, 2019 5444 Westheimer Road, Suite 400 Houston, Texas 77056 T 713.780.4100 | F 713.780.0838 CONTENTS Project Overview ........................................................................................................................................................1 Approach ....................................................................................................................................................................1 Define .....................................................................................................................................................................2 Measure ..................................................................................................................................................................5 Analyze ...................................................................................................................................................................6 Improve ..................................................................................................................................................................9 Control ................................................................................................................................................................. 10 References ............................................................................................................................................................... 12 LIST OF FIGURES Figure 1: Preferred Channel Alternative.....................................................................................................................3 Figure 2: Delft3D Model Mesh ...................................................................................................................................4 Figure 3: Comparison of Tidal Amplitude ...................................................................................................................7 Figure 4: Comparison of Tidal Velocities ....................................................................................................................7 Figure 5: Salinity Tolerance of Common Bay Species .................................................................................................8 Figure 6: Vessel Wake Modeling Extents ...................................................................................................................9 LIST OF TABLES Table 1: Vessel Wake - Comparison of Annual Sediment Mobilized (CY/year) ..........................................................9 Table 2: Summary of Modeling Results ................................................................................................................... 11 PROJECT OVERVIEW The Port of Corpus Christi Authority (PCCA) is requesting permit authorization from the U.S. Army Corps of Engineers (USACE) – Galveston District for the PCCA to conduct dredge and fill activities related to the deepening of a portion of the Corpus Christi Ship Channel (CCSC). The project would deepen the portion of the CCSC from Harbor Island into the Gulf of Mexico, an overall distance of approximately 13.8 miles (Station 110+00 to Station -620+00) as shown in Figure 1 below. The proposed project is needed to accommodate transit of fully laden very large crude carriers (VLCCs) that draft approximately 70 feet. The deepening activities would be completed within the footprint of the authorized CCSC channel width. The proposed project does not include widening the channel; however, some minor incidental widening of the channel slopes is expected to meet side slope requirements and to maintain the stability of the channel. The project would generate approximately 46.3 million cubic yards (MCY) of new material. On behalf of PCCA, AECOM has conducted a number of modeling studies to assess potential project impacts and to optimize the project design where needed. This analysis provides an in-depth review of the various models completed to date and the results achieved. APPROACH AECOM seeks to thoroughly examine its projects and plans through the lens of the community, engineering practices, environmental resiliency, and economic well-being. The Six Sigma standard endeavors through key performance metrics to lead to products that meet the high-quality standards that communities whom AECOM interacts with deserve. The utilization of this approach ultimately culminates in an environment where quality is the core tenet of every project, whether it's a building, treatment plant, or port development. This review will utilize the Six Sigma approach known as DMAIC to summarize the modeling that AECOM has implemented in considering the Corpus Christi Ship Channel Deepening Project. DMAIC is an acronym for a list of steps that one should take to develop informed, refined solutions. Define Measure Analyze Improve Control In reference to the modeling for the Corpus Christi Ship Channel Deepening DMAIC can be broken down into the following steps: 1. Define: PCCA has proposed the deepening of the CCSC from the Gulf of Mexico to Harbor Island up to a depth of -75 feet Mean Lower Low Water (MLLW). PCCA understands that this project may potentially directly or indirectly impact the community, environment, and economy. To address these concerns, PCCA has undertaken several outreach activities for the sake of transparency and environmental studies including several modeling efforts. For the sake of this analysis, we will focus on summarizing the modeling which addresses the environmental variables. 1 2. Measure: To determine what impacts this course of action could potentially have, specific variables or metrics must be identified as the measurement system with which the project outcomes will be evaluated. Validating a set of metrics and means of measuring changes is an important step in this process. The metrics modeled include tide, water velocity, shoaling, and salinity. These will be measured through well-established, proven models and methods. 3. Analyze: The results of the measurements are benchmarked against historical real-world data and thoroughly examined to determine the magnitude and effect of changes on the surrounding environment. 4. Improve: If the analysis identifies results or impacts which are deemed adverse then solutions must be created in order to avoid, minimize, or mitigate for those impacts. 5. Control: A feedback loop is formed through consistent and continuous monitoring which leads to process and product improvement. DEFINE The CCSC is currently authorized by the USACE to project depths of -54 feet and -56 feet Mean Lower Low Water (MLLW) from Station 110+00 to Station -330+00 as part of the Corpus Christi Ship Channel Improvement Project (CCSCIP). The currently authorized width of the CCSC is 600 feet inside the jetties and 700 feet in the entrance channel. The proposed project would deepen the channel from Station 110+00 to Station -72+50 to a maximum depth of -79 feet MLLW (-75 feet MLLW plus two feet of advanced maintenance and two feet of allowable overdredge), and from Station -72+50 to Station -330+00, the channel would be deepened to a maximum depth of -81 feet MLLW (-77 feet MLLW plus two feet of advanced maintenance and two feet of allowable overdredge). The project includes a 29,000-foot extension of the CCSC from Station -330+00 to Station -620+00 to a maximum depth of -81 MLLW (-77 feet MLLW plus two feet of advanced maintenance and two feet of allowable overdredge) to reach associated bathymetric contour in the Gulf of Mexico. The Channel Deepening Project extents are shown below in Figure 1. 2 Figure 1: Preferred Channel Alternative Model Mesh: The Delft3D Model was utilized in multiple phases of the modeling efforts. AECOM selected a mesh (modeling extent) that encompasses and surpasses the reasonably expected impacted areas. The Delft3D model configuration was adopted from an existing TxBLEND model developed by the Texas Water Development Board (TWDB, 2011). TxBLEND is a version of the BLEND model, developed by Dr. William Gray of Notre Dame University, (Gray, 1987), which was modified by TWDB engineers for use in the shallow bays and estuaries of Texas. In Figure 2 below, the modeling extent is shown in blue. 3 Figure 2: Delft3D Model Mesh o Hydrodynamics: Tide and velocity are measured utilizing historical data as a benchmark and a well- established model known as the Delft3D model configuration. The use of an established model validates that the measurement system being used is well founded with a proven track record and will yield pertinent results. o Shoaling: The amount of material that will infill the new channel profile is based on historical data as a benchmark and a well-established methodology of Rosati and Kraus (2009). o Salinity: Salt levels are measured utilizing historic and collected data as a benchmark and the Delft3D model configuration. The use of this established model validates that the salinity measurement system being used is well founded and will yield pertinent results. o Vessel Wake: Wake is a multifaceted variable which is explored by comparing the suspension of sediment on the shoreline as a result of the waves caused by a vessel moving through a body of water against the suspension of sediment caused by ambient conditions. 4 MEASURE o Hydrodynamics: o The spring-tide range in