Wave and Circulation Modeling of Infrastructure Installations at Rota Harbor in the Northern Marianna Islands

Lihwa Lin

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Conference: 2019 ASEE Annual Conference & Exposition
Location: Tampa, Florida
Publication Date: June 15, 2019
Start Date: June 15, 2019
End Date: June 19, 2019
Conference Session: Ocean and Marine Division Technical Session 1
Tagged Division: Ocean and Marine
Page Count: 18
DOI: 10.18260/1-2--33547
Permanent URL: https://peer.asee.org/33547
Download Count: 451

Paper Authors

biography

Lihwa Lin U.S. Army Corps of Engineers

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Dr. Lin is a Senior Research Civil Engineer in the Coastal and Hydraulics Laboratory at the U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi. Dr. Lin earned his master's degree in Ocean Engineering from Oregon State University, and Ph.D. in Civil Engineering from the University of Florida. Dr. Lin is also appointed as adjunct professor at Civil and Environmental Engineering Department, Jackson State University, MS. He offers one of two courses, ‘Linear Wave Mechanics and Theory’ and ‘Ocean Wave Spectral Analysis and Applications’ in the fall semester.

Dr. Lin’s research interests include field studies, physical and numerical modeling of coastal processes; inlet and navigation channel risk analysis; morphodynamics and sediment transport; coastal engineering project assessment and coastal climate information. Recent works include Dana Point Harbor, Pillar Point Harbor, and Noyo Harbor, CA, Grays Harbor, WA, Matagorda Bay, Corpus Christi Bay, and Galveston Bay, TX, Point Judith Harbor, RI, Cleveland Harbor, OH, Buffalo Harbor, NY, and Hilo Harbor, HI.

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Abstract

Rota Harbor is located on the northwest coast of the Rota Island in the US Commonwealth of the Northern Mariana Islands (CNMI), approximately 3,800 mi west of Hawaii. Rota island is small (85.5 km2), 17 km long and 8 km wide with a highest elevation of 500 m on Mt. Manira. The harbor was designed and built by the US Army Corps of Engineers (USACE) between 1978 and 1985. It lies 60 km northeast of Guam and 90 km southwest of Tinian at latitude 14o 10’ N, longitude 145o 14’ E. The study area is located on a sandy peninsula, surrounded by fringing coral reef. Adjacent to Rota Harbor, the natural reef is approximately 920 feet wide with depths ranging from 0.5 to 1.5 m. The Harbor consists of an entrance channel of 210 m long, 91 m wide, and 6 m deep; a turning basin of 135 m long, 55 to 122 m wide, and 5 m deep; a revetted mole of 165 m long and 3 m high; a basin extension of 85 m long, 46 m wide and 5 m deep.

A harbor feasibility study for the navigation improvements has been underway aiming at efficient and safe passage of waterborne commerce among major islands in the region, including Rota, Saipan, Tinian, and Guam. Because local strong wind wave and current conditions can disrupt navigation and delay port operations, proposed improvements to harbor require a comprehensive analysis of wind, wave, and circulation to determine safety of vessels entering and passing through the channel to access mooring and docking inside the harbor.

The USACE Engineer Research and Development Center and Honolulu District were assisting CNMI Government, Commonwealth Ports Authority to investigate structural alternatives to improve navigation and protection of Rota Harbor. The numerical modeling effort was conducted to evaluate access, usability and impacts of infrastructure installations for improving future capacity and safer navigation at the harbor.

Wave and hydrodynamics numerical models of a Coastal Modeling System (CMS), developed and maintained at ERDC, were applied with field measurements and hindcasting data. Three structural alternatives were proposed and evaluated for design incident waves from three directions in the north-northwest sector at two water levels (local mean and high water). The alternatives included (1) Alt 1 – a detached shore-parallel breakwater, approximately 75 m long, just offshore of the existing entrance channel, (2) Alt 2 – attached north breakwater, approximately 340 m long, lies primarily on the existing reef adjacent to the channel and extend beyond the edge of the reef flat, and (3) Alt 3 – a dogleg breakwater, approximately 445 m, extends Alt 2 seaward to connect to Alt 1. Field data including current and wave measurement at three ADCPs installed outside harbor, by the navigation channel, and in the turning basin were collected from 2 December 2016 to 3 March 2017. The field data were used to calibrate and validate the CMS models.

For evaluation of alternatives, the CMS model output was saved at three (3) transects along the navigation channel and two (2) transects across the turning basin. The model maximum wave heights and current magnitude calculated along these transects were used in the comparison of alternatives. The analysis of alternatives was compared to the existing harbor breakwater configuration to determine extent of wave energy and current speed reduction in the channel and harbor basin. The effect of detached breakwater alone (Alt 1) could induce strong return currents in the navigation channel. Model results show while both north breakwater (Alt 2) and dogleg breakwater (Alt 3) reduce return currents in the channel, Alt 3 also reduces most storm wave energy and current strength in the harbor basin and wharfs. Both engineering and environmental factors with the construction cost were taken into consideration the final decision of the harbor breakwater modification. More model result and corresponding analysis of alternatives were provided in the full paper.

Citation
Format

Lin, L. (2019, June), Wave and Circulation Modeling of Infrastructure Installations at Rota Harbor in the Northern Marianna Islands Paper presented at 2019 ASEE Annual Conference & Exposition , Tampa, Florida. 10.18260/1-2--33547

TY - CPAPER
AB - Rota Harbor is located on the northwest coast of the Rota Island in the US Commonwealth of the Northern Mariana Islands (CNMI), approximately 3,800 mi west of Hawaii. Rota island is small (85.5 km2), 17 km long and 8 km wide with a highest elevation of 500 m on Mt. Manira. The harbor was designed and built by the US Army Corps of Engineers (USACE) between 1978 and 1985. It lies 60 km northeast of Guam and 90 km southwest of Tinian at latitude 14o 10’ N, longitude 145o 14’ E. The study area is located on a sandy peninsula, surrounded by fringing coral reef. Adjacent to Rota Harbor, the natural reef is approximately 920 feet wide with depths ranging from 0.5 to 1.5 m. The Harbor consists of an entrance channel of 210 m long, 91 m wide, and 6 m deep; a turning basin of 135 m long, 55 to 122 m wide, and 5 m deep; a revetted mole of 165 m long and 3 m high; a basin extension of 85 m long, 46 m wide and 5 m deep.

A harbor feasibility study for the navigation improvements has been underway aiming at efficient and safe passage of waterborne commerce among major islands in the region, including Rota, Saipan, Tinian, and Guam. Because local strong wind wave and current conditions can disrupt navigation and delay port operations, proposed improvements to harbor require a comprehensive analysis of wind, wave, and circulation to determine safety of vessels entering and passing through the channel to access mooring and docking inside the harbor.

The USACE Engineer Research and Development Center and Honolulu District were assisting CNMI Government, Commonwealth Ports Authority to investigate structural alternatives to improve navigation and protection of Rota Harbor. The numerical modeling effort was conducted to evaluate access, usability and impacts of infrastructure installations for improving future capacity and safer navigation at the harbor.

Wave and hydrodynamics numerical models of a Coastal Modeling System (CMS), developed and maintained at ERDC, were applied with field measurements and hindcasting data. Three structural alternatives were proposed and evaluated for design incident waves from three directions in the north-northwest sector at two water levels (local mean and high water). The alternatives included (1) Alt 1 – a detached shore-parallel breakwater, approximately 75 m long, just offshore of the existing entrance channel, (2) Alt 2 – attached north breakwater, approximately 340 m long, lies primarily on the existing reef adjacent to the channel and extend beyond the edge of the reef flat, and (3) Alt 3 – a dogleg breakwater, approximately 445 m, extends Alt 2 seaward to connect to Alt 1. Field data including current and wave measurement at three ADCPs installed outside harbor, by the navigation channel, and in the turning basin were collected from 2 December 2016 to 3 March 2017. The field data were used to calibrate and validate the CMS models.

For evaluation of alternatives, the CMS model output was saved at three (3) transects along the navigation channel and two (2) transects across the turning basin. The model maximum wave heights and current magnitude calculated along these transects were used in the comparison of alternatives. The analysis of alternatives was compared to the existing harbor breakwater configuration to determine extent of wave energy and current speed reduction in the channel and harbor basin. The effect of detached breakwater alone (Alt 1) could induce strong return currents in the navigation channel. Model results show while both north breakwater (Alt 2) and dogleg breakwater (Alt 3) reduce return currents in the channel, Alt 3 also reduces most storm wave energy and current strength in the harbor basin and wharfs. Both engineering and environmental factors with the construction cost were taken into consideration the final decision of the harbor breakwater modification. More model result and corresponding analysis of alternatives were provided in the full paper.

AU - Lihwa Lin
CY - Tampa, Florida
DA - 2019/06/15
PB - ASEE Conferences
TI - Wave and Circulation Modeling of Infrastructure Installations at Rota Harbor in the Northern Marianna Islands
UR - https://peer.asee.org/33547
DO - 10.18260/1-2--33547
ER -