STUDY TITLE: Real-Time Opportunity for Development Environmental Observations 

(RODEO)

REPORT TITLE: Benthic and Epifaunal Monitoring During Wind Turbine Installation and 

Operation at the Block Island Wind Farm (BIWF), Rhode Island – Project Report

OCS STUDY NUMBER: BOEM 2020-044

NUMBER OF PAGES: Volume 1 (main report) 263; Volume 2 (Appendices) 380

CONTRACT NUMBER: M15PC00002, Task Orders M17PD00015 and 140M0119F0025

SPONSORING OCS REGION: Office of Renewable Energy Programs

APPLICABLE PLANNING AREA(S): North Atlantic

FISCAL YEAR(S) OF PROJECT FUNDING: FY 2017–2020

COSTS BY FISCAL YEAR: TO M17PD00015: FY17: $19,011.99; FY18 $221,014.18; 

FY19: $497,430.58; FY20: $383,850.72 

TO 140M0119F0025: FY20: $299,878.86

CUMULATIVE PROJECT COST: TO M17PD00015: $1,121,307.47

TO 140M0119F0025: $299,878.86

COMPLETION DATE OF REPORT: 26 September 2020

PROJECT MANAGER: Anwar Khan

AFFILIATION: HDR

ADDRESS: 9781 S Meridian Blvd Suite 400, Englewood, CO 80112

PRINCIPAL INVESTIGATOR(S)*

: Zoë Hutchison, Monique LaFrance Bartley, Paul 

English, John King, Sean Grace, Boma Kresning, Christopher Baxter, Kristen Ampela, 

Mark Deakos, Anwar Khan

KEY WORDS: Block Island Wind Farm (BIWF), environmental monitoring, benthos, 

epifouling 

BRIEF ABSTRACT: Benthic and epifouling monitoring was conducted within the BIWF 

Project area for four consecutive years (2016 to 2019) after turbine installation. Three 

rounds of sampling and laboratory analyses were conducted with samples collected at 

Turbines 1, 3, and 5. Results indicated that within four years the submerged sections of 

the BIWF jacket foundation structures became dominated by mussels (Mytilus edulis) and 

associated species, and that significant modification of the seabed has occurred within
the footprint of the turbine foundations, with the area underneath Turbine 1 exhibiting the 

fastest rate of change.

BACKGROUND: The purpose of the RODEO Program is to make direct, real-time 

measurements of the nature, intensity, and duration of potential stressors during the 

construction and initial operations of selected proposed offshore wind facilities. The 

purpose also includes recording direct observations during the testing of different types 

of equipment that may be used during future offshore development to measure or 

monitor activities and their impact producing factors.

Data collected under the RODEO Program may be used as input to analyses or models 

that are used to evaluate effects or impacts from future offshore activities. This Program 

is not intended to duplicate or substitute for any monitoring that otherwise may be 

required to be conducted by the developers of the proposed projects. Also, RODEO 

Program monitoring is coordinated with the industry and is not intended to interfere with 

or result in delay of industry activities.

The BIWF is the first facility to be monitored under the RODEO Program. The benthic 

and epifouling monitoring surveys were implemented in accordance with a pre-approved 

field sampling plan, which included a project-specific health and safety plan. Monitoring 

methods, observations, results, and conclusions from three rounds of benthic and 

epifouling sampling, as well as laboratory analyses of samples collected at Turbines 1, 

3, and 5, are presented in this report.

OBJECTIVES: The monitoring was intended to provide additional information necessary 

for BOEM’s evaluation of environmental effects of future facilities and data to improve 

accuracy of models and analysis criteria employed to establish monitoring controls and 

mitigations.

RESULTS AND CONCLUSIONS: Four years post installation, the turbine foundations 

between the intertidal mark and seabed were densely populated by mussels (M. edulis) 

and associated species. Several epifaunal species on the structures became more

common over time, including: anemones, sponges, and the invasive tunicate Didemnun 

vexillium. The coral Astrangia poculata was observed near the base of the foundations in 

Years 2 and 3. Changes in the mobile epifaunal community were also evident. For 

example, sea stars were present but not common in Year 2; but in Year 3, they became 

more abundant at the base and on the bottom of the foundations. Abundance of black 

sea bass (Centropristis stiata) around the foundations was observed between Years 2 

and 3. A large increase in the incidence and abundance of juvenile mussels settling on 

the seafloor beyond the foundation footprints of Turbine 1 and up to distances of 90 

meters (m) away also was observed. Patches of adult mussel dominance were observed 

up to 42 m from the center of foundation structure of Turbine 1 and appear to be 

associated with highly modified seabed conditions and macrofauna in Year 3.

The seabed underneath the turbine foundations, especially under Turbine 1, was altered 

from a clean coarse sandy/polychaete association to a fine grained, organically enriched 

sediment supporting dense mussel aggregations. Within the four-year study period, the 
changes in seabed characteristics underneath the foundations occurred along a gradient, 

with the area underneath Turbine 1 exhibiting the greatest degree and fastest rate of 

change, and Turbine 5 the least change. Isolated patches of seabed beyond the footprint 

of Turbine 1 but within 30 m of the center point of the foundation also appeared to 

transition with respect to organic content. The most noticeable rate of transition below 

Turbine 1 may be linked to seabed stability, underscoring the highly localized (turbine 

specific) nature of benthic responses that were observed.

It was also estimated that 

epifaunal growth on the 

turbine foundations has 

added approximately 1,025 

kilograms of weight to each 

turbine jacket leg at the 

BIWF. Because of this, the 

mean drag force (per unit 

length) on the leg increased

from approximately 2543 N 

to 4313 N during an

extreme current event 

(velocity of 2 m/per 

second). This represents a 

maximum of 75 to 85

percent increase in drag 

force (per unit length) due to 

epifaunal growth on the leg 

structure. The total drag 

force on the simplified 

BIWF jacket structures in 

an extreme current event 

was estimated to be 

483,056 N, whereas it was considerably higher (1,347,360 N) for the larger and deeper 

monopile structures, such as those being considered for future offshore wind projects.

The overall conclusion of the study was that while the effects of the turbines on the benthic 

habitat four years after installation remain localized, they are profound given the marked

change from a sandy habitat to a habitat characterized by mussel aggregations with 

associated organic matter, sediment fines and macrofaunal communities.

STUDY PRODUCT(S): 

HDR. 2020. Benthic and Epifaunal Monitoring During Wind Turbine Installation and 

Operation at the Block Island Wind Farm, Rhode Island – Project Report. Final 

Report to the U.S. Department of the Interior, Bureau of Ocean Energy 

Management, Office of Renewable Energy Programs. OCS Study BOEM 2020-

044. Volume 1:263 pp; Volume 2:380 pp.

Four years after installation, the submerged sections of the BIWF jacket 

foundations and the area underneath the turbines became dominated by 

mussels and associated species.
* P.I.’s affiliation may be different than that listed for Project Manager.

 

Block 

Island