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3.0 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

Chapter 3 describes the current environment for resources that may be affected by Alternative A (No 

Action – Conduct Surveys and Mapping for Coastal and Marine Data Collection with Current Technology 

and Methods, at Current Funding Levels), Alternative B (Conduct Surveys and Mapping for Coastal and 

Marine Data Collection with Equipment Upgrades, Improved Hydroacoustic Devices, and New Tide 

Stations), and Alternative C (Upgrades and Improvements with Greater Funding Support), and the 

potential environmental consequences associated with the alternatives. 

Sections 3.4 through 3.13 discuss the resources analyzed, and Section 3.14 discusses the resources that 

were considered but dismissed from further analysis. The resources analyzed and dismissed are listed 

below:

Resources Analyzed

• Habitats

• Marine Mammals

• Sea Turtles

• Fish

• Aquatic Macroinvertebrates

• Essential Fish Habitat

• Seabirds, Shorebirds and Coastal Birds, and Waterfowl

• Cultural and Historic Resources

• Socioeconomic Resources

• Environmental Justice

Resources Dismissed

• Air and Water Quality

• Soils and Geology

• Airborne Noise for Human Receptors

• Select Freshwater Taxa
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UNDERWATER SOUND

The ambient marine and freshwater soundscape is composed of different types of sound: 

1. natural biological sounds, 

2. natural physical sounds, and 

3. human-made sounds. 

Natural biological sounds include sounds produced by fish, birds, marine mammals, invertebrates, 

and other animals that produce and use sound to perform various life functions. Natural physical 

sounds include sounds produced by the physical environment such as sounds from rain, lightning, 

wind, waves, the movement and breaking of ice, volcanic eruptions, earthquakes, and other 

physical phenomena. Human-made sounds include those from human activity such as sounds from 

vessel engines, oil and gas exploration (seismic airguns), drilling, construction, dredging 

(excavating), fishing, sonar, and echo sounders (NOAA, 2016). Since human-made sounds are 

relatively new to aquatic soundscapes and are considered unwanted, these sounds are 

interchangeably referred to as noise.

Unlike other means of communication used by animals on land involving the senses, such as visual 

communication and chemical communication (e.g., smell), sound propagates faster and farther 

underwater than in air. The properties of sound enable its production and reception to be highly 

efficient means of communication over the vast distances that make up the marine environment. 

Aquatic animals have evolved to rely on sound as a primary method for communication and for 

gaining information about the surrounding environment (NOAA, 2016). Therefore, understanding 

how to characterize and assess sound is critical to analyzing the impact of noise on aquatic animals.

Sound refers to vibrations which cause pressure changes that travel as a wave through a medium, 

such as air or water. In air, sounds are typically characterized by pitch and intensity. Although 

sounds in air and sounds in water are compared using the same metrics, the physical differences 

between air and water result in the same sound having different speed, pitch, and intensity.

● Speed. In general, sound travels much faster and farther in water than in air. Sound travels 

faster in denser mediums; however, the density of seawater varies with the water’s salinity 

(salt concentration), temperature, and pressure (depth). On average, sound travels at 

about 1,500 meters per second (m/s) (3,500 miles per hour [mph]) in seawater compared 

to 340 m/s (760 mph) in air.

● Pitch. The pitch of a sound is the frequency, or repetition rate, of the sound wave and is 

measured in hertz (Hz) and kilohertz (kHz). Sound waves with higher frequencies are 

perceived as higher pitch sounds. The frequency of sound impacts the distance a given 

sound travels, in general, low frequency sounds travel farther than high frequency sounds. 

Some sounds, particularly low-frequency ones, can travel hundreds of kilometers 

underwater.

● Intensity. The intensity, or loudness, of a sound is represented as the amplitude of the 

sound wave which is the change in pressure as the sound wave passes. Sound waves with 

larger amplitudes are perceived as louder sounds. Intensity also depends on characteristics 

of the medium in which the sound is traveling. Since intensity depends on both the sound 

and the medium, intensity is typically measured in decibels (dB), which is a relative unit on 

a logarithmic scale that compares the sound pressure to a reference pressure. The 

reference pressure is different for different mediums. In air, decibels use a reference 
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pressure of 20 microPascals (μPa) such that they are scaled to the range of human hearing, 

so by definition, a 0 dB sound in air is the lowest limit of human hearing. Humans perceive 

a 10 dB increase as a doubling of loudness. In water, decibels are scaled using a reference 

pressure of 1 μPa. Since dB in air and dB in water use different reference pressures, sound 

intensity reported in dB in air is not the same as sound intensity reported in underwater dB 

(DOSITS, No Date-a).

The figure below provides a simple representation of how sound travels in air compared to water.

Source: DOSITS, No Date-a 

Sound Traveling in Air Versus Water

The table below compares sound intensity in air to sound intensity in water for common sounds. 

Intensity Comparison for Typical Airborne and Underwater Sounds

Sound

Sound Intensity in Air

(dB re 20 μPa)

Sound Intensity 

Underwater

(dB re 1 μPa)

Threshold of human hearing (1,000 Hz) 0 26*

Very quiet living room 40 66*

Normal speech (1 meter) 60 86*

Jet airliner (10 meters) 104 130*

Fin whale call (100 meters) 114* 140

Human threshold of pain (at ear drum) 140 166*

Some military artillery 160 186*

Beluga echolocation call (1 meter) 194* 220

Source: NRC, 1994

*Nominal levels after conversion to alternate medium.

The potential impact of underwater sound on receptors is related to both the characteristics of the 

sound received and the sensitivity of the receptor. As sound emanates from a source, the intensity 

of the sound decreases with distance from the source; thus, receptors located further from a source 

receive lower intensities of sound. Just as humans have a limited range of perceptible sound 

frequencies outside of which sounds are undetectable, marine animals have different ranges of 

perceptible sounds and rely on the use of sound for different activities. The vast majority of sounds 

generated by NOS activities would be outside the frequency range of human sound perception both 
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in air and underwater; however, some marine animals (e.g., marine mammals) can perceive and 

potentially be impacted by these sounds. Given the great differences between how a single sound 

is received and processed by different marine animal receptors, NOS determined that the impact 

of sound would be best assessed at the receptor level for the biological resources of marine 

mammals, sea turtles, fish, aquatic macroinvertebrates, and birds.

3.1 AFFECTED ENVIRONMENT METHODOLOGY

The affected environment summarizes the current physical, biological, social, and economic environments 

of the “action area,” which includes the United States (U.S.) territorial sea; the contiguous zone; the U.S. 

Exclusive Economic Zone (EEZ); rivers; states’ offshore waters; and coastal and riparian lands for projects 

such as the installation, maintenance, and removal of tide gauges. This includes the U.S. portions of the 

Great Lakes and internal waters including Lakes Tahoe, Mead, Champlain, Okeechobee, and major rivers 

such as the Mississippi, Missouri, Hudson, and Columbia rivers. For each resource, the affected 

environment describes the elements or components of the resource that may be potentially affected by 

the alternatives.

3.2 ENVIRONMENTAL CONSEQUENCES METHODOLOGY

The environmental consequences analysis considers how the condition of a resource would change as a 

result of implementing each of the alternatives and describes the impacts in terms of types (direct, 

indirect, cumulative, beneficial, adverse), context, intensity, and significance. The types of impacts are 

defined in Section 3.2.1 and the development of significance criteria is described in Section 3.2.2 below. 

The impacts analysis is performed using a framework that follows a logical sequence of analytical steps 

for each resource under each alternative:

• Impact Causing Factors. Evaluate proposed activities to identify which elements of the activities 

could lead to impacts - the impact causing factors. A systematic consideration of causes and 

effects is used to derive the impact causing factors from known actions and characteristics that 

define the activities.

• Detailed Analysis of Impacts. Evaluate the impact causing factors to produce a detailed analysis 

of the impacts. Assess the context and intensity of the impacts from each impact causing factor, 

then evaluate the impacts from all impact causing factors to define significance for the alternative.

• Significance Criteria. Develop and apply criteria that are standards for evaluating the significance 

of the impacts caused by the proposed activities. 

3.2.1 Types of Impacts

According to the Council on Environmental Quality’s (CEQ) National Environmental Policy Act (NEPA) 

Regulations at 40 Code of Federal Regulations (CFR) 1500-1508 (1978), direct and indirect effects are 

defined as: 

Direct effects: Effects that are caused by the action and occur at the same time and place (40 CFR 

1508.1(g)(1)). 

Indirect effects: Effects that are caused by the action and occur later in time or are farther removed in 

distance but are still reasonably foreseeable. Indirect effects also include “induced changes” in the human 

and natural environments (40 CFR 1508.1(g)(2)).