The ocean, coast, and rivers support a number of established human uses, as well as an expanding array of new uses. These include well-established uses of the ocean, such as ports and harbors; commercial and recreational fishing; traditional hunting, fishing, and gathering; commerce and transportation; oil and gas exploration and development; sand and gravel mining; environmental and conservation activities; scientific research and exploration; security, emergency response, and military readiness; and tourism and recreational activities. The ocean also provides cooling water for thermoelectric power plants that use coal, natural gas, or nuclear fuel. In many cases, while the activity itself is well-established, the intensity of use has been escalating. In addition, there are several new or growing human use categories, such as aquaculture; maritime heritage and archeology; and, of course, offshore renewable energy.

Each of the uses listed above comes with its own set of environmental, regulatory, social, and economic filters that have potential to reduce MHK’s potential applicability at any given location. For MHK, the committee identified a number of categories into which these filters might fall (shown in the right-hand column of Figure 1-1). Examples of each category are presented in Table 7-1, although it should be recognized that some of the filters fall under more than one category. Because of the large impact these filters have on the percentage of the resource that could be practically available, they are explored in more detail in the following sections.

Environmental Filters

MHK devices are likely to have a number of effects on the physical, biological, and ecological environment of rivers and the ocean. These environmental effects are in addition to the back effects addressed in earlier chapters that are created by the MHK device or array and reduce the available energy. Placing and operating the devices can have physical impacts on the subsurface, the water column, and the water surface (e.g., alteration of the bottom substrate, scour and/or sediment buildup, changes in wave or stream energy, turbulence, space taken up by devices operating at the sea surface). When looking beyond the impact of one or a few devices, large arrays of MHK devices could have significant effects on the physical environment. It would be important to compare the impact of an MHK array with the impact of other electricity generators having the same average power output.

The dynamic nature of the devices (for example, moving blades on turbines) has potential to lethally and/or behaviorally impact marine mammals, fish, and diving birds. The relatively slow speeds at which

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