A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect water or for storage of water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities. The first known appearance of dam occurs in 1165. However, there is one village, Obdam, that is already mentioned in 1120. The word seems to be related to the Greek word taphos, meaning "grave" or "grave hill". So the word should be understood as "dike from dug out earth". The names of more than 40 places (with minor changes) from the Middle Dutch era (1150–1500 CE) such as Amsterdam (founded as 'Amstelredam' in the late 12th century) and Rotterdam, also bear testimony to the use of the word in Middle Dutch at that time.

The deep sea or deep layer is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms (1800 m) or more. Little or no light penetrates this part of the ocean, and most of the organisms that live there rely for subsistence on falling organic matter produced in the photic zone. For this reason, scientists once assumed that life would be sparse in the deep ocean, but virtually every probe has revealed that, on the contrary, life is abundant in the deep ocean. From the time of Pliny until the late nineteenth century...humans believed there was no life in the deep. It took a historic expedition in the ship Challenger between 1872 and 1876 to prove Pliny wrong; its deep-sea dredges and trawls brought up living things from all depths that could be reached. Yet even in the twentieth century scientists continued to imagine that life at great depth was insubstantial, or somehow inconsequential. The eternal dark, the almost inconceivable pressure, and the extreme cold that exist below one thousand meters were, they thought, so forbidding as to have all but extinguished life. The reverse is in fact true....(Below 200 meters) lies the largest habitat on earth. In 1960, the Bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam, at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean. If Mount Everest (8,848 metres) were submerged there, its peak would be more than a mile beneath the surface. The Trieste was retired, and for a while the Japanese remote-operated vehicle (ROV) Kaikō was the only vessel capable of reaching this depth. It was lost at sea in 2003. In May and June 2009, the hybrid-ROV (HROV) Nereus returned to the Challenger Deep for a series of three dives to depths exceeding 10900 meters. It has been suggested that more is known about the Moon than the deepest parts of the ocean. Little was known about the extent of life on the deep ocean floor until the discovery of thriving colonies of shrimps and other organisms around hydrothermal vents in the late 1970s. Before the discovery of the undersea vents, it had been accepted that almost all life on earth obtained its energy (one way or another) from the sun. The new discoveries revealed groups of creatures that obtained nutrients and energy directly from thermal sources and chemical reactions associated with changes to mineral deposits. These organisms thrive in completely lightless and anaerobic environments in highly saline water that may reach 300 °F (150 °C), drawing their sustenance from hydrogen sulfide, which is highly toxic to almost all terrestrial life. The revolutionary discovery that life can exist under these extreme conditions changed opinions about the chances of there being life elsewhere in the universe. Scientists now speculate that Europa, one of Jupiter's moons, may be able to support life beneath its icy surface, where there is evidence of a global ocean of liquid water.

Environmental engineering is the branch of engineering concerned with the application of scientific and engineering principles for protection of human populations from the effects of adverse environmental factors; protection of environments, both local and global, from potentially deleterious effects of natural and human activities; and improvement of environmental quality. Environmental engineering can also be described as a branch of applied science and technology that addresses the issues of energy preservation, protection of assets and control of waste from human and animal activities. Furthermore, it is concerned with finding plausible solutions in the field of public health, such as waterborne diseases, implementing laws which promote adequate sanitation in urban, rural and recreational areas. It involves waste water management, air pollution control, recycling, waste disposal, radiation protection, industrial hygiene, animal agriculture, environmental sustainability, public health and environmental engineering law. It also includes studies on the environmental impact of proposed construction projects. Environmental engineers study the effect of technological advances on the environment. To do so, they conduct studies on hazardous-waste management to evaluate the significance of such hazards, advise on treatment and containment, and develop regulations to prevent mishaps. Environmental engineers design municipal water supply and industrial wastewater treatment systems. They address local and worldwide environmental issues such as the effects of acid rain, global warming, ozone depletion, water pollution and air pollution from automobile exhausts and industrial sources. At many universities environmental engineering programs are offered at either the department of civil engineering or the department of chemical engineering at engineering faculties. Environmental "civil" engineers focus on hydrology, water resources management, bioremediation, and water treatment plant design. Environmental "chemical" engineers, on the other hand, focus on environmental chemistry, advanced air and water treatment technologies and separation processes. Additionally, engineers are more frequently obtaining specialized training in law (J.D.) and are utilizing their technical expertise in the practices of environmental engineering law. Most jurisdictions also impose licensing and registration requirements.

A gas flare, alternatively known as a flare stack, is a gas combustion device used in industrial plants such as petroleum refineries, chemical plants, natural gas processing plants as well as at oil or gas production sites having oil wells, gas wells, offshore oil and gas rigs and landfills. In industrial plants, flare stacks are primarily used for burning off flammable gas released by pressure relief valves during unplanned over-pressuring of plant equipment. During plant or partial plant startups and shutdowns, flare stacks are also often used for the planned combustion of gases over relatively short periods. Gas flaring at many oil and gas production sites protects against the dangers of over-pressuring industrial plant equipment. When petroleum crude oil is extracted and produced from onshore or offshore oil wells, raw natural gas associated with the oil is brought to the surface as well. Especially in areas of the world lacking pipelines and other gas transportation infrastructure, vast amounts of such associated gas are commonly flared as waste or unusable gas. The flaring of associated gas may occur at the top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-level flare in an earthen pit. Preferably, associated gas is reinjected into the reservoir, which saves it for future use while maintaining higher well pressure and crude oil producibility. The Obama administration implemented rules curbing flaring, and subsequently the Trump administration attempted to delay implementation of the rules. In October 2017 a federal magistrate judge vacated the Department of Interior's move to delay implementation.

Global warming, also referred to as climate change, is the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid-19th century, and in paleoclimate proxy records covering thousands of years. In 2013, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) in the lowest emissions scenario, and 2.6 to 4.8 °C (4.7 to 8.6 °F) in the highest emissions scenario. These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing. Future climate change and associated impacts will differ from region to region around the globe. Anticipated effects include increasing global temperatures, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely changes include more frequent extreme weather events such as heat waves, droughts, heavy rainfall with floods and heavy snowfall; ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels. Because the climate system has a large "inertia" and greenhouse gases will remain in the atmosphere for a long time, many of these effects will persist for not only decades or centuries, but for tens of thousands of years to come. Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC), whose ultimate objective is to prevent dangerous anthropogenic climate change. Parties to the UNFCCC have agreed that deep cuts in emissions are required and that global warming should be limited to well below 2.0 °C (3.6 °F) compared to pre-industrial levels, with efforts made to limit warming to 1.5 °C (2.7 °F). Public reactions to global warming and concern about its effects are also increasing. A global 2015 Pew Research Center report showed that a median of 54% of all respondents asked consider it "a very serious problem". Significant regional differences exist, with Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) among the least concerned.

Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR), is an energy recovery ventilation system using equipment known as a heat recovery ventilator, heat exchanger, air exchanger, or air-to-air heat exchanger which employs a cross flow or counter-flow heat exchanger (countercurrent heat exchange) between the inbound and outbound air flow. HRV provides fresh air and improved climate control, while also saving energy by reducing heating (and cooling) requirements for many applications including vehicles. Energy recovery ventilators (ERVs) are closely related; however, ERVs also transfer the humidity level of the exhaust air to the intake air.

Hurricane Irma is an extremely powerful tropical cyclone that is currently making landfall in Cuba and is threatening the Southeastern United States. It is the strongest hurricane ever recorded in the Atlantic basin outside the Caribbean and Gulf of Mexico, and is tied with the 1935 Labor Day hurricane as the strongest landfalling cyclone on record in the Atlantic basin as well as the strongest Atlantic hurricane since Wilma of 2005 in terms of maximum sustained winds, the most intense in terms of pressure since Dean in 2007, and the first of such intensity to make landfall anywhere in the Atlantic since Felix in 2007. Irma is also the first Category 5 hurricane on record to affect the northern Leeward Islands, and only the second hurricane on record to make landfall in Cuba at such an intensity, with the other being a hurricane in 1924. A typical Cape Verde hurricane, Irma developed on August 30 near the Cape Verde Islands from a tropical wave that had moved off the west African coast two days prior. It is the ninth named storm, fourth hurricane, and second major hurricane of the 2017 Atlantic hurricane season. Under favorable conditions, Irma rapidly intensified shortly after formation, becoming a Category 2 hurricane within a mere 24 hours. It became a Category 3 hurricane (and therefore a major hurricane) shortly afterward; however, the intensity fluctuated for the next several days due to a series of eyewall replacement cycles. On September 5, Irma became a Category 5 hurricane, and by early the next day, Irma reached peak intensity with 185 mph (295 km/h) winds and a minimum pressure of 914 mbar (914 hPa; 27.0 inHg). This ties it as the second-strongest Atlantic hurricane by wind speed, surpassed only by Allen of 1980 which reached wind speeds of 190 mph (305 km/h). Irma sustained these 185 mph (295 km/h) winds for 37 hours, surpassing Allen's record, which had sustained 180 mph (285 km/h) winds for 18 hours. In addition, Irma achieved one of the longest durations of Category 5 strength winds ever on record. Irma's low pressure also makes it the strongest tropical cyclone worldwide in 2017 so far. It caused catastrophic damage in Barbuda, Saint Barthélemy, Saint Martin, Anguilla and the Virgin Islands as a Category 5 hurricane. Irma was the strongest hurricane to strike the northern Leeward Islands and one of the worst storms to hit the region, along with Hurricane Donna in 1960 and Hurricane Luis in 1995. As of September 9, the hurricane has caused at least 24 deaths.

Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the movement of the fluids. This area of civil engineering is intimately related to the design of bridges, dams, channels, canals, and levees, and to both sanitary and environmental engineering. Hydraulic engineering is the application of the principles of fluid mechanics to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water. Before beginning a hydraulic engineering project, one must figure out how much water is involved. The hydraulic engineer is concerned with the transport of sediment by the river, the interaction of the water with its alluvial boundary, and the occurrence of scour and deposition. "The hydraulic engineer actually develops conceptual designs for the various features which interact with water such as spillways and outlet works for dams, culverts for highways, canals and related structures for irrigation projects, and cooling-water facilities for thermal power plants."

A hydrophone (Ancient Greek ὕδωρ = water and φωνή = sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change. Such piezoelectric materials, or transducers, can convert a sound signal into an electrical signal since sound is a pressure wave. Some transducers can also serve as a projector, but not all have this capability, and some may be destroyed if used in such a manner. A hydrophone can "listen" to sound in air but will be less sensitive due to its design as having a good acoustic impedance match to water, which is a denser fluid than air. Likewise, a microphone can be buried in the ground, or immersed in water if it is put in a waterproof container, but will give similarly poor performance due to the similarly bad acoustic impedance match.

Pellet heating is a heating system, in which wood pellets (small pellets from wood chips and sawdust) are combusted. Other pelletized fuels such as straw pellets are used occasionally. Today's central heating system which run on wood pellets as a renewable energy source are comparable in operation and maintenance of oil and gas heating systems.