Glossary of Restoration Terminology 1.58-Year Return Period Discharge (Q1.5) The discharge with a return period of 1.58 years, derived from the observed annual maximum flow series. [Watson et al. 1999]. 2-Year Return Period Discharge (Q2) The discharge with a return period of 2 years, derived from the observed annual maximum flow series. [Watson et al. 1999]. Abatement Reducing the degree or intensity of, or eliminating, pollution. Abiotic Not living, refers to the non-living components of an ecosystem; also refers to non-biological processes (e.g., sediment deposition). Ablation The process by which ice and snow waste away as a result of melting and/or evaporation. Abrasion (1) Removal of streambank soil as a result of sediment-laden water, ice, or debris rubbing against the bank. (2) The process of wearing down, or wearing away, stream bed and bank material by friction of solid particles moved by gravity, water, ice, or wind. Absolute time Geologic time measured in years. Compare to relative time. Absorption The process by which substances in gaseous, liquid, or solid form are assimilated or taken up by other substances. Accretion The process of sediment accumulation due to flowing water. Acid Has a pH of water less than 5.5; pH modifier used in the U.S. Fish and Wildlife Service wetland classification system; in common usage, acidic water has a pH less than 7. Acidic (1) The condition of water or soil in which the amount of acid substances are sufficient to lower the pH below 7.0. (2) A material with a pH of less than 7.0 (opposite of alkaline). Soil nutrients are generally less soluble and less available to plants in moderately or strongly acid soils. Agricultural lime is commonly applied to acidic soils to increase the pH. Acid rain Rainfall with a pH of less than 7.0. Long-term deposition of these acids is linked to adverse effects on aquatic organisms and plant life in areas with poor neutralizing (buffering) capacity. Accretion Vertical accumulation of inorganic or organic material. Trout Headwaters, Inc. PO Box 222 Livingston, MT 59047 (406) 222-3554 www.troutheadwaters.com Copyright © 2014 Trout Headwaters, Inc. All rights reserved. 1 Acre A measure of area equal to 43,560 ft2 (4, 046.87 m2). One square mile equals 640 acres. Acre-foot (acre-ft., or af) The volume of water needed to cover an acre of land to a depth of one foot; equivalent to 43,560 cubic feet (ft3) or 325,851 gallons. Active Channel Width The portion of the channel where sediment actively moves and\or permanent vegetation generally does not become established. Active floodplain A floodplain in which the 1-3 year flood reaches bankfull capacity. Floodplains become active or inactive through channel change or through changes in annual flood frequency (i.e., upland watershed condition). Active storage capacity The total usable reservoir capacity available for seasonal or cyclic water storage. It is gross reservoir capacity minus inactive storage capacity. Adaptation (1) The condition of showing fitness for a particular environment, as applied to characteristics of a structure, function or entire organism; also, the process by which such fitness is acquired. (2) A modification of a species that makes it more fit for reproduction and/or existence under the conditions of its environment. Adfluvial Refers to fish that hatch in streams, migrate to a lake or shore to mature, and return to their natal stream to spawn. Adsorption The adherence of gas molecules, ions, or molecules in solution to the surface of solids. Aeolian Sediment deposited by wind. Derived from Greek mythology; Aeolus was god of the winds. Aeration Any active or passive process by which intimate contact between air and liquid is assured, generally by spraying liquid in the air, bubbling air through water, or mechanical agitation of the liquid to promote surface absorption of air. Aerobic (1) Occurring only in the presence of molecular oxygen (said of certain chemical or biochemical processes, such as aerobic decomposition); (2) Characterizing organisms able to live or be active only in the presence of free oxygen or air, and conditions that exist only in the presence of air or free oxygen. Contrast with Anaerobic. Affluent (stream) A stream or river that flows into a larger one; a tributary. Afterbay A reservoir that regulates fluctuating discharges from a hydroelectric power plant or a pumping plant. Aggradation Trout Headwaters, Inc. PO Box 222 Livingston, MT 59047 (406) 222-3554 www.troutheadwaters.com Copyright © 2014 Trout Headwaters, Inc. All rights reserved. 2 (1) A long-term, persistent rise in the elevation of a streambed caused by sediment deposition. (2) A progressive buildup or raising of the channel bed and floodplain due to sediment deposition. (3) The geological process by which streambeds, floodplains, and the bottoms of other water bodies are raised in elevation by the deposition of material eroded and transported from other areas. Typically a stream that is undergoing aggradation over a long section of its length has an excess supply of sediment. (4) Aggradation indicates that stream discharge and/or bed-load characteristics are changing. Opposite of Degradation. Aggrading Accumulating sediment or deposition; in reference to stream beds. Aggregate Sand, gravel, crushed stone, or slag, usually having a known range of particle sizes. Used either with a cementing medium to form concrete, or alone as in a roadway bed or for railroad ballast. Agricultural pollution Liquid and solid wastes from all types of farming, including runoff from pesticides, fertilizers, and feedlots; erosion and dust from plowing; animal manure and carcasses; and crop residues and debris. "A" horizon Organic soil zone immediately below the surface of the ground, from which soluble material and fine- grained particles have been moved downward by water seeping through the soil. Varying amounts of organic matter can give the "A" horizon varying colors, usually ranging from gray to black. Sometimes called topsoil. A-Jacks (E-SenSS) A proprietary product for scour protection, consisting of precast concrete units. Each unit has six legs, which interlock with other A-Jacks when the units are placed in the stream, thus providing greater stability. The units are available in various sizes from Armortec, Inc., Bowling Green , KY. Algae Microscopic plants that grow in sunlit water containing phosphates, nitrates, and other nutrients. Algae, like all aquatic plants, add oxygen to the water and are important in the fish food chain. Alevin The life stage of salmon and trout immediately following the egg stage. Hatchlings still have their yolk sacs attached to them, and they live within the spaces in the gravel. Algal bloom The rapid proliferation of passively floating, simple plant life, such as blue-green algae, in and on a body of water. Alkaline (1) Material with a pH greater than 7 (opposite of acidic); (2) pH modifier in the U.S. Fish and Wildlife Service wetland classification system; (3) in common usage, a pH of water greater than 7.4. Allochthonous Material originating offsite that is subsequently transported onsite through the action of water, gravity, or other mechanisms. Alluvial (1) Deposited by running water; (2) Refers to the transport of material by flowing water normally in a river or stream. (3) Referring to deposits of silts, sands, gravels and similar detrital material, which have been transported by running water. Trout Headwaters, Inc. PO Box 222 Livingston, MT 59047 (406) 222-3554 www.troutheadwaters.com Copyright © 2014 Trout Headwaters, Inc. All rights reserved. 3 Alluvial aquifer A water-bearing deposit of unconsolidated material (sand and gravel) left behind by a river or other flow water. Alluvial deposit Clay, silt, sand, gravel or other sediment deposited by the action of running, ponded, or receding water. Alluvial fan Depositional landforms whose surface forms a segment of a cone that radiates downslope from the point where the stream moves from a steep gradient to a flatter gradient and suddenly loses some sediment transport capacity. Typical of arid and semiarid climates, but not confined to these areas. Alluvial plain Flood plains produced by the filling of the valley bottom with alluvium. Alluvial plains are usually composed of fine mud, sand and gravel, but can include cobbles, boulders and organic material. Alluvial stream (1) Self-formed channels composed of silts, clays, sands, gravel, or cobble, and characterized by the ability to alter their boundaries and patterns in response to changes in discharge and sediment supply. (2) A stream whose channel boundaries are composed of appreciable quantities of the sediments transported by the stream flow. An alluvial stream is free to adjust its dimensions of size, shape, pattern, and slope in response to changes in flow and sediment. Alluvium (1) A general term for all deposits (gravel, sand, silt, clay, or other particulate rock material) resulting directly or indirectly from the sediment transport of streams, including the sediments collected in riverbeds, floodplains, lakes, fans, and estuaries; (2) Sediments transported by the flowing water of a river or stream; (3) A general term for detrital deposits made by streams on riverbeds, floodplains, and alluvial fans, especially a deposit of silt or silty clay laid down during times of flood. The term applies to stream deposits of recent time. It does not include subaqueous sediments of seas or lakes. (4) A general term for all material deposited by a modern stream anywhere along its course. Alluvium would include sediments laid down in river beds, flood plains, lakes, fans, and estuaries. Alpine snow glade A marshy clearing between slopes above the timberline in mountains. Alternate bars Depositional features on opposite sides of the channel formed when the low-water channel of a stream meanders within the banks of a straight section of the stream.