SUMMARY

This report describes the natural and anthropogenic factors believed to influence water-quality conditions in the Yellowstone River Basin (YRB). Major water-quality issues in the YRB are sediment, trace elements, toxic compounds, salinity, and stream-habitat degradation. Land and water uses that relate to these issues include grazing, agriculture, mining, oil production, and residential expansion into rural areas.

The physiography parallels the structural geologic setting that is generally composed of several uplifts and structural basins. Contrasts in climate and vegetation reflect topographic controls and the midcontinental location of the study unit. Surface-water hydrology reflects water surpluses in mountainous areas dominated by snowmelt runoff, and water deficits in the remainder of the study unit. Principal ground-water aquifers are Tertiary sandstones and unconsolidated Quaternary deposits.

Human population, though sparsely distributed in general, is growing most rapidly in a few urban centers and resort areas, mostly in the northwestern part of the YRB. Land use is areally dominated by grazing in the basins, and economically dominated by mineral-extraction activities. Forests are the dominant land cover in mountainous areas. Cropland is a major land use in principal stream valleys. Water use is dominated by agriculture overall, but mining and public-supply facilities are major users of ground water. Coal and hydrocarbon production and reserves distinguish the YRB as a principal energy-minerals resources region. Current metallic-ore production or reserves are nationally significant for platinum-group elements and chromium.

Other investigators integrated multiple environmental factors to subdivide the YRB into ecological regions that serve as a starting point for an initial environmental stratification of the study unit. Ecoregions, geologic groups, and general land-cover and land-use categories were used in combination to define 18 environmental settings in the YRB that collectively describe about 89 percent of the study unit. These 18 settings are initial candidates for targeted study components that will be used to assess and compare water-quality conditions.

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_____1980b, Land use and land cover, 1976, Ekalaka, Montana; North Dakota; South Dakota: U.S. Geological Survey Land Use Series L-137, scale 1:250,000.

_____1980c, Land use and land cover, 1973, Glendive, Montana; North Dakota: U.S. Geological Survey Land Use Series L-138, scale 1:250,000.

_____[1983a], Land use and land cover, 1980, Arminto, Wyoming: U.S. Geological Survey Open-File Land Use Series 83-571-1, scale 1:250,000.

_____[1983b], Land use and land cover, 1981, Casper, Wyoming: U.S. Geological Survey Open-File Land Use Series 83-572-1, scale 1:250,000.

_____[1983c], Land use and land cover, 1980-81, Sheridan, Wyoming; Montana: U.S. Geological Survey Open-File Land Use Series 83-112-1, scale 1:250,000.

_____[1984a], Land use and land cover, 1980, 1982, Ashton, Idaho; Mont.; Wyo.: U.S. Geological Survey Open-File Land Use Series 84-0324-1, scale 1:250,000.

_____[1984b], Land use and land cover, 1976-1981, Billings, Montana: U.S. Geological Survey Open-File Land Use Series 84-0313-1, scale 1:250,000.

_____[1984c], Land use and land cover, 1980, Cody, Wyoming: U.S. Geological Survey Open-File Land Use Series 84-878-1, scale 1:250,000.

_____[1984d], Land use and land cover, 1980, 1982, Driggs, Idaho; Wyoming: U.S. Geological Survey Open-File Land Use Series 84-0325-1, scale 1:250,000.

_____[1984e], Land use and land cover, 1980, Forsyth, Montana: U.S. Geological Survey Open-File Land Use Series 84-039-1, scale 1:250,000.

_____[1984f], Land use and land cover, 1982, Lander, Wyoming: U.S. Geological Survey Open-File Land Use Series
84-0547-1, scale 1:250,000.

_____[1984g], Land use and land cover, 1981-1983, Thermopolis, Wyoming: U.S. Geological Survey Open-File Land Use Series 84-0548-1, scale 1:250,000.

_____[1985], Land use and land cover, 1982, 1984, Roundup, Montana: U.S. Geological Survey Open-File Land Use Series 85-0315-1, scale 1:250,000.

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_____1987, Digital elevation models: U.S. Geological Survey, National Mapping Program Data Users Guide 5, 38 p.

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Allochthonous refers to materials, such as organic sediments, that originate outside a given ecosystem and thus provide external inputs of food energy or nutrients.

Alluvium consists of clay, silt, sand, gravel, or other unconsolidated material deposited by a stream or other body of running water as a sediment in the bed of a stream or on a floodplain or delta, or as a fan at the base of a mountain.

Anticline is an arched fold in which the rock layers dip away from the axis of the fold.

Aquifer is a body of rock that contains sufficient saturated, permeable material to yield substantial quantities of water to wells and springs.

Armored streambed is one having a coarser assemblage of particle sizes in the surface layer of bed material as compared to the subsurface composition. This condition results when the sediment-transport capacity of the stream over a wide range of flows is sufficient to move only the finer particle sizes of bed material.

Badlands refers to areas having intricately dissected topography resulting from fluvial erosion and characterized by high drainage density and steep, mostly barren sideslopes with narrow interfluvial ridges.

Bedrock is a general term for the consolidated (solid) rock that underlies soil or other unconsolidated surficial material.

Board foot is a unit of lumber measurement equal to 0.305 meter (1 foot) square by 25.4 millimeter (1 inch) thick.

Breccia refers to a coarse-grained clastic rock, composed of angular fragments bound by mineral cement or in a fine-grained matrix. The sharp edges and unworn corners of the fragments composing breccia differentiate it from conglomerate.

Caldera is a large, basin-shaped volcanic depression having a diameter many times greater than that of the included vent or vents.

Clastic rocks are composed principally of broken rock fragments that are derived from pre-existing rocks or minerals and have been transported from their place of origin. The most common clastic rocks are sandstone and shale.

Climax community refers to the final or stable biological community in a developmental series that is self-perpetuating and in equilibrium with the physical habitat.

Colluvium is heterogeneous, unconsolidated, incoherent soil or rock material.

Confined aquifer is bounded above and below by impermeable beds or by beds of distinctly lower permeability than that of the aquifer itself. In addition, the water level in a well open to a confined aquifer rises above the top of the aquifer.

Cubic meter per second (m³/s) is the rate of discharge representing a volume of 1 cubic meter passing a given point during 1 second and is equivalent to about 264 gallons per second, or 35.31 cubic feet per second.

Discharge is the volume of water (or generally, the volume of liquid plus suspended material) that passes a given point within a given period. Discharge also is called flow.

Disseminated refers to a mineral deposit in which the desirable mineral occurs as scattered particles in the rock, but in sufficient quantity to make the deposit an ore.

Dissolved refers to a substance present in true chemical solution. In practice, however, the term includes all forms of substances that will pass through a 0.45-micrometer membrane filter, and thus may include some very small (colloidal) suspended particles.

Domestic water use is water for household purposes, such as drinking, preparing food, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens. This water use is also called residential water use.

Drainage basin (drainage) is the total area drained by a stream and its tributaries. The area of a drainage basin is called drainage area and usually is determined planimetrically from topographic maps.

Ephemeral stream is a stream or reach of a stream that flows briefly only in direct response to precipitation in the immediate locality and whose channel is at all times above the water table.

Fault is a fracture in bedrock along which movement of the bedrock has occurred.

Flood plain is the lowland that borders a river, usually dry but subject to flooding when the stream overflows its banks.

Foreland structure is a geologic structural feature located along the edge of a stable continental platform and marginal to a belt of folded mountains.

Formation is a body of rock identified by unique physical characteristics and relative position.

Gaging station is a particular site on a stream, canal, lake, or reservoir where systematic observations of hydrologic data are obtained.

Greenstone belt refers to elongate areas within Precambrian shields that are characterized by altered or metamorphosed basic igneous rocks and sedimentary rocks forming one or more metamorphosed volcano-
sedimentary piles.

Hogback refers to a sharp-crested ridge formed by the outcropping edges of steeply inclined resistant rocks, and produced by differential erosion.

Infiltration is the flow of water into soil at land surface, as contrasted with percolation, which is movement of water through soil layers or other surficial material.

Intermittent stream is a stream or reach of a stream that flows only certain times of the year when it receives water from springs or from some surface source such as melting snow.

Intrusive rocks are igneous rocks formed by emplacement of magma in pre-existing rocks.

Limestone is dense rock formed by chemical precipitation of calcium carbonate from solution in water.

Megagram is a unit of mass equivalent to 1,000 kilograms, one metric ton, or 1.102 short tons.

Metasedimentary rocks are sedimentary rocks that show evidence of having been subjected to metamorphism.

Milligrams per liter (mg/L) is a unit expressing the concentration of chemical constituents in solution as mass (milligrams) of solute per unit volume (liter) of water. Concentration of suspended sediment also is expressed in milligrams per liter and is based on the mass of sediment per liter of water-sediment mixture.

Orographic refers to precipitation patterns that result when moist air encounters a topographic barrier and is forced to rise over it; for example, the increase in precipitation with elevation on the windward slopes of a mountain range and the rain-shadow of decreased precipitation on the leeward side of the range.

Particle size (grain size) is the diameter, in millimeters, of any given sediment particle. (See particle-size classification.)

Particle-size classification used by the U.S. Geological Survey:

Classification Particle-diameter range, in millimeters

Clay 0.00024-0.004

Silt .004-.062

Sand .062-2.00

Gravel 2.00-64.0

Peak discharge (peak flow, flood peak) is the maximum instantaneous discharge during a specified time interval. The series of annual peak discharges at a gaging station is used to determine the recurrence interval (frequency) and exceedance probability of floods.

Pediment refers to a broad, gently sloping, rock-floored erosional surface or plain of low relief, typically developed at the base of an abrupt, receding mountain front or plateau escarpment.

Perennial stream is a stream that flows continuously.

Permeability is a measure of the relative ease with which a porous or fractured medium can transmit a liquid under a potential gradient (the capacity of a rock to transmit a fluid such as water or petroleum).

pH is a measure of the acidity or alkalinity of water. It is defined as the negative logarithm of the hydrogen-ion concentration. This property is dimensionless and generally has a range from 0 to 14, with a pH of 7 representing neutral water. A pH of greater than 7 indicates the water is alkaline, whereas a pH value less than 7 indicates an acidic water.

Placer deposit is a surficial mineral deposit, usually of a heavy mineral, formed by mechanical concentration of mineral particles from weathered debris.

Porosity is the property of a rock or soil that refers to the voids that the material contains. It may be expressed quantitatively as the ratio of the volume of voids to total volume of the material.

Porphyry refers to an igneous rock that contains conspicuous phenocrysts (relatively large crystals) in a fine-grained groundmass.

Public-supply water use is water withdrawn by public and private water suppliers and delivered to users. Public suppliers provide water for a variety of uses, such as domestic, commercial, thermoelectric power, industrial, and public water use.

Recharge is the process by which water is absorbed and added to the saturated zone (aquifer), either directly into a body of rock or indirectly by way of an adjacent body of rock. Also, it is the quantity of water that is added to the saturated zone.

Riparian vegetation refers to plants growing in near-stream locations where more moisture is available to plants than in adjacent upland areas, and where the dominant species of adjacent upland vegetation are absent or compose a minor part of the community.

Sandstone is the consolidated equivalent of sand. (See particle-size classification.)

Saturated zone is the subsurface zone in which all openings are full of water and are under hydrostatic pressure equal to or greater than atmospheric pressure.

Sediment is unconsolidated solid material that originates mostly from disintegrated rocks and is transported by water or air. Also, it may include chemical and biochemical precipitates or decomposed organic material, such as humus.

Shale is the consolidated equivalent of clay. (See particle-size classification.)

Shear zone is a tabular zone of rock that has been crushed and brecciated by many parallel fractures due to shear strain. Shear zones often are mineralized by ore-forming solutions.

Siltstone is the consolidated equivalent of silt. (See particle-size classification.)

Silviculture (forestry) is the care and cultivation of forest trees.

Skarn refers to lime-bearing silicates derived from limestone and dolomite with the introduction of large amounts of Si, Al, Fe and Mg.

Stock is an igneous intrusion having less than 100 km² of surface exposure; resembles a batholith except in size.

Stratification refers to a statistical design for study or sampling in which a population is first divided into groups, or strata, having greater homogeneity than the whole population, according to relevant characteristics; then information is gathered about each group, often by selecting a sample from each.

Stratiform refers to geologic structure having the form of a layer, bed, or stratum; consisting of roughly parallel bands or sheets.

Streamflow is the discharge in a natural channel. Although the term "discharge" can be applied to a flow of a canal, the word "streamflow" is used only to describe the discharge in a stream. The term "streamflow" is more general than "runoff," since streamflow may be applied to discharge whether or not it is affected by diversion or regulation.

Superimposed refers to a stream or drainage system that has cut down from above by erosion, through the formations on which it developed, onto rocks of different structure lying beneath.

Surface water is an open body of water such as a stream or lake.

Terrace is a steplike landform above a stream and its floodplain, representing a former, abandoned floodplain of a stream.

Unconsolidated refers to sediment grains that are loose, separate, or unattached to one another.

Unsaturated zone is the zone between the land surface and the water table. It includes the capillary fringe. Generally, water in this zone is under less than atmospheric pressure, and some of the voids may contain air or other gases at atmospheric pressure.

Volcaniclastic refers to a clastic rock containing volcanic material.

Water table refers to the upper surface of the saturated zone where the water pressure is equal to atmospheric pressure.

Water year refers to the 12-month period from October 1 to September 30, and is designated by the calendar year in which it ends. Thus, the water year ending on September 30, 1995, is called water year 1995.

Yield is the constant or final pumping rate from a well in liters per minute at which a well-acceptance test is conducted.