1041 Permit: The 1041 Land Use authorities give counties and municipalities control over” projects of statewide interest,” such as pipelines and water projects, within their boundaries. These powers were granted through House Bill 1041 (1974).

absolute water right: An absolute, or perfected water right, is a water right that is granted permanent status when water has been physically diverted or controlled and put to beneficial use. A water right is granted for a specific amount of water to be put to a beneficial use from a specific point of diversion or control, for a certain purpose and for some rights a specified period of use.

abandonment: Abandonment is the loss of all or part of a water right due to non-use or the failure to prove diligence on a conditional water right resulting in the loss of the right and its placeholder status relative to other water rights. Absolute water rights are only declared abandoned by the water court when the water right holder expresses an intent to abandon the right.

acid rain: Rainfall contaminated by sulfur dioxide released into the atmosphere through the burning of fossil fuels, primarily coal. Acid rain may damage plants, animals and sensitive ecosystems.

acre-foot: An acre-foot is the standard unit of measurement for standing or stored water. It is the amount of water required to cover one acre of land (43,560 square feet) one foot deep. An acre-foot is equal to 325,851 gallons. Depending on how much water is used for outside irrigation, an acre-foot can meet the needs of one to two single-family households fora year.

adjudication: A judicial process through which the existence of a water right is confirmed by court decree. With the court decree, the water right is given its priority among all other water rights, determining its place in line, or seniority, when there is not enough water to meet the needs of all users.

administration: Administration is the action taken by the State Engineer’s Office when there is not enough water physically available to meet the demands of all water rightsholders within a river basin. Through the process of administration, senior water rights are satisfied by shutting off water supplies to junior water rights, beginning with the most recent priority dates and moving back chronologically, until the all the supply of water available for diversion is expended.

af: acre-feet / acre-foot – An acre-foot is the standard unit of measurement for standing or stored water. It is the amount of water required to cover one acre of land (43,560 square feet) one foot deep. An acre-foot is equal to 325,851 gallons. Depending on how much water is used for outside irrigation, an acre-foot can meet the needs of one to two single-family households fora year.

algae bloom: A sudden onset of rapid growth of aquatic plant life caused by the introduction of high amounts of nutrients in a waterway. Runoff from agricultural and/or urban areas carrying large amounts of fertilizers, detergents or other compounds that promote plant growth can be the cause of an algal bloom. The sudden proliferation of algae rapidly decreases the amount of oxygen available for fish and other aquatic life and can cause a large fish kill.

AOP: Annual Operating Plan

appropriation date: An appropriation date is the earliest date approved by the water court demonstrating that a water rights holder intends to put water to beneficial use. The appropriation date places a water right in chronological order among other water rights, with those older being senior to it and those younger characterized as junior. In times of shortage, the oldest rights have first priority, with remaining water allocated in chronological order until there is no more water available for use. The older a water right’s appropriation date, the greater its value due to the likelihood it will have water in times of short supply.

aquifer: An aquifer is an underground geologic formation containing water that can be tapped through wells or springs. There are two types of aquifers: tributary and non-tributary. A tributary aquifer is hydrologically connected to surface water sources, such as rivers, streams and lakes. Removing water from tributary aquifers depletes the connected surface water sources as well. Non-tributary groundwater is not physically connected to any surface water sources.

arid / semi-arid: Aridity describes the relative lack of rain or snowfall to an area. Arid areas generally receive less than 10″ of rain per year on average. In arid areas, plant and animal life forms must be adapted to living without significant moisture. A semi-arid area receives more precipitation annually than the arid areas, between 10″ and 20″ per year, yet is still considered relatively dry. Colorado, as a whole, is considered to be semi-arid, since the entire state receives on average approximately 17″ of precipitation annually.

artesian well: An artesian well taps underground water which is under sufficient pressure that water rises to the surface naturally.

Article III(e) of 1922 Colorado River Compact:  Provides that the Upper Division states are not to withhold water and the Lower Division states are not to require the delivery of water which cannot reasonably be applied to domestic and agricultural uses.

augmentation plan: Augmentation plans are court-approved plans allowing diversion of water from a convenient location in exchange for providing an equivalent amount of water to a river or stream at another point that satisfies senior water rights. Augmentation plans allow for the use of water without causing injury to other downstream water users.

basin: A basin is an area of land that collects water as either snow melt or rainfall and drains into a common body of water, such as a stream or a river.

beneficial use: Beneficial use is the legal basis for allowing all diversions of water from surface and groundwater supplies. Water that is removed from the state’s rivers, streams and underground must serve a beneficial purpose to mankind, either economically, socially, recreationally, hygienically or other ways, or it is not granted a right. To allow water resources to benefit the greatest number of people, use of water must be reasonably efficient. A water right is a right to use the amount of water necessary to accomplish beneficial use without waste.

Black Lakes: The Black Lakes are two reservoirs situated near the top of Vail Pass at the headwaters of Black Gore Creek. Their primary function is to augment low wintertime stream flows on Gore Creek. Combined, they store approximately 300 acre-feet of water.

Biological Opinion: A document that is the product of formal consultation, stating the opinion of the Service on whether or not a Federal action is likely to jeopardize the continued existence of listed species or result in the destruction or adverse modification of critical habitat.

Boulder Canyon Project Act: Effective June 25, 1929, authorized construction of Hoover Dam and the All American Canal and requires contracts with the Secretary of the Interior for use of water stored in Lake Mead.

Bureau of Land Management (BLM):  The Bureau of Land Management is a federal agency within the U.S. Department of the Interior that administers more than 247.3 million acres of public lands in the United States which constitutes one-eighth of the landmass of the country. The agency manages 221 wilderness areas, 23 national monuments and some 636 other protected areas as part of the National Landscape Conservation System totaling about 30 million acres.

Bureau of Reclamation: The U.S. Bureau of Reclamation (USBR, BOR, BuRec, Reclamation) is a federal agency within the U.S. Department of the Interior whose historical purpose was to open the lands of the western U.S. to settlement through the construction of water projects to irrigate arid lands. They were responsible for building many of the west’s major water projects, damsreservoirs, tunnels and canals, building over 180 projects in 17 western states. Their primary mission has recently evolved into the role of water managers, rather than builders of new water projects.

call: A call begins with a senior water user’s request to a division engineer or ditch rider to restrict the use of water among junior water users, since there is not enough water in the system to allow all  water diversions. Starting with the most junior user, water diversions are shut-off until the more senior rights are satisfied.

C-BT  abbreviation for Colorado-Big Thompson project

cfs: CFS is an acronym for cubic feet per second. A cubic foot per second is one cubic foot of water passing by a single point for one second. CFS is the standard unit of measure for water that is in motion, such as water flowing in rivers and streams. A flow rate of one cfs would mean that 7.48 gallons passed by a point of reference in one second or 448.8 gallons of water in one minute. Over the course of 24 hours, a flow of one cfs would produce 646,317 gallons or almost the equivalent of two acre-feet per day.

check structure: A device used to control the flow, pressure or direction of water through a canal or irrigation system. Check structures allow for more efficient use of water in a canal by regulating flows in a manner where less water is needed to accomplish a beneficial use.

Colorado-Big Thompson Project: The Colorado-Big Thompson Project (C-BT) is the single largest diverter of Colorado River water in Colorado and is the biggest transmountain diversion in the state. The C-BT collects the headwaters of the Colorado River in Grand County, annually sending in excess of 200,000acre-feet of water through the Alva B. Adams tunnel on the eastern end of Grand Lake to farms and cities in northeast Colorado. The C-BT is a complex system of reservoirs, pumps, pipelines, canals and other water structures for collecting and distributing water and generating hydroelectric power. Its operations are set out in Senate Document 80,passed on June 24, 1937 by the 75th Congress, which specifies that the purpose of the C-BT was to provide a supplemental water supply for northeast Colorado. The project began construction in 1938 and was completed in 1957.Agricultural users owned 85% of the shares at the time the project was completed, however, growing municipalities now own the majority of the water shares. Green Mountain Reservoir in Summit County is part of the Colorado-Big Thompson project. Of its 152,000 acre-foot capacity, 100,000 acre-feet has been set aside for the benefit of the West Slope.

Colorado River Compact: Water allocation problems along the full length of the Colorado River prompted the 1922 Colorado River Compact between Colorado, Wyoming, Utah, New Mexico, Nevada, Arizona and California. The Colorado River was split into Upper Basin and Lower Basin segments, with Lee’s Ferry in Arizona serving as the dividing point and it was agreed to apportion the waters of the Colorado River to these two basins. Each basin would than allocate water among its states. In 1948,the Upper Basin states of Colorado, Wyoming, Utah and New Mexico agreed on apportioning the Upper Basin’s share.

Colorado River endangered fish: Four species of native fish are listed as endangered under the Endangered Species Act (ESA) in the Colorado River basin in the State of Colorado. A Recovery Program has been established to fulfill the goal of bringing populations of these four endangered fish back to self-sustaining levels. Recovery Program efforts may affect stream flow regimes and reservoir operations throughout the West Slope of Colorado.

The four fish are the humpback chub (Gila cypha), the bonytail (Gila elegans), the razorback sucker (Xyrauchen texanus) and the Colorado pikeminnow (Ptychocheilus Lucius,formerly called the Colorado squawfish.) These are warm water fish,residing primarily in lower elevation stretches of the Colorado River west of Rifle, on the White River in Rio Blanco County and in the Yampa River in Moffat County.

Colorado River Water Conservation District (CRWCD): The Colorado River Water Conservation District (CRWCD), also known as the River District, is a governmental entity formed in 1937. It evolved from the Western Colorado Protective Association, which was a group dedicated to protecting the Colorado River from threats of out-of-basin diversions. The present day River District’s mission is to protect and conserve the waters of the Colorado River within Colorado for beneficial use. It is a policy-making entity that can hold water rights, fund water projects, litigate, lobby for legislation and mediate disputes affecting the district.

The River District represents all or part of 15 West Slope counties, including: Grand, Summit, Eagle, Pitkin, Routt, Garfield, Moffat, Rio Blanco, Gunnison, Mesa, Delta, Montrose, Ouray, Hinsdale and Saguache counties. Each county has one representative seated on the River District’s Board of Directors appointed by the county’s Board of Commissioners for three-year terms. The River District is principally funded by a tax assessment based on value of a land owner’s property mill levy.

Colorado Water Conservation Board (CWCB)The Colorado legislature created the CWCB within the Department of Natural Resources in 1937. The board is comprised of 10 voting members appointed by the Governor and confirmed by the Senate and 5 non-voting members. The CWCB’s mission is to “conserve, develop, protect, and manage Colorado’s water for present and future generations.”

A compact is an agreement among states, approved by Congress, resolving interstate matters. When compacts are made concerning rivers, the compact establishes how states along a river allocate its water. Colorado has entered into nine interstate compacts agreeing to terms and conditions of water allocation.

compensatory storage: Compensatory storage is a concept pioneered by the Western Colorado Protective Association, an organization that became the Colorado River Water Conservation District in 1937. This principle contends that transmountain diversions should provide a stored water supply to the basin of origin to compensate, or mitigate, for the effects of the diversion. Transmountain diversions reduce the potential for future in-basin water use, growth and development, and compensatory storage is designed to protect the basin of origin. This principle was first applied to the Colorado-Big Thompson and resulted in the construction of Green Mountain ReservoirRuedi Reservoir is the compensatory portion of the Fryingpan-Arkansas project.

conditional right:  A conditional water right is a legal right that holds a place in line for a planned water project this is not yet complete. Conditional rights are granted to provide the time to get a water diversion or storage project planned and constructed without losing the priority date of when the project was originally conceived. Evidence that plans to develop the project are still moving forward must be proven to a water court judge every six years in an act called “diligence” to keep the conditional water right on the books and preserve its place in line among other water appropriators.

conjunctive use: Conjunctive use is the coordinated use of both ground and surface water resources to maximize the availability of both. In wet periods, surface water will generally be the preferred water source, and excess surface water may be used to recharge underground aquifers. During drought periods when surface water is scarce, a greater reliance can be placed on ground water to meet consumptive needs. The Front Range, with substantial ground water resources, is increasingly looking to conjunctive use as a way to optimize their water supplies.

conservancy district: A conservancy district is a taxing body created for the purpose of constructing, paying for and operating water projects. A conservancy district can cover a very large area of the state or a very small one, depending upon how many people agree to be included and the area benefiting from the project or projects.

conservation district: A conservation district is a policy-making body that is chartered by the General Assembly of Colorado for the purpose of protecting and developing the water resources of a portion of the state. Many conservancy districts can be located within the boundaries of a conservation district. There are four water conservation districts in Colorado: The Colorado River Water Conservation District (CRWCD) covers northwest and west central Colorado, the Southwestern Water Conservation District (SWCD) covers the southwest corner of the state, the Rio Grande Water Conservation District (RGWCD) covers the San Luis Valley and the Republican River Water Conservation District (RRWCD) represents the Republican River Basin in eastern Colorado.

consumptive use: Consumptive use is the amount of water that does not return to its source after it has been diverted and put to beneficial use. Not all water is physically consumed when it is diverted. Unconsumed water that returns to a water supply through a municipal or industrial wastewater system or an irrigation system’s tailwater is called return flow. Return flows are then available for other downstream water users.

dam:  A dam is a physical structure that impounds and controls the flow of a waterway, backing up water to allow for the diversion or storage of water. Dams moderate the flow of water by absorbing flood or high season flows and controlling the amount of water that is subsequently released downstream. A dam is not the equivalent of a reservoir, though constructing dams on rivers and streams typically form reservoirs behind them.

decree: An official document issued by the court defining the priority, amount, use, timing and location of a water right.

depletion: A depletion is the amount of water lost to a river system or aquifer when water is diverted from it. 

desalination: The process of removing dissolved salts from brackish groundwater or seawater or other saline waters. (Desalinization is used as an interchangeable term.)

diligence: Diligence is the effort accomplished by a conditional water right holder to physically use water for a beneficial purpose, thereby perfecting that water right and making it absolute. Diligence must be proved to the water court every six years for the conditional right to remain on the books and hold its place in line. When diligence is not satisfactorily proved to the water court, it can be declared abandoned and its conditional decree date lost.

Dillon Reservoir:  Denver Water, the principal water provider for the Denver metro area, owns and operates Dillon Reservoir, which borders the Towns of Silverthorne and Dillon in Summit County. Dillon Reservoir stores inflows from the Blue River and smaller basin tributaries and transports the water under the Continental Divide through the Roberts Tunnel to the southern end of Denver’s water collection system.

discharge permit: A permit required by the federal Clean Water Act to introduce effluent, or waste water, into waters of the state.(see also National Pollutant Discharge Elimination System or NPDES.)

ditch rider: “Ditchrider” is the nickname applied to anyone who manages a ditch system,canal network or water distribution system and is responsible for ensuring that senior water rights are met first or that ditch company members receive the amount of water owned.

diurnal: Diurnal describes the fluctuations of streamflow throughout the day. The rate of snowmelt increases with periods of sun exposure and increased temperature. Streamflows increase after the sun exposure of daylight hours and corresponding decrease after periods of darkness.

diversion: The removal of water from its natural course or location by means of ditches, headgates, reservoirs, pipeline, conduit, well, pump or other structure or device.

drawdown: The lowering of reservoir water levels by releasing stored water or pumping ground water. A reservoir may be drawn down during the winter months to make room for spring flood flows caused by melting snows.

drip irrigation: An efficient irrigation practice where small, steady flows of water are released to individual plants through a network of irrigation hoses and tubes. This is an expensive but efficient irrigation practice.

drought: Drought occurs when precipitation is less than average for a lengthy period of time. The term is very subjective, and there are different interpretations of what constitutes a droughts. Physiological drought occurs when the amount of precipitation is unable to adequately sustain endemic flora and fauna. Agricultural drought is declared when precipitation is inadequate to sustain the growth of agricultural crops.

Eagle Mine: The Eagle, or Gilman, Mine is a big part of Eagle County’s mining heritage and is located near the now-abandoned town of Gilman, which previously housed the miners. Zinc and lead were mined there until it was no longer profitable. By 1977 mining activity had nearly ceased. The mining left behind leaky mines and tailings piles that contributed heavy metals to the Eagle River. The Eagle River was declared impaired because of the toxic inflows and the Eagle Mine became an EPA Superfund site. Water leaking from the mine still must be treated at a water treatment plant east of Minturn to maintain the quality of Eagle River water.

Eagle Park Reservoir: Eagle Park Reservoir is situated in Eagle County near Tennessee Pass at an elevation of 10,700 ft. The reservoir formerly served the Climax Mine’s molybdenum mining operations as a tailings pond, but was cleaned-up and converted into a clean water reservoir in 1998, and stores 3,300 acre-feet of water. Water is released from Eagle Park Reservoir into the East Fork of the Eagle River.

Eagle Park Reservoir provides water to the shareholders of the Eagle Park Reservoir Company, who are Vail Associates, Eagle River Water & Sanitation District, Upper Eagle Regional Water Authority, Eagle County, and the Colorado River Water Conservation District. Through an exchange agreement with the Cities of Colorado Springs and Aurora, Eagle Park Reservoir Company also owns 1,000 acre-feet of water in the Homestake Project.

Eagle River Assembly: The Eagle River Assembly is an informal organization of municipalities, water agencies and private industry, from both within and outside of Eagle County, with interests in the water resources of the Eagle River. Formed in 1993, the Assembly came about as a result of the contentious proposed Homestake II project to explore cooperative solutions for the collective water needs of all of the parties involved. The group consists of representatives from Eagle County; the Towns of Avon, Eagle, Gypsum, Minturn, Red Cliff and Vail; Vail Resorts; Upper Eagle Regional Water Authority; Eagle River Water and Sanitation District; Colorado River Water Conservation District; Cyprus Climax Metals Company; City of Aurora; City of Colorado Springs; Denver Water; and Pueblo Board of Water Works.

East Slope: The East Slope of Colorado is the portion of the state that lies east of the Continental Divide. The East Slope includes the North Platte, South Platte, Arkansas and Rio Grande River basins. Most of Colorado’s population lives on the East Slope, though most of the precipitation falls on the West Slope, or the portion of Colorado west of the Continental Divide.

effluent: Effluent is any outflow of water. In connection with human water uses, the term effluent is most often used in the context of water whose quality has been impaired by human use, animal use or otherwise compromised by its diversion for its natural source. Treated effluent is the term used for discharges from wastewater treatment plants and returned to a river, stream or other water source.

eutrophication: Eutrophication is the process where nutrient loading contributes to the decline of water bodies and their eventual conversion to land. Through nutrient loading, bodies of water gradually become boggy or marshy and slowly fill in with organic matter that displaces water. This process can be accelerated by human activities that either load waters with excess nutrients stimulating plant growth or through silt loading.

exchange: An exchange is an agreement between parties where water can be diverted or stored at one point, in exchange for an equivalent amount of water being released or bypassed at another point on a river system In an exchange, the diversion or storage of water and the release or bypass of water from another point must occur simultaneously to prevent injury to other water users. Exchanges must be approved by the State Engineer’s Office, who will ensure that the exchange functions properly.

fecal coliform: Fecal coliform is a bacteria present in the intestinal tracts of humans and warm-blooded animals. When introduced into water systems, it contaminates the water and may spread disease.

federal reserved water right: The federal government has claimed that whenever it reserves a portion of land, for instance Indian reservations and national parks, that an implied water right is attached to that land to fulfill the purpose of the land’s reservation. These rights were first established in the landmark Winters v. U.S. (1908) case. The claim to these water rights is very contentious, because these rights are in many cases not asserted at the time of the land’s reservation, instead coming later with large senior claims.

“First in time, first in right:” First in time, first in right is a term synonymous with the prior appropriation system. This phrase denotes how those with the oldest, and therefore most senior appropriations of water have priority over other younger, or more junior, water rights during times of insufficient water supply.

free river: Free river conditions occur when there is more water than all perfected water rights on a river system, enabling any water user, with or without water rights, to use water from that waterway. A free river is most likely to occur during the spring runoff or on streams that have few water users.

Front Range: Front Range refers to the band of large municipalities that sit along the eastern foothills of the Rocky Mountains in Colorado. This region is marked by intense development and harbors a majority of the state’s population. The Front Range stretches from the northern communities of Fort Morgan, Fort Collins and Greeley, near the Colorado-Wyoming border, through the Denver metropolitan area and south to Colorado Springs and Pueblo. The term “I-25 corridor” is synonymous with the Front Range, since these communities are all in close proximity to this traffic artery. The Front Range generally lacks the surface water resources necessary to support its population, agriculture and industries and has become increasingly reliant upon transmountain diversions to augment its natural water supplies.

futile call: A futile call occurs when a downstream senior water right cannot be satisfied, even after upstream junior water rights are curtailed. This can occur when a water source completely dries up or when transit losses, the amount of water lost through evaporation and seepage as it passes along a water way, completely consume the amount of the junior right.

Grand River: Grand River was the name of the reach of what is now the Colorado River upstream of its confluence with the Green River in Utah. A West Slope Congressman,  Representative Edward Taylor, fought for renaming the Grand River to the Colorado River, finally securing Congressional approval in 1921. Colorado’s Grand County, which harbors the headwaters of the Colorado River, and the City of Grand Junction still bear the vestiges of the river’s former name.

Green Mountain Reservoir: Green Mountain Reservoir (GMR) was the first feature of the Colorado-Big Thompson project to be built. The West Slope fought against the original C-BT project because its depletions of Colorado River water would impair the West Slope’s water supply and would severely hamper its ability to grow. From negotiations between the two sides, the idea of compensatory storage was born, which offers protection to the basin of origin through mitigation. In exchange for allowing the project to proceed, the C-BT project included Green Mountain Reservoir to keep West Slope water users from feeling the impacts of the upstream transmountain diversions and to allow for future West Slope growth. Initially the reservoir was apportioned into two pools of water. The most senior of these two pools, or the first to fill, was the 52,000 acre-foot “replacement pool” from which water would be released to replace Colorado River water transmountain diverted by the C-BT “out of priority” . The remaining 100,000 acre-feet (AF) were for present and future uses on the West Slope. This is known as the Compensatory Storage Pool or Power Pool, since hydroelectric energy is generated as the water is being released.

After the 1977 drought, reservoir operations were modified to divide the reservoir into four pools of water: The 52,000AF C-BT replacement pool, the Silt Project Pool containing 5,000 AF to mitigate the effects of constructing the water project near the West Slope town of Silt, a 66,000 AF Historic Users Pool (HUP) and a 20,000AF Contract Pool. Western Colorado water users that developed reliance upon Green Mountain water prior to 1977 have their needs met through the HUP pool. The Contract Pool meets the needs of industrial water users and post-1977 domestic and irrigation uses, pursuant to individual water contracts through the Bureau of Reclamation.

groundwater: Ground water is any water that exists beneath the earth’s surface. Where it exists in substantial amounts, it may be tapped for human use or may even flow freely to the surface. There are two kinds of groundwater: tributary and designated, or non-tributary. Tributary groundwater is hydrologically connected to surface water, since any depletion of that groundwater will affect the flow or level of the surface water it is connected to. Designated groundwater is only remotely connected to surface water. Designated groundwater is managed by a modified prior appropriations doctrine. If aquifers are depleted faster than they are recharged, the aquifer cannot sustain itself and will begin to run dry. Ownership of designated groundwater in Colorado is principally determined by surface land ownership.

groundwater recharge: Groundwater recharge is the flow of water into a groundwater basin or aquifer. Recharge occurs naturally or can happen through human intervention to stimulate the recharge through construction of seepage ponds or the active reinjection of water into the ground (see conjunctive use.)

head: Head is the force (pressure) created by a volume of water. The more water captured over a given location, the more head. Head represents potential energy which is realized when that water is released. Flowing water creates more head as the distance and/ or angle of its fall increases.

headgate: A headgate is a structure that controls the amount of water entering a diversion. A headgate can completely shut off a diversion, reduce the flow of water to a measured amount or permit the free flow of water. Headgates can be located at the top of a diversion or along a ditch or canal that serves multiple diversions.

Heeney Slide: The small town of Heeney sits at the southwest end of Green Mountain Reservoir in Summit County. It lies atop unstable soil formations at the base of a historic slide area. In the winter of 1963-64, the U.S.Bureau of Reclamation, which built, owns and operates Green Mountain, rapidly emptied the reservoir to work on the dam. The rapid lowering of the reservoir level was followed by two areas of earth movement that moved slowly over an extended period of days, one of which was under the Town of Heeney.

This slide area again came into prominence during the extreme drought conditions experienced in the summer of 2002. Expected full utilization of the reservoir to satisfy West Slope water demands threatened to bring the reservoir down to levels not seen since the winter of ’63 -’64. The Bureau of Reclamation declared that the final 27,000 acre-feet of water in the reservoir could not be released from Green Mountain Reservoir without threatening resumption of slide activity. This policy is currently a point of contention between all parties with a stake in Green Mountain Reservoir.

“Highest and best use:” This term is associated with the movement of water resources to beneficial uses that produce the highest financial return. This term is a value judgment that all parties may not agree upon.

historic use: Historic use documents the physical diversion and consumptive use of a water right over a period of time. Private diversion records or State Engineer’s office records typically document a water user’s historic use.

Historic Users Pool (HUP): The Historic Users Pool, or HUP, is a group of western Colorado water users that have historically benefit from releases of water out of Green Mountain Reservoir.

Homestake Reservoir: The drought period of the 1950’s spurred Colorado Springs and Aurora to secure additional water for transmountain diversion. The two cities purchased water rights in Eagle County on Homestake Creek and its tributaries in1956. At that time, Eagle County had yet to experience any resort development and sustained just a minimal population. The Homestake Project was originally conceived in four phases and only the first phase, construction of Homestake Reservoir, has been completed. Homestake Reservoir sits high on the East Fork of Homestake Creek in southeast Eagle County. The reservoir also collects water from French, Fancy, Missouri and Sopris Creeks. The majority of the reservoir’s water is sent through a tunnel bored underneath the Continental Divide to Turquoise Lake in Lake County. From Turquoise Lake, water is transported to the Cities of Aurora and Colorado Springs. The reservoir was completed in 1967. It diverts approximately 28,000 acre-feet of water per year.

Homestake II: After work was completed on Homestake reservoir, planning began on the second phase of the project, or Homestake II as it came to be known. A protracted battle ensued over the ability of Colorado Springs and Aurora to develop this project. In 1988, Eagle County denied the Homestake II Project’s “1041” land use permit. The project as originally designed was declared dead by the sponsoring cities in the1990’s after losing several court rulings.

The Homestake II Project would have taken approximately 30,000 acre-feet of water annually from Cross and Fall Creeks within the boundaries of the Holy Cross Wilderness. The proposed project called for 57,000 feet of tunnels, 3,000 feet of pipeline and four diversion structures. Water collected from Homestake II would have been delivered to the existing Homestake reservoir for subsequent delivery to the Front Range. The cities still retain the water rights for Homestake II.

hydroelectric: Hydroelectric power generation is the production of electricity from running or falling water, either from free-running watercourses or releases from a dam.

hydrograph: A hydrograph is the graphic depiction of varying water levels at a given measuring point over a period of time. A hydrograph can record fluctuations over the course of one day, showing the diurnal fluctuations of flows, over the period of days, weeks, months or years.

hydrologic cycle: The hydrologic cycle is the circulation of water from the earth’s surface to its atmosphere and back to earth again by taking on different forms such as snow, rain or vapor. The earth has a constant amount of water present. However, water moves from place to place and from one form to another through evaporation, transpiration (the release of water by plants), condensation and precipitation.

injury: Injury is the act of depriving a senior water right owners of their full water right. New water rights, changes of water rights, exchange and substitution agreements are only allowed if they do not injure other water users or uses.

irrigation district: An irrigation district is a public organization that supplies water to residents of the district through diversions, canals, laterals, pipes and other water transport systems primarily for the purpose of agricultural irrigation.

minimum stream flow: Colorado recognizes the benefits of water flowing in the state’s rivers and streams. The Colorado Water Conservation Board (CWCB) has been granted the exclusive authority to hold water rights for the minimum flows necessary to protect the natural environment.

Minute 319 Colorado Delta Pulse FlowA 2012  addendum to the U.S. – Mexico Water Treaty of 1944 created the opportunity for a pulse flow of approximately 105,392 acre feet being released to the riparian corridor of the Colorado River Delta from Morelos Dam at the U.S. – Mexico border from March 23, 2014 to May 18, 2014. Progress Report.  National Geographic article and video.

Mitigation: Mitigation is the remedy of negative consequences of certain actions. Mitigation is required or requested for most water development projects. Mitigation may be required when constructing reservoirs, diverting large quantities of water from a stream or transferring water from one basin of the state to another. Mitigation can take the form of constructing new wetlands, building new storage to compensate for a loss of water, repairing a stream channel and any other action deemed prudent by affected parties.

native fish: Rivers and streams in Colorado host a combination of native, or naturally occurring, fish species and introduced non-native species transplanted from outside the state. Native fish may be forced to compete with the non-native fish for habitat and food and non-native fish can be predatory to native species. Most non-native fish were principally introduced as sport fish, such as rainbow, brook and brown trout, or as food for sport fish.

non-consumptive: Any use of water that does not consume or deplete water through its use is non-consumptive. Recreation and aesthetics are examples of water use that are non-consumptive.

non-point source pollution: Non-point source pollution comes from diffuse sources that can only be broadly identified. This may come in the form of rain or snow melt runoff carrying sediments, wastes, bacteria and toxic agents that are harmful to existing water quality.

Northern Colorado Water Conservancy District (NCWCD): The Northern Colorado Water Conservancy District, often referred to as “Northern Water,” is the legal contracting entity for and recipient of project water from the Colorado-Big Thompson Project (C-BT).

over-appropriation: A stream or river is over-appropriated when it does not have enough water to meet the needs of all the water rights holders. Many rivers and streams in Colorado are over-appropriated, especially in dry years, in which case the water rights system determines which water users have a right to use water.

penstock: A penstock is a man-made conduit for moving water in a controlled manner. Penstocks send water to turbines for electrical generation or to waterwheels to produce dynamic energy.

percolation: Percolation is the infiltration of water through porous soils. Water percolates through soils as it moves down to groundwater basins or aquifers.

perfected right: A water right is considered perfected when water is actually put to beneficial use.

pheatophytes: Pheatotophytes are a class of plants with long root systems capable of tapping the water table or other groundwater supplies. Concern exists over the loss of water due to proliferation of pheatophyte species such as tamarisk, which can reduce the amount of water otherwise available for human and environmental benefit.

Piney Lake: Piney Lake, north of the Town of Vail on Red Sandstone Road, is owned by Denver Water. No water is diverted from the natural lake for Denver’s benefit.

priority date: A priority date is the date assigned to a water right by the water court, reflecting the first time water was put to beneficial use or when a conditional right was secured. The older the priority date, the more senior a water right is and the more likely it will be entitled to water during dry periods. The more recent the priority date, the more junior a water right, and the less likely it will receive water in times of scarcity.

priority system: The priority system was established when Colorado was still a territory to solve disputes over ownership and use of water. The system prioritizes use of water based upon who used water first. Those who put water to beneficial use first retain the senior right to continue using that water before newer users. When there is not enough water to satisfy all of the water users, the junior, or most recent user, must curtail or forego use until senior rights are fulfilled.

point source pollution: Point source pollution is a contaminant discharged to a water body at a known point such as from a drain or waste outlet.

potable water: Potable water is water that is fit for human consumption either through its natural purity or due to treatment removing or neutralizing impurities.

prior appropriation: Prior appropriation is the basis for Colorado’s water laws and its priority system of allocating water. The prior appropriator, or the first person to put water to a beneficial use, has the superior right to use water in instances when there is not enough water to meet the needs of all water users. Water users who put water to beneficial use after others must subordinate their use to those who previously established a water use.

public trust: The doctrine of public trust espouses that essential human resources, such as air and water, are owned by all people and these resources should be preserved and protected for the common public benefit. Public interest in these resources includes not only economic uses, but also values such as aesthetics, environmental protection, recreation, and others. Governmental entities, as the guardians of the public trust, must be held responsible for preserving the qualities of these resources in an optimal state for the public good.

The public trust doctrine is embraced by some as a preferred system for determining water use over the present priority system.

raw water: Raw water is water collected directly from its native source before treatment to bring it up to drinking water standards.

recreational in-channel diversion (RICD): Recreation is the most recent use of water that is eligible for a water right in Colorado. In a RICD, a quantified amount of water is permitted to remain in the stream for recreational uses and will be protected from uses that would diminish the decreed flow under the priority system. This use of water does not require the diversion of water outside of its normal course, but must show a measure of capture and control of the flow for the beneficial purpose. Kayak and other whitewater recreation courses are the most popular form of RICDs and are non-consumptive in their use of water.

reservoir: A reservoir is a body of stored water impounded by a dam. Reservoirs are constructed to provide drought protection, flood control, recreation and water for present and future use.

return flow: Water that returns to streams and rivers after it has been put to use is called a return flow. In most cases when water is used, not all of it is consumed and the remainder is returned to lakes, rivers or streams. When irrigating fields, for example, some water will typically flow off the land, referred to as tail water, and return to a waterway. Another portion will return after seeping into the ground, slowly percolating back to streams as groundwater. In municipalities, most of the water used in homes flows to wastewater treatment plants, where it will be treated and returned to a water source.

riffle: A riffle is a stretch of stream or river where the flow of water is disturbed by rocks, contributing to the oxygenation of water. Riffles are productive areas of a stream and are essential habitat for aquatic invertebrates, fish and other aquatic plant species.

riparian area: A riparian area is any portion of land that borders a natural water course and serves as a transitional zone between the waterway and upland areas. Riparian areas can be sensitive ecosystems hosting species of plants and animals that are dependent upon a wet environment.

riparian doctrine: A body of water law called riparian law evolved in the wet climate of England and later took hold in the eastern United States. Riparian law grants the right to divert water based upon ownership of land adjoining a waterway. Anyone residing on property which contains or borders a waterway has the right to divert as much water as they need as long as they do not injure other downstream users. Riparian law is not feasible in Colorado due to the semi-arid climate.

riprap: Riprap is a protective layer of rocks, cement or other objects that prevent the erosion or sloughing off of streambanks and can themselves collect sediments carried by the stream to reinforce the bank structure.

river basin: A river basin is the land area that naturally drains into a particular water course. The eight largest river basins in Colorado are the Colorado, South Platte, North Platte, Arkansas, Rio Grande, San Juan, White and Yampa River basins.

river reach: A river reach is any segment of river that has a similar physical and/ or biological characteristic to it.

Ruedi ReservoirRuedi Reservoir is located on the Fryingpan River, which begins in southwest Eagle County and drains into northern Pitkin County. The reservoir was constructed as compensatory storage to mitigate diversions of water to the Front Range through the Fryingpan-Arkansas Project (Fry-Ark). It was anticipated that the reservoir would meet the water needs of the expected industrial development of oil shale in western Colorado. However, the oil shale boom went bust, leaving a substantial amount of uncontracted water remaining in the reservoir.

The reservoir maintains stream flows in the Fryingpan River’s lucrative trout fishery, which is an economic boon to the Town of Basalt and the surrounding region. A portion of the reservoir’s water is contracted to meet the water needs for private entities and municipalities, and a more recent use for Ruedi water is streamflow augmentation to assist in the recovery of endangered fish species in the Colorado River.

salinity: Salinity refers to the amount of salts dissolved in water. High salinity levels may be toxic to fresh water fish, harm vegetation and impact irrigated agriculture.

The western U.S. has tremendous deposits of salt in many of its soils remaining from when the land was covered with seawater over the millennium. Streams running through salt deposits dissolve and carry salts downstream and irrigating salt-laden soils results in saline return flows. As the Colorado River flows through the southwest, it picks up large amounts of salts from natural deposits and return flows,degrading its quality.

salt: A salt is a natural compound formed from two elements, or by the reaction between an acid and a base, that join themselves with an ionic bond. Sodium chloride, or common table salt, is the most well known salt. Magnesium chloride, calcium carbonate (also known as lime or limestone), calcium carbonate (gypsum) and potassium chloride are other examples of salts. The bond that combines the paired elements as a salt is readily broken by water, making salts an easily dissolved contaminant to water supplies.

soil moisture: Soil moisture is the measure of water content in the ground that has direct bearing on the soil’s ability to sustain plant and animal life as well as how much precipitation the soil will absorb during the next precipitation event. Soil moisture is measured in the upper layers of soil where evaporation and plant transpiration of available moisture occurs.

spillway: A spillway is a component of a dam allowing for a controlled, rapid release of water. Spillways prevent the breaching or over-topping of dams during flood conditions by offering a second option for releasing water from a reservoir in addition to sending water through the normal outlet works.

spring runoff: Spring runoff is the increased stream and river flows occurring as snow melts with warmer spring and early summer temperatures. The vast majority, 80%, of Colorado’s surface water comes from melting snows and the highest streamflows usually occur during the months of May, June and July. Spring runoff flows are often referred to as “flood flows” since historically runoff flows flooded lowlands and over topped streambanks,especially prior to the construction of dams and reservoirs designed to capture these flood flows.

subordination: Subordination is the voluntary relinquishment of a water right’s priority to selected or all junior water rights. A large water project or transmountain diversion may subordinate its water rights to protect in-basin water rights or to allow for an increment of new water development that otherwise would be precluded by a strict adherence to the priority system.

substitution: Similar to an exchange, a substitution involves taking water from one point of diversion while releasing water from another source to satisfy downstream senior rights. In a substitution, the diversion and the release do not happen at the same time. Substitutions occur mostly between reservoirs. Instead of releases of water occurring at the same time as the diversion, releases will take place at specified times in the future or as calls come on the river and the demands necessitate releases. Substitutions must be approved by the State Engineer’s Office, which administers these arrangements.

surface water: Any water that is above ground in lakes, rivers, streams, reservoirs, etc.is referred to as surface water. Surface water ultimately comes from snowmelt and rainwater that has collected above ground. Surface water is a renewable, though inconsistent, source of supply.

surge irrigation: A form of flood irrigation where pulses of water are send down furrows to disperse irrigation water over a field. Using the impetus provided by the surges, a smaller volume of water is required to irrigate an entire field. In traditional flood irrigation, a large volume of water is needed to create the head (pressure) necessary to spread water over the entire irrigated area. Surge irrigation loses less water to deep percolation and reduces the amount of tailwater sent back to waterways.

total dissolved solids (TDS): Total dissolved solids is a measurement of minerals and other compounds dissolved in water. TDS concentration is usually expressed in milligrams per liter. The higher the level of dissolved minerals, the”harder” the water and the lower the water quality. High levels of TDS from salts can harm irrigated farmland, rendering it incapable of supporting crops or diminishing its ability to do so.

TMD: abbreviation for transmountain diversion

transit loss: Transit loss is the amount of water lost as it flows from one place to another. A number of factors may contribute to transit loss, including:evaporation, seepage into the streambed, and uptake by vegetation in the riparian area, among others. Transit losses are charged against the quantity of water released from reservoirs as they make their way downstream to intended points of diversion or storage.

transbasin/ transmountain diversion: A transbasin diversion is the removal of water from one river basin to another river basin. A transmountain diversion is the removal and transport of water across the Continental Divide. These diversions of water are 100% consumptive since no water from the diversion will return to the basin of origin’s waters as return flow. Colorado water law (Coffin v. Left Hand Ditch)provides for transmountain diversions by allowing the diversion of water from where it naturally flows to where it is needed within the state, regardless of distance.

inappropriate: Available water that is not yet claimed by an existing water right.

Upper Basin Compact: In1948, the states of the Upper Basin, which includes Colorado, Wyoming,Utah and New Mexico, agreed to the Upper Colorado River Basin Compact.This interstate agreement first allocates 50,000 acre-feet of the Upper Basin’s share to the portion of Arizona that resides in the Upper Basin then allocates 51.75% of the remainder to Colorado, 11.25% to New Mexico, 23% to Utah and 14% to Wyoming.

“Use it or lose it:” This often misapplied expression refers to the ability of the state to declare water rights that have fallen into disuse as abandoned. Before taking away all or portion of a water right, the state must show in water court that the owner no longer intends to use the water. A water rights owner can challenge the state’s assertion and retain their rights by telling the court they still intend to put the water to use in the future. It is erroneously assumed that the “use it or lose it” rule forces water rights holders to wastefully use their full entitlement of water or risk having all or part of their rights taken away.

virgin flow: Virgin flow is the streamflow quantity that would naturally exist in a waterway without diversions.

Water Court: Water Court is the mechanism by which water rights are adjudicated and therefore officially recognized by the State of Colorado. Water judges are district judges appointed by the Colorado Supreme Court and have jurisdiction in the determination of water rights, the use and administration of water, and all other water matters within the jurisdiction of the water divisions.

water trade: A water trade is swapping of ownership of water stored in different reservoirs or from different “pools” within a reservoir. This does not involve diversions or releases to meet downstream needs.

water right: A water right is a private property right in the State of Colorado that establishes in what priority a water user may use water for a beneficial purpose. The priority in which someone can divert water to put it to a beneficial use is granted by the water courts in the State of Colorado. A water right allows diversion of a certain amount of water, in a specified order among other water users, from a certain point along a body of water and for a specified purpose. The older, or more senior, the water right, the fewer other water users whose needs must be satisfied before the user is allowed to divert water. The younger, or more junior, the water right, the greater number of senior water rights that must be satisfied before a junior right can divert water.

As private property, water rights can be bought, sold,inherited, traded, exchanged, donated or otherwise disposed of as the owner sees fit. The value of the right is based primarily upon its seniority, which dictates how likely the right will produce water when supply is limited.

watershed: Watersheds are areas of land that catch precipitation and drain into a body of water. Watershed can refer to either small collection areas that feed into streams or small bodies of water or they can refer to large areas such as river basins.

well permit: The State Engineer’s Office (SEO) issues permits to drill water wells that specify the rate of withdrawal, intended use and location. The Groundwater Management Act of 1957 recognized that tributary groundwater extraction depletes surface water supplies and is subject to the prior appropriation doctrine.

West Slope: “West Slope” is an informal geographic term describing the portion of Colorado west of the Continental Divide. The West Slope is in the Colorado River Basin. The West Slope of Colorado receives roughly 80% of the entire state’s precipitation, yet its population is a fraction of that found in the metropolitan areas along Colorado’s Front Range, or East Slope.

wetland: Wetlands are unique and sensitive areas that are either flooded or saturated with water for all or parts of the year and which support vegetation and animals that are adapted to living in these wet conditions. Wetlands include areas such as bogs, marshes, swamps and similar environments. Wetlands are often transitional zones between aquatic and terrestrial areas, encompassing characteristics of both.

The U.S. Army Corps of Engineers, which governs wetlands, specifies that wetlands are defined by three criteria: hydrology that indicates saturation or inundation with water; hydrophytes or the presence of plant life specifically adapted to a water saturated environment; and hydric soils which are most often saturated with water.

The loss of wetlands through development must be mitigated, or replaced,pursuant laws designed to protect the functions and habitats of wetlands.

Xeriscape: A combination of seven common-sense gardening principles that save water while creating a lush and colorful landscape.