Chatfield Reservoir Reallocation Study

Acre-foot:  An acre-foot is a unit of volume commonly used in reference to large-scale water resources. One acre-foot of water is equivalent to one foot in depth covering an area of one acre, or approximately 326,000 gallons of water.  The average suburban household uses approximately one-half of an acre-foot per year. 

Alternative:  One of a number of options identified in an environmental impact statement for study and analysis of impacts and benefits.  Following detailed analysis, one alternative is selected for implementation.

Aquifer:  An aquifer is an underground layer of water-bearing sediment (rock, gravel, sand, silt or clay) from which groundwater can be extracted using a well. Much of the water in the deep aquifers has been trapped there for hundreds of thousands of years.  While this water is relatively clean and often needs little treatment before drinking use, the resource is finite and can be depleted over time.

"Call" on water rights:  A demand to the State Engineer by an entity owning water rights, in order for water in a stream system to reach their diversion works in order to yield water as expected from that water right.  If a senior water right holder "calls" for its water rights, upstream junior water right holders are required to allow water to flow downstream to the senior right holder.

Clean Water Act: The federal law that sets forth how the United States will restore and maintain the chemical, physical and biological integrity of the country's waters (oceans, lakes, streams and rivers, ground water and wetlands). The law provides protection to the country's surface waters from both point and non-point sources of pollution.

Colorado Water Conservation Board: The state agency vested with the authority to appropriate water of streams and lakes in amounts that are determined to be necessary to preserve the natural environment to a reasonable degree.

Confluence: A flowing together of two or more streams.

Conservation-Multipurpose Pool: An existing designation by the U.S. Army Corps of Engineers for the storage capacity in Chatfield Reservoir that is allowed to hold multipurpose water, located between 5,385 and 5,432 feet above mean sea level.

Colorado Water Conservation Board (CWCB):  A division of the State of Colorado's Department of Natural Resources.  Responsible for aiding in the protection and development of the waters of the state, including water project planning and finance, stream and lake protection, flood hazard identification and mitigation, weather modification, river restoration, water conservation and drought planning, water information, and water supply protection. The Board consists of 15 members that are appointed by the Governor of Colorado.  Eight voting members represent the state's major water basins: the South Platte, North Platte, Arkansas, Rio Grande, Gunnison/Uncompahgre, Colorado Mainstem, Yampa/White and the San Juan/Dolores/San Miguel. One voting member represents the City and County of Denver, and the tenth voting member is an Ex-Officio, the Executive Director of the Department of Natural Resources. 

Corps:  U.S. Army Corps of Engineers.  A division of the U.S. Department of Defense.  The federal agency that is responsible for investigating, developing and maintaining the nation's water and related environmental resources. The federal sponsor of the Chatfield Reservoir Storage Reallocation Study. 

Endangered Species Act: The federal law that governs how
animal and plant species whose populations are dangerously in decline or close
to extinction will be protected and recovered. The law protects not only
threatened and endangered species, but also the ecosystems upon which they
depend.

Feasibility Report/Environmental Impact Statement: A full disclosure document required by federal environmental law that details the process through which a federal project was developed, determines the viability of the option, considers of a range of reasonable alternatives, analyzes the potential impacts resulting from each alternative, and demonstrates compliance with other applicable federal environmental laws and executive orders.

Flood Control Pool: An existing designation by the U.S. Army Corps of Engineers for the storage capacity in Chatfield Reservoir to hold flood waters, located between 5,432 and 5,500 feet above mean sea level.

Gravel Pit Storage:  An excavated pit, generally with a clay stone floor and sand and gravel walls, that can be used to store water.  Some pits are lined with bentonite slurry wall or clay liner to prevent water from seeping through the gravel pores.

Ground Water: Water found below the earth's surface, such as in an aquifer.

Inactive/Sediment Pool: An existing designation by the U.S. Army Corps of Engineers for the storage capacity at the bottom of Chatfield Reservoir located between 5,377 and 5,385 feet above mean sea level.  This pool elevation would not be affected by a reallocation.

Joint Flood Control-Conservation Pool: A proposed designation for storage capacity in Chatfield Reservoir to hold multipurpose water and flood waters, as defined by the reallocation alternatives of the feasibility report/environmental impact statement.  Under alternative three, this pool would be confined to the elevations between 5,385 and 5,444 feet above mean sea level, creating 20,600 acre-feet of additional storage for multipurpose water than is currently allowed.  Under alternative four, this pool would be confined to the elevations between 5,385 and 5,437 feet above mean sea level, creating 7,700 acre-feet of additional storage for multipurpose water than is currently allowed.

Maximum Surcharge/Spillway Design Flood Pool: An existing designation by the U.S. Army Corps of Engineers for the storage capacity at the top of Chatfield Reservoir located between 5,500 and 5,521.6 feet above mean sea level.  This pool elevation would not be affected by a reallocation.

Mean Sea Level: The average height of the sea relative to a single point on land (a datum) after high frequency motions are averaged out; the basis for mapping the elevation of terrestrial features

Mitigation: Reasonable measures taken to avoid, minimize, rectify, reduce or compensate for impacts to the physical environment resulting from federal actions.  Federal law requires agencies to identify all relevant and reasonable mitigation measures, including avoiding the impact altogether by not taking a certain action or parts of an action; minimizing impacts by limiting the degree or magnitude of the action and its implementation; rectifying the impact by repairing, rehabilitating, or restoring the affected environment; reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action; and/or compensating for the impact by replacing or providing substitute resources or environments.

Multipurpose Water:  Water supply used for a variety of uses, such as municipal, industrial, agricultural and/or recreational uses, or for maintaining fisheries and wildlife habitat.

National Environmental Policy Act (NEPA): Federal legislation that requires federal agencies to evaluate the environmental impacts of all proposed federally-funded or permitted actions and to consider reasonable alternatives to those actions.

National Historic Preservation Act (NHPA): Federal legislation that requires federal agencies to evaluate the impact of all proposed federally-funded or permitted projects on historical and archaeological sites listed on, or eligible for listing on, the National Register of Historic Places, and to consider reasonable alternatives to those actions.

Non-Renewable Water: Water resources from a deep underground aquifer which have been trapped in for hundreds of thousands of years.  This resource is not replenished by rain fall or melt-off, so the finite supply can be depleted and becomes more costly to extract water over time as the aquifer level drops.

On-Channel: Refers to the location of Chatfield Reservoir directly on the South Platte River, where the reservoir captures flows from the river.

Pool Elevation: The maximum elevation in feet above mean sea level that a stored volume of water can rise in a flood control facility, as designated by the U.S. Corps of Engineers.

Reallocation: Refers to a change in the designation of storage space in Chatfield Reservoir, which would effectively "merge" the existing multipurpose pool with a portion of the existing flood control pool, creating a newly-designated joint flood-conservation pool.   This newly allocated storage space would serve a dual purpose, primarily for storing flood waters and secondarily for storing multipurpose water.

Record of Decision (ROD): A document prepared by the lead federal agency that outlines the decision and documents the required implementation and mitigation measures needed to complete a federally-funded or permitted project.

Renewable Water: Surface water resources that are replenished by seasonal rains and melting snowfall, such as rivers, streams and lakes. 

Reservoir: An impoundment of collected water controlled by a dam.

Return Flows: The unused portion of water that returns to a stream or river after a beneficial use.

Reuse: To use again, to intercept for subsequent beneficial use--either directly or by exchange--water that would otherwise return to the stream system.

Semi-arid: characterized by very little annual rainfall, usually from 10 to 20 in. (25 to 50 cm)

Spillway: A channel that carries surplus water over or around a dam or other obstruction from a reservoir, lake, or the like.

Storage Capacity: A volume of space in Chatfield Reservoir that is available to hold water.

Surface Water:  Surface water is water that collects in a river, stream, lake, wetland or ocean.  Surface water is naturally replenished by precipitation and naturally lost to evaporation.

Watershed: An area from which water drains into a river, river system, or other body of water.

Water Rights: The right of a user to use water from a water source, such as a stream, tributary or aquifer. 

In Colorado, the seniority of water rights is determined by appropriation dates. The first person/entity to use a quantity of water from a water source for a beneficial use has a right to continue to use up to their full allocation annually for that purpose (provided the water source can supply it). Then the user with the next earliest appropriation date may use their full allocation and so on. In times of drought, users with junior appropriation dates might not receive their full allocation or even any water at all. 

Water Yield: Refers to the amount of water that can be dependably supplied from the raw water sources of a given water supply system.

Wetlands: Areas with standing water of a high water table either permanently or for some significant period each year. Generally includes swamps, marshes, bogs and areas with water-loving vegetation that grows in or around water.