above mean sea level - The elevation (on or below the ground) or altitude (in the air) of an object, relative to the average sea level datum.
acre-foot – The amount of water it would take to cover an acre to a depth of one foot. An acre-foot is 43,560 cubic feet or 325,851.4 gallons.
alluvial aquifer – An aquifer composed of alluvial deposits such as gravel, sand, silt, and/or clay. Alluvial aquifers are generally shallower and fluctuate more than sedimentary and fractured rock aquifers.
alluvium – Sediment deposited by flowing water (such as clay, silt, sand, gravel, or similar small broken-down natural material) deposited in a streambed, flood plain, lake bed, or other bottomland feature.
aquifer – A permeable underground geologic formation such as sand, gravel, permeable sedimentary rock, or fractured bedrock, that is filled with water (saturated). Aquifers are capable of storing and discharging useful quantities of water to wells, springs, or surface water features like rivers. An aquifer is called “confined” when it is overlain by a layer of rock or clay that water cannot move through, and “unconfined” when it is not. Note that an aquifer is not an underground lake.
bank storage – Water that infiltrates the floodplain and recharge the near-stream alluvial aquifer, and can become a source of subsequent stream flow.
base flow – The portion of stream flow that is derived solely from groundwater discharge. Conversely, base flow is that part of the stream or river flow that does not come from surface runoff. In drier climates base flow is often the sole source of flow in streams like the San Pedro River where it can be relatively variable, even stopping altogether and leaving the stream channel dry during seasons when plants and trees are leafed-out and contributing to evapotranspiration.
capture – Groundwater intercepted by pumping. Specifically, the decrease in outflow from an aquifer to vegetation, streams, or other surface water features, or an increase in inflow to an aquifer, caused by pumping groundwater.
cone of depression – An underground depression in the groundwater levels of an unconfined aquifer in the shape of an upside-down cone. This results from groundwater pumping drawing water to a well (or a number of wells in the same vicinity) and lowering nearby water levels in the shape of the upside-down cone. (In a confined aquifer, the upside-down cone shape occurs in the pressure head surrounding the pumped well.)
cubic foot per second (cfs) – A common unit of measure used to characterize the rate of discharge in a stream or river.
discharge – A process where water flows out of, or is released from, an aquifer, or past an arbitrary point in a stream channel, such as a gaging station. Discharge can be natural (for example, from springs, streams, or through evapotranspiration) or human caused (for example, pumping or from dams). Human-caused groundwater discharge is also called “withdrawal.”
drainage basin – An area of land that drains all the streams and rainfall to a common outlet. Also called a “watershed”.
ephemeral stream flow – Flow that occurs in an otherwise dry channel for a brief period in direct response to precipitation.
evapotranspiration – The combined loss of water from a given area by evaporation (liquid water changing into water vapor and rising off land or water surfaces) and transpiration from plants (when plants release water, drawn from the ground, as vapor into the air from their leaves during the process of growing)
floodplain – The plain adjacent and generally parallel to a river or stream that provides temporary storage for flood water (water in excess of the stream channel capacity) during large rainfall runoff events.
gaining stream or gaining reach – A stream or reach of a stream that receives water from the groundwater system
gallons per capita per day (GPCD) – The number of gallons of water used, on average, per person per day for a defined area. GPCD may include all water withdrawn from ground or surface storage (residential, industrial, commercial, agricultural) or only residential withdrawals, and it may include withdrawals exclusively or it may be calculated as withdrawals minus return flow and incidental recharge. Thus, when comparing GPCDs, it is important to know how they were calculated.
groundwater – The water that is stored underground in an aquifer
groundwater model – An approximate representation of a groundwater flow system based on numerical groundwater flow equations that are in turn based on the physics of groundwater flow. Typically, these mathematical equations are solved using computer codes such as MODFLOW or MIKESHE. Different computer codes (or “programs”) have different strengths and weaknesses.
indicators of groundwater sustainability (or sustainability indicators) – Measurements of groundwater-related characteristics based on data collection efforts that provide evidence about the condition of the groundwater system and (or) how it has changed.
intermittent stream, spatial – During base flow conditions, a spatially intermittent stream contains both wet segments (base flow) and dry segments at different locations at a given time. Also called “interrupted perennial.” The San Pedro River is both a spatially and temporally intermittent stream.
intermittent stream, temporal – During base flow conditions, a temporally intermittent stream contains reaches that are flowing at one time of the year and not flowing or are dry at another time of the year. The San Pedro River is both a spatially and temporally intermittent stream.
irrigation – Water diverted from a stream or pumped from the ground to grow crops. Excess irrigation water may be returned to the stream or ground through return flow.
losing stream or losing reach of a stream – A stream or reach of a stream that loses water to the groundwater system.
near-stream alluvial aquifer – An aquifer made of stream alluvium, typically of relatively shallow depth and generally parallel to a stream, and distinct from a regional aquifer or a perched aquifer.
non-indicator and climatic reference data – Data included in the WHIP that are helpful to look at alongside the Sustainability Indicators, and currently include: precipitation, groundwater pumping, population estimates.
perched aquifer – An aquifer that occurs above the regional water table, and that occurs when there is an impermeable or relatively impermeable layer of rock or sediment (clay layer) above the regional water table but below the land surface. Distinct from a regional aquifer or near stream alluvial aquifer.
perennial stream flow – A stream reach where water flows continuously in a natural stream channel throughout the year.
precipitation – Water released from clouds in the form of rain or frozen particles such as sleet, snow, or hail. Precipitation is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth.
pumping – The process whereby water is removed from an aquifer by a pump.
rainfall runoff – Water that flows across the land and (or) into perennial, intermittent, or ephemeral stream channels as a result of rainfall events.
reach – A section of a stream or river along which similar hydrologic, biologic, and/or geomorphic conditions exist, such as discharge, depth, area, and slope as well as channel characteristics and vegetative communities. A reach refers to a small section of a river rather than its entire length.
recharge – The process where water sinks into the ground (infiltrates) either by natural processes (such as at mountain fronts or through stream beds) or through human management actions (such as detention or recharge basins, dry wells, or infiltration trenches), and eventually enters an aquifer.
regional aquifer – For the Upper San Pedro Basin, the aquifer lies across and underneath the basin and between the mountains, and as distinct from a local perched aquifer or a near-stream alluvial aquifer. The Upper San Pedro basin regional aquifer is well connected to the near-stream alluvial aquifer along much of the river, in the vicinity of the floodplain.
riparian area – The interface between land and a river or stream. Plant habitats and communities along the river margins, banks, and flood plain are called riparian vegetation. Riparian vegetation is characterized by plants that require certain surface water flows or groundwater levels for their roots to access to survive.
river basin – The area of land that surface water runoff may flow across on its way to a river or stream. A sub-basin is a smaller section within a larger river basin.
San Pedro Riparian National Conservation Area – The area managed by the U.S. Bureau of Land Management that was established by the U.S. Congress in 1988 to protect the riparian area and the aquatic, wildlife, archeological, paleontological, scientific, cultural, educational, and recreational resources of the public lands surrounding the San Pedro River.
silt and clay layer – A layer of fine-grained alluvium that frequently occurs near the center of inter-mountain basins in the west such as the Upper San Pedro Basin. Silt and clay layers tend to have low permeability and retard the infiltration of water to the deeper regional aquifer.
spring – A location where groundwater or submerged stream flow emerges and flows or seeps out at land surface.
stream gage – A structure installed beside a river that contains equipment that measures and records the water level (called gage height or stage) of the river as a means to estimate discharge. Through measurements of the channel shape, the river stage, and manual measurements of the discharge, a stage-discharge relationship is established that is then used to automatically estimate discharge.
subwatershed – A drainage area smaller than a watershed or basin that drains into the main stream directly or into other streams that drain into the main stream. The subwatersheds of the Upper San Pedro Basin include the Sonoran subwatershed, the Sierra Vista subwatershed, and the Benson subwatershed. These subwatersheds are arranged linearly along the Upper San Pedro Basin.
surface water – Water located above ground level, on the Earth’s surface, such as rivers, streams, wetlands, springs or seeps, and includes intermittent streams when they flow in response to rain or groundwater discharge.
sustainability indicators – See “indicators of groundwater sustainability.”
sustainable yield groundwater use – The use of groundwater in such a manner that there is enough groundwater for social, economic, and environmental systems to function adequately, both at a given time and into the distant future. As of 2021, there is adequate groundwater supply in the Upper San Pedro Basin for economic and societal needs. Sustainable groundwater use there is thus dependent on maintaining an adequate groundwater supply to sustain baseflow in the river for aquatic species to survive and to maintain the San Pedro River riparian system.
water levels – The elevation of the water table at a given location, typically accessed via a well.
water management – Human management of water including the human use, cost, rights, location, movement, detention, retention, recharge, and extraction of water, among other actions.
watershed – An area of land that drains all the streams and rainfall to a common outlet. Also called a “drainage basin.”
withdrawal – Human caused discharge of water from an aquifer, typically by pumping groundwater from a well (see “pumping”).
well – A deep hole made in the ground through which water can be removed or recharged.
wet-dry map – An annual map of the lengths of wetted channel in a spatially intermittent stream reach at a specific time of the year (most commonly the driest time of the year).