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Environmental water demands (or environmental flow) refers to how much water is needed in a watercourse to sustain a healthy ecosystem. Defining environmental water demand goes beyond the ecology and hydrol-

ogy of a system and should include consideration for how much water is required to achieve an agreed

upon level of river health, as determined by the water-using community. Arizona’s native ani-mals and plants depend upon dynamic flows commonly described according to the natural flow regime. The natural flow regime con-tains five elements of water flow: magnitude (how much), duration (how long), frequency (how often), timing (how predictable) and rate of change (how variable). These species are part of larger riparian (along the stream)

or aquatic (within the stream) ecosystems sus-tained by water in streams and aquifers that

often vary widely depending on the year and season. Important biological events like reproduc-

tion are cued within these ecosystems by seasonal flood events (e.g. timing) and constant flows (e.g. dura-

tion). The natural flow regime is graphi-cally displayed in Figure 1 through a sea-sonal hydrograph of the San Pedro River.

Although significant amounts of water flow through and are used by the environment, it is not generally rep-resented as a piece of the total demand “pie”. Statewide water demand is shown in Figure 2 by comparing the relative scale of human water demands by sector to the minimum, median, and maximum stream flows avail-able in the environment. The total size of the pie chart of human demands (far left) reflects the 6.8 million acre-feet withdrawn or diverted by municipal, industrial, and agricultural water using sectors in 2006. Median annual stream flow on major perennial streams (right side of figure) is about double the amount used by all human demand sectors, while maximum flood flows are six times greater.

Water is an increasingly scarce resource and is essential for Arizona’s future. With Arizona’s population growth and

continued drought, citizens and water managers have been taking a closer look at water supplies in the state. Municipal, industrial, and agricul-tural water users are well-represented demand sectors, but water supplies and management to benefit the environment are not often consid-ered. This bulletin explains environmental water demands in Arizona and introduces information essential for considering environmental water demands in water management discussions. Considering water for the environment is impor-tant because humans have an interconnected and interdependent relationship with the envi-ronment. Nature provides us recreation oppor-tunities, economic benefits, and water supplies to sustain our communities.

Figure 1. Elements of Environmental Flow Occurring in Seasonal Hydrographs

Environmental Flows and Water Demands in ArizonaA University of Arizona Water

Resources Research Center Project

MinimumFlows

1.2 maf

MedianFlows

12.2 maf

MaximumFlows

40.8 mafMunicipalGW8%

MunicipalSW14%

AgriculturalGW28%

AgriculturalSW45%

IndustrialGW4%

IndustrialSW1%

SW= Surface WaterGW= Groundwatermaf = Million acre-feet

Total HumanDemand in 2006 = 6.8 maf*

Figure 2: Human Demand and Current Flow in Arizona (circle size indicates relative amount of water)

*In 2006 an additional 0.016 maf of effluent was also used to meet demand

Data Sources: ADWR 2010 (streamflow as measured by gages), WRDC 2011 (human demand)

Data Source: USGS stream gage data

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Interactions between Arizona’s streamflow, groundwater, and human demands are shown in Figure 3. Note that all human sectors return some water to the environment after use. Also, water traveling through a river to farming or domestic uses downstream can support aquatic and riparian ecosystems along the way. These connections between environmental and human demands create opportunities for mutually beneficial water management.

To consider the environment alongside other water sectors, we must study the water demands of ecosystems. Figure 4 shows a geographic representation of where in Ari-zona streams have been studied, with Table 1 providing companion information for what element(s) were explored; both are color coded based on the number of elements studied. Although some Arizona streams have been studied for all five flow elements, most do not address the flow demands and responses for the whole ecosystem. The geography of where we know something about science of environmental flow needs and responses in Arizona is in part driven by the legal, social, economic, and political land-scape of the state, with some rivers receiving more studies then others because of available funding, community interest, or laws that apply to the river.

Industrial Use

Stream�

ow

= Demand

= Recharge

GroundwaterContribution

to Flow

Stream�owRecharge

Riparian Evapotranspiration

Agricultural Use

Municipal Use

GroundwaterData Source: WRDC 2011

Figure 4: Location of Streams Studied for Environmental Flow Needs or Flow Responses

Figure 3: Water Demand and Use in Arizona

(Arrows indicate relative size of demand and recharge)

Data Source: WRRC 2011

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Magnitude Duration Frequency Timing of

Flow Rate of Change

Agua Fria RiverS

(22%)NS NS

S (22%)

NS

Arivaca Creek S S NS NS SAravaipa Creek S S NS NS S

Babocomari River S NS NS S NSBill Williams River S S S S S

Bonita Creek S NS NS NS NS

Cienega Creek SS

(88%)S

S (88%)

S (88%)

Cherry Creek S NS NS NS NS

Colorado River S SS

(67%)S S

Eagle Creek S NS NS NS NSE. Verde River S NS NS S NS

Gila RiverS

(45%)NS

S (10%)

S (23%)

NS

Hassayampa River S S S S SLittle Colorado River S S S S S

Oak Creek S NS S S NSPinto Creek S S S NS NS

Rincon Creek SS

(61%)S

S (61%)

S

Sabino Creek S S NS NS SSalt River S NS NS NS NS

San Francisco River S NS NS NS NSSan Pedro River S S S S SSanta Cruz River S S NS NS S

Sonoita Creek S NS S NS SSycamore Creek S S S NS NS

Tanque Verde Wash S NS S NS SVerde River S S S S S

River Name(% Studied)

Table 1: Rivers Studied for Environmental Flow Needs and Flow ResponsesS = Reach (% of stream surveyed), S = Entire stream surveyed, NS = Not surveyed

To determine the extent of information available on environmental flow needs and responses in Arizona the WRRC identified and reviewed ninety-two studies for the Arizona Environmental Water Needs Assessment. This review revealed that only 20% of all Arizona stream reaches have been studied: 35% of all perennial (those that flow year-round) and 8% of all intermittent (those that flow part of the year). Of the studies reviewed, 53 pro-vided quantified information on flow needs, flow responses, or both. Most looked at multiple species; studies on the flow needs and responses of riparian trees such as cottonwood, willow and tamarisk were most common. The remaining 39 studies reviewed provided either descriptions of flow needs and responses, e.g., increased flooding frequency caused greater abundance, or did not describe flow needs or responses at all, providing instead information on economic values or reports from monitoring efforts.

Statewide, ecosystem-level flow requirements remain poorly understood. Only five studies in Arizona have defined flow volumes needed for a riparian or aquatic ecosystem. Truly dynamic recommendations for minimum flows for each season, ranges of flow needs, frequency, rate of change, and size of flood flows are available for one river in the state, the Bill Williams River. Small scale studies that prescribe flows for a single reach exist in some areas, but cannot be applied across basins or regions. Two areas of agreement have emerged from studies done across the state: (1) riparian areas need both access to sufficient groundwater and carefully-timed flood flows to maintain water levels for established plants and for new plant growth; and (2) change to any element of flow can impact Arizona’s aquatic and riparian ecosystems if flows are altered beyond the range of tolerance of native species.

Data Source: WRRC 2011

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Information on the relation-ships between components of flow and biological factors may be used for considering potential impacts of future water decisions. Areas need-ing protection or restoration can be identified by compar-ing various environmental flow demands, such as spe-cies-specific water demands, with current conditions. A sample process for how this information may be used to assess vulnerability is shown in Figure 5.

These pages present a brief overview of the information available for Arizona; more detailed information orga-nized by region (see below) are available on the WRRC website and in hardcopy, by request. Additional resources to help inform planning efforts throughout the state are available by contacting the WRRC.

ReferencesArizona Department of Water Resources (ADWR). (2010) “Arizona Water Atlas: Volume 1 Executive Summary.” Phoenix, Arizona: ADWR, Office of Water Management. Nadeau, J; S.B. Megdal. (2011) “Arizona Environmental Water Needs Assessment Report and Methodology Guidebook.” Water Resources Research Center.Water Resources Development Commission (WRDC). (2011) “Environmental Working Group - Arizona’s Inventory of Water-Dependent Natural Resources.”

Bulletin prepared by: Brittany Choate Xiu, Kelly Mott Lacroix, & Leah Edwards

Figure 5: Sample Process for Identifying and Addressing Vulnerability(for demonstration purposes only, not an actual vulnerability assessment)

Contact InfoFor assistance applying information about environmental water uses and needs in water planning, questions about methods used to create this bulletin or requests for our environmental water demand data please contact:

Kelly Mott LacroixEmail: klacroix@email.arizona.edu Phone: (520) 621-3826

The WRRC offers public presentations about this information as well as direct support for water planning processes as part of our Connecting the Environment to Arizona Water Planning (EnWaP) project.

wrrc.arizona.edu

+

Protections(e.g., conservation land,

Wild and Scenic River Designation)

+

Stressors(e.g., increasing population,

climate change impacts)

=

Potential Vulnerability(areas where there are

resources and stressors but no or few protections)

Known Resources(e.g., springs, perennial streams,)

Sample Process for Identifying and Addressing Vulnerability

Areas of potentialvulnerability

Species Flow Requirements(to understand how much water species in

vulnerable areas need)

Current Flow Levels and Depth to Water(to understand how much water species

currently have)

Management Options to Mitigate Vulnerability

(e.g., seasonal pumping restric-tions in sensitive areas, water conservation requirements

+

North/NortheasternLittle Colorado River near Greer, AZ. Photo

Credit: Arizona Department of Water Resources

How Can This Information be Applied?

1. Determine how environmental flows interact with other demand sectors

2. Identify factors putting environmental flows at risk3. Identify studies needed to address

key information gaps about environmental flows4. Determine local priorities for ecosystems5. Develop scenario analyses for water planning that incorporates the environment

Regional Bulletins Available

SoutheasternGila River near Three Way, AZ. Photo Credit:

Arizona Department of Water Resources

Colorado RiverColorado River at Imperial National Wildlife

Refuge, Arizona. Photo Credit: Arizona Department of Water Resources

CentralVerde River, AZ. Photo Credit: Arizona

State Parks