Environmental Flows and Water A University of Arizona Water Resources Research Center Project Demands in Arizona ater is an increasingly scarce resource and is essential for Arizona’s future. Figure 1. Elements of Environmental Flow WWith Arizona’s population growth and Occurring in Seasonal Hydrographs 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 Data Source: to sustain our communities. USGS stream gage data Figure 2: Human Demand and Current Flow in Arizona Environmental water demands (or environmental flow) (circle size indicates relative amount of water) 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- Maximum ogy of a system and should include consideration for Flows how much water is required to achieve an agreed Industrial 40.8 maf Industrial SW Municipal upon level of river health, as determined by the GW 1% GW 8% water-using community. Arizona’s native ani- 4% mals and plants depend upon dynamic flows commonly described according to the natural Municipal SW flow regime. The natural flow regime con- 14% Agricultu ral Minimum tains five elements of water flow: magnitude SW Flows Agricultural (how much), duration (how long), frequency 45% 1.2 maf GW (how often), timing (how predictable) and 28% Median Flows rate of change (how variable). These species 12.2 maf are part of larger riparian (along the stream) Total Human or aquatic (within the stream) ecosystems sus- Demand in 2006 = 6.8 maf* SW= Surface Water tained by water in streams and aquifers that GW= Groundwater maf = Million acre-feet 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- *In 2006 an additional 0.016 maf of effluent was also used to meet demand tion). The natural flow regime is graphi- Data Sources: ADWR 2010 (streamflow as measured by gages), WRDC 2011 (human demand) 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. 1 Figure 3: Water Demand and Use in Arizona (Arrows indicate relative size Streamow Riparian of demand and recharge) Evapotranspiration Industrial Use Agricultural Use Municipal Use = Demand = Recharge Groundwater Streamow Contribution Recharge to Flow Groundwater Data Source: WRDC 2011 Figure 4: Location of Streams Studied for Environmental Interactions between Arizona’s streamflow, Flow Needs or Flow Responses 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. Data Source: WRRC 2011 2 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. Table 1: Rivers Studied for Environmental Flow Needs and Flow Responses S = Reach (% of stream surveyed), S = Entire stream surveyed, NS = Not surveyed Timing of Rate of Magnitude Duration Frequency River Name Flow Change (% Studied) S S Agua Fria River NS NS NS (22%) (22%) Arivaca Creek S S NS NS S Aravaipa Creek S S NS NS S Babocomari River S NS NS S NS Bill Williams River S S S S S Bonita Creek S NS NS NS NS S S S Cienega Creek S S (88%) (88%) (88%) Cherry Creek S NS NS NS NS S Colorado River S S S S (67%) Eagle Creek S NS NS NS NS E. Verde River S NS NS S NS S S S Gila River NS NS (45%) (10%) (23%) Hassayampa River S S S S S Little Colorado River S S S S S Oak Creek S NS S S NS Pinto Creek S S S NS NS S S Rincon Creek S S S (61%) (61%) Sabino Creek S S NS NS S Salt River S NS NS NS NS San Francisco River S NS NS NS NS San Pedro River S S S S S Santa Cruz River S S NS NS S Sonoita Creek S NS S NS S Sycamore Creek S S S NS NS Tanque Verde Wash S NS S NS S Verde River S S S S S Data Source: WRRC 2011 3 Figure 5: Sample Process for Identifying and Addressing Vulnerability Information on the relation- Sample Process for Identifying(for demonstration and Addressing purposes Vulnerability only, not an actual vulnerability assessment) 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 Areas of potential can be identified by compar- vulnerability Known Resources Protections Stressors Potential Vulnerability ing various environmental (e.g., springs, perennial streams,) (e.g., conservation land, (e.g., increasing population, (areas where there are flow demands, such as spe- Wild and Scenic River climate change impacts) resources and stressors but cies-specific water demands, Designation) no or few protections) 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 Management Options to Species Flow Requirements Current Flow Levels and Depth to Water Mitigate Vulnerability detailed information orga- (to understand how much water species in (to understand how much water species (e.g., seasonal pumping restric- nized by region (see below) vulnerable areas need) currently have) tions in sensitive areas, water are available on the WRRC conservation requirements website and in hardcopy, by request. Additional resources to help inform planning efforts throughout the state are available by contacting the WRRC. How Can This Information be Applied? Regional Bulletins Available 1. Determine how environmental flows interact with other demand sectors 2. Identify factors putting environmental flows at risk 3. Identify studies needed to address Colorado River key information gaps about Colorado River at Imperial National Wildlife North/Northeastern Refuge, Arizona.