Upper Snake River Basin Water Stewardship Assessment
Upper Snake River Basin Water Stewardship Assessment
Upper Snake River Basin Water Stewardship Assessment 2 1. EXECUTIVE SUMMARY 1.1 PURPOSE Concerns about the adequacy of water supplies in the Upper Snake River Basin date nearly from the start of the first irrigation withdrawals in the late 1800s. Considerable documentation describes the development of irrigated agriculture and the resultant complexities of surface water and ground water management in the area, particularly at the basin scale. This report presents a view of these challenges through a particular lens—companies with significant but indirect agricultural dependency.
The purpose of this report is to assess the major water resource challenges and opportunities within the Upper Snake River Basin. This water resource assessment is then evaluated from the risk perspective of companies that depend on agricultural products. There is considerable interest in both fostering sound water stewardship and mitigating possible supply chain risks for companies that source crops in the region. We propose recommendations towards achieving both these goals. Importantly, we also identify key stakeholders that must be engaged throughout the implementation of water stewardship activities.
1.2 BASIN REVIEW The Upper Snake River Basin is characterized by one of the largest and most productive aquifers in the country. Even in the absence of development, the Eastern Snake Plain Aquifer (ESPA) is highly connected to surface water, both gaining from and losing water to streams and creeks throughout the aquifer. Within this complex hydrologic backdrop developed one of the most productive agricultural regions in the country. Beginning in the late 1800s, extensive irrigation systems were built to compensate for inadequate growing-season precipitation. With the construction of major reservoirs, agriculture expanded quickly in the first half of the 20th century.
Agricultural development has created a highly modified water balance within the basin, diverting large volumes of surface water for irrigation and incidentally increasing aquifer storage in the process. By the 1950s, new pump and irrigation technology allowed farmers to more easily irrigate cropland with ESPA groundwater. In the 1970s and 1980s, improvements in irrigation efficiency reduced incidental recharge from surface irrigation. Periods of severe drought also occurred in the past several decades. These events reversed the trajectory of aquifer storage and began a trend of aquifer depletion that continues today.
Declines in ESPA storage levels have in turn resulted in decreased discharges from groundwater to surface water.
In light of declining aquifer storage, the Conjunctive Aquifer Management Plan (CAMP) was developed by the State of Idaho to comprehensively manage the basin to mitigate future water risk. The plan proposes implementation of specific mitigation activities over the next 30 years, including aquifer recharge, groundwater to surface water conversion, and demand reduction.
Upper Snake River Basin Water Stewardship Assessment 3 1.3 SUSTAINABILITY ASSESSMENT As a result of declining ESPA discharges to springs and streams, surface water users have begun to face significant water shortages.
In order to protect their water rights, these surface water users have sought regulatory relief through the curtailment of junior water rights held by ESPA groundwater users. The outcome is an environment of increasing water supply insecurity, particularly for groundwater users. Growers in the Upper Snake River Basin face a number of additional water-related risks in addition to water scarcity.
- Water quality concerns continue to grow in the basin, particularly regarding nutrient and sediment pollution in the Twin Falls area.
- Fish and wildlife are increasingly vulnerable to decreased stream flows and reduced water quality.
- Future climate change is expected to increase water scarcity through decreased snowfall and increased temperatures. The complexities of conjunctive (both surface and ground water) management necessarily tie the fates of all water users in the basin. While groundwater-dependent users are already being impacted, all water users in the basin will face increasing uncertainty—whether due to decreased water availability or the impacts of potential future litigation and regulation. 1.4 WATER STEWARDSHIP RECOMMENDATIONS For companies engaged in water stewardship in the agricultural supply chain, the most immediate question is how to mitigate anticipated water resource impacts in order to reduce risks to growers. We identify four categories of possible water stewardship activities: stakeholder engagement, water quantity mitigation, water quality improvement, and fish and wildlife protection. These categories correspond to the major sources of risk. Within these categories, there are on-field and off-field opportunities to implement water stewardship activities.
Implementation of the CAMP, already in its fifth year, has established a clear set of water resource management priorities and determined the primary measures for implementation. As feasible, corporate water stewardship activities should be aligned with this effort, leveraging existing stakeholder buy-in to achieve outcomes that both reduce supply chain risks and support CAMP objectives. A key conclusion of this assessment is that improvements in irrigation efficiency must be considered carefully with regard to potential impacts—both beneficial and adverse. For groundwater users, there are likely limited opportunities for significant efficiency gains.
For surface water users, changes in irrigation practices could further exacerbate water shortages. Such changes need to be considered with respect to overall basin sustainability, local hydrologic conditions, and the significance of co-benefits such as pollution mitigation.
Upper Snake River Basin Water Stewardship Assessment 4 Outlined below are general water stewardship actions that can be developed by companies to support supply chain risk mitigation in the Upper Snake River Basin. These recommendations are intended to guide the development of more detailed stewardship planning efforts. (1) Clarify water stewardship objectives relative to the identified categories of water risk and the scale of desired sustainability outcomes. (2) Engage stakeholders to develop a coordinated action plan for corporate water stewardship activities in the basin.
(3) Coordinate with the CAMP implementation process and multi-stakeholder committee to ensure alignment of objectives.
(4) Assess water supply sources and on-field practices for supply chain connected growers to determine risk mitigation potential. (5) Prioritize on-field water use activities that maximize co-benefits such as reduced pollutant loading or increased stream flows.
Upper Snake River Basin Water Stewardship Assessment 5 CONTENTS 1. EXECUTIVE SUMMARY ___ 2
1.1 Purpose ___ 2
1.2 Basin review ___ 2
1.3 Sustainability assessment ___ 3
1.4 Water stewardship recommendations ___ 3
2. INTRODUCTION ___ 6
2.1 Overview ___ 6
2.2 Approach ___ 6
3. PART I: BASIN REVIEW ___ 7
3.1 Watershed overview ___ 7
3.2 Water resources ___ 10
3.3 Water use ___ 16
3.4 Water administration and management ___ 20
4. PART II: SUSTAINABILITY ASSESSMENT AND STEWARDSHIP PLANNING ___ 26
4.1 Sustainability assessment ___ 26
4.2 Stewardship planning ___ 32
4.3 Conclusions ___ 41
REFERENCES ___ 44
Prepared by The Nature Conservancy with support from the General Mills Foundation. Special thanks to Rob Van Kirk from the Henry’s Fork Foundation who contributed significant review and discussion to support this report.
Upper Snake River Basin Water Stewardship Assessment 6 2. INTRODUCTION 2.1 OVERVIEW This report presents a sustainability assessment and stewardship plan for the Upper Snake River Basin in Idaho. The Upper Snake River Basin was selected due to its significance as a major growing region in a basin with apparent water availability concerns. Part I provides an overview of water resources in the Upper Snake River Basin. This section of the report also describes the governance and management landscape. Part II presents an assessment of water resource sustainability relative to current and future risks.
The report then reviews the major types of stewardship activities that could mitigate this water risk. The report concludes with recommendations for companies that recognize the value in corporate stewardship for mitigating water risk. 2.2 APPROACH The Upper Snake River Basin is undeniably a complex water system, whether in terms of hydrologic processes or water allocation. Describing the full complexity of the basin and its management is beyond the scope of this report. In defining the purpose of this document, we have chosen an approach that focuses on identifying the key challenges most relevant to corporate water stewardship and supply chain considerations in the Upper Snake River Basin.
The original proposal for this assessment focused on the eastern plain area from Rexburg to American Falls. However, hydrologic and administrative boundaries generally include a larger geographic area. Accordingly, the available information and data sources reported here generally refer to Upper Snake River Basin at large or the Eastern Snake River Plain Aquifer. For this assessment, we have utilized reports and research from key institutions in the basin including Idaho Department of Water Resources (IDWR), U.S. Geological Survey (USGS), and the University of Idaho. We have also consulted expert opinion from key stakeholders involved in the science and management of the basin.
The results and recommendations presented in this report are intended to describe the range of available opportunities for corporate water stewardship. Additional planning processes will be necessary to further define specific stewardship actions.
Upper Snake River Basin Water Stewardship Assessment 7 3. PART I: BASIN REVIEW 3.1 WATERSHED OVERVIEW 3.1.1 Basin at a glance The Idaho segment of the Upper Snake River Basin1 extends from basin headwaters at the Wyoming border to King Hill, where the river emerges from a deep canyon incised into lava rock. Major hydrologic components include the Snake River, the Eastern Snake River Plain Aquifer (ESPA), Malad River drainage, and Salmon Falls Creek (Figure 1).
The basin covers an area of approximately 35,800 square miles in eastern Idaho—more than 40% of the state—with the ESPA itself comprising 10,800 square miles of that total (Van Kirk 2008, Konikow 2013). More than 500,000 people live in the Upper Snake River Basin. The most recent State inventory of the basin indicates that the population is increasing at a modest annual rate of 1-2 percent (IWRB 1998).
The climate is arid to semiarid with sagebrush and bunch grasses dominating the natural landscape. Within the eastern plain, annual precipitation is low (8 to 10 in.). Precipitation during the growing season is negligible with the system largely dependent on winter and early spring precipitation in tributary watersheds. Mountain ranges north and east of the ESPA receive 40 to 60 inches of precipitation annually, primarily as snowfall (IWRB 1998, USGS 1992). A smaller but still significant amount of precipitation falls on mountain ranges to the south. Regional and global climate variability also drive precipitation (Van Kirk 2008).
Several periods of widespread drought have occurred in the past 100 years including periods of severe drought in 1987–1992 and 2000– 2007 (USACE 2009, Wise 2010).
One of the most prominent hydrologic features of the Upper Snake system is the strong connection between surface and ground water. Tributaries to the north and east of the ESPA (approximately from Ashton to Sun Valley) terminate on the eastern Snake Plain and infiltrate into the large volcanic rock aquifer. The Snake River itself alternately contributes to and receives water from the aquifer, depending on water table elevation and underlying geology. 1 The Idaho segment of the Upper Snake River Basin is defined hydrologically as the region draining to the USGS gauge at King Hill. Using this area allows for the full accounting of inflows and outflows within the basin, including groundwater.
A more restricted area upstream of Milner dam is also referred to as the “upper Snake River”. This area corresponds to the administrative boundaries for all points of diversion and storage upstream of Milner dam. In this report, the “Upper Snake River Basin” will refer to the larger area extending from headwaters to King Hill.
Upper Snake River Basin Water Stewardship Assessment 8 Figure 1. Map of the Upper Snake River Basin within Idaho. Also shown are Snake River tributaries and the ESPA boundary (solid black line). From Idaho Department of Water Resources (IDWR). 3.1.2 Agriculture and industry Agriculture and related agricultural services remain the primary economic drivers in the basin with an estimated $10 billion in goods and services generated annually. Agriculture is both the largest sector of the area economy and the biggest consumptive user of water. In the upper Snake basin, there are nearly 2.9 million acres of harvested cropland which includes more than 2.4 million acres of irrigated land.2 The four largest crops by annual harvested area are hay, wheat, barley and potatoes (Table 1).
2 Derived using county-level data from the 2007 USDA Census of Agriculture.
Upper Snake River Basin Water Stewardship Assessment 9 Crop Acres harvested Percent of total Hay 917,567 32% Wheat 664,789 23% Barley 459,753 16% Potatoes 289,680 10% Corn 248,032 9% Sugar beets 150,065 5% Beans 42,782 1% Other 121,723 4% Table 1. Annual crop totals by acre harvested for the primary agricultural crops in Upper Snake River Basin counties (2007 USDA Census of Agriculture). Figure 2. Estimated growing locations for the region’s major crop types in the Upper Snake River Basin.
Cropland estimates are for the year 2012 and provided by the USDA Cropland Data Layer Program.
Upper Snake River Basin Water Stewardship Assessment 10 Throughout the basin, hay and grains dominate the agricultural landscape (Figure 2). Adjacent to and downstream of American Falls Reservoir, sugar beets, beans and corn are also important commodities. In addition to agriculture, dairy production and aquaculture are also important to the regional food production industry. According to current estimates, the aquaculture industry in Idaho ranks as one of the largest in the country producing 75% of domestically farmed trout. In the Upper Snake River Basin, aquaculture facilities are concentrated in the Thousands Spring reach area near Twin Falls.
These businesses are highly dependent on sufficient and high quality spring discharge from the ESPA (Slaughter 2012).
Major hydropower facilities also exist in the Upper Snake River Basin accounting for roughly a third of the state’s hydroelectric production (total capacity is approximately 700 megawatts) (IWRB 1998). The largest hydropower facilities by total capacity are shown in Table 2. Hydropower production is dependent primarily on reservoir operations and spring and early summer runoff. Additional hydropower facilities further downstream on the Snake River are also dependent on basin flows. Facility name Stream Capacity (MW) Palisades Snake River 176.6 American Falls Snake River 92.3 Bliss Snake River 75.0 Lower Salmon Snake River 60.0 Milner Snake River 59.5 Twin Falls Snake River 43.7 Upper Salmon Snake River 34.5 Gem State Snake River 23.4 Malad Malad River 21.7 Table 2.
Major hydroelectric facilities by total capacity in the Upper Snake River Basin (after IWRB 1998). 3.2 WATER RESOURCES 3.2.1 Water availability Surface water Within the basin, surface water processes are highly modified from base or natural flow conditions. Natural streamflow conditions that were once driven primarily by snowmelt have since become carefully managed through diversions and reservoir operation in order to satisfy water user rights (Van Kirk 2008).
In terms of total discharge, the headwaters of the Snake River account for the majority of streamflow within the Upper Snake River Basin (Figure 3). The Henrys Fork is also an important tributary to the system accounting for more than a quarter of average annual discharge. Additional
Upper Snake River Basin Water Stewardship Assessment 11 tributaries along the perimeter of the ESPA account for the remainder of streamflow within the system. Figure 3. Schematic representation of the relative contribution of average annual discharge within the Upper Snake River Basin, where thicker blue lines indicate greater reach discharge (from Cosgrove 2006).
Natural surface flows are driven primarily by mountain snow accumulations with the majority of rainfall being lost as evapotranspiration (Van Kirk 2008). Under natural streamflow conditions, discharges are highest in the late spring during snowmelt and lowest during fall and winter. The result of flow regulation for irrigation and power generation purposes has been the augmentation (increase) of base flows while peak flows have been diminished.
The largest storage reservoirs within the basin are located along the main stem of the Snake River (Table 3). More than two-thirds of all reservoirs in the basin are operated by U.S. Bureau of Reclamation, primarily serving purposes of irrigation and flood control. Additional objectives include power generation, municipal and industrial withdrawals, recreation, and instream flows for fish and wildlife. The management of storage reservoirs (i.e. the timing of filling and spilling) is highly dependent upon the seniority of water rights. Additional discussion on water rights administration is provided later in this report.
Upper Snake River Basin Water Stewardship Assessment 12 Reservoir Completed Stream Purpose Storage (ac-ft) American Falls 1978 Snake River Irrigation, Power 1,672,600 Palisades 1957 Snake River Irrigation, Flood, Power, Recreation 1,200,000 Jackson Lake 1916 Snake River Irrigation, Flood 847,000 Blackfoot 1911 Blackfoot River Irrigation, Municipal 350,000 Salmon Falls 1911 Salmon Falls Creek Irrigation 182,700 Island Park 1938 Henrys Fork Irrigation 135,200 Lake Walcott 1906 Snake River Irrigation, Power 95,200 Henrys Lake 1910 Henry's Lake Outlet Irrigation 90,400 Ririe 1976 Willow Creek Irrigation, Flood, Recreation 80,500 Oakley 1916 Goose Creek Irrigation 77,400 Milner 1906 Snake River Irrigation, Power 50,000 Table 3.
Reservoirs in the Upper Snake River Basin with storage greater than 50,000 ac-ft, listed in order of decreasing storage (after IWRB 1998).
Groundwater Geologically, the ESPA is characterized by a history of volcanic activity. Following periodic episodes of explosive volcanism associated with the Yellowstone hotspot, basaltic lava flowed across the plain, becoming interspersed with gravel and ash. These basalt-dominated layers are highly permeable to water and have created the conditions for one the largest and most accessible aquifers in the United States (Konikow 2013). Wells drilled in the area indicate that the effective aquifer depth is approximately 800-1,200 feet. Below this depth, geologic layers become increasingly dense with less water storing capacity.
While generally considered to be highly permeable and unconfined, there remains considerable heterogeneity within the aquifer geology (Garabedian 1992). Gravel and sand dominate the fringes of the aquifer plain and are also associated with deposits of silt and clay. These deposits are less permissive of water movement and can lead to locally isolated areas of perched or confined water tables. Even in the central region of the Eastern Snake Plain dominated by basaltic rock, water movement is non-uniform. Groundwater flow or conductivity tends to be the greatest along the direction of lava flows and within basalt layer gaps.
The general trajectory of water flow is southwesterly but actual flow directions and velocities are highly dependent upon localized geologic conditions (Figure 4). This is important to note when considering water management actions since the timing and magnitude of specific hydrologic outcomes are not readily generalizable.
Upper Snake River Basin Water Stewardship Assessment 13 Figure 4. Generalized directions of groundwater flow in the ESPA area (from Graham and Campbell, 1981). Due to the highly permissive underlying geology, the ESPA is a dynamic system with continual fluxes in water storage. In contrast to confined or fossil aquifers, the ESPA water balance is significantly influenced by recharge pathways. Aquifer recharge is dominated by incidental recharge through irrigation losses—tributary underflow, precipitation, and streamflow seepage also playing an important role. With irrigation losses accounting for more than half of the annual aquifer recharge, the overall picture of the ESPA is a highly modified system influenced heavily by agricultural water use practices.
Surface and groundwater interaction The dominant hydrological characteristic of the basin is the dynamic interaction of surface and groundwater. Along the length of the Snake River within the basin, the river and its tributaries alternately gain and lose water between the larger ESPA and smaller perched aquifers. Additionally, the direction and magnitude of these interchanges are often dependent upon stream flow volumes and water table elevations. These patterns of surface and groundwater interaction have been well described (IWRB 1998). But while the general patterns of connectivity are understood, the complex
Upper Snake River Basin Water Stewardship Assessment 14 interactions of location, stream flow, and groundwater levels mean that predicting the impacts of water management activities is highly context specific. For example, groundwater recharge activities may actually augment stream flow rather than contribute to aquifer storage. In addition to surface water interactions, the ESPA also feeds important springs near the American Falls and Thousand Springs reaches of the Snake River. Discharge from these springs is significant—Thousands Springs alone accounts for almost 40 percent of ESPA discharge (IWRB 1998).
Below Milner dam, these springs can account for the entire flow within the Snake River. Discharge at these springs is directly dependent upon aquifer storage, with higher discharges occurring at higher aquifer storage levels.
3.2.2 Water quality Surface water quality In keeping with other water resource elements of the basin, the view of surface water quality concerns is similarly mixed in the Upper Snake River Basin. In general, pollutants increase in concentration in the downstream direction throughout the basin (Clark 1994). In particular, pollutant concentrations are the highest at the mouths of tributary basins and in the reach between Milner and King Hill (also known as the Middle Snake River). In terms of pollutant types, nutrients, sediment, and pesticides are the most common contaminants and all three are highly associated with agricultural practices.
Farm fertilizer application contributes more than two-thirds of the total budget for both nitrogen and phosphorous. Similarly, evidence indicates that on-field practices can have significant impacts on sediment loads (IWRB 1998). Reservoirs act as sediment and nutrient sinks, concealing the full impact of land use practices.
The most recent spatial data set available from the Idaho Beneficial Use Reconnaissance Program (BURP) indicates that more than 70% of assessed streams and lakes do not meet beneficial use criteria.3 Of these assessed streams, more than 5,000 miles of streams are listed as 303(d) impaired waters requiring determination of formal pollution limits. Causes for impairment determinations include sediment, nutrients, pesticides, dissolved oxygen, thermal modification, habitat alteration, and flow alteration. Several pollutant limits have already been developed for reaches throughout the basin. The first pollutant limits or TMDLs (total maximum daily loads) were established for reductions in total phosphorous with a recent status update report indicating that concentrations have decreased very little (IDEQ 2013).
Additional limits are expected to be phased in for other pollutants including nitrogen and flow alteration.
A basin perspective indicates that agriculture is a major driver of water quality concerns in addition to other point sources such as livestock production, food processing, and aquaculture operations. The scale of these water quality impacts is heavily dependent on streamflow and connected aquifer 3 Beneficial use criteria are established by the State for specific stream reaches and lakes. Categories of beneficial use include water supply, aquatic life, recreation, wildlife habitats, and aesthetics (IDEQ 2014).
Upper Snake River Basin Water Stewardship Assessment 15 spring discharge.
Considerable work remains for adequately mitigating pollutant concerns and the agricultural sector will likely be an important stakeholder in this effort. Figure 5. Current status (2010) of streams and lakes in the Upper Snake River Basin. Waters determined to be “not supporting” of one or more beneficial use categories are highlighted in red. Data from IDEQ. Groundwater quality National, state, and regional groundwater quality programs have conducted monitoring in the Upper Snake River Basin with most of the sampling focused on the Eastern Snake River Plain. Overall groundwater quality in the basin is considered to be good in large measure due to the sheer size of the aquifer and the relatively high recharge rate.
However, there exist localized areas of water quality pollution.
The vulnerability of groundwater supplies to pollutants is dependent on four primary drivers: water table elevation, recharge or infiltration rate, soil type, and land use activities (IWRB 1998). A review of the ESPA by Idaho’s Department of Environmental Quality (IDEQ) in 1991 found that areas of greatest vulnerability were irrigated cropland with shallow or perched aquifers underneath. Compounding concern about these most vulnerable areas is the fact that most domestic wells source water from shallower groundwater depths.
Upper Snake River Basin Water Stewardship Assessment 16 Nitrate levels are a particular concern across the ESPA with possible sources including fertilizers, decaying organic matter, livestock facilities, and sewage discharge (IWRB 1998).
Areas most affected are located along the aquifer margins and the Thousand Springs area. The springs in particular have been a focal area for continued monitoring after the observance of increasing nitrate levels during the 1990s (IDEQ 2006). Estimates of nitrogen loading indicate that fertilizer application and other agricultural activities may contribute more than half of total nitrate loads. Other pollutants of concern in the ESPA are pesticides related to agriculture. Statewide monitoring projects have focused on locations with both groundwater vulnerability and pesticide use. Monitoring results in the Magic Valley area (near Twin Falls) indicated the detection of pesticides at several well locations (ISDA 2009).
The USGS National Aquifer Water Quality Assessment (NAWQA) program has conducted a more comprehensive look at water quality in the ESPA (Frans 2012). Well sampling beginning in 1992 has monitored 87 different pesticides. At least half of the sampled wells indicated the presence of pesticides. The herbicide atrazine was the most commonly detected pesticide, found in both domestic and public-supply wells. However, well samples indicated contaminant levels were significantly below health concern thresholds. 3.3 WATER USE 3.3.1 History of water use The history of water use in the Upper Snake River Basin is closely intertwined with American settlement and the development of irrigated agriculture.
Beginning with the 1862 Homestead Act, national policy has driven the establishment of one of the country’s most significant agricultural areas within an otherwise semi-arid landscape (Slaughter 2004). Even before the advent of federal irrigation development programs, more than 300,000 acres of the basin were irrigated by surface flow diversions (largely in the Henrys Fork, Upper Snake River, and Wood Rivers) (Garabedian 1992). By the early 1900s, diversions for irrigation demand were large enough to deplete entire reaches of the Snake River (IWRB 1998). After passage of the 1902 Reclamation Act, land development policy was buttressed with the construction of reservoirs, providing the necessary enabling conditions for the agriculturally productive Upper Snake River Basin of today.
By the middle of the 20th century, most of the significant reservoir storage had been developed (Van Kirk 2008). By this time, more than 500,000 acres were farmed using surface water diversions for primarily flood and furrow irrigation. Total diversions were roughly 8 to 10 million acre-feet with much of the irrigation water infiltrating into the aquifer or returning as stream flows (Garabedian 1992). An elaborate system of canals—primarily unlined with high leakage rates—had been built to carry surface water to irrigated land. During this period, total ESPA storage actually increased above baseline levels due to incidental infiltration of excess canal leakage and irrigation water.
Around this time, two significant changes in water use occurred. The first development was an increase in the use of groundwater. Some of this groundwater was used to irrigate new farmland; in other areas, farmers switched from surface to ground water supply (Figure 6).
Upper Snake River Basin Water Stewardship Assessment 17 Figure 6. Historical changes in surface and ground water acreage in the ESPA (from Cosgrove 2006 after Garabedian 1992). Concurrent with increasing use of ESPA groundwater was a transition from gravity to sprinkler irrigation. This increase in sprinkler irrigation was initially attributable primarily to groundwater users but gained adoption by surface water users as well (Garabedian 1992). Irrigation application efficiencies significantly increased while maintaining crop production levels (IWRB 1998). In part as a result of these efficiency gains, surface water diversions began to decrease in the 1970s and this trajectory continues today.
These decreased surface water diversions have in turn decreased the flow of irrigation-related infiltration to the aquifer.
The net result of these two changes—increased groundwater abstraction and decreased recharge incidental to surface irrigation—has been a significant shift in the trajectory of ESPA storage. Previous agricultural practices had steadily increased the available groundwater supply through infiltration of surface water into the aquifer. Mid-century changes in irrigation practices precipitated a decline in aquifer storage for the first time since major farming activities began in the basin. This continuing trajectory of aquifer storage is well evidenced through changes in aquifer storage elevations since 1980 (Figure 7).
Upper Snake River Basin Water Stewardship Assessment 18 Figure 7. Map showing groundwater elevation changes in the ESPA from 1980–2008 (from IWRB 2011). 3.3.2 Current water use Agriculture remains the largest water user—both in terms of total withdrawal and consumptive use—within the Upper Snake River Basin (Figure 8) (ESPA CAMP 2009). Currently, there are some 2.4 million acres of irrigated land in the basin including 2.1 million acres within the ESPA boundary (Van Kirk 2008, ESPA CAMP 2009). Approximately 1 million acres are irrigated with surface water upstream of Milner Dam and another 0.8 million acres are irrigated with ground water from the ESPA.
The remainder (0.6 million acres) is irrigated with a combination of surface and ground water including tributaries on the perimeter of the ESPA.
In terms of total volume, an estimated 10.1 million acre-feet is withdrawn annually for irrigation (Van Kirk 2008). More than half this total volume—about 6.6 million acre-feet—returns to the system as aquifer recharge or return flows. The consumptive fraction of irrigation water use is estimated at 3.7 million acre-feet annually, or roughly a third of total withdrawals.
Upper Snake River Basin Water Stewardship Assessment 19 Figure 8. Estimates of sector water withdrawals for all 24 counties within the Upper Snake River Basin. Left panel shows surface and ground water withdrawals in millions of gallons per day (Mgal/d) where numeric values indicate total (surface plus ground) withdrawals.
Right panel indicates sector withdrawals relative to overall surface and ground water totals. Data are estimates from the USGS National Water Use Information Program in 2005. Domestic, commercial, municipal, and industrial (DCMI) water use accounts for approximately 400,000 acre-feet annually (IWRB 1998). This figure includes a wide range of activities including household use, public supply, food processing including sugar refining and potato processing, Idaho National Engineering and Environmental Laboratory (INEEL) water use, and a range of commercial water users. Fish hatcheries are the largest DCMI water user throughout the basin (235,000 acrefeet in 1995).
Relative to agriculture, DCMI is a small water user though projections expect this use to increase with future population growth (IWRB 2009).
Basin irrigation flows Volume (million acre-feet) WITHDRAWALS Surface water in Water District 1 7.3 Groundwater from ESPA 1.2 All other surface and ground water 1.6 Total 10.1 RETURNS Infiltration to ESPA 4.0 Other irrigation returns 2.6 Total 6.6 Table 4. Mean irrigation related flows within the Upper Snake River Basin from 1958-2007 (after Van Kirk 2008). While irrigation continues to be the primary water user in the basin, other non-consumptive water users are also economically significant (Van Kirk 2008). Hydropower generation is also important
Upper Snake River Basin Water Stewardship Assessment 20 water user and factors significantly in the management of reservoirs (Van Kirk 2008).
Additionally, an economically important recreational fishing industry is dependent upon surface water flows, particularly in the upper tributaries of the basin (Loomis 2006). 3.4 WATER ADMINISTRATION AND MANAGEMENT 3.4.1 Water rights Historically, water rights were established simply by meeting beneficial use requirements.4 Since 1963 for groundwater and 1971 for surface water, water rights can only be established through a formal permitting and licensing procedures (IDWR 2014). Following the prior appropriation doctrine, Idaho manages rights according to the “first in time is first in right” approach typical of many western states (Tuthill 2013).
Under this system, water is delivered in order of decreasing priority where the oldest water rights have the highest priority.
In 1987, IDWR began administering an adjudication process to formally define all water rights in the Upper Snake River Basin including historical or beneficial use rights. Since 1992, the Idaho Department of Water Resources has maintained a moratorium on the processing and approval of water development permits in the Snake River Basin above Weiser (IWRB 1998). The basin is considered closed, precluding the addition of new significant water users (some exceptions exist for domestic, stock, and municipal users).In the Upper Snake River Basin, three categories of water rights exist: natural flow, storage water, and groundwater. Within the basin, more senior natural streamflow rights are located predominantly in the Magic Valley area downstream of Milner and in the Henrys Fork Basin. Almost all groundwater rights are junior to both natural flow and storage water rights. Each type of water right is administered differently:
- Natural flow rights refer to diversions of natural stream or spring flows and are quantified in terms of instantaneous stream discharge (cubic-feet per second).
- Storage water rights refer to surface water stored in and released from reservoirs. Storage water rights are quantified in terms of annual storage (acre-feet per year).
- Groundwater rights are quantified in terms of pumping rates (cubic-feet per second). Water rights are additionally defined with regard to the purpose, season of use, point of diversion, and place of use. For most irrigation water rights, water use is restricted to the growing season from April through October. While water rights are generally associated with real property rights, it may be possible to transfer or change a right relative to the point of diversion, place of use, period 4 Beneficial uses include irrigation, stock-watering, manufacturing, mining, hydropower, municipal use, aquaculture, recreation, and fish and wildlife (IDWR 2014).
Upper Snake River Basin Water Stewardship Assessment 21 of use, or nature of use. Such changes require formal consideration by IDWR to ensure, among other considerations, that the change does not injure other water rights.5 Previously, surface water rights were managed separately from groundwater. Events in the 1990s and early 2000s set in motion a shift towards joint or conjunctive management of both surface and ground water.6 The water rights adjudication process initiated in 1987 led IDWR to exercise authority over groundwater rights administration in the Thousand Springs and American Falls areas.
Also around this time, concerns were growing about the impact of groundwater pumping on spring flows, eventually culminating in legal petitions or “delivery calls” by senior surface water users against groundwater users (Slaughter 2012).
As a result of these changes, both surface and groundwater diversions are now conjunctively managed according to water right priority dates. In years when insufficient water is available to meet all water rights, IDWR seeks to mitigate impacts to senior water users through an administrative process that includes the possibility for negotiation, mitigation, or curtailment. In this environment of water insecurity, groundwater users have sought to protect their rights through litigation and mitigation (Slaughter 2012).
One avenue for groundwater mitigation has been the purchase of unused reservoir water (Whelan 2013).
Storage water right holders can lease their rights into a State managed rental pool. Under threat of curtailment, groundwater users have utilized this rental pool water to mitigate the impacts of pumping on surface water flows in the Thousand Springs area (Patton 2012). While rental pool water offers the opportunity to offset surface water discharge impacts, there is considerable uncertainty with this approach. Such mitigation is dependent on adequate water availability and subject to administrative restrictions including priority for certain users and point of use locations (IDWR 2013).
The end result of the shift to conjunctive management is an environment of considerable uncertainty and risk. The existing administrative and legal tools offer incomplete, and costly, remedies for addressing these conflicts. 3.4.2 Water institutions and management There are a number of institutions, both state and private, that are responsible for the management and delivery of water resources. Described below are the key organizations that play an active role in basin water management activities. 5 IDWR utilizes a complex spreadsheet tool based on aquifer modeling data in order to determine the hydrologic impacts resulting from any proposed water right change.
6 The legal basis for conjunctive surface and ground water management is codified in the 1951 Idaho Ground Water Act which called for restrictions where groundwater abstraction affects senior water rights or is in excess of natural recharge rates.
Upper Snake River Basin Water Stewardship Assessment 22 Idaho Department of Water Resources The Idaho Department of Water Resources (IDWR) is the primary State agency responsible for the management of water resources. IDWR manages a number of programs including comprehensive basin planning, minimum stream flow assessment, water project financing, water supply banks and water rentals.
In the Upper Snake River Basin, IDWR also oversees the delivery and distribution of water through the authority of water districts.
Idaho Water Resources Board The Idaho Water Resource Board (IWRB) was created by the Idaho Legislature in 1965. Comprised of eight members appointed by the governor, the Board was initially charged with development and implementation of the state water plan. In 1974, the Board and the existing Department of Water Administration were combined to form the present-day Idaho Department of Water Resources. The Board, with assistance from IDWR Planning and Technical Division staff, is involved in court appeals, adoption of administrative rules, water bank administration, state water planning, and negotiations with the Federal government and Indian Tribes.
Bureau of Reclamation The US Bureau of Reclamation manages eight dams through its Upper Snake Field Office: Little Wood River, American Falls, Grassy Lake, Island Park, Jackson Lake, Minidoka, Palisades, and Ririe Dams. Reclamation manages these dams primarily for irrigation purposes (based on water rights) but also considers secondary factors such as flood control, hydropower, fish and wildlife, and recreation (Van Kirk 2008). Reservoir operation rule curves can have significant impacts on stream flow in reaches throughout the basin.
Water is stored in the reservoir system and accrued to storage water rights according to the prior appropriation system.
Generally, water is stored in the highest-elevation reservoirs first regardless of where the water right is held. To the greatest extent possible, downstream reservoirs are depleted first, regardless of the physical location of the water right. If and when a storage right is exhausted, the user may obtain and use additional storage water, if available, through the Upper Snake rental pool. The practice of storing water as high in the system as possible throughout the year maximizes water availability and minimizes the probability that water will be spilled at Milner Dam.7 State water districts The State has created water districts, overseen by Watermasters, which are responsible for delivering water to ditches, canals, and other diversion points (Tuthill 2013).
Water District 1 is the largest in the state and includes most of the Upper Snake River Basin upstream of Milner Dam. Actual water allocations are determined on a daily basis utilizing a computer-based system to manage the more than 300 diversion points (IDWR 1997). The general procedure is to “calculate 7 The Snake Basin has historically been managed according to the “two rivers” concept, whereby all flows upstream of Milner dam are managed independently of those downstream. The result is to effectively set a zero flow target at Milner dam (Tuthill 2013, Van Kirk 2013). Additionally, this has important implications for the management of water rights whereby upstream appropriations are managed independently from those downstream.
Upper Snake River Basin Water Stewardship Assessment 23 natural flows, allocate those flows in order of priority... and then determine stored water used and storage supplies remaining”. Beginning in 2002, water districts have also been created for the management of groundwater distribution. Watermasters in these districts are responsible for diversion monitoring and enforcement of mitigation or curtailment actions (Tuthill 2013). Irrigation districts One of the oldest formal water user groups, irrigation districts primarily serve to develop irrigation projects including construction of canals and other infrastructure (IDWR 2014).
These districts also oversee the delivery of water to irrigation users. An important distinction is made between state authorized irrigation districts versus canal companies which are private corporations with the primary function of delivering water to shareholder members. In the Upper Snake River Basin, there are at least 10 irrigation districts and nearly 100 private irrigation companies (Van Kirk 2013).
Ground water districts Similar to irrigation districts, ground water districts are organized groups of groundwater users having state authority to construct and operate water resource projects (Tuthill 2013, IDWR 2014). One of the primary purposes of ground water districts is to “develop and operate mitigation plans designed to mitigate” adverse impacts to senior water uses caused by groundwater abstraction. Such mitigation activities typically include the acquisition of unused water and the implementation of aquifer recharge projects. Nine ground water districts have been established within the ESPA.
3.4.3 Conjunctive Aquifer Management Plan With projections of decreasing aquifer storage and growing conflicts between senior and junior water users, the State legislature directed the Idaho Water Resources Board to develop a comprehensive management plan for the ESPA. The Conjunctive Aquifer Management Plan (CAMP) is the result of this process and describes the goals, objectives, and proposed implementation actions for aquifer management (IWRB 2009). The plan recommendations reflect the perspectives of a broad group of stakeholders and serve to balance feasibility constraints with improvements in water management outcomes, focused primarily on securing adequate water supply for all users.8 The CAMP establishes short and long-term targets for managing water use within the ESPA towards “stabilizing and improving spring flows, aquifer levels, and river flows” (Table 5).
This phased implementation process reflects the complexity of the system and the need to carefully monitor the impact of implemented measures. The short-term or Phase I target is an annual increase in aquifer storage by 300,000 acre-feet within the first 10 years of implementation. The long-term target for aquifer storage is an annual increase of 600,000 acre-feet by 2030.
8 It is important to note that environmental objectives (including environmental flows) are not well defined within the context of CAMP (Whelan 2013). Allowance is made within adaptive management provisions for further defining environmentally-related activities and outcomes.
Upper Snake River Basin Water Stewardship Assessment 24 The cost estimate for implementing Phase I is estimated at $70–100 million over 10 years. Achieving the long-term objective is estimated to cost more than $600 million. Importantly, the CAMP recommendations are largely unfunded with proposed water user funding still under development.
There exists considerable interest in developing alternative funding mechanisms to achieve these objectives including participation from private businesses (Tuthill 2012). Action Short-term annual target (thousand acre-feet) Long-term annual target (thousand acre-feet) Ground to surface water conversion 100 100 Managed aquifer recharge 100 150-250 Demand reduction 250-350 Surface water conservation 50 Crop mix modification 5 CREP and other fallowing 40 Buy outs and buy downs No target Weather modification 50 No target Table 5. Summary of proposed activities and associated annual hydrologic targets for CAMP shortand long-term objectives (after IWRB 2009).
The most recent progress report on CAMP implementation indicates that more than $52 million has been spent on aquifer management activities since plan inception (IWRB 2013). Activities amounting to more than 175,000 acre-feet per year have been successfully implemented. These activities are comprised primarily of managed aquifer recharge (117,111 acre-feet per year on average) with contributions from ground water conversion and demand reduction (Table 6). Importantly, not all management activities will have equivalent outcomes on aquifer storage. There is continued debate regarding the impact of aquifer recharge activities with some experts indicating that recharge activities above American Falls may not significantly increase long-term storage (Kruesi 2012).
Irrespective of the quantitative outcomes to date, the CAMP process has been highly successful in demonstrating the feasibility of a collaborative and comprehensive approach to water management in the Upper Snake River Basin. The State and other stakeholders have made significant time and monetary investments to develop this plan. Where previously water user groups were atomized and uncoordinated, the State has successfully implemented an established planning and implementation framework supported by a diverse group of stakeholders. This effort presents an ideal opportunity to engage in water stewardship within the basin—indeed, successfully implementing water stewardship activities outside of this framework would likely be difficult.
Upper Snake River Basin Water Stewardship Assessment 25 Table 6. Progress on CAMP implementation from 2009–2012. Note that volumes are not necessarily reflective of direct increases in aquifer storage levels (from IWRB 2013).
Upper Snake River Basin Water Stewardship Assessment 26 4. PART II: SUSTAINABILITY ASSESSMENT AND STEWARDSHIP PLANNING 4.1 SUSTAINABILITY ASSESSMENT Given the complexities of hydrology and management within the basin, it is not possible to point to a single sustainability metric. Rather, it is necessary to consider physical water resource constraints (water quantity and quality) within the greater sociological context (regulation, management, and economic development) in order to characterize the future of water within the upper basin.
Highlighted below are the most significant water-related impacts expected to affect agricultural production throughout the basin.
4.1.1 Aquifer depletion Assessment of the sustainability of the Upper Snake River Basin reveals a system which has been characterized as over-allocated except in years of above average precipitation (Whelan 2013). The water budget deficit is most readily revealed by the trajectory of ESPA groundwater levels. Since the 1950s, groundwater levels have been declining at an annual rate of at least 200,000 acre-feet (Table 7). The current shortfall is likely even larger given the trajectory of increasing groundwater abstraction, decreasing incidental surface water infiltration, and decreased water availability9 (Figure 9).
Aquifer storage flows Volume (million acre-feet) INFLOW Irrigation infiltration 4.0 Tributary underflow and river seepage 2.2 Eastern tributaries 0.7 Total 6.9 OUTFLOW Spring discharge 5.9 Groundwater pumping 1.2 Total 7.1 NET CHANGE -0.2 Table 7. Estimated average annual water budget for the Eastern Snake River Plain Aquifer (ESPA) from 1958-2007 (after Van Kirk 2008). Updated estimates for current values would show a greater annual deficit due to smaller values for irrigation infiltration and spring discharge and larger values for pumping. 9 In addition to changes in water use, aquifer storage is also highly responsive to drought conditions (IWRRI 2004).