By Meghan M. Carter

No doubt many of you have seen these or similar headlines this spring: “Possible Water Curtailments Even in a Good Year”[i] and “New Idaho Department of Water Resources Order Would Force 900 Groundwater Users to Curtail Use.”[ii] These news stories were in response to an order issued by the Idaho Department of Water Resources (“Department”) in April. The order outlines the updated methodology the Department uses to determine injury to surface water users in the Eastern Snake Plain by groundwater users diverting water from the Eastern Snake Plain Aquifer.[iii]

Understanding what the headlines mean can stump even a seasoned water law attorney. Fear not, in this article I will provide some history, terminology, and summaries of where things stand today with water use on the Eastern Snake Plain.

The Eastern Snake Plain Aquifer

This spring’s headlines are rooted in the history of water use on the Eastern Snake Plain and the hydrologic connection between surface water and the Eastern Snake Plain Aquifer (“ESPA”). Surface water percolates through the ground to the ESPA which underlies some 10,800 square miles of southern Idaho.[iv] The ESPA has a strong hydrologic connection to the Snake River, and it discharges to the Snake River through gaining reaches and springs. Most natural inputs to the ESPA come from mountain runoff. However, incidental recharge from irrigation practices on the Eastern Snake Plain in the early 20^th Century massively and artificially increased ESPA water levels and subsequently increased discharge to the Snake River.[v]

In the early 1950s, irrigation practices started to change. Sprinkler irrigation began to be favored over flood irrigation, and demand for water increased. In addition, pumping technology and cheaper energy prices lead to increased groundwater pumping.  These trends paired with a series of droughts resulted in reduced water recharge to the aquifer, greater groundwater extraction from the aquifer, and a steady decline in the volume of water in the ESPA.[vi]

Following a three-year downtrend in aquifer levels, Department data shows that 2023’s aquifer levels are approaching the lowest since the 1950s.[vii] These declines are occurring despite above-average snowpack in the mountains feeding the ESPA this year.[viii]

Interlude for Some Water Law

Idaho is a prior appropriation state, meaning the first (senior) use of water takes priority over subsequent (junior) uses of that same water.[ix] This is a harsh legal doctrine that does not place a value on the type of water use. Nor does prior appropriation allow for the reduction of water use across all water users. Instead, the senior user’s water right is fully met before junior users can take any water.

The process the Department uses to administer water rights in priority is called water rights administration. If a senior water use is not being met, the water user can file a delivery call with the Department. A delivery call is a request for water rights administration seeking to have the Department ensure senior water uses are met before junior water uses.[x] Once a delivery call is filed, the Department determines whether the senior water use is being materially injured and if so, which junior water rights should be curtailed.

Idaho administers groundwater and surface water conjunctively. This means if there is a known and legally recognized hydraulic connection between groundwater and surface water, they are administered together in priority.[xi] The Department uses a groundwater model, the Eastern Snake Plain Aquifer Model (“ESPAM”), to help conjunctively administer water use on the Eastern Snake Plain. ESPAM models groundwater inputs and outputs throughout the ESPA based on differing weather and irrigation practices. The effort to develop ESPAM started in 2000.[xii] Version 1.1 was used between 2005 and early 2012. Version 2.1 was used thereafter until   Version 2.2, was released in 2021.[xiii]

Because surface water use was generally developed before groundwater use, many groundwater rights are junior to surface water rights. The dynamic has resulted in fierce conflict between surface and groundwater users in the Eastern Snake Plain.

The Surface Water Coalition Delivery Call

In 2005, conflict between surface and groundwater users over reduced availability of surface water came to a head. A group of surface water irrigation entities, known as the Surface Water Coalition (“Coalition”) filed a delivery call with the Department, asking for the Department to curtail junior groundwater use to ensure adequate water supply for senior surface water users.[xiv]

The Coalition’s delivery call alleged that “data collected by the United States Bureau of Reclamation over the past six years indicates an approximate 30% reduction in reach gains to the Snake River between Blackfoot and Neeley, a loss of about 600,000 acre-feet.”[xv] Further, “[t]he recently recalibrated ESPA groundwater model identifies groundwater pumping as a major contributor to declines in the source of water fulfilling senior surface water rights.”[xvi]

The Director of the Department issued an interlocutory order within a month of the Coalition’s delivery call,[xvii] amending or supplementing the order several times, ultimately issuing his seventh supplemental order in 2007.[xviii] A hearing was held in 2008.[xix]

After the hearing, the Director issued an order, concluding that “[g]round water pumping has hindered [Coalition] members in the use of their water rights by diverting water that would otherwise go to fulfill natural flow or storage rights.”[xx] However, he ultimately determined that “junior groundwater users could continue to divert if they provided water in the amount of predicted shortage to members of the SWC that were attributable to their depletions.”[xxi]

The Director also concluded that “requiring curtailment to reach beyond the next irrigation season involves too many variables and too great a likelihood of irrigation water being lost […] .”[xxii] Therefore, the Director held that ongoing administration is needed, which brings us to the “Methodology Order” and its subsequent amendments through 2023.[xxiii]

The Methodology Orders

Because the Coalition’s water supply varies from year to year, ongoing administration requires a yearly evaluation of water availability and water need. That yearly evaluation is outlined in what is known as the Methodology Order, first issued in 2010 (and amended numerous times since). The Methodology Order is “a single, cohesive document by which the Director will quantify material injury in terms of reasonable in-season demand and reasonable carryover.”[xxiv]

The terms “material injury,” reasonable in-season demand (“RISD”), and “reasonable carryover” represent key concepts in the Methodology Order. “Material Injury” is defined as “[h]inderance to or impact upon the exercise of a water right caused by the use of water by another person as determined in accordance with Idaho law […].”[xxv] A determination of material injury depends upon a number of factors, including the amount of water available from the senior’s water source, the efficiency of the senior’s water system, and the availability of alternative points of diversion for the senior’s water rights.[xxvi] RISD is the projected volume of water needed during the relevant evaluation year to grow crops within each entity’s service area.[xxvii] The RISD is calculated using historic demands of a baseline year or years (“BLY”) as “corrected during the season to account for variations in climate and water supply between the BLY and actual conditions.”[xxviii] Reasonable carryover is “the difference between a baseline year demand and projected typical dry year supply.”[xxix]

The Methodology Order outlines nine steps for making a material injury determination each year. The steps can be summarized as follows. In April, the Department makes a prediction of how the demand for the upcoming irrigation season compares to the previous year’s carryover. If there is a predicted shortage, groundwater users must demonstrate “their ability to secure and provide a volume of storage water or to conduct other approved mitigation activities that will provide water to the injured members of the [Coalition].”[xxx] Next, during the mid-irrigation season (usually in July), the Department will evaluate actual crop water needs, issue a revised forecast of supply, and establish when groundwater users must provide the Coalition with water that year.[xxxi] At the end of the irrigation season, the Department determines the amount of carryover water that is owed to the Coalition.[xxxii]

The process outlined in the Methodology Order allows the Department to timely administer water rights in the Eastern Snake Plain so that the Coalition does not suffer material injury to its water rights.

Changes to the Methodology Order

The Methodology Order has been amended several times to address legal findings made by the Water Court[xxxiii] upon judicial review. However, the Fifth Amended Methodology Order, issued in April 2023, made changes based on the Department’s further data acquisition and additional analyses. The changes were made because “the Director should use available data, and consider new analytical methods or modeling concepts, to evaluate the methodology.”[xxxiv]

Specifically, the Fifth Amended Methodology Order contains two significant changes. First, while the Fourth Amended Methodology Order used an average of the years 2006, 2008, and 2012 for the BLY, the Department determined that data obtained from 2014-2021 indicated that particular average of years no longer satisfied the criteria for a BLY.[xxxv] The Director found that the criteria for a BLY were satisfied by 2018 and 2020.[xxxvi]  The Director then selected 2018 as the new BLY, concluding that using 2018 for the BLY “protects the senior while excluding extreme years from consideration.”[xxxvii]

Second, the ESPAM analysis was changed from steady-state to transient simulation. Steady-state is a condition of a system that does not change in time,[xxxviii] whereas transient simulation attempts to predict changes over time. Early versions of ESPAM used a steady-state analysis to calculate impacts of water use on the ESPA. When using a steady-state analysis, ESPAM “can only model increases in aquifer discharge to the Snake River resulting from continuous curtailments of an identical magnitude and location until the impacts of curtailment are fully realized.”[xxxix] This calculation does not account for the time to reach steady state or when the impacts would be realized. The current ESPAM can perform a transient simulation which “predict[s] the timing of changes in river reach gains.”[xl]

To illustrate the difference between steady-state and transient model simulation, the Director ran ESPAM simulations using both steady-state and transient for 2023.  The Director found that curtailment using the steady-state analysis will only offset 9-15% of the predicted shortfall, while a transient analysis will offset the full predicted shortfall.[xli] This means that using transient analysis stands to provide the senior water users more water at the time and place needed.  But it also means that the Department would have to curtail more junior groundwater rights to meet the needs of the Coalition in a particular year.

The Director of the Department held a hearing on the Fifth Amended Methodology Order in June 2023. On July 19, 2023, the Director issued two orders. The first, Post-Hearing Order Regarding Fifth Amended Methodology Order, addresses the issues discussed at the hearing.[xlii] The second, a Sixth Final Order Regarding Methodology for Determining Material Injury to Reasonable In-Season Demand and Reasonable Carryover (“Sixth Amended Methodology Order”),[xliii] “correct[s] data in the Fifth Methodology Order found to be in error during the June 6 Hearing” and edits “other non-substantive matters in the Fifth Methodology Order.”[xliv] The Sixth Amended Methodology Order did not change the selection of BLY or the use of transient model simulations. It is expected that a petition for judicial review of the orders will be filed. Although the Sixth Amended Methodology Order is not yet set in stone, it nevertheless has implications for all water users in the Eastern Snake Plain, surface, and groundwater users alike.

Why it Matters

In April 2023, based on the Fifth Amended Methodology Order, the Director determined that “ground water rights-bearing priority dates later than December 30, 1953, must be curtailed to produce the volume of water equal to the predicted” shortfall.[xlv] This is much earlier than curtailment dates determined in April in prior years. For example, the curtailment date for 2022 was December 25, 1979,[xlvi] in 2019 it was August 25, 1991,[xlvii] and in 2016 it was February 8, 1989.[xlviii] While the mid-season evaluation of actual need showed there was no shortfall,[xlix] the changes present in the Fifth and Sixth Amended Methodology Orders are still relevant as they will continue to apply in the future.

Ordering curtailment or mitigation for a larger pool of groundwater users can be costly. The April 2023 predicted shortfall was 75,200 acre-feet of water.[l] To put that in perspective, one acre-foot of water is 325,851 gallons and one dairy cow is estimated to need 35 gallons of water per day.[li] The cost for water right rentals is $23 per acre-foot, which equates to almost $1.73 million.[lii] In years where there is a water shortfall, the option to rent may not be available. The uncertainty of water rights rentals has resulted in groundwater users implementing multiple mitigation strategies, such as compensating for their use with groundwater recharge or reducing the amount of water used.[liii] Groundwater recharge requires infrastructure and groundwater users must spend money not only to build the infrastructure but to identify a suitable site and obtain water rights. Reduction of water use means less crops grown, and less money earned, which affects livelihoods and the Idaho economy. This is an issue that affects so many in Idaho, so keep your eyes open for further headlines.

Meghan M. Carter is a deputy attorney general representing the Idaho Department of Water Resources. She’s been in her position for 10 years and is amazed at what she still doesn’t know about Idaho water law. The views expressed in this article do not reflect those of the Office of the Attorney General or IDWR.

[i] Possible Water Curtailments Even in a Good Year, AG Proud (May 1, 2023), https://www.agproud.com/articles/57506-possible-water-curtailments-even-in-a-good-year.

[ii] Clark Corbin, New Idaho Department of Water Resources Order Would Force 900 Groundwater Users to Curtail Use, Idaho Capital Sun (Apr. 28, 2023), https://idahocapitalsun.com/2023/04/28/new-idaho-department-of-water-resources-order-would-force-900-groundwater-users-to-curtail-use/.

[iii] Fifth Amended Final Order Regarding Methodology for Determining Material Injury to Reasonable In-Season Demand and Reasonable Carryover, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, American Falls Reservoir District #2, Burley Irrigation District, Milner Irrigation District, Minidoka Irrigation District, North Side Canal Company, and Twin Falls Canal Company, No. CM-DC-2010-001 (Idaho Dept. of Water Resources, filed Apr. 21, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230421-Fifth-Amended-Final-Order-Regarding-Methodology.pdf.

[iv] Wesley Hipke, Paul Thomas, and Noah Stewart-Maddox, Idaho’s Eastern Snake Plain Aquifer Managed Aquifer Recharge Program, 60 Groundwater 648, 648 (2022).

[v] Id. at 648–49.

[vi] Id. at 649.

[vii] Interview with Jennifer Sukow, Engineer, Idaho Dept. of Water Resources (July 5, 2023).

[viii] Water Supply Snow Water Equivalency, Idaho Department of Water Resources (Mar. 16, 2021), https://idwr.idaho.gov/water-data/water-supply/snow-water-equivalency/.

[ix] I.C. § 42-106 (“As between appropriators, the first in time is first in right.”)

[x] IDAPA 37.03.11.010.04.

[xi] IDAPA 37.03.11.010.03.

[xii] Enhanced Snake Plain Aquifer Model Version 2.1 Final Report, 4 (Jan. 18, 2013), available at https://research.idwr.idaho.gov/files/projects/espam/browse/ESPAM_2_Final_Report/ESPAM21FinalReport.pdf.

[xiii] Jennifer Sukow, Model Calibration Report Eastern Snake Plain Aquifer Model Version 2.2, Idaho Department of Water Resources (May 2021), https://research.idwr.idaho.gov/files/projects/espam/browse/ESPAM22_Reports/ModelCalibrationRpt/ModelCalibration22_Final.pdf.

[xiv] Petition for Water Right Administration and Designation of the Eastern Snake Plain Aquifer as a Ground Water Management Area, In the Matter of the Petition for Administration by A & B Irrigation District, American Falls Reservoir District #2, Burley Irrigation District, Milner Irrigation District, Minidoka Irrigation District, North Side Canal Company, and Twin Falls Canal Company (Idaho Dept. of Water Resources, filed Jan. 14, 2005), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/swc-delivery-call/SWC-20050114-SWC-Call-Secondary-Filing.pdf.

[xv] Id. at ¶ 16

[xvi] Id.

[xvii]Order, In the Mater of Distribution of Water to Various Water Rights Held by or for the Benefit of A&B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Feb. 14, 2005), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/swc-delivery-call/SWC-20050214-First-Order-in-Response-to-Surface-Coalition.pdf.

[xviii]Seventh Supplemental Order Amending Replacement Water Requirements, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Dec. 20, 2007), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/swc-delivery-call/SWC-20071220-Seventh-Supplemental-Order-Amending-Replacement-Water-Requirements.pdf.

[xix] The three-year delay between the initial conflict and the hearing on the conflict stemmed from requests for schedule changes and a case challenging the Conjunctive Management Rules, the administrative rules governing a delivery call between surface and ground water users.

[xx] Opinion Constituting Findings of Fact, Conclusions of Law and Recommendation, 29, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Apr. 29, 2008), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/swc-delivery-call/SWC-20080429-SWC-Rec-Order.pdf.

[xxi] Final Order Regarding the Surface Water Coalition Delivery Call, 4, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Sept. 5, 2008), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/swc-delivery-call/SWC-20080905-SWC-Final-Order.pdf.

[xxii] Id. at 5.

[xxiii] Id. at 6.

[xxiv] Second Amended Final Order Regarding Methodology for Determining Material Injury to Reasonable In-Season Demand and Reasonable Carryover, 2, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al., No. CM-DC-2010-001 (Idaho Dept. of Water Resources, filed June 23, 2010), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20100623-Amended-Final-Order.pdf.

[xxv] IDAPA 37.03.11.010.14.

[xxvi] IDAPA 37.03.11.042.

[xxvii] Id. at 12

[xxviii] Final Order Regarding the Surface Water Coalition Delivery Call, supra note 21, at 5.

[xxix] Second Amended Final Order Regarding Methodology for Determining Material Injury to Reasonable In-Season Demand and Reasonable Carryover, supra note 24,at 22.

[xxx] Id. at 34–36.

[xxxi] Id. at 36.

[xxxii] Id. at 37–38.

[xxxiii] Per Idaho Supreme Court Administrative Order, all petitions for judicial review regarding the administration of water rights from the Department are assigned to the Adjudication Court of the Fifth Judicial District. Administrative Order, In the Matter of the Appointment of the SRBA District Court to Hear All Petitions for Judicial Review from the Department of Water Resources Involving Administration of Water Rights, (Dec. 9, 2009), available at http://srba.state.id.us/Images/sct%20order.pdf.

[xxxiv] Fifth Amended Final Order Regarding Methodology for Determining Material Injury to Reasonable In-Season Demand and Reasonable Carryover, supra note 3, at 1.

[xxxv] Id. at 11.

[xxxvi] Id. at 12.

[xxxvii] Id.

[xxxviii] Id. at 30.

[xxxix] Id.

[xl] Id.

[xli] Id.

[xlii] Post-Hearing Order Regarding Fifth Amended Methodology Order, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed (July 19, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230719-Post-Hearing-Order-Regarding-Fifth-Amended-Methodology-Order.pdf.

[xliii] Sixth Final Order Regarding Methodology for Determining Material Injury to Reasonable In-season Demand and Reasonable Carryover, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed July 19, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230719-Sixth-Final-Order-Regarding-Methodology.pdf.

[xliv] Id. at 2.

[xlv] Final Order Regarding April 2023 Forecast Supply (Methodology Steps 1-3), 4, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Apr. 21, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230421-Final-Order-Regarding-April-2023-Forecast-Supply-Methodology-Steps-1-3.pdf.

[xlvi] Final Order Regarding April 2022 Forecast Supply (Methodology Steps 1–3), 5, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Apr. 20, 2022), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20220420-Final-Order-Re-April-2022-Forecast-Supply-Methodology-Steps-1-3.pdf.

[xlvii] Final Order Regarding April 2019 Forecast Supply (Methodology Steps 1–3), 6, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Apr. 11, 2019), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20190411-Final-Order-Regarding-April-2019-Forecast-Supply-Steps-1-3.pdf.

[xlviii] Final Order Regarding April 2016 Forecast Supply (Methodology Steps 1 -3), 6, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed Apr. 19, 2016), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20160419-Final-Order-Regarding-April-2016-Forecast-Supply-Meth-Steps-1-3.pdf.

[xlix] Order Revising April 2023 Forecast Supply and Amending Curtailment Order (Methodology Steps 5 & 6), In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Dept. of Water Resources, filed July 19, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230719-Order-Revising-April-2023-Forecast-Supply-and-Amending-Curtailment-Order-Methodology-Steps-5-6.pdf.

[l] Final Order Regarding April 2023 Forecast Supply (Methodology Steps 1-3), supra note 45, at 6.

[li] Water Use Information, https://idwr.idaho.gov/water-rights/water-use-information/.

[lii] Water Supply Bank Pricing, https://idwr.idaho.gov/iwrb/programs/water-supply-bank/pricing/.

[liii] IGWA’s Amended Notice of Mitigation, In the Matter of Distribution of Water to Various Water Rights Held by or for the Benefit of A & B Irrigation District, et al. (Idaho Ground Water Appropriators, Inc., filed June 1, 2023), available at https://idwr.idaho.gov/wp-content/uploads/sites/2/legal/CM-DC-2010-001/CM-DC-2010-001-20230601-IGWAs-Amended-Notice-of-Mitigation.pdf.