City & Cty. of Denver v. Consol. Ditches of Water Dist. No. 2 , 444 P.3d 278 ( 2019 )


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    ADVANCE SHEET HEADNOTE
    July 1, 2019
    
    2019 CO 68
    No. 16SA291, City & Cty. of Denver v. Consol. Ditches of Water Dist. No. 2—Water
    Law—Priorities—Exchange and Substitution Operations.
    Under a 1940 water use agreement, Denver agreed, in lieu of making releases from
    certain streambed reservoirs to replace seepage and evaporation losses, not to reuse or
    successively use return flows from water imported from the western slope. Earlier
    litigation established that this reuse prohibition in the 1940 agreement applies only to
    return flows derived from decreed water rights from Colorado River sources with
    appropriation dates before May 1, 1940; Denver may therefore use return flows derived
    from sources that were appropriated or acquired after that date. The question in this
    appeal is whether the 1940 agreement prohibits Denver from using return flows from
    water imported from the Blue River system under exchange and substitution operations
    decreed in 1955 and administered under a 1946 priority date using water stored in the
    Williams Fork Reservoir under a 1935 priority as a substitute supply.
    Because the water imported through the Roberts Tunnel under Blue River
    exchange and substitution operations is a source acquired by Denver after May 1, 1940,
    the supreme court concludes that the resulting return flows are not subject to the 1940
    Agreement and Denver may reuse and successively use them. Accordingly, the supreme
    court affirms the judgment and decree of the water court.
    The Supreme Court of the State of Colorado
    2 East 14th Avenue • Denver, Colorado 80203
    
    2019 CO 68
    Supreme Court Case No. 16SA291
    Appeal from the District Court
    Weld County District Court, Water Division 1, Case No. 12CW5
    Honorable James F. Hartmann, Water Judge
    ______________________________________________________________________________
    Concerning the Application for Water Rights of the City and County of Denver, acting
    by and through its Board of Water Commissioners in Douglas, Jefferson, Arapahoe,
    Denver, Broomfield, Weld, Adams, and Park Counties.
    Applicant-Appellee:
    The City and County of Denver, acting by and through its Board of Water
    Commissioners,
    v.
    Opposers-Appellants:
    Consolidated Ditches of Water District No. 2; Parker Water and Sanitation District;
    Central Colorado Water Conservancy District; City of Aurora; and Farmers Reservoir
    and Irrigation Company,
    and
    Opposers-Appellees:
    Bijou Irrigation Company and Bijou Irrigation Ditch, Centennial Water and Sanitation
    District, City and County of Broomfield, City of Brighton, City of Commerce City, City
    of Louisville, City of Thornton, City of Westminster, Coors Brewing Company, East
    Cherry Creek Valley Water and Sanitation District, Fairmount Cemetery Company,
    Farmers High Line Canal, Fulton Irrigation Ditch Company, Henrylyn Irrigation
    District, New Brantner Extension Ditch, Northern Colorado Water Conservancy
    District, Platte Valley Irrigation Company, Public Service Company of Colorado, South
    Adams County Water and Sanitation District, South Suburban Park and Recreation
    District, Denver County Club, Upper Cherry Creek Water Association, and United
    Water and Sanitation District,
    and Concerning
    Appellees Pursuant to C.A.R. 1(e):
    Corey DeAngelis, Division Engineer, Water Division No. 1; and Kevin Rein, State
    Engineer.
    ______________________________________________________________________________
    Judgment Affirmed
    en banc
    July 1, 2019
    ______________________________________________________________________________
    Attorneys for Applicant-Appellee City and County of Denver:
    Patricia L. Wells
    Daniel J. Arnold
    Casey S. Funk
    Denver, Colorado
    Attorneys for Opposer-Appellant Consolidated Ditches of Water District No. 2:
    Hoskin Farina & Kampf, P.C.
    William A. Hillhouse II
    Eliza F. Hillhouse
    John P. Justus
    Grand Junction, Colorado
    Law Office of Brice Steele, P.C.
    Brice Steele
    Brighton, Colorado
    Attorneys for Opposer-Appellant Parker Water and Sanitation District:
    Krassa & Miller, LLC
    Robert F. T. Krassa
    Boulder, Colorado
    Attorneys for Opposer-Appellant Central Colorado Water Conservancy District:
    Lawrence Jones Custer Grasmick, LLP
    Kim R. Lawrence
    David P. Jones
    Wesley S. Knoll
    Johnstown, Colorado
    2
    Attorneys for Opposer-Appellant City of Aurora:
    Hamre, Rodriguez, Ostrander & Dingess, P.C.
    John M. Dingess
    Peter C. Johnson
    Denver, Colorado
    Attorneys for Opposer-Appellant Farmers Reservoir and Irrigation Company:
    Fairfield and Woods, P.C.
    Joseph B. Dischinger
    Beth Ann J. Parsons
    Beth Van Vurst
    Dean C. Hirt, III
    Denver, Colorado
    Attorneys for Opposer-Appellee Northern Colorado Water Conservancy District:
    Trout Raley
    Bennett W. Raley
    Douglas M. Sinor
    William Davis Wert
    Denver, Colorado
    Attorneys for Appellees Pursuant to C.A.R. 1(e) Corey DeAngelis, Division Engineer,
    Water Division No. 1; and Kevin Rein, State Engineer:
    Philip J. Weiser, Attorney General
    Paul L. Benington, First Assistant Attorney General
    Denver, Colorado
    Attorneys for Amicus Curiae Board of County Commissioners of Summit County,
    Colorado:
    Petros & White, LLC
    Charles B. White
    David S. Hayes
    Denver, Colorado
    Attorneys for Amicus Curiae The Colorado River Water Conservation District:
    Peter C. Fleming
    Jason V. Turner
    Glenwood Springs, Colorado
    Attorneys for Amicus Curiae City of Colorado Springs:
    City Attorney’s Office
    Michael Gustafson
    Colorado Springs, Colorado
    3
    Hill & Robbins, P.C.
    David W. Robbins
    Matthew A. Montgomery
    Denver, Colorado
    Attorneys for Amici Curiae Eagle River Water & Sanitation District and Upper Eagle
    Regional Water Authority:
    Porzak Browning & Bushong LLP
    Glenn E. Porzak
    Boulder, Colorado
    Attorneys for Amici Curiae Grand Valley Water Users Association, Orchard Mesa
    Irrigation District, and Ute Water Conservancy District:
    Williams Turner & Holmes, P.C.
    Kirsten M. Kurath
    Grand Junction, Colorado
    Attorneys for Amicus Curiae Middle Park Water Conservancy District:
    Cazier & McGowan
    Stanley W. Cazier
    Granby, Colorado
    Attorneys for Amicus Curiae Palisade Irrigation District:
    Dufford, Waldeck, Milburn & Krohn, LLP
    Nathan A. Keever
    Grand Junction, Colorado
    No appearance on behalf of: Bijou Irrigation Company and Bijou Irrigation Ditch,
    Centennial Water and Sanitation District, City and County of Broomfield, City of
    Brighton, City of Commerce City, City of Louisville, City of Thornton, City of
    Westminster, Coors Brewing Company, East Cherry Creek Valley Water and Sanitation
    District, Fairmount Cemetery Company, Farmers High Line Canal, Fulton Irrigation
    Ditch Company, Henrylyn Irrigation District, New Brantner Extension Ditch, Platte
    Valley Irrigation Company, Public Service Company of Colorado, South Adams County
    Water and Sanitation District, South Suburban Park and Recreation District, Denver
    County Club, Upper Cherry Creek Water Association, and United Water and Sanitation
    District.
    JUSTICE MÁRQUEZ delivered the Opinion of the Court.
    4
    ¶1    This appeal from the water court in Water Division 1 represents the latest chapter
    in litigation over a 1940 water use agreement (1940 Agreement) between the City and
    County of Denver, acting by and through its Board of Water Commissioners (Denver)
    and the ditch company members of Consolidated Ditches of Water District No. 2
    (Consolidated Ditches).1 The purpose of the 1940 Agreement was to resolve the parties’
    disputes regarding seepage and evaporation losses from three of Denver’s streambed
    reservoirs located on the South Platte River. Under the 1940 Agreement, in lieu of making
    releases from the streambed reservoirs to replace seepage and evaporation losses, Denver
    agreed not to reuse or successively use2 return flows from water imported from the
    western slope and used in Denver’s municipal water system.
    ¶2    Earlier litigation in Case No. 81CW405 established that this reuse prohibition in
    the 1940 Agreement applies only to return flows derived from decreed water rights from
    Colorado River sources with appropriation dates before May 1, 1940 (the date Denver
    entered into the agreement); Denver may therefore use return flows derived from sources
    1Consolidated Ditches of Water District No. 2 presently consists of the following member
    ditch companies: New Brantner Extension Ditch Company, Brighton Ditch Company,
    Farmers Independent Ditch Company, Fulton Irrigation Ditch Company, Lupton Bottom
    and Lupton Meadows, Meadow Island No. 1, Meadow Island No. 2, Beeman Ditch &
    Milling Company, Platteville Irrigating & Milling Company, Platte Valley Irrigation
    Company, and Western Mutual Ditch Company.
    2“‘Reuse’ means a subsequent use of imported water for the same purpose as the original
    use; ‘successive use’ means subsequent use of the water by the importer for a different
    purpose.” Grand Valley Water Users Ass’n v. Busk-Ivanhoe, Inc., 
    2016 CO 75
    , ¶ 48 n.7,
    
    386 P.3d 452
    , 465 n.7.
    5
    that were appropriated or acquired after that date. City & Cty. of Denver v. Consol. Ditches
    Co. of Dist. No. 2 (Consolidated Ditches), 
    807 P.2d 23
    , 38 (Colo. 1991). The question in this
    appeal is whether the 1940 Agreement prohibits Denver from using return flows from
    water imported from the Blue River system under exchange and substitution operations
    that use water stored in the Williams Fork Reservoir under a 1935 priority as a substitute
    supply.
    ¶3     This issue arose out of Denver’s application in Case No. 04CW121 to adjudicate
    and quantify reusable lawn irrigation return flows (LIRFs) for use as a substitute supply
    in exchanges and augmentation plans. In its application, Denver sought confirmation
    that it could include among its sources of LIRFs the return flows from water imported
    through the Roberts Tunnel under Blue River exchange operations using the Williams
    Fork Reservoir as a substitute supply.       Consolidated Ditches objected to Denver’s
    inclusion of these return flows, arguing that their reuse is prohibited under the 1940
    Agreement.
    ¶4     The water court bifurcated the issues involving the applicability of the 1940
    Agreement into this separate case, No. 12CW05. Denver filed a C.R.C.P. 56(h) motion for
    determination of a question of law, and Consolidated Ditches filed a competing
    C.R.C.P. 56(c) motion for summary judgment, both raising essentially the same question:
    whether the 1940 Agreement prevents Denver from using return flows from water
    imported through the Roberts Tunnel under Blue River exchange and substitution
    operations using Williams Fork Reservoir water as a substitute supply.
    6
    ¶5    In a written order, the water court resolved these competing motions in Denver’s
    favor, ruling that Denver’s Blue River system water, which was decreed in 1955 with an
    appropriation date of June 24, 1946, is a source of water that was not owned,
    appropriated, or acquired by Denver prior to May 1, 1940, and therefore is not subject to
    the 1940 Agreement. The court reasoned that Blue River system water is imported
    through the Roberts Tunnel under a 1946 priority date, whether it is imported after
    diversion in priority, or after out-of-priority diversions enabled by Denver’s exchange
    operations using water released from Williams Fork Reservoir as a substitute supply. The
    water court thus held that Denver may reuse or successively use imported water
    attributed to the Blue River system. The water court later entered its findings of fact,
    conclusions of law, judgment, and decree, which incorporated its earlier order on the
    parties’ competing C.R.C.P. 56 motions.     Consolidated Ditches and other opposers
    appealed.
    ¶6    Consolidated Ditches contends that the 1940 Agreement applies to prevent Denver
    from reusing or successively using water imported through the Roberts Tunnel under
    Blue River exchange and substitution operations. It argues that under the so-called
    “character of exchange rule,” the water diverted by exchange takes on the “character” of
    the substitute supply—here, the water stored in the Williams Fork Reservoir under a 1935
    priority. Thus, it contends, the return flows from the water imported through the Roberts
    Tunnel are derived from a source with an appropriation date before May 1, 1940. Denver
    responds that the water court correctly concluded that the 1940 Agreement does not
    7
    apply to prohibit Denver from reusing or successively using water imported under the
    Blue River exchange operations because those operations were decreed in 1955 and are
    administered under a 1946 priority. In other words, the return flows are derived from a
    source that was acquired by Denver after May 1, 1940.
    ¶7    We agree with Denver. At the time it entered the 1940 Agreement, Denver could
    not import water through the Roberts Tunnel by exchange (or otherwise). Denver’s
    ability to divert water from the Blue River system by exchange or substitution using
    Williams Fork Reservoir water as a source of substitute supply was adjudicated in 1955,
    and the exchange is administered under a June 24, 1946 priority, consistent with the
    appropriation date of Denver’s rights in the Blue River system. Thus, for purposes of the
    1940 Agreement, we hold that the water imported through the Roberts Tunnel under Blue
    River exchange and substitution operations is a source acquired by Denver after May 1,
    1940. Accordingly, the return flows from those operations are not subject to the 1940
    Agreement and Denver may reuse or successively use those return flows.
    ¶8    We disagree with Consolidated Ditches that the so-called “character of exchange
    rule” requires a different result here. The character of exchange concept has emerged as
    an unofficial, permissive practice recognized by the State Engineer, but it does not appear
    in statute, nor have we expressly applied it in case law or defined its scope. We therefore
    decline to adopt a mandatory character of exchange “rule” that applies rigidly to all
    exchange operations. Whatever its scope or applicability in other circumstances, the
    character of exchange principle is unnecessary here to ensure that the purpose of the 1940
    8
    Agreement is fulfilled or to avoid injury to Consolidated Ditches. It is undisputed that
    current importations of water through the Moffat Tunnel under pre-1940 priorities more
    than fully offset the streambed reservoir seepage and evaporation losses that prompted
    the 1940 Agreement. If anything, application of the character of exchange principle to
    bar Denver’s reuse of water imported through the Roberts Tunnel by exchange or
    substitution would only enlarge the existing windfall in Consolidated Ditches’ favor.
    ¶9     Accordingly, we affirm the judgment and decree of the water court.
    I. Background
    ¶10    Given the complexity of the factual and legal background in this case, it is
    necessary to set both out in detail to understand the issues before us. First, we describe
    the relevant aspects of Denver’s transmountain water systems at issue. We then discuss
    the background and content of the 1940 Agreement. Finally, we review our two prior
    decisions interpreting the agreement, City & County of Denver v. Fulton Irrigating Ditch
    Co., 
    506 P.2d 144
    (Colo. 1972), and Consolidated Ditches, 
    807 P.2d 23
    .
    A. Denver’s Transmountain Water Systems
    ¶11    Denver’s extensive and complex water supply system includes rights to several
    sources of water tributary to the Colorado River originating on the western slope of the
    Continental Divide. Denver also owns and operates collection systems, reservoirs, and
    tunnels to import water from these Colorado River basin sources for use on the eastern
    slope. The transmountain system components relevant to this dispute are the Fraser and
    9
    Williams Fork systems, the Williams Fork Reservoir, and the Blue River system. The
    following map (Water Collection System Map) provides an overview of these systems.
    10
    11
    1. Fraser and Williams Fork Systems (Moffat Tunnel Collection
    System) and the Williams Fork Reservoir
    ¶12    The Fraser River and the Williams Fork River are tributaries of the Colorado River
    on the western slope of the Continental Divide. Denver has rights to divert water from
    these rivers through the Fraser River and Williams Fork Diversion Projects, which were
    decreed in 1937 by the Grand County District Court in Civil Action No. 657 with an
    appropriation date of July 4, 1921.
    ¶13    Water diverted from both the Fraser and Williams Fork River collection systems
    is imported through the Moffat Tunnel. The Fraser River Diversion Project diverts water
    from the Fraser River and its tributaries and since 1936, has delivered that water through
    the Moffat Tunnel to the eastern slope for storage and use.3 The Williams Fork River
    Diversion Project includes the Gumlick Tunnel and the Vasquez Tunnel. The Gumlick
    Tunnel is used to import water diverted from the headwaters of the Williams Fork River
    and its tributaries. Starting in 1940, and before the completion of the Vasquez Tunnel in
    approximately 1958, the Gumlick Tunnel water was delivered to Clear Creek (a tributary
    of the South Platte River) for subsequent exchange. Since approximately 1958, the water
    imported through the Gumlick Tunnel has been conveyed through the Vasquez Tunnel
    to the Fraser River Diversion Project, where it is subsequently conveyed through the
    Moffat Tunnel to the eastern slope.
    3See the Moffat Tunnel Collection System Map, infra, for an illustration of the location of
    the Fraser River, Williams Fork River, and the Moffat Tunnel.
    12
    ¶14      Additionally, Denver stores water in the Williams Fork Reservoir, an on-channel
    reservoir that impounds water on the Williams Fork River above its confluence with the
    Colorado River. The Williams Fork Reservoir was also decreed in 1937 in Civil Action
    No. 657, but with an appropriation date of November 10, 1935. The Williams Fork
    Reservoir lies downstream from the Williams Fork River collection system; Denver
    therefore cannot physically deliver water from that reservoir directly to the eastern
    slope.4 Instead, when a senior call is in effect, Denver releases the water stored in the
    Williams Fork Reservoir as replacement water in exchange and substitution operations
    to allow Denver to continue to divert and store water out of priority at its Fraser River
    and Williams Fork River collection systems, or, as relevant here, at its Blue River
    collection system. Per the 1940 Agreement and the Amended Ruling and Order in Case
    No. 81CW405 following this court’s decision in Consolidated Ditches, Denver does not
    reuse return flows from water imported through the Moffat Tunnel under its 1921 Fraser
    River and Williams Fork River Diversion Projects, including water diverted from these
    two projects using Williams Fork Reservoir water as a replacement source.
    4   See Moffat Tunnel Collection System Map, infra.
    13
    14
    2. Blue River System (Roberts Tunnel Collection System)
    ¶15    Water rights in the Blue River have been the subject of substantial litigation in both
    state and federal court, resulting in a 1955 federal decree, followed by a suite of
    supplementary and amendatory orders, judgments, and decrees. Because Blue River
    exchange and substitution operations are part of this complex history, we both describe
    the Blue River system and briefly review the relevant decrees establishing the June 24,
    1946 priority date for administration of these operations.
    a. Blue River Diversion Project
    ¶16    Like the Williams Fork and Fraser Rivers, the Blue River is also a tributary of the
    Colorado River on the western slope. The Blue River Diversion Project consists of Dillon
    Reservoir and the Roberts Tunnel. Dillon Reservoir is an on-channel reservoir that
    impounds water on the Blue River and several tributaries above the Blue River’s
    confluence with the Colorado River. The Blue River Diversion Project collects water at
    the confluence of the Snake River, Blue River, and Ten Mile Creek. This water can be
    stored in Dillon Reservoir for later transport through the Roberts Tunnel, or it can be
    placed directly in the Roberts Tunnel and conveyed to the North Fork of the South Platte
    River on the eastern slope. Denver began importing water through the Roberts Tunnel
    in 1964.
    ¶17    Denver also releases water stored in the Williams Fork Reservoir to make
    replacements under Blue River system exchange and substitution operations. The Blue
    River exchange allows Denver to continue to operate the Blue River Diversion Project
    15
    when its 1946 priorities would otherwise be curtailed by senior downstream calls by
    releasing water stored in the Williams Fork Reservoir to satisfy downstream senior water
    rights on the Colorado River. The Blue River substitution is similar to the exchange in
    that it involves the release of water stored in the Williams Fork Reservoir, albeit at the
    direction of the U.S. Secretary of the Interior and in substitution for the amount of water
    that Denver would otherwise owe to Green Mountain Reservoir5 to complete the annual
    fill of that reservoir under its more senior (1935) priority. Under this arrangement,
    Denver releases water from the Williams Fork Reservoir for beneficiaries of Green
    Mountain Reservoir in substitution for releases that otherwise would be made from
    Green Mountain Reservoir but for interference by Denver’s Blue River Diversion Project.
    ¶18   Denver has always reused the return flows from water that it imports through the
    Roberts Tunnel under its 1946 priorities, including water diverted by exchange or
    substitution using Williams Fork Reservoir water as a substitute supply. From 19896 to
    2015, Denver imported an average of 5,482 acre-feet per year of water attributable to Blue
    River exchange and substitution operations, with greater amounts in dry years. Annual
    return flows from this imported water averaged 2,505 acre-feet during that period.
    5 Green Mountain Reservoir is located on the Blue River downstream from Dillon
    Reservoir. See Roberts Tunnel Collection System Map, infra. Green Mountain Reservoir
    generates hydroelectric power through the United States Bureau of Reclamation’s Green
    Mountain Powerplant.
    61989 was the first year Denver separately tracked water imported through the Roberts
    Tunnel using Williams Fork Reservoir water as a replacement supply.
    16
    17
    b. Blue River Decrees
    ¶19    The Blue River direct flow diversion right and Dillon Reservoir storage rights were
    decreed by the Summit County District Court in 1952 in Civil Action Nos. 1805 and 1806.
    These rights were assigned a priority date of June 24, 1946 based on the district court’s
    finding that construction on both the Blue River Diversion Project and Dillon Reservoir
    commenced on that date. Notably, Denver appealed the Summit County District Court’s
    decision, contending that its priority date should relate back to events earlier than 1946,
    including to the filing of plats, surveys and construction related to (later abandoned)
    configurations for the project, and surveys for the Williams Fork River and Fraser River
    Projects. City & Cty. of Denver v. N. Colo. Water Conservancy Dist., 
    276 P.2d 992
    , 999–1002
    (Colo. 1954). We rejected those arguments and concluded that “Denver had no fixed and
    definite plan and no definite point of diversion” for the Blue River prior to 1946. 
    Id. at 1003.
    We affirmed Denver’s Blue River rights but remanded the case with instructions to
    adjudicate rights to Green Mountain Reservoir. 
    Id. at 1015.
    ¶20    On remand to the Summit County District Court, the United States joined the
    proceeding, and removed Civil Action Nos. 1805 and 1806 to the U.S. District Court for
    the District of Colorado, where the cases were renumbered 5016 and 5017 and were
    consolidated with pending Civil Action No. 2782.
    ¶21    In 1955, the federal district court entered a final decree in the consolidated cases
    that addressed the rights of several parties to use and store water from the Blue River and
    other Colorado River tributaries. See generally Findings of Fact & Conclusions of Law
    18
    & Final Decree, United States v. N. Colo. Water Conservancy Dist., Civ. Nos. 2782, 5016,
    & 5017 (D. Colo. Oct. 12, 1955) (1955 Decree). Much of the 1955 Decree addresses the
    Colorado-Big Thompson (CBT) Project, which includes Green Mountain Reservoir and
    transports water from the Colorado River through a series of reservoirs and tunnels to
    the eastern slope of the Continental Divide. See generally City of Colo. Springs v. Climax
    Molybdenum Co., 
    587 F.3d 1071
    , 1074–77 (10th Cir. 2009) (describing complex procedural
    history of adjudication and administration of water rights on Blue River).
    ¶22    The 1955 Decree resulted from a lengthy stipulation that represents a settlement
    reached by all parties to the consolidated cases regarding Denver’s and others’ rights in
    the Blue River. See 1955 Decree at 29–43. Under this stipulation, the United States
    recognized Denver’s 1946 Blue River rights decreed by the Summit County District Court
    in Civil Actions Nos. 1805 and 1806, and Denver agreed that its Blue River rights are
    subject to the right of the United States to fill Green Mountain Reservoir each year. 
    Id. at 31.
    As relevant here, paragraph 4(c) of the stipulation allows Denver to operate the Blue
    River system ahead of Green Mountain Reservoir by exchange, using water stored in the
    Williams Fork Reservoir as a replacement source:
    The City and County of Denver . . . will at all times bypass water in
    quantities sufficient to meet all legal calls of downstream water rights on
    the Blue River, and within Colorado below the confluence of that stream
    with the main stream of the Colorado River, having priorities earlier than
    the respective priority dates of said cit[y]. This obligation adequately to
    provide water for the priorities on the Blue River and the Colorado River
    antedating [Denver’s June 24, 1946 priority date] may be fulfilled by
    replacement storage by and on the Blue River or on the Williams [Fork]
    River . . . .
    19
    
    Id. at 32–33.
    The stipulation requires the U.S. Secretary of the Interior to approve the
    replacement plan. 
    Id. It further
    requires that “[t]he water to be exchanged shall be on
    hand and in storage when the exchange is proposed.” 
    Id. at 33.
    Finally, the stipulation
    requires Denver to reuse and make successive use of return flows from the Blue River “so
    as to reduce or minimize the demands of such city upon Blue River water,” 
    id. at 35,
    “within legal limitations and subject to economic feasibility,” 
    id. at 34.
    ¶23    After entry of the 1955 Decree, litigation regarding the consolidated Blue River
    cases continued. As relevant here, references to Denver’s right to operate exchanges
    appear in a string of supplemental orders and decrees. In 1964, the federal district court
    entered an additional decree reaffirming Denver’s “right . . . to exchange water lawfully
    impounded on the Williams Fork River or Blue River, as provided for in paragraph 4(c)
    of [the] 1955 stipulation.” Decree at 4, United States v. N. Colo. Water Conservancy Dist.,
    Civ. Nos. 2782, 5016, & 5017 (D. Colo. Apr. 16, 1964) (1964 Decree). And in 1978, the
    federal district court entered a supplemental decree reaffirming that Denver may store
    water at Dillon Reservoir and propose exchanges of water, subject to the consent of the
    U.S. Secretary of the Interior, and subject to the release of water to the extent necessary to
    complete the annual fill of Green Mountain Reservoir. See Supplemental Judgment &
    Decree at 3, United States v. N. Colo. Water Conservancy Dist., Civ. Nos. 2782, 5016, & 5017
    (D. Colo. Feb. 9, 1978). In 1991, a Memorandum of Agreement between the United States
    and Denver affirmed the terms and conditions under which the Williams Fork Reservoir
    water may be substituted for water otherwise storable in Green Mountain Reservoir, thus
    20
    allowing Denver to store and use an equivalent amount of water in Dillon Reservoir that
    would otherwise need to be released from Dillon Reservoir to fill Green Mountain
    Reservoir. And finally, in 1992, the federal district court entered another decree in the
    consolidated Blue River cases that specifically addressed the priority date for
    administration of Denver’s Blue River exchange using water from the Williams Fork
    Reservoir. See Findings of Fact, Conclusions of Law & Judgment & Decree, In re Water
    Rights of the U.S., Civ. Nos. 2782, 5016, & 5017, & No. 88CW382 (D. Colo. Nov. 10, 1992)
    (1992 Decree). There, the court ordered that “[i]n the administration of exchanges to
    storage in Dillon Reservoir or diversions through the Harold D. Roberts Tunnel using
    waters released by Denver from its Williams Fork Reservoir, the State Engineer shall use
    as the priority of exchange for such purposes the priority date of June 24, 1946 as though
    adjudicated in the first available adjudication following that date.” 
    Id. at 10.
    ¶24      Although from the scattered references in these decrees, it does not appear that
    the Blue River exchange was formally decreed as an appropriative right of exchange,7 it
    is clear that the exchange operations were adjudicated through the various Blue River
    7   In the 1992 Decree, the federal district court observed that
    Denver does not here seek to adjudicate an appropriative right of exchange
    between Williams Fork Reservoir and the Harold D. Roberts Tunnel or
    Dillon Reservoir. Instead, Denver claims to make such exchanges by the
    exercise of the right decreed to its Williams Fork Reservoir after complying
    with the requirements of paragraph 4(c) in the 1955 Stipulation and
    paragraphs 2 and 5 of the 1964 Decree in the Consolidated Cases.
    1992 Decree at 3–4.
    21
    decrees and are administered under a June 24, 1946 priority, consistent with the
    appropriation date awarded to the Blue River system rights in Civil Action Nos. 1805 and
    1806.
    ¶25      With this background in mind, we now turn to the 1940 Agreement.
    B. The 1940 Agreement
    ¶26      Denver operates three large streambed reservoirs in the South Platte River Basin
    on the eastern slope: the Antero, Cheesman, and Eleven Mile Canyon Reservoirs. Denver
    operates these reservoirs on a gauge-height basis, which means the inflow and outflow
    to these reservoirs is regulated to maintain water stored in the reservoirs at a steady
    gauge height. This method makes no adjustments or releases to offset evaporation losses,
    however, and the burden of such evaporation is borne by downstream appropriators.
    Although the State Engineer now has statutory authority to order releases from reservoirs
    to compensate for evaporation losses, see § 37-84-117(5), C.R.S. (2018),8 at the time of the
    1940 Agreement, the State Engineer did not charge streambed reservoirs for evaporation
    or seepage losses. Consolidated 
    Ditches, 807 P.2d at 27
    .
    8   Section 37-84-117(5) provides:
    The state engineer may order that an owner of a reservoir release an amount
    of water from the reservoir that, in the determination of the state engineer,
    is necessary to prevent evaporation on the surface of the reservoir from
    depleting the natural flow of the stream running through the reservoir that
    would otherwise be available for use by other appropriators.
    22
    ¶27    Concerned about these losses that the reservoirs were causing to the South Platte
    River, particularly given the addition of the Eleven Mile Canyon Reservoir to this system,
    several irrigation companies banded together as Consolidated Ditches Company of
    District No. 2 to negotiate with Denver to replace these losses. These negotiations led to
    the 1940 Agreement between Denver, Consolidated Ditches, its individual members, and
    the State Engineer.
    ¶28    The preamble to the 1940 Agreement states that the parties desired to “adjust,
    settle and determine all differences between [them] respecting seepage and evaporation
    from streambed reservoirs of the City and County of Denver now in existence.” The
    preamble also observed that it was the State Engineer’s practice not to charge streambed
    reservoirs for seepage or evaporation losses and that the operation of Denver’s reservoirs
    was creating a burden on appropriators. In recognition of this situation, under section 4
    of the 1940 Agreement, Denver agreed not to reuse imported water9 as follows:
    9 As a general rule, appropriators of water have no automatic right to reuse or
    successively use water after its initial application to a beneficial use, and the return flows
    become tributary to the stream, subject to diversion and use under existing priorities.
    City of Thornton v. Bijou Irrigation Co., 
    926 P.2d 1
    , 65 (Colo. 1996). However, a different
    standard has developed for “foreign” or “imported” water brought into a watershed or
    stream system from an unconnected source, such as water brought from the western
    slope to the eastern slope using transmountain tunnels. 
    Id. at 66.
    Our statutes and case
    law establish “a right of reuse for importers of transmountain water that does not exist
    for appropriators of native water.” 
    Id. at 68;
    see also § 37-82-106(1), C.R.S. (2018)
    (“Whenever an appropriator has lawfully introduced foreign water into a stream system
    from an unconnected stream system, such appropriator may make a succession of uses
    of such water by exchange or otherwise . . . .”); Town of Estes Park v. N. Colo. Water
    23
    It is understood and agreed that the City and County of Denver may make
    or permit any nonconsumptive use of water to create electric power, to
    dilute sewage, or the like while such water is on its way to its place of
    principal and ultimate beneficial use; and the City agrees that it will not use or
    attempt to use or lease any water, irrespective of source, which shall have been once
    used through its municipal water system and such water shall be allowed to become
    part of the nearest convenient natural water course.
    (Emphasis added.)
    C. The Fulton Decision
    ¶29    This restriction on Denver’s reuse of return flows under section 4 of the 1940
    Agreement has generated substantial litigation, starting in the 1970s with Fulton Irrigating
    Ditch Co., 
    506 P.2d 144
    . Fulton concerned a 1969 agreement between Denver and Coors
    Brewing Company, under which Coors was to divert water at the confluence of Clear
    Creek and the South Platte River, and Denver was to replace that water with water
    imported from the western slope that had been used in a sewage plant and discharged as
    effluent. 
    Id. at 151.
    Several ditch company signatories to the 1940 Agreement challenged
    this arrangement as violating the 1940 Agreement. 
    Id. at 146.
    We held that Denver, in
    the absence of an agreement to the contrary, had the right to reuse and successively use
    water that it imported from the western slope. 
    Id. at 146,
    149. However, we also upheld
    Conservancy Dist., 
    677 P.2d 320
    , 326 (Colo. 1984) (“Subject to contractual obligations, . . . a
    developer of foreign water has the right to use, reuse, successively use, and dispose of
    such water.”). Thus, the restriction on reuse and leasing of return flows in section 4 of
    the 1940 Agreement limits Denver’s right as an importer of foreign water to reuse and
    make successive uses of water it imports from the western slope. In the absence of this
    contractual limitation, Denver has the right to reuse water it imports to the eastern slope.
    § 37-82-106(1); Fulton Irrigating Ditch 
    Co., 506 P.2d at 147
    –49.
    24
    the validity of the 1940 Agreement and concluded that Denver could not exchange water
    under the Coors agreement. 
    Id. at 146,
    153.
    ¶30   In dicta, this court identified two potential future issues regarding the scope of the
    1940 Agreement. First, we noted the “windfall” or “bonanza” problem caused by a
    potential increase in water importation, but not in evaporation losses:
    We can visualize that the amount of foreign water returned to the river after
    use far exceeds the evaporative loss from Denver’s streambed reservoirs. If
    so, the effect of the 1940 agreement is to create a bonanza for the defendants
    and other downstream users at the expense of Denver and Western
    Colorado.
    
    Id. at 153.
    We observed, however, that Denver had not sought a determination of whether
    the disparity between return flows and evaporation losses rendered the 1940 Agreement
    void as against public policy by reason of wastage. 
    Id. Additionally, we
    raised, but did
    not address, whether the 1940 Agreement applied to water that had not been
    appropriated when the Agreement was made:
    [T]he plaintiffs did not request in their declaratory judgment action a
    determination of whether the 1940 agreement . . . applies to water not
    appropriated at the time the agreement was made. We, of course, can
    express no opinion concerning [this] possible contention[].
    
    Id. D. Case
    No. 81CW405: The Consolidated Ditches Litigation
    ¶31   We had the opportunity to address these issues in Consolidated Ditches, 
    807 P.2d 23
    .
    The dispute in that case concerned Denver’s application in Case No. 81CW405 (Water
    Division 1) for approval of a plan to reuse effluent from transmountain sources—
    including the Blue River, the Williams Fork River, and the Fraser River—in an
    25
    augmentation plan for golf course irrigation wells. 
    Id. at 25,
    30, 32. Consolidated Ditches
    opposed the application, arguing that the 1940 Agreement prohibited Denver from
    reusing any transmountain return flows. 
    Id. at 25.
    ¶32    Following a lengthy trial, the water court issued detailed factual findings and legal
    conclusions regarding the scope of the 1940 Agreement. As relevant here, the water court
    reasoned that the principal purpose of the 1940 Agreement was to “eliminate the burden
    on the [South Platte R]iver caused by evaporation from the streambed reservoirs,” and
    that it was “reasonable to assume that [the parties] anticipated that the gain to the river
    from the agreement would be roughly equivalent to the loss from evaporation.” The
    water court concluded that the goal of the 1940 Agreement would be achieved by limiting
    its effect “to waters [that] were appropriated at the time it was executed” and by
    construing the 1940 Agreement not to apply to waters appropriated or acquired by
    Denver after May 1, 1940. 
    Id. at 25,
    31.
    ¶33    Based on the evidence before it, the water court found that in 1940, Denver
    imported 38,672 acre-feet of water from the Fraser River and Williams Fork River
    Diversion Projects, which resulted in 12,506 acre-feet of effluent return flow. 
    Id. at 36.
    By
    comparison, the estimated evaporation losses from the three streambed reservoirs
    amounted to 10,142 acre-feet. 
    Id. Thus, in
    1940, the return flows exceeded evaporation
    losses by 2,364 acre-feet, or approximately 123%. See 
    id. at 26.
    By comparison, in 1978,
    Denver imported 224,240 acre-feet from the Colorado River system (two-thirds of which
    came from the Blue River Diversion Project), resulting in return flows of 74,110 acre-feet,
    26
    as compared to streambed reservoir evaporation losses of approximately 13,911 acre-feet.
    
    Id. at 36.
    Thus, in 1978, the return flows from all imported water exceeded evaporation
    losses by 60,199 acre-feet, or 532.7%. See 
    id. ¶34 The
    water court observed that in 1940, the parties were considering a joint
    development of Blue River resources and that it must have been evident that if those
    resources were developed, large quantities of Blue River water would be available for
    importation into the South Platte Basin. In other words, it was likely that importation of
    transmountain water would grow, yet the amount of evaporation from the streambed
    reservoirs would likely continue at historic rates. 
    Id. at 31.
    Given the quantity of water
    that could be available for reuse, there was no reason to believe that Denver would intend
    to confer such a “bonanza” on Consolidated Ditches in the form of additional return
    flows. 
    Id. In short,
    it seemed “dubious that Denver would agree—or Consolidated
    Ditches expect—that an ever[-]increasing price be paid for a static benefit.” 
    Id. ¶35 The
    water court concluded that the circumstances surrounding the 1940
    Agreement showed that “the parties were attempting to solve the problem of evaporation
    as it existed at that time, and did not intend that the agreement should bind water
    appropriated in the future.” 
    Id. The water
    court thus decreed, as relevant here, that the
    Agreement did not prohibit Denver from reusing, successively using, and disposing of
    return flows from water derived from decreed Colorado River sources with
    appropriation dates subsequent to May 1, 1940, or with respect to water rights acquired
    by Denver subsequent to that date. 
    Id. It reasoned
    that its interpretation was fair to both
    27
    parties, noting that although the return flows from pre-1940 western slope appropriations
    result in “somewhat of a bonus” to Consolidated Ditches, “the divergence is not
    unreasonable.” 
    Id. ¶36 Both
    Denver and Consolidated Ditches appealed parts of the water court’s ruling
    to this court. 
    Id. at 26.
    As relevant here, we acknowledged that the principal purpose of
    the 1940 Agreement was to eliminate the burden on the South Platte River from
    evaporation losses, 
    id. at 36,
    and upheld the water court’s ruling that the 1940 Agreement
    only precludes Denver from “reusing, successively using, or disposing of effluent return
    flows derived from decreed water rights from Colorado River sources with appropriation
    dates preceding May 1, 1940,” 
    id. at 26.
    Thus, per the water court’s decree, the 1940
    Agreement does not prohibit Denver from reusing return flows from water derived from
    Colorado River sources with appropriation dates after May 1, 1940, or with respect to
    water rights acquired by Denver after that date. 
    Id. at 31.
    ¶37    In examining whether existing disparities between evaporation losses and return
    flows from sources subject to the 1940 Agreement rendered the agreement void by reason
    of wastage, we reviewed the water court’s findings regarding amounts of water imported
    in 1940 from the Fraser River and Williams Fork River Diversion Projects as compared to
    amounts imported in 1978. 
    Id. at 36.
    In so doing, we recognized that water from the Blue
    River Diversion Project is not subject to the 1940 Agreement.         
    Id. Specifically, we
    observed that “[o]f the 224,240 acre-feet of transmountain water imported by Denver in
    1978, . . . almost two-thirds . . . came from the Blue River Diversion Project, which had an
    28
    appropriation date of June 24, 1946, and was not subject to the 1940 agreement.” 
    Id. (emphasis added).
    However, we did not discuss exchange operations in our decision, and thus, it
    is not clear from Consolidated Ditches how the Agreement applies to water diverted by
    exchange or substitution.
    II. Procedural History
    ¶38    Having provided the extensive but necessary background to understanding the
    issues before us, we turn to the procedural history of this case. First, we discuss the
    bifurcation of the issues here from the underlying LIRF case. Then we discuss the parties’
    competing motions under C.R.C.P. 56 and the water court’s rulings.
    A. Bifurcation of Issues Regarding the 1940 Agreement from the
    Underlying LIRF Case
    ¶39    As previously noted, the issues in this appeal initially arose in Denver’s
    application in Case No. 04CW121 to adjudicate and quantify reusable LIRFs for use in
    exchanges and augmentation plans. Among the claims for relief in its application,
    Denver sought confirmation that the Williams Fork Reservoir water was not subject to
    the 1940 Agreement or the ruling in Case No. 81CW405 “if exchanged to another structure
    acquired after 1940 or under an exchange priority junior to May 1, 1940”—in other words,
    if used as a substitute supply for water delivered through the Roberts Tunnel in Blue
    River exchange operations. Consolidated Ditches objected to Denver’s inclusion of
    return flows from Blue River exchange operations using water stored in the Williams
    Fork Reservoir as a substitute supply, arguing that the 1940 Agreement barred the reuse
    of such return flows. Denver then filed an unopposed motion to bifurcate these issues.
    29
    On January 12, 2012, the water court granted Denver’s motion and bifurcated the
    following issues into this case, No. 12CW05:
    All issues involving the scope and effect of the 1940 Agreement, including
    but not limited to the issue of whether water rights decreed in [Civil Action
    No.] 657, Grand County District Court, are not subject to the 1940
    Agreement if stored in Dillon Reservoir by exchange from Denver Water’s
    1935 Williams Fork Reservoir priority, and imported to the east slope
    through the Roberts Tunnel.
    ¶40   All objectors who were parties in Case No. 04CW121 were made parties to Case
    No. 12CW05. The water court then entered a decree in the LIRF case on May 15, 2012.
    Paragraph 24.5 of that decree provided that Denver and Consolidated Ditches had
    stipulated that Denver would reduce the amount of its reusable LIRFs by 8.3% (a
    stipulated approximate measure of the disputed LIRFs) until the bifurcated issues in Case
    No. 12CW05 were resolved.
    B. The Parties’ C.R.C.P. 56 Motions
    ¶41   As this case proceeded, Denver filed a C.R.C.P. 56(h) motion for determination of
    a question of law, asking the water court to determine whether the 1940 Agreement
    prevents Denver from reusing return flows from water imported from the western slope
    under the Blue River system exchange using water released from the Williams Fork
    Reservoir as a source of substitute supply. Consolidated Ditches filed a competing
    C.R.C.P. 56(c) summary judgment motion on the same issue.             Whether the 1940
    Agreement applies to this imported water determines whether Denver may reuse or
    successively use the water and, thus, whether it may include the water in its
    quantification of reusable return flows in the LIRF case. Opposer Central Colorado Water
    30
    Conservancy District (Central) filed a response to Denver’s motion, and West Slope
    Amici10 filed an amicus curiae brief in opposition to Consolidated Ditches’ motion.
    C. The Water Court’s Rulings
    ¶42   On July 12, 2016, the water court issued an order resolving the parties’ C.R.C.P. 56
    motions, ruling that Denver’s Blue River system water right, which was decreed in 1955
    with an appropriation date of June 24, 1946, is a source of water that was not owned,
    appropriated, or acquired by Denver prior to May 1, 1940, and therefore is not subject to
    the 1940 Agreement. It concluded that “the Blue River System water imported by Denver
    has a priority date of 1946, regardless of whether Denver imports the water after
    diversion in priority or after an out-of-priority diversion enabled by Denver’s decreed
    exchange plan, with substitute water released from [the] Williams Fork Reservoir.” The
    water court therefore held that Denver may reuse or successively use imported water
    attributed to the Blue River system. The court rejected Consolidated Ditches’ argument
    that the “character of exchange” principle renders the 1935 priority of the Williams Fork
    Reservoir substitute supply the “operative right” for purposes of the 1940 Agreement.
    Instead, the court reasoned, the relevant date for determining whether the 1940
    Agreement applies is the 1946 administrative priority date of Denver’s Blue River
    10West Slope Amici include the Colorado River Water Conservation District, Board of
    County Commissioners of Summit County, Middle Park Water Conservancy District,
    Eagle River Water & Sanitation District, Upper Eagle Regional Water Authority, Grand
    Valley Water Users Association, Orchard Mesa Irrigation District, Ute Water
    Conservancy District, and Palisade Irrigation District.
    31
    exchange, not the 1935 priority date under which Denver stores water used for substitute
    supply.
    ¶43   Denver and Consolidated Ditches agreed that the July 12, 2016 Order resolved the
    issues that would be contested at trial, and Denver moved for entry of decree based on
    the water court’s order. Central opposed Denver’s proposed decree, arguing that the
    decree should include additional terms and conditions requiring Denver to import a
    certain amount of water through the Moffat Tunnel—water that is subject to the 1940
    Agreement and may not be reused.
    ¶44   On September 25, 2016, the water court issued an order resolving Central’s
    opposition and rejecting Central’s request for additional decree language. The water
    court concluded that even in the absence of a decree condition that Denver import a
    specific amount of nonreusable western slope water each year, ample safeguards already
    ensure that Denver replaces evaporation depletions. Further, the water court reasoned,
    Central’s requested decree condition would require Denver to import far more
    nonreusable water than it had imported in 1940, and would thus result in an “even larger
    windfall” of imported water deposited into the South Platte watershed compared to the
    evaporation losses the 1940 Agreement addressed.
    ¶45   On September 30, 2016, the water court entered its final decree, which adopted its
    findings and conclusions regarding the 1940 Agreement from its July 12, 2016 Order. The
    water court reiterated that the Blue River water imported by Denver has a priority date
    of 1946, regardless of whether Denver imports the water after diversion in priority, or by
    32
    exchange or substitution using water released from the Williams Fork Reservoir. Thus,
    the water court concluded, water diverted from the Blue River is not subject to the 1940
    Agreement, and “Denver may reuse or successively use that water, provided such uses
    are consistent with the Blue River Decree.” The water court further ordered that the LIRF
    decree in case No. 04CW121 be modified to remove the 8.3% reduction in Denver’s
    amount of reusable LIRFs pending resolution of the issues bifurcated into case No.
    12CW05.
    ¶46   Consolidated Ditches appealed and asks this court to reverse the water court’s
    determination that the Blue River water diverted by exchange or substitution is not
    subject to the 1940 Agreement. Additional parties and amici ask this court either to
    reverse or affirm the water court’s ruling for various reasons.11 Our analysis below
    addresses the substantive arguments made by Consolidated Ditches and other parties
    regarding the application of the 1940 Agreement in this dispute. To the extent that we
    have not expressly addressed other arguments made by the parties or amici, we note that
    we have considered these arguments and found them to be either unpersuasive or
    beyond the scope of the water court’s orders being appealed.
    11 In addition to Consolidated Ditches and Denver, we received briefing from
    Opposers-Appellants Central Colorado Water Conservancy District, the City of Aurora,
    Farmers Reservoir and Irrigation Company, and Parker Water and Sanitation District, as
    well as Opposers-Appellees Northern Colorado Water Conservancy District and the State
    Engineer and Division Engineer for Water Division 1. We also received briefing from
    West Slope Amici and the City of Colorado Springs.
    33
    III. Analysis
    ¶47   As discussed above, our decision in Consolidated Ditches established that the 1940
    Agreement applies only to return flows derived from decreed water rights from Colorado
    River sources with appropriation dates before May 1, 1940; Denver may reuse or
    successively use return flows derived from sources that were appropriated or acquired
    after that date. The question before us now is whether the 1940 Agreement prevents
    Denver from reusing return flows derived from water imported through the Roberts
    Tunnel under Blue River exchange and substitution operations using Williams Fork
    Reservoir water as a replacement source.
    ¶48   As discussed above, water in the Williams Fork Reservoir physically cannot be
    delivered transmountain because it sits below the Williams Fork and Fraser River
    collection systems. The question here is whether the reuse prohibition in the 1940
    Agreement applies when the Williams Fork Reservoir water is used instead as a source
    of replacement supply in exchange and substitution operations.
    ¶49   Denver argues that the return flows at issue are derived from the Blue River
    exchange operations, which were adjudicated in the 1955 Decree and are administered
    under a 1946 priority. Denver contends that because the Blue River exchange is a source
    that was acquired after May 1, 1940, it is not subject to the 1940 Agreement.
    ¶50   Consolidated Ditches argues that the return flows are derived from the Williams
    Fork Reservoir water, which has a 1935 priority date, and therefore, these return flows
    are subject to the 1940 Agreement. Consolidated Ditches’ argument rests squarely on
    34
    application of the so-called “character of exchange rule,” the notion that water diverted
    by exchange takes on the “character” of the substitute supply. Under this view, the
    Williams Fork Reservoir substitute supply is “moved” (by legal fiction) to the upstream
    diversion point, such that the water taken at that point by exchange takes on the
    “character” of that substitute supply. In other words, under the legal fiction created by
    the exchange, the water taken at the Blue River upstream diversion point is effectively
    the Williams Fork Reservoir substitute supply water, and the reuse prohibition in the
    1940 Agreement applies to that water when it is imported through the Roberts Tunnel
    because the water’s 1935 date of appropriation predates the 1940 Agreement.
    ¶51   We disagree with Consolidated Ditches and conclude that, for purposes of the
    1940 Agreement, the water imported through the Roberts Tunnel under Blue River
    exchange and substitution operations is a source acquired by Denver after May 1, 1940.
    Accordingly, the return flows from those operations are not subject to the 1940
    Agreement, and Denver may reuse or successively use them. At the time of the 1940
    Agreement, Denver could not import water through the Roberts Tunnel by exchange (or
    otherwise). Denver’s ability to divert water from the Blue River system by exchange or
    substitution using Williams Fork Reservoir water as a substitute supply was adjudicated
    in the 1955 Decree, and the exchange is administered under a June 24, 1946 priority,
    consistent with the appropriation date of Denver’s rights in the Blue River system.
    ¶52   We further disagree with Consolidated Ditches that we must apply the “character
    of exchange rule” here. Nothing in statute mandates that water diverted by exchange
    35
    must take on the “character” of the substitute supply, and although we have
    acknowledged the concept in past cases, we have never expressly applied it or defined
    its scope. We therefore decline to adopt a mandatory character of exchange “rule” that
    applies rigidly to all exchange operations. Whatever its scope or applicability in other
    circumstances, the character of exchange principle is unnecessary here to ensure that the
    purpose of the 1940 Agreement is fulfilled or to avoid injury to Consolidated Ditches.
    Accordingly, we affirm the judgment and decree of the water court.
    A. Standard of Review
    ¶53    We review a water court’s resolution of questions of law in competing C.R.C.P. 56
    motions de novo. City & Cty. of Denver v. City of Englewood, 
    2013 CO 50
    , ¶ 15, 
    304 P.3d 1160
    , 1164; see also Select Energy Servs., L.L.C. v. K-LOW, L.L.C., 
    2017 CO 43
    , ¶ 12, 
    394 P.3d 695
    , 698 (“This court reviews a grant of summary judgment de novo, and all doubts as to
    the existence of a triable issue of fact must be resolved against the moving party.”).
    Similarly, the interpretation of a contract is a question of law we review de novo. Fed.
    Deposit Ins. Corp. v. Fisher, 
    2013 CO 5
    , ¶ 9, 
    292 P.3d 934
    , 937.
    B. Exchanges
    ¶54    We begin with a brief review of exchanges. An exchange is a water management
    practice administered by the State Engineer that allows a junior appropriator to divert
    water out of priority by introducing a substitute supply above the downstream senior
    calling right. See §§ 37-83-104, -80-120(2)–(4), C.R.S. (2018); Empire Lodge Homeowners’
    Ass’n v. Moyer, 
    39 P.3d 1139
    , 1155 (Colo. 2001). By making a sufficient substitute supply
    36
    available to the downstream senior appropriator, the junior appropriator may continue
    to divert, at its decreed point of diversion, water that it would otherwise have to allow to
    pass to the downstream diversion point of the senior calling right. Empire 
    Lodge, 39 P.3d at 1155
    . Per statute, the replacement water is provided as a substitute for the water
    diverted upstream. § 37-80-120(2)–(4). Because it is provided in lieu of the water being
    diverted upstream, the substitute supply must mimic the water at the upstream diversion
    point in terms of quality, quantity, and continuity to meet the requirements of the
    downstream calling right, without impairing the rights of others. See § 37-80-120(3)
    (requiring substituted water to be of a “quality and continuity” to meet requirements of
    senior appropriator’s use); § 37-92-305(5), C.R.S. (2018) (requiring substituted water to be
    of a “quality and quantity” to meet requirements for which senior appropriator’s water
    normally has been used). An exchange reduces the amount of water available for
    beneficial use in the specific stream reach between the upstream diversion point and the
    downstream introduction of the substitute supply, but neither increases nor decreases
    the physical supply of water. Colo. Water Conservation Bd. v. City of Central (City of Central),
    
    125 P.3d 424
    , 436 (Colo. 2005).
    ¶55    We observed in Empire Lodge that there are four critical components of an
    
    exchange. 39 P.3d at 1155
    (citing Casey S. Funk & Amy M. Cavanagh, Basic Exchange 101,
    1 U. Denv. Water L. Rev. 206, 207 (1998)). First, the source of substitute supply must be
    above the calling water right. See § 37-80-120(2) (requiring the substitute supply to be
    provided to more senior appropriators); § 37-83-104 (allowing a reservoir owner to
    37
    deliver stored water into the public stream to supply appropriations from said stream
    and to take an equal amount “higher up”); § 37-92-305(5) (“Substituted water shall be
    accepted by the senior appropriator . . . .”).    Second, the substitute supply must be
    equivalent in amount and of suitable quality to the downstream appropriator.
    § 37-80-120(3) (providing that substituted water must be of a “quality and continuity” to
    meet requirements of senior appropriator’s use); § 37-92-305(5) (“quality and quantity”).
    Third, there must be available natural flow at the point of natural upstream diversion.
    § 37-80-120(4) (providing that supplier of substitute water may take equivalent amount
    for beneficial use “to the fullest extent possible without impairing the availability of water
    lawfully divertible by others”); § 37-83-104 (allowing diversions “higher up” if no injury
    to others); § 37-92-305(5) (permitting supplier of substitute water to take equivalent
    amount at his point of diversion or storage if such water is available without impairing
    the rights of others). Fourth, the rights of others cannot be injured when implementing
    the exchange. § 37-80-120(4) (allowing supplier of substitute water to take equivalent
    amount for beneficial use “to the fullest extent possible without impairing the availability
    of water lawfully divertible by others”); § 37-83-104 (permitting appropriator to take by
    exchange “[w]hen the rights of others are not injured thereby”).
    ¶56    Although the State Engineer may allow the operation of the exchange in the
    absence of a decree confirming it, Empire 
    Lodge, 39 P.3d at 1155
    , “a practice of substitution
    or exchange may constitute an appropriative water right and may be adjudicated as any
    other water right,” City of 
    Central, 125 P.3d at 436
    . Where an exchange is adjudicated, it
    38
    receives a priority date consistent with the date it began operating, without application
    of the postponement doctrine. Empire 
    Lodge, 39 P.3d at 1155
    ; City of 
    Central, 125 P.3d at 436
    , 442 n.4. In City of Central, relying on the statutory language in section 37-80-120(4),
    we rejected the argument that water exchanges obtain priority dates only vis-à-vis other
    exchanges, rather than the entire stream system. 
    See 125 P.3d at 436
    , 442 n.4. Instead, we
    concluded that the adjudication of an exchange assigns it a priority date against the entire
    stream system like any other appropriative right. 
    Id. The priority
    date for an adjudicated
    exchange secures the appropriator’s right to operate the exchange against other
    appropriative rights on the stream system, and represents the date the appropriator
    provided adequate notice of its intent to operate an exchange and the scope of such an
    exchange. See 
    id. at 443–44.
    C. The Character of Exchange “Rule”
    ¶57    Consolidated Ditches argues that the 1940 Agreement prohibits Denver from
    reusing the return flows from Blue River exchange and substitution operations because,
    under the so-called “character of exchange rule,” the water diverted from the Blue River
    system and imported through the Roberts Tunnel takes on the “character” of the Williams
    Fork Reservoir substitute supply released under those operations. Thus, Consolidated
    Ditches argues, the return flows from water imported through the Roberts Tunnel under
    Blue River exchange and substitution operations are subject to the 1940 Agreement
    because they are derived from Williams Fork Reservoir water, which is a source that was
    appropriated prior to May 1, 1940.
    39
    ¶58    The origins of the “character of exchange rule” are somewhat of a mystery. The
    “rule” exists nowhere in our state statutes. Nothing in the many statutory provisions
    addressing exchange operations requires the water diverted upstream to take on the
    character of the downstream substitute supply. These statutory provisions instead reflect
    that the substitute supply must mimic the water taken at the upstream diversion point in
    terms of quality, quantity, and continuity to meet the requirements of the downstream
    calling right.   See § 37-80-120(3) (“Any substituted water shall be of a quality and
    continuity to meet the requirements of use to which the senior appropriation has
    normally been put.”); § 37-92-305(5) (“[S]ubstituted water shall be of a quality and
    quantity so as to meet the requirements for which the water of the senior appropriator
    has normally been used . . . .”).
    ¶59    The notion that water diverted by exchange takes on the character of the substitute
    supply seems to emanate from the view of an exchange as the equivalent of “moving”
    the substitute supply (by legal fiction, instead of an actual pump and pipeline) to the
    upstream diversion point. In other words, the water taken by exchange at the upstream
    diversion (exchange-to) point is effectively the substitute supply. This court has never
    formally endorsed this legal fiction, however.
    ¶60    Not only is the “character of exchange” principle absent from our statutes, it is
    unclear what is meant by the “character” of the substitute supply. The briefing before us
    reveals disagreement over the scope of that term, and whether it refers simply to the type
    of source (e.g., foreign, nontributary, fully consumable native water), or more broadly
    40
    encompasses benefits attached to the substitute supply (such as the right of reuse or a
    succession of uses), priority dates, decretal restrictions (such as type or place of use),
    contractual limitations, or simply “all legal characteristics.”
    ¶61    Our cases have mentioned the character of exchange principle only twice, in City
    of Thornton v. Bijou Irrigation Co., 
    926 P.2d 1
    (Colo. 1996), and Centennial Water & Sanitation
    District v. City & County of Broomfield (Centennial), 
    256 P.3d 677
    (Colo. 2011). But in neither
    case did we expressly apply the principle or hold that it functions as a mandatory “rule”
    applicable to all exchange operations. Nor did we purport to define the “character” of
    water encompassed by the concept or suggest that it applies to substitutions.
    ¶62    Our first mention of the character of exchange principle appeared in Bijou, where
    it came up twice. In that case, Thornton had acquired shares of CBT water and other
    assets from the Water Supply and Storage Company 
    (WSSC). 926 P.2d at 19
    –20, 54.
    WSSC obtained the CBT water under an Allotment Contract with the Northern Colorado
    Water Conservancy District (NCWCD). 
    Id. at 54–55.
    Under that contract, “all lands,
    facilities, and serviced areas which receive benefit from the allotment [of CBT water]
    (whether water service is provided by direct delivery, by exchange, or otherwise) shall
    be situated within the boundaries of [NCWCD].” 
    Id. at 58–59.
    Thornton proposed an
    internal ditch exchange that would pump CBT water outside the boundaries of NCWCD
    and replace it with water from Thornton’s other rights. 
    Id. at 54.
    ¶63    Thornton contended that the character of exchange principle should apply to
    permit its extra-district use of CBT water, arguing that the “substitute supply water
    41
    becomes CBT water through the ‘character of exchange’ rule.”12 
    Id. Thus, it
    argued,
    although CBT water would physically leave the boundaries of NCWCD under its
    proposed plan, the water remained in the district for purposes of legal analysis. 
    Id. ¶64 The
    water court rejected Thornton’s argument, labeling the character of exchange
    rule a “‘legal fiction’ that cannot disguise the removal of CBT water from the district.” 
    Id. at 55.
    We affirmed, holding that the proposed exchange would result in benefits to
    Thornton outside the district, a result prohibited by the contract and applicable NCWCD
    rules, regardless of whether the character of exchange rule applied. 
    Id. at 59.
    Thus, we
    concluded that “we need not discuss the applicability or validity of this rule.” 
    Id. at 60
    n.51.
    ¶65     The character of exchange principle also came up in our discussion of Thornton’s
    proposed change of certain seepage water rights to municipal uses. 
    Id. at 61.
    The seepage
    rights consisted of return flows from irrigation that relied in part on water diverted by
    exchange using CBT water rights as a source of downstream substitute supply. 
    Id. The water
    court prohibited Thornton from taking seepage water for municipal use outside
    the district to the extent that it was derived from CBT water. 
    Id. We observed
    that the
    water court “apparently applied the character of exchange rule” to classify the irrigation
    water diverted by exchange as CBT water. 
    Id. We then
    affirmed the water court’s denial
    12Under Thornton’s articulation, the CBT water “trades places” with the down-ditch
    replacement supply, such that the substitute supply takes on the character of the water
    diverted upstream and vice-versa.
    42
    of Thornton’s proposed “change of use and subsequent extra-district use of return flows
    deriving from irrigation with CBT water.” 
    Id. Looking to
    the contractual limitations on
    that water, including a provision that specifically addressed the use and reuse of seepage
    and return flows attributable to the use of CBT water, 
    id. at 61
    & n.52, we concluded that
    we could not approve Thornton’s proposed change of use and credit for return flows “to
    the extent that these flows consist of CBT water,” 
    id. at 62.
    Thus, we affirmed the trial
    court’s denial of seepage credit from CBT waters to Thornton. 
    Id. ¶66 This
    holding could be viewed as an implied application of the character of
    exchange principle to preserve contractual restrictions on a substitute supply, although
    we did not expressly rely on the principle in our reasoning. Certainly the driving factor
    in that ruling was the clear intent to keep all benefits from the CBT water within the
    district. That said, reliance on the character of exchange principle was not necessary to
    conclude that Thornton’s proposed change of use of the accrued seepage for municipal
    purposes amounted to an extra-district benefit from the use of CBT water. In other
    words, the use of CBT water as in-district replacement in the irrigation exchange would
    have produced (prohibited) benefits to Thornton outside the district regardless of
    whether the irrigation water diverted by exchange took on the character of the CBT water
    used as a substitute supply.
    ¶67   More recently, in Centennial, we stated the rule, but did not apply it, and it was not
    necessary to our holding in that 
    case. 256 P.3d at 684
    . Centennial concerned whether
    Broomfield could satisfy the “can and will” test and the “first step” requirement for its
    43
    application for conditional appropriative rights of exchange. 
    Id. at 680.
    In discussing the
    difference between a plan for augmentation and a conditional appropriative right of
    exchange, we explained:
    In contrast [to a plan for augmentation], an appropriative right of exchange
    allows a strict one-to-one diversion of upstream water in exchange for
    providing continuity with a source of substitute supply at a point
    downstream, in an amount and of a quality suitable to what would have
    been available to water users in that location. Empire 
    Lodge, 39 P.3d at 1155
    .
    The diversions at the upstream point take on the character of the water right used
    as a source of downstream substitute supply. 
    Id. Therefore, an
    operating
    exchange will reduce stream flow only in the exchange reach—i.e., the
    segment of river between the downstream source of substitute supply and
    the upstream point of diversion—and will only create a limited potential
    for injury.
    
    Id. at 684
    (emphasis added). This reference to the character of exchange principle
    appeared in a general discussion of exchanges. And importantly, our holding in that case
    did not concern the resulting characteristics of water diverted by exchange. Moreover,
    although we cited Empire 
    Lodge, 39 P.3d at 1155
    , for this articulation of the character of
    exchange principle, our discussion there focused on the “four critical elements” of an
    exchange. Thus, to the extent we relied on Empire Lodge in Centennial, we were referring
    to an exchange operator’s upstream diversions being limited by the amount and quality
    of water that the exchange operator is able to substitute downstream.
    ¶68   Later in Centennial, in rejecting Broomfield’s argument that the water court erred
    in analyzing its proposed sources of supply individually, we explained why the water
    court correctly analyzed whether each individual proposed source was non-speculative:
    Because exchanges involve a delivery of substitute supply water to the stream and
    continuity with an upstream diversion, a non-injurious diversion at the upstream
    44
    point must take on the character of the water right used as a source of downstream
    substitute supply. See Empire 
    Lodge, 39 P.3d at 1155
    . Therefore, a
    municipality’s entitlement to a conditional decree for appropriative rights
    of exchange is subject to the water court’s determination that the applicant
    intends to acquire and can and will acquire suitable sources of substitute
    supply.
    
    Centennial, 256 P.3d at 686
    (emphasis added). There, we referenced the character of
    exchange principle in the context of our conclusion that a source-by-source analysis of
    substitute supplies is required to determine whether an appropriator has fulfilled the
    “can and will” and “first step” requirements. See 
    id. Again, we
    cited Empire Lodge. 
    Id. But we
    did not actually apply the character of exchange principle in Centennial to decide
    whether a particular use of water diverted by exchange was foreclosed. See 
    id. Nor did
    we explain what is meant by the “character” of the substitute supply. See 
    id. ¶69 That
    said, we have implicitly relied on the character of exchange concept in at least
    two cases to ensure that an importer of water retains the full benefit of the reusability of
    that imported water. See § 37-82-106(1), C.R.S. (2018) (permitting importer of foreign
    water to “make a succession of uses of such water by exchange or otherwise”). In Water
    Supply & Storage Co. v. Curtis, for example, the character of exchange principle arguably
    undergirded our holding that the reusable nature of imported water used as a substitute
    supply carried through to the water stored by exchange in that case. See 
    733 P.2d 680
    , 685
    (Colo. 1987). Similarly, in City of Florence v. Board of Waterworks, we acknowledged that
    the reusability of the substitute supply (return flows attributable to foreign water) carried
    through to water stored by exchange in reservoirs. 
    793 P.2d 148
    , 149–52 (Colo. 1990).
    There, we held that the water stored by exchange could be reused or successively used to
    45
    extinction. 
    Id. at 153.
    Arguably, this result relied at least in part on a character of
    exchange principle.
    ¶70    Despite the absence of guidance from the legislature or this court, the “character
    of exchange” concept appears to have emerged as an unofficial, yet widespread,
    permissive practice recognized by the State Engineer. See Ans. Br. Appellees State
    Engineer & Division Engineer, Water Division 1, at 29 (“As the administrators of
    exchanges, the Engineers know of no mandatory character-of-exchange rule, but have
    regularly permitted the water diverted upstream to take on the character of the substitute
    supply as necessary to accomplish an appropriator’s non-speculative purposes,
    consistent with water court decrees, and without impairment to the rights of others.”).
    ¶71    We conclude that, at a minimum, the character of exchange concept reflects the
    statutory requirements applicable to a substitute supply. That is, an exchange operator’s
    upstream diversions are limited by the amount and quality of water the operator is able
    to substitute downstream, which avoids injury by ensuring that the downstream senior
    appropriator receives water comparable to what would have been available had the
    upstream diversion not occurred. Beyond that, the character of exchange concept serves
    as a flexible tool to preserve the fully reusable character of transmountain water used as
    a substitute supply in exchanges, see § 37-82-106(1), consistent with Colorado’s
    longstanding water management policy of maximizing the beneficial use of waters in the
    state, see § 37-92-102(1)(a), C.R.S. (2018); Frees v. Tidd, 
    349 P.3d 259
    , 263 (Colo. 2015). It
    also functions as an administrative tool for the State and Division Engineers to accurately
    46
    account for water stored in reservoirs throughout the state. And it may, in some
    instances, serve to preserve decretal limitations or contractual restrictions on a substitute
    supply. See 
    Bijou, 926 P.2d at 61
    –62.
    ¶72    But in the absence of legislative guidance, we decline to hold that the character of
    exchange concept functions as a mandatory rule that rigidly applies to all exchange
    operations, or even that it necessarily always encompasses “all legal characteristics” of
    the substitute supply. Such a mandatory rule would neither cultivate flexibility nor
    optimize the beneficial use of the state’s waters.
    D. Water Imported Under Blue River Exchange and
    Substitution Operations Is Not Subject to the 1940 Agreement
    ¶73    Turning now to the present dispute, we conclude that the water court correctly
    determined that the 1940 Agreement does not apply to prohibit Denver from reusing or
    successively using water imported under Blue River exchange and substitution
    operations using Williams Fork Reservoir water as a substitute supply.
    ¶74    Importations under Blue River exchange and substitution operations could not
    occur without an upstream diversion (exchange-to) point. However, at the time it entered
    the 1940 Agreement, no upstream diversion point existed; Denver had not shown an
    intent to divert water from the Blue River system at that time (by exchange or otherwise).
    See N. Colo. Water Conservancy 
    Dist., 276 P.2d at 998
    , 1003 (rejecting Denver’s argument to
    treat the Blue River project, the Williams Fork project, and the Fraser River project as
    units of a single project, given that the Blue River involves a separate stream and tunnel
    system; concluding that “Denver had no fixed and definite plan and no definite point of
    47
    diversion” on the Blue River prior to 1946). Denver’s ability to divert water from the Blue
    River system by exchange or substitution using Williams Fork Reservoir water as a source
    of substitute supply was first adjudicated in 1955, and the exchange is administered
    under a June 24, 1946 priority, consistent with the appropriation date of Denver’s rights
    in the Blue River system—the date construction on that transmountain system
    commenced. Thus, we conclude that for purposes of the 1940 Agreement, the water
    imported through the Roberts Tunnel under Blue River exchange and substitution
    operations is a source acquired by Denver after May 1, 1940. Accordingly, the return
    flows from those operations are not subject to the 1940 Agreement and Denver may reuse
    or successively use them.
    ¶75   We disagree with Consolidated Ditches that the so-called “character of exchange
    rule” requires a different result here. Although we acknowledge that some of our cases
    have implicitly applied the character of exchange principle to preserve the reusability of
    transmountain effluent in exchange plans, here, Consolidated Ditches seeks to apply it to
    render the return flows from imported water non-reusable. And to the extent that
    Consolidated Ditches seeks application of the character of exchange rule to preserve what
    it perceives to be a contractual restriction on the Williams Fork Reservoir water, we
    conclude that the application of the character of exchange principle here is not necessary
    to fulfill the primary purpose of the 1940 Agreement, which was to replace seepage and
    evaporation losses from Denver’s three streambed reservoirs. As described above, that
    purpose is already more than met by importations through the Moffat Tunnel of Fraser
    48
    River and Williams Fork River water under their 1921 priorities. See Consolidated 
    Ditches, 807 P.2d at 36
    –37. Indeed, applying the principle here would disserve the core purpose
    of the Agreement’s restrictions on reuse, in that it would exacerbate the already growing
    disparity we acknowledged in Consolidated Ditches when we drew the line at sources with
    appropriation dates before May 1, 1940.
    ¶76    Consolidated Ditches contends that it does not make sense to “count” Williams
    Fork Reservoir water for purposes of the 1940 Agreement when it is imported through
    the Moffat Tunnel, but not when it is imported through the Roberts Tunnel. But this
    argument again rests on the character of exchange principle; it assumes that the water
    imported through the Moffat Tunnel through exchange operations on the Williams Fork
    River or Fraser River takes on the character of the Williams Fork Reservoir substitute
    supply and that return flows from such water are subject to the 1940 Agreement only by
    virtue of the Williams Fork Reservoir’s 1935 priority date.
    ¶77    However, our analysis and holding in Consolidated Ditches did not hinge on any
    implicit application of the character of exchange concept. We did not discuss exchange
    operations using Williams Fork Reservoir water as a substitute supply in that opinion. If
    anything, our descriptions of the water imported through the Moffat Tunnel (from the
    Williams Fork River and Fraser River) focused exclusively on the 1921 appropriation
    dates of those sources. See 
    id. at 26.
    In other words, even to the extent that Moffat Tunnel
    water discussed in that case included water diverted by exchange (and our opinion is
    silent on this point), we did not rely on the 1935 appropriation date of the Williams Fork
    49
    Reservoir substitute supply to conclude that such water was subject to the 1940
    Agreement. Nor was it necessary to rely on the character of exchange to conclude that
    return flows from water imported through the Moffat Tunnel were subject to the 1940
    Agreement. Even without applying the character of exchange principle, water imported
    from the Fraser and Williams Fork River by exchange would be subject to the 1940
    Agreement because those sources had appropriation dates prior to May 1, 1940.
    ¶78    We drew a line in Consolidated Ditches at sources with appropriation dates prior to
    May 1, 1940, recognizing the rough balance achieved by that line.             Under the
    circumstances here, and considering the core purpose of the 1940 Agreement, which is
    already more than met by importations through the Moffat Tunnel, we decline to apply
    the character of exchange principle to exacerbate an already growing disparity in
    Consolidated Ditches’ favor that it is reasonable to assume the parties to the Agreement
    never intended. There is no suggestion that Consolidated Ditches’ interests in ensuring
    the offset of evaporation losses will not be met if Denver is permitted to reuse return
    flows from the Blue River exchange. To the extent that Consolidated Ditches suggests it
    will be “injured” by not getting the benefit of its bargain under the Agreement, we again
    emphasize that the core problem sought to be resolved was the dispute over seepage and
    evaporation losses. Consolidated Ditches’ interests in having those losses fully replaced
    are protected both by ongoing importations through the Moffat Tunnel, and by the State
    Engineer’s authority to order releases of water from reservoirs to compensate for
    evaporation losses if necessary. See § 37-84-117(5).
    50
    ¶79    There is also no suggestion that Denver will use the Blue River system exchange
    to decrease the amount of Fraser River and Williams Fork River water it imports, thereby
    reducing the amount of water subject to the 1940 agreement. That said, we agree with
    the water court that the ditch companies may seek relief from the State Engineer and file
    an appropriate action if they believe that Denver’s diversions, or lack of diversions, from
    certain western slope sources are causing injury to their water rights.
    IV. Conclusion
    ¶80    We reaffirm that the primary purpose of the 1940 Agreement was to address the
    problem of evaporation losses resulting from three of Denver’s reservoirs on the eastern
    slope, and that the 1940 Agreement applies only to water rights appropriated by Denver
    on or before May 1, 1940. Because the water imported through the Roberts Tunnel under
    Blue River exchange and substitution operations is a source acquired by Denver after
    May 1, 1940, we conclude that the resulting return flows are not subject to the 1940
    Agreement and Denver may reuse and successively use them. Accordingly, we affirm
    the judgment and decree of the water court.
    51