I concur in the majority opinion insofar as it holds that the judgment of the trial court, upholding the Board’s order of determination, must be reversed. I agree that although the subject provisions of the Water Code should not be interpreted to permit the Board to altogether extinguish the presently unused portion of a riparian right, they may be interpreted in a manner consistent with the relevant constitutional provision (Cal. Const., art. X, § 2; formerly art. XIV, § 3) to permit the Board to undertake a present quantification of the right in order to bring about certainty and thereby promote the efficient and beneficial use of the water resources of this state. I do not agree, however, that in the course of such a determination the Board has the power to fix such a right at the level of its present user and “determine that the future riparian right shall have a lower priority than any uses of water [the Board] authorizes before the riparian in fact attempts to exercise his right.” {Ante, at p. 359.) In my view the exercise of such a power would be plainly inconsistent with the provisions of article X, section 2, of our state Constitution; the considerations which have led the majority to interpret the relevant Water Code provisions to preclude the extinguishment of the unused portion of a riparian right also demand that the same provisions be read to preclude the procedure here approved. I conclude, in short, that in permitting the Board to assign less than riparian status to the unused portion of a riparian right, the majority has essentially approved the extinguishment of that portion of the right—and thereby has reached a result inconsistent with its fundamental holding and the clear command of the Constitution.
Article X, section 2 of our Constitution provides as here relevant: “The right to, water or to the use or flow of water in or from any natural stream *367or water course in this State is and shall be limited to such water as shall be reasonably required for the beneficial use to be served, and such right does not and shall not extend to the waste or unreasonable use or unreasonable method of use or unreasonable method of diversion of water. Riparian rights in a stream or water course attach to, but to no more than [,] so much of the flow thereof as may be required or used consistently with this section, for the purposes for which such lands are, or may be made adaptable, in view of such reasonable and beneficial uses; provided, however, that nothing herein contained shall be construed as depriving any riparian owner of the reasonable use of water of the stream to which the owner’s land is riparian under reasonable methods of diversion and use, . . .” (Italics added.) In my view this language, which is declared in the same constitutional provision to be self-executing, establishes two basic principles; (1) No right, whether riparian or otherwise, to the use of water in a natural stream or water course permits the unreasonable use of such water or the use of an amount greater than is required for beneficial uses. (2) A riparian right attaches to that amount of water which may be reasonably required for such beneficial uses as the riparian’s land is presently or may in the future be made adaptable. Thus the constitutional provision both places restrictions on present user and establishes the scope of the riparian’s entire right, looking in the latter respect to both present and future user.
I agree with the majority that the Legislature, in setting up a procedure for statutory adjudication of rights to water in a stream system, has acted in a manner consistent with these constitutional principles. I also agree that in the course of such a proceeding the Board is empowered to determine the nature and scope of all rights to water in a given stream system, whether riparian or otherwise. (See Wat. Code, §§ 2501, 2769.) This, in my view, is in no way inconsistent with the constitutional provision. I do not agree, however, that if the Board elects (see § 2501) to include riparian rights within its determination, it may act in such a manner as to effectively deny full riparian status and priority to the presently unused portion of any riparian right. The majority, in authorizing this result, reads the relevant legislation more broadly than the Constitution will permit.
Water Code section 2769 indeed provides that the decree of determination “shall in every case declare as to the water right adjudged to each party, the priority, amount, season of use, purpose of use, point of diversion, and place of use of the water; . . .” (Italics added.) The majority conclude, presumably on the basis of this language, that “the *368Board is authorized to decide that an unexercised riparian claim loses its priority with respect to all rights currently being exercised” and that, to avoid harmful uncertainty, “the Board may also determine that the future riparian right shall have a lower priority than any uses of water [including appropriative uses] it authorizes before the riparian in fact attempts to exercise his right.” (Ante, at p. 359.) When, we are told, the riparian at some future time proposes to exercise the portion of his right which has been thus “prioritized,” the Board is to evaluate his proposed use “in the context of other proposed uses of water in the stream system, and to determine whether the riparian use should be permitted in light of the state’s interest in promoting the most efficient and beneficial use of state waters.” (Ante, at p. 359, fn. 15.) In making this determination, the majority states, “the Board may not grant the unexercised riparian claim a priority with respect to existing rights that is higher than it granted at the time the decree became final.” (Id.)
In my view the foregoing has the obvious effect of downgrading the unused portion of a riparian right to less than riparian status. The riparian, when and if at some future time he determines to utilize some portion of his land which had previously remained unused, or to modify existing uses on his land, will be required to demonstrate to the Board not only that the amount of water claimed is “reasonably required for the beneficial use” he proposes (Cal. Const., art. X, § 2) but also that the proposed use, viewed in “the context of other proposed uses of water in the stream system, . . . should be permitted in light of the state’s interest in promoting the most efficient and beneficial use of state waters.” {Ante, at p. 359, fn. 15.) At this point, then, the riparian will stand on the same footing as the nonriparian. His unused riparian right, insofar as it occupies the preferred riparian status contemplated by the Constitution, will have been effectively extinguished. This, in my view, the Constitution will not permit.
I share the majority’s concern—and that of the Board—over the severe problems of uncertainty caused by “dormant” riparian rights. As pointed out by the Governor’s commission in its recent final report, such uncertainty not only hampers the local and statewide management and supervision of water uses but has historically resulted in recurrent and costly litigation. (Governor’s Com. to Review Cal. Water Rights Law, Final Rep. (Dec. 1978) pp. 21-25.) Clearly one means of avoiding this uncertainty is through the unified statutory adjudication procedure contemplated by section 2500 et seq. of the Water Code, whereby the Board is empowered to “determine ... all rights to water of a stream *369system whether based upon appropriation, riparian right, or other basis of right.” (§ 2501; italics added.) Insofar as this procedure contemplates a present quantification of all such rights, I perceive no constitutional impediment to it. Thus if the Board in its wisdom concludes that its determination shall include riparian as well as other rights, it may in my view undertake proceedings directed to this end. Insofar as any particular riparian right is concerned, however, the Board may not in my opinion undertake such a present quantification unless it is able to determine, on the basis of an adequate record, the amount of water that “may be required or used ... for the [reasonable and beneficial] purposes for which such lands are, or may be made adaptable. . . .” (Cal. Const., art. X, § 2.)
We stated in Tulare Dist. v. Lindsay-Strathmore Dist. (1935) 3 Cal.2d 489 [45 P.2d 972], in the context of a private adjudication, that the present determination of the scope and quantity of a riparian right must be limited to the extent of its present user, the trial court retaining jurisdiction to determine whether any proposed future riparian use is a reasonable beneficial use. “As to such future or prospective reasonable beneficial uses,” we observed “it is quite obvious that the quantity of water so required for such uses cannot be fixed in amount until the need for such use arises.” (Id., at p. 525.) This language, as I read it, does not represent constitutional interpretation; rather it is grounded in purely practical considerations. It may well be that a court, faced with a water rights dispute among competing litigants, riparian and otherwise, should conclude for reasons of institutional competence that a consideration of reasonable future uses lies beyond the proper scope of its inquiry. This does not necessarily mean, I would suggest, that the State Water Resources Control Board, in the context of a comprehensive proceeding directed to the determination of all rights to water in a stream system, must be similarly limited. The issue is a practical one: whether it be feasible or possible to develop evidence, opinion and otherwise, which would reasonably support a finding justifying present quantification of a riparian right in both its present and future aspects. The future aspect of that right, as described in the Constitution, includes that amount of water reasonably required for any reasonable and beneficial use to which the subject land may properly be made adaptable. In many cases it may well be possible, in light of evidence of historical and reasonably foreseeable future uses, to arrive at a reasonably accurate estimate of this amount. In other cases, owing to great diversity in foreseeable land use patterns in a given area, it may not be. In any event it is my view that the Constitution, as implemented by those provisions of the Water Code setting up the *370procedure of statutory adjudication, permits the Board to undertake a determination of this kind in all cases in which it considers itself equipped to do so. Whether in any particular case the evidence before the Board supports the determination made is of course a matter for the courts.
It is clear that present quantification of water rights, to the extent that it may be achieved with respect to any particular stream system, will operate to foster that certainty necessary to the efficient administration and use of the waters within that system. To the extent that riparian as well as other rights can be quantified, the riparian owner and other interested parties will be made aware of the total amount of water comprehended within his right. The amount of any particular right that remains “dormant” under present use will become a sum certain, subject to negotiation and disposal by the owner to appropriators and other nonriparian users. There may of course be cases where a riparian owner of a quantified right may choose to retain the whole or a significant part of his entitlement, allowing the unused and untransferred portion to remain “dormant,” but such cases will become rarer as such owners, assessing the present and projected uses of their lands, come to view their water right as a disposable asset of certain scope.
I conclude for the foregoing reasons that the Board, in the context of a statutory adjudication of rights to water within a given stream system, has the power to presently quantify all such rights—including the future aspect of riparian rights. The Constitution, as I read it, offers no obstacle to such a procedure, and the relevant statutes clearly contemplate it. What the Constitution does not permit, in my view, is the actual or virtual extinguishment of the future aspect of riparian rights—either through outright extinction or through the device, adopted by the majority, of consigning that aspect of the right to some lesser status, to be administered by the Board on the same basis as all other rights in the stream when the riparian proposes to use it. Under our Constitution the riparian right, in both its present and future aspects, is primary in priority. The majority, in allowing the future aspect of the right to be denigrated to a lower status, does so in the face of a clear constitutional command to the contrary.
I would reverse the judgment and remand to the trial court for further proceedings in light of the views herein expressed.
Appellant’s petition for a rehearing was denied October 25, 1979. Clark, J., Richardson, J., and Manuel, J., were of the opinion that the petition should be granted.