delivered the opinion of the court:
Defendants, George Kissner and Glen Weaver, d/b/a Kissner & Weaver Farm Implement Company, and Owen Rainwater, constructed earthen levees on their property which obstructed the natural flow of water and thereby caused injury to adjacent farmland owned by plaintiff, Norman Meyers. More than five years after the levees were constructed, plaintiff commenced this action against defendants in the circuit court of Wayne County to obtain both injunctive relief and damages. After finding that plaintiff’s damage claim was time barred under section 13 — 205 of the Code of Civil Procedure (Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205), the circuit court issued an injunction requiring that a portion of the levees be modified. Plaintiff now appeals. Defendants have all cross-appealed. For the reasons which follow, we reverse and remand with directions to enter judgment in favor of defendants.
The record before us shows that plaintiff and defendants own adjacent parcels of farmland along the Skillet Fork River in Orel Township, Wayne County. The river meanders wildly through the area, making it difficult for us to present a concise description of the relationship between the various tracts of land involved. For the purpose of this discussion, however, we think it sufficient to say that, generally speaking, plaintiff’s land lies downstream from the parcels owned *139by defendants. On the other hand, most of defendants’ property lies south of the river’s bank, while most of the land owned by plaintiff lies to the north. Although the question was disputed, evidence was presented which indicated that the topography is such that water falling upon the area would, if unobstructed, drain naturally in a southerly or southeasterly direction.
In 1977, defendants Kissner and Weaver erected a large earthen levee on their property. The levee began near the middle of their land next to a small body of water known as Horse Creek, extended to an area just short of the confluence of Horse Creek and the Skillet Fork River, then continued along the southern bank of the Skillet Fork River until it reached the eastern boundary of their property. Prior to this time, the Skillet Fork River was in the process of cutting a new channel in a southerly or southeasterly direction. There is no dispute that the purpose of the levee was to contain the water and to prevent the river from flooding across their ground.
The year after Kissner and Weaver finished their levee, defendant Rainwater began construction to extend the levee along that portion of the southern bank of the river which ran through his property. Construction of the Rainwater section was completed in the middle of 1979. Although the Illinois Department of Transportation, Division of Waterways, did not issue permits for the construction of any part of defendants’ levees, the evidence showed that the levees were not subject to the State’s permit requirements.
As they were intended to do, the levees obstructed the natural drainage pattern. This, in turn, caused injury to plaintiff’s property, which became noticeable almost immediately. Testimony established that after the levees were completed, the river channel became deeper and wider, and the water current became stronger. Increased erosion, washing and scouring of plaintiff’s land took place and, as a result, the quality of plaintiff’s soil deteriorated and the market value of his property declined. In 1986, plaintiff ultimately decided to bring legal action against defendants to obtain redress for these injuries. Plaintiff’s complaint, as amended, was in two counts. Both counts were based on the same factual allegations. They differed only in the type of relief requested. Count I sought a mandatory injunction to require defendants to remove the levee, while count II prayed for money damages.
In their answers to plaintiff’s complaint, defendants raised as an affirmative defense that plaintiff’s cause of action was untimely under the applicable statute of limitations. They subsequently amended their answers to raise as an additional affirmative defense that count I of *140plaintiff’s complaint, which sought injunctive relief, was also barred by the doctrine of laches. In addition, defendant Rainwater filed a counterclaim for contribution against defendants Kissner and Weaver pursuant to the Contribution Among Joint Tortfeasors Act (Ill. Rev. Stat. 1985, ch. 70, pars. 301 through 305).
Defendants each moved for summary judgment as to count II of plaintiff’s complaint, which sought money damages. The sole basis for defendants’ motions was that plaintiff had not filed suit until more than five years after the earthen levees had been constructed and that the suit was therefore barred by section 13 — 205 of the Code of Civil Procedure (Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205), the statute of limitations applicable to actions to recover damages for injury to real property. Defendants’ motions were granted, and judgment was entered by the court in favor of defendants and against plaintiff on count II. On a motion by Kissner and Weaver, the court also dismissed Rainwater’s counterclaim for contribution.
After Kissner, Weaver, and Rainwater unsuccessfully attempted to obtain summary judgment in their favor on count I of plaintiff’s complaint, the cause proceeded to trial before the court, sitting without a jury, solely on the question of whether plaintiff was entitled to the injunctive relief he had requested. Following the trial, at which extensive testimony was adduced, the court found that plaintiff had proved the allegations of count I and that defendants’ levees, as constructed, improperly obstructed the natural water flow and caused injury to plaintiff’s land. The court further found that defendants had failed to establish that plaintiff was guilty of laches in asserting his claim. The court determined, however, that additional evidence was necessary in order to assess the extent of injunctive relief which should be granted. A subsequent hearing was therefore held on this question. Based on the evidence presented at the hearing, the circuit court determined that complete removal of the levees was not required. Instead, it simply ordered certain modifications to that portion of the levee located on Owen Rainwater’s property. From this judgment, plaintiff appeals and defendants cross-appeal.
On this appeal, plaintiff contends that the circuit court committed reversible error when it reopened the case sua sponte to take additional evidence on possible alternative remedies. Plaintiff further contends that the circuit court’s judgment is infirm insofar as it granted plaintiff less than the full injunctive relief he requested. On his cross-appeal, defendant Rainwater asserts that the circuit court’s judgment was contrary to the manifest weight of the evidence and that even the limited injunctive relief granted should be set aside. Defendants *141Kissner and Weaver make no similar claim. To the contrary, they argue that, if the merits of the case are reached, the circuit court’s judgment should be sustained as it is. All defendants, however, assert that the circuit court should have granted judgment in their favor on the grounds that count I was time barred under either the statute of limitations or the doctrine of laches. Defendant Rainwater also argues, in the alternative, that the circuit court erred in dismissing his contribution counterclaim against Kissner and Weaver.
Of these various issues, the only one which requires discussion is defendants’ claim that count I was untimely, for we believe that it is dispositive of this appeal. As a preliminary matter, we note that there is no dispute that count II of plaintiff’s complaint, which sought money damages, was subject to the five-year limitations period provided in section 13 — 205 of the Code of Civil Procedure (Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205). (Firestone v. Fritz (1983), 119 Ill. App. 3d 685, 687, 456 N.E.2d 904, 906-07.) That statute expressly •provides that a plaintiff must bring a cause of action to recover damages for an injury done to real property within five years “after the cause of action accrued.” Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205.
Where, as here, the injury complained of consists of the unnatural overflow of water over the plaintiff’s property, the question of when a cause of action for that injury accrues depends on the cause of the overflow. When a structure is placed on dominant land which unreasonably increases the flow of water onto the servient land and the structure is not necessarily injurious, but may be used in a way which may or may not result in injury, the cause of action does not accrue until the use of the structure causes injury. (Gass v. Metro-East Sanitary District (1989), 186 Ill. App. 3d 1077, 1084, 542 N.E.2d 1229, 1234.) On the other hand, where the injury occurs as a result of the construction or the proper operation of a structure which is permanent and which is necessarily injurious by reason of its construction, then the injury itself is considered permanent, and the limitations period runs from the date that the construction was completed, or from the time when the plaintiff knew or should have known of his injury and its cause. (186 Ill. App. 3d at 1084-85, 542 N.E.2d at 1234-35.) It has been held, moreover, that the fact that flooding may be uncertain in time, duration, and extent does not prevent an improvement, which displays obvious potential to cause an unnatural overflow upon completion, from constituting an immediate, permanent injury. Firestone v. Fritz, 119 Ill. App. 3d at 688, 456 N.E.2d at 907.
In this case, evidence was presented which would support a finding that the offending levees were permanent and that they were *142“necessarily injurious by reason of [their] construction.” According to the evidence, there was no possibility that the levees could have been used in a way that was not injurious to plaintiffs farmland. Their very reason for existence was to block the Skillet Fork River as it was beginning to shift its channel southward across defendants’ property, to contain the water running through the river, and to prevent the river from flooding their property. Once the natural drainage pattern was obstructed in this way, the water flow had to go somewhere else, and that was upon plaintiff’s property. According to the record, the levees caused the velocity of the river to increase and the channel of the river to grow deeper and wider, resulting in increased erosion, washing, and scouring of plaintiff’s soil.
Under the principles cited above, the limitations period therefore ran from the time of completion of construction of the levees or, at most, from the time when plaintiff knew or should have known of his injury and its cause. There is no dispute that the section of the levee constructed by Kissner and Weaver was completed in 1977 and that the construction of the portion of the levee belonging to Rainwater concluded in 1979. There is also no question that plaintiff realized that these levees were causing injury to his property shortly after they were completed and that this discovery was made more than five years prior to the time when plaintiff finally decided to file suit in 1986. The circuit court therefore concluded that plaintiff’s claim for money damages was time barred under section 13 — 205 (111. Rev. Stat. 1987, ch. 110, par. 13 — 205), thus entitling defendants to summary judgment on count II of his complaint.
Plaintiff has not appealed the circuit court’s entry of summary judgment against him on count II and does not now attempt to dispute that his damage claim was untimely. Plaintiff contends, however, that his claim for injunctive relief is not subject to the same five-year limitations period, but is limited instead only by the period necessary for a servient landowner to establish a prescriptive right to obstruct the natural drainage flow and thereby cause water to overflow upon the property of a dominant owner. According to plaintiff, that period is 20 years. Plaintiff asserts that because the 20-year period had not yet run here, he was entitled to bring suit to enjoin the obstruction at any time. Although there is some force to this argument, we do not believe that it can withstand careful scrutiny.
Plaintiff is correct that a servient landowner who erects a levee or other barrier which obstructs the natural drainage of surface waters and causes those waters to back up upon the property of a dominant landowner may acquire a right to continue the obstruction if *143certain conditions are met. This right, when it exists, is in the nature of a prescriptive easement. (Montgomery v. Downey (1959), 17 Ill. 2d 451, 458, 162 N.E.2d 6, 10-11.) To establish such a right, the servient owner must show that the invasion caused by the obstruction, i.e., the overflow or flooding, took place with the knowledge and acquiescence of the dominant landowner; that it was both adverse and uninterrupted; and that it occurred for the full prescriptive period, which has historically been set at 20 years. (Nelson v. Gundlock (1983), 120 Ill. App. 3d 117, 119, 457 N.E .2d 1052, 1053; Wills v. Babb (1906), 222 Ill. 95, 106, 78 N.E. 42, 44.) This traditional 20-year prescriptive period is a product of the common law (see Chicago & Northwestern Ry. Co. v. Hoag (1878), 90 Ill. 339, 348-49), and appears to have been adopted, by analogy, from the statutory limitations period applicable to the acquisition of title to land by adverse possession (see Roller v. Logan Landfill, Inc. (1974), 16 Ill. App. 3d 1046, 1052, 307 N.E.2d 424, 429; 28 C.J.S. Easements §16, at 659 (1941)).
Plaintiff reasons that because the 20-year period governs the creation of a prescriptive right to obstruct the natural flow of surface water, it must also serve as the governing period of limitation for actions by a dominant landowner against servient owners to challenge such obstructions. We disagree. A threshold problem with such a rule is that if it applies to an action by a dominant landowner for equitable relief, there is no reason it should not also apply to an action by a dominant landowner for damages. The defense of easement by prescription has, after all, been equally available in actions at law for damages as in suits in equity.
The historic availability of the defense in damage actions is well illustrated by Chicago & Northwestern Ry. Co. v. Hoag (1878), 90 Ill. 339, 348-49, one of the earliest decisions by our supreme court to discuss the right of a landowner to obtain a prescriptive easement to cast water upon an adjoining owner’s property. There, the landowner suffering the overflow of water sought money damages only. No injunction or other equitable relief was requested. Yet, the court’s disposition leaves no doubt that had a prescriptive easement been established, the plaintiff landowner’s action would have been barred.
The reason this creates a problem is that the legislature has determined, through enactment of section 13 — 205 of the Code of Civil Procedure (Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205) and its predecessor provisions, that actions for damages resulting from injury to real property must now be brought within five years of when the cause of action accrues. If plaintiff’s theory were correct, this five-year limitations period would therefore be reduced to a nullity.
*144To avoid this problem, plaintiff would evidently have us treat such damage actions as a limited exception to the 20-year common law rule. As support for this theory, plaintiff relies on the fact that, in the context of actions for injury to real property, the language of section 13 — 205 of the Code (Ill. Rev. Stat. 1985, ch. 110, par. 13 — 205) specifically refers only to recovery of damages. Claims for equitable relief are not mentioned. This omission, however, does not have the significance plaintiff would suggest.
As a general rule, suits in equity are not subject to statutory limitations periods. Technically, they are governed instead by laches. (Trustees of Schools v. American Surety Co. (1940), 307 Ill. App. 398, 406, 30 N.E.2d 513, 517.) Hence, one would not normally expect them to be expressly included in the statute setting the limitations period. This does not mean, however, that same period set forth in the statute does not apply with equal force to corresponding suits in equity. To the contrary, the law is well established that “in fixing the period in which equitable rights and claims will be barred by laches, equity follows the law, and generally courts of equity will adopt the statute of limitations period.” (Brown v. Goodman (1986), 147 Ill. App. 3d 935, 941, 498 N.E.2d 854, 858.) Accordingly, where a claim for equitable relief is not brought until after the limitations period for the corresponding legal action has expired, it too will be time barred, even if the delay in filing suit has caused no prejudice to the defendant. 147 Ill. App. 3d at 941, 498 N.E.2d at 858; Schlossberg v. Corrington (1980), 80 Ill. App. 3d 860, 864-65, 400 N.E.2d 73, 76.
We fail to see how any other rule could be justified where, as here, the legal and equitable claims are based on the same basic set of facts, charge the same wrongful conduct, and involve the same permanent injury. If separate limitations periods were available, as plaintiff urges, a litigant whose damage action had been dismissed for failure to comply with the requisite five-year limitations period could simply modify his pleadings to include a prayer for injunctive relief, delete his request for money damages, and bring an entirely new action anytime he wanted up to expiration of the 20-year period. This, however, could raise serious res judicata problems.
Under the doctrine of res judicata, a final judgment on the merits by a court of competent jurisdiction constitutes an absolute bar to any subsequent action involving the same claim, demand, or cause of action. (Page v. Illinois Central Gulf R.R. (1987), 162 Ill. App. 3d 744, 746, 516 N.E.2d 431, 432-33.) For purposes of the doctrine, the dismissal of a claim on statute of limitations grounds constitutes such a final judgment on the merits. (Sankey Brothers, Inc. v. Guilliams *145(1987), 152 Ill. App. 3d 393, 398, 504 N.E.2d 534, 538.) That equitable relief was not sought in the original action will not prevent the doctrine from operating, for res judicata extends not only to all matters which were actually decided, but also to all matters which could have been raised or determined. Moreover, even though a single group of operative facts may give rise to the assertion of different types of relief, or different theories of relief, it is still a single cause of action that exists. (Page v. Illinois Gulf Central R.R., 162 Ill. App. 3d at 746, 516 N.E.2d at 433.) Accordingly, it has been recognized that, under the doctrine, an action in law can bar a subsequent suit in equity, or vice versa. (Hagee v. City of Evanston (7th Cir. 1984), 729 F.2d 510, 515 n.10 (applying Illinois law).) The theory advanced by plaintiff fails to account for these principles.
We recognize that the courts of Illinois have not spoken with a single voice on when res judicata comes into play (see Best Coin-Op, Inc. v. Paul F. Ilg Supply Co. (1989), 189 Ill. App. 3d 638, 652, 545 N.E.2d 481, 490), and the doctrine is easier to state than to apply. Even if the doctrine were inapplicable, however, plaintiff’s argument for separate limitations periods would nevertheless offend the public policy against the splitting of claims or causes of action.
The rule against claim splitting, which is closely related to the doctrine of res judicata, has developed in order to ensure that litigation will come to an end and that no person will be unnecessarily harassed with a multiplicity of lawsuits. That rule provides that where a demand or right of action is in its nature entire and indivisible, it cannot be split up into several causes of action and be made the basis of many separate suits. Rather, the law requires that both in law and in equity a plaintiff must present all grounds of recovery he may have. (Best Coin-Op, Inc. v. Paul F. Ilg Supply Co., 189 Ill. App. 3d at 657, 545 N.E.2d at 493.) As the example given above illustrates, however, plaintiff’s theory would effectively jettison this requirement where, as here, a single, permanent injury has been sustained.
Given these problems, we must conclude that in cases such as this, equity must indeed follow the law. Accordingly, where, as here, an obstruction to the natural flow of water is permanent in nature, all actions to obtain redress for permanent injury to real property caused by such obstructions must be commenced within the five-year period specified by section 13 — 205 (Ill. Rev. Stat. 1985, ch. 110, par. 13— 205), whether the relief sought consists of money damages or a mandatory injunction to require that the obstruction be removed.
This holding is in no way inconsistent with the 20-year period recognized at common law for the establishment of a prescriptive *146easement. That period remains. Until the requisite 20 years have elapsed, a servient landowner’s obstruction of the natural water flow will still not ripen into a prescriptive easement. Correspondingly, the dominant landowner will retain his right to have the natural water flow kept free from obstruction. If the obstruction and attendant injury are permanent in nature, however, the dominant landowner will simply be barred from seeking legal or equitable relief for injury to his property caused by the obstruction once more than five years have elapsed since the cause of action accrued.
For a landowner to thus be left with a right which can no longer be enforced is not as anomalous as it may seem. Under the law of Illinois, statutes of limitation simply limit the time within which an action must be brought or remedies must be enforced. (La Pine Scientific Co. v. Lenchos (1981), 95 Ill. App. 3d 955, 958, 420 N.E.2d 655, 658.) They are therefore generally considered to affect only a party’s remedy and do not alter substantive rights. (Lambert v. Village of Summit (1982), 104 Ill. App. 3d 1034, 1040, 433 N.E.2d 1016, 1021.) As a result, being left with an unenforceable right is inherent whenever a limitations period operates to bar a claim. (See, e.g., Fleming v. Yeazel (1942), 379 Ill. 343, 345-46, 40 N.E.2d 507, 508 (limitations statute does not extinguish debt, but merely eliminates remedy for its enforcement).) The situation here is no different.
We note, moreover, that where an offending obstruction is not necessarily injurious and the injury alleged is not permanent, the continued viability of the 20-year prescriptive period may have much more tangible consequences. As we have already explained, the cause of action will accrue and the limitations period will begin to run in such a case from the date of the last overflow. By the time the last overflow occurs, however, the flooding of the dominant owner’s property may have been going on for 20 years. Thus, even if the dominant landowner brings suit within five years of the latest overflow, and his remedies for that injury are not barred by the limitations period, his claim may still be defeated if, by the time suit is brought, the 20-year prescriptive period has elapsed and all the other elements necessary to establish a prescriptive easement have been established.
In any case, because the injury here was permanent and because plaintiff’s claim for injunctive relief in count I was not brought until more than five years after that claim accrued, the claim is untimely and should have been dismissed. Accordingly, the judgment of the circuit court of Wayne County is reversed, and the cause is remanded with directions to enter judgment in favor of defendants and against plaintiff on count I of plaintiff’s complaint. In view of this disposition, *147we need not reach defendant Rainwater’s alternative argument that the circuit court erred in dismissing his counterclaim for contribution.
Reversed and remanded with directions.