Tenaris Bay City Inc. v. Ellisor: Reaffirming But-For Causation and Expert Proof in Catastrophic Flood Litigation

I. Introduction

In Tenaris Bay City Inc. v. Ellisor, No. 23‑0808 (Tex. May 23, 2025), the Supreme Court of Texas reversed a multimillion-dollar judgment obtained by homeowners whose properties flooded during Hurricane Harvey. The Court held that, even in the context of an historic natural disaster, plaintiffs must prove that their specific properties would not have flooded but for the defendant’s tortious conduct. Mere showing that the defendant increased flooding in the area, or that it was “a factor” in regional flooding, is not enough.

The decision re‑emphasizes two interlocking requirements in Texas negligence and flooding law:

• Proximate cause always includes both substantial-factor causation and but-for causation; and
• In complex hydrological settings—especially following a catastrophic storm—expert testimony is generally required to establish property‑specific causation and to rule out other plausible causes such as the storm itself.

The Court concluded that the homeowners’ expert, engineer Gabriel Novak, did not perform the necessary hydrological analysis and expressly declined to offer a but-for opinion for any of the thirty properties. In the absence of such evidence, the Court held there was “no evidence” of cause in fact and rendered judgment for Tenaris on all theories—negligence, negligence per se (under Water Code § 11.086), and negligent nuisance.

II. Factual and Procedural Background

A. Hurricane Harvey and the Tenaris Facility

The plaintiffs were homeowners in Van Vleck and Bay City, Matagorda County. Tenaris Bay City Inc. operated a pipe fabrication facility on land previously used as a sod farm. Because conversion of a sod farm (highly pervious) into an industrial facility (substantially impervious) raises obvious flooding concerns, Tenaris retained Fluor Enterprises to design and build a drainage system. Jones & Carter reviewed Fluor’s design and recommended approval; the county drainage district approved the plan.

The drainage system included detention ponds and a raised berm surrounding them, intended to capture stormwater and prevent uncontrolled runoff. Part of the case focused on alleged design flaws—particularly directing a large volume of water to a feature labeled “Outflow 1”—and on construction/maintenance deficiencies, including a berm section built a foot lower (43 feet) than specified (44 feet).

Hurricane Harvey struck in August 2017. Evidence characterized Harvey as “the most significant tropical cyclone rainfall event in United States history” in terms of scope and peak rainfall since the 1880s. In Matagorda County, Harvey dropped 21.6 inches of rain over four days and caused more than $500 million in property damage. Expert and lay evidence suggested the county was not the single hardest‑hit part of Texas, but Harvey was still one of the worst storms in local memory.

Thirty homes owned by the plaintiffs flooded. They alleged Tenaris’s drainage design and related conduct caused or exacerbated flooding on their properties.

B. Claims, Trial, and Court of Appeals

The plaintiffs sued Tenaris, Fluor, and Jones & Carter on several tort theories:

• Negligence;
• Gross negligence;
• Negligence per se based on Texas Water Code § 11.086 (unlawful diversion or impoundment of surface water); and
• Negligent nuisance.

Jones & Carter settled before trial; Fluor settled after trial. The plaintiffs’ properties were grouped into three “zones,” and the case proceeded on liability only, with damages stipulated at $2.8 million if Tenaris were found liable.

On gross negligence, the trial court directed a verdict for Tenaris. The remaining negligence-based theories went to the jury. The plaintiffs’ causation case rested primarily on the testimony of civil engineer Gabriel Novak, who criticized the design and alleged that too much water was routed to “Outflow 1,” causing “additional flooding elsewhere in Van Vleck or Bay City.”

The jury found Tenaris liable for negligence, negligence per se, and nuisance as to all three zones. The trial court rendered judgment on the $2.8 million stipulation plus interest. The Fourteenth Court of Appeals (Houston) affirmed, concluding that there was legally sufficient evidence that Tenaris was a “substantial factor” in bringing about the plaintiffs’ harm. Tenaris Bay City, Inc. v. Ellisor, 704 S.W.3d 37 (Tex. App.—Houston [14th Dist.] 2023).

III. Summary of the Supreme Court’s Opinion

The Texas Supreme Court reversed and rendered judgment for Tenaris, holding that:

1. On this record, there was legally insufficient evidence of but-for causation—a required element of proximate cause—for any of the thirty homes.
2. Novak’s testimony showed, at most, that Tenaris’s drainage design caused “additional flooding” in the general area and was “a factor” in the plaintiffs’ flooding. He repeatedly admitted he had not done the hydrological analysis necessary to determine:
   • Whether Tenaris’s conduct was a substantial factor (as opposed to merely “a factor”), and
   • Whether any of the houses would have remained unflooded but for Tenaris’s alleged negligence.
3. Proximate cause under Texas law always requires both:
   • Cause in fact, which includes:
   • But-for causation, and
   • Substantial factor causation;
   • and Foreseeability.
   The plaintiffs proved, at most, contribution to flooding (i.e., some substantial factor in area flooding), but not but-for causation for these particular homes.
4. This failure of causation proof defeats all three theories—negligence, negligent nuisance, and negligence per se—even though the plaintiffs argued these were distinct.
5. The Court refused to extend or analogize to the relaxed causation standard in Bostic v. Georgia-Pacific Corp., 439 S.W.3d 332 (Tex. 2014), emphasizing that Bostic’s modification of but-for causation applies only in extremely limited contexts (like asbestos exposure) where tracing specific causal contributions is “not humanly possible.” Here, Novak acknowledged he could do the necessary analysis but did not.
6. In a case of this complexity—multiple properties, relatively flat terrain, numerous hydrological variables, and an unprecedented storm—expert testimony was required to establish causation. Lay testimony alone could not support a but-for finding.
7. Evidence that the plaintiffs’ properties had never flooded before, even in heavy rains, was insufficient to prove Tenaris caused the Harvey flooding, given the numerous potential changes (impervious cover, subsidence, climate, cumulative development, and the exceptional nature of Harvey itself).

The Court’s broader message is encapsulated in its formulation of the “natural, default explanation” for Harvey-related flooding:

“The natural, default explanation for flood damage during a historic and unpredictable rain event is the storm itself, not the actions of neighboring property owners. Those who wish to prove otherwise must demonstrate, with reliable evidence, that their flood damage would not have occurred if not for their neighbor's tortious actions.”

IV. Detailed Legal Analysis

A. Proximate Cause and the Reassertion of But-For Causation

The Court begins from settled Texas negligence doctrine:

• Negligence requires duty, breach, and damages proximately caused by the breach. Rodriguez-Escobar v. Goss, 392 S.W.3d 109, 113 (Tex. 2013); IHS Cedars Treatment Ctr. v. Mason, 143 S.W.3d 794, 798 (Tex. 2004).
• Proximate cause consists of:
  • Cause in fact (itself composed of but-for and substantial-factor elements), and
  • Foreseeability. See Pediatrics Cool Care v. Thompson, 649 S.W.3d 152, 158 (Tex. 2022); Goss; Crump; Ford v. Ledesma, 242 S.W.3d 32 (Tex. 2007).

The Court quotes Rogers v. Zanetti, 518 S.W.3d 394, 403 (Tex. 2017), to stress that a cause-in-fact test that omits the but-for component is “incomplete.” Defining proximate cause purely in terms of “substantial factor” is therefore legally deficient.

The jury charge here correctly reflected Texas law. It defined proximate cause as:

“a substantial factor in bringing about an injury, and without which cause such injury would not have occurred.”

The Court’s central holding is that the evidence, even taken in the light most favorable to the verdict, fails the but-for part of this test. Novak’s testimony might support the conclusion that Tenaris’s design was a contributing factor—perhaps even a substantial factor—in some incremental flooding in the area. But there was no evidence that, absent Tenaris’s alleged negligence, any of the thirty homes would have remained unflooded during Harvey.

1. Novak’s Admissions on Causation

The Court extensively quotes Novak’s trial testimony. Critically, he admitted:

• He could not answer the question, “what caused these poor folks to have their homes flooded during Hurricane Harvey,” as to any specific home.

  Q: “As far as to the specific homes?”
  A: “No, I cannot answer that question.”
  
  Q: “You can't answer it about any of these places here in Van Vleck or down south in Bay City where the plaintiffs live, can you?”
  A: “... as far as a detailed analysis? No.”

• He had not done the detailed hydrological work (topography, soil maps, waterway studies, computer models) that, by his own account, would be necessary to determine the cause of flooding at each plaintiff’s home:

  Q: “But you haven't [done] a general flooding analysis at all about what happened in Van Vleck, Texas, have you, sir?”
  A: “No. I have not.”

• As to Tenaris’s role, his opinion was only that Tenaris’s conduct was “a factor,” not that it was a “substantial factor,” and certainly not that it was a but-for cause:

  Q: “Do you have an opinion ... whether ... the storm water drainage design ... was a substantial factor in bringing about the flooding of plaintiffs' properties?”
  A: “My opinion is that the failure of the Fluor design and its implementation was a factor in the flooding of the plaintiffs' properties.”

This testimony is affirmative evidence of an omission in causation proof: Novak was capable of doing the work needed to opine on property‑specific causation but chose not to. The Court treats this not simply as a lack of express but-for language, but as a substantive failure to perform the underlying analysis that could support any reliable but-for conclusion.

2. Excluding Other Plausible Causes

The Court links Novak’s failure to perform a full analysis to the broader line of cases requiring experts to address and reasonably exclude alternative causes:

• Helena Chem. Co. v. Cox, 664 S.W.3d 66, 80–81 (Tex. 2023);
• JLG Trucking, LLC v. Garza, 466 S.W.3d 157, 162 (Tex. 2015);
• Crump, 330 S.W.3d at 218.

The Court reiterates that expert testimony on causation is “fundamentally unreliable” if the expert does not exclude other plausible causes with reasonable certainty. Here, Novak:

• Did not attempt to quantify how much water Tenaris’s system contributed to particular flows;
• Did not model the with‑and‑without‑Tenaris scenarios; and
• Did not attempt to separate the effects of Tenaris’s system from:
  • The unprecedented rainfall of Hurricane Harvey;
  • Background hydrological features;
  • Broader development patterns; or
  • Other environmental factors in the region.

This failure, in the Court’s view, strips his testimony of probative value on but-for causation.

The upshot: causation-in-fact is not satisfied merely by showing that a defendant added some water to an already massive flood. Plaintiffs must show that this addition made the difference between no flooding (or materially lesser flooding) and the flooding they actually experienced.

B. The Role and Limits of Expert Testimony in Complex Flood Litigation

The Court directly addresses whether expert testimony was needed to prove causation. The plaintiffs and the court of appeals argued that lay testimony could suffice. The Supreme Court disagreed, holding that in this kind of case, expert testimony is indispensable.

Relying on Mack Trucks, Inc. v. Tamez, 206 S.W.3d 572, 583 (Tex. 2006) (“Expert testimony is required when an issue involves matters beyond jurors' common understanding”), the Court emphasizes:

• Before trial, plaintiffs’ own counsel conceded that they needed expert causation testimony; the trial court agreed.
• Novak himself confirmed the technical sophistication required: U.S. Geological Survey topographic maps; detailed drainage analysis; computerized hydrological models; soil maps; and study of waterways.

The Court then analogizes to City of Keller v. Wilson, 168 S.W.3d 802, 829 (Tex. 2005), where it held that determining whether a development’s detention ponds increased flooding on neighboring lands required expert hydrological analysis. In City of Keller, the Court noted that such calculations involved “hydrological formulas, computer models, and mathematical calculations”—not matters within ordinary juror experience.

In Tenaris, the flood dynamics were, if anything, more complex:

• Relatively flat terrain;
• Multiple small channels and drainage paths;
• Massive areal rainfall from Harvey;
• Variations in ground permeability, elevation, and development; and
• Interplay of wind, impervious surfaces, and background drainage networks.

Under these circumstances, the Court concludes:

“When thousands of properties are flooded during a historic coastal rainfall, proving that your property's flood damage was caused by your neighbor rather than simply by the storm will generally require proof by expert testimony.”

This is an important practical rule. It signals that, after a major storm in a developed coastal region, plaintiffs will rarely be able to rely on eyewitness stories or lay speculation about “where the water came from.” They must instead present expert hydrological modeling that draws a defensible connection from the challenged conduct to the specific flooding on their particular parcels.

C. Negligence, Negligence Per Se, and Nuisance: A Unified Causation Requirement

The plaintiffs tried to diversify their legal theories—negligence, negligence per se, and negligent nuisance—perhaps hoping that causation requirements or standards of proof might differ between them. The Court rejected that maneuver.

1. Negligent Nuisance

An actionable nuisance in Texas may be:

• Intentional;
• Negligent; or
• In limited instances, based on strict liability for ultra-hazardous activities.

Citing Crosstex N. Tex. Pipeline, L.P. v. Gardiner, 505 S.W.3d 580, 604–09 (Tex. 2016), the Court emphasizes that a negligent nuisance is governed by ordinary negligence principles. That means plaintiffs must prove:

• Duty;
• Breach;
• Proximate cause (including but-for causation); and
• Damages.

The nuisance portion of the jury charge mirrored the negligence charge: it defined proximate cause as a substantial factor “and without which cause such injury would not have occurred.” Consequently, the causation failure that doomed the negligence claim likewise defeats the negligent nuisance claim.

2. Negligence Per Se under Water Code § 11.086

“Negligence per se” is, as the Court notes, simply negligence where the standard of conduct is borrowed from a statute or regulation. See Mo. Pac. R.R. v. Am. Statesman, 552 S.W.2d 99, 102 (Tex. 1977). Breach is established by showing violation of the statute, but causation and damages remain subject to the ordinary negligence framework.

Here, the plaintiffs’ negligence per se claim was based on Texas Water Code § 11.086, which provides in part:

(a) No person may divert or impound the natural flow of surface waters in this state, or permit a diversion or impounding by him to continue, in a manner that damages the property of another by the overflow of the water diverted or impounded.

(b) A person whose property is injured by an overflow of water caused by an unlawful diversion or impounding has remedies at law and in equity and may recover damages occasioned by the overflow.

Two points are critical:

1. The statute’s own text re‑states causation requirements: liability arises only when:
   • Property is injured by an overflow “caused by an unlawful diversion or impounding,” and
   • Available damages are those “occasioned by the overflow.”
2. Courts applying § 11.086 have held that plaintiffs must prove their damages “would not have resulted but for such unlawful diversion.” The Court cites:
   • Contreras v. Bennett, 361 S.W.3d 174, 178 (Tex. App.—El Paso 2011, no pet.);
   • Benavides v. Gonzalez, 396 S.W.2d 512, 514 (Tex. App.—San Antonio 1965, no writ) (construing a predecessor statute).

The jury charge reflected this: it instructed that “[t]he diversion or impounding of surface water, if any, must have caused damages to Plaintiffs' properties and without which cause such injury would not have occurred.”

In effect, the Court rejects any idea that § 11.086 creates a kind of “strict liability for any incremental overflow.” Plaintiffs must still show the statutorily unlawful diversion or impoundment was a but-for cause of the damages they claim. Again, because Novak did not perform the required analysis, the statutory claim fails for the same reason as ordinary negligence.

D. Treatment and Distinction of Key Precedents

1. Bostic and the Strict Limits on Relaxing But-For Causation

The plaintiffs and the court of appeals arguably leaned on Bostic v. Georgia-Pacific Corp., 439 S.W.3d 332 (Tex. 2014), which adjusted the but-for requirement in asbestos cases. In Bostic, the Court recognized that in multi-source asbestos exposure, requiring a plaintiff to prove which specific fibers from which defendant actually caused the disease is “not humanly possible.” Instead, the Court required proof that the defendant’s exposure was a substantial factor and that the plaintiff’s total dose from that defendant exceeded a certain threshold.

In Tenaris, the Supreme Court:

• Emphasizes that Bostic is tied to the “unique nature of asbestos disease” and situations where specific but-for tracing is functionally impossible.
• Reiterates that this relaxed standard “will apply only in rare cases,” citing Rogers, 518 S.W.3d at 403.
• Distinguishes the case at bar: Novak admitted he could perform the hydrological modeling to determine property-specific causation but did not. This is not a situation where causation proof is “not humanly possible”—only where it is time-consuming and complex.

Therefore, the Court refuses to lower the but-for bar in catastrophic flooding cases.

2. City of Keller v. Wilson: Hydrology Requires Experts

As noted above, City of Keller involved alleged increased flooding from a housing development. There, too, the Court held that expert hydrological testimony was required to show whether detention ponds and drainage features increased flood levels on neighboring lots. Tenaris extends and reaffirms this principle in the post‑Harvey context.

The Court underscores the structural similarity:

“Calculating the effect of detention ponds and absorption in a grassy drainage ditch forty-five feet wide and over two hundred yards long required hydrological formulas, computer models, and mathematical calculations.”

Tenaris applies the same reasoning across a much larger area with far more complex flows, effectively saying: where hydrological effects are not obvious and unilateral (e.g., single channel, single operator), non-expert intuition is insufficient for causation.

3. Tarrant Regional Water District v. Gragg: No Relaxation of But-For Causation

Plaintiffs placed heavy reliance on Tarrant Regional Water District v. Gragg, 151 S.W.3d 546 (Tex. 2004), a case involving downstream damage from flood releases at a dam. They read Gragg as both:

• Approving causation based on lay testimony; and
• Relaxing the but-for standard in flooding litigation.

The Court rejects this interpretation and clarifies Gragg on two fronts:

1. But-for requirement persisted in Gragg.
   Gragg itself stated that the landowner “was required to prove that the same damaging floods would not have occurred under the same heavy rainfall conditions had the dam not been constructed.” 151 S.W.3d at 554. Tenaris quotes this line approvingly, underscoring that even in government flooding cases, the plaintiff must show that without the challenged structure, the same damage would not have occurred.
2. Different hydrological context.
   In Gragg, water was released from a single gate, traveled in a single river, and damaged a single ranch:

   “Demonstrating causation was therefore not nearly as complicated as doing so in a case like this one, where an extraordinary volume of rain fell on vast swaths of acreage in a relatively flat area and then moved from one property to another in ways that are not at all obvious to non-experts.”

   The flows were more direct and traceable; cause-and-effect could be inferred more readily from a mix of expert and lay testimony.

Thus, Tenaris uses Gragg to reinforce, not weaken, the but-for standard and to highlight how hydrological complexity controls whether lay evidence alone can support a causation finding.

E. The “Act of God” Context and the Court’s Evidentiary Default Rule

While the Court does not technically frame this as an “act of God defense,” its rhetoric clearly positions Harvey as the baseline causal explanation for the flooding. Several passages are significant:

• “Houses all throughout this flood-prone region were at risk of flooding during the storm, regardless of the presence of nearby industrial facilities.”
• “But pinning the consequences of a historic act of God on your neighbor is no small thing.”
• “The natural, default explanation for flood damage during a historic and unpredictable rain event is the storm itself, not the actions of neighboring property owners.”

From these, we can infer a practical evidentiary presumption:

• In ordinary times, if a drainage structure fails and a single nearby property floods, it may be reasonable to assume the structure caused the damage (subject to proof).
• But after a truly extraordinary storm that floods thousands of properties, the baseline assumption is that the storm alone is sufficient to explain most or all of the flooding.

To recover in such a setting, plaintiffs must produce reliable, property-specific evidence that:

• Under the same storm conditions, their particular properties would have remained dry (or materially less damaged) if the defendant’s conduct had not occurred.

This logic informs the holding that evidence of “no prior flooding” is insufficient:

• Coastal communities change over time;
• Subsurface conditions, development patterns, and climate variability evolve; and
• It is unsurprising that an unprecedented storm produces first‑time flooding even absent any specific defendant’s negligence.

The Court effectively warns against inferring causation from “post hoc, ergo propter hoc” reasoning: the mere fact that Tenaris’s facility was built before Harvey and that plaintiffs flooded for the first time during Harvey does not establish that Tenaris caused the flooding.

V. Impact and Implications

A. For Flood and Hurricane Litigation in Texas

Tenaris will have substantial implications for future hurricane and flooding suits in Texas, particularly in the Gulf Coast and other flood‑prone regions:

1. High bar for plaintiffs in regional-catastrophe cases.
   When a major storm causes widespread flooding, plaintiffs must go beyond:
   • Evidence that the defendant’s facility increased runoff;
   • Evidence that the facility was poorly designed, constructed, or maintained; or
   • Testimony that the property never flooded before.
   They will need credible, often expensive hydrological modeling to demonstrate but-for causation property by property.
2. More frequent grants of summary judgment and directed verdicts.
   Defendants can use Tenaris to argue “no evidence” of but-for causation when plaintiffs’ experts:
   • Speak only in terms of contribution or incremental flooding;
   • Fail to perform with/without modeling; or
   • Admit that they have not excluded other plausible causes (e.g., the storm itself).
3. Narrow space for “common sense” jury inferences in complex hydrology.
   Jurors’ intuitive impressions about where floodwater seems to have come from are unlikely to suffice absent robust expert support. Courts reviewing verdicts will be prepared to treat lay-based causation findings as speculative in complex multi‑factor flooding environments.

B. For Land Developers, Industrial Facilities, and Engineers

For defendants like Tenaris—industrial operators, developers, governmental entities—Tenaris is both a sword and a shield:

• Shield: Even when evidence of negligent design or maintenance exists (e.g., a berm built lower than specified, lack of maintenance), plaintiffs must still prove that these shortcomings were the but-for cause of their particular damage. Showing a defective drainage facility is not, by itself, sufficient evidence of liability in a catastrophic storm.
• Sword (or incentive): At the same time, the opinion implicitly encourages better documentation and modeling at the design and construction stages. If operators can produce their own sophisticated hydrological modeling showing that their systems do not materially increase flooding of adjacent parcels (or that any increase is negligible), they will be in a strong position to defeat causation at early stages.

The decision also places added professional stakes on engineering firms. If an engineer’s design is attacked, but the plaintiff’s own expert has not done hydrological work commensurate with standard engineering practice, that expert’s opinions may be disregarded as non-probative on causation.

C. For Trial Strategy and Expert Practice

Tenaris is a cautionary tale about the precision and scope of expert testimony:

• Experts must align with legal standards. Saying a defendant was “a factor” is insufficient when the law demands both “substantial factor” and “but for.” Counsel should ensure experts understand these distinctions and are prepared (if supported by their analysis) to give opinions framed in legally relevant terms.
• Experts must do the work they describe as necessary. Novak freely listed the steps needed to determine causation, then admitted he had not performed them. This admission became a linchpin for the Court’s ruling. Future experts will need to avoid this gap between theory and practice.
• Defense counsel can exploit incomplete expert work. By eliciting concessions that an expert has not:
  • Modeled alternative scenarios;
  • Quantified flow contributions; or
  • Considered key variables (topography, soils, other development),
  defense attorneys can set up powerful “no evidence” challenges on appeal.

D. For Statutory Water and Nuisance Claims

From a doctrinal standpoint, Tenaris resists any trend toward using nuisance or § 11.086 to sidestep causation requirements:

• Nuisance is not a back door to strict liability. When pled as negligent nuisance, it remains subject to all elements of negligence, including but-for causation.
• Water Code § 11.086 does not eliminate proximate cause. The statute is not a free‑standing strict liability regime for any and all increases in water levels; the overflow must still have caused the plaintiff’s damage in a but-for sense.

Thus, while these causes of action remain powerful in appropriate cases, plaintiffs cannot avoid doing the hard causation work by re‑labeling their claims.

VI. Key Concepts Explained

1. Proximate Cause

“Proximate cause” in Texas is a legal term that bundles together two distinct ideas:

• Cause in Fact: The defendant’s conduct actually played a role in producing the harm. This has two subparts:
  • But-for causation: If the defendant had not acted (or had acted properly), the injury would not have occurred.
  • Substantial-factor causation: The defendant’s conduct was important enough in the chain of events that it can be fairly said to have caused the harm, not just in a trivial or remote way.
• Foreseeability: The type of harm suffered was sufficiently predictable that a reasonable person in the defendant’s position should have anticipated it.

Both must be proved; showing only that a defendant contributed in some way is not enough without proof that the injury would not have occurred otherwise.

2. Negligence Per Se

Negligence per se allows a plaintiff to use a statute to define the breach of duty. If:

• A statute was designed to protect a certain class of persons from a certain type of harm; and
• The defendant violated that statute;

then the violation is treated as a breach of duty as a matter of law. However:

• The plaintiff still must prove that this statutory violation proximately caused the harm.

In Tenaris, § 11.086 supplied the duty and breach standard; causation and damages still had to be proven under common-law principles.

3. Nuisance (Negligent Nuisance)

A nuisance is a substantial interference with the use and enjoyment of land. When the interference arises from negligence (rather than intentional acts or inherently dangerous activities), it is called “negligent nuisance” and depends on proving:

• That the defendant failed to exercise reasonable care; and
• That this negligence proximately caused a substantial interference (e.g., flooding, noise, pollution) with the plaintiff’s property.

Tenaris confirms that negligent nuisance does not have a relaxed causation test; it uses the same proximate cause elements as ordinary negligence.

4. Expert Testimony in Technical Causation Issues

Courts require expert testimony when the causal mechanisms are outside everyday knowledge. Hydrology after a major storm—impacts of detention ponds, berm heights, and flow routing—is a prime example. Jurors cannot reliably parse technical cause and effect under these circumstances without expert assistance grounded in appropriate data and modeling.

VII. Conclusion: The Significance of Tenaris Bay City Inc. v. Ellisor

Tenaris Bay City Inc. v. Ellisor is a significant reaffirmation and clarification of causation doctrine in Texas, especially in the context of catastrophic flooding:

• It reiterates that but-for causation is indispensable to proximate cause in negligence, negligent nuisance, and negligence per se claims, including those under Water Code § 11.086.
• It emphasizes that in complex flooding scenarios following historic storms, expert hydrological analysis is generally required to prove that a defendant’s conduct turned a would‑have‑been‑dry property into a flooded one.
• It cautions that proof of negligence alone—even serious engineering or maintenance lapses—does not automatically establish causation in the face of a powerful natural event.
• It sharply limits any temptation to extend Bostic’s relaxed causation standard beyond truly exceptional contexts where tracing causation is “not humanly possible.”
• It clarifies that nuisance and statutory water claims cannot be used to bypass ordinary causation requirements.

In a broader sense, the opinion articulates a normative stance about assigning legal responsibility for damages during “acts of God.” When unprecedented storms strike and widespread flooding follows, the law will treat the storm as the default explanation. To shift that responsibility to a neighbor, a developer, or a governmental entity, plaintiffs must meet a demanding evidentiary burden: they must show, with reliable expert support, that their particular damage would not have occurred but for the defendant’s tortious conduct.

Tenaris thus stands as an important precedent in Texas tort law, shaping the future of flood-related litigation and reinforcing the centrality of rigorous, property‑specific causation proof whenever plaintiffs seek to attribute the consequences of a historic natural disaster to human actors.