But‑For Causation in Catastrophic Flooding: The Texas Supreme Court’s Decision in Tenaris Bay City Inc. v. Ellisor

I. Introduction

The Supreme Court of Texas’s decision in Tenaris Bay City Inc. v. Ellisor (No. 23‑0808, opinion delivered May 23, 2025) is a significant modern statement on causation in negligence cases arising from catastrophic natural events, particularly flooding after Hurricane Harvey. The Court squarely addresses what a plaintiff must prove to hold a private actor liable for property damage that occurred during an extraordinary storm affecting thousands of properties across a region.

The core holding is both simple and demanding: when a historic rain event is the obvious, “default” explanation for flooding, plaintiffs must offer reliable, typically expert, evidence that their particular properties would not have flooded but for the defendant’s tortious conduct. It is not enough to show that the defendant’s facility added some water to the system or contributed to “additional flooding” in the general area.

The decision clarifies and reinforces several key doctrines:

The dual components of cause-in-fact—“but-for” causation and “substantial factor” causation—are both mandatory and cannot be collapsed into one.
Negligence, negligent nuisance, and negligence per se (including under Texas Water Code § 11.086) all require proof of but-for causation.
Expert testimony is required when determining causation involves complex hydrological questions beyond common experience.
The relaxed causation framework applied in asbestos cases like Bostic v. Georgia-Pacific Corp. is confined to narrow circumstances and does not extend to flooding cases where a more precise analysis is possible.

The case therefore stands as an important precedent for flood litigation, environmental and infrastructure-related torts, and the evidentiary burdens plaintiffs must meet when seeking to attribute disaster-related damage to private actors rather than to the disaster itself.

II. Case Background

A. The Parties and the Facility

The respondents (plaintiffs below) are homeowners whose thirty residences are located in or around Van Vleck and Bay City in Matagorda County, a flood-prone area on the Texas Gulf Coast.

The petitioner, Tenaris Bay City Inc. (“Tenaris”), operates a pipe fabrication facility in Bay City. The site was formerly a sod farm—a permeable, absorbent land use. When Tenaris developed the site into a large industrial facility with significant impervious cover (buildings, paving), it needed an engineered drainage system to manage stormwater runoff.

Tenaris retained Fluor Enterprises to design and build the drainage system. Jones & Carter, another engineering firm, reviewed and recommended approval of the plan to the county drainage district, which approved it. The system included detention ponds and a raised berm, with stormwater ultimately routed to a point on the property referred to as “Outflow 1.”

B. Hurricane Harvey and the Plaintiffs’ Flooding

In August 2017, Hurricane Harvey struck the Texas Gulf Coast. Evidence at trial described Harvey as:

“the most significant tropical cyclone rainfall event in United States history, both in scope and peak rainfall amounts, since reliable rainfall records began around the 1880s.”

Harvey caused over $500 million in property damage in Matagorda County alone. The county received 21.6 inches of rain over four days, and witnesses characterized Harvey as either the worst or second-worst hurricane in local memory.

The plaintiffs’ thirty homes flooded during Harvey. They contended that the design and construction of Tenaris’s drainage system—particularly the concentration of runoff toward Outflow 1 and an allegedly defective berm and maintenance—caused or worsened the flooding of their properties.

C. The Lawsuit and Trial

The plaintiffs sued Tenaris, Fluor, and Jones & Carter, asserting:

Negligence
Gross negligence
Negligence per se (based on Texas Water Code § 11.086)
Negligent nuisance

Jones & Carter settled before trial; Fluor settled after trial. The properties were grouped into three geographic “zones,” and the first phase of trial addressed liability only.

The plaintiffs’ primary causation evidence was the testimony of a civil engineer, Gabriel Novak. He:

Criticized Fluor’s decision to route a “very large drainage basin” to Outflow 1.
Opined that the design allowed too much water to be directed there.
Testified that Tenaris’s design caused “additional flooding elsewhere in Van Vleck or Bay City.”

However, as becomes crucial on appeal, Novak expressly admitted that he had not done the detailed hydrologic and topographic analysis necessary to determine whether Tenaris’s system was the but-for cause of flooding at any of the thirty specific houses.

At the close of evidence:

The trial court directed a verdict for Tenaris on gross negligence.
The negligence, negligence per se, and nuisance claims were submitted to the jury.
The jury found Tenaris liable on all three theories across all three zones.
The parties agreed on total damages of $2.8 million, and judgment was entered for that sum plus interest.

D. The Court of Appeals’ Decision

The Fourteenth Court of Appeals (Houston) affirmed the judgment. See Tenaris Bay City, Inc. v. Ellisor, 704 S.W.3d 37 (Tex. App.—Houston [14th Dist.] 2023).

Focusing on whether Tenaris’s conduct was a “substantial factor” in bringing about the harm, the court of appeals concluded the evidence was legally sufficient to support causation, relying both on Novak’s testimony and lay testimony from homeowners.

E. The Supreme Court of Texas Review

Tenaris sought review, arguing that the plaintiffs had not produced legally sufficient evidence of but-for causation—i.e., that their homes would have remained unflooded absent Tenaris’s alleged negligence.

The Supreme Court granted review, reversed the court of appeals, and rendered judgment for Tenaris on all claims.

III. Summary of the Opinion

Chief Justice Blacklock, writing for the Court, framed the central question: did the plaintiffs prove that Tenaris’s conduct, rather than Hurricane Harvey and other environmental factors, was the but-for cause of the flooding of their particular homes?

The Court held they did not, for several interrelated reasons:

No property-specific but-for causation evidence. Novak admitted that he could not—and did not—offer an opinion about what caused flooding at any specific plaintiff’s home, because he had not done the necessary hydrological modeling and drainage analysis.
Failure to exclude alternative causes with reasonable certainty. Novak did not attempt to rule out the extraordinary rainfall of Hurricane Harvey and other environmental factors as sufficient causes of the flooding, making his causation testimony fundamentally unreliable.
“Additional flooding” in the area is not enough. Evidence that Tenaris’s drainage design caused “additional flooding” in the region did not establish that any of the thirty homes would have stayed dry but for Tenaris’s conduct.
Expert testimony was required on causation in this complex hydrological context. Given the complexity of water movement in a large, flat, flood-prone area during a historic storm, the cause of flooding was beyond jurors’ common understanding; therefore, expert testimony was necessary and could not be dispensed with.
All theories—negligence, negligent nuisance, and negligence per se under Water Code § 11.086—require proof of but-for causation. The plaintiffs could not salvage their verdict by pointing to different doctrinal labels; each claim required the same causation showing they failed to make.
Lay testimony and “never flooded before” history were insufficient. Homeowners’ testimony that their properties had not previously flooded, even in heavy rains, did not establish that Tenaris’s plant was the but-for cause of Harvey flooding, given multiple evolving environmental risks and the unprecedented nature of Harvey.

The Court emphasized a basic policy and doctrinal premise: in the context of a historic storm like Harvey, “the natural, default explanation for flood damage … is the storm itself, not the actions of neighboring property owners.” To overcome that default, plaintiffs must present reliable evidence that their flood damage would not have occurred if not for the neighbor’s tortious actions.

Because no such evidence existed, the Court concluded that any jury finding of but-for causation rested on speculation rather than evidence. It therefore reversed and rendered judgment that the plaintiffs take nothing.

IV. Detailed Analysis

A. Precedents and Doctrinal Framework

1. Elements of Negligence and Proximate Cause

The Court begins by restating the canonical elements of negligence in Texas:

Existence of a legal duty;
Breach of that duty; and
Damages proximately caused by the breach.

This formulation, drawn from Rodriguez-Escobar v. Goss, 392 S.W.3d 109 (Tex. 2013), and IHS Cedars Treatment Ctr. v. Mason, 143 S.W.3d 794 (Tex. 2004), sets the stage for a deeper exploration of proximate cause.

Proximate cause in Texas has two elements:

Cause in fact; and
Foreseeability.

The Court’s focus here is on cause in fact, which itself has two components:

“But-for” causation – the injury would not have occurred without the defendant’s act or omission; and
“Substantial factor” causation – the conduct was a substantial factor in bringing about the injury.

The Court cites Pediatrics Cool Care v. Thompson, 649 S.W.3d 152 (Tex. 2022), Transcontinental Ins. Co. v. Crump, 330 S.W.3d 211 (Tex. 2010), Ford Motor Co. v. Ledesma, 242 S.W.3d 32 (Tex. 2007), Gunn v. McCoy, 554 S.W.3d 645 (Tex. 2018), and Rogers v. Zanetti, 518 S.W.3d 394 (Tex. 2017), to reinforce this dual requirement.

In Rogers, the Court emphasized that a cause-in-fact definition omitting but-for causation is “incomplete.” This opinion builds directly on that: even if conduct is a “substantial factor,” liability cannot attach without proof that the harm would not have occurred in the absence of that conduct.

2. Substantial Factor vs. But-For Causation

The decision addresses a frequent source of confusion: “substantial factor” is not an alternative to but-for causation. It is an additional requirement. The Court spells this out:

“[The] cause-in-fact standard thus ‘requires not only that the act or omission be a substantial factor but also that it be a but-for cause of the injury or occurrence.’”

Thus, proof that Tenaris’s drainage design was “a factor” or even a “substantial factor” in regional flooding could not substitute for evidence that these particular thirty homes would not have flooded in Harvey absent Tenaris’s conduct.

3. Excluding Alternative Causes with Reasonable Certainty

The Court relies on a line of cases holding that expert causation testimony is unreliable if the expert does not reasonably rule out other plausible causes:

Helena Chem. Co. v. Cox, 664 S.W.3d 66 (Tex. 2023)
JLG Trucking, LLC v. Garza, 466 S.W.3d 157 (Tex. 2015)
Transcontinental Ins. Co. v. Crump, 330 S.W.3d 211 (Tex. 2010)

In those cases, the Court rejected causation opinions that did not engage meaningfully with alternative explanations. Here, Novak:

Admitted he had not performed a flooding analysis for the area or any specific home.
Made no attempt to determine whether Harvey’s rain and other conditions were sufficient to cause the flooding even without Tenaris’s alleged design flaws.

By failing to exclude Harvey itself and other environmental factors as plausible sole causes, Novak’s testimony did not meet the reliability standard imposed by these precedents.

4. When Expert Testimony Is Required

The Court relies on Mack Trucks, Inc. v. Tamez, 206 S.W.3d 572 (Tex. 2006), for the principle that expert testimony is required when an issue lies beyond the ken of ordinary jurors. The plaintiffs themselves had acknowledged before trial that expert testimony was necessary to establish causation.

The Court analogizes to City of Keller v. Wilson, 168 S.W.3d 802 (Tex. 2005), another flooding case, where the Court held that determining whether a real estate development increased flooding on neighboring land required hydrological modeling and expert analysis:

“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.”

Similarly, in Tenaris, Novak testified that a proper causation analysis would require:

Use of U.S. Geological Survey topographic maps;
Detailed drainage analysis;
Computerized hydrological modeling;
Review of Natural Resources Conservation Service soil maps; and
Study of all relevant waterways.

Because such analysis was needed yet not performed, and because the hydrology of Harvey flooding across a wide, flat region is far from obvious to lay factfinders, the Court concludes that only competent expert testimony—of the sort Novak conceded he did not provide—could support a causation finding here.

5. Nuisance Doctrine and Crosstex

On the nuisance claim, the Court cites Crosstex North Texas Pipeline, L.P. v. Gardiner, 505 S.W.3d 580 (Tex. 2016), which clarifies that an actionable nuisance can arise from:

Intentional conduct,
Negligence, or
Strict liability for certain ultra-hazardous activities.

Where, as here, the nuisance theory is a negligent nuisance theory, it is “governed by ordinary negligence principles,” including proof of proximate cause. The jury charge in Tenaris mirrored this, defining proximate cause for nuisance to include both foreseeability and “without which cause such injury would not have occurred”—i.e., but-for causation.

6. Negligence Per Se and Texas Water Code § 11.086

The plaintiffs’ negligence per se claim was grounded in Texas Water Code § 11.086, which prohibits diverting or impounding the natural flow of surface water “in a manner that damages the property of another by the overflow of the water diverted or impounded.”

The Court emphasizes two points:

Negligence per se is still negligence. It replaces only the breach-of-duty element with proof of statutory violation. It does not alter the requirement to prove proximate cause. See Mo. Pac. R.R. v. Am. Statesman, 552 S.W.2d 99 (Tex. 1977).
§ 11.086 itself embeds a causation requirement. It grants remedies when property is injured by an overflow of water “caused by” an unlawful diversion or impoundment (and allows recovery of damages “occasioned by the overflow”).

The Court cites Contreras v. Bennett, 361 S.W.3d 174 (Tex. App.—El Paso 2011, no pet.), which held that under § 11.086 “the plaintiff carries the burden to prove the unlawful diversion caused damages to plaintiff's property which would not have resulted but for such unlawful diversion.” It also notes Benavides v. Gonzalez, 396 S.W.2d 512 (Tex. App.—San Antonio 1965, no writ), which interpreted a similar predecessor statute.

The jury charge in Tenaris explicitly echoed this but-for requirement. Thus, the plaintiffs’ failure on but-for causation doomed their negligence per se claims alongside their ordinary negligence and nuisance claims.

7. Bostic, Asbestos, and the Limited Relaxation of But-For Causation

Plaintiffs argued that Bostic v. Georgia-Pacific Corp., 439 S.W.3d 332 (Tex. 2014), softened the but-for causation requirement. In Bostic, an asbestos case, the Court recognized that asbestos exposure typically results from numerous, diffuse sources over a lifetime, making it “not humanly possible” to identify which fibers from which defendant actually caused the disease.

Accordingly, the Court did not require proof at that granular level, but it still imposed rigorous evidence of sufficient exposure attributable to each defendant.

In Tenaris, the Court sharply limits the reach of any such relaxation:

It notes that Bostic was tied to the peculiar nature of asbestos injury and the impossibility of tracing individual fibers.
It stresses that this more flexible approach applies only in “rare cases.” See also Rogers v. Zanetti, 518 S.W.3d 394 (Tex. 2017).
It holds that Bostic is inapplicable here because, by Novak’s own admission, it was possible—though perhaps costly or time-consuming—to determine the hydrological effect of Tenaris’s facility on the flooding of each property.

Thus, where an expert concedes that rigorous, property-specific analysis is feasible and knows what it would entail, Bostic cannot be invoked to excuse the failure to perform that work.

8. Gragg and Flood-Gate Discharges

The plaintiffs leaned heavily on Tarrant Regional Water District v. Gragg, 151 S.W.3d 546 (Tex. 2004), another flooding case, to argue that flood causation can be proven without strict adherence to but-for analysis or without extensive expert testimony.

The Court rejects this reading on both counts:

But-for causation remained central in Gragg. The Court there stated explicitly that the plaintiff “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.”
The hydrological context in Gragg was far simpler. The case involved water discharged from a single floodgate, traveling downstream along a river, causing damage to a single ranch. The causal pathway was more linear, and expert plus lay testimony sufficed.

By contrast, Tenaris concerns:

A sprawling industrial facility with complex internal drainage;
Water flowing across relatively flat coastal terrain;
Multiple small channels, varying rainfall patterns, soil permeability, wind, impervious cover, and interactions with adjacent flows; and
Thirty separate homes across two communities, each with unique siting and conditions.

Given this complexity, the Court concludes that Gragg does not undercut the need for rigorous expert analysis and traditional but-for proof in this context.

B. The Court’s Legal Reasoning Applied to the Record

1. The Central Deficiency: No Proof These Homes Would Have Stayed Dry “But For” Tenaris

The Court’s causation analysis turns entirely on the expert record, particularly Novak’s testimony.

Novak:

Opined that Tenaris’s design was flawed and routed excessive water to Outflow 1.
Testified that Tenaris’s conduct caused “additional flooding elsewhere in Van Vleck or Bay City.”
Admitted, however, that he:
- Had not done any flooding analysis at all for the affected area;
- Had not done a “detailed analysis of any of the specific plaintiff[s’] homes”;
- Could not answer what caused the flooding at “any of these places” where the plaintiffs lived; and
- Could not offer even a general conclusion about what caused any plaintiff’s home to flood because he had “not done the work” required.

He acknowledged that he could have done such work—using topographic data, hydrological modeling, soil maps, and waterway studies—but did not.

At one point, when directly asked whether Tenaris’s design and implementation were a substantial factor in bringing about the flooding of plaintiffs’ properties, he softened his answer to say only that the failure of the design and its implementation was “a factor” in the flooding.

Crucially, he never:

Used but-for language;
Stated that plaintiffs’ homes would have remained unflooded absent Tenaris’s conduct; or
Presented results of any property-specific modeling or analysis supporting such a conclusion.

In the Court’s view, this is not an incidental or semantic gap. It reflects the absence of the core causation element:

“None of Novak’s testimony supports the conclusion that Tenaris’s defectively designed facility was a but-for cause of the flood damage suffered at the properties in question.”

Because the only qualified causation expert declined to affirm but-for causation and admitted he had not done the necessary analysis, there was, as a matter of law, no evidence from which a reasonable jury could find that Tenaris’s conduct made the difference between a dry home and a flooded home.

2. The “Default” Cause: Hurricane Harvey as the Baseline Explanation

The Court’s reasoning is framed by the context of an extraordinary natural event:

“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.”

This is not a formal “act of God” defense, but it functions similarly. In situations where:

Thousands of properties across a wide region are flooded; and
The storm is historic in intensity and scope;

the baseline assumption is that the storm caused the damage. A plaintiff seeking to shift responsibility must affirmatively prove that, but for the defendant’s negligence, the plaintiff’s home would not have flooded even though many other properties in the area did flood.

Absent such evidence, attributing the damage to the defendant “rests only on speculation, not on evidence.”

3. Evidence of Negligence Is Not Evidence of Causation

The plaintiffs pointed to various alleged defects:

Part of the berm constructed at 43 feet instead of the designed 44 feet;
Failures in maintenance of the drainage system; and
Regulatory and design criticisms of the facility’s stormwater handling.

The Court treats this as, at most, evidence of breach of duty. It does not prove that the plaintiffs’ damage would not have occurred “without which cause.”

The Court draws a contrast:

In a typical car accident, the same evidence (how the vehicles collided) may prove both negligence and causation.
In large-scale flooding, proof that a defendant misdesigned a facility only establishes its capacity to contribute to flooding; it does not show that its contribution crossed the threshold between dry and flooded for any particular property.

Thus, the Court reinforces a familiar but often blurred principle: breach and causation are distinct elements; strong proof of the former does not automatically satisfy the latter, particularly in complex, multi-cause scenarios.

4. The Limits of Lay Testimony and “Never Flooded Before” Evidence

The plaintiffs and the court of appeals also relied on homeowner testimony:

That their properties had never previously flooded, even during heavy rains; and
That they observed large amounts of water coming from the direction of the Tenaris facility.

The Supreme Court finds this insufficient:

Near the Gulf Coast, a property’s flood risk can change over time due to subsidence, land use changes, climate patterns, storm tracks, and other developments.
It is not “unexpected” for a neighborhood to experience its first flooding event during “one of the wettest and most destructive hurricanes in Texas history.”

Moreover, given that the plaintiffs themselves recognized that expert analysis was necessary to establish causation, and given Novak’s testimony about the complexity of the hydrology, lay testimony cannot fill the gap created by the absence of a meaningful expert opinion on but-for causation.

5. Application Across All Theories of Liability

The Court methodically rejects any suggestion that plaintiffs could prevail on one theory even if they fail under another:

Negligence: Requires proximate cause (including but-for causation). Failed.
Negligent nuisance: Governed by ordinary negligence principles (Crosstex); the jury charge properly demanded proof that the nuisance was a but-for cause of the damage. Failed.
Negligence per se under § 11.086: Still requires proximate cause; § 11.086’s text itself requires proof that the overflow “caused” the damage and that damages were “occasioned by” the overflow. Failed.

Thus, the Court does not merely reverse on one theory; it renders a complete take-nothing judgment on all claims.

6. The Role of the Jury Charge

The Court notes that the jury instructions:

Correctly defined proximate cause to encompass both substantial-factor and but-for causation; and
Applied this definition consistently to negligence, nuisance, and negligence per se claims.

This matters because appellate review of legal sufficiency is tied to the charge given. Since every theory submitted included a but-for requirement, the plaintiffs’ failure on that element necessarily undermines every liability finding.

C. Impact and Implications

1. Flood and Disaster Litigation in Texas

This decision will significantly shape future flood and disaster-related tort claims in Texas, especially where:

A catastrophic storm or widespread weather event is the obvious background cause; and
Multiple actors (public or private) could potentially be blamed for contributing to flooding.

Key implications include:

Heightened evidentiary burden on plaintiffs. Plaintiffs cannot rely on general evidence that a development worsened flooding in the area. They must marshal property-specific expert analysis showing that, in the storm as it actually occurred, their own property would have stayed dry but for the defendant’s conduct.
Greater use of sophisticated hydrological modeling. Engineering experts will need to deploy detailed topographic, rainfall, soil, and flow modeling, and courts will expect to see this level of rigor when causation is contested.
Increased litigation cost and complexity. The type of detailed modeling described by Novak is expensive, potentially limiting suits to those with enough damages or collective resources to justify the expense.
Narrower path to liability for private actors in catastrophic events. Where a storm itself is easily sufficient to cause region-wide flooding, defendants may be less frequently held liable absent clear, quantified evidence that their actions tipped the balance for particular properties.

2. Clarification of Texas Water Code § 11.086 Litigation

Section 11.086 is frequently invoked in disputes between landowners over surface water diversion. The Court’s reading here reinforces:

That § 11.086 suits are not strict liability regimes for any increase in water flow;
That plaintiffs must show their property was damaged by overflow that would not have occurred but for the unlawful diversion or impounding;
That even in the face of obvious diversion (e.g., an engineered facility), the causation requirement can be dispositive.

Future § 11.086 plaintiffs will need to present:

Evidence that the defendant’s diversion indeed changed water flow to their property; and
Evidence—likely expert—that the diverted flow was sufficient to transform a no-damage scenario into a damage scenario under the actual rainfall conditions experienced.

3. Nuisance and Environmental/Infrastructure Torts

The decision reinforces Crosstex’s insistence that negligent nuisance claims track ordinary negligence elements, including proximate cause. Plaintiffs cannot use “nuisance” as a more plaintiff-friendly label to sidestep strict causation burdens.

For environmental and infrastructure-related torts (e.g., runoff from industrial facilities, upstream development, road and drainage projects), Tenaris signals that:

Courts will demand precise, property-specific causation proof; and
Evidence of poor design, noncompliance, or even regulatory violations is not enough without a solid causation chain to the specific injury alleged.

4. The Limited Reach of Bostic-Style Relaxed Causation

Some plaintiffs had hoped to rely on Bostic to ease causation burdens in complex multi-source harm scenarios beyond asbestos. Tenaris cuts against that trend.

It reaffirms that:

Bostic was driven by a unique scientific impossibility (tracing asbestos fibers to specific defendants);
That impossibility does not exist in hydrology, where modeling can, in principle, be done; and
Absent such impossibility, traditional but-for causation remains the rule, even if proof is difficult or expensive.

5. Appellate Scrutiny of Expert Causation Testimony

Finally, Tenaris is part of a broader line of Texas Supreme Court decisions actively policing the reliability and sufficiency of expert causation evidence. The Court is willing to:

Disregard expert opinions that do not meaningfully analyze or exclude alternative causes;
Treat an expert’s candid concessions about the limits of his work as dispositive against the party bearing the burden of proof; and
Render judgment (rather than remand) when the evidence is legally insufficient as a matter of law.

Trial courts and litigants should expect close scrutiny of whether expert opinions truly address the specific, but-for causation question in complex multi-cause settings.

V. Clarifying Key Legal Concepts

1. Proximate Cause, Cause in Fact, and Foreseeability

Proximate cause is the legal concept that links a defendant’s conduct to a plaintiff’s injury in a way that justifies liability.
It has two components:
- Cause in fact – did the conduct actually play the necessary role in producing the harm?
- Foreseeability – was the general type of harm reasonably foreseeable at the time of the conduct?

Tenaris focuses on cause in fact and does not re-examine foreseeability. It assumes that flooding is a foreseeable risk of defective stormwater design and answers only the factual: did that design actually cause these homes to flood in Harvey?

2. “But-For” Causation vs. “Substantial Factor”

In plain terms:

“But-for” causation asks: would this harm have happened anyway if the defendant had done everything right? If yes, there is no but-for causation; if no, but-for causation is present.
“Substantial factor” asks: was the defendant’s conduct more than a trivial or theoretical contributor to the harm?

Texas requires both. A defendant might be a substantial contributor to a condition (e.g., adding more water to a system already flooding) without being the but-for cause of the plaintiff’s specific harm (if the harm would have occurred even without that contribution).

3. Negligence Per Se

Negligence per se is a doctrine where:

A statute or regulation sets a standard of conduct.
A person in the class the statute aims to protect suffers the type of harm the statute aims to prevent.
A violation of the statute is treated as the breach of duty element of negligence.

However, negligence per se does not eliminate the other elements of negligence. The plaintiff must still show:

Causation (both cause in fact and foreseeability), and
Damages.

Tenaris exemplifies this: even assuming Tenaris violated § 11.086, the plaintiffs had to prove that this unlawful diversion or impounding was the but-for cause of their property damage.

4. Negligent Nuisance

“Nuisance” in Texas is a type of injury—a condition that substantially interferes with the use and enjoyment of land. It is not, by itself, a stand-alone tort distinct from negligence or other theories.

A negligent nuisance claim alleges:

The defendant negligently created or maintained a condition that substantially interfered with the plaintiff’s property use and enjoyment; and
The plaintiff suffered resulting harm (e.g., flooding).

As Crosstex and now Tenaris clarify, negligent nuisance uses the same proximate cause analysis as ordinary negligence.

5. Expert Testimony and “Matters Beyond Common Understanding”

Courts draw a line between:

Questions that ordinary jurors can evaluate based on everyday experience (e.g., who had the green light in a car accident?), and
Questions involving specialized scientific, technical, or professional knowledge.

Hydrology during a historic hurricane—how much runoff comes from a given facility, where it flows, how it interacts with natural and built features, and whether it changes flood depth enough to flood a particular house—is in the latter category. Expert testimony is needed, and if the expert expressly admits not having done the necessary work, the plaintiff cannot rely on mere lay impressions or generalized statements to fill the gap.

VI. Conclusion

Tenaris Bay City Inc. v. Ellisor is a strong reaffirmation and clarification of Texas causation doctrine in the context of catastrophic natural events and complex hydrological systems. The Court insists that:

Cause-in-fact requires both but-for and substantial factor causation.
Negligence, negligent nuisance, and negligence per se (including under § 11.086) all require proof that the plaintiff’s injury would not have occurred but for the defendant’s conduct.
In complex flooding cases, causation is a subject for experts, not lay speculation.
Where a historic storm like Harvey provides the obvious background cause, plaintiffs must present rigorous, property-specific evidence that the defendant’s conduct made the decisive difference.

The decision narrows the path to recovery against private actors for Harvey-related flooding and similar disasters, but it does so by applying existing principles of proximate cause with unusual clarity and rigor. By describing the storm as the “natural, default explanation” and requiring plaintiffs to overcome that default with reliable expert evidence, the Court signals that Texas tort law will not readily shift the costs of historic natural catastrophes onto neighboring landowners absent compelling causation proof.

For lawyers, engineers, insurers, and policymakers, Tenaris stands as a key precedent governing the intersection of infrastructure, land development, and flood risk in a changing climate, and it underscores the centrality of precise, scientifically grounded causation evidence in modern tort litigation.