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When It Rains, It Pours: Navigating Cross-Lot Drainage Claims

January 23, 2020

Many of us are familiar with the terms “El Niño” and “La Niña” from our local weather reports. These periodic changes in surface temperatures over the Pacific create two distinct weather patterns in California. La Niña years are typically dry and sometimes create drought conditions. Alternatively, the El Niño pattern often causes significant rainstorms in our mountains and coastal plains.

Then, another predictable pattern follows, and things get messy.

Heavy rains over Southern California often give rise to property damage claims from down-gradient property owners against their uphill neighbors, due to cross-lot drainage issues. These claims can become quite contentious as emotions get in the way of objectivity.

In some cases, downstream property owners may fail to recognize their responsibility to accept cross-lot drainage or the consequences of rear and side-yard improvements lacking adequate drainage capacity. This can result in damaged site works or flooded buildings.

Conversely, upstream property owners may create an increase in water flow and velocity in an area of their property, resulting in significant erosion and flood damage to their downstream neighbors.

Attorneys who litigate or defend these kinds of property claims typically rely on forensic civil engineers like myself to get to the heart of the matter.

California’s drainage law is based primarily on “good neighbor policies” of what constitutes reasonable action. These accepted principles give every landowner a right to discharge surface water in a reasonable manner, where the lower-elevation landowners have an obligation to accept the upper-elevation landowner discharges equal to its preconstruction flow volumes and velocities. Essentially, every landowner must take reasonable care to avoid damage to adjacent property.

A proper civil engineering design on a property will focus on cross-lot drainage for upstream properties, ensuring that the drainage improvements will not increase the volume or velocity of surface flows beyond their natural conditions to the detriment of downstream landowners. Conversely, the downstream property has an obligation to provide the necessary drains and swales to receive upstream stormwaters and transfer the drainage to the next downstream lot or public right of way without increasing its flow or velocity.

When civil engineering experts are retained to address a cross-lot drainage claim, we apply the scientific method of hydrology and hydraulics to determine existing conditions and recommended repairs. Hydrology analysis determines the amount of rainfall at a particular area from historical rainfall records. This is often described as the “fate of a raindrop.” Stormwater drainage is typically designed for a 25-, 50- or 100-year storm event, depending on the type of infrastructure.

The hydraulics portion of our investigation analyzes the drainage design as it applies to the hydrological storm flow when sizing drainage features, such as storm drain pipes and open-channel swales. Slope, friction, material, and age are typical hydraulic factors used to design the proper drainage conveyance infrastructure. Aerial topographical maps provide a baseline of historical grading and drainage features. A site visit, including measurements of current drainage features, provides a snapshot of existing conditions near the time of the rainfall event leading to a claim. Calculations of before and after conditions help determine the potential liability of the upstream and/or downstream parties. Further calculations may then be prepared to provide permanent repair recommendations.

In closing, while we may not be able to control the amount of rain Mother Nature has in store for us each year, there are measures available to ensure that both upstream and downstream property owners are adequately protected from the effects of cross-lot drainage.

After all, good drainage makes good neighbors.


John O’Donnell
Construction Expert in Civil Engineering, Xpera Group

This article was originally published by Xpera Group which is now part of The Vertex Companies, LLC.

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