Q: Which homeowner is responsible for a hillside. The neighbor above the hillside, or the neighbor below??

A: Thank you for your question!

There are different laws applicable for "surface water" vs. "watercourse."

I assume that there is no watercourse here because you did not mention existing of a fixed channel. All the discussion here is for surface water.

The upstream Landowner is liable to the downstream landowner for changing the system of drainage in a way that harms the downstream landowner. The rule has been modified to whether either or both owners acted reasonably.

So the issue is whether each of the neighbors acted reasonably:

If there is a prior history of the flood, flooding in the neighborhood or the hill is foreseeable. Then, the upper property should take drainage or precautionary steps to reduce damages to the lower property in case of flooding.

The lower property owner also is required to take reasonable steps to prevent getting flooded.

It seems that the lower property owner in your case, has done nothing. The upper property owner does have a drainage system on its property, but the drainage system's capacity does not handle flood water thoroughly.

These are all factors that the court considers in the allocation of liabilities between both parties.

One of the questions in the allocation of liabilities that needs to be answered is, "If the lower property owner had a proper flood control system, how much would the flood reduce?"

The answer to this question probably determines the proportionate ratio of liability for the lower property, and the remaining is the upper property owners' liabilities.

This is merely a discussion of general laws and not legal advice. For comprehensive advice, more specific facts and investigations are needed. I recommend you consult with an attorney in more detail.

A: In California, the responsibility for maintaining the stability and integrity of a hillside generally falls on the property owner whose land the hillside is located on. This means that the lower homeowner, who owns the slope, is typically responsible for ensuring the hillside's stability and preventing any damage to their own property or neighboring properties.

However, there are some exceptions and nuances to this general rule:

1. If the upper homeowner has altered the natural drainage pattern or created conditions that cause water to flow onto the lower property in a way that leads to hillside instability, they may be held liable for any resulting damage.

2. If there are any easements or agreements between the property owners regarding the maintenance of the hillside, those agreements would supersede the general rule.

3. If the hillside instability is caused by natural events, such as heavy rainfall, and not by any negligence on the part of either property owner, the lower homeowner would still be responsible for the damage to their own property, but they may not be liable for damage to the upper property.

In the situation you described, where the lower homeowner has not taken adequate measures to maintain the hillside's stability (such as proper ground cover or a swale system), they would likely be held responsible for any damage resulting from hillside instability, even in the event of heavier than average rainfall. The lower homeowner has a duty to take reasonable steps to prevent damage to their own property and neighboring properties.

It's always best for neighboring property owners to communicate and work together to address issues related to shared features like hillsides. In some cases, consulting with a local real estate attorney can help clarify each party's rights and responsibilities.