Most of our back/side yard is 3'-5' lower than our neighbors'.During winter rainstorms water drains under the fence from their barely landscaped yard and stands in low spots AND at our house slab. A newly installed 75 gal sump which we pump out doesn't solve the problem, especially since we removed a large Monterey Pine on the fence line at their request. Think there's now a CA law requiring residents to keep water originating on their property to on that property. I'll try again to talk to them, but I would prefer to hire a professional with drainage experience to write a report or talk to them about it? Sugggestions besides engineer? Rainy season won't go on forever! GThanks a million
Can you pass the buck elsewhere?
Water needs to go to a lower place - storm drain or elsewhere. Typically you'd connect low spots with a drainage conduit (french drain [buried channel of gravel/pebbles], or plastic drainage pipes) and connect that to an even lower area like a storm drain or sewer. If you can't connect low spots, you can protect them by placing drainage conduits across the path water would likely run.
You might also use pumps to help the process along if gravity is inadequate.
You could also install a dry well, which is basically an underground tank for the water to collect. It's perforated to eventually drain, so permeability of surrounding soil needs consideration.
I know the law says water on a property should be contained, but what if that's the natural state of the land? E.g. If a creek flows between properties, very little can be done to stop it short of redirecting the creek elsewhere.