The setup

In a hillside subdivision, several backyards share a single drainage swale along the rear lot lines. Water from the uphill lots flows through each yard in turn, then drops into a channel that leads to a detention area. For years, nobody thought about it.

In spring, the uphill neighbor replaces an old split-rail fence with a solid privacy fence, with boards set tight to the ground and a concrete footing along the bottom. The fence runs right across the swale where it enters the downhill neighbor's yard.

What happened

Illustrative example. Not a real job or customer.

In August, a heavy thunderstorm sends runoff down the swale. The water reaches the new fence and backs up, spreading sideways until it finds a lower path: around the end of the fence and down the side yard of the downhill house, straight to a window well. The well fills and water pours through the window into a finished basement bedroom.

  1. The downhill homeowner discovers water in the bedroom about an hour after the storm and shuts off power to the room.
  2. They photograph the water in the room and, once it is safe outside, photograph the fence, the debris line along it, and the path water took to the window well.
  3. They bail the window well and clear its drain, then start extraction inside.
  4. Cleanup removes the carpet, pad and lower drywall in the bedroom, cleans the area and dries it over several days.
  5. The homeowner talks with the uphill neighbor, sharing the photos rather than accusations.
  6. Both contact the HOA, which pulls the subdivision's drainage plan showing a platted drainage easement along the rear lot line.

The uphill neighbor modified the fence, raising the bottom boards and adding an opening where the swale crosses. Both neighbors cleared a section of the channel. No later storms that season caused problems. The downhill owner's insurer asked detailed questions about the source of the water, and the photos of the fence and debris line helped explain it.

Decision points in this example

  • IfYou suspect a neighbor's project changed your drainageDocument first with photos taken during or right after the storm, then approach the neighbor calmly.
  • IfYour HOA has architectural rulesAsk whether fence designs across drainage easements are restricted, and request the drainage plan.
  • IfNeighbors cannot agreeAsk the HOA, and the Town of Castle Rock or Douglas County, about the easement and the approved grading.
  • IfYour insurer asks about third-party responsibilityShare what you documented and let the insurer decide whether to pursue it.

If you are planning a fence, wall or garden on a slope

General information for Castle Rock, not a quote or professional advice. In an emergency, call 911.