Slope Maintenance Guidelines

Many homes in Diamond Bar are located at the top or along the base of privately-owned hillsides. In some instances, these slopes are maintained by a homeowners association (HOA) or are part of a Lighting and Landscape Assessment District (LLAD). In all other cases, it is each owner’s individual responsibility to maintain and repair one’s slopes, including drainage devices.

Slope maintenance responsibility also includes ongoing vegetation management, including the removal of weeds and overgrown brush. Municipal Code Section 22.34.030(d)(1)(a) expressly states that “slopes adjacent to a public highway shall be maintained in a neat and clean manner, free of weeds and debris…Overgrown vegetation that harbors rats or other vermin, or attains such growth as to become a fire hazard when dry or that is otherwise noxious, dangerous or unsightly shall be prohibited.”

It is important to be aware that slope movement or failure can cause significant property damage and, in the most extreme cases, even threaten the safety of residents. The following guidelines include many simple and inexpensive housekeeping practices homeowners can implement to help maintain their slope property.

Please Note: Your responsibility to remove overgrown slope vegetation and weeds is not limited to the Los Angeles County Fire Department’s brush clearance requirements for structural fire prevention purposes. As prescribed in the Municipal Code, all slope areas must be continually maintained to preserve Diamond Bar’s reputation as a safe, attractive community.


All slope improvements, including walls, fences and plant material shall be maintained in a manner that does not detract from the appearance of the immediate neighborhood.

Inspect & Maintain Slope Drains. Water causes most slope stability problems. When water saturates the soil, it makes the soil heavier and reduces the hillside’s ability to withstand the force of gravity. As the winter rains approach, it is therefore particularly important that all homeowners regularly inspect their v-ditches or any other drainage ways on their slopes to make sure they are kept clean and free of any debris or other obstructions. Also, repair any cracks or gaps in these devices to ensure that water will not be allowed to seep into the slope. Slope drainage devices that are unable to properly convey runoff can lead to slope instability (landslides) and significant property damage.

Install Drought-Tolerant Ground Cover. Landscaping selected for slope planting should develop deep root structures, require little water and be fire retardant; avoid ice plant because it is heavy and has a shallow root structure. Hillside landscaping is very effective in providing slope erosion control. Replant bare spots as soon as possible. However, if heavy rain is in the forecast, consider temporarily installing some type of erosion control product to prevent soil from being washed away.

Do Not Over-Irrigate Slope Landscaping. Consider consulting a landscape professional for advice concerning appropriate watering schedules. Watch for irrigation runoff. It may indicate that the ground is already saturated. Over-saturation of the ground is not only unnecessary and expensive, but can cause subsurface damage.

Do Not Drain Directly to Slopes. Water should not be allowed to sheet-flow or to drain directly over the top of slopes. This tends to cause erosion, which can be difficult to control and severe damage may result rather quickly.

Do Not Dispose of Soil or Debris on Slopes. Loose soil or debris should not be left on or tossed over slopes. Loose soil soaks up water more readily than compacted fill. In addition, it is not compacted to the same strength as the slope itself and will tend to slide when laden with water and may even affect the soil beneath it. The sliding may clog terrace drains below or may cause additional damage in weakening the slope. If you live below a slope, try to be sure that loose fill is not dumped above your property.

Do Not Allow Water to Pond Against Retaining Walls. Retaining walls are built to withstand the ordinary moisture in the ground and are, where necessary, accompanied by sub-drains to carry off the excess moisture. If water is permitted to pond against them, it may seep through the wall and cause the soil adjacent to the foundation to swell resulting in significant structural damage to the wall.

Monitor Movement & Property Condition Changes. Be observant of damage potentially caused by slope movement, such as widening cracks in flatwork or walls, or doors and windows that stick. Consider measuring, photographing and/or marking cracks to determine if they are growing over time. Other warning signs may include water flowing or seeping out of the base of the hillside, substantial erosion or other significant earth movement on the face of the slope. Also be attentive to any major rotation or tilting of retaining walls and/or drainage devices on or near the slope.

Discuss Slope Concerns with Neighbors. Get to know your neighbors. Be observant of potential problems on neighboring properties. If your neighbors are over-irrigating or have broken sprinklers, tell them. If you see water draining from their property onto the slope or their terrace drains are blocked or damaged, tell them. Water backed up on their property may eventually reach you. Water backed up in surface drains will tend to overflow and seep into the terraces, creating less stable slopes.


Repair and protection of hillsides properties may require some grading work to address possible slope problems. In most instances, any grading work not only requires engineering design, but also may require permits from the City. The best approach is to present the proposed work plan to City staff for permit determination before proceeding. This could avoid undertaking any unpermitted work that might impact the integrity of the property or result in code violations. Please contact the City’s Engineering Division at (909) 839-7040 for further information.