Hint: Water Always Flows Downhill …
Assessing drainage conditions around properties and how to improve them are both simple and at times complicated. Simple because everyone knows that water flows downhill; so you start out knowing generally what direction it is likely to go. Far more complicated, however, are designing commercial or residential property lot drainage systems based on technical analyses of how much water flow to expect, where it will go and what needs to be done to prevent damage. At Helfrich Associates, we are most often called in when drainage conditions have been long neglected and/or when there is real damage to property and structures. In Southern California with our abundant sunshine, it is tempting to put off addressing drainage problems until after our relatively short, but sometimes intense rainy season. Those fast-moving thunderstorms in August or that first gentle rain in the fall disappears and then nothing happens until January or February when the bulk of our seasonal rain arrives (sometimes in buckets).
By then it is often too late, and that’s when the sandbags appear at fire houses in foothill communities with the approach of an El Nino storm cycle. Poor drainage conditions and neglected problems can then cause significant property damage due to flooding, water intrusion and soil erosion. In addition, there is always the possibility in Southern California of expansive soil movement and an entire slope slipping away (mud slides).
For these reasons, Helfrich Associates recommends that we and you begin your drainage-related assessments in November each year after the first major rains of the season. In addition to newly discovered roof leaks (discussed last month), property owners can often see evidence of surface water ponding and water seepage into the house near the floor. Then continue in June of the following year to see how things are going and to maintain or make any additional repairs to landscaping and drainage systems.
To avoid big surprises later in our rainy season, we recommend the following inspections and actions before the next rain starts falling:
- Homes should be provided with roof drains, gutters and downspouts, and these systems should be checked for damage at least twice per year.
- All drainage devices should be checked at least twice per year to ensure that they are not blocked. All blockages should be cleared.
- Drains at the top of slopes should prevent water from overflowing onto the slope.
- Terrace drains and brow ditches on slopes or at the tops of slopes are designed to carry runoff water to an appropriate discharge point. These drains should be checked at least twice per year and cleaned of any accumulation of dirt and other debris. Water that backs up in surface drains will overflow and seep into the slope, creating instability.
- Water should not be permitted to collect or pond in yard areas. This water will either seep into the ground (loosening the soils) or will overflow onto the slope. Once erosion is started, it is difficult to control and severe damage can occur quickly.
- Loose soil or debris should not be left on slopes. Loose soils soak up water more readily than compacted fill and will often slide downslope. This material may clog terrace drains and may cause additional slope damage.
- Slopes should not be over-irrigated. Naturally, ground cover will require some moisture during the hot summer months, but during the wet season, irrigation can cause heavy ground cover to move, which not only destroys the cover, but also may begin slope surface erosion. Heavy ground cover can cause surface sloughing when saturated due to the increased weight and weakening of the near surface soil.
- Water should not be allowed to collect against foundations, retaining walls or basement walls. These walls are typically built to withstand the effects of normal soil moisture and may require subsurface drains to collect and transfer excessive water away from the structures.
- Swales that have been graded around the home or on the lot should not be blocked. These swales are typically constructed to provide drainage toward the driveways, street, or other positive outlet.
- Building pad and slope surfaces should be periodically inspected for rodent activity. Burrowing rodents will reduce slope stability by allowing additional water infiltration and channeling of surface runoff into the slope soils.
As you can see from our recommendations, property owners and their landscape service providers can do a lot to maintain or improve their existing drainage systems. There are times, however, when you should consider seeking the help of a structural engineering firm due to the persistence or the scope of problems before they get out of control.
Helfrich Associates has performed hundreds of property geotechnical, soil and drainage assessments in the Southwest. We’ve designed and engineered effective drainage systems for the most challenging of locations to help property owners keep that water moving downhill in a controlled, orderly flow and away from buildings, homes, pools, patios, landscaping, garages and other structures. Money spent on preventative drainage maintenance and control systems is well worth the investment—especially when the clouds burst unexpectedly.