In general, public often regards the natural terrain as stable --
"terra firma". This is of course an erroneous concept.
Nature is always at work, altering the landscape.
Hills and mountains are worn down by mass wasting (erosion,
landsliding, creeping soil, etc.) and the valleys and low-land
collect these products. Thus, the natural process is towards
leveling the terrain. Periodically (over millions of years)
major land movements rebuild mountains and hills, and these
processes begin over again. In some areas these processes
are very slow, and in others they occur at a relatively rapid rate.
The development of hillsides for residential use is carried out,
insofar as possible, to enhance the natural stability of the site
and to minimize the probability of instability resulting from the
grading necessary to provide homesites, streets, yards, etc. This
has been done by the developer and designers on the basis of geologic
and soil engineering investigations. However, in order to be successful,
the slope and drainage provisions and facilities must be
maintained by you, the homeowner.
As a homeowner you are accustomed to maintaining your home;
that is, you expect to paint your house periodically,
clean out clogged plumbing, repair roofs, etc. Maintenance of
a hillside homesite must be considered on an even more serious
basis because neglect can result in serious consequences.
In most cases, lot and site maintenance can be provided along
with normal care of the grounds and landscaping. Any costs of
maintenance are far cheaper to you than repair after neglect.
Most hillside lost problems are associated with water.
Uncontrolled water from a broken pipe, septic tank, excess
landscape watering, or wet weather cause most damage. Wet weather
is the principal time of slope problems in California because the
rainfall is quite variable and may be torrential or prolonged.
Therefore, drainage and erosion control are important aspects of
homesite stability and the provisions built into the developed lot
must not be altered without competent professional advice.
Maintenance of the provisions must be carried out to assure
their continued operation. Therefore, we offer the following
list of "Do's" and "Don'ts" as a Guide to you:
DO
1. Check roof drains, gutters and downspouts to be sure
they are clear. Depending on your location, if you do not
have roof gutters and downspouts, you may wish to install
them because roof and their wide space can shed tremendous
quantities of water. Without gutters or other adequate
drainage provisions, water falling from the eaves, collects
against the foundation and basement walls which is undesirable.
2. Clear drainage ditches and check them frequently
during the rainy season. Ask your neighbors to do likewise.
3. Check interceptor (brow) ditches at the top of slopes
to be sure that they are clear and that water will not overflow
the slope, causing erosion.
4. Be sure that all drain outlets and weep-holes are
open and clear of debris, vegetation and other material which
could block them in a storm. If blockage is evident, have it cleared.
5. Check for loose fill above and below your property
if you live on a slope for terrace.
6. Limit watering or stop altogether the watering during
the rainy season when little irrigation is required.
Over-saturation of the ground can cause major subsurface damage.
7. If you change landscaping on the slopes, disturb the soil
as little as possible and use drought resistant type plants that
require a minimum amount of landscape irrigation.
8. Watch for water backup inside the house at sump drains
and toilets, since this indicates drain or sewer blockage.
9. Watch for wet spots on your property. These may be natural
seeps or in indication of a broken water or sewer line.
In either case, obtain competent advise regarding the problem
and its correction.
10. Exercise ordinary precaution. Your house and building
site were constructed to meet standards which should protect
against most natural occurrences, provided you do your part
in maintaining them.
DON'T
1. DON'T over-irrigate slopes or leave a hose or
sprinkler running unattended on or near a slope.
Ground cover and other vegetation will require moisture
during the hot summer months, but during the wet season
irrigation can cause ground cover to pull loose, which not
only destroys the cover, but also starts serious erosion.
Fifteen minutes watering per day is considered the maximum
necessary to develop and maintain good plant growth in
Southern California.
2. DON'T alter lot grading without competent advice.
The man-made slopes on your lot were designed to carry away
water runoff to a place where it can be safely distributed.
3. DON'T block, or alter ditches which have been graded
around your house or lot pad. These shallow ditches have been
put there for the purpose of quickly removing water toward the
driveway, street or other positive outlet.
4. DON'T block or alter ditches or drains. If several
homes rely on the same facilities, it is a good idea to check
with your neighbors. Water backed up on their property may
eventually reach you. Water backed up in surface drains will
overflow and infiltrate slopes, which leads to instability.
Maintain the ground surface upslope of lined ditches to ensure
that surface water is collected in the ditch and is not permitted
to collect behind or flow under the lining.
5. DON'T permit water to collect or pond anywhere on your lot.
Such water will either seep into the ground, causing unwanted
saturation, or will overflow onto slopes and begin erosion.
Once erosion is started, it is difficult to control, and severe
damage may result rather quickly.
6. DON'T direct water over slopes even where this may seem
a good way to prevent ponding. This tends to cause erosion
and slope instability.
7. DON'T let water pond against foundation, retaining
walls and basement walls. These walls are built to withstand
the ordinary moisture in the ground and, where necessary, are
accompanied by subdrains to carry off excess subsurface water.
However, excess surface water must be directed away from these
structures.
8. DON'T connect roof drains, gutters or downspouts to
existing subsurface drains which may not have been designed
for that purpose. Instead, collect the water in lined ditches
or unperforated pipes and conduct it to a storm drain, paved road
or a suitable area of natural ground. Where such channel flow is
directed onto natural ground, it must be converted to sheet flow
unless a suitable natural channel exists.
9. DON'T discharge surface water into septic tanks or
leaching fields. Not only are septic tanks constructed for
a different purpose, but they will tend, because of their
construction, to accumulate additional water from the ground
during a heavy rain. Overloading them artificially during the
rainy season is bad from a slope stability standpoint, and is
doubly dangerous since their overflow can pose a serious health
hazard. We generally recommend that the use of septic tanks be
discontinued as soon as sewers are made available.
10. DON'T try to compact earth in trenches by flooding with
water. Not only is flooding the least efficient way of compacting
fine-grained soil, but this could saturate and reduce the bearing
capacity of supporting soils.
11. In conclusion, your neighbor's slope, above or below
your property, is as important to you as the slope that is within
your property lines. For this reason, it is desirable to develop a
cooperative attitude regarding hillside maintenance, and we recommend
developing a "good neighbor" policy. Should conditions develop off
your property which are undesirable from indications given above,
necessary action should be taken by you to ensure that prompt
remedial measures are taken.