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Re: How much water on a Mediterranean hill?

Mike,

I'd think that you can get practical advice from your area by talking to 
a builder about whatever "rules of thumb" they have for grading hillsides 
 and more importantly, to locate professionals who can advise on what's 
safe in your area. Or try extension and soil conservation services for 
guidelines in your area.  If your garden is on a slope that's no steeper 
than the one your house was put on, or if it's the original hillside, and 
not steepened by cut-and-fill, it's very likely that you can terrace it 
with making it unstable. The main thing in engineering it is to create 
good drainage at the contact between native soil and backfill, and to 
make sure that all terrace walls are very freely draining.  If a terrace 
wall acts like a dam, the weight of water behind it will likely cause 
failure.  I would guess that only the worst-designed slopes will fail 
from summer irrigation [if irrigation is not excessive, most of the waer 
should be taken up by the planting].  In any case the major concern is 
winter rains -- especially the biggest expected rain event after soils 
are largely saturated.  In San Jose, it would vary widely, but you're 
probably talking about, say 5 inches or more in 48 hours every several 
years -- and that's what your hillside has to be engineered for.  I would 
hope that a Mediterranean planting, even when being established, wouldn't 
take more than the equivalent of one inch prcipitation per week.

You'll find a couple of articles on steep hillside gardens in California, 
if you browse past issues of Horticulture magiazine.  Only see it in the 
local library, and don't have the references.

Loren Russell, Corvallis, Oregon
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