How well does your garden stand up to heavy rain? Do you find areas
where water collects and stands for several days? Water-eroded gullies
on hillsides? Signs of flooding near driveways and walkways?
Drainage channels can carry surplus water off slopes and paved
areas and away from your house. Here, drainage ditches in four gardens
flaunt their function. Instead of sending water into underground pipes,
they move runoff in rock channels and fabricated stream beds that
outline a house, curve around slopes, or weave between mounded planting
Above left, San Diego landscape architect Joseph Yamada fitted a
stone gutter at the base of the hillside surrounding Robert Mann’s
house. Wrapping two sides of the house, the 2-foot-wide bed picks up
water from roof downspouts and runoff from the upper slopes, funneling
it to a city storm drain at the lower edge of the property. Cobbles
placed in a mix of soil and Portland cement give the shallow,
3-inch-deep course a natural-looking, impermeable surface.
In the Northwest, poorly draining clay soil, heavy winter and sring
rains, and sloping lots combine with high groundwater levels to make
drainage engineering a necessity. Seattle designer David Poot
controlled these problems by installing the natural-looking swale shown
He created the 12- to 18-inch-deep stream bed by mounding earth on
each side; the raised areas allow plant roots to grow above the high
water table. To handle the quantity of water the gully collects, he
laid 4-inch perforated PVC drainpipe in the bed and covered it with
river rock. While the hidden pipe carries storm water quickly to the
street, high-level ground water can also seep into the rock channel and
get taken away.
Because rains fall fast and hard in the desert, gardens there have
to be prepared for sudden summer “gullywashers.” The path in
Loraine and Don Allen’s Phoenix garden (at top on facing page) is
designed to handle them. Made of decomposed granite, it runs from the
back garden between planting beds to the street. Rather than channel
all runoff from the property, its granular surface allows some water to
percolate into the soil.
In the Tucson garden at right, granite boulders and stones slow the
flow of water so the ground can soak it up. Landscape architect Joe
Prchal placed the creek bed in a low spot near a patio and contoured the
ground around it, so that water from the hard-surfaced patios and walks
is diverted to it. Any surplus flows through an opening at the bottom
of the garden wall and into a natural arroyo.