How well does your garden stand up to heavy rain? Do you find areaswhere water collects and stands for several days? Water-eroded gullieson hillsides? Signs of flooding near driveways and walkways? Drainage channels can carry surplus water off slopes and pavedareas and away from your house. Here, drainage ditches in four gardensflaunt their function. Instead of sending water into underground pipes,they move runoff in rock channels and fabricated stream beds thatoutline a house, curve around slopes, or weave between mounded plantingbeds.
Above left, San Diego landscape architect Joseph Yamada fitted astone gutter at the base of the hillside surrounding Robert Mann’shouse. Wrapping two sides of the house, the 2-foot-wide bed picks upwater from roof downspouts and runoff from the upper slopes, funnelingit to a city storm drain at the lower edge of the property. Cobblesplaced 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 sringrains, and sloping lots combine with high groundwater levels to makedrainage engineering a necessity. Seattle designer David Pootcontrolled these problems by installing the natural-looking swale shownabove. He created the 12- to 18-inch-deep stream bed by mounding earth oneach side; the raised areas allow plant roots to grow above the highwater table.
To handle the quantity of water the gully collects, helaid 4-inch perforated PVC drainpipe in the bed and covered it withriver rock. While the hidden pipe carries storm water quickly to thestreet, high-level ground water can also seep into the rock channel andget taken away. Because rains fall fast and hard in the desert, gardens there haveto be prepared for sudden summer “gullywashers.” The path inLoraine and Don Allen’s Phoenix garden (at top on facing page) isdesigned to handle them. Made of decomposed granite, it runs from theback garden between planting beds to the street.
Rather than channelall runoff from the property, its granular surface allows some water topercolate into the soil. In the Tucson garden at right, granite boulders and stones slow theflow of water so the ground can soak it up. Landscape architect JoePrchal placed the creek bed in a low spot near a patio and contoured theground around it, so that water from the hard-surfaced patios and walksis diverted to it. Any surplus flows through an opening at the bottomof the garden wall and into a natural arroyo.