Retaining Water On-site
Retaining water on-site will help replenish the existing water table and provide habitat for local wildlife. It will help to reduce erosion and the associated sediment deposits in streams. By not allowing water to run along hot impervious surfaces, we can help to prevent increased estuarial water temperatures.
Replace gutters with French drains.
By eliminating gutters from the edge of a roof, stormwater will flow evenly off all sides of the building. The stormwater is then allowed to absorb into the ground where it lands rather than being forced to a few points.
Positive drainage, or grading the soil away from the building, is essential in avoiding water damage to the foundation. In addition, a French drain system allows some water to absorb where it lands and carries excessive water to a lower spot on the site. More information on French Drains.
Harvesting rainwater can be as simple as placing a rain barrel under downspouts. The barrels will hold nutrient rich rainwater for plant use. Water can be used directly from the barrels (link several together with a hose for more storage space) or stored in smaller containers such as empty plastic gallon jugs for later use.
Rain barrels can be an empty, clean garbage bin to more engineered barrels that are available at most garden shops. More information on rain barrels.
Harvest greywater for use in the garden.
Please consider this section as an introduction to greywater systems. Please check with your permitting department to determine what kinds, if any, of greywater systems are allowed in your jurisdiction.
Greywater refers to wastewater from your home that does not pose any danger to spread infection or contamination. It includes wastewater from bathtubs, showers, bathroom washbasins, and clothes washing machines. Greywater from sinks, showers and appliances can replace fresh water to irrigate gardens. Greywater should be applied below the surface where possible (e.g., via drip line on top of the soil, under mulch; or in mulch-filled trenches) and not sprayed.
Greywater should be judiciously distributed throughout your garden, avoiding over saturation on any one area. It should be applied only at the plant root base, not on the leaves and not on vegetables.
Preferred greywater sources are first: bath, shower and bathroom sink as the concentration of soaps in the amount of water is less. Second: washing machine rinse cycle and utility sink. Consideration should be made to use biodegradable soaps rather than harsh commercial soaps.
Install dry wells to allow rainwater to percolate slowly into the soil.
Dry wells are small pits, usually two to three feet wide and deep, filled with gravel. These pits hold stormwater and allow it to slowly infiltrate into the ground at a slow rate. Dry wells are used where underground drainage pipes end and at the base of downspouts. These systems are very simple, but can provide filtering, absorption, trapping and some biological treatment in areas too tight for other treatments.
Use dry streambeds to distribute rainwater from downspouts.
Streambeds that are dry and serve an aesthetic purpose when there is no rainfall can be used to carry water to a low lying area during a storm event.
Add rain gardens to low-lying areas.
Rain gardens are a grading and planting technique designed to daylight drainage and hold water on site longer in order to let it infiltrate slowly into the groundwater system. Rain gardens are low-lying areas, created with specific layers of soil and organic mulch, which naturally filter rainwater over the days following storm. Where traditional storm drains carry storm water runoff directly to local streams and rivers, rain gardens filter and reuse this water, reducing stormwater pollution.
Additional benefits of a rain garden include providing shade, windbreaks and absorbing noise. They require little maintenance once established and are ideal wildlife habitats. More information on rain gardens.
Select proper plants.
In the Bay Area where there is plenty of water during one portion of the year and none during the other half, special consideration should be made when selecting plant material. Plants such as willow, birch, alder, wax myrtle, rushes, clump sedges, and yellow-eyed grass should be able to tolerate such extreme conditions.
Terraced slopes will slow water velocity and create more surface area, which helps to reduce water runoff and erosion. Terraced slopes are also aesthetically appealing.
Install swales on slopes under 15 degrees.
On gentle slopes (less than 15 degrees) broad, shallow ditches or swales that follow the contours of the land will hold storm runoff. Over time, they fill up with silt and form terraces, which can be planted and mulched.
Use boomerang swales on slopes over 15 degrees.
On slopes steeper than 15 degrees, dig boomerang swales. These v-shaped berms point downhill and form basins that direct water to a tree. Dig them in a net pattern, starting at the top of a slope. Size them so they don't catch so much runoff that the soil of the berm becomes saturated and bursts. Soil type and steepness will affect the size of the boomerangs.
Use straw bales to reduce erosion.
Straw bales placed in a terrace can also slow water on a steep slope. They should be placed on a level area that is parallel to the existing contour. The bales should be pinned to the ground with willow or bamboo stakes.
Planting a native tree or bush at the ends of the straw bale row will help prevent erosion. When it rains, the bales soak up water like a sponge and water the trees. The bales will decompose in a few years, and the line of trees you have planted will hold the hillside in place with their roots.
Use level spreaders.
A level spreader is a gentle slope of land that converts concentrated, erosive runoff into a dispersed, sheet-flow pattern. Spreading water across a vegetated slope slows water velocity, which increases infiltration and reduces erosion. Level spreaders can also be used as the pretreatment lawn strip to carry runoff from a driveway or patio to a bioretention facility.
Use check dams.
Check dams are constructed of loosely placed rocks, which allow water to gradually seep through them. They can be used to slow down the flow of water at the base of a hill.
Wattling bundles are a living erosion control net.
The very old technique of wattling can help to minimize erosion, redevelop riparian corridors, reduce steepness of slope, and replace a creek-like channel with a stairway of living plants. In the fall or spring, make bundles of willow, cottonwood, alder, etc. 12-24" long and 5" wide of twigs .5 to 1.5" in diameter. Bind the bundles with two raps of twine and place them in a trench that is parallel to the existing contour. The bundles do not need to be covered with soil and they will root on their own. More information on wattling bundles.
Ponds will retain water and provide wildlife habitat.
In addition to the aesthetic and wildlife habitat benefits associated with ponds, unlined ponds can retain stormwater allowing it to reenter the groundwater table slowly.
If mosquitoes are a concern, add mosquito fish, or Gambusia affinis, to the pond. These small fish eat mosquito larvae immediately upon hatching from eggs. They require no feeding and care is limited to protecting them from garden sprays and from chlorine or other chemicals used to clean the pond. Mosquito fish do not lay eggs, but rather give birth to live young, and require no special environment, as most other fishes do, for depositing and hatching the eggs. It is important to note that mosquito fish should never be placed in any natural habitat, such as lakes, streams, rivers, creeks, etc. More information on mosquito fish.
For chemical-free mosquito control around patio areas, citronella and catnip plants are effective in repelling mosquitoes. Sprays made from the essence of these plants are available on the internet on sites such as NoTox, Inc.
Buffer waterway edges.
Plant material, when placed along the edges of streams and ponds will help to filter pesticide and fertilizer run-off before it enters the waterway. You should avoid running grass to the edge of a waterway.
Naturally filtered pool.
An article in the March 2003 issue of Landscape Architecture Magazine reported on a method of building a chemical-free swimming pool. A German company, BioNova, designed this pool with two zones: one for swimming, the other planted as a biological filter. The pool requires no chemicals and vacuuming only twice a year. The planted area maintenance consists of occasionally removing dead plant material. These natural pools are more common in Europe and are slowly making their way into the United States.
There are many ways to increase the efficiency of your irrigation system. Match the method: drip (individual, in-line, or sub-surface drip systems), sprinklers, or soaker hoses to the situation, the soil, and the plants.
Most importantly do not water paved areas! Adjust the spray pattern, relocate sprinkler heads or change spray nozzles as necessary. Avoid evaporation and reduce fungal growth by using spray irrigation in the early morning hours between 4 and 7:00 a.m.