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Water Efficient Landscape Plan

Water Efficient Landscape Plan

Develop a Landscape Plan that limits water and energy use while preserving or enhancing the natural environment.  This can done by done by selecting native or regionally-appropriate vegetation and trees; avoiding or limiting cool-season grasses; and planting trees to provide summer shading of buildings, streets and parking areas.

Intent:

Landscaping water use accounts for approximately 50% of a home's total water needs. Conservation of this valuable resource through such techniques as hydrozoning, reducing turf area, and selecting regionally appropriate plants is a key component to responsible building. Thoughtful selection and placement of plants can also reduce heating/cooling loads of a home, provide habitat for native fauna, and minimize the heat-island effect of developments.

 Additional Information / How to Implement:

Select landscaping materials and vegetation to fit site conditions. Regionally appropriate plants are hardy plants that can withstand local water and temperature conditions such as freeze, heat, drought, and rain. Regionally appropriate plants will also not be overly prolific or invasive, and will be able to coexist with other native plants over time.  Other benefits of landscaping with native plants: minimizes maintenance (reduces emissions of equipment); fosters wildlife habitat.

When planning for the revegetation of a site, consider the multiple services that natural areas can provide: natural habitat, storm water processing, shading, wind break, etc. Trees that shade the streets can keep a neighborhood cool while also increasing the neighborhood’s attractiveness. Properly selected plants can be grouped to serve as a bioretention zone. Deciduous trees allow the sun’s rays through in winter and provide shade in the summer. Evergreens can provide an effective windbreak. Careful selection and integration of trees and vegetation can reduce a developer’s initial costs while providing value to a development/neighborhood later. When planting trees, several factors should be taken into account such as the value of shading (trees shading asphalt will mitigate a site’s temperature more than trees shading landscaped areas), maintaining a safe distance from the house (especially in areas prone to natural disasters), ultimate tree size, etc.

Developers may wish to consider enforcing guidelines for the protection of onsite vegetation. Some developers even fine builders for damage to areas designated for protection.

If grinding and scattering cleared plants, care should be taken to grind only regionally appropriate plants. Grinding of invasive species can increase their propagation and result in the ultimate destruction of native species.

One of the best ways to reduce energy consumption is through passive solar design of a home – using orientation, overhangs, fenestration, etc. Landscaping to reduce energy consumption is only part of the whole effort.

It is good practice to limit ratio of turf area to total landscaped area due to maintenance requirements of turf versus native plants and regionally appropriate trees and vegetation. In some areas, there may be restrictions on the percentage of turf that the front yard must contain. Research has shown that homeowners are comfortable with having as little as 50% of the front yard composed of turf. Fewer regulations are imposed on turf-to-landscaping ratio in the backyard, so good gains might be made more easily there. For research on turf and landscape of front yard with native species, see: Nassauer, Joan. 1995. Messy Ecosystems, Orderly Frames. Landscape Journal, 14 (2), 161-170.

In areas with low annual rainfall, one way to account for water usage is through the development and implementation of a water budget. Below is Built Green Colorado’s Water Budgeting information.

Water Budgeting

 Description

Calculate the water needs of irrigated landscapes based on plant types, land area and irrigation system efficiency. Use the calculated water budget to apply water according to the needs of the plants and manage irrigation. Overall property water budgets can be developed to include both indoor and outdoor water requirements.

 Basic Practice Guidelines

 a.    The landscape design process should incorporate a general outdoor annual water budget to be used as a guideline for irrigation design and long-term landscape management. The water budget should be developed by the landscape architect or designer as part of the plant selection and grouping process (turf, trees, shrubs, ground covers, etc.).

 b.    The irrigation maintenance process should be based on calculation of a monthly and annual water budget for existing sites.

 c.   Calculate the site landscape water budget by summing the water requirements calculated for each hydrozone of the landscape using either of these general formulas:

      Approach #1, when Reference ET is known:

      Water Budget = (ETo)(Kc)(LA)(0.623) 

                                          IE

      Water Budget = Water Needed for Plants (gallons per year)

     ETo = Reference evapotranspiration (inches per year) for bluegrass in your area

     Kc = Crop coefficient for plant type (See Appendix E for more information.)

     LA = Landscaped Area (square feet)

     0.623 = Conversion Factor (to gallons per square foot)

     IE = Irrigation Efficiency (varies based on irrigation system)

 

      Approach #2, when Reference ET is not known:

      Water Budget = Land Area (sq. ft.) x Estimated Plant Water Use (gallons/sq. ft.)

     Where: Estimated Plant Water Use = Estimated water use in gallons/sq. ft. for the metro-Denver Front Range area. For other areas, water use estimates may need to be increased or decreased based on climate and location characteristics. Water use estimates may also be increased or decreased based on climate and location characteristics.  Water use estimates may also be reduced when more efficient irrigation systems such as drip irrigation are used.

 

d.   The water budget provides the annual irrigation that the site needs in order to thrive in addition to natural precipitation. The annual water budget assumes a normal year of natural precipitation (14 inches of annual precipitation for the Front Range area). In either wetter or drier years, the water budget will need to be adjusted.

 e.    The rate at which plants lose water to the surrounding air is called evapotranspiration (ET). Temperature, humidity, wind and light all influence the ET rate. When watering, it is only necessary to replace the amount of water that has been lost due to ET.

 f.    In order for water budgets to be accurate, it is necessary to provide accurate information on factors such as crop coefficients. See the GreenCO web site (www.greenco.org) and Appendix E for recommended crop coefficients to be used in calculating water budgets.

 g.   It should be noted that the ET0 (reference ET) in the water budget equation does not reflect that Kentucky bluegrass can be attractive and viable at much lower ET rates and can be very drought tolerant. For properly established turf, the actual irrigation water needs of turf can vary, depending on desired appearance.

 h.   The water budget does not apply to the initial establishment period for plantings, which can vary from 2-4 weeks for annuals to several growing seasons, depending on plant type and the timing of planting. One year is typical for many perennials and shrubs to become established.

 i.      Water features, outdoor pool(s), and/or any other outdoor water uses should be included in the water budget.

 j.    If a property manager/landscaper knows the water budget for each month, he/she can compare actual use to the site water budget and adjust irrigation practices accordingly. Excessive water use may also be attributed to irrigation system deficiencies, which should be corrected.

 k.    Evapotranspiration (ET) or "smart" irrigation controllers can facilitate landscape irrigation according to the needs of the plants (and therefore the water budget).

      1.    Low water-use plants don't automatically save water (they are easily and, frequently, over-watered). Using a "smart" controller can insure the proper irrigation is applied to low water-use plants.

      2.    High water-use plants (such as turf) don't automatically waste water. They are also often over-watered. Using a "smart" controller can insure the proper irrigation is applied to high water-use plants.

 l.    Often the retrofitting of poor irrigation systems and the use of "smart" controllers will provide a payback in saved water. To calculate the payback time, use the water budget to measure how much water is actually needed, versus how much has historically been used, along with local water rates and irrigation system cost.

 m.   GreenCO provides a simple water budget calculator on its Website at www.greenco.org. Green Industry professionals can use this calculator with customers to demonstrate that water budgeting is a manageable approach to understanding water needs for a given property and adjusting watering practices accordingly.

 Regional or Industry Considerations/Adaptations

 a.    Water budgets can be used by water utilities to determine how much water is needed versus how much the utility sells or has.

 b.    Water budgets can be used by water utilities to determine how much water they need versus how much they sell or have. The difference is how much water could be saved, or how much more water needs to be purchased.

 c.   Water budgeting approaches adopted by utilities typically include ET-based irrigation scheduling combined with tiered pricing for increasing water usage. Tiered pricing, by gradually increasing the price of water as consumption rises, provides incentive to conserve. At the time of this manual’s publication, this approach had been adopted in other water-limited states such as California and Arizona. See Centennial Water and Sanitation District in Highlands Ranch, Colorado, for information on their program http://www.highlandsranch.org

 d.   Colorado’s Water Efficient Landscape Design Model Ordinance (see www.dola.state.co.us/smartgrowth/) is based on water-budgeting with a goal of 15 gallons/square foot/year of water required for a landscaped area.

 e.    Check the GreenCO Website (www.greenco.org) for more information on water budgeting techniques.

 

Key References

Ash, T. 1998. Landscape Management for Water Savings How to Profit from a Water-Efficient Future. Orange County, CA: Municipal Water District of Orange County.

Resources:

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