Improving The 2015 Model Water Efficient Landscape Ordinance

The California Model Water Efficiency Landscape Ordinance promotes water efficient landscapes in new developments and retrofitted landscapes. The Department of Water Resources in California developed the ordinance. It is designed to use California’s limited water supply in an efficient manner for landscape irrigation. According to the ACWA 50% of water used in urban areas is used outdoors. This is the type of legislation we see starting in California and moving east to other states with limited water resources.

The California Department of Water Resources started the process of updating the Ordinance of January 30, 2016. This was the first stakeholder session and I was able to gain valuable insight for improvements from Lance Sweeney, President of Sweeney & Associates, Inc. Lance has been in the industry for 35 years and through his leadership, his firm has become internationally recognized for its commitment to water conservation through the advancement of efficient irrigation technologies. Below are the recommended changes Lance would like made to the MWELO.

1. Revise the ETAF based on the WUCOLS ratings.

Adjust the ranges and remove gaps. While WUCOLS is not scientifically based, it is the best source available for estimating the water use qualities of plants. The plant factor ranges from WUCOLS seem to be skewed to the high side and there are gaps between water use ratings.

  • a. The plant factor range for Low Water Use (LWU) planting is set at between 10% and 30% of ET. This is a 300% range. So a LWU plant can use water at the 10% rate or three times that amount at the 30% rate. It just seems like too great a spread in potential water use.
  • b. Why are there gaps between the water use values of Low Water Use (10%-30%) and Moderate Water Use (40%-60%)? There is also a gap between the Moderate Water Use and High Water Use values (70% – 90%). It seems like there must be plants who’s water use falls into these gaps.
  • c. Suggest the following values be used for non-turf plantings:
    • Very Low Water Use <10% of ET
    • Low Water Use 10% – 25% of ET
    • Moderate Water Use 25% – 50% of ET
    • High Water Use 50% – 100% of ET
  • d. As there is more scientific data available for turf grass I suggest that the following values be used. Values have been included for synthetic turf that will be justified in another point below.
      • Warm Season Grass 60% of ET
      • Cool Season Grass 80% of ET
      • Synthetic Turf Grass (Sports) 10% – 25% of ET
      • Synthetic Turf Grass (Passive) 5% of ET

2. Revise the Special Landscape Area (SLA) as it applies to the MAWA and ETWU.

Currently the MWELO applies an ETAF of 100% ET for both the MAWA and ETWU calculations. The following are issues with this condition:

    • a. The result is by mathematical rule the ETWU will always equal the MAWA.
    • b. This creates an ETWU that is likely far larger than the actual water use of the landscape. The resulting ETWU is an unrealistic amount of water use for most projects and causes false water use projections for a community.
    • c. This eliminates the need to design proper hydrozones in the landscape as they all will have the same water use rating in the current system.
    • d. If a landscape area is irrigated with Recycled Water (RCW) the entire irrigated landscape is a SLA, but any swimming pools, spas or other water features (assuming potable water) would be regular landscape areas. In this case, using the current calculations and assigning the entire irrigated landscape an ETAF of 100% makes it impossible to successfully meet the WELO calculation.

I would suggest using the Special Landscape Area (SLA) ETAF of 100% for calculation of the MAWA only. For calculation of the ETWU, use the standard hydrozone ETAF’s and a multiplier to increase the amount of water applied to the SLA. In no case should the multiplier provide a final ETAF of greater than 100%. This will allow the ETWU to more accurately reflect the needs of the landscape and provide a more accurate projected water use for the project.

3. Clarify the designation of recreation areas as Special Landscape Areas.

  • a. The 2010 version of the MWELO specifically mentioned recreational turf as being an SLA, but the 2015 version has simplified the definition to “recreation areas”. I would hope that this means that all landscape in recreation areas is to be considered an SLA? I have always felt that recreation areas should be allowed more water than a commercial, i.e. non-residential, site. But, I have met strong resistance to this definition. Can this definition be clarified?
  • b. Could this SLA status also extend to public swimming pools? While private residential swimming pools are often unused through much of the year, public pools are much more frequently used and represent a great benefit to the community.

4. Specify the way trees are to be handled in the landscape.

Trees represent a problem in calculating the WELO water use. We have found that different cities treat trees differently. The issue is that by definition, specifically in the matter of root depth, trees should be a separate hydrozone from other plant materials. I would like the state to provide some clear direction to simplify the way that tree irrigation water use is calculated. Issues with trees as follows:

  • a. The area of a tree, being defined by its canopy area, can lead to double counting of landscape areas (plantings under trees) and the counting of non-landscape areas (where a tree canopy is over pavement, hardscape, etc.).
  • b. Trees come in many sizes (canopy area and height) and the canopy size of trees will vary through their life span.
  • c. Trees should be irrigated separately from the rest of the landscape, but many trees will not require irrigation once they become established.
  • d. Some agencies have directed us to simply ignore the trees (as they assume the irrigation is temporary) while others want us to account for the trees, but offer no clear method of doing so.

Trees are the highest value plant material in the landscape and offer the greatest benefit. They should be considered an asset to the community. I have the following suggestions.

  • a. Define the exact method to count the water use of trees.
  • b. Define trees as small (10 foot canopy), medium (10 – 20 foot canopy), or large (+20 foot canopy).
  • c. Calculate the tree canopy area as being additional to the ground plane landscape area.
  • d. Use the combined ground plane and tree canopy areas in the calculation of the MAWA and ETWU.
  • e. If the tree irrigation is to be temporary (less than three years), allow for it to be removed from the ETWU.
  • f. Considering the environmental benefit of trees, I suggest that they be counted as a Special Landscape Area.

5. Specify the way swimming pools should be treated as landscape areas.

    • a. Set actual ETAF for pools. Almost no city that I have submitted WELO calculations to allows for anything lower than 100% ET to be used for swimming pools. 
    • b. Set refill efficiency (100%). For some reason cities require the refill rate of pools to be set the same as a spray system. I believe that this is in response to the EPA’s water use calculation, but a pool refill system is 100% efficient as no water is lost in the process. 
    • c. Consider a lower ETAF if a pool cover is installed. Perhaps 50% of the normal rate. 
    • d. Consider public swimming pools to be Special Landscape Areas. 

6. Allow for non-irrigated areas!

  • Many landscape architects can  provide effective, water conserving solutions in the landscape that require no irrigation. These include extensive, permeable unirrigated areas (gravel or bark mulch) and synthetic turf areas. Due to the MWELO’s definition of a landscape area, the water saving potential of this practice cannot be counted in the calculations.

LEED 2009 WEc1.1 calculations allow for the use of these unirrigated areas to be counted as landscape areas and they are frequently used in the landscape. I suggest a similar practice be included in the MWELO.

7. How to treat synthetic turf.

  • Synthetic turf systems can be classified as passive use (front yards, medians, landscape) and active (sports fields). The potential water use of these systems is far less than that of living turf. The use of these systems should receive credit in the landscape water use calculations. I suggest the following:
  • a. All synthetic turf areas should be counted as Special Landscape Areas for the MAWA calculation.
  • b. For the ETWU, passive synthetic turf grass should be counted as a Low Water Use Planting (at 5% of ET) to allow for occasional wash down to clean the turf surface.
  • c. For the ETWU, active synthetic turf grass, with a cooling or watering system, should be counted as a Moderate Water Use Planting (at 25% of ET) to allow for cooling during active use and more frequent wash down.
  • d. For the ETWU, active synthetic turf grass, without a cooling or watering system, should be counted as a Low Water Use Planting (at 10% of ET) to allow for more frequent wash down.

8. Allow for contributions from alternative water sources.

  • Irrigation water is being supplied from many non-traditional water sources in California. In some cases, these water sources are mandated through storm water control ordinances. Currently there is no way to receive any credit in the MWELO calculations for the use of on-site collected storm water, rain water, grey water, or other alternative water sources.
  • If the water volumes of these alternative sources can be calculated, they should be used against the ETWU as a benefit, thus reducing the ETWU. This will encourage the continued use of these alternative sources.

9. Focus on the planting!

  • Achieving the WELO water conservation goals is 95% based on the landscape planting design and about 5% on the irrigation design. The landscape design has thousands of possible water use plantings, control over the entire landscape area and this results in tremendous possible variations in water use. The irrigation portion is either spray or drip. Selecting drip irrigation results in less than 10% reduction in water use over a spray system. And with the MWELO directing more and more irrigation to drip, the result is that irrigation plays a minor role in achieving the water reduction goals of the MWELO.
  • This fact is seeming lost to many in the landscape architecture community. The WELO calculation is viewed as an “irrigation thing”. I suggest that hydrozoning and the MWELO be taught in the universities producing landscape architects and become part of the landscape architecture licensure exam. This would strengthen the ability of the designers to meet the goals of the MWELO.

10. Train plan check staff!

  • I frequently interact with city plan check staff that are unfamiliar with the details of the WELO. Some of these staff interpret the vague points of the WELO in their own way, regardless of how the local agency has written the ordinance. In some cases, I have had multiple plan checkers from the same city disagree on how to interpret the WELO. Unfortunately, some plan checkers are incorrect in their reading of the WELO and cause undo project delays redlining and rejecting projects that are clearly in compliance with the ordinance.
  • Training of local agency staff should be required prior to their being allowed to plan check projects submitted for WELO compliance. This will facilitate the water conservation goals of the MWELO.
Thank you Lance for putting so much thought into your suggestions and thank you to the Department of Water Resources for proactively reaching out to landscape professionals and seek their help on improvements. If you have additional recommendations you would like to see we welcome them in the comments section.  If you enjoyed this article please consider subscribing or following me on twitter @H2oTrends.


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