|TEXAS URBAN LANDSCAPE GUIDE|
|INDEX WaterWise Principles PlantSelector Contributors Links|
|A supplement to the Best Management Practices Manual produced by the Texas Water Conservation Task Force.|
In addition to education about watering needs of plants, the water budget is useful when a utility intends to focus on helping customers reduce waste by providing a target water use rate that can be used as a benchmark to compare with the customer's monthly water use patterns. To help a customer increase the efficiency of their irrigation system, water audits (surveys) and dedicated metering are recommended approaches.
Water-Use Surveys, Metering, and Budgeted Water Use
Irrigation surveys3 are designed to determine water use rates of irrigation systems and the steps needed to improve irrigation efficiency through ensuring that water is distributed uniformly over each hydrozone. The primary principle in irrigation efficiency is the same level of irrigation volume applied across landscape materials with similar water needs, and limited to the amount that replenishes soil water in the root zone. (If using reclaim water or water with high TDS an additional volume or"leaching fraction" of water should be applied in order to force salts below the root zone). The Irrigation Association (IA) has detailed BMP and training for irrigation professionals to perform on irrigation system survey. The TAMU turf program also offers irrigation training.
Utilities should begin by performing irrigation system surveys on municipally-owned and/or other publicly-owned irrigation systems. Customers who could benefit from surveys include golf couse, schools, churches, other commercial facilities with large turf area, and possibly residential customers with large irrigated areas. The water-use surveys, at a minimum, should include:
Even well-designed irrigation systems require regular maintenance to perform efficiently. To get the best results from irrigation surveys, they should be peformed at the beginning os the irrigation season. The utility can include notices in bills to remind customers of seasonal maintenance needs. For accounts with water budgets, the utility should provide notices each billing cycle showing the relationship between budgeted water usage and actual consumption. Websites and software improvements allow utilities to provide month-to-month feedback to customers with water budgets. For larger utilities a service can be provided. Simpler comparisons of average water use of all customers or customers in same billing cycle can be used to give a customer a"measuring stick" of their water use. This is useful because many customers do not irrigate or only irrigate fraction of ETo and thus the average use is typically lower than ETo for a larger utility. (Smaller utilities serving suburban customers should use this approach with caution, as per capita suburban use is typically higher than urban or rural water usage.) Soil moisture technology can be used when soil conditions allow, and landscape managers are familiar with their use and maintenance to provide a closer estimate of actual evapotranspiration.3
Dedicated irrigation meters may be required for all commercial and/or industrial accounts with automatic irrigation systems or if for all accounts if the lot is above a minimum size. For municipalities with ordinance-making powers, this can be accomplished by ordinance. Otherwise, dedicated meters may be implemented in utility service rules as a new customer policy. This approach assists customers in evaluating their monthly water use outdoors. It also gives the utility immediate feedback on water use during peak demand periods for outdoor water use and the ability to direct messages regarding the actual amount of water needed to their customers. Cities with dedicated irrigation meters have found that historically, such customers have used peak water at rates higher than ET4.
Irrigation System Design
Two major elements of irrigation system design are readily apparent, and of importance to a utility, the use of hydrozones, and proper spacing of irrigation heads. A third element, pressure regulation, can also result in water waste if the system is not properly designed. Low water use landscape designs, when incorporating irrigation systems, must also make the proper use of hydrozones. Plants with similar water use needs should be on the same zone(s) in order to reduce water use wherever possible. Drip and Microirrigation can be used on zones with mulched beds and shrubs as appropriate. The use of non-irrigated zones is also recommended. Proper controllers must be used which can run separate zones for different times per run.
Texas' licensed irrigator requirement allows a local utility to ensure that properly trained personnel are involved in irrigation system design. The utility should keep a list of licensed irrigators available for its customers, and work with new residential and commercial developers to ensure that properly licensed individuals are involved in designing new irrigation systems. This can be accomplished as an educational effort, providing lists to customers, but can also be enforced using an ordinance or services rules by providing fines for those who do not used licensed irrigators to design irrigation systems. The EPA Water Sense program also offers certification for irrigation designers that have been certified by the IA. If the utility chooses the irrigation design approach, the utility should also provide information on climate-appropriate landscape design and efficient irrigation equipment and management for new customers and change-of-service customer accounts (See Section 3 for more detail).
To serve as a model, the utility should install demonstration landscapes, and use climate-appropriate, water-efficient landscaping at water agency facilities. Demonstration sites should be properly signed, and should include SWAT irrigation controllers (see below), rain and/or soil sensors, drip and micro-irrigation hydrozones to demonstrate efficient irrigation technology. Separate landscape meters on these demonstration landscapes will allow the utility to track water demand, and provide another potential educational tool. Utilities which require landscape irrigation meters can require copies of properly sealed irrigation system designs as part of the meter application and approval process.
Minimum Standards and Upgrades
Irrigation system design and maintenance components and landscape design may be systematically upgraded through use of municipal ordinance-making powers or utility service rules. Minimum water efficient design features can be mandated for new construction, while existing systems or landscapes are offered incentives to upgrade. A standards and upgrades element of an irrigation system approach can include:
A rain sensor captures precipitation and prevents the automatic sprinkler system from operating during the rain. A high quality sensor will retain moisture based upon the quantity of rain, and interrupt sprinkler cycles after rainfall while the sensor is still moist. Sensors should:
Soil moisture sensors (SMS) use a variety of technologies to estimate the water content of soil. The most sophisticated and accurate, neutron probes, are not available for use in typical municipal utility situations due to cost and radioactivity concerns. Others include tensiometers, and various electromagnetic sensors. Tensiometers are tradiitonaly cnsiderd tohe most accurate of these, but also require constant maintenance.
Pipes and meters
Pipe and meter specifications can be used to limit the size of irrigation system piping to 5/8" in order to restrict peak flow capacity of the system. Some cities have found that developments where 1" diameter or larger pipe and meters have been used in residential developments result in transient pressure problems as most residential customers tend to irrigate at the same time of day (evening, or early morning and on weekends)6.
Turfgrass area limits are used to decrease the overall water budget of a landscape, and the limit the use of spray irrigation, since turfgrass landscapes do not do well with drip irrigation. An alternative approach to limiting the location and types of irrigation heads, the limit on turfgrass area can sometimes be applied to specific landscape areas such as, industrial, commercial, and institutional landscapes that are not likely to be used for recreation, or such limits may be applied to buffer areas or median strips. Areas which are not typically regulated in this fashion include common areas which could be used for recreation at schools, churches, playgrounds or apartment buildings, and residential back yards.
Buffers, medians and entrances
Buffer or median areas represent additional savings when all landscaped areas less than five feet in any dimension are restricted to drip or other surface or subsurface (non-spray) irrigation system or no irrigation system.
Evapotranspiration (ET) is the term used to describe the combined loss of water from plant and soil surfaces through evaporation and transpiration. Transpiration serves two basic functions for plants: |
The measurements for ETa parameters require a level of equipment and destruction of plant material so as to be impractical in all but research applications. As a result several decades ago equations were developed to express the relationship between environmental factors, such as temperature, wind, solar radiation, relative humidity, and precipitation to the flux of water through ET. These equations of which there are several are collectively referred to as reference or potential ET. A more thorough discussion of the ET equations can be found at the University of Idaho's Kimberly R&E Center. This manual introduces enough information to understand the basic limits and attributes of ET so that water conservation personnel can better understand how it can be used in planning for and implementing a water conservation program.
In order to apply reference or potential ET (ETo or PET) to a lawn or specific plants a crop coefficient which has been empirically determined is used. This coefficient is used to ensure that the water replaced by irrigation does not exceed that used by the plant since the last irrigation event. Rainfall occurring between irrigation events can be used to offset some of the irrigation as long as it is measured. The original research to evaluate these coefficients assured that the soil water reservoir would be refilled to 100% of its capacity at each irrigation event. Subsequent research and simple observation over the years since the original coefficients were developed have determined that landscape plants can survive and even thrive with less than 100% replacement of soil water. This is due to mechanisms in the plant itself which reduce the transpiration rate in response to less water availability in the root zone.
Researchers who have quantified these reductions in water use refer to these approaches as "deficit irrigation", and calculate the water savings by introducing an additional coefficient into the equation. The resulting equation for calculating irrigation amounts is:
I = (Kc x PET x Dc) - RThe ET equation above can be used, when irrigated area is known to develop water budgets in terms of volume of water to be applied. Water budges can be used to develop rate structure, which increase dramatically when a customer exceeds the amount of water budgeted for their landscape. Water budgets can also be used to determine a demand forecast based upon service area size, total irrigated landscape area, and a "typical" landscape palette from which an "average" crop coefficient can be estimated. Smart Water Application Technology (S.W.A.T.) has been developing irrigation controllers which can mechanically use ET information to limit the amount of water applied. Irrigation controller technology has been improving over the past several years with controllers using both historical ET and some using satellite feeds of current ET measurements. Not all controllers can be adjusted to meet irrigation schedules or deficit irrigation goals but continued improvement in technology can be anticipated in future years.