Chasing Distribution Uniformity (DU) vs Reducing Net ET° for lowering costs.
Distribution Uniformity (DU), when used as one of the factors for adjusting Landscape Water Budgets, should not be higher than can be reasonably maintained over time. Irrigation systems are inefficient and costly to maintain; landscape water budgets should reflect this relationship to landscape water requirements.
See WatrWise Consulting’s Post – “Uniformity Efficiency or Performance…”.
Spray and rotor sprinklers rarely exceed 50% and 60% DU respectively. Drip systems can attain Emission Uniformity or EU (not DU) approaching 90% but this is misleading in that soil type, plant type and size (root zone footprint) vs. emitter quantity, spacing or placement, and emission rate are rarely ideal; leading to much lower “performance” more realistically represented by 60-70% (all related to soil, plant, water relationships). The terms “performance”, “DU”, “EU” and “efficiency” are frequently interchanged so put another way, efficiency is “water used beneficially by the plant material divided by the amount of water applied” (measured at the water meter). Performance is the word often used to describe the combination of uniformity and efficiency.
An adjustment for Landscape Water Budgets of 70-90% EU for drip systems watering mature plant material may indicate low water requirements (deficit watering) because typically drip systems are not expanded to properly water mature plants that have outgrown their original emitter installation – quantity of emitters, emitter flow rate and placement. Drip systems watering mature desert adapted landscapes that have not been expanded for mature plants may deficit water the landscape. These landscapes may be healthy because they are “desert adapted” and have “gone native”.
Because sprinkler systems have lower performance than drip systems, they are often the focus for efforts to improve performance and reduce water use on properties where turf-grass dominates the neighborhood. Much time, effort and money is expended maintaining turf-grass and the irrigation systems that water it. Quite a bit more time, effort and money than an equal area of desert adapted landscaping.
As the landscape matures and the irrigation systems continue to age, increased maintenance requirements will follow accordingly. These increased maintenance requirements are often deferred; the landscape may suffer even though water use may increase to compensate for poor performance of the irrigation systems.
“Improvement” projects may be undertaken to fix deferred maintenance; but rarely do they improve the performance of the irrigation systems by more than a few percentage points. Even though a project improves performance by a few percentage points… the extra effort, time and money used to maintain higher performance (50-60% or higher DU/EU) ongoing, will most likely negate any return on investment.
Simply stated; expectations of sustaining high performing irrigation systems come with a correspondingly high cost of maintenance (ROI).
This brings us to “Reducing Net ET°”. Reducing net ET° (reduce net water requirements) is a fancy way of saying, trade high cost landscaping for lower cost landscaping.
This is done by removing high cost, high net ET°, non-functional turf-grass areas and replace with lower cost landscaping. Non-functional turf-grass areas are turf-grass areas in the neighborhood that are sloped, odd shaped, narrow or shaded. Slopes and oddly shaped areas are hard to maintain and irrigate. Turf-grass and trees are competitors in the landscape and are one of the hardest situations for landscapers to manage. Shade is only one of the areas of competition; water and nutrients are two more.
Evaluating your property for opportunities to reduce net ET° can be one of the most rewarding ways to lower your operating costs; by reducing maintenance costs and water requirements for the property.
Improvements, like reducing net ET°, should be funded by your Reserve Account. Developing a Landscape Master Plan will allow for funding improvements over time (phases), while achieving the goals of the Landscape Master Plan.
Many Reserve Accounts do not include line items for landscape and irrigation improvements, even though they are similar to roads, roofing, pools and equipment, paint etc..