Introducing the Course Coefficient – A Water Use Benchmarking Tool

Key Takeaways

• The Course Coefficient is a way to compare actual water use to expected water demand.
  
  
• To calculate and track the Course Coefficient, courses need a good measure of total water use, an annual evapotranspiration (ET) estimate for their area, and an accurate measurement of their irrigated acreage and surface water area.
  
  
• A Course Coefficient less than 1.0 indicates that less water is being used than expected based on ET demand.
  
  
• Tracking the Course Coefficient over time quantifies the impact of water conservation efforts and highlights opportunities to improve.
  
  
• As more courses calculate and share Course Coefficient data, they will benefit from benchmarking and being able to compare their water use efficiency with similar facilities in their area and around the country.

Example of the Course Coefficient Calculation 

Step 1: Calculate annual water use

The units used to represent annual water use vary. Many courses have records for total gallons or total acre feet used. The first step is to convert this data into inches of water used across the entire property annually. You will see this can also be done by month.

For example, let’s say a golf course records through a metering device that 63,000,000 gallons of water were delivered to the property last year. To convert this to acre-inches, divide 63,000,000 by 27,154 (the conversion factor for gallons to acre-inches). That equals 2,320.1 acre-inches of water used annually. If records are in acre-feet, simply multiply by 12 to convert to acre-inches. 

Step 2: Calculate annual water demand

The Course Coefficient is the ratio of total water used (acre-inches of water) to the total water demand for a property each year. Demand is determined with knowledge of the annual ET, the irrigated acreage, and the surface water acreage. In this example, we will use ET data from the OpenET website. For this property, the reference ET (ET_o) was 39 inches of water for the year.

Now we need to calculate total water demand by multiplying this ET_o by the total irrigated and surface water acreage. This property has 71 acres of irrigated turf and 1.2 acres of lakes filled with irrigation water. Add the turf and lake acreage to equal 72.2 acres. Multiply the sum of the turf and lake acreage (72.2 acres) by the annual ET_o (39 inches) to yield 2,815.8 acre-inches of water, the total water demand for this property last year. 

Step 3: Calculate the Course Coefficient 

The Course Coefficient is simply a ratio of water use to water demand. In this example, we’ll divide the annual water use (2,320.1 acre-inches) by the estimated annual water demand of 2,815.8 acre-inches to get a Course Coefficient of 0.82. In this case, the course is using 18% less water than the anticipated demand for that year.

What the Course Coefficient Tells You

The Course Coefficient compares actual water use to estimated water demand. If the Course Coefficient is less than 1.0, the course is using less water than the anticipated demand for that year. The Course Coefficient will fluctuate from year to year based on weather, varying approaches to irrigation, or different water demands on the course. For example, if a course is reseeding naturalized areas one year, the coefficient will very likely increase because of the additional water needed to germinate and establish the seed. On the other hand, if a course converts large playing areas from cool-season to warm-season grasses, the Course Coefficient would be expected to decrease once the new turfgrasses are fully established. Tracking the Course Coefficient over time will build an increasingly informative picture of water use that can help superintendents make decisions, evaluate how changes to the course or maintenance program impact water use, and provide more information about water use to golfers and decision-makers.

The Course Coefficient can also be calculated by month, which delivers further insight into water use throughout the year. For courses that overseed, the coefficient may increase significantly in the fall during seeding and again in the late spring and early summer during the transition period to facilitate bermudagrass recovery (Figure 1). For courses growing cool-season grasses in hot climates, a comparison of the coefficient to courses with warm-season grasses in the area can be a compelling benchmarking tool to make the case for conversion.

What the Course Coefficient Does Not Include

The Course Coefficient does not include a number of factors that will cause it to vary over time. For example, rainfall is not included in the calculation. Rainfall indirectly influences the ET_o calculation, but the intensity and duration of rainfall will affect soil moisture and plant water needs differently. For example, a steady 1-inch rain over several hours may eliminate the need to water for several days or more depending on the time of year. A 3-inch downpour with lots of runoff may not offset irrigation demand for more than a day, especially on courses with significant mounds and slopes that sheet away water. Water regulators typically use 50% of the recorded rainfall to calculate ET minus rain. While we considered including rain in the Course Coefficient calculation, simplicity was our goal across climates. We feel the calculation is cleaner without the confounding effect of rainfall, especially in areas where rain events can be very sporadic or highly variable in intensity. In a rainy year, a course is more likely to have a lower Course Coefficient than a dry year.

The calculation also does not consider a crop coefficient, irrigation system uniformity, leaching requirements, irrigation water loss due to wind and evaporation, and leaking pipes or lakes. While these are all valid factors that influence water use, they are highly variable from one property to another. The beauty of a simple benchmark is that course officials can not only review data from their own property, they can easily compare with other courses in the region that also track their Course Coefficient. If a course has a much higher Course Coefficient than some of its neighbors, managers and decision-makers can investigate why this might be the case. The Course Coefficient is not a water budget tool, but it can alert a course that there are opportunities to improve water use. Courses might conduct further investigation and utilize the USGA Water Budget Tool to take a closer look at the factors not included in the Course Coefficient calculations to get a better estimate of expected water use.

Does a Low Course Coefficient Indicate a Course Is a Low Water User?

The answer is not necessarily. If a course has a low Course Coefficient and irrigates a limited amount of turf, I would categorize it as a low water user. However, if a course with the same Course Coefficient was instead managing 400 acres of turf and 20 acres of lakes over two courses, I would say that they are efficient in the amount of water applied per irrigated acre, but they are not necessarily a low water user. A strong argument could be made that a course with excess turf and excess surface water is using more water than the average facility and therefore they would not be considered a low water user.

This is a limitation of the Course Coefficient – it can be a great indicator of how well a course uses water per irrigated acre, but it does not depict total water use at a facility and the potential room for improvement through water conservation measures like turf reduction or removing unnecessary lakes. As you’ll see in one of our case studies, decreasing the area of irrigated turf and using significantly less water overall may also be accompanied by an increase in Course Coefficient if some of the water savings are reallocated to the remaining turf. Every time there is a significant change in the course itself or how it is maintained, that will essentially become a new benchmark for the Course Coefficient going forward.

Case Studies

Let us now shift gears and apply Course Coefficient data to case studies of four courses that have used different methods to conserve water. The golf course examples include a cool-season grass course in the high desert of New Mexico, two partially overseeded courses in Arizona, and a course in California that converted from cool- to warm-season grasses on fairways, tees and roughs. As you might imagine, total water use is a sensitive piece of information at each facility. Therefore, only the Course Coefficient values have been presented. OpenET was used to calculate the annual reference ET_o for each property for consistency.

The courses in these case studies are all using fundamental water conservation strategies like applying wetting agents throughout the year, raising and leveling sprinklers, replacing worn sprinkler nozzles, utilizing portable moisture meters and constantly scouting to guide irrigation schedule adjustments. These courses have also found ways to go above and beyond to conserve water, and those efforts will be the focus of the case studies.

Course 1 – Cool-Season Grasses in the High Desert

The evaporative demand in the high desert of New Mexico is extreme in the summer months. Daily ET_o rates can reach 0.5 inches in the dry, sunny and windy summer season. Water can be scarce and annual water costs can reach over $1 million for an 18-hole facility. The sand-capped fairways at this golf course offer excellent drainage, but the droughty sand provides little moisture retention. This golf course has implemented many strategies to reduce water consumption. The most impactful have been the following:

Subsurface drip irrigation

Using subsurface drip irrigation for island tees and localized areas of the rough reduces water use by 50% to 80% in those areas compared to overhead irrigation. However, the area irrigated by drip is a small fraction of the total irrigated turf acreage. Therefore, while important for water savings and reducing weed-control efforts around the tees, subsurface drip irrigation is not a significant contributor to water conservation across the property. 

Precision irrigation

Various types of soil moisture monitoring equipment are used in fairways and roughs – including in-ground soil moisture sensors and radiometers mounted on golf course equipment. Portable moisture sensors are used on greens, approaches and sparingly in fairways.

New irrigation system

The facility installed a new irrigation system over the past five years. While some may expect a big water savings from a new system, the change in water use depends on how efficient the previous system was. Our experience has shown that a new system may provide 5% to 8% water savings. 

Focusing on firm conditions and water conservation

A commitment among the facility leadership and golfers to focus on water conservation has been a big part of successful water management at this course. They have focused on turf health and playability over turf color, and they recognize that off-color areas in fairways and roughs are desirable and a good indication that the team is not overwatering. 

As we noted earlier, a Course Coefficient of 1.0 means that the course is using the amount of water that would be expected over a given time period based on ET. Anything below 1.0 represents water conservation in the context of water use per irrigated acre. Looking at the Course Coefficient data for this course, it certainly seems that they are doing a fantastic job of using water efficiently while continuing to produce a premier golf experience.

The Course Coefficients for this property are some of the lowest I have seen throughout the West, especially at a facility that provides such great conditioning. An important part of the water conservation success at this property is the agronomic staff. While tools, equipment, growth regulators and wetting agents can all help, water savings are ultimately derived from the dedication of the maintenance team. This team scrutinizes every drop of water applied. Not only has this level of dedication led to water savings, but the golfers are over the moon about the firm and fast playing conditions.

Course 2 – Partially Overseeded Course in Southern Arizona

This is an older 18-hole facility that is in a transition phase as they prepare for a large-scale renovation. Much of the motivation for the renovation is architectural change, but water conservation is an important consideration as well. Two water sources are used for irrigation, both of which are metered. Part of the renovation will be to convert playing surfaces from a hodgepodge of bermudagrasses to new hybrid warm-season grasses (bermudagrass or zoysiagrass) that can be expected to perform at a high level with less water inputs. The project will begin in 2027, so the water conservation story to date does not include turf conversion.

What is interesting about this course is that the Course Coefficient decreased by about 15% when a new superintendent took over in early 2023. The water savings can be attributed to a change in approach that focused on providing firm and fast conditions and only applying enough water to sustain healthy turf that is able to recover from golf and maintenance traffic. Golfers have been extremely happy with the improved playing conditions and have accepted turf that is green, but not as lush green as before.

Note that the Course Coefficient in 2020 was lower during the COVID-19 pandemic when watering was reduced because there was no play. Other than 2020, the years prior to 2023 had an average Course Coefficient of 0.90. After the new superintendent took over, the coefficient is significantly lower – averaging 0.77 over a two-year period. This illustrates the potential water savings that can come from a change in philosophy without investing in major renovations or new technology. While there are limits to what can be accomplished, reviewing the approach to watering is a good place for courses to start if they want to save water.  

Course 3 – Partially Overseeded Course in Southern Arizona

Golf courses built before 1980 in Arizona often had more than 90 acres of irrigated turf, which is the current limit. This course is in that category. In fact, this course once irrigated over 120 acres of grass with 70-80 acres overseeded each year. The combination of a large turf acreage and not enough water meant this course had to employ a deficit irrigation strategy. Consequently, the Course Coefficient prior to extensive turf reduction was approximately 0.80 in the years 2007 and 2008. The course struggled to provide good turf quality throughout the summer under this irrigation regime and recognized change was necessary and imminent. 

Rather than drastically reduce irrigated turf all at once, it was removed in phases. This approach was much more palatable to the membership. It also allowed this course to achieve a significant reduction in annual water use. But turf reduction is not the only success story for this property. The irrigation system was replaced in the mid-2000s and since that time I would be hard pressed to find anyone in the industry that has paid more attention to optimizing soil moisture consistency and achieving a firm playing surface while still providing good aesthetics. Soil moisture readings are collected almost daily from approximately 10 acres of their fairways. The team mostly relies on portable soil moisture meters and collect data on a 10- to 12-pace grid. They are also experimenting with radiometers and in-ground soil moisture monitoring equipment in the hope of decreasing the staff time required to assess fairway soil moisture. A dedicated team reviews that information and makes percentage adjustments to individual sprinklers daily.

Turf reduction has allowed the course to reduce annual water use and redirect some water to primary playing areas to improve conditions. The Course Coefficient is higher than others presented in this article, with an average of 1.1 over the last five years. So, why did I include this course in an article about water conservation? This course has reduced their annual water consumption significantly, mostly through turf reduction and a focus on maintaining soil moisture consistency. They are applying water at or just marginally over the anticipated annual demand, but there are several factors that help explain that. This is a more-traditional golf course with many large trees over 75 feet tall. These trees compete with the turf for water and lead to increased irrigation demand of 20%-30% along tree corridors. Additionally, the soil is very shallow and provides little plant available water and poor water storage. The course also has a lake that is using more water than evaporation would explain, indicating the lake is leaking. 

This is a case where the course has evaluated their Course Coefficient and recognizes the number is marginally higher than expected. If not for their efforts to provide firm, dry conditions and optimize soil moisture consistency, the value would be significantly higher. Remember as well that a higher or lower Course Coefficient does not necessarily connect with total water use. This course uses less water than in the past because of their turf reduction and efforts to optimize soil moisture consistency, but the Course Coefficient increased over that time because they increased irrigation to meet demand requirements on fewer acres to improve playing conditions. Using the Course Coefficient gives this course an idea of how they are performing in their current irrigated footprint and highlights opportunities to continue improving.

Course 4 – California Conversion

The water story over the past six years has been interesting at this California golf course. Before 2022, the course grew cool-season grasses exclusively, which is common in their area. High water costs and more-frequent droughts and water restrictions were strong motivations to convert fairways, tees and roughs to hybrid bermudagrass. Additionally, summer temperatures have been getting hotter in this area and the cool-season grasses were showing severe stress, even with a robust management program. Water costs exceeded $1 million annually at this property and it is anticipated that the water savings from the turf conversion will cover the cost of the project in eight years or less. The regrassing project also included a little over 2 acres of irrigated turf reduction.

It is interesting that during the project year, the Course Coefficient remained about the same as the previous years. We have found this is common in turf conversion projects and encourage superintendents to communicate that no water savings should be expected during a conversion year, even when converting from cool- to warm-season turf. Even drought-tolerant turfgrass requires extra water for a successful establishment. However, after the project year (2021), the Course Coefficient reduced by 18%. This reduction translates to approximately 30% annual water savings. The water story at this course is a great example of the impact that a turf conversion project can have on the long-term sustainability of a property, and it shows that Course Coefficients can be a great way to track and highlight water conservation efforts.

Concluding Comments

An experienced multicourse operator shared a story with me recently that relates to the Course Coefficient concept. This operator began a financial benchmarking study for the golf course agronomy operation at each of their facilities. The idea was to identify what an average and acceptable budget may be. They discovered a large disparity in the line items within each maintenance budget, and needed more information. They took an additional step and grouped courses together that had similar characteristics. Then, they had to dig deeper with the individual superintendents to identify and explain the differences between courses, which were almost always justified. Trying to benchmark budgets didn’t necessarily help the course operator compare courses in their portfolio, but it did help them identify outliers and understand the reasons why. Sometimes those reasons were unavoidable characteristics of the property. Some courses need more money for maintenance, just like some courses need more water to maintain acceptable playing conditions. However, one of the multicourse operator’s facilities had a strikingly high gas budget. Through some clever camera work, they identified that someone had been routinely stealing gas from the property!

Similar outliers can be discovered using the Course Coefficient as a water benchmarking tool. The tool does not identify why some courses are higher or lower than expected, but it does draw attention to disparities. Superintendents can then take a deeper dive into what might be driving higher-than-expected water use and where the opportunities to improve might be. Is it droughty, sandy soils? Are there hundreds of water-thirsty trees? Are the lakes leaking? Is the team irrigating without enough attention to water use? I am hopeful that tracking the Course Coefficient is a trend that spreads nationally so courses can share information and understand not only where they stand in relation to annual ET demand, but how their water use efficiency compares to similar courses. This creates opportunities for learning, improvement and better communication about golf course water use.