Golf course irrigation has become a highly engineered science of pumps, piping, sprinkler heads, controls, automation, and telemetry, configured to maximize efficiency and conservation. Advances in system design have been driven by architect and player expectations for optimum turf conditions and the endless struggle between turf disease and fertility. Decisions about application rates, frequency, duration, and coverage have become more technical, with the added pressures of balancing expectations, performance, and environmental awareness. All of these factors have forced a keen focus on the most important resource for any irrigation system-water.
Understanding Demand
At its core, irrigation for healthy turfgrass, whether on a golf course or elsewhere, needs to distribute enough water to compensate for differences between usable precipitation and turf transpiration. Water demand, therefore, is variable throughout the growing season, accounting not only for changes in precipitation conditions but also factors that influence evapotranspiration, such as soil composition, air temperature, wind speed, solar radiation, relative humidity, the turfgrass species, and cut height. Water demand is also influenced by the efficiency, capacity, and function of the irrigation system.
Water demands are seasonal but not insignificant relative to competing uses and costs. An 18-hole golf course, for example, may require average irrigation rates of less than 100,000 gpd (gallons per day), but peak rates during dry periods can reach 400,000 gpd, with total annual demand of more than 20 million gallons. At an average utility cost of $5 per 1,000 gallons (U.S. EPA, n.d.), this equates to an annual water bill of $100,000. Additional water may be needed for landscaping, water features, and amenities such as turf tennis courts, which can eat up more than 4,000 gallons from an irrigation water budget, per week and per court.
An accurate estimate of water- demand is critical to the design of an effective irrigation system but can be difficult to achieve when considering all the potential variables. Weston & Sampson has developed an analytical model that estimates seasonal irrigation water-demand based on precipitation data from a nearby National Oceanic and Atmospheric Administration (NOAA) station, latitude-specific evapotranspiration rates estimated by the Thornthwaite method (Thornthwaite, n.d.), the irrigated acreage, and various usage factors like precipitation, system functionality, soil capacity, and turf sensitivity.
Drilling bedrock wells for irrigation purposes, shown here, can be expensive, but it also has long-term cost benefits when compared to rising utility costs.
The model considers normal, drought, and severe-drought precipitation conditions and can be calibrated to actual precipitation and usage values. The model output for a typical 18-hole golf course in New England, with eight acres of tees and greens, 32 acres of fairway, 35 acres of rough, and 5 acres of landscaping, is summarized above. The model output highlights the significant difference between average and peak (rainless) rates and the variability of demand, not only over a season but also in response to increasingly drier conditions.
As a factor of safety, golf courses often rely on multiple primary and secondary water sources to meet seasonal demand. Selection of water source(s) is inextricably linked to the hydrogeologic setting. In areas with favorable hydrology and productive aquifers, on-site surface water and/or groundwater sources may be available to meet the irrigation demand. Development of on-site water sources, like the drilling of bedrock wells, can be expensive, but it also has long-term cost benefits when compared to rising utility costs.
Where surface water and groundwater resources are limited, purchased public water may be the only option. In more arid or coastal regions, courses have adapted by using recycled wastewater or seawater desalination for golf irrigation.
Source water evaluation should consider long-term sustainability, especially during seasonal dry periods, as well as regulatory restrictions for withdrawals that may impact neighboring resources. For surface water, the U.S. Geological Survey (USGS) has developed a very useful web-based application named “StreamStats” that estimates seasonal flows for selected perennial watercourses throughout the U.S. (USGS, n.d.). For groundwater, a long-duration pumping test during the summer months is the best way to evaluate the sustainable yield. The above graph shows how three days of continuous pumping determined that the sustainable rate for test well TW-3 was 100 gallons per minute (gpm), significantly lower than the startup rate of 250 gpm.
Special Conditions
A typical golf course irrigation pump system.
Groundwater sources can be especially sensitive to the effects of long-duration pumping cycles, as prolonged periods of low water levels promote aquifer depletion and leave the borehole vulnerable to oxidation, bacterial growth, and sedimentation. The best-management practices for groundwater wells optimize pump settings and shorten the pumping cycles to minimize these impacts. However, shorter pump cycles necessitate higher sustainable-source rates to meet the irrigation demand. From the previous example concerning test well TW-3, a shorter (16-hour) pump cycle will increase the peak demand (24-hour) rate from 273 gpm to 409 gpm, an increase of 33%.
It’s important to note that public water sources may be subject to conservation restrictions during drought emergencies, especially for recreational uses. The sustainable yield of public sources may also be influenced by limits on the period-of-use or pipe diameters and fittings that restrict flow rates. Sustainable yields for wastewater and desalination sources may be limited by treatment efficiencies and requirements for disposal of system effluent.
Golf course irrigation systems typically utilize multiple high-capacity pumps that operate/cycle during non-golf, low-evapotranspiration (evening) hours. The logistics of relatively short cycle times require system pumps to operate at significantly higher rates than the water sources allow. Using the example from the New England course that irrigates 80 acres of turf and landscape, if the peak water demand of 393,012 gpd was delivered in six hours, the distribution pumps would need to operate at rates of more than 1,100 gpm, about four times the water source rate of 273 gpm.
Pond Storage As A Solution
Irrigation pond management should consider the aesthetics of pond stage, water quality and vegetation, the potential for sedimentation and leakage, and permit conditions for bypass flow.
The gap between source and distribution rates, however, can be made up from pond storage. Water storage is used to achieve the desired flow rates, volumes, cycle times, and line pressures for irrigation. The bigger, the better, ideally sized to accommodate a minimum pump-intake depth of 10 feet below pond stage and several days of peak irrigation without recharge. To put this in perspective, a 1-acre pond holds approximately 325,000 gallons per foot of storage, roughly equivalent to a single day of irrigation.
Golf course architects design irrigation ponds to function as storage and golf features, strategically positioned to impound water courses and stormwater in addition to challenging golfers. Direct piping from other sources to the pond provides greater control over the use of these resources to maintain the pond stage. Pond management should also consider the aesthetics of pond stage, water quality and vegetation, the potential for sedimentation and leakage, and permit conditions for bypass flow. Pond bathymetry and hydrogeologic surveys provide useful information for pond management. New options for large-volume underground storage can be utilized when ponds are not practical or when conditions warrant tighter controls on evaporative losses.
In summary, from a hydrogeologist’s perspective, golf course irrigation boils down to three critical design elements:
- water demand
- source(s)
- storage.
Consideration of these three elements in chronological order, and in line with the following recommendations, will lead to a properly designed and effective irrigation system:
- Water demand estimates should consider normal, drought, and severe-drought conditions.
- Water source(s), storage, and distribution should be designed for peak demand and function efficiently at average and peak rates.
- Selection of source options should be based on a water-supply feasibility analysis that prioritizes use of on-site water resources.
- Source evaluation should consider long-term sustainability.
- Source yields should be optimized and consider the effects of operational logistics and regulatory restrictions.
- Storage is utilized to fill the gap between source and distribution rates.
- Storage should be sized to provide several days of peak irrigation without recharge.
- Storage selection and management should consider aesthetics, water quality, and advances in underground options.
Works Cited
- Thornthwaite, C. W. (n.d.). online_Thornthwaite.
Retrieved from Potential Evapotranspiration byThornthwaite Method: https://ponce.sdsu.edu/onlinethornthwaite.php - U.S. EPA. (n.d.). Data and Information Used by
WaterSense. Retrieved from WaterSense: https://www.epa.gov/watersense/data-and-information-used-watersense - USGS. (n.d.). USGS StreamStats. Retrieved from StreamStats | U.S. Geological Survey - USGS.gov: https://
www.usgs.gov/streamstats PRB+
Rob F. Good, Jr., CPG, LEP, is a Senior Technical Leader (Hydrogeology) in Weston & Sampson’s Rocky Hill, Connecticut office. He can be reached at good.rob@wseinc.com.
Published in PRB+, July 2024.