Turfgrass and Environmental
Research Online...Using Science to Benefit Golf

Scientists at The Ohio State University used computer simulations to describe water movement in putting greens constructed by three different methods: USGA recommended,
California, and natural soil push-up. These simulations provide an excellent understandingof how different putting green construction methods affect water movement.

Volume 5, Number 17
September 1, 2006

PURPOSE
The purpose of USGA Turfgrass and Environmental Research Online is to effectively communicate the results ofresearch projects funded under USGA’s Turfgrass and Environmental Research Program to all who can benefit
from such knowledge. Since 1983, the USGA has funded more than 290 projects at a cost of $25 million. The private, non-profit research program provides funding opportunities to university faculty interested in working on environmental and turf management problems affecting golf courses. The outstanding playing conditions of today’s
golf courses are a direct result of using science to benefit golf.

EditorResearch Director

Jeff Nus, Ph.D.
1032 Rogers Place
Lawrence, KS 66049
jnus@usga.org(785) 832-2300(785) 832-9265 (fax)Michael P. Kenna, Ph.D.
P.O. Box 2227
Stillwater, OK 74076
mkenna@usga.org(405) 743-3900(405) 743-3910 (fax)

USGA Turfgrass and Environmental Research Committee
Steve Smyers, Chairman
Julie Dionne, Ph.D.
Ron Dodson
Kimberly Erusha, Ph.D.
Ali Harivandi, Ph.D.
Michael P. Kenna, Ph.D.
Jeff Krans, Ph.D.
Pete Landschoot, Ph.D.
James Moore
Jeff Nus, Ph.D.
Paul Rieke, Ph.D.
James T. Snow
Clark Throssell, Ph.D.
Pat Vittum, Ph.D.
Scott Warnke, Ph.D.
James Watson, Ph.D.
Craig Weyandt, CGCS

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Dynamics of Water Flow in Putting
Greens via Computer Simulation
Ed McCoy and Kevin McCoy
with each documented by written guidelines (2,10). On the other hand, push-up green soil profiles have evolved from decades of sand topdressing applied to native soil. Whereas each has asandy surface layer, or rootzone, the thickness of
this layer and the type of material underlying the
sandy rootzone varies for each particularconstruction method.
There has long been an interest in how
rootzone properties and soil material layering
influence water flow within contoured putting
greens. Measurement of this water flow is often
accomplished by frequent monitoring soil watercontent using probes that are placed in the soil
profile (4, 7, 8). By examining the time sequenceof water contents following rainfall, irrigation, or
turf water uptake, the rate and direction of waterflow can be inferred from water content changes.
These studies have directly documented how layered soils increase water retention within a sandyrootzone by the formation of perched water, the

SUMMARY
Computer simulations of soil water flow were constructed for a USGA, California, and push-up putting green
using HYDRUS-2D. The simulations generated animationsof soil water content over a seven-day period for full-size
greens having natural surface contours and supporting aclosely mown turfgrass stand. Also generated was drainage
rate and actual turfgrass evapotranspiration (ETa). Rainfall
and evapotranspiration scenarios were selected to challenge
thehydrologic response of these three putting greens and aturfgrass response protocol allowed the appraisal of water
related turfgrass stress.
The simulations demonstrate the utility of deeper rootzone, as seen in the USGA and California greens, in providing a direct connection with subsurface drainage elements and displacing perched water below turfgrassrooting.
Alternatively, the shallow rootzone of the push-up green
quickly became saturated during rain and remained nearlyso for 42 hours, leading to aeration stress of the turf.
During rain, the thickness of water perching was selflimited in the USGA green but continued to expand, forming a pattern relative to drainage spacing, in the California
green.
The simulations show that perched water can form inboth USGA and California greens and, in both greens, may
serve as a reservoir for subsequent water uptake by the turf.
This perched water was, however, locally short-lived inboth greens as down slope lateral flow removed it from thecrest of steeper slopes within each green.
The first appearance of drought stress was associatedwith the local absence of water perching in both the USGA
and California greens, and appeared earlier in the California
green due to the lesser water holding capacity of the rootzone.

Putting green soil profiles are frequently classified into three general categories: USGA,
California, and push-up style greens. The USGA
and California profiles are purposely constructed
ED MCCOY, Ph.D., Associate Professor; and KEVIN MCCOY,
Software Technician; School of Natural Resources, The Ohio State
University, Wooster, OH.
USGA Turfgrass and Environmental Research Online 5(17):1-15.
TGIF Record Number: 115166

Organic enriched layers that form within the surface of putting green rootzones have hydraulic properties much different than the lower rootzone layer.

1Figure 1. Soil profile layers used in the water flow simulation for a USGA, California and push-up green. In addition to layer
thickness, the hydraulic properties of the organic enriched and lower rootzone layers were different for each simulation and are
given in Table 1. This view shows a 10-fold exaggeration of the vertical scale.

of statistical techniques substantially adds toexperimental costs due to the need for replicationand the possible inculsion of nonsensical treatments in order to isolate specific factors
Computer simulation of water flow in soils
can remove many of these experimental limitations. A simulation can be built to represent a fullsize putting green and capture flow events
throughout the soil profile. Also, a simulation
allows us to challenge the system under climatic
scenarios that rarely occur at a specific location.
And because simulations do not generate random
errors, they need not be replicated. Yet the qualityof a simulation output is solely reliant on the quality of the parameters used to describe the system.
Much care must be taken in specifying the values
for these parameters.

propensity of this water to migrate down slope
creating lateral non-uniform water contents, andhow organic and soil amendments in the rootzone
appear to modulate this response.
Experimental studies of water flow ingreens, however, have limitations due to the highcost of construction, maintenance, instrumentation, and monitoring. Consequently, these studies
have employed less than full-size greens with relatively few sensors that capture data over widely
spaced time intervals and/or for a limited duration.
The result is a somewhat incomplete picture thatcan miss a specific water flow process and/or generate findings that only relate to the climate at the
study location. Also, experimental studies
inevitably contain errors and require statisticalanlysis for proper interpertation of the results. Use
2The objective of this study was to generaterealistic simulations of water flow in USGA,
California, and push-up style putting greens. For
this we chose the software package HYDRUS-2D(9), which has been employed for a variety of
applications including irrigation and drainage
design, study of irrigated land salinization, transport of pesticides and toxic trace elements, andanalyses of riparian systems (11). We sought toconstruct simulations for mature, full-size greens
having natural surface contours, built according to
published guidelines, and supporting a closely
mown turfgrass stand. Rainfall and evapotranspiration scenarios were selected to challenge thehydrologic response of these three putting greens.

green were subsequently created below this surface. In each case, the putting surface consists ofa 10-ft false front at 5% slope, a 30-ft lower landing area at 1.5% slope, a 6-ft terrace face at 15%
slope, a 41-ft upper landing area at 1.5% slope,and a 13-ft section falling away off the back of thegreen at 1% slope. Smooth curve transitions also
occurred between each of these surfaces and thetotal elevation change across the green was 2.5 ft.
The USGA green soil profile (Figure 1)
consisted of a 12-inch thick rootzone overlying a
4-inch thick gravel layer placed upon an 8-inch
thick clay loam subgrade soil. Gravel-filled
drainage trenches (6-inches wide by 8-inchesdeep) were placed in the subgrade and spaced 15
feet apart. To represent the influence of turf rooting and organic matter accumulation within thesurface layer of the rootzone (1), this 12-inch
layer was further subdivided into to a surface, a 2inch thick organic enriched layer, and a 10-inch
thick lower rootzone layer.
The California green soil profile (Figure1) consisted of a 12-inch thick rootzone overlying
an 8-inch thick clay loam subgrade soil. Gravelfilled drainage trenches (6-inches wide by 8-inches deep) were placed in the subgrade and spaced
15 feet apart. Although maximum drain spacing is

The Putting Green Soil Profiles
The simulations were designed to describewater flow through a two-dimensional slice
through the center of a typical putting green. To
accomplish this, we enlisted to help of Mr. Jason
Straka, ASGCA, Senior Design Associate with
Hurdzan/Fry Design, Inc., who provided putting
green surface elevation data along a 100-ft transect. The respective soil profiles corresponding toa USGA green, a California green, and a push-up

GreenConstruction

Layer

Total
Porosity

Air-Filled † Capillary †Porosity
Porosity

Ksat

(%)

(%)

(%)

(in h-1)

USGA

Organic Enriched ‡Lower Rootzone

46
40

20
24

26
16

6
20

California

Organic Enriched
Lower Rootzone

45
39

22
27

23
11

12
40

Push-up

Organic Enriched
Lower Rootzone

46
42

12
14

34
28

4
8

† Air-filled and capillary porosities are defined at 30 cm tension.
‡ The organic enriched layer is the surface 2 inches of the soil profile.
Table 1. Total porosity, air-filled porosity, capillary porosity, and saturated hydraulic conductivity values of the organic enriched
and lower rootzone layers of the simulated putting greens3A montage of windows is shown to illustrate the steps in the simulation and animation process. The soil profile cross section isdivided into thousands of discrete nodes each of which are assigned to the appropriate soil material (lower left). Hydraulic properties are assigned to these nodes, and an environmental scenario is created (lower center). The simulation is run to create anenormous amount of numerical data (upper left). This data is assembled via a separate graphics program (upper center andright). Individual time slices of the color plots are assembled into animations by another program (lower right).

surface, a 2-inch thick organic enriched layer, anda 2-inch thick lower rootzone layer.

not specified for a California green, we chose thisdrainage system configuration to be consistent
with the USGA green scenario. Also, consistent
with the USGA green, the 12-inch rootzone was
subdivided into to a surface, a 2-inch thick organic enriched layer, and a 10-inch thick lower rootzone layer.
The push-up green soil profile (Figure 1)
consisted of a 4-inch thick rootzone overlying a
16-inch thick clay loam soil. For consistency withthe other green designs, 6-inch wide by 8-inch
deep gravel-filled drainage trenches were spaced
15 feet apart across the green with the upper surface of the drainage trench placed 10 inches below
the surface of the green. As with the other scenarios, the 4-inch rootzone was subdivided into to a

Rootzone Properties
In addition to soil layer thickness and orientation, the water flow simulation requires information on the hydraulic properties of each layer.
Specifically, this information consists of parameters of the water retention curve and the saturated
hydraulic conductivity. Our intention in this work
was to simulate water flow within greens thatadhered to the respective guidelines (when available) but also placed more emphasis on watertransmission than on water retention. In otherwords, our aim was to generate hydraulic proper-4

Figure 2. The rates of water drainage (inch3 h-1) over the first four days of the simulation for the USGA, California, and pushup greens. Drainage resulted from a 1 inch h-1 rainfall rate from hours 1 to 5 for the USGA and California greens and from a0.25 inch h-1 rainfall rate over the same interval for the push-up green.

ties that corresponded to a rootzone having sandparticle sizes on the coarse side of the acceptable
range. We did this for the lower rootzone layer of
the USGA and California greens by generating
hydraulic properties of a construction rootzone
mix since the lower rootzone layer of a maturegreen is expected to have hydraulic properties
similar to the rootzone mix of a newly built green(Dr. Norm Hummel and Mr. James Thomas, personal communication). The organic enriched layer
for each green was intended to contain about 6%
organic matter (by weight). Thus, the construction rootzone mix properties for each green were
adjusted as to appropriately reflect this organic
enrichment.
Finally, in order to supply the most realistic information to the simulation, we generated
candidate hydraulic properties from in-house data
and then provided this information to Dr. Norm
Hummel (Hummel & Co. Inc.) and Mr. James
Thomas (Thomas Turf Services, Inc.) for a criticalreview. Following their review, we adjusted thehydraulic properties of both the organic enriched
and lower rootzone layers as appropriate. Our
approach to generating hydraulic properties of thepush-up green rootzone was similar to that for the
USGA and California greens but was more subjective because there are no published descriptions of the most prevalent rootzone
characteristics.
The hydraulic properties of the rootzone
layers for the USGA, California, and push-up
greens are given in Table 1. The USGA green
rootzone had hydraulic properties characteristic of
minimally amended and fairly uniform mediumcoarse sand. This is indicated by small total andcapillary porosity values and large Ksat and airfilled porosity values, when compared to recommended UGSA guidelines. The California green
rootzone had hydraulic properties characteristic ofunamended and uniform medium sand withgreater Ksat and air-filled porosity values andsmaller total and capillary porosity values than the
USGA rootzone. The push-up green rootzone had
5Contoured surfaces found on most putting greens are an important feature that was considered in this analysis.

hydraulic properties as would be expected fromyears of consistent and frequent topdressing using
quality topdressing sand.
In all cases, organic enrichment resulted in
an increase in total and capillary porosity values
and a reduction in air-filled porosity and Ksat values. Finally, the clay loam subgrade had a Ksat

greens. In each case, 50% of the roots were present in the 0- to 1-inch increment, 32.5% in the 1to 2-inch increment, 10% in the 2- to 4-inch increment, 5% in the 4- to 5-inch increment, and 2.5%in the 5- to 6-inch increment. No roots were present below 6 inches depth and this same pattern
was employed across the entire green surface.
In HYDRUS, drought stress is simulatedby the inability of turf roots to take up soil water
when the water content surrounding the root isless than some specified value. In this work, wechose a water content of 10% (by volume) as
indicating the onset of reduced root water uptake.
This is consistent with our field studies (5) wherein "footprinting" on experimental greens wasobserved to occur at this level of soil water content. Further, as the local water content falls below
10% (by volume), root water uptake is progressively reduced.
HYDRUS is also capable of simulating
soil aeration stress on the root wherein water
uptake is limited via inadequate local air-filled
porosity (defined as total porosity minus the local
water content). Another term for aeration stress is"wet wilt" as defined by Dernoeden (3). In thisstudy, wet wilt occurred when the local air-filled
porosity was 10% (by volume) and water uptake
was progressively reduced as air-filled porosity
declined below this value.

value of 0.02 in h-1 and the gravel had a Ksat valueof 4700 in h-1 characteristic of these respective
materials.
Turfgrass Rooting and Response Protocols
A powerful feature of HYDRUS 2D is theability to include in the simulation a plant that is
capable of responding to the soil water status. In
this particular case study we included the best
available information corresponding to a closely
mown turfgrass species. This included specifying
the distribution of turfgrass rooting and indicating
at what soil water status the turf would sufferwater-related stress.
The turfgrass rooting information consisted of specifying the proportion of the total rootsystem that occurs within selected depth increments. To isolate soil profile and rootzone property responses in this work, we chose to employ anidentical rooting pattern for each of the three6The Simulation Scenario

between the hours of 8:00 am and 8:00 pm with nowater uptake during the intervening hours. This
hourly ET rate over a 12-hour daylight period
yielded a daily atmospheric demand (referred toas ETcrop) of 0.17 inches of water.
Our choice of this value was based on thework of McCoy and McCoy (5) wherein daily
ETcrop values corresponding to putting green turf
were generated for a 20-year period at each of six
locations throughout the US. Examining the distribution of the April-September daily ETcrop values from this previous study indicated that ourselected rate of 0.17 inch day-1 was about one
standard deviation greater than the mean for
Phoenix, AZ, two standard deviations greater thanthe mean for Boulder, CO,and three standard deviations greater than the mean for Columbus, OH.
So our selected ETcrop value represents a moderately above-average drying event for Phoenix, andsomewhat extreme drying event for Boulder, anda severely extreme drying event for Columbus.

The simulation runs for 168 hours, beginning at 12:00 am and continuing for seven days.
Initially (at hour 0), the soil profile is moist withequilibrium water contents corresponding to thepresence of a water table 0.5 inches below thedrainage trenches. At hour 1 rainfall occurs acrossthe USGA and California greens at a precipitation
rate of 1.0 inch h-1 and continuing for four hours.
This high intensity rainfall delivering four inchesof rain was selected to challenge the infiltrationand drainage capabilities of each green. Because
the push-up green was incapable of infiltrating
four inches of rain, the precipitation rate for this
scenario was adjusted down to 0.25 inch h-1 yielding one inch of total rainfall. No additional precipitation or irrigation occurred on any of thegreens after this initial event.
Subsequently, a diurnal evapotranspiration
cycle was imposed on these greens and consistedof an atmospheric demand of 0.014 inch h-1

AnimateAnimation 1. Water content (% by volume) within the soil profile of a USGA putting green over a period of 162 hours. Rainfall
occurs from hour 1 to 5 and a diurnal ET cycle occurs throughout the seven days of the simulation. The vertical dimension is
exaggerated 10-fold for the 100-ft long by 2-ft deep slice through the green.

7

This was consistent with our goal to challenge thewater retention properties of the simulated greens.
Having supplied all required data for the
problem, each seven-day simulation was run on a
3.4 gHz personal computer, requiring a run timeof about eight days and generating about 180 Mbof data. Output from the simulation includes volumetric soil water content, drainage rate, andactual turfgrass evapotranspiration (ETa) overseven days. The water content values are generated for all soil depth and lateral distance values
included in the problem (e.g. the entire area of
Figure 1).
The drainage rate values are the total forseven drainage trenches and the ETa values are theintegrated response across the green surface. It is
important to note that the ETa values are the actual turfgrass evapotranspiration rates in response to
an atmospheric demand. As such, if any portion of
the root system is exposed to limiting water content or air-filled porosity values this will reflect
drought or aeration stress and the ETa values as
generated by the simulation will be less than the
0.014 inch h-1 atmospheric demand used in thesimulation.

(from 3 to 3.5 hours). The upper surface of theperched water zone occurs at the interface
between green and blue, or at water contents ofabout 27% (by volume). This perched water, however, accumulates only to a limited extent in a
USGA green so that the continued rainfall (from3.5 to 5 hours) simply displaces an equivalent volume of water into the gravel layer. This implies
that if the 1 inch h-1 rain rate were to continue
indefinitely, there would be no further accumulation of water within the soil profile and an equivalent volume of water would just as rapidly bedrained from the soil.
Water flow through the gravel starting at
3.5 hours is evident by the large water content values within the gravel layer just above the interface
with the subgrade. This distribution of water within the gravel layer reaches its maximum extent atfour hours with the characteristic pattern of lower
water contents adjacent to the drainage trenchesand (within the flat reaches) higher water contents
in between. This pattern remains stationary during
the final hour of rain indicating a steady rate ofwater flow from the gravel into the drain. Finally,
during the rain period, the subgrade transitions
from very wet to nearly saturated.
Although there is a slight decline in rootzone water contents during the hour following therain, the results clearly show the establishment ofa uniformly thick perched water layer from hours
six to 12. This perched water layer appears to be
only about three inches thick, characteristic of thelesser water retaining rootzone employed in thissimulation. If the simulation were to have used arootzone mix with smaller air-filled porosity values and greater capillary porosity values, thiswould have resulted in a thicker perched waterlayer. The uniformity of water perching across thegreen is, however, rather short-lived as downslope, lateral water flow in the more steeply
sloped sections removes the perched water fromthe crest of these slopes. This becomes apparent at
24 hours as evidenced by lower water contents
above the rootzone/gravel interface at the crest of
the terrace face and, to a lesser degree, at the highpoint of the green and the crest of the false front.
Down slope lateral water flow in sloped, USGA

Results
Water Flow and Drainage in the USGA Green
A time sequence of volumetric soil watercontents within the USGA green soil profile isshown in Animation 1. In this view, the coloredarea is the entire soil profile of this simulation andwater contents within this soil profile are shownby a color scale. The time slices are spaced at 0.5
hours during the early phases of the animation andprogressively increase to 12 hours at the end of
the animation.
The first time slice of this animation iscoincident with the start of the rainstorm, so subsequent time slices (from 1.5 to 5 hours) show
water infiltration into the soil. Also shown is theaccumulation of perched water above the interface
between the lower rootzone and gravel layers
8The results of these simulations show how rootzone properties, the soil profile and surface contouring interact to influence irrigation requirements.

greens has been experimentally observed by bothPrettyman and McCoy (7) and Frank et al. (4).
After 24 hours, lateral flow has substantially slowed so that for the remaining hours of thesimulation (from 24 to 162 hours) the rootzone
simply becomes progressively drier due to water
uptake by the turf. It is interesting to observe during this period that the organic-enriched layer
maintains greater water contents than the adjacentportion of the lower rootzone. This is because thesoil of the organic enriched layer has greater water
holding properties than the lower rootzone layer(Table 1). Also the progression of drying appears
to be independent of rootzone depth. This is interesting in that water uptake is shown to occur in the
6- to 12- inch depth increment even though roots
were not present below six inches. Seemingly, thewater retained at these deeper depths was adequately "wicked" nearer the surface and taken up
by the roots. Consequently, perched water occurring from 9- to 12-inches deep can apparently
serve as a reservoir for subsequent turf uptake inthese systems.
Viewing the progression of drying acrossthe green, however, shows more intense rootzone
drying in regions of the green where the perchedwater was removed at 24 hours. Thus, the crest of
the terrace slope, the high point of the green, andthe crest of the false front all show more extreme

drying throughout the rootzone than other areas of
the green. This is consistent with experimental
observation of putting green slope effects on rootzone water content by Prettyman and McCoy (8)and Frank et al. (4).
Drainage in the USGA green began a 3.4
hours and within one hour increased to its maximum rate of 45.8 inch3 h-1, for a 1-inch thick slice
through the green (Figure 2). This rate remained
steady till 15 minutes after rain stopped when thedrainage rate decreased, rapidly at first and thenmore slowly. Twelve hours after rain ended, thedrainage rate had decreased by over two orders ofmagnitude. In the USGA green, the maximum
drainage rate was comparable to the rainfall rate
across the green such that had this rain rate continued indefinitely, water ponding on the surface
and runoff would have never occurred.

Water Flow and Drainage in the California
Green
The time sequence of volumetric soil
water contents within the California green soil
profile, shown in Animation 2, employs the samelayout and time slices as the USGA green. Early inthe simulation, as with the USGA green, water9

infiltration results in the formation of perchedwater, in this case occurring above therootzone/subgrade interface. Unlike the USGA
green, however, continued rain results in theperched water zone progressively approaching thesoil surface till at the end of the rain the soil isnearly saturated to the surface. This progressive
wetting of the rootzone, however, does not occur
uniformly across the green but mostly forms a pattern relative to the gravel-filled drainage trenches.
In this case, water perching approaches the green
surface mid-way between the drainage trenches
yet remains deeper over the trench.
A lateral pattern of water contents coincident with drainage trenches in a California-stylegreen was also observed experimentally by
Prettyman and McCoy (7). This pattern forms
because a California green lacks a gravel layer
underlying the rootzone so that water must travel
laterally rather long distances through the rootzone before entering a drainage trench.

Following the rain, however, the zone ofperched water recedes rapidly at first and thenmore slowly so that by 30 hours, the drain trenchinduced pattern has disappeared and the perchedwater zone has a thickness of about three inches
distributed somewhat uniformly across the green.
The exception to this is the absence of perching at
the crest of the terrace face and a 5-inch thickperched water zone at the base of the terrace face.
For the remaining hours of the simulation(from 30 to 162 hours) the rootzone simply
becomes progressively drier due to water uptake
by the turf. During this period, the dynamics ofwater flow in the California green is similar to thatseen in the USGA green. The principal difference
between these simulations is that the upper 6 inches of the California green is much drier for thesame time slice than the USGA green. This is dueto the smaller capillary porosity values andreduced water retention of the California rootzone
sand as compared with the USGA rootzone mix.

AnimateAnimation 2. Water content (% by volume) within the soil profile of a California putting green over a period of 162 hours.
Rainfall occurs from hour 1 to 5 and a diurnal ET cycle occurs throughout the seven days of the simulation. The vertical dimension is exaggerated 10-fold for the 100-ft long by 20-inch deep slice through the green.

10Animate

Animation 3. Water content (% by volume) within the soil profile of a push-up putting green over a period of 162 hours. Rainfall
occurs from hour 1 to 5 and a diurnal ET cycle occurs throughout the seven days of the simulation. The vertical dimension is
exaggerated 10-fold for the 100-ft long by 2-ft deep slice through the green.

Drainage in the California green began 3.1
hours into the simulation and achieved its maximum rate of 28.3 inch3 h-1 just as the rain ended(Figure 2). The drainage rate subsequently
declined, rapidly at first and then more slowly.
The California green required 31 hours before thedrainage rate had slowed to at rate 2-orders ofmagnitude less than its peak. In the California
green, the maximum drainage rate was about 60%of the rainfall rate implying that had this rain ratecontinued indefinitely, water would have ponded
on the green. The slower maximum drainage ratein the California green than the USGA green is inagreement with the measurements of Prettyman
and McCoy (6).

Water Flow and Drainage in the Push-up
GreenWater infiltration into the push-up green
and the interruption of flow at the rootzone/clay
loam interface resulted in a virtually saturated soil
profile when the rain ended at hour 5 (Animation
3). This situation remained virtually unchanged
until hour 24 when water contents declined to the25-35% range at the crest of the terrace face. It
was not until hour 42, however, before most of theremaining areas of the rootzone followed suit,
opening up air-filled pore space for adequate soil
aeration. The exception was the base of the terrace
face and low point of the green where the soil
remained wet.
This overall result is substantially different
11from the USGA and California green observations
and is due to the 8-inch thick layer of fine textured
native soil between the base of the rootzone andthe drainage trench. This disconnect between the
sandy rootzone and the drainage system results inlong-lived water accumulation following rain. It isalso important to note that this water saturation
occurred with just one inch of rainfall.
After 68 hours all regions of the surface
four inches had dropped below a water content of
35%, opening air-filled porosity for adequate gas
exchange. This led to a laterally uniform drying of
this layer throughout the remainder of the simulation. At the end of the simulation, water contents
were greater across the surface of the push-up
green than the USGA or California greens becauseof the increased water retention of the push-up
green rootzone layers (Table 1).
Whereas drainage rates were roughly similar for the USGA and California greens, drainage
behavior in the push-up green was quite different

from the others (Figure 2). Drainage in this green
began at 14 hours (well after the end of the rain)
and peaked at a rate of 0.064 inch3 h-1 at 35 hours.
Because no drainage occurred during the rain
event, it is inevitable that surface ponding would
occur if this 0.25 inch h-1 rain had continued. This
demonstrates how a relatively impermeable finetextured soil can serve as a disconnect between
rainfall and drainage within these push-up greens.
Finally, the decline in drainage rate following thepeak in this push-up green was gradual, unlikethat seen in the USGA and California greens.
Turfgrass Evapotranspiration
Turfgrass response to soil water status isshown by tracking actual turfgrass ET (ETa)throughout the simulation (Figure 3). Given an
atmospheric demand of 0.014 inch h-1 between 8
a.m. and 8 p.m. for each of the seven days, an ETa

Figure 3. Simulated, actual turfgrass ET (inch h-1) over 7 days for the USGA, California, and push-up greens. Turfgrass ET
resulted from an atmospheric demand value of 0.014 inch h-1 from 8 am to 8 pm for each of the 7 days. Water associatedturfgrass stress is indicated when ETa values are less than the atmospheric demand.

12

value less than this would indicate water associated stress according to the simulation protocol.
Further, stress observed early in the simulation
following the rainstorm is regarded as a soil aeration (or wet wilt) stress due to inadequate air-filled
porosity within the soil where roots reside. Stressobserved late in the simulation is regarded as
drought stress due to inadequate soil water contents within the depth increment of turf rooting.
Soil aeration stress was observed from thesimulation results of the push-up green, occurring
mostly throughout the first two days (Figure 3).
During daylight hours of the first day, ETa averaged 42% of atmospheric demand and in the second day averaged 88%. The reduced severity ofaeration stress on the second day matches the progressive opening of air-filled porosity as localized
water contents dropped below 35% (Animation
3). No soil aeration stress was observed from thesimulation results of either the USGA or
California greens (Figure 3). Even though thewater content animations for these greens showed
substantial differences in water perching, watercontents in both cases had sufficiently declined
throughout the depth of rooting so as to provide
adequate air-filled porosity. The ability of thesegreens to avoid aeration stress is likely due to thegravel layer of the USGA green and the exceptionally high permeability of the California green,each leading to adequate drainage.
Drought stress, as defined in the simulation protocol, appeared on day 3 in the California
green and on day 4 in the USGA green (Figure 3).
Although drought stress increased in its severity
on subsequent days, both greens showed a daily
pattern of lesser stress in the morning with a deepening stress later in the afternoon. This suggests
an overnight replenishing of water within theregion of turfgrass rooting from the perched waterretained below this depth. Although this response
has not been documented from experimental
water content measurements, it is frequently
observed that turf showing drought stress in theafternoon appears to be sufficiently hydrated thefollowing morning.
As with the water content animations
where values in the upper six inches of the

California green are much drier for the same timeslice than the USGA green, turf drought in the
California green precedes that in the USGA green.
This, again, is due to the lesser water retention of
the California green rootzone sand (Table 1).
Finally, drought stress was not observed till day 7of the push-up green simulation, even though thisgreen received 25% of the total rainfall of theother greens.
The results in Figure 3 show actual turfgrass ET across the entire green surface. Not
apparent in this figure is the localized responsethat can be inferred from the water content animations (Animations 1 to 3). Thus, the early onset ofdrought stress in the USGA and California greens
were isolated principally to the crest of the terrace
face and, to a lesser degree, the high point of thegreen and the crest of the false front. These locations are precisely where the perched water disappeared first. Down slope versus upslope differences in turf drought stress within high sand content putting greens was observed experimentallyby Prettyman and McCoy (8).

Conclusions
Throughout the seven days of this simulation, 70, 63 and 9% of the total rainfall drained
from the USGA, California, and push-up greens,
respectively. Thus, even though the amount of
rainfall occurring on the push-up green was 25%of the others, a disproportionate small fraction of
the rainfall found its way to the drainage trenches
in the push-up green. Cumulative evapotranspiration over the seven-day simulation was 27% in
both the USGA and California greens as contrasted with 106% in the push-up green. The reason
why ET in the push-up green exceeded 100% was
because some water initially present in the soil
profile was used in evapotranspiration over theseven days.
These facts, together with the other simulation results, emphasize that water flow in USGA
or California greens are relatively similar whencompared to a push-up green. This is principally
because both USGA and California greens employ
13

deep (12-inch), sandy rootzones that (1) establish
a direct connection with the subsurface drainage
system and (2) displace layer interfaces well
below the ground surface.
Differences in water flow that did occur
between USGA and California greens included
the progressively deepening pattern of water
perching during rain in the California green when,at the same time, water perching thickness was
self-limited in the USGA green. Associated withthis is the slower maximum drainage rate in the
California green. Another difference was that the
California green showed an earlier onset ofdrought stress than the USGA green.
These differences are principally due tothe presence of a gravel drainage layer in the
USGA green and the lesser water holding capacity of the California green rootzone. Yet, both systems’ perched water was short-lived at the crest of
the steeper slopes. Further, perched water that was
retained in the rootzone was taken up by the turf
in both systems even though rooting did notextend into this zone. Consequently, the first onsetof drought stress in both cases was localized to thecrest of the terrace face and, to a lesser degree, thehigh point of the green and the crest of the false
front.
Finally, although there is substantial evidence that the simulations accurately depict waterflow in these greens, it is important to rememberthat the greens were subject to extreme environmental conditions and that the simulations used arootzone with emphasized transmission
attributes.

bentgrass greens USGA Turfgrass andEnvironmental Research Online 2(17):1-12.
(TGIF Record 91751)
2. Davis, W. B., J. L. Paul, and D. Bowman. 1990.
The sand putting green: Construction and management. Publ. 21448. Univ. of California Div. ofAgric. and Nat. Resour., Davis. (TGIF Record
14801)
3. Dernoeden, P. H. 2006. Understanding wet wilt.
USGA Green Section Record 44(2):7-9. (TGIF
Record 110213)
4. Frank, K.W., B.E. Leach, J.R. Crum, P.E.
Rieke, B.R. Leinauer, T.A. Nikolai, and R.N.
Calhoun. 2005. Effect of rootzone material anddepth on moisture retention in undulating USGA
putting greens. USGA Turfgrass andEnvironmental Research Online 4(11):1-9. (TGIF
Record 105278)
5. McCoy, E.L., and K.R. McCoy. 2005. Putting
green rootzone amendments and irrigation water
conservation. USGA Turfgrass and Environmental
Research Online 4(8):1-9. (TGIF Record 103631)
6. Prettyman, G.W., and E.L. McCoy. 2002. Effectof profile layering, root zone texture, and slope on
putting green drainage rates. Agron. J. 94:358364. (TGIF Record 79589)
7. Prettyman, G.W., and E.L. McCoy. 2003.
Profile layering, root zone permeability and slope
affect soil water contents during putting-green
drainage. Crop Sci. 43:985-994. (TGIF Record
86302)

Acknowledgements
This research was supported by funds
received from the USGA’s Turfgrass andEnvironmental Research Program and the Ohio
Turfgrass Foundation.

8. Prettyman, G.W., and E.L. McCoy. 2003.
Localized drought on sloped putting greens withsand-based root zones. USGA Turfgrass andEnvironmental Research Online 2(4):1-8. (TGIF
Record 85739)

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