Good drainage is critical to maximise the performance of any turf construction project (sports field, golf green, racetrack etc.) or landscaping project (lawns, amenity parklands, garden beds etc.).
There are several factors that influence how well a surface will drain including:
- The rootzone material or topsoil used. In soil, water flows down through the open pores between the soil particles. The volume of flow is dependent on the total pore space, pore size distribution (i.e., transmission pores) and the continuity between them and this is primarily determined by the soil’s particle size distribution, particle shape & arrangement (structure).
- Surface levels (localised depressions) & gradient or shape. These are critical factors as the longer the period that excess water remains on the surface, the greater the potential for the surface to be damaged during use.
- Compaction due to heavy use or intensive maintenance practices will reduce the amount of water that can move into (infiltration) and down through (drainage) the soil. Compaction will also reduce aeration (air exchange) which is necessary for root growth and microbial activity.
Most of our community sports fields and parklands are constructed from fine-textured local soils which have a significant clay and/or silt content (e.g., clay loams & sandy loams).
These soils have poor drainage and are prone to compaction and waterlogging which can result in extremely soft surfaces in winter and extremely hard surfaces in summer. The slow draining nature of these local soils can also reduce their playability and usability in wet weather.
Sands are often used to construct high performance sports surfaces (e.g., premier sports fields, putting greens etc.). Sands have better drainage & aeration characteristics and are more resistant to compaction than heavier soils which is of great advantage in winter when these surfaces can become saturated. However, not all sands are suitable as many have poor drainage rates due to their particle size distribution and particle shape.
In any project, poor drainage will result in the soil remaining saturated for longer than desired. A saturated soil has an unstable surface that is easily damaged. When a saturated soil is played on or even trafficked by vehicles (e.g., mowers), the surface can quickly ‘cut-up’ result in significant surface damage.
When selecting materials to be used for construction purposes, the drainage rate, permeability or more technically the saturated hydraulic conductivity of the rootzone material or topsoil is of major importance.
The saturated hydraulic conductivity is a quantitative measure of a soil’s ability to transmit water under saturated conditions.
In simple terms, it is the amount of water that passes through a soil in a set amount of time and is generally reported in mm/hr (or cm/hr).
In Australia, there are three main methods commonly used for measuring the drainage rate (or saturated hydraulic conductivity) of sand & topsoil.
ASTM F1815-2011 Method
This method is often referred to as the USGA method as it came out of the United States Golf Association (USGA) recommendations for a method of putting green construction which has undergone several revisions over the past 50 years. The sample is compacted with a falling hammer so that a total potential energy of 3.03 J/cm2 is exerted across the core and then uses the constant-head method to measure the hydraulic conductivity.
This method achieves about 95 to 99% compaction which is comparable to a heavily used playing surface like a golf green or a high-grade playing field. This method is only suitable for sands & sand-based mixes and not fine or medium textured soils such as sandy loams and loams. This method has been widely used for more than 30 years in Australia for measuring the drainage rate of construction & topdressing sands for greens, tees, sand-based sports fields and other highly trafficked turfgrass areas. It has also been used since the mid to late 2000’s for the testing of media for stormwater biofilters & raingardens. This method is internationally recognised and there is a wealth of knowledge & experience relating to acceptable ranges for various applications e.g., both high performance & community sports fields as well as sand belt push-up greens and USGA style putting greens.
AS4419-2003 Method
This method was part of the Australian Standard AS 4419-2003 Soils for landscaping and garden use, however, the requirement to test the drainage rate of Landscape Soils (on grade) was dropped from the 2018 revision.
This method uses a light level of consolidation and the constant-head method to measure hydraulic conductivity. It is suitable for soils with some structure and variability in particle sizing. Like the ASTM F1815 method, there is a wealth of knowledge & experience relating to acceptable ranges for various applications, for example the suitability of topsoil material for landscape use, garden beds & general lawn areas. Testing to this method is also a requirement of Vic Roads Section 720 – Landscape Works (2018) for site won & imported topsoil.
Drop Method
The Drop method was developed by Keith McIntyre and Bent Jakobsen at the ACT Government’s City Parks Technical Services Unit in Canberra during the 1990’s. It is primarily suited to structural sandier soils for landscaping and sports field use. This method uses plastic tubes which are loosely filled with soil at field capacity. The tubes are generally dropped 8, 16 & 32 times from a height of 15cm to provide different levels of compaction. The falling-head method is used to measure the hydraulic conductivity (and bulk density) for each level of compaction.
The number of drops used reflect the compaction commonly experienced for passive amenity turf (8 drops), active amenity turf (sports fields) (16 drops) and horse racing tracks/professional performance sports fields (32 drops). Thirty-two drops give about 80% of full compaction and is representative of a moderately used playing field. This method is now a testing requirement for Soil for Turf & Lawns (underlay & sports fields) in AS4419-2018 and in the Specifications for soils and landscaping of constructed Melbourne Water assets (2020).
Key Message
Good drainage is critical for the success of any turf or landscaping project and drainage rates are one of the most important criteria for selecting suitable materials. With three test methods in common use, it is easy to see how this can lead to confusion. Given this, there are several important points to keep in mind:
- Each of the three methods will give vastly different results for the same sand or topsoil sample
- There is no magical conversion factor between the different test methods
- You can’t compare samples tested with one method with samples tested with another method
- Don’t use the acceptable range of one method for another method’s test result
- Check the specification to ensure you know what method to use when submitting samples
- Specification’s that do not reference a test method are not worth the paper they are printed on
STRI Australia can provide advice on which method is most appropriate for your situation and test samples to all three methods.
ReferencesAS 4419-2003 & -2018 Soils for Landscaping & Garden Use ASTM F1518 2011: Standard Test Methods for Saturated Hydraulic Conductivity, Water Retention, Porosity and Bulk Density of Athletic Field Rootzone CRC for Water Sensitive Cities, Adoption Guidelines for Stormwater Biofiltration Systems (July 2015) McIntyre, K. & Jakobsen, B. (1998). Drainage for SportsTurf and Horticulture. Kambah, Australia: Horticultural Engineering Consultancy. Specifications for soils and landscaping of constructed Melbourne Water assets (2020) USGA recommendations for a method of putting green construction. United States Golf Association, Liberty Corner, N.J. (2018) Vic Roads Section 720 – Landscape Works (2018) |
