Technical
After the wettest winter on record, drainage is under the spotlight on sports surfaces. Mike Beardall examines the facts and explains the various methods available
treat potential troubles with water. Too often, pipe drainage systems are
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installed automatically, with not enough thought being given to the soil physics of water movement. Soil is made of minerals originally derived
from rock, and from organic matter from vegetation, water and air. Most of the soil is made of the mineral fraction derived from the parent material which is frequently located under the soil. Most soils in the UK have formed on top of glacial or alluvial secondary deposits. This is frequently boulder clay derived from glacial erosion and deposition. However, the origination of all this material is from rock. The mineral fraction is divided into a very
wide size range of particles. These are divided into the fractions:
- Sand: 0.05mm-2.0mm - Silt: 0.002mm-0.05mm - Clay: <0.002mm Soil Texture
This is a measure of the relative proportions of sand, silt and clay in a soil. Soils are often classified according to their texture and often provides a fair indication of how it will drain. The soil texture triangle is used to classify a soil based on the relative percentages of sand, silt and clay.
Structure
Structure is a term that describes the way in which the individual soil particles join together to form larger aggregates. A well structured soil is usually
rainage problems can best be avoided if grounds managers and greenkeepers understand the soil conditions they have, and how they can diagnose and
characterised by an intensive system of small aggregates, or crumbs, gradually leading into larger blocks further down the soil profile. Well structured soils are established on
sites that have been left undisturbed for many years. The smaller particles in a soil form aggregates under the influence of clay, organic matter, earthworm activity and grass root activity.
How do these affect drainage?
Water moves through a soil in the spaces between the soil particles. These are called the pores. In a soil with a high clay and/or silt content, the pore spaces are very small, and are usually much larger in a sand dominated soil. A well structured soil contains a system of inter-connected very large pores that enables efficient water movement. Downward water movement is faster in a
soil where the pore spaces are large, hence sandy soils drain faster than clay/silt soils and well structured soils drain faster than poorly structured soils. Compaction reduces pore size and causes a deterioration in structure. Barry Pace, contracts manager of
Speedcut Contractors, says; “Breaking up compaction is one of the keys to keeping surfaces playable. As well as a good drainage system in place, surfaces that have become compacted will not let water through.” “Air injection systems, such as the Gwazae, push air in under force and break up compacted soil. Because the surface is hardly disturbed, it can be a good way of treating fine sportsturf areas like golf greens, around goalmouths and under racecourse jumps.” “The key to good drainage systems is looking at the soil conditions underneath to work out the best form of long-term drainage treatment.”
The key to good drainage systems is looking at the soil conditions underneath to work out the best form of long-t
term drainage treatment Barry Pace PC APRIL/MAY 2014 I 117 ”
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