Chapter one

Identifying the problems

1.1
The needs of sport

Turf surfaces used for sport must be moist enough to sustain the grass, but not so moist as to affect adversely the quality of play. They will vary in character according to the special requirements of different games and the standard of provision that can be afforded. For instance, the artificial drainage system which a first-division soccer club might feel was essential to ensure play in all but the worst weather conditions could not normally be afforded or justified by the average sports club, or by a local authority responsible for the provision and maintenance of playing fields out of public funds.

Those involved in new constructions are very frequently asked to specify the usage that can be expected from the final turf surface. Such a request seems reasonable, especially from a club or educational establishment for which use has to be matched to a fixture list or integrated into a fixed timetable. In this respect, however, grass pitches can be a problem. Although grass is ideal as a playing surface when fit for play, it is not so reliably programmable as the more expensive synthetic surfaces.

An improvement in the quality of a surface, suiting it better to the skills of the game, can often be quite easy to assess. For example, the pace of a cricket pitch can be determined by the rebound of a cricket ball dropped dead onto the playing surface from a height of 4.88 m (16 ft). A bounce height of less than 508 mm (20 in) is slow, 508–635 mm (20–25 in) easy paced, 635–726 mm (25–30 in) fast, and so on. The time a perfectly weighted bowl will take to roll to a stop over a standard distance of 30 yards (27.42 m) can be used to assess objectively the pace of a bowling green. A slow green will require a weighty, robust delivery to achieve the distance but will rapidly decelerate as it reaches the mark, rolling to a halt in only 8–10 seconds after release. This compares with 14–18 seconds for a fast green where the bowl can be delivered with much less weight, or the 21 seconds that can be achieved on New Zealand's Cotula greens.

Improved performance in terms of the number of games a surface will take in a given period, though often asked for, is difficult to specify. Intensive use probably begins at two adult games a week and accumulative damage can become critical at three games a week, even if play is avoided when the surface is squelchy. One game played on a squelchy surface, at any time in the winter, may so damage the sward as to affect performance for the rest of the season.

If play is confined to the summer period or to children of 12 or under, these criteria change dramatically. Five games per week, avoiding squelchy conditions, might represent intensive use by children, but here the quality of play can be a problem, concentrating damage down the centre of the pitch and especially in the goal areas.

These conclusions on wear are supported by evidence of the following type.

1. A senior club playing first and second team games on their main home pitch may well average two games per week each season. By the end of the season most of these pitches are badly in need of far more renovation work than the average school or parks pitch would expect to get.

2. An extensive vegetation and soil survey of league soccer pitches at the end of one season revealed how frequently pitch deterioration was blamed by the groundsman on the one game that was played when it should not have been (Thornton, 1978). The trouble is that once the sward has been broken there is virtually no chance of recovery during the winter. Instead, bared areas tend to extend because of the low shear strength of the non-root-bound surface.

3. Tear wear begins when a stud or heel breaks into the surface. This is most likely to happen when the surface is wet. A well-drained soil, though moist, will often feel firm underfoot. Under these conditions the weight of a child is scarcely sufficient to cause studs to penetrate but, with adults, stud penetration may be readily achieved. This explains the big difference in the effect of child and adult use, a point not always taken into account by those who advocate the dual use of school playing fields by children and adults.

4. A qualitative scale used in agriculture to monitor surface wetness after drainage makes use of the following hierarchy of categories:

(a) hard and cracked;

(b) firm and dry but not cracked;

(c) firm and moist;

(d) moist and soft;

(e) squelchy in patches;

(f) squelchy all over;

(g) pools of standing water;

(h) surface awash.

If we could persuade referees, who are the only people officially sanctioned to cancel a game, to cancel all games when at least one third of the surface is squelchy, and to allow games only exceptionally, i.e. no more than one game in a week, when the surface remains moist and soft, the staying power of our swards would be greatly enhanced.

5. Even with the same soil and the same general intensity of use, effects determined by climate, shading and standard of maintenance may also modify performance, as in the following examples.

(a) Features of climate such as rainfall and temperature vary significantly across Britain. Thus, in Wales, there is a risk of ‘puddling’ or ‘poaching’ because of excess soil moisture from September onwards, whereas in East Anglia, the same conditions are not to be expected until the beginning of December. In the north they have more frequently to face the dual hazards of rain and frost.

(b) Shading by grandstands can weaken growth through reduction in light intensity, reduced evaporation and increased persistence of frost.

(c) Height of cut, frequency of cutting, regular over-seeding with the stronger-growing grasses, proper fertilizing, pest control, special treatment and care of goal areas, the immediate treading back of turf torn out during play: all these features, in addition to good drainage, distinguish good maintenance from bad and affect the survival of a sward through the winter.

(d) Park pitches or school pitches cannot always be patrolled out of hours to stop boys ruining the goal areas by ‘kicking in’. Children would rather have the alternatives of mini-goals and a mini-pitch of their own but too few of these are provided.

With so many factors contributing to the fate of a sward in use through the winter it would be foolhardy at present to predict the consequences of any particular pattern of usage defined solely in terms of hours of play. What can be said is that sound construction, good maintenance, a dry climate and discretion in use will all contribute favourably.

1.2
Effects of poor drainage

Poor drainage quickly becomes apparent as soon as too much play is permitted in wet weather. It may then be too late to remedy the situation until the winter is over and meantime, poor playing conditions, cancellations and disruption of fixture lists will probably be difficult to avoid. It is, however, the long-term effects which are likely to be most damaging. Excess surface moisture over a long period will generally lead to:

• greatly reduced aeration of the soil;
• reduced root development;
• less resistance to tear wear;
• less resistance to drought;
• inefficient use of plant nutrients;
• late and slow growth in the spring;
• increased susceptibility to disease.

The end result is a grass cover insufficiently durable to support the amount of use normally expected from a winter games pitch.

Most of our sports-field drainage problems are not to be attributed to the ill effects of too high a ground watertable. More typically, water from a shower of rain fails to penetrate below the immediate surface even though the soil beneath is quite dry. The problem, in fact, is one of free water perched over trapped air.

Though air appears to be empty space available for filling by water, air must be able to escape before water can move in to take over the space that the air occupied. The problem becomes clear when water is poured too rapidly into a narrow-necked bottle. The water cannot get in if it blocks the only passage through which the air can get out. This is very similar to the situation in soil when a period of intense rain floods the surface and the infiltration of water is then impeded by water obstructing the upward escape routes for air. Thus drainage can become as much a matter of the movement of air as the movement of water.

The problem of the competition for pore space between water and air becomes worse the more uniform the pore size. Given a range of pore sizes the capillary forces will ensure that eventually the water is preferentially drawn into the smallest pores. This leaves the air to coalesce into progressively larger bubbles in the larger pore spaces, making escape even more difficult unless the large pores form part of a continuous channel linked through to the surface. Here is one benefit that earthworms, old root runs, cracks and soil granulation can confer to the mature soil, but this structure may be lost during disturbance and stockpiling. It explains why the click of air bubbles bursting can often be heard if one jumps to shudder the soil round a temporary pool of surface ponded water.

Only where the soil is well endowed with large pores and is closely underlaid by a drained gravel bed is air likely to be pushed down through the soil and cleared along with the drainage water. In all other circumstances it has probably to be cleared back up to the surface, a possibility more likely to occur in response to light rain that fails to flood the whole surface. The gentle fine rain that the farmer prefers can be safely absorbed by a well-structured soil into the small pores within soil aggregates, leaving the large pores between aggregates free for the simultaneous escape of the displaced air. However, on the ‘poached’, de-structured surface of an abused sports field the whole soil is small-pore in character and a false surface water table can be rapidly established over a drier layer of air-locked pores.

This is the classic situation that requires drainage water to be by-passed through specially installed, freely permeable, vertical slits, linking the surface directly though to the underdrains.

1.3
Climate

Climatic effects of importance to sports turf are not to be summarized simply by reference to temperature and rainfall considered separately. Frequently, it is an evaporative effect caused by the interaction of rainfall and temperature that more clearly distinguishes the nature of the climatic stress and the manner in which grass growth is affected in different parts of the country.

Because the range of climatic data available in published form for the whole of Great Britain and Northern Ireland is very limited, detailed consideration of climate, as it affects the construction and maintenance of sports turf, will be illustrated by reference to an analysis based only on the figures for England and Wales (Table 1.1). All the figures used are average values for the period 1941–70, and have been directly extracted from, or derived from, information available in Meteorological Office or Ministry of Agriculture publications. However, take note of the Meteorological Office warning: ‘…it is an unusual year that follows the average pattern.’

From the data on average monthly rainfall, quoted in Table 1, it is evident that rainfall in Britain is fairly uniformly distributed throughout the year with amounts generally higher in the north and west. The figures for potential transpiration in England and Wales quoted in Table 1.2 show that roughly 500 mm (20 in) of this is returned annually, direct to the atmosphere. This loss varies little throughout England and Wales because it is mainly determined by the input of solar energy, a feature of latitude. However, the input of solar energy varies tenfold between midsummer and mid-winter, hence the special significance of the figures for excess winter rainfall (Table 1.2).

Field capacity, in so far as it represents the normal drained state, three days after saturation, reflects the combined effect of site drainage and pore-size composition. It does not guarantee the ideal air/water balance of 70% of total pore space filled with water and 30% free for aeration that would benefit healthy root activity. If the site is poorly drained, e.g. an enclosed hollow, the soil within it may remain waterlogged for long after the three-day period has elapsed, continuing to receive water as it drains down from higher up the slope. But even if the site is not in a receiving location, or does not restrict water loss, the pores of the soil may be so small that they cannot be cleared of the water they hold by capillarity, against the force of gravity, but only in response to the much slower process of evaporation upwards. However, a well-structured soil (Figure 1(c)) in a free-draining site will lose water from the large, more than 30 µm diameter pores, between the water-stable, particle aggregations, and thereby will admit air. Meantime, the small pores, less than 30 µm in diameter, between the soil particles bound together within the aggregates, will retain their water, much of it released only in response to root absorption. A freely drained, well-structured soil, left undisturbed after saturation, may well, in three days or less, achieve an ideal, air/water state for healthy root activity, but it may also still be sufficiently wet to smear and poach into a compact, destructured state, if animals, humans, or heavy machines are allowed to traffic across it. Only a frozen soil or a dry, clay-rich soil has sufficient structural cohesion to resist collapse in these circumstances. Thus, because even our free-draining, well-structured loam soils are liable to fill up and hover around or above field capacity from sometime in the autumn to sometime in the spring, throughout this period

TABLE 1.1 District values of total rainfall and number of rain-days* 1941–70 (Data abstracted from information supplied by Meteorological Office)

TABLE 1.2 Digest of agro-climatic data of special significance for sports turf

this period they will be liable to poach if used for rigorous games by adults when wet enough to feel soft.

Dates indicating the extent of this poaching risk in England and Wales are listed in Table 1.2 (wet growing days). The areas chosen as examples in England and Wales are all fairly low lying and are representative of the north (Lancashire), the south (Hampshire), the east (Norfolk), the west (Dyfed) and the centre (Leicestershire). These show that there is a risk of poaching damage throughout our winter playing season— early September to mid May—in the north and west. In the east and the south there is a good chance that this risk will not begin until well into the playing season—late November or early December—and will be over by the beginning of April.

When we take into account the risk of frost, which can further aggravate the problem of surface water retention, the figures in Table 1.2 clearly indicate how the north of England is likely to lose out on both wetness and frost, indicating a special need for drainage and under-soil heating, whereas the south is the region most favoured.

By contrast, when the figures indicative of summer drought risk are considered (Table 1.2) these show that it is in the east, south and central regions of England that provision for irrigation might well be considered.

The start and the end of the growing season, as recorded in Table 1.2, is based on a threshold value for soil temperature of 6°C (43°F) at 300 mm (12 in) depth. Well below the surface the seasonal trends are more easily distinguished, uncomplicated by short-term effects of day-and-night or day-to-day fluctuations.

At 6°C on the surface, seeds will readily germinate. However, experience in West Wales suggests that the threshold value of 9–10°C (48–50°F) at the more easily reached depth of 250 mm (10 in) corresponds well with the onset of vigorous grass growth.

Soil temperature is well worthwhile monitoring weekly, from the end of February to the end of May, and again from the beginning of September to the middle of November, following the onset of growth in the spring and the cessation of growth in the autumn (Appendix 7). This can be done most easily under a uniform, fully exposed sward, each time using a metal spike to create a new hole for a metalshielded soil thermometer to record the temperature at the required depth. Leave the thermometer in place for at least two minutes to equilibrate. Record the information in a diary, or on a graph, plotting temperature according to date. Also, at the same time, make notes on the weather, and any vegetation response such as grass starting to grow, daffodils starting to bloom, apple trees in blossom, tortoise stirring from its winter hibernation. All such events, both at the start and the end of the growing season, will be seen to be related to soil temperature, and the reasons for variations, one year to another, explained. In time, the pattern of soil temperature response for the locality will become evident and put to practical use for predicting when best to sow seed or apply fertilizer, with good prospects of achieving the desired response.

Using the growing season dates in Table 1.2 to indicate the period over which soil temperature

is likely to favour growth, and the grazing season dates as indicating the soil moisture state, we can estimate the number of days in the spring and autumn when soil temperatures encourage growth but the roots supporting this growth have to function in a soil that is likely to be too wet for adequate aeration. Note the widely varying length of this period for the five regions of England and Wales being considered. These figures have been derived from the difference in days between the date given for the start of the growing season in spring and the end of the poaching risk, plus the days between the date given for the return of the poaching risk in autumn and the end of the growing season. These totals point to very clear regional differences in the growing conditions likely to be experienced by grass across England and Wales. It could well be this feature of climate that has most to do with the variable performance in Britain of ‘continental’ grass species such as Poa pratensis (smooth-stalked meadowgrass). This potentially highly desirable, sports turf species, that does so well in parts of the USA, is claimed to be successful in Norfolk, but the many varieties so far tested in Dyfed have all succumbed hopelessly to disease.

It would be interesting to know more about the performance of Poa pratensis in the other regions, intermediate between these two extremes—for example, is Leicestershire favourable but Lancashire not?

The purpose of this brief review of some of the direct and indirect effects of climate on soil conditions has been to show how variable this can be even within the relatively small area represented by the lowlands of England and Wales. The extent of this variation is such that it should not be ignored when interpreting the behaviour of existing pitches, or designing new, anywhere in Britain. For example, we should be less willing to compromise on an overall design rate of 50 mm (2 in) per 24 hours for drainage in the north and west of Britain than in the south-east; more inclined to include Poa pratensis in a seeds mixture for sports turf in the south and east of England and less so elsewhere in Britain; more inclined to consider undersoil heating for professional sport in the north, east and inland areas of Britain, and more inclined to make provision for irrigation in the south-east.

1.4
Soil texture and soil structure

In site preparation for playing fields the first step is to provide a true surface, relieved and protected by peripheral interception drainage. The next step is to make certain that the soil on the playing area will infilter the water required to sustain grass growth and clear excess so as to maintain an adequately aerated soil environment for healthy root development. The means by which any given soil will have to be managed to achieve the desired air/water balance will depend on its texture. The extent to which it is already appropriately organized will depend on its structure.

While the qualities of soil structure are those concerned with the shape and stability of the functional units, loose particles, granular aggregates, clods, etc. into which the raw materials are organized, and through which the nature of the living space is determined, qualities of soil texture are those reflecting the nature of the primary components, stones, sand, silt, clay and organic matter.

1.4.1
Soil texture

Where the organic matter content does not exceed about 10% by weight (25–35% by volume), soil texture will be determined mainly by the particle-size composition. A simple and commonly used classification of particle-size grades is given in Table 1.3.

The use of a single dimension to define these particles assumes their shape to be square or spherical, but in practice this defines the ranges of particles which behave on sieving or sedi

TABLE 1.3 Classification of particle-size grades

Particle	Abbreviation	Size (mm)
Stones		larger than 8
Coarse gravel	CG	8–4
Fine gravel	FG	4–2
Very coarse sand	VCS	2–1
Coarse sand	CS	1–0.5
Medium sand	MS	0.5–0.25
Fine sand	FS	0.25–0.125
Very fine sand	VFS	0.125–0.060
Coarse silt	CZ	0.060–0.020
Fine silt	FZ	0.020–0.002
Clay	C	less than 0.002

mentation as if they were spheres of the given diameter, i.e. these are ‘nominal’ size categories. The gradings offered by sand and gravel suppliers usually refer to quantities of materials passing (or failing to pass) certain sieve sizes.

As mineral soils are made up of a mixture of particle-size grades, it is useful to recognize the simple distinctions between soils sufficiently sandy to be classed for practical purposes as sands (soils more than 70% sand), others sufficiently clay-rich to be regarded as clays (soils more than 40% clay), and the rest, loams, weak or strong according as the clay content is above or below about 15%.

Sands will drain freely and their open structure will not collapse with physical abuse but, unless fortified with organic matter, they are liable to be both hungry and thirsty.

Clays readily hold water. They swell and shrink very actively in response to wetting and drying. Hence, given the right sequence of weather conditions, they can break up into a fine, fracture tilth at the surface and free-draining, deep cracks below. Also, clay particles carry a charge which enables them to store important plant nutrients in a readily available state, thereby promoting fertility.

The wide range of particle sizes present in loams encourages inter-packing and hence fineparticle dominance of the pore system (Figure 1.1(b)). In their natural state loams have insuf-ficient sand to avoid the need for structure development to facilitate drainage and insufficient clay to structure themselves by intensive cracking. They are dependent on biological processes to be physically conditioned into the water-stable, granular state which is typical of a loam in ‘good heart’. This structure allows for water and nutrient retention within granules and free drainage between (Figure 1.1(c)) but is liable to collapse under physical abuse or decay of the organic binding agents.

If a system of granular aggregation disintegrates, the open structure will readily collapse to a compact arrangement of individual particles, very liable to hold water to the exclusion of air. Only clay-textured soils have sufficient clay to develop the binding strength necessary to resist collapse in the absence of any assistance from organic binding agents. A loam, therefore, is potentially a problem soil. It is dependent on assistance from organic agents and biological processes for both the development and retention of the open structure that it, like any other soil, requires to meet the demands of normal plants for easy root access, through well-aerated channels to adequate reserves of water. But both the biology and the open structure are liable to be adversely affected by human activity, e.g. failure to return organic residues, elimination of the vital soil organisms and physical abuse leading directly to soil recompaction, much of which would appear to be inevitable under the management considered to be appropriate for sports turf.

The soil texture classes distinguished on a triangle of texture (Figure 7.1(a)) make no reference to stones or organic matter content, but no classification of soil texture is complete without some further, qualifying reference to these components—details are given in Appendix A, section A.5.2, pages 219–222.

Simple tests enabling soil texture and soil structure to be assessed are also described in Appendix A.

1.4.2
Soil structure and drainage

The extent to which water will either accumulate on the surface of the soil, or infilter, will depend on the intensity of the rainfall and the nature of the soil's pore system, i.e. its structure. Pore sizes required for rapid infiltration and air release are large enough to be seen by the naked eye (macro-pores), the smallest correspond to those that would be formed by close-packed, very fine sand. Most soils in Britain have sufficient silt and clay in their make-up for these very fine particles to fill all the potential macro-pore space between any sand particles present, creating a structure entirely dominated by water-holding micro-pores (Figure 1.1). Thus for most soils in Britain, soil compaction must be avoided if the rapid infiltration of surface water is to be satisfactorily achieved.

Though sands and loamy sands, being more than 70% sand, may avoid becoming micro-pore dominated even when compact, and some soils that are adequately clay-rich may periodically regenerate an open structure by intensive cracking, for the great majority of soils, the loams, an open, free-draining structure can only be developed by a combination of cracking, root activity, worm tunnelling and worm aggregation. However, this favourable, water-stable structure can be dispersed during storage and will fail to regenerate if earthworm activity is discouraged (Stewart and Scullion, 1989). It can be churned out of existence by foot traffic if the surface is wet. It is at most risk when our winter games season is at its peak and most cattle farmers would have their animals corralled on concrete. It is surprising, therefore, that any of our recreational areas escape long periods of waterlogging during the winter.

The best hope for intensively used grass surfaces is to utilize adequately sandy surfaces linked to some system of sand-stabilized, vertical drainage. The aim should be to by-pass any compaction within the indigenous soil, clearing excess water laterally to a linked system of under-drains for final discharge off site.

The only alternative to sand or sand-modified soils for recreational use is to select a well-granulated, worm-worked, naturally free-draining soil and a site requiring minimal regrading so as to avoid the major soil disturbance of cut-and-fill. Use should then be controlled to give absolute priority to the well-being of the soil and the biological components responsible for its conditioning—see Tables 6.1 and 6.2.

1.5
Soil texture amelioration

For the satisfactory drainage of structureless soil it may be expedient to amend the texture to provide an adequate infiltration rate. To achieve this, sufficient sand must be added to bring the percentage of medium plus fine sand particles to at least 70%. Depending upon the range of particle sizes present in the particular sand selected, the total proportion of sand to silt and clay may have to be anything up to 90% to ensure a sufficient content of sand in the medium-plus-fine range. Thus, in practice, the ratio of sand to topsoil could vary from 2:1 to as much as 5:1. A method of calculating the amount of a specific sand required for the textural amelioration of a particular topsoil is described in Appendix 3.

1.6
Gradients and undulations

Although level grass surfaces are capable of being drained artificially, a slight slope is desirable as a means of encouraging surface run-off following intense rainfall. Depending on the standard of play anticipated, for team games a uniform gradient of between 1:50 and 1:100 should be aimed at. Whenever possible, pitches should be sited so that they are as level as possible along their length with the crossfall occurring over their width.

To prevent ponding, particularly where major grading is involved, it is of the utmost importance that the final consolidation of both the subsoil and the playing surface is very carefully carried out to avoid any chance of subsequent, differential settlement. Even a hollow left in a clay subsoil could retain water infiltrating through the topsoil and result in that part of the pitch becoming wetter than the rest. It is worth noting that a general slope of 1:50, on the surface, will not be sufficient to ensure the complete emptying of a surface depression 5 m (16 ft) in diameter, if the dip in the depth of the hollow exceeds 50 mm (2 in).

1.7
Use and design rate

The extent to which artificial drainage is likely to be required depends not only on the natural drainage capacity of the land and the rainfall expectancy, but also on the type and amount of use to which the playing surface may be subjected. Use factors which should be taken into account include:

• the games to be catered for;
• the standard of play;
• the number of games and training sessions per pitch, weekly;
• the pattern of use, e.g. weekends only, or weekends and mid-week, or both;
• the age of the players, e.g. adults, school children, or both;
• cancellation repercussions, e.g. loss of gate money or problems overtime-tabling;
• extent of any additional, casual use, e.g. for training or by local children kicking into a goal. Casual use leading to localized severe wear can become such a problem that it may be worthwhile providing a purpose-made alternative on land specifically set aside.

A knowledge of these factors is necessary to enable the designer to arrive at an appropriate rate of drainage sufficient to satisfy the requirements of a given set of circumstances. This may be anywhere between an agricultural rate of 12 mm (0.5 in) of rainfall a day (24 hours) for a public recreation ground in the south-east of England, and 12 mm (0.5 in) an hour for golf and bowling greens. For the average winter games pitch it is likely that a design rate of 50 mm (2 in) a day will be adequate.

This means that the only grounds likely to have a natural drainage rate good enough to meet the requirements of winter games are those with the right kind of sand content in the topsoil and a free-draining subsoil. However, most sports grounds in Britain are based on soils with a much lower sand content than the 70% which is required and, therefore, most demand the assistance of some form of supplementary artificial drainage.

Where a gradient has been improved by major grading operations, thereby disrupting the natural drainage channels, extra provision will have to be made for the interception of extraneous water encroaching through the subsoil or as surface run-off.

1.8
The site

A thorough diagnosis of a drainage problem takes time and can be expensive.

1.8.1
Type of information required

1. An accurate plan of the area showing the banks and other physical features with details of any existing rights of way, drainage runs, manhole, siltpits, outfalls, perimeter drains, ditches and public utilities conveying gas, water, electricity or sewage.

2. A grid survey of surface levels at a minimum of half-metre height intervals to provide for contours of the area to be drained. Also record outfall levels and related benchmark.

3. Evidence from soil pits of the nature and extent of soil variation across the site to a depth of at least 500 mm (20 in). For a natural, undisturbed site, use evidence of variation in slope and vegetation to define areas likely to be uniform in character and dig trial holes in the centre of each of these. Then, confirm boundaries by auger examination of soil between the initial trial holes. On an existing pitch, which may well be on disturbed land, explore first within the four corner areas, in both goalmouths and at the centre, then supplement with auger examination. The evidence from the corner areas should indicate the general nature of the soil construction and the evidence from the goalmouths and the centre may well indicate any previous remedial action taken to cope with severe wear. The following features should be recorded:

(a) the depth and character of both topsoil and subsoil;

(b) the depth and type of other material such as rock, sand and buried rubbish that might affect the drainage layout;

(c) whether ground water is present and, if so, the estimated level of the watertable at different seasons;

(d) whether the stone content of the soil to drain depth is such that it could cause serious problems in trench excavation, subsoiling, etc.

4. Further examination of any existing drains and outfalls to ascertain their depth, capacity and condition, and the nature and extent of any backfill.

5. Notes on vegetation and any minor surface irregularities to be taken into account when soil sampling.

6. Location of representative soil samples taken for mechanical and/or chemical analysis. In some cases visual examination of auger borings may provide all the information required.

7. Information on the history of the field, especially information of any constructional work, drainage and maintenance that might previously have been carried out. Interviews with people familiar with past performance to help establish why particular problems have arisen.

8. Copies of specifications, plans and relevant correspondence relating to previous work.

1.8.2
Interpretation of information obtained

1. If existing rights of way, water courses or public utilities traverse the area, the appropriate authorities will have to be approached to establish the nature of any restrictions they may wish to impose.

2. The existence or absence of perimeter catchment drains will help to determine whether water is reaching the site from surrounding areas either on the surface or along underlying strata. The absence of efficient perimeter interception is often a prime cause of water-logging problems.

3. The colour of the soil profile can be a useful pointer to its condition. Tints of blue, dark grey, olive green or black usually indicate that aeration is poor because of permanent waterlogging. Rust-coloured mottling, usually localized to old root runs, suggests that the soil is prone to waterlogging only at certain times of the year. On the other hand a profile which is a uniform shade of brown or reddish brown generally signifies that aeration is good and that there are no serious drainage problems.

4. Where there is an existing drainage system, it is important that the flow from the outfall and through inspection chambers and silt-pits is checked during a wet period, ideally in winter. Lack of flow at these times does not necessarily mean that the pipe system is at fault. Lack of any substantial drain flow response to heavy rainfall, combined with persistent surface ponding, probably indicates that surface water is not able to infiltrate through the topsoil to reach the pipe drains below. This is perhaps the most common form of drainage failure and can usually be demonstrated by the relative dryness of the soil below 50 mm (2 in).

5. Surface undulations and depressions, particularly on fine-textured soils, tend to nullify the advantages of having a slight gradient as they can effectively impede surface run-off. Even if examined during drought, the vegetation may provide clues to the normal state of affairs in these hollows. For example, infestation by sedges and rushes indicates waterlogging for long periods.

6. Both chemical and physical soil analysis is necessary to determine the important inherent characteristics of the soil, i.e. its potential fertility, its potential to drain and its potential to be changed.

1.9
Differences in drainage requirements of agricultural land and sports grounds

Land configuration, soil and the nature of use intended are the main factors governing the type and design of the artificial drainage required. Differences between the drainage requirements for farm land and sports turf have their origin in the very artificial and disturbed nature of many of our playing-field soils, and the extremes of wear to which they are often subjected.

1.9.1
Nature of site

For agricultural purposes the natural slope of the land and the natural texture of the soil must generally be accepted. For sport, on the other hand, it is sometimes possible, or even essential to import soil, or to modify texturally the indigenous soil, for example, by incorporation of sand.

Now that efficient earth-moving equipment is freely available, levelling by cut-and-fill and artificial grading are procedures commonly used to provide the uniform surfaces required for sport. Thus sports turf surfaces are fre-quently based on disturbed and biologically degraded soils.

However, while a farmer has to contend with a multitude of drainage situations varying in size, shape and slope, the person with playing surfaces to drain has more predictable situations to deal with. Every field on a farm may be different, but football pitches and bowling greens, for example, are each very much of a kind, wherever they are. This makes it reasonable to work towards fairly standardized designs to meet the individual needs of the different sports.

1.9.2
Nature of use

For successful farming it is necessary to have an open, water-stable structure, at least to plough depth. To preserve this ideal state, excessive and untimely cultivations must be avoided and caution exercised over grazing and the passage of vehicular traffic. The whole success of farming requires that the creation and preservation of an open, topsoil structure is continually kept in mind.

A true clay topsoil, appropriately structured, may infilter water at a rate as high as 250 mm (10 in) per hour and, if effectively mole-ploughed to drain across to an underground pipe system, may achieve an overall peak discharge rate of 50 mm (2 in) per day. Such a soil avoids ever becoming really waterlogged but, in practice, will maintain this level of performance only so long as the mole channels continue to function and the management of the land does nothing to degrade its structure.

Unfortunately, the farmer's open structure is neither strong nor long lasting. It can be dispersed by bad weather and damaged by machinery and the treading of animals. It can be dissipated if not continually regenerated from within by the appropriate soil biology. On a sports ground a similar open soil structure can be poached out of existence by players treading the surface while it is wet. This risk to structure is greatest when the need for rapid infiltration of excess surface water is most urgent, at the very time of year when agriculturists would advise staying off. It can also be lost if the topsoil has been stockpiled prior to spreading and will threaten trouble for years after construction. A farmer is usually in the fortunate position of being able to exercise some control over the timing of his various farming operations and the grazing of stock. A groundsman, faced with pitches unfit for play, fixture lists prepared weeks or months in advance, and players with only limited free time available, has to accept the referee's arbitration based solely on whether play of a reasonable standard can proceed without risk to the players. If the surface cuts up, however, such indiscriminate use may initiate a trend in sward deterioration that cannot be arrested until grass growth resumes in the spring.

Because a farmer can control his pattern of field use he can preserve his soil structure or help to regenerate it periodically by cultivation. This generally takes care of the problem of surface infiltration and makes it possible to limit the height of the permeable fill over the pipe drains to that required to intercept mole drainage. However, because topsoil structure is unlikely to survive winter use we now realize that, for sport, methods must be devised to continue artificial drainage interception right through to the surface.

Until the mid-1960s the drainage of sports grounds followed very closely the principles and practices used for the drainage of agricultural land. When the cost of land for sports ground purposes began to increase substantially it became widely appreciated that, to improve the quality of the pitches and increase the number of games played each week, would require improved drainage, but the methods of drainage then practised were far from adequate for the task. Even expensive schemes of pipe drainage, thought by experts to be well designed and efficiently executed, were often found to be largely ineffective when used for play in winter. The sight of a muddy playing surface with relatively dry soil at 75 mm (3 in) and no significant flow in the pipe system is by no means an uncommon spectacle.

In the late 1960s and 1970s the author, amongst others, began to develop an interest in new methods by which the problems of topsoil impermeability on sports grounds could be overcome. One result was a paper given to the annual National Playing Fields Association Conference for Local Authorities and published in booklet form under the title Drainage Problems on Playing Fields (Stewart, 1971). The main recommendation that emerged from this research was to use sand to form a direct link to the underdrains, either in the form of a superimposed ameliorated sand topsoil, or confined to narrow vertical slits at close centres. The situation gradually finding acceptance today is that satisfactory drainage design rates can only be maintained by techniques which are not only more sophisticated than hitherto but also much more expensive.

1.10
Cost

Though soil drainage can now be organized with a reasonable expectation of achieving a specific design rate, the problem in practice is to bring the new techniques within reach of the client's financial resources.

Fortunately there are usually two or more different arrangements that will give approximately the same rate of drainage so that by juggling with such features as length, width and depth of slits, different grades of fill, spacing of underdrains, etc. it is possible to arrive at the most economical permutation. Key factors in the equation are often the cost of sand and gravel and the labour and machinery costs for excavating the trenches and slits. (Chapter 4 has detailed information on design criteria.)

1.10.1
Winter games pitches—soccer and rugby

Complete schemes

For the efficient drainage of sports grounds the importance of ensuring that surface water is able to find its way fairly rapidly through the topsoil to the pipe underdrains is now probably well understood. It is not always appreciated, however, that the extra cost of achieving this desirable state of affairs, e.g. by the inclusion of slit drains at 1 m spacing (Chapter 11), can be two to three times the cost of a conventional pipe drain layout for the same area. As an example of comparable costs (UK, 1988), if a senior-size soccer pitch cost £19 000 to drain satisfactorily to a design rate of 50 mm (2 in) a day, an approximate breakdown of this total might be:

Installation of outfall, manholes, main pipes and lateral underdrains	£3 000
Slit drainage	£12 000
Preparation and seeding of slits and damaged areas	£3 500
Minimum initial fine sand topdressing before allowing play	£500
Total	£19 000

The spacing of the lateral underdrains for the slit drainage system described above is likely to be of the order of 15–20 m (16–22 yards), whereas the old type conventional system without slit drains would probably have been designed with laterals at a much closer spacing of 6.5 m (7 yards). On this basis the capital costs in 1988 of a pipe laterals only scheme, plus manholes, main and outfall, would probably have been in the region of £8000, i.e. much less than half the cost of a slit drainage scheme for the same size of pitch.

With slit drainage the financial implications for maintenance have also to be borne in mind. It will be found that unless steps are taken to repeat the initial application of fine sand topdressing, at least once a year, the slits will gradually become so soil capped that they will no longer be able to perform their function of channelling water from the surface to the pipe underdrains. In addition, if the soil is at all clay-rich, there is always a tendency for depressions to form along the lines of the slits as an effect of soil shrinkage during the summer (Figure 6.1).

It is therefore of vital importance that, in addition to the capital cost of installation, there must also be included in maintenance budgets a sum sufficient to ensure that dressings of fine sand can be applied annually. A slit drainage scheme not protected in this way could eventually turn out to be a waste of money.

Further information on cost benefit implications for the drainage of winter games pitches is given in Chapter 5.

Staged schemes

Clubs and authorities may find that the cost of improving the drainage of their grounds in one go is beyond their means. However, it is often possible by phasing the work into stages that are financially manageable, or by adopting DIY methods, to achieve the necessary improvements over a period of time.

When upgrading an existing scheme a lot depends on the condition of the existing pipe laterals and the kind and depth of backfill used. If the pipe system is still in good order and the backfill is suitable for linking up with sand/ gravel slits, the way ahead should be fairly straightforward. On a football pitch, for example, the worst parts are usually the central area and the goalmouths. These could be slit drained first, leaving the treatment of other bad areas to subsequent years.

If it is found that some, or all, of the laterals are no longer in working order through pipe damage or inadequacies in the backfill, these will have to be repaired or replaced before slitting can proceed, but again, this could be part of a phased programme.

1.10.2
Hockey

Hockey is difficult, as the game requires a small ball to roll evenly along the surface and is played during the winter season, when the combined hazards of excess rainfall, frost and studded footwear make this particularly difficult to achieve.

If slit drainage is required it will be essential to avoid any risk of depressions forming along the lines of the slits. To achieve this a carpet, 100–125 mm (4–5 in) in depth, formed of suitably ameliorated sand topsoil, should be laid over the surface after slitting. If so designed at the outset the spacing of the slits can be marginally increased but should not exceed 1200 mm (4 ft). The total cost is likely to exceed that of a simple slit scheme by at least 70%.

Although the initial application of fine sand topdressing before any play is allowed will not be required, it will still be necessary, for the reasons explained in section 6.2, for fine sand top dressings to be applied annually thereafter.

1.10.3
Difficult sites

On tip sites, or where there are obstacles at depth, trenching with standard equipment is not likely to be possible. On such sites heavier machinery is usually necessary. This is expensive to operate and may leave a much wider trench than is actually necessary. Thus not only does more spoil have to be excavated and taken away, but an increased amount of backfill has to be brought in. It therefore becomes essential on economic grounds to keep the number of pipe laterals to an absolute minimum, installing them at the maximum effective spacing. To help with this an intermediate, linking tier of shallower gravel channels may be introduced between the pipe drains and the slits (Chapter 3, page 54 and Chapter 4, pages 71–74). Any extra cost will depend on the trenching difficulties, especially the deep trenching required for the installation of the third tier of pipe laterals.

1.10.4
Main use in summer

Where little heavy use takes place in the winter months and there is only light use such as cricket, athletics and casual play to contend with in the summer, it may be possible to use a shallow, single tier of close-spaced laterals. This might be achieved satisfactorily with a miniaturized, pipe-assisted, slit system, discharging directly into a main, off the playing area (Chapter 4, page 69). With no pipe laterals required and given appropriate installation machinery, the cost might be about the same as for an ordinary slit system, but again, special maintenance, including regular sand topdressing, will be necessary to maintain the permeable link through to the surface.

1.10.5
Fine turf areas

For facilities such as golf greens and bowling greens a very high rate of drainage is expected. It may be achieved by placing a carpet of ameliorated sand topsoil, 300–400 mm (12–16 in) in depth, over a gravel bed with pipe drains underneath (Chapter 10). This is an expensive form of construction, at least five times as much per square metre as a slit system, and very careful maintenance is essential, which is also expensive.

A much cheaper alternative for crown bowls or a golf green is to steeply grade both subsoil and topsoil so that they run parallel and shed all excess water to the periphery (Chapter 9, page 144 and Chapter 11, page 171). The final configuration of the surface, however, will have to conform to the requirements of the game and maintenance will still have to be of a very high standard.

1.10.6
Control of use

Unfortunately there is one cost factor over which there is little control. In section 1.1, reference is made to a soil survey of league grounds which disclosed that pitch deterioration was frequently blamed by the groundsman on the one game played when it should not have been. This is perhaps one of the most difficult situations that can confront a groundsman. No matter how unfit for play he may consider the pitch to be, the sole arbiter on whether play should proceed is the referee, but his remit covers only the safety of the players and the quality of the play that will be possible. The referee need not be concerned with the effect that play may have on the pitch or the cost of the remedial measures that will have to be taken to make good the damage.

The groundsman will also be aware that any move towards a general improvement in the playing surface brought about by better drainage can bring in its wake a clamour for greater intensity of use. In these circumstances it is possible to sympathize with the groundsman who feels that unless decisions over use are left in his hands, he is on a hiding to nothing.

1.11
The importance of a clear, concise and comprehensive specification

For contractors and direct labour departments of public authorities to have a clear understanding of drainage work requirements, it is essential to prepare a sound and properly detailed specification. This should include appropriate drawings and a bill of quantities suitable as a basis for tendering.

Not only is a well drawn up specification essential for best results, it is also necessary to enable contractors to tender on a common basis. A loosely worded specification, or no specification at all, makes it impossible for tenders to be fairly compared.

If a contractor finds himself obliged to submit a specification with his quotation, he often words it in such a vague and equivocal manner that it is virtually impossible to arrive at any precise conception of what is to be provided for the money. Where it is the usual practice for the lowest tender to be accepted a situation may arise where a contractor, either through lack of the required experience, or because of uncertainty about the authority's requirements, quotes an unrealistically low price. He may then finish up doing a bad job to avoid losing money, or may himself lose money trying to do a good job. Either way it is unsatisfactory and all concerned are likely to suffer, including reputable firms which may find themselves at a disadvantage through trying to maintain good standards.

An increasingly serious problem is that those involved in soil disturbance, i.e. architects, surveyors, engineers, consultants, contractors, etc. are not always well informed on the biological basis of soil fertility and its significance for drainage. The scientific content of this work has of late tended to change faster than the personnel concerned. It is vital, therefore, that all are properly trained and keep abreast of developments. It is a sad state of affairs when only the most recent recruit is conversant with the latest developments and the boss is isolated from enlightenment by his defensive adherence to tradition. One aim of this book is to help senior personnel to update themselves, beyond rigid recipes to a more scientific understanding of general principles that will give them the confidence, not just to follow but to lead.

Where knowledge is lacking there is often a tendency to pass the buck to the contractors in the sometimes mistaken assumption that they are the experts. The practice of simply defining the end-product in terms of function, drainage design rate, or minimum time to playability after rain can lead in the end to expensive remedial measures and possible litigation.

A contractor is in business to make money and he can only do this if he is competitive. In the real world of commerce the sharp practice often necessary to achieve a competitive advantage can only be avoided by the employing authority setting out its requirements in sufficient detail to ensure that they are fully understood. Only then can the specification and terms of contract be effectively enforced by the employer while the work is in progress.

There is a good moral reason for insisting on the employing authority itself preparing a detailed specification: it is manifestly unfair to put this time-consuming task onto the contractors when only one will get the contract. One practical consequence of this practice is that all the necessary preliminary investigational work on levels, soil samples, materials and design data may not be properly carried out by the contractor submitting the lowest tender. These limitations will then only emerge after both parties are irrevocably committed to a cost ceiling that is quite inadequate.

The right of contractors to be given proper specifications when invited to tender, including the guidance inherent in the bills of quantities, should be more generally recognized. It is with this in mind that the following recommendations are made.

1. Those authorities responsible for carrying out drainage work on sports grounds should always have ready access to staff or consultants adequately qualified in the up-to-date techniques of land drainage.

2. Tenders for the drainage of sports grounds should not be invited except on the basis of properly prepared specifications.

3. The subject of field drainage should be given increasing priority in the courses organized by professional bodies whose members are likely to be engaged in the provision and maintenance of sports grounds and playing fields.

4. Staff of public authorities and private firms (consultants and contractors), either propos-ing to, or already practising in the field of land drainage, should be encouraged to attend refresher courses to keep them abreast of modern practice.

1.12
Site supervision and checking of materials

1.12.1
Supervision

Today the scientific nature of drainage design is such that as little as possible should be left to chance. From the information given in Chapter 4 on design criteria it is clear that if a given rate of drainage is to be achieved all the specification requirements—design and materials—must be complied with explicitly. No deviation from the specification should be permitted without the express consent of the drainage designer, in writing.

It follows from this that the client organization must exercise very close supervision of the work. It is strongly advised, therefore, that the drainage designer or a specialist consultant be retained to approve materials before use and check the various stages of the work as it proceeds. In addition, it is an advantage if there is a groundsman on the spot who can act as an observer. Ideally, everyone concerned with supervision should be briefed on the specification in the presence of the contractor's site agent and foreman so as to provide an opportunity for misunderstandings to be cleared up before work begins. Thereafter, the job of anyone acting in the role of clerk of works is to have close liaison with the contractor. He should be present when each new phase of the work is due to begin and should confirm the suitability of the materials delivered on site, the procedures to be adopted and the standard of work expected. He should also be present to approve each phase of the work as it is completed. In the event of disputes he should briefly record his observations in writing, leaving

TABLE 1.4 Stewart zones defining sand and gravels of particular value for the construction, drainage and maintenance involved in sports-turf provision

a copy with the foreman and passing the original to the consultant or the client.

If drainage work is put out to contract, and forms part of a main contract, it should be made quite clear to the main contractor that on no account should any work be sub-let to another firm without the client's expressed agreement in writing. The client should satisfy himself that the sub-contractor chosen has adequate practical experience of the type of drainage work to be carried out and is fully conversant with the requirements of the specification.

1.12.2
Precise specification checks of sands and gravels used in sports field construction and maintenance

Because existing systems of classification used in Britain for specifying sands and gravels are intended primarily to serve the needs of the concrete industry, it has been found necessary to develop an alternative system for sports turf. This is summarized in Table 1.4 and is discussed more fully in Chapter 7. It is these materials to which reference will be made from Chapter 2 onwards. They will be referred to as Stewart zone trench gravels, blinding sands or topsoil sands or, more commonly, just trench gravels, blinding sands or topsoil sands without reference to their Stewart zone origin. The limits of these zones are described analytically in Tables 1.4 and 7.1, and graphically in Figure 7.6.

Although the designs featured in this book have been matched to a closely specified range of materials that are commonly available, it does not mean that materials outside this range are necessarily useless. A locally available material may have a distinct cost benefit and, by some modification of the general design, may well be utilized to advantage by someone adequately trained to calculate the necessary adjustments. Experience suggests, however, that not all contractors or technicians are aware of what may be available outside that provided by a narrow range of suppliers whose primary purpose is to meet the needs of the building and concrete industry. The advice is to shop around yourself before accepting pronouncements, favourable or unfavourable.