HYDROLOGICAL FUNDAMENTALS OF BOG DRAINAGE

A. I. Ivitsky

ByeZomssim Research Institute of Reclamation m d Water Economy, Minsk, BSSR

SUMMARY: This paper considers the following problems:

The principles of reclamation by drainage; The drainage rates (optimal groundwater regime) and new approaches to their determination; The theory of drain spacing calculations for drainage and irrigation; It allows groundwater dynamics and the required water regime of drained bogs to be estimated; The method of calculation of the water yield of peat soil; The method of calculation of drainage runoff from fen bogs; The dependence of evaporation and transpiration coefficient on climate. groundwater table and crop yield.

FONDEMENTS HYDROLOGIQUES DE L'ASSECHEMENT DES MARAIS

RESUME : En partant des donndes fournies par des observations pluriannuelles et en s'appuyant sur des recherches th6oriques l'auteur dtudie les problsmes suivants :

Principes actuels qui prgsident 1 l'assschement par drainage ; Degrds d'assschement des marais (rdgime optimal des eaux souterraines) et nouvelles mdthodes pour les ddterminer en fonction de l'influence de la nappe souterraine et des facteurs climatiques sur la teneur en humi- dit6 et en air, en fonction aussi de l'influence de la nappe souterraine sur la pr6sence d'oxygsne et de gaz carbonique ; Thdorie du calcul de l'espacement entre les drains (canaux d'irrigation et d'assschement), ce qui permet de connartre la dynamique des eaux souterraines et le rdgime hydraulique des marais drain& ; MBthode de calcul de l'apport en eau des tourbilres ; MCthode de calcul de l'ikoulement de drainage dans les marais d'assbche- ment ; Influence du climat, de la nappe souterraine et de la culture sur 1'Bva- poration et sur le coefficient de transpiration. Certains des r6sultats obtenus par l'auteur sont publi6s dans des manuels

qui traitent d'hydrologie, d'hydrog6ologie et de mise en valeur des terres et qu'on utilise dans la RSS de BiBlorussie et dans les autres rspubliques sovi6tiques pour Blaborer des projets de drainage de rdgions tourbeuses.

97

Topic I

Reclamation by drainage should be designed and constructed scientifically according to the following principles (Ivitsky, 1966).

1. Reasonable and adequate utilization of water resources of the entire catchment area, taking into account the water requirements of the near future and those of a later date. Maintenance of desired water ievels in regulated rivers and the water regime in the entire catchment area. The possibility of controlling the water regime and rele- vant air, heat and nutrition regimes in soil.

2.

3.

4. The extension of peat soil life. 5. The construction of durable and effective systems which

6. combined both drainage and irrigation. Comprehensive or multi-purpose solutions of the problems of water resources such as water transport, water supply to agriculture and industry, fishing, hydro-electric engineering, construction of recreation facilities.

To satisfy the above principles of modern drainage reclamation, it is necessary:

a. to control runoff by the construction of reservoirs. In this way it will be possible to retain the greater portion of spring runoff within a reservoir, and then release it for industry, irrigation, etc in the dry summer periods. This principle is being adopted in the drainage scheme for the Polesskaya low-land in the Byrelorussian SSR where it is planned to build 34 reservoirs. reclamation projects should embrace not only the drained parts of the catchment, but its entire area. The combina- tion of reclamation, hydro-technical, forestry and agri- cultural activities and techniques should be directed at the improved use of the water resources of the entire catchment area. These activities include:-

b.

-wide-spread construction of ponds on small rivers, streams, gorges and man-made water courses for the purpose of accumulating the greater portion of spring runoff; -measures for control of water erosion as evidenced by ravines and gullies in the catchment should be antici- pated; -reafforestation throughout the catchment area that im- proves the conservation of water in the entire catchment area, rather than its individual parts; -snow detention, contour ploughing on light soils and deep ploughing and deep ripping (1 m depth) on heavy soils, suitable crop rotations, etc;

c. to build control gates to maintain a desired water level in small regulated rivers and ponds near settlements for everyday needs and recreation.

d. to construct drainage-irrigation systems for two-way opera- tion creating an optimal moisture-aeration regime for crops,

98

Ivitsky

e.

f.

g- h.

i.

both in excess moisture and drought periods; to maintain the level of the groundwater table low enough to permit proper drainage; to plan crop rotations on peat soils which include perennial grasses ; to drain shallow-deposit low-level bogs for use as meadows; to apply pump drainage where hydrogeological conditions permit, including the use of groundwater for irrigation of drained lands and better control of soil moisture; to use subdrainage, to stabilize the banks of open ditches in unstable soils; to use adequate methods of drainage.

In order to be able to design a combined drainage-irrigation system properly, it is necessary to determine the optimum soil moisture regime required for the successful growth of crops on the drained area.

Moisture and air content are basic soil characteristics. But in the case of a high groundwater table, which is a typical condition when bogs are drained for agricultural uses, there is a relation- ship between soil moisture, the water table level and climatic factors. Since the groundwater level can be defined more easily than the soil moisture content it is reasonable to express the optimal water regime for bog drainage conditions in terms of the optimal level of the groundwater table.

The drainage rate of peat soil (ie the optimal groundwater regime) can be determined in two ways: from the relation between the soil moisture content of peat and air capacity and the main factors affecting these, and from the aeration regime of the soil (Ivitsky 1962, 1966, 1971).

capacity with the level of the groundwater table and climatic factors, have been developed from long-term investigations (Ivitsky 1971).

The following equations relating peat moisture content and air

where

W

V H h

is the peat soil moisture content, % of total moisture capacity ; is the air volume in the soil, % of porosity P; is the level of the groundwater table, m; is the distance from the soil surface to the point for which W and V values are required, m;

ED, EN is the air humidity deficit and total rainfall during the time from the beginning of the waiting period, as deter- mined by the author's method (accumulation of sprin positive mean daily air temperature, to a total value of 130 C) to the moment when W and V values are to be found;

a e is the base of the natural logarithms;

99

Topic I

n is 1.4, but according to experimental data may range from 1.3

A an empirical factor determined experimentally. For low-level to 1.5;

bogs on a permeable layer, A has an average value of 1.2 and may range from 1.1 to 1.4 depending on the nature of the evaporating surface. It is larger for crops with a high

transpiration rate. . transpiration rate (grass) and smaller for crops with a low

Expressions for the optimal level of groundwater table were derived after transformation of these equations. Groundwater levels of this type result in optimal moisture content and aeration of peat soils:

Bh + Cm + d(Bh + CbL + (2C - Bh') (B - -*) I (3) Hw = B - Cm2

Bh + Sm + /(Bh + Sm)' + (2s - Bh2) (B - Sm2) (4) Hy =

B - Sm2 where

H and H are the optimal groundwater levels for optimal mois- W Y

ture content and aeration in peat soils.

B = 2A, 4-1 J""" (5)

A1 = 1.1 to 1.2 for peat soils of low-level bogs on a permeable formation ;

m = 1.6 for 0 < H C 0.5 m

m = 1.7 for 0.5 < H f 1.0 m

m = 1.8 for 1.0 < H 6 1.5 m

The rest of the notation is the same as in (1) and (2).

known for each stage of growth of a given crop, the corresponding optimal groundwater level for the year under varying climatic con- ditions can be easily estimated and the optimal groundwater regime or drainage rates can readily be plotted by using equations (3) and (4).

Table 12 shows optimal groundwater levels (drainage levels) for dry and wet years estimated by equations (3) and (4). For optimal moisture content and aeration of a peat soil Kostyakov's data (1960) are taken.

If optimal moisture content and aeration of a peat soil are

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Ivitsky

The studies of aeration in soil show that there is a relation- ship between oxygen and carbon dioxide in a peat soil which depends the groundwater levels. The maximum oxygen and minimum carbon dioxide content are found in arable and subsurface layers of peat soils when the groundwater table is lowered to 120 or 130 cm (Ivitsky 1962).

crop yields according to soil moisture content , nitrification and germination processes , the following levels for groundwater table for low-level bogs (Ivitsky 1966) are proposed (Table 13).

Based on the two new methods described, and on the analysis of

In the formula:-

Hb is the maximum groundwater level at the beginning of the maximum spring rise, cm;

Ws is the snow water to the moment of snow melt (excluding surface runoff) ;

Po is the free porosity;

Hn is the permissible groundwater level for the maximum spring rise, cm.

The levels of the groundwater table in Table 12 show that the deepest values apply in wet years, and the lower ones, for the years when the soil moisture content is average. In dry years the lower

’ values should be decreased by 10 to 15%. In order that the level of the groundwater table can be controlled so that it can be raised or lowered as required it is essential that the drainage network be adequate for this purpose. Thus it is necessary to determine the optimal distance between the drains for drainage and channels for irrigation. For this purpose the following theoretical formulae, have been developed which cover reclamation requirements for all natural conditions (Ivitsky 1971) .

I to estimate the distance between drains for drainage:

where

E is the drain spacing, m; k is the permeability, m/day; T is the time during which the groundwater level should be

lowered from U to H along a line equidistant from two drains , days. Depending on the required drainage intensity , values of 5 to 15 days may be assumed;

a is a coefficient which accounts for the portion of the drain cross-section that is occupied by the base flow.

101

Topic I

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102

Ivitsky

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103

Topic I

F At a >, 3 a is calculated from

E a = (10)

8a I[d E --In tn- II 4a

where

a is the depth of the confining layer below the drain bottom,

II = 3.14; d is the external diameter of a drain; m;

In is the natural logarithm; tn is hyperbolic tangent symbol.

At - < 3, a is defined by the more cumbersome expression after Averianov or by a specially prepared graph a

- $J(H - u)I[2t - H - U + 2ho + $J(H - U) + 4011- 2h0

R = [ 2 t - H - u -

.. . (11) where

t is the drain depth, m; U,H is the groundwater level mid-way between drains at the

beginning and at the end of the time T, m; is the difference of elevation between the water level near a drain and the drain floor, m;

$ is the coefficient accounting for the nature of the fall of the groundwater level. When the depression curve drops such that it remains parallel to its original situation, as usually occurs in spring time, then cp = 1. If the depression curve drops in such a manner that. its position near a drain remains unchanged, as occurs in -the summer- autumn period when there is no back-water in the regulating network, then Q = 0;

N is the rainfall which, within period T, percolates through to the groundwater table, m;

V is the evaporation which has its source in groundwater, during period T, m;

6 is the water yield of peat soil which may be calculated with the help of the following formula*) (Ivitsky, 1966; 1971) I

ho

H U are the estimated groundwater levels at the end and at the beginning of the time T, including their prescribed values (H,U) and water yield changes at different distances from the drain, m.

”

*) for mineral soils

104

Ivi t s ky

The following analytical expressions are obtained :

t - H - h

E 1- d

0 H = H - I P

(t - U) (1 - $) + @(t - H) - ho (14) E In- . d

U = U + P

When drains are installed in a confining bed the ideal condition, a = 0, CI = 1. Thus, formula (9) is valid for any depth of a confining bed.

2. If the drainage network is to be used for subsurface irrigation, where water from reservoirs or from rivers percolates through the drains then with a constant head H the distance between drains is given by: 0

where

E is the drain spacing in metres for irrigation, the level of groundwater half-way between drains is raised from h, to h,

by the head H measured frcnn the drain floor in m during time T;

yield 6.

0

y is the free porosity, it is approximately equal to the water

The remaining notation is the same as for (91 above. For various hydrological and infiltration calculations in connection with drainage systems it is important to know the drainage runoff value.

the test plot "Sloust" and on 9 years of observation of the two test plots "Volma" the following formulae have been developed for the estimation of the maximum rate of drainage runoff from low-level bogs having a base flow*).

Based upon 12 years of observations of the drainage runoff on

-- - (16) SR

q = t m

i

= 2 . 7 K for bogs with phreatic groundwater feed,

*) L. B. Nizovtseva assisted in this work.

Topic I

5 = 3 . 5 K for bogs with phreatic and artesian (17) feed, the units of K being m/day.

= 0 . 0 4 3 c I (18)

where

is the annual maximum rate of drainage runoff, l/sec. ha;

is a factor characterizing the peat soil permeability;

is a factor which accounts for the annual rainfall;

is the annual rainfall, mm;

5 E

w is the catchment area, ha;

C is a coefficient of variation;

C is a coefficient of asymmetry; V

S

For the same purpose the following formula is also proposed:

2 a(h - h ) (h + ho + 2a) 0 EL

ck q = 8

where

q is the rate of drainage runoff, l/sec ha;

C is a scale factor;

h

C = lo’, if the permeability k is in m/sec; is the excess height of the groundwater level measured in metres above the bottom of the drain midway between the drains, m; is the excess height of groundwater level near the drain, measured in metres above the bottom of the drain; ho

The estimation of evaporation is very important for calcula- tions of drainage systems. Based on observations and theoretical assumptions, the following relationships between evaporation and other important parameters (climate, groundwater level, yield) have been found (Ivitsky 1958).

a. for evaporation from peat soil without vegetation

b. for evaporation from peat soil under timothy grass

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Ivitsky

c. for the transpiration coefficient of timothy grass

where

V is the mean daily evaporation from peat soil without

D is air saturation deficit, either mean daily, or, total

w H is the distance of groundwater table from the surface, m;

'I! n varies between 1, 3 and 1.5

'T

'n

vegetation or total during the time T, mm;

during the time T, mm; is the wind speed, m/sec;

01 is an empirical factor varying from 0.93 to 1.0;

is the total evaporation for a soil carrying timothy grass, during the vegetation period, mm; is the total evaporation from the same soil and at the same groundwater level, but with no vegetation, and during the same vegetation period, mm;

is the timothy grass yield (dry mass) , in 100 kg/ha;

vegetation period, mm;

'y D is the total saturation deficit of the air during the above

According to A. A. Cherkasov the above expression (21) for the transpiration coefficient is valid for wheat in the Zavolzhic region, for cotton in Central Asia and for sugar beet in the Vororiezh region (Chevkasov 1958) .

References

Ivitsky, A. I. 1958. Osnovnye dostizheniya meliorativnoi nauki v oblasti proektirovaniya i raschetov osushitelnykh sistem v BSSR (Important advances in reclamation science in the field of design- ing and calculating drainage systems in the BSSR). In: bstiz- heniya meliorativnoi nauki v BSSR, Minsk, Izd. Akad. Nauk BSSR. Ivitsky, A. I. 1962. Novyi podkhod k opredeleniyu norm osusheniya melioriruemykh pochv (A new approach to the determination of drainage rates of reclaimed soils). Dokl. Akad. Nauk BSSR, 6(121.

Ivitsky, A. I. 1966. 0 printsipakh i sposobakh osushitelnoi melio- ratsii (On the principles and methods of drainage for land reclama- tion. Izv. Akad. Nauk BSSR. Ser. Selskokhoz. Nauk, No. 1.

Ivitsky, A. I. 1966. Obshchee uravnenie vodootdachi gruntov (Gene- ral equation of groundwater yield). bkl. Akad. Nauk BSSR, lO(11).

Ivitsky, A. I. 1971. Vlashnost i vozdushnyi rezhim torfyanoi pochvy v zavisimosti ot klimaticheskikh faktorov i urovynya gruntovykh vod (Moisture content and aerations of peat soils under different clima- tic conditions and groundwater levels) In: Nauchnye issledovaniya PO gidrotekhnike v 1969 g., v.2, Leningrad, Energiya.

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Topic I

Ivitsky, A. I. 1971. K teorii rascheta osushitelnykh sistem (A contribution to the theory of drainage system calculation) Minsk, Urozhai.

Ivitsky, A. I. 1971. Uchet dinamiki vodootdachi gruntov pri ras- chetakh ponizheniya gruntovykh vod (Accounting for groundwater yield dyamics in the forecasting of lower groundwater levels). In: Nauchnye issledovaniya PO gidrotekhnike v 1969 g., vol. 2, Lenin- grad, Energiya.

Kostyakov, A. N. 1960. Osnovy melioratsyi (Fundamentals of reclama- tion work). Moscow, Selkhozgiz.

Cherkasov, A. A. 1958. Melioratsiya i selskokhozyaistvennoe vodo- snabzhenie (Land reclamation and agricultural water supply). Moscow, Selkhozgiz.

DISCUSSION

Prof. L. Wartena (The Netherlands) : In your paper you mentioned some additional measures, particularly, you pointed to the necessity of including perennial grasses in crop rotations. I did not quite understand why this is necessary.

A. I. IVitSky (Byelorussian SSR): Perennial grasses in a crop rotation are very important because they decrease the rate of decay of organic matter and require a smaller quantity of ground- water thus reducing washing out of decay products. In Gorki, Mogilev region, tile drainage was installed more than a century ago and organic matter still continues to decay.

108