Country Papers 11

Development of drainage in Turkey over the last 25 years and its prospects for the future S.Sener Village Affairs Research Insti~ute, Menemen, lzmir, Turkey

Physiography and land use

1

The total area of Turkey is 780 580 km2 of which 23 500 km 2 is situated in Europe. The land under cultivation at present is 27 699 0 I 0 ha. Pasture and grazing land covers 21 745 690 ha and forests 15 135 090 ha. An account of the land use pattern in Turkey is given in Table 1. Table I Land use pattern in Turkey (TOPRAKSU 1978) Type ofland use

Area

%

ha Cultivated agricultural land Dryland farming Irrigated area Vineyard and orchards

22607340 2990880 2 100790 27699010

2 3

Pasture and grazing land Forests and shrubs Forests Bushes and shrubs

4

Settlements

5 6

Unproductive land Lakes

21745690

35.6 28.0

15135090 8333 380 23468470

30.2

569400 3 212 180 I 102390

0.7 4.1 1.4

77797140

100.0

Turkey has a population of 50 million. About 55 per cent of the population lives in rural areas and 61 per cent of the labour is employed in agriculture. Physiographically, Turkey can be divided into four regions with different characteristics. Coastal lands In the north and in the south high mountain ranges stretch parallel to the coast, forming small terraces and bottom lands with the exception of some large alluvial deltas formed by the rivers. The alluvial soils comprise the largest and most important group 236

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of arable soils. Elevations vary from sea level to 150m. Salinity and drainage constitute the main problems in the coastal lands. Central Anatolian Plateau A high plateau located in the central part of the country, is divided by rivers into many irregular areas. This region has different landscapes, such as mountains, bench lands, closed basins and some narrow alluvial plains. The elevation varies from 800 to 1500 m. Most of this plateau is suited for agricultural use, especially for grain production. Mountain lands This area shows a very rough relief and has steep slopes with elevations generally between 1500 and 4000 m. Vegetal cover changes from weedy, mostly barren rocky surface to dense forests. Basin lands ofThrace · The whole European part of the country except the Istrance Mountain Ranges consists of basin lands. It is an open and divided plain having an undulating topography in the center. Most of these basin lands are suitable for agriculture.

2

Climate and rainfall

Turkey has in general a semi-arid climate with extreme temperatures. Almost the whole Anatolian plateau has hot, dry, dusty summers and cold, windy, damp winters, but in the Eastern Anatolian region the summers are cool and short and the winters are severe and long. The Mediterranean climate with short, wet winters and long, warm, sunny summers, prevails in the southern and western part of the country. The average annual rainfall is 670 mm, but varies from a minimum of 220 mm to a maximum of2420 mm. There is a great variation in space and time. Meteorological data show that over 90% ofTurkey has not enough soil water during the crop growing season, and for good agricultural production irrigation is essential in most parts of the country.

3

Drainage and salinity problems with regard to soil conditions

The soils of Turkey vary considerably in ferti lity. The soils of the Central Anatolian Plateau reflect the semi-arid steppe condition of the region. Here low rainfall coupled with sparse plant cover of short grasses has resulted in the formation of limestone as parent material. The character of the terrain handicaps the development of deep · natural soils in this highland area and most of the soils are thin and easily erodable. Overgrazing and deforestation of the sloping lands have led to an intensification of the soil erosion problem. ·

237

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More productive soils, comprising of clay and lime underlain by deep sand-silt and clay strata are found in the coastal and lowland regions of Turkey. These areas cover nearly one-seventh of the total cropland of Turkey. The capabilities of these alluvial soils for crop production range from low, due to frequent fl ooding or low natural fertility, to very high . They have greater potential for increased agricultural production than any other group of soils. According to the General Improved Soil Map of Turkey which is prepared by TOPRAKSU (1966- 197 1), 2 775 110 ha of cultivated land has drainage problems, which is 3.6 percent of the total area of77 797 140 ha. On the other hand I 518 720 ha of cultivated land (2.0% of the total area) has salinity or alkalinity (sodium) problems. These soil types are classified into five categories according to the extent of the problem: Light saline soils : 0. I 5-0.35% soluble salts, ESP < l 5; Saline soils : Soluble salts > 0.35%, ESP < 15; : Soluble salts < 0.15%, ESP > 15; Alkali (sodic) soils Light saline and alka li soils: 0.15-0.35% soluble salts, ESP > I 5; Saline a nd alkali soils : Soluble salts > 0.35%, ESP > I 5. Dominant salts accumulated in the soils are chlorides (NaCI, CaCI2 , MgCIJ, sulphates (Na2 S04, MgS0 4), nitrates (NaN03, KN0 3), carbonates and bicarbonates (Na2 C03, NaHC03) , a nd bo ron salts in certain a reas. Sodium salts occur most frequently, but calcium and magnesium compounds are common too.

4

The main areas where surface or subsurface drainage has been installed in the past 25 years

Although very simple individual surface and subsurface drainage systems have been found in Anatolia since Roman and Ottoman time, only extensive and planned work on this subject has been sta rted since 1950 o n a project basis. In those years ·and a few years ago, some big irrigation projects such as Seyhan, Cumra, Menemen and Alpu were completed and irrigated agriculture was started in these rather flat alluvial and hydromorfic alluvial soils. As soon as irrigation started crop yields doubled. But the following years irrigated agriculture brought new problems to the farmers such as high watertables, salinity and alkalinity. On the other hand new dams and irrigation schemes came under construction whereby sufficient drainage had to be provided. In the 1960's an intensive land reclamation and drainage program was initiated by the government with the assistance of international organizatio ns, such as the International Development Agency (IDA), European Investment Bank (EI B) and International Bank for Reconstruction and Development (IBRD). As a result of this programme surface and subsurface drainage works have been started in 21 big irrigation projects (Table 2 and Figure l). Surface and subsurface drainage works are mostly completed in these projects. However, in the coastal plains the lowlands below 2.00 m elevation which require pumping for drainwater disposal are for economic reason still in a future drainage project phase. 238

Table 2 The most important land development and drainage projects in the last 25 years in Turkey Name of the project

Total area (ha)

Land levelling

Subsurface drainage

area (ha)

cut or fill (m 3fha) 750 665 700 452 700 577 700 700 560 700 700 572 700 800 830 639 600 600 700 685 647

Seyhan (Adana) Gediz (Manisa) Ak~ay (Nazi II i) Berdan I, II (Tarsus) Uluirmak (Nigde) Kopriicay (Antalya) lgdir (Kars) Ercis (Van) Kazova (Tokat) Alpu (Eskisehir) M. Kemalpasa (Bursa) Silifke (Mersin) Cumra (Konya) Nusaybin (Mardin) Sarimsak1i (Kayseri) Ceyhan (Adana) Carsamba (Samsun) Bafra (Samsun) Kartalkaya (K .Maras) Erzincan Bigadic (Ba1ikesir)

181 300 110495 18050 27706 2 1095 24215 67473 2300 22950 23200 16250 6005 5800 8600 12405 107996 50000 30000 23368 10520 3403

139100 69620 13150 17520 17750 18000 66000 1600 15000 17940 13200 3300 4500 6500 8900 97200 20000 15000 18527 10099 2492

Total

773131

575398

area (ha) 47300 45400 3517 11160 11860 7526 36093 I 000 3860 9300 6861 2350 I 000 1800 1350 6050 . 33 173 10122 2100 5000 2500 249322

Surface drainage la teral length (ha) (mfha)

100 100 100 100 75 - 87 125 100 100 100 75 100 125 100 100 138 125 125 100 100 115

139100 69620

Land reclamation (ha)

18000 66000

32350 1863 3374 4415 840 36093

15000

2 100

5265

Land consolidation (ha)

69620

1400 14000

10000 3 300 2500 8900 97200 20000 15000 6000 2000 1 500

10000

466885

103 535

4 500

2000

8000

99520

~ ~ ·-:...., {l

tv

Vol

\0

;;; "'._ ._

Country Papers I!

~irrigated

miiiiJ drained marsh ~flood protected

Mediterranean sea

c=J planned irrigation

P subsurface drainage (planned) • dam in operation • dam under construction • dam designed

Figure I Dams and irrigation/drainage projects in operation, under construction, and planned in Turkey

Besides those 2 1 big projects there have been many separate drainage projects all over the country. According to the 1986 statistics of Koy Hizmetleri (Village Affairs) General Directorate, land development, installation of surface and subsurface drainage systems and application of soil amendment was carried out by this organization in 1985 on 752 470 ha. Subsurface drainage was installed on 427 220 ha. Approximately 20 000 ha has been proposed for subsurface drainage installation in 1986. Gediz River Valley Drainage Project (near Izmir) The Gediz River Valley Drainage Planning Office was founded in 1963. Thereafter intensive sub~urface drainage installation began with financial support of the European Investment Bank in 1964. In approximately 46000 ha subsurface drainage systems have been installed since that time. Another 24 000 h·a still requires subsurface drainage or rehabilitation works (such as installing plastic drain pipes instead of broken or clogged tile drains). Land consolidation projects and drainage projects will be applied together in most of these areas.

5

Future irrigation and drainage projects

According to the State Hydraulic Works (DSI), the governmental authority dealing with the construction of dams and big irrigation project~, by the end of 1986 100 dams and hydroelectric power plants were in operation. Only 9 dams are for domestic water supply, 4 for hydroelectric power and I for flood control purpose. The other 86 dams were constructed mostly for irrigation purposes. 240

Country Papers II

On the other hand 66 dams are under construction; among these the Ataturk Dam on the Firat River (Euphrates) which has 48 700 x 106 m 3 water storage capacity and will irrigate 870 000 ha of dryland in south-eastern Turkey and will produce 8900 x 106 kWh hydroelectric power each year. With this capacity it will be one of the most important dams in the world. When these 66 dams are completed I 509 ISO ha new land will be irrigated. There are also 30 dams in final design and it is expected that 228 280 ha will be irrigated from these dams; 31 dams are in project phase and planned to irrigate 364 200 ha. Today the total irrigated area is about 3.5 million ha. So when all these projects are completed, the total area irrigated will be doubled by the end of this century. All this irrigated land will require somehow surface or subsurface drainage. Subsurface drainage installations are still going on in most of the former drainage projects such as· Gediz, Carsamba and Bafra projects. The projects in Table 3 are the most important irrigation and drainage projects of Turkey in the near future. All these plains will receive irrigation water and electric power for pumping from the Ataturk Dam which will be completed in 1989. Irrigation in Urfa-Harran Plain will start in 1991. Table 3 Future irrigation and drainage projects of Turkey Name of the project

Arca(ha)

Urga-Harran Plains Gravity Irrigation Lower Mardin-Ceylanpinar Plains Gravity Irrigation Upper Mardin Plain Pumping Irrigation Siverek-Hilvan Plains Pumping Irrigation Bozova Plain Pumping Irrigation Suruc-Basiki and Birecik Plains Pumping Irrigation

142000 158000 190000

Total

870000

180000

55000 145000

6

Drainage criteria in relation to various types of land use

6.1

Surface drainage criteria

Open drainage canal capacities for disposal of surface run-off are calculated according

to one of the following run-off prediction methods: I The curve number method of the US Soil Conservation Service, for watersheds up to 800 ha; 2 The SCS standardized hydro graph method, for watersheds bigger than 800 ha; 3 The rational equation method, for flood control structures. After calculation of surface run-ofT, Manning's flow equation is used and open drainage canal dimensions are determined.

241

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6.2

Subsurface drainage criteria

A detailed groundwater table map and barrier map is prepared during the survey of the drainage area. Augerholes are ~rilled in grid points 400 m apart up to 3.0 m depth. Hydraulic conductivity values (K) are determined by means of these augerholes. The average of 4 to 6 values in neighbourhood holes are used for calculating drain spacings. The drainage coefficient is assumed 2 mm/day for irrigated areas. After collecting these data the Toksoz and Kirkham nomograph in Figure 2 is used for calculating the drain spacing. The following is an example of drain spacing calculation in Manisa- SaruhanliNuriyeprojectin 1985. Given: Average hydraulic conductivity (K) of 6 auger holes

K = 0.56 m/day h = 8.00 m (depth to barrier) H = 0.60 m R = 2 mm/day (drainage coefficient) 2r = O.lOm(drainpipediameter) Solution: L = H (K _ 1) = 0.60 (_!>.56 _ 1) = 2 1.5 and~= 8.00 = 80 h R 8.00 '0.002 2r 0.10 Using the nomograph in Figure 2 gives 2S h =

8.5 and S = 8 x 8.5

= 68.0 m,

which is the calculated drain spacing for that particular area. The groundwater table is kept generally 0.90 to 1.50 m below ground level depending on the rootzone of the major crops and taking into account the salinity of the groundwater. For this reason lateral drains are laid at a depth varying from 1.50 to 2.10 m, but in most cases at 1.80 m below the surface.

7

Drainage construction

The trencher is the most common and convenient machine for installing subsurface drainage systems. Former trenchers made in U.S.A. arc replaced by German or Dutch made trenchers which are lighter and faster (Figure 3). Excavators are used in constructing or cleaning of open drainage canals (Figure 4). The flexible perforated PVC pipes are used for agricultural drainage applications. They are manufactured in Turkey as 50-200 m coils with a diameter range of 50 mm to 200 mm. Its flexible quality enables easy installation into the trenches and its spiral 242

Country Papers II

L;~(~-1) 1~,-----,------.---.--.-.------.------,---r--.r;

800 ~----~----~~--~~~------,_------r-~~~~

~

~ ~r

I

~

- ---1-----t

1oo~-----.------.----.--.-.-------rm 80~-----+------+---~--~4-----~~w---4---4-_,~

2S

h

Figure 2 Nomograph for solution of Kirkham's equation (after Toksoz)

construction gives it a higher resistance to various pressures. Sand and gravel envelopes (8 to I 0 mm) around the plastic pipes are used as filter material (Figure 5). According to 1986 prices subsurface drainage installation cost per ha is about 90 000 TL or US$ 120. Costs for surveying, design and control of the construction are not included into these figures.

243

C'mmll'l' raper.\' II

FIJ! 'German made Schacn· w:n~ho:r m np.:r;uion m t.u11iy.: ncar Man"a ( 19X6)

hgurc 4 An cxcavawr dcanmg the bed of Kum Creek

244

111

Manisa ( 1W