Journal ofAgricultural Engineering Vol. 43(1): Jan.-March, 2006
Performance Evaluation of Drainage Systems in Waterlogged Coastal Sandy Clay Loam Soil at a Pilot Area in Krishna Western Delta A. Srinivasulu 1, T. V. Satyanarayana2, M. Raghu Babu 3 and H. V. Hema Kumar4 ABSTRACT Pipe and open subsurface drainage systems were installed in an area of 12 ha in farmers' fields at Uppugunduru pilot area in Krishna Western Delta (KWD) in South India to combat the problems of water logging (depth of water table, oto 2.04 m) and salinity (ECe, 1.0 to 52.7 dS mol; pH, 6.5 to 8.8). Ten pipe drains were laid at three different spacing of 30,45 (design) and 60 m using two types of synthetic envelope materials, namely nylon mesh and geo-textile. Six open drains were laid at 50 m spacing. Monitoring of the performance of drainage systems for a period of 3 years from 1999-00 to 2001- 02 indicated that the average discharge from the pipe drains laid at 30 m spacing was the highest in all the years when compared to the pipe drains laid at 45 and 60 m spacing. As the spacing increased, the drain discharge decreased. However, no definite trend was observed with regard to the effect of envelope material on drain discharge. The water table, which used to be very close to the ground surface during the main crop period from October to January, could be lowered by 0.25 to OAm below the ground surface because of drainage systems. A total of 765.13 tons of salts were disposed through the drainage systems during the period of three years.
C
onsiderable irrigation potential has been created in India to sustain agricultural production against the vagaries of rainfall that is scarce and unevenly distributed in space and time. It was a major factor for enhancing
food production in irrigated areas and for India reaching self-sufficiency in cereal grains. However, the introduction of irrigated agriculture in arid and semi~arid regions of the country has resulted in the development of twin problems of water logging and soil salinisation, with which considerable areas of canal commands either have gone out of production or experienced reduced yields. It is estimated that an area of 8.4 million ha is affected by soil salinity and alkalinity in India, of which about 5.5 million ha water logged saline area is distributed in the irrigation canal commands. In addition to this, about 2.5 million ha area is estimated to suffer from coastal salinity problems in different states of India. Krishna delta, one of the oldest canal commands of the country (150 years old) commanding 0.3 million ha of land in Krishna and West Godavari districts on the eastern side and 0.23 million ha of land in Guntur and Prakasham districts on the western side is no exception to the above situation. The ever-increasing pressure for land and water
resources demands that the areas affected by water logging and salinity are reclaimed for sustainable agriculture. The subsurface drainage technology has been used for reclamation of water logged and salt affected lands in many parts of the country. Subsurface drainage systems installed using Bell mouthed perforated stone ware pipes (100 mm dia., 60 cm length with 6 mm dia perforations) as drain pipes and coarse sand as the envelope material at Endakuduru village in Krishna eastern delta near Machilipatnam in coastal Andhra Pradesh had effectively reclaimed the water logged and salt affected soils (AICRPAD 1986-1998). In the drained areas, soil conditions improved significantly and yield of paddy, sugarcane, betel vine and turmeric increased by 30, 19, 30 and 11 %, respectively as compared to the yield obtained from the fields that were not drained. Subsurface drainage systems were also installed during 1994 - 96 on a large scale in over 15,000 ha in Rajasthan to combat the problems of water logging and salinity in Chambal command area under Canadian Government assisted project, RAJAD (Sewaram et al. 2000) and in about 1,200 ha in Haryana state under the Netherlands assisted project, HOPP (Achthoven 2000). In these works, corrugated perforated UPVC drain pipes and synthetic materials as drain envelope were used. The
J,2Scientist and Principal Scientist, (alesrinu@ yahoo. com and
[email protected]) respectively, Andhra Pradesh Water Management Project. Bapatla-522101. 3Scientist , A1CRP on Use of Saline Water in Agriculture. Bapatla-522101, Andhra Pradesh 4Assistant Professor, College of Agricultural Engineering, Bapatla - 522/01. Andhra Pradesh
A. Srinivasulu', T.Y. Satyanarayana1, M. Raghu Babu 2 and H.V. Hema Kumar'
commissioning of the system was done using drain laying equipment. These projects have been proved to be successful and taking them in to account, an Indo- Dutch Network project was started in the year 1996 to suggest suitable reclamation technology for combating the twin problems of water logging and salinity in Krishna Western Delta (KWD) and Nagarjuna Sagar Project Right Canal Command (NSPRCC) in Andhra Pradesh. Under this project, subsurface pipe and open drainage systems were installed in 8 and 5 ha area, 'respectively in farmers' fields at Konanki pilot area in the year 1999 (Srinivasulu et aI., 2003). Due to the installation of drainage systems, the water table, which used to be almost at the ground surface during the paddy crop-growing (late kharif/ monsoon) season could be lowered by 0.2 to 0.35 m. Under the same project, another pilot area comprising of water logged and salt affected fields of farmers in KWD near Uppugunduru village in Prakasham district was selected to conduct operational research. Pipe and open drains were constructed in 12 ha area to reclaim the lands. The hydraulic performance of these drainage systems and their influence on the control of water logging at the pilot area is presented in this paper.
period. The numbers of irrigations vary from 10 to 13. The area was suffering from serious problems of water logging due to canal irrigation and high groundwater salinity (due to proximity to sea)
Pre-drainage Investigations In order to carry out pre-drainage water table investigations at the pilot area, twelve observation wells were installed to a depth of 6 m in the year 1997. The depth to water table from the ground surface was found to vary between 0 m in crop season to 2.04 m in summer. Farmers were not adopting proper drainage measures to dispose excess water. Chemical analysis of soil samples collected from three different layers of 020; 20-50 and 50-100 cm, indicated that the concentration of soluble salts in soil saturation extracts (EC) ranged from 1.0 to 52.7 dS m- I with an average of 4.5 dS mi. Though pH of saturated extract of soils varied between 6.4:6 and 8.93, half of the soils had pH in the range of 8.0 to 8.9. There was not much variation in pH (7.3 to 7.9) of water collected from observation wells, but the EC of water varied in the range of 52.1 to 100.3 dS m- I indicating that the groundwater is highly saline. The hydraulic conductivity of soils ranged from 0.36 to 0.47 m d- I with a geometric mean of 0.38 m d-I. In the area where pipe drainage system was proposed, the average hydraulic conductivity was 0.4 m d- I •
MATERIALS AND METHODS
Study Area The pilot area is located near Uppugunduru village in Prakasham district of Andhra Pradesh in India. It is situated at a distance of 15 km to the west of Bay of Bengal at an elevation of 1.5 m above mean sea level. It lies in the tail end of KWD and is commanded by Commamur canal. A natural drain exists on the southern side of the pilot area, which flows towards Bay of Bengal. The pilot area spreads over 20.92 ha and has 46 farm holdings ranging in size from 0.12 to 0.83 ha. The average annual rainfall in the area is 844 mm, of which about 60% occur during the southwest monsoon from June to September. Torrential rains are also expected during September~November due to occurrence of cyclonic storms. The topography of the pilot area is flat with less than 0.1 % slope. The land is dyked to form small units for rice cultivation. The elevation difference between the highest and the lowest points is about 0.7 m. The ground water is shallow and highly saline. It is therefore not suitable for irrigation and hence, only canal water is used for irrigation. The average salinity of irrigation water is 0.6 dS m-I. Flooding method of irrigationis adopted, in which irrigation water is allowed to flow from one field to the other during the entire crop
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Farmers grew only single crop of rice during monsoon and canal water supply season and left the fields barren -during the remaining period due to soil salinity and lack of irrigation facilities. However, fodder crop like sunhemp used to be glOwn as relay crop by some farmers after paddy but the growth and yield of it used to depend on the late season rains and the residual soil moisture. It was observed that the paddy crop had been suffering due to soil salinity and water logging problems and hence, low yields varying between 1.9 to 3.0 t ha- I were observed. The planted seedlings were stunted in their growth due to poor root growth and had less tillering ability. This lead to repeated transplanting, which increased cost of cultivation. Based on the results of pre-drainage investigations carried out at the pilot area during the years 1996-99 (Table 1), the drainage system was designed.
Subsurface Drainage Systems Installation Pipe and open drainage systems were designed and constructed at the pilot area in June 1999 (Satyanarayana et al. 2000). Using Hooghoudt's equation, the design 9
Jan.-March, 2006
Performance Evaluation of Drainage Systems in Waterlogged Coastal Sandy Clay Loam Soil
Table 1. Results of pre-drainage investigations used in the design of drainage systems S. No. Design Parameters
Specifications
1. Hydraulic conductivity
Oo4md- 1
2 Drainage coefficient
2.0mmd- 1
3 Hydraulic head above the drains
0.3m
in the control of water logging, the depth to ground water table was measured from twelve old observation wells spread all over the pilot area and 33 new observation wells installed in the area drained by pipe drainage system at regular intervals. As mentioned earlier, the drain water collected in to the sumps of closed and open subsurface drainage systems was pumped into the natural drain passing at the southern end of the field. The hours of pumping on each day and the rate of pumping were noted to arrive at the quantity of drainage effluent being disposed out of the pilot area through the drainage systems. Some time after initiating the pumping activity, the lateral pipe drains were exposed in the inspection chambers and the flow from them stabilizes. At this stage, the discharges from individual pipe drains were measured volumetrically. The quality of effluent from the drainage systems and the quality of ground water in the observation wells were also monitored regularly.
4 Depth to impervious layer below drains 8.7m 5 Equivalent depth
3048m
drain spacing was found as 45 m. In addition to the design spacing of 45 m, two additional spacings of 30 and 60 m were also proposed for testing in order to verify the effect of spacing on salinity reduction and control of water logging. The particulars of drainage systems are given in Table 2. Ten lateral pipe drains varying in length from 150 to 170 m were installed parallel on one side of the collector pipe. Perforated UPVC pipes were also used as drain pipes and synthetic materials such as geo-textile and nylon mesh were used as envelope materials. The lateral pipes were placed at a depth of 1.2 to 1.35 m below the ground level and the collector line was placed at 1.40 to 1.95 m depth. In addition to this, an open drainage system with six open drains at 50 m spacing was installed. As the land was relatively flat, pumped outlets were inevitable to dispose the drain water collected from the drainage systems into the natural drain.
RESULTS AND DISCUSSION
The hydraulic performances of drainage systems at Uppugunduru pilot area, their role in the control of water logging and amounts of salts disposed through drainage systems are presented and discussed in the following sections. Hydraulic Performance of Pipe Drainage System The particulars of discharge from all the ten drains of pipe drainage system during the three consecutive years after installation of the systems are given in Table 3. The average discharge from the drains laid at 30 m
Performance Monitoring of Drainage Systems In order to evaluate the performance of drainage systems
Table 2. Details of drainage systems constructed at the pilot area S.No. 1.
2 3 4 5 6 7 8 9
10
11 12 13
Particulars Drained Area Year of installation Type of system Spacing Drain depth Lateral pipe drain Collector pipe Envelope material Inspection chambers Sump cum Inspection chamber Dimensions of open drains Type of outlet Method of installation
Pipe drains 7 ha
1999 Composite 30, 45 and 60 m 1.2 to 1.35 m Dia 0.08 m Slope 0.1 % Dia 0.16 m Slope 0.14 % Geo textile and Nylon mesh Total No.7 Depth 1.8 m Dia 0.75 m Total No. 1 Depth 204 m Dia 1.2 m Pumped Poclain and Manual labour 10
Open drains 5 ha 1999 Singular 50m 1m
Sump-l no. Depth2.0mDiaO.75 m Bottom width 0.4 m Side slope 1: 1 Pumped Poclain and Manual labour
A. Srinivasulu 1, T.y. Satyanarayana 1, M. Raghu Babu 2 and H.Y. Hema Kumar'
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Table 3. Discharge from pipe drains (mm d· l ) at Uppugunduru pilot area SL No.
Lateral Name
Spacing (m)
Envelope material
Year 1999-2000 Peak Average
2000-2001 Peak Average
2001-2002 Peak Average
1
CDl
30
Nylon mesh
3.95
1.28
3.06
1.38
2.02
1.27
2
CO2
30
Geo-textile
1.37
3.23
1.42
2.58
1.63
3
cm
30
Nylon mesh
3.8 4.57
1.85
4.53
1.89
3.92
2.28
Average for drains with 30 m spacing
1.5
1.56
1.73
4
CD5
45
Geo-textile
2.67
1.02
2.84
1.25
2.94
1.37
5
CD6
45
Nylon mesh
2.54
0.86
2.34
1.02
2.19
1.09
6
cm
45,60
Geo-textile
1.73
0.64
1.56
0.76
1.17
0.75
Average for drains with 45 m spacing
0.84
1.01
1.07
7
CD8
60
Geo-textile
8
CD9
60
Nylon mesh
1.3
0.48
1.31
0.54
0.82
0.55
9
CDlO
60
Geo-textile
1.39
0.61
1.44
0.63
0.75
0.53
1.02
0.41
Average for drains with 60 m spacing
1.35
0.51
0.5
spacing was the highest in all the years when compared to the drains laid at 45 and 60 m spacing (Satyanarayana et al. 2002). For a given spacing, the average discharge generally increased over the years, possibly due to better crop activity with reclamation of land. No definite trend was available with regard to the effect of envelope material on drain discharge.
0.56
0.72
0.46
0.51
used to be close to the ground surface during the main crop period (late kharifseason) from October to January (Figure I). After installation of drainage systems, the water table was significantly lowered by 0.25 to 0.4 m below the ground surface during the crop season in the years 1999-00, 2000-01. Salts Disposed
Influence of Drainage Systems on Lowering of Ground Water Table
The estimated quantity of salts disposed through drainage systems during the three consecutive years are shown in Table 4. A total of 567.21 and 197.92 tons of salts
Before installation of drainage systems, the water table ----------_ ... _ - -
Month
as
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= os
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,Q ~
::g"" os
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