Evalution of Subsurface Drainage Design Relationships in Ardabil and Khuzestan Provinces

In the last decades, water supply in the basin level has been considered significantly compare to the drainage and land reclamation issues. This research was conducted to evaluate of dominant relations on subsurface drainage design for specific characteristics of three agricultural zones in IranParsabad in Ardebil province, Karoon and Amirkabir agro-industries in Khozestan province. In Moghan irrigation network, agricultural areas at outlet of basin were exposed to water logging due to the ground water level raise, just 5 years after the construction of main canals. Sugar cane is implanting in Kuzestan province since 40 years ago in agro-industries equipped to the sub-surface drainage systems and continued as &ldquosugar cane development and lateral industry plan&rdquoby now. In each region, an experimental area was selected which was characterized with lateral drains in different lengths and distance from each other. The level of water table variation, electrical conductivity of irrigation and drainage water, and volume of irrigation water were recorded during the experiments period (1-4 months). According to the results(i) In Moghan region, drainage coefficient was less than 1 mm/day in 80% of measurements, which was almost 50% less compare to the values which was supposed in design manual. Accordingly, the modified drainage coefficient is suggested for future drainage network design in each site. (ii) The level of water table in Moghan drainage network was more than 1 m. Accordingly the distance between the lateral can increased 10 % while the water table level is still under the critical level. (iii) In Karoon Agro-industry drainage coefficient was 13 mm/day which was been almost 40 % higher than that was supposed in design manual (8 mm/day). On the other hand, the water table level was above the control level (1 m) for 5 days after irrigation mainly due to the over irrigation. It was suggested to the modification of irrigation scheduling according to the sugar cane water requirement. (iv) The subsurface drain type in Amirkabir agro-industry decreased the water table level to under the critical level after 2 days. Water table level reached to 40 cm from the soil surface after irrigation and then decreased 50 cm per day, in average. Regarding to the sugar cane resistant to the saline and water-logging conditions, increase of 100% in drain spacing (80 m) was concluded to provide the land drainage requirements. Also, by increasing the drain spacing, some portion of sugar cane water requirement can be supplied from the ground water, but yield might be decreased 10-15 % due to the saline water and water-logging conditions.