Investigations on surface and subsurface drainage requirements at regional scale

Abstract Amongst the three drainage basins in Haryana (India), the inland drainage basin is most prone to surface stagnation, rise in groundwater table and soil salinization. In order to understand the surface and subsurface drainage requirements of this basin, a number of groundwater regime maps (groundwater table contour map, depth to groundwater table map, groundwater fluctuation map and groundwater quality map) were prepared to assess long‐term groundwater table behaviour in a part (comprising Rohtak and Jhajjar districts) of this basin for the period 1984–98. Groundwater movement was observed to occur towards the central part of the study area, a possible cause of waterlogging and degradation in groundwater quality. The groundwater levels during the past two and a half decades (1974–98) registered a rise varying from 1 to 19 m with an average rise of 21 cm yr−1. The rainfall data of Rohtak and Jhajjar districts for the period (1975–98) were analysed for different frequencies of exceedance to determine 1, 2 and 3 days of consecutive rainfall. The surface drainable surplus was calculated taking into account the water storage in the soil profile, infiltration rates and evaporation that varied from 30–35, 35–40 and 5 mm day−1 respectively. The drainable surplus for consecutive 1, 2 and 3 days' rainfall for a 5‐year return period was 161, 113 and 0 m3 s−1 respectively. The existing surface drainage system with a capacity of 170 m3 s−1 and with availability of dead storage, could handle 1 and 2 days' consecutive rainfall for a 5‐year return period when full initial storage of 30–35 cm (equivalent to 50% of the available moisture) is available in the soil profile. From the groundwater regime maps, it was also estimated that nearly 16% of the study area (57 932 ha) required treatment with subsurface drainage. Therefore, a groundwater model (SWAP) was used to predict the subsurface drainable surplus considering various inputs related to the water balance of the area. The subsurface drainable surplus over the simulated years ranged between 0.4 and 1.92 mm day−1. This range is quite close to the recommended range of the subsurface drainage coefficient for this region on the basis of field trials. The study of irrigation and drainage maps of the area revealed that there is a need to strengthen field surface drains and introduce subsurface drainage in the area. As such, the methodology proposed in this paper could be used to investigate drainage requirements on a regional scale. Copyright © 2006 John Wiley & Sons, Ltd.