Theme 1-11-Surface drainage requirement in irrigated command of Central Gujarat

Abstract

The Mahi Right Bank Canal (MRBC) command area (Figure 1) is characterized by a generally flat topography, restricted natural drainage, comparatively heavy soils and semi-arid climate, all of which are conducive to the development of problem of waterlogging. There is immediate need of accelerated efforts to provide efficient drainage and scientific water management in the area so as to ensure sustained agricultural production and prevent environmental degradation. A study on the daily rainfall data of the 16-raingauge stations in the area reveals that advance showers of high intensity are quite common. However, the rains may not be effective as far as agricultural operations are concerned as they are usually followed by long dry spells. Critical dry spells also occur during the kharif season when irrigation becomes essential even in crop like paddy. Prolonged dry spells will necessitate irrigation in other crops as well. Total rainfall during wet spells occurs in the command area is nearly 726 mm in 91 days. The rainfall surplus during first, second, third and fourth wet spells are of the order of 46%, 26%, 18% and 10% respectively. Due to accumulation of rainwater and the excess irrigation water from the canal system, surface drainage has become a prime need in most part of the command area. In the absence of rainfall-runoff relationship for want of provision in the drainage system , estimation of drainage requirement has been made by different approaches . The graphical method to estimate drainage coefficient is better substitution for the command area over the two methods namely rainfall depth-duration method and USAD-SCS-CN method. The drainage coefficient varies from 16 to 30 mm day –1 for the entire command. M R B C command area having the largest culturable command area in the central Gujarat has been focused in the present study.