Abstract:
Dry season irrigation water scarcity is a major problem in Bangladesh. During the dry period most of the land remains fallow in the coastal area due to saline water intrusion and lack of irrigation water. For the intensification of agricultural production and protection of lives and livelihoods of the coastal communities, 139 polders were implemented in the coastal zone of Bangladesh. In the South-Eastern part of Bangladesh receives plenty of freshwater flow from the Padma and lower Meghna river through Arial Khan, Bishkhali, Buriswar and Lohalia River. As surface water irrigation is considerably less energy demanding than groundwater irrigation, Polder 41/1 has been selected as study area to assess the availability of dry season surface water for irrigation. This polder is situated in Barguna district which is in the eastern part of the southwest region of Bangladesh. Buriswar river is the main source of surface water of this polder. Salinity of this river remains below 2ds/m in all over the year. In this study, dry season irrigation assessed depending on the surface water availability in the canal system of the polder 41/1.
A mathematical model is developed in this study for assessing the water availability in the canal system inside the polder. Command area of existing canal and croplands are identified from existing Digital Elevation Model (DEM) and high-resolution satellite image (Sentinel-2 and Google earth). All the existing canal and regulators are incorporate in the hydrodynamic model of polder 41/1. Irrigation water demand and water withdrawal effects are also determined for each canal. In this study, three scenarios are developed for understanding the water availability at different condition. Scenarios are developed based on the local experience which are 1) regulator control gates are always open without water withdrawal, 2) regulator control gates are always open with water withdrawal and 3) regulator control gates are used as flushing with water withdrawal. The last scenario indicates regulators gates are open when river stage is greater than canal inside the polder and it is closed when river water level is lower than the canal water level. Pumping or water withdrawal from the canals have been considered based on irrigation water requirement for each canal. In this study, daily minimum water depth for 6-hours duration is classified into three categories (water depth 0.00 to 0.50m, 0.50 to 1.0m and water depth >1.0m). It is considered that irrigation is not possible if the water depth is less than 0.50 m.
