Development of water allocation mechanism for water stressed and abundance area under changing environmental condition

Abstract

Water is one of the most used (and abused) natural resources on the earth. Water resources are particularly vital for the Agriculture sector. Irrigation has been a determining factor in sustaining the self-sufficiency of Bangladesh in food grain production. In addition to the agriculture sector, domestic and industrial sectors have also been important consumptive water users. Water is a limited resource spatially and temporally. Therefore, this resource should be allocated among different sectors and users in an equitable and efficient way. This aspect of allocation of water is stated explicitly in SDG 6 on water and its sub-goals. Water management in Bangladesh and elsewhere is becoming more challenging due to growing demand and increasing conflict among users.

The decision support tool, Water Evaluation and Planning System (WEAP) developed by Stockholm Environmental Institute (SEI) is increasingly being applied in managing water resources systems in diverse environments across the world. This study employed this toll for Gazipur and Manikganj districts, where the former area is water abundant and the latter is water stressed. Being the adjacent areas to the capital Dhaka, these districts are considered as commercially and industrially important area in Bangladesh. Water resources of this area is distributed unevenly over space and time (between and within years) making it a scarce resource in most places and situations. These districts are used to compare in respect of water resources availability, demands, unmet demands and managements.

For water allocation, water demands of the different sectors for the base year 2016 and 2020 have been estimated. Water demands have been projected for the year 2030 and 2050. Water demand of domestic sector has been estimated for base year 2016, 2020 and for future years 2030 and 2050. Water demand of agricultural sector has been divided into crop water demand and livestock water demand. Crop sector water demand has been assessed using meteorological data by using FAO CROP WAT 8.0 software. Major crops like Boro and Wheat are considered for determining irrigation water requirements. Irrigation water requirements have been assessed for the year 2016, 2020 and projected for the year 2030 and 2050. Questionnaire survey has been conducted to find out water requirements of different type of industries and commercial units. Water demands of cattle, buffaloes, goat, fowl and duck have been determined separately. For surface water resources, river discharges have been simulated using seasonal autoregressive integrated moving average (SARIMA) model. For groundwater, output of groundwater study conducted by Bangladesh Agricultural Development Corporation (BADC) has been used. Upstream and downstream water quality of major rivers have been compared. Surface and groundwater quality have been compared with national and international standards. Using hydrological Tennant method, Environmental flow of all relevant rivers have been estimated. GIS shape file, all sectoral demands, surface water, groundwater data have been incorporated in the WEAP model for water allocation and simulated. Finally, five scenarios have been developed. First scenario has been considered water consumption by demanding sectors without any management in 2016, 2020, 2030 and 2050. Second scenario described regular growth of water demand by all sectors with effective water management. Third scenario described the regular growth of water demand by all sectors with effective water management but no growth of water demand in the industrial sector. Domestic demand site management 11.5 percent and increasing irrigation efficiencies up to 2 percent in 2030 and up to 4 percent in 2050 have been considered as management in water demanding sectors. No unmet water demand has been found in Manikganj in the first three scenarios. But unmet water demand was found for Gazipur. For Gazipur, another two scenarios have been formulated to elucidate water scarcity. Forth scenario has been formulated to replace intensively irrigated boro rice with low water demanding vegetables. Water management have been selected as like the third scenario. But still unmet water demand prevailed. So, the fifth scenario has been formulated to introduce with industrial water reuse increased up to 35 percent in 2030 and 55 percent in 2050. Scenario IV and V have been the modified situation of scenario III. So, finally, five scenarios have been formulated for the allocation of water in the study area.

In the current trend without water management, water demand in Gazipur will increase up to 4.37 billion cubic meters (bcm) in 2030 and 7.52 bcm in 2050. Scenario I has been introduced with regular growth of water demand with no management and regulation. The unmet demand was projected to increase to 1.82 bcm in 2030 and 6.42 bcm in 2050. For scenario II, total water demand in Gazipur was projected as 1.82, 2.80, 4.37, and 7.52 bcm for 2016, 2020, 2030, and 2050 respectively. No unmet demand was found in 2016. But unmet demands were found 0.18, 1.42, and 5.71 bcm for 2020, 2030 and 2050, respectively. Scenario III for water scarce district Gazipur resulted in, total water demand 1.82, 2.80, 2.81, and 2.83 bcm for 2016, 2020, 2030, and 2050, respectively. No unmet demand was found in 2016. But the unmet demands were found 0.179, 0.207, and 0.264 bcm for 2020, 2030 and 2050 respectively. After considering three scenarios, unmet demands were found in the water scarce Gazipur district. Boro rice was found to be an intensively irrigated crop in the study area. The scenario IV has been developed to change the cropping pattern in the low flow dry season. This scenario replaced the boro rice from the cropping pattern and introduced vegetables in the dry season. Water demand in scenario IV for Gazipur resulted in 1.37, 2.36, 2.42, and 2.50 bcm for 2016, 2020, 2030, and 2050, respectively. The unmet demands were found to be 0.16, 0.11, and 0.936 bcm for 2020 and 2030 accordingly. Finally, scenario V for Gazipur has been formulated with higher water reuse in the industrial sector. There was no unmet water demand in the Gazipur district. For Manikganj, minimum water demand has been found at 481.20 million cubic meters (mcm) for scenario III in 2050, maximum water demand at 534.80 mcm for scenario I in 2020, which are the reasons for the decreasing trend of crop land. There was no unmet water demand for Manikganj for all scenarios. Industrial waste water reuse has been found as a good guideline for lowering water demands. District level restriction on new industries has been found successful for lowering water demands. Vegetable cultivation instead of rice cultivation has been found effective in lowering irrigation water demands. Finally, district specific water uses guidelines or micro level water policy have been found to be very useful in improving water scarcity.