Distributional equity of irrigation water and its impact on productivity of some deep tube well command areas

Abstract

Equity is an increasingly important concern for irrigation, but has not been yet addressed sufficiently by studies in this area after its implementation. The objectives of this study were to assess equity in water distribution among the stakeholders in deep tubewell irrigated area and to identify the impacts of water equity in productivity. Three deep tubewell irrigated areas named East Togori, West Togori and Bhavanipur under Gazipur District are selected for the study with command areas of 35, 28 and 26 hectares respectively. Although the capacities of these tubewells are enough to irrigate their total command areas, fields of tail ends do not get enough water. So, inequity in water distribution frequently occurs in these irrigated areas. Three main irrigation canals of these tubewell irrigation areas were selected for carrying out the study. Water reaches in each part of three selected canals was calculated at head, middle and tail ends of each canal. For this study, 12 numbers of sample fields from each deep tube well command area totaling to 36 numbers of sample fields were used to calculate how much water reaches to each field. The total irrigation water depth values were used to get the distributional equity. The equity coefficient and Gini coefficient are widely used to measure equity. The value of equity coefficient ranges from 0 to 1 where 1 is the most equitable condition and 0 is the worst. The Gini coefficient is used as a measure of inequality of water distribution. A low Gini coefficient indicates more equal water distribution, while a high Gini coefficient indicates more unequal distribution. A semi-structured questionnaire survey has been conducted through the direct personal interview technique from selected 36 fields. The questionnaires were followed to collect necessary data such as crop yield data, irrigation water availability and its status of distribution, etc. from the farmers of the study area in 2011-12 Boro season. In this case crop yield of the study area is calculated. Then impacts of water equity on crop yield were analyzed. The Equity coefficients of East Togori, West Togori and Bhavanipur Deep Tubewell irrigated area under study were found 0.4436, 0.7027 and 0.7471 respectively. The Gini Coefficients of East Togori, West Togori and Bhavanipur Deep Tubewell irrigated area under study were found 0.4754, 0.4427 and 0.4370 respectively. The coefficients thus computed using two methods show that inequity in irrigation water distribution exists in the study area. The highest crop yield (7901.97 kg/ha) was found at head ends of Bhavanipur Deep Tubewell irrigated area applying 863.60 mm of irrigation water, while the lowest crop yield (4214.39 kg/ha) was found at tail ends of East Togori Deep Tubewell irrigated area applying 444.50 mm of irrigation water. The highest crop yield of West Togori Deep Tubewell irrigated area was 7111.78 kg/ha, when the applied total depth of irrigation water was also the highest i.e., 749.30 mm, while the lowest crop production (5004.58 kg/ha) was found at tail ends of West Togori Deep Tubewell irrigated area applying the lowest amount of water (482.60 mm). The water productivity diminishes from head ends to tail ends with the reduction of irrigation water. When more equal water distribution is achieved along the canal, difference of crop yield between head ends and tail ends gets reduced. Bhavanipur Deep Tubewell irrigated area achieved higher equity coefficient (0.7471) and crop yield difference between head ends and tail ends was found 30%, while tail end fields received 43.13 % of less irrigation water than head ends. So, there is much scope to minimize the inequity in water distribution by proper distribution of excess water from head ends to tail ends. Equitable water distribution is to be ensured for achieving better crop production. The difference of amount of water delivered at head and tail end must be reduced to minimum.