The effective development of agriculture in a zone of insufficient moisture is determined by the reliable functioning of the irrigation system, the environmentally favorable state of irrigated lands, the availability of the necessary water resources for irrigation, and the use of sound farming systems. Systematic management of factors ensuring the agricultural land productivity is a complex expert – methodological and technological process. Optimization of the process is possible through the use of digital technologies, in particular, the geoinformation web-based decision support system being developed. The purpose of the work was to substantiate the conceptual provisions of the development and operation of a geoinformation system with a web-platform implementation. The system is designed to collect, store, analyze and provide information necessary for integrated management, narrowing the search area for a rational solution based on the provided results of system research, to increase the validity of decisions made. The methodological basis of the geographic information web system was the results of many years of research in the field of information and analytical substantiation of ecosystem water use in agriculture, information and digital technologies, statistical methods, mathematical modeling. The principles of forming an expert web system necessary for jointly solving environmental, technical and operational problems of ensuring the sustainable development of the land reclamation and water management complex and agriculture on irrigated lands have been developed. The principles of its operation have also been defined, providing user-friendly and reliable tools based on web and geoinformation technologies. The expert geoinformation web-based system has a modular structure and includes measurement and diagnostic, modeling, analytical, and service blocks. Special software has been developed: “Geoinformation web-based decision support system for the integrated management of the reclamation and water management complex of the Republic of Kalmykia.”