The Castanhão Reservoir Carrying Support Project is an innovation in water resources because for the first time extreme environmental conditions, which are characteristic of tropical semiarid regions, such as droughts, are considered in the process of quantifying the permitted loads from fish-farming and other activities. Furthermore, this project provides an easy-to-interface computational tool that allows assist in water resources management, coupling hydrology and water quality. Moreover, this project also considers through an innovative way the internal nutrient (phosphorus) load that is released from the bottom of the reservoir under low oxygen conditions. Overall, this project incorporates all the processes that affect nutrient concentrations in reservoirs under two climatic conditions (dry and rainy seasons), as well as during drought events. More details of the innovative nature of the project can be found in the journal papers listed in Section 7 - Materials.

Field surveys, laboratory analyses and computer model development/improvement will be carried out until April/2024, when the final project presentation and discussion will be conducted together with the different institutions, fish farmers and other water users involved. Furthermore, a computer program is being developed to provide an user-friendly interface for use by water managers. We have also been planning a second phase of the project, in which we intend to replicate the methodology and apply/refine the computer tool to 10 additional strategic reservoirs in the state of Ceará. The idea is to propose measures to mitigate nutrient concentration in the reservoirs, such as a plan to increase sanitary coverage in the cities upstream the reservoir, as well as the use of better feed to optimize fish farming, and the use of new technologies to control the nutrient load from sediments, such as artificial aeration at the bottom of the reservoirs.

COGERH has performed water and sediment sampling, laboratory analyses, and hydrologic measurements in the watershed and reservoir. UFC has developed/validated the model to predict the dynamics of water quality in the reservoir and is working on the development of the computational tool that will be used to assist water management. UFC has also conducted specialized laboratory analysis. Fish farmer association and Ministry of Aquaculture have provided data on the fish production and feed.

The innovation will primarily benefit the fish farmers who are located inside the reservoirs, as the carrying support knowledge will guide the best-management practices for the activity and potentially reduce the number of fish kills. The water treatment companies and industries will also treat a raw water with better quality, thus reducing the water treatment costs. Finally, water resources management companies will also minimize the conflicts among water users in committee meetings.

One of the main results of this project is the creation of an integrated database including hydrologic, water quality and sediment data for the largest multiple-use reservoir in Latin America. Another outcome is the development of a computational tool to evaluate scenarios and propose alert systems not only to prevent kills, but also to improve water management for other water users, bringing water quality dynamics to water resources management, through a new methodology adapted to tropical semiarid regions, with the feedback from institutions and society. This project also has been qualified human resources through various master's and doctoral projects, in addition to the publication of international scientific papers (see Section 7).

The biggest challenge was bringing together all the stages of the project to produce and discuss the main results. The fish farmers, at beginning, did not believe in the proposal and a lot of fake news was published, so trying to convince them and show that they would be the major beneficiaries was challenging. Furthermore, gathering field data at a large scale, training personnel for specialized laboratory analyses, carrying out sophisticated computational analysis and promote an efficient water management administration through this project was also challenging. Finally, bringing together and continuously updating all this information into a computer program continues to be challenging.

For the success and continuity of this project, it is essential to have the operational support of the Water Resources Management Company, making monitoring more frequent, thus making the computational tool increasingly accurate. The high degradation of Brazilian semiarid reservoirs is a reality, and water quality management must be a priority, incorporating not only the company's infrastructure, but also all human resources trained during this project. The increasingly accurate model, under different water quality conditions (more years), will tend to reduce environmental problems resulting from water quality degradation, for example fish kill cases.

There are several other Brazilian states and regions around the world (Australia, parts of Africa, China, USA, for example) with similar environmental conditions of seasonality/water scarcity, as observed in Ceará, in the Brazilian semiarid. Through this project, we can replicate the same methodology offering adaptations in the case of larger/smaller reservoirs and/or with permanent/intermittent water flows. This project has already been discussed in several conferences and meetings with other global environmental agencies (USGS, EPA, ANA). Moreover, its main results have been published in peer-reviewed journals (see Section 7). This suggests that the innovation has a potential to be incorporated by other countries or regions.

The collaboration involving research institutions, governmental agencies, and society, also including broad discussions with the national and international community, has a great potential to promote scientific/technological advances in the field that result in effective improvements in water resources management. The political, technical and financial support from the water resources management company also allowed the university group to reach higher levels of research findings, technological development and practical application of the results. Additionally, the involvement of undergraduate and graduate students in the activities also contributed for a better human-professional formation and to the feasibility of the project.