Firstly, I am not an expert. However, I can certainly state that the international politics in Middle East and North Africa is mostly never affected by a single issue, be it the GAP project, Iraqi War, or any other conflict or consensus. The GAP project has both positive effects and drawbacks for the southeastern region of Turkey which the Kurdish population is the majority. The project aimed at building infrastructure for the region which is dry in soil. The positive effects could be considered as infrastructure development (the southeastern region is underdeveloped in terms of infrastructure), economic benefits to the region, and addressing the unemployment issue in the region. I also would like to note that PKK which is an active terrorist organization recruits its members mostly from the southeastern region. The economic development within the region could hamper PKK from recruiting members from the region (assumption). Moreover, it is also important to analyze the relationship between PKK, Syrian government, and Iraqi government. The current relationship between these bodies are formed by territorial conflicts because of the YPG's (the extension of PKK) presence in the northern Syria and the presence of PKK in the northern Iraq. Since Euphrates and Tigris rivers are also shared by these states, PKK's position seems plausible in order to further alienate the two states from Turkey and distract a possible collaboration of three states in fighting with terrorism in the region. The question whether the case is related to green-grabbing and water-grabbing is a matter of debate. However, the speech act securitizing the issue, I believe, is related to the power dynamics within the region. The persistent objection of Watercourses Agreement by Turkey has been simply subjected to national sovereignty concerns. Turkey initially did not want to lose control over the rivers and therefore refused. Yet, the change in decision could be stemmed by several factors including the finalization of the project, the wish for stabilization in region, accumulating international support etc.
I know I have answered your questions maybe out of your topic by mostly including international relations concepts, but I hope this answers your questions. I can gladly answer your further questions.