The Choctaw and Chickasaw Nations of Oklahoma (Nations) are currently developing a broad yet detailed Regional Water Plan that will identify water management strategies to ensure the social, environmental and economic needs of their 22-county jurisdictional territory are met, now and in the future. One of the many concerns for the Nations is a proposed inter-basin transfer which would remove a large amount of water from the Kiamichi Basin. The Red River Basin RiverWare model developed by the Tulsa District Corps of Engineers (Corps) and discussed in a previous presentation uses historical hydrology on a daily time step, and known reservoir configurations and operating rules to manage reservoir releases and hydropower generation. This model was modified for use in the investigation of instream flow needs, lake level management plans, and water availability and reliability in the Kiamichi Basin under many possible diversion scenarios. This paper describes the collaborative process with the Corps, the various modifications made to the model, some preliminary findings and proposed future enhancements.