Whenever the department has discretion to expend funds appropriated for the purposes either through the officers and employees of the department or in the form of grants-in-aid to local governmental authorities, it shall decide with reference to the use of grants-in-aid according to the availability and adequacy of the facilities under the control of the local governmental authorities, as compared with the facilities of the department for furnishing the services required to be rendered; such funds shall be made available according to uniform rules to all local authorities performing similar functions. In formulating such rules, the department has the power to:
T.C.A. § 71-1-115